Antifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts

Antifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Antifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts Dailami S. A Masokano, Usman O. A Shuaibu, Jude E. Emurotu, Pinkie Ntola This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6965908/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Nov, 2025 Read the published version in Discover Materials → Version 1 posted 10 You are reading this latest preprint version Abstract Banana ( Musa spp ), mango ( Mangifera indica ) and pineapple ( Ananas comosos ) peel aqueous extracts were employed to synthesize zinc oxide nanoparticles (ZnONPs), namely; ZnO-BPE, ZnO-MPE and ZnO-PPE, respectively. A reference sample, ZnO-ppt (without fruit peel extract) was also synthesized by simple precipitation. These were calcined at 500 ºC and characterized using x-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), UV-visible spectroscopy (UV-VIS), Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA/DTG), scanning electron microscopy-electron dispersive x-ray (SEM-EDX) and Transmission electron microscopy (TEM) techniques. The XRD of the samples revealed a hexagonal wurtzite crystalline structure typical of ZnONPs, with the Debye Scherrer’s crystallite sizes ranging from 21-38 nm. FTIR spectra of the samples showed Zn-O vibration bands at ~521 cm -1 while the UV-vis showed a narrow band gap in the range of 2.41-2.85 eV, and good UV light absorption in all the samples. The SEM images showed significant differences in the morphology of the samples, including spherical-hexagonal shape for the ZnO-ppt sample, and flower-like shaped particles for the ZnO-MPE. Antifungal assay showed that all the samples are active against Trichosporon sp and Aspergilus niger isolates. Highest zones of inhibitions were obtained for the ZnO-MPE against Trichosporon sp. , while the ZnO-PPE sample showed the lowest MIC of 62.5 µg/ml against Aspergilus niger . Photodegradation potential of the samples against 10 ppm methylene blue solution showed 73-91 % degradation under UV-light irradiation. The best performing photocatalyst, ZnO-MPE, sustained its degradation efficiency over three regeneration cycles. Zinc oxide Nanoparticles Green synthesis Catalyst Methylene blue Photodegradation Antifungal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1.0 Introduction Metal oxide nanoparticles have continued to receive great attention due to a wide range of applications [ 1 ], [ 2 ]. The tunable properties of metal oxide nanoparticles such as surface area, porosity, and morphology—all associated with active surface phenomena—have increased their effectiveness and expanded their range of uses. Biological and organic moieties can be used to alter or improve these properties to suit intended use in biological and environmental science [ 2 ]. For instance, utilizing plant aqueous extracts as reducing/stabilizing agents sufficiently changed parameters such as particle size, crystallinity, surface area, porosity, morphology, and photoluminescence. But for many decades, there has been no universal method for synthesising and/or stabilizing metallic nanoparticles with the right surface modifications for a range of uses [ 3 ]. Due to their natural abundance, biocompatibility, non-toxicity, environmental friendliness, affordability, and chemical and thermal stability, zinc oxide nanoparticles (ZnONPs) is one of the few metal oxides that have drawn more attention [ 4 ], [ 5 ]. These are widely celebrated as potential photocatalysts due to their single oxidation state and suitable bandgap energy, and also as an antimicrobial agent, among numerous other applications [ 6 ], [ 7 ]. ZnO with n-type semiconducting properties has drawn a lot of interest because of its numerous uses in electronics, optics, and medicinal research [ 8 ], [ 9 ]. Recently, its application in photocatalysis and as antifungal agent has been investigated explosively [ 10 ], [ 11 ], [ 12 ]. Interestingly, ZnONPs are generally considered non-toxic and harmless by various regulatory bodies including the U.S Department of Food and Drugs Administration (FDA, article number: 21CFR182.8991) [ 4 ]. Furthermore, compared to other metal oxides, ZnONPs synthesized using a green approaches are potentially effective and beneficial for clinical and environmental applications. For example, ZnONPs are widely reported to show high potential in the photodegradation of organic dyes and for the treatment of various infectious diseases [ 13 ], [ 14 ], [ 15 ]. In the last few decades, various researchers have put efforts to fine-tuning the properties of ZnONPs to enhance their activities by employing various synthesis approaches. Popular synthetic routes investigated in the literature include precipitation, sol-gel, microwave-assisted, hydrothermal, thermal decomposition, solution combustion, and biogenic (or phyto-assisted) synthesis methods [ 16 ]. The biogenic method is regarded as "green" since it does not use auxiliary solvents or generate harmful waste. Further, this method can be used to prepare a large sample in a single batch, and, hence, is readily scalable and cost-effective. Plants contain an amazing variety of phytochemicals, such as alkaloids, flavonoids, saponins, steroids, tannins, phenolic acids, and other bioactive compounds, which are found in various parts including the fruits, flowers, leaves, roots, shoots, stems, bark, and seeds. Some of these naturally occurring secondary metabolites can function as stabilizing and reducing agent during the biogenic synthesis of ZnONPs [ 17 ]. In comparison to conventional physical and chemical processes, the biogenic synthesis of ZnONPs using plant aqueous extracts is conducted at room temperature (or a temperature below 100 ºC) and a neutral (or basic) pH, making it more cost-effective and environmentally benign [ 18 ], [ 19 ]. Phytochemicals in aqueous extracts of various plant parts can affect ZnONPs' shape, surface area, porosity, particle size, and other electrical and surface characteristics. Common plant components parts such as leaves, flowers, fruits, and fruit peels are being extensively studied for the biogenic synthesis of ZnONPs. For example, leaf aqueous extracts of various medicinal plants such as Cyanometra ramiflora [ 20 ], Hibiscus rosasinensi [ 21 ], Cassia fistula and Melia azedarach [ 22 ] and others have been used to synthesise ZnONPs for antimicrobial and photocatalytic applications. Fruit peels, often discarded as waste, hold a wealth of nutritional, medicinal, and environmental benefits. These outer layers of fruits, such as mangoes, oranges, lemons, bananas, etc., are rich in bioactive compounds such as flavonoids, phenolic acids, and dietary fibre. Generally, the dominant polar phytochemicals, flavonoids and phenolic acids, play a significant role in dictating the mechanism of the biogenic synthesis of ZnONPs, which include: (i) Reduction of the Zn 2+ ions in the metal salt solution, and (ii) Capping and stabilizing the ZnO nanoparticles formed, thereby preventing particle agglomeration. These mechanisms in turn influence the size, morphology and surface area, as well as the biological and photochemical properties of the synthesized ZnONPs [ 23 ]. In recent years, fruit peel aqueous extracts have been used to synthesise ZnONPs due to cost-effectiveness and environmental pros [ 23 ], [ 24 ]. The most investigated fruit peels include Citrus sinensis (L.) [ 25 ], [ 26 ], Ananas comosus (L.) [ 27 ], [ 28 ], Citrus limon (L.) [ 29 ], Musa acuminate [ 30 ], [ 31 ], Mangifera indica (L.) [ 32 ] and Malus domestica [ 33 ]. Antimicrobial and photocatalytic applications of ZnONPs synthesized using fruit peel extracts has been well studied and documented [ 17 ], [ 19 ], [ 23 ], [ 24 ], [ 34 ]. To the best of our knowledge, there was no report on the systematic study the antifungal and photocatalytic potentials of a series of ZnONPs synthesized using various fruit peel extracts under similar conditions. Thus, we report the biogenic synthesis of a series of ZnONPs using banana, mango and pineapple peel aqueous extracts as capping/reducing agents, and investigate how the particles’ properties, such as size, surface area, morphology and bandgap, affect the antifungal and photocatalytic potentials of the synthesized ZnONPs. 2.0 Experimental 2.1 Materials Double distilled water was used as reaction medium throughout the study. Zinc nitrate hexahydrate (Zn(NO 3 ) 2 ⋅6H 2 O) was supplied by MOLYCHEM India (98%, P. Code: 19982), while the methylene blue, sodium hydroxide and ethanol were supplied by Sigma Aldrich (98–99%). All the chemicals were of high purity and used exactly as supplied, with no additional purification required. Banana ( Musa spp ), mango ( Mangifera indica ) and pineapple ( Ananas comosos ) peels were sourced from roadside fruit sellers within Lokoja metropolis, Kogi State, North-Central Nigeria. 2.2 Sample Preparation Methods The fruit (banana, mango and pineapple) peels were obtained as waste materials from roadside fruit sellers within Lokoja metropolis, Nigeria. These waste materials were washed thoroughly with tap water to remove debris and any fleshy part of the fruits, cut into smaller pieces, rinsed thoroughly with distilled water, and dried under sunlight for five (5) days. The dried samples were then oven dried at 60 ºC for two days, crushed into powder using mortar and pestle and sieved through a 200 micron stainless steel laboratory mesh. The fine powders were stored in a desiccator for further use. 2.2.1 Preparation of the fruit peel aqueous extracts In each case, the aqueous extracts of the respective fruit peels (banana, mango and pineapple) were prepared by weighing 10 g of the peel powder in a 500 ml beaker to which 200 ml distilled water was added. The mixture was then stirred on a hot magnetic stirrer at 80 ºC for two (2) hours. The mixture was then cooled to room temperature and allowed to stand for 10 minutes, filtered through a muslin cloth to get a clear supernatant, followed by proper filtration through a Whatman No. 1 filter paper with pores of 25 µm. The clear aqueous extracts of the banana, mango and pineapple peels were labelled as BPE, MPE and PPE, respectively, and kept in a refrigerator for further use. 2.2.2 Biogenic synthesis of the ZnONPs The fruit peel aqueous extracts (BPE, MPE and PPE) were used for the biogenic synthesis of the ZnONPs. In each case, 100 mL of the aqueous extract was mixed with 0.25 M of zinc nitrate hexahydrate (Zn(NO 3 ) 2 ⋅6H 2 O; 98%, P. Code: 19982) dissolved in 100 mL distilled water. The pH of the mixture was then adjusted to 12 using 0.25 M NaOH. The mixture was stirred on a magnetic stirrer at 80°C for 2 hrs, and then cooled in an ice bath to allow complete precipitation. Centrifugation was used to separate the precipitates at 5000 rpm for 5 minutes. The recovered solids were further washed with distilled water and ethanol to remove both organic and inorganic impurities, and the centrifugation was repeated five times under similar conditions. The recovered solids were then placed in a crucible dried overnight in an oven at 90°C, and calcined for 2 hours at 500°C to obtain the biosynthesized ZnONPs. These were labelled as ZnO-BPE, ZnO-MPE and ZnO-PPE, respectively, and stored in a desiccator for further use. 2.2.3 Precipitation synthesis of ZnO NPs A reference sample was prepared (without any fruit peel extract) using a simple precipitation method. Exactly 100 mL of 0.25 M solution of NaOH was added gradually to 100 mL of 0.25M zinc nitrate hexahydrate (Zn(NO 3 ) 2 ⋅6H 2 O; 98%, P. Code: 19982) until precipitation was complete. The mixture was continuously stirred at 80 ºC for 2 hours, cooled to room temperature, and the precipitates formed were filtered, rinsed severally with distilled water, dried overnight in an oven at 90°C, and then calcined at 500°C for 2 hours. This sample was labelled as ZnO-ppt and stored in the desiccator for further use. 2.3 Characterization of the synthesized ZnONPs Thermal analysis (TGA/DTG) of the synthesized ZnONPs was carried out using a thermo-balance (STA 6000, PerkinElmer) by heating the samples from 50 to 1000 ºC at a heating rate of 2 ºC/min under continuous flow of air. X-ray diffractograms of the ZnONPs were obtained using a D8-Advance multipurpose X-ray diffractometer from Bruker with Cu-K α radiation (λ = 1.5406 Å) generated at 40kV and 45mA. The measurements were run within a range of 2 ϴ = 5–70° with a step size of 0.034°. Data were background subtracted such that the phase analysis was carried out for a diffraction pattern with zero background. Phases were identified from the match of the calculated peaks with the measured ones until all phases were identified within the limits of the resolution of the results. Results were interpreted using the ICDD: PDF database 1999 and evaluated using EVA software from BRUKER. FT-IR spectra of the samples were recorded using a Perkin Elmer model ‘Spectrum 100’ spectrometer in the wavenumber range of 400–4000 cm − 1 . About 20 mg of each sample was analysed after a background scan was run prior to the characterization of each sample. UV-visible diffuse reflectance spectra (UV-vis. DRS) of the samples were recorded on a Cary 5000 UV-Vis-NIR spectrophotometer from Agilent. Samples were prepared in a metallic sample holder and BaSO 4 was used as standard and diluent. About 200 mg of each sample was mixed with an equal amount of BaSO 4 , ground thoroughly into fine powder and placed in the metallic sample holder. Measurements were carried out at ambient temperature in the wavelength scan range of 200–700 nm. The textural properties of the samples were studied using N 2 -physisorption at -196 ºC. The N 2 adsorption/desorption isotherms were recorded on a Tristar II 3020 instrument from Micromeritics. Prior to analysis, samples were degassed at 200 ºC for 12 hours under a constant flow of nitrogen gas. Specific surface areas (S BET ) were determined from the BET equation in the pressure range 0.05 < P 0 < 0.30. The average pore diameters were calculated from the BJH desorption isotherms. The cumulative pore volume was obtained from the desorption isotherms at P/P 0 ~ 1.0. Field emission gun scanning electron microscopy (FEGSEM) and transmission electron microscopy (TEM) techniques were used for the microscopy study, using a Zeiss Ultra Plus model FEGSEM and JOEL 2100 model TEM instruments, respectively. SEM samples were placed on a copper grid coated with carbon tape. The TEM samples were prepared by sonication in ethanol for 10 min, placed on a copper grid coated with a carbon film and then dried under a UV lamp. 2.4 Antifungal study of the synthesized ZnONPs Antifungal study was carried out using the disc diffusion method [ 35 ]. Four fungal isolates ( Trichoderma viridae, Trichosporon sp, Mucor sp and Aspergilus niger ) were employed for this study. To prepare the inocula plates, 20 mL of sterile Potato Dextrose Agar (PDA) were poured into Petri dishes and allowed to solidify, and then 24 hours prepared test cultures were swabbed on the solidified PDA media and allowed to dry for 10 minutes. Discs (made using Whatman No. 1 filter paper) of 7 mm size impregnated with four different concentrations (500, 250, and 125 and 62.5 µg/ml) of the ZnONPs suspension in deionized water (DI) were then placed aseptically on the prepared culture plates, and allowed to sit at room temperature for 30 minutes for compound diffusion. The plates were then incubated for 24 hours at 37 ºC. Antifungal activity was measured based on the zones (in mm) surrounding the discs that show clear growth inhibition on the agar plates. 2.4.1 Determination of minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) To determine the MIC and MFC of the synthesized ZnONPs, sterile 96-well plates and Potato Dextrose Broth (PDB) were used. Four different concentrations (500, 250, and 125 and 62.5 µg/ml) of the ZnONPs suspensions were prepared by micro tube dilution method [ 36 ]. In a total volume of 2 mL, about 0.1 mL of the standardized fungal inoculum was added followed by incubation at room temperature for 2 days. Results were checked for the tubes that shows visible growth or turbidity. The tube with minimum concentration that shows no visible growth or turbidity is considered as the MIC for that sample against a given fungal isolate. All tubes that show no visible growth were sub-cultured on a PDA plate and incubated for another 2 days at room temperature. The plates were observed for visible growth. The least concentration that shows no visible growth is recorded as the MFC for that sample against a given fungal isolate. 2.5 Photodegradation of Methylene Blue The synthesized ZnONPs were applied for the photodegradation of methylene blue (MB) under UV light irradiation. Reaction was performed at ambient temperature and pressure for a total period of 120 minutes using a round bottomed flask as reactor, 100 W mercury lamp as UV light source, 10 ppm MB dye concentration and 100 mg catalyst loading. In each case, a 100 mg of the synthesised ZnONPs was added to 100 ml of the 10 ppm MB dye solution and this was continuously stirred 30 minutes under dark to achieve adsorption-desorption equilibrium before UV irradiation. Samples were taken at 15 minutes interval for 120 minutes. The ZnONPs in the sample were first separated by centrifugation at 10,000 rpm for 5 minutes, and the clear supernatants were analysed by UV visible spectrophotometer in the wavelength range of 200–800 nm. The percentage of MB dye degradation (D) was calculated using the the following equation: Degradation Efficiency, D (%) = [(A 0 -A t )/A 0 ] *100 …………………….. (1) Where A 0 and A t represents the absorbance of the MB solution at t = 0 minutes and at sampling time (t), respectively. 3.0 Results and Discussion 3.1 TGA and DTG analysis of the synthesized ZnONPs The thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) curves of the synthesized ZnONPs before and after calcination at 500 ºC are presented in (supplementary information, Figure S1 ; Fig. 1 ). The analysis was carried out under airflow within the temperature range of 50 to 1000 ºC with a ramp rate of 2 ºC/min. Prior to calcination treatment, all the samples showed significant weight loss (25–45 wt%). Three distinct phases of significant weight loss were noted in the biogenic synthesized samples (supplementary information, Figure S1 ). First, below 200°C, water evaporation and removal of volatile organic molecules was observed based on the DTG curve (Figure S1 ). This accounted for about 10% weight loss in the early stage of the TGA curve. Second, the rise in temperature between 200 to 450 ºC led to an increase in the skeletal disruption and breakdown of organic molecule/biomolecules (which served as stabilizing/capping agent for the biogenic synthesis of the ZnONPs) was observed resulting in a significant weight loss of 20 to 30%. This temperature range is responsible for the nucleation and crystal growth of the ZnO nanoparticles [ 4 ]. Third, a weight loss of about 5%, as the temperature was increased above 450 ºC, was observed in all the samples. This higher temperature weight loss could be attributed to the degradation of carbon residues from the volarization of biomolecules in the second stage, as well as other inorganic impurities [ 37 ]. The ZnO-ppt sample showed a smooth continuous weight loss below 500 ºC, which could be attributed to the removal of water molecules, surface hydroxyl groups and nitrate groups from the substrates used during the precipitation synthesis of the sample. The observed weight loss (TGA) correlates well with the respective derivate weight (DTG) for all the analysed samples. Figure 1 shows the TGA and DTG plots of the samples after calcination at 500 ºC. The TGA/DTG characterization was carried out to determine the thermal and chemical stability of the samples post calcination treatment. The TGA curve (Fig. 1 (A)) showed a negligible weight loss of 1.0 wt% for the ZnO-MPE sample due to the removal of adsorbed moisture from the nanoparticles' surface [ 38 ]. The corresponding DTG curve (Fig. 1 (B)) showed two exothermic peaks below 200 ºC, which strongly suggests the removal of surface adsorbed water molecules and/ or total dehydration of the sample. The DTG of the ZnO-ppt sample showed similar behaviour as the ZnO-MPE, but with higher total weight loss of 4.1%. Both ZnO-BPE and ZnO-PPE showed similar profiles with broad DTG peaks below 400 ºC and total weight loss of about 5.2%. The broadness of the DTG peaks in these samples could be due to the removal of strongly adsorbed water molecules within the pores of the nanoparticles. All the samples showed smooth continuous weight loss, which strongly suggests the absence of organic molecules or carbon deposits on the surface of the calcined samples. Further, the TGA and DTG results for the biogenic synthesized samples suggest the potential of the phytochemicals in banana, mango and pineapple peels to serve as capping/reducing agents to biofabricate ZnONPs, and results in materials with different thermal and chemical stability. 3.2 XRD of the synthesized ZnONPs XRD was used to analyze the crystal structure and particle sizes of the synthesized ZnONPs (Fig. 2 ). The samples showed similar diffraction peaks typical of hexagonal wurtzite crystalline structure of ZnO at 2θ values and crystal planes ( hkl ) of ca. 31.95º (100), 34.54º (002), 36.38º (101), 47.64º (102), 56.78º (110), 62.96º (103), 68.20º (112) and 69.36º (201) respectively, consistent with the joint committee on powder diffraction standards (JCPDS file number: 36-1451) [ 4 ], [ 39 ]. Few low intensity peaks outside the standard ZnO crystal structure could be due to baseline calibration error or minor impurities in the samples. Table 1 shows crystallite sizes of the samples calculated using the Debye-Scherrer’s method (Eq. (1)) by measuring the full width at half maxima (FWHM) of the most intense peak (2θ = ca. 36.50 ± 0.2 (101)). Table 1 Bulk and surface properties of the synthesized ZnONPs Sample ZnO-ppt ZnO-BPE ZnO-MPE ZnO-PPE XRD ref. peak (2θ/degrees) 36.38 36.64 36.48 36.39 FWHM 0.23 0.35 0.40 0.29 Crystallite size (nm) a 38.00 25.20 21.80 30.10 Band gap energy (eV) b 2.45 2.83 2.41 2.85 BET surface area (m 2 /g) 28.62 31.85 37.72 29.89 BJH Pore diameter (nm) 8.92 10.56 13.13 9.60 Cummulative pore volume (cm 3 /g) 0.13 0.18 0.26 0.15 a = Calculated/obtained from XRD using Debye-Scherrer equation b = Calculated/obtained from Tauc Plot using the UV-vis spectral data Crystallite size, L = (kλ)/β cosθ …………………….. (1) Where L is the crystallite size (in nm), k is constant (usually 0.89 for a Cu-kα radiation source), λ is the wavelength of x-ray radiation (usually 0.154 nm for a Cu-kα radiation source), β is full width at half maximum of the reference peak (in radians), and θ is the reference Bragg’s angle (in degrees) [ 39 ]. A significant change in the particle sizes was observed, with ZnO-MPE showing a smaller particle size of 21.80 nm. The decreasing order of crystallite sizes was as follows; ZnO-ppt = 38.00 nm > ZnO-PPE = 30.10 nm > ZnO-BPE = 25.20 nm > ZnO-MPE = 21.80 nm (Table 1 ). This trend is in direct agreement with the intensity of the XRD peaks. One of the major advantages of the biogenic synthesis of NPs is nanosizing [ 40 ]. Thus, varying the fruit peel extracts resulted in the decrease in crystallite sizes of the synthesized ZnONPs, hence, validating part of the hypothesis of this research work. A similar observation was reported in the literature when different plant parts were investigated [ 40 ], [ 41 ]. 3.3 FT-IR spectra of the synthesized ZnONPs Figure 3 presents the FT-IR spectra of the synthesized ZnONPs. A vibration frequency at about 521 cm − 1 was attributed to Zn-O vibration modes of the ZnONPs, while peaks at 1380 and 1635 cm − 1 were assigned to stretching vibrations of the H 2 O and C = C/C = O bonds, respectively [ 38 ]. It is believed that the peaks at 1380 and 1635 cm − 1 observed in all the samples are due to adsorbed water and CO 2 molecules from the atmosphere. The low intensity broad peaks at 3400 cm − 1 are due to bending/stretching vibrations of hydroxyl groups in adsorbed moisture on the surface of the samples. 3.4 UV-visible spectra of the synthesized ZnONPs To determine the absorption property and, consequently, the bandgap energy ( E g ) of the synthesized ZnONPs, UV-visible diffuse reflectance (UV-vis. DRS) spectroscopy was utilized. The samples were examined within the wavelength range of 200–700 nm, and the Tauc method was used to compute the band gap energies (Table 1 ). A typical wurzite crystal phase of ZnO has a broad UV-vis absorption spectrum with maximum around 364 nm, which results in O 2p Zn 3d (π-π*) electronic excitation from the VB to the CB, leading to photocatalytic activity [ 42 ]. Figure 4 showed the UV-vis. DRS spectra of the synthesized ZnONPs. Broad absorption bands in the range of 200–400 nm (UV-region) appeared in all the samples. ZnO-ppt and ZnO-MPE showed slightly broader spectra extending into the visible region, which could lead to enhanced optical properties of the samples. Another crucial factor that must be taken into account in photocatalytic investigations is bandgap energy (E g ). Typical bandgap energy of bulk ZnO is 3.37 eV, but this work reported ZnONPs with narrow (indirect) bandgap energies in the range of 2.41–2.85 eV, elucidated based on the Tauc method (Table 1 ; supplementary information, Figure S2). Similar bandgap energies are reported elsewhere [ 34 ]. The bandgap typically lowers as particle size rises; this is due to the quantum size effect, which causes the bandgap to eventually decrease as particle size increases. However, the claim that the bandgap solely depends on the particle size factor is not always accurate. Numerous other parameters, including the synthesis method, morphology, lattice strain, particle size, crystal defect, and surface roughness, can also cause the decrease in the bandgap of the ZnONPs [ 38 ]. Although it is challenging to identify the precise variables that have altered the optical bandgap in the synthesized samples, it may be one or a combination of the previously listed factors. Additionally, the absorption spectrum's broad peaks (Fig. 4 ) and presence of multiple peaks indicates that the synthesised samples have structural defects capable of influencing the photabsorption and excitation energy (E g ) of the materials. It is therefore understood that the lower bandgap observed in the synthesized ZnONPs could be due to confinement effects arising from the biogenic synthesis method employed [ 43 ], since this synthesis approach is known to generate surface defects. Overall, the low bandgap energy (Table 1 ) reflects a low energy requirement to excite electron from the valence band (VB) to the conduction band (CB), which could lead to better antifungal and photocatalytic performance of the samples. 3.5 Surface area and porosity of the synthesized ZnONPs Figure 5 shows the N 2 adsorption–desorption isotherms for the synthesized ZnONPs. All the samples showed type IV isotherms typical of mesoporous materials. The ZnO-ppt sample showed H 2 -type hysteresis, while the biogenic synthesized samples showed H 3 -type hysteresis, in the relative pressure (P/P 0 ) range of 0.4-1.0. These findings suggests the presence of mesopores in all the synthesized ZnONPs, which is in agreement with other report [ 4 ]. The Brunauer–Emmett–Teller (BET) surface area, and the Barrett–Joyner–Halenda (BJH) pore volume and pore diameter of the samples are presented in (Table 1 ). The biogenic synthesis was found to influence both the surface area and porosity of the materials. The ZnO-ppt showed the smallest surface area of 28.62 m 2 /g, while the surface area of the biogenic synthesized samples in decreasing order follows; 37.72 m 2 /g (ZnO-MPE) > 31.85 m 2 /g (ZnO-BPE) > 29.89 m 2 /g (ZnO-PPE). This trend is consistent with theory and also in good agreement with the particle sizes of the samples calculated based on the Scherer’s method (Table 1 ). Average BJH pore diameter and cumulative pore volume were found to be in the ranges 8.92–13.13 nm and 0.13–0.26 cm 3 /g, respectively. These observations are comparable with the literature [ 34 ]. 3.6 Structural Morphology and Composition of the synthesized ZnONPs The structural morphology of the synthesized ZnONPs was examined using SEM and TEM, while the composition of the samples was ascertained using EDX spectroscopy. Figure 6 presents the SEM images and the corresponding EDX spectra for ZnO-ppt and ZnO-MPE, respectively. The ZnO-ppt showed evenly distributed spherical shaped particles with little particle agglomeration, while the ZnO-MPE showed flower-like morphology. This remarkable change in morphology in the biogenic synthesized sample indicated the influence of the synthesis approach on the morphology of the nanoparticles. SEM of the ZnO-BPE and ZnO-PPE showed flakes-like and cloud-like morphology, respectively (supplementary information, Figure S3), with higher degree of agglomeration when compared to the previous samples. The EDX spectra of all the samples showed Zn and O as dominant peaks, at 0.5 KeV for O and 1.0, 8.4 and 9.0 KeV for Zn, confirming the formation of the ZnONPs [ 44 ]. Other significant peaks include C at 0.2 KeV and two unlabelled Cu between 2.0 and 3.5 KeV, arising from the carbon coated copper grit used during sample preparation. TEM images confirmed the morphologies obtained from SEM for all the samples (supplementary information, Figure S4). However, for the ZnO-ppt sample, hexagonal shaped particles were also observed at 50 nm magnification, in addition to the spherical shaped particles (supplementary information, Figure S5). It is widely argued that TEM provides a better means to study particle size of ZnONPs. This is undoubtedly true when dealing with particles of similar morphology. But in this study where samples with different morphologies are compared, XRD is considered more suitable. Nevertheless, both techniques can alternatively serve as a powerful tool for the determination of particle sizes of nanomaterials. 3.7 Antifungal Potentials of the synthesized ZnONPs Four food-spoilage fungal isolates ( Trichoderma viridae, Trichosporon sp, Mucor sp and Aspergilus niger ) were used to test the antimicrobial potential of the synthesized ZnONPs at different concentrations viz; 500, 250, 125 and 62.5 µg/ml using the disc diffusion method. Figure 7 illustrates the antifungal efficacy of the ZnO-ppt and ZnO-MPE against Trichosporon sp at 250 µg/ml concentration. The zone of inhibition's (ZI) diameter differed with fungal isolates and concentration of the ZnONPs (Table 2 ). Highest ZI values were recorded against Trichosporon sp at 500 µg/ml for all the tested ZnONPs, and the values were seen to decline as the concentration decreases. The ZnONPs tested showed susceptibility against the fungal isolates at least at the high concentration (500 µg/ml), except for ZnO-ppt against Trichoderma viridae and ZnO-BPE against Trichoderma viridae and Mucor sp . All the tested samples were inactive at the lowest concentration (62.5 µg/ml), with the exception of the ZnO-PPE sample against Trichosporon sp and Aspergilus niger . Overall, the samples were more effective against Trichosporon sp and least active against Trichoderma viridae . This observation can be explained based on physiological and biochemical differences between the two microbes. For example, Trichoderma viridae grows optimally at 20–25 ºC and wider pH range of 4–9, while Trichosporon sp prefers a more narrow temperature and pH range of 20–25 ºC and 5–7, respectively [ 45 ]. Further, the cell wall of Trichoderma viridae composed primarily of chitin and beta-glucans, which act as stronger defense system against external threat compared to the cell wall of Trichosporon sp composed of mannans and beta-glucans, known to provide a much weaker defense. It is also reported that Trichoderma viridae produce a wide range of enzymes such as celluloses, xylanases, and proteases, whereas Trichosporon sp produces few enzymes such as lipases and amylases [ 46 ]. These enzymes may serve to defend the cells against external threats, thereby minimizing the effect of the tested ZnONPs on the fungal isolates. The exact method of interaction between nanoparticles and cell organelles that triggers antimicrobial activity is still unknown, despite several attempts to explain how they infiltrate microbial cells. In general, four methods of penetration have been established: (1) the nanoparticles attach to the cell membrane and disrupt it; (2) the Zn ions produce reactive oxygen species (ROS) that harm the microbial DNA; (3) the ionic forms of the nanoparticles interfere with ATP synthesis and DNA replication; and (4) the nanoparticles interact with amino acid and nucleic acid moieties of the cell membrane by forming thiols or phosphates [ 44 ]. Figure 8 compares the antifungal potentials of the ZnONPs against Trichosporon sp at a concentration of 250 µg/ml. Often than not, the antimicrobial properties of ZnONPs have been linked to particle size of the nanoparticles [ 47 ], [ 48 ]. Although a direct correlation between particle size and antifungal activity could not be established for this study, the smaller particle size of the ZnO-MPE could have contributed, in addition to other factors such as morphology and surface area, to its higher antifungal potential. In a recent study by Pariona and co-workers, the antifungal activity of ZnO was reported to be shape-dependent [ 49 ]. Thus, particle size and morphology play a crucial role on in the high antifungal potential of the ZnO-MPE sample. Table 2 Antifungal activity (Zones of Inhibition) of the synthesized ZnONPs Test Organisms Concentration (µg/ml)/ Inhibition zone (mm) Control (Ketaconazole (mg/ml))/ Inhibition Zone (mm) 500 250 125 62.5 20 ZnO-ppt Trichoderma viridae 0 0 0 0 18 Trichosporon sp 8.76 7.75 0 0 22 Mucor sp 8.79 8.43 7.99 0 19 Aspergilus niger 8.10 8.00 7.47 0 18 ZnO-BPE Trichoderma viridae 0 0 0 0 18 Trichosporon sp 11.40 8.47 0 0 22 Mucor sp 0 0 0 0 19 Aspergilus niger 10.61 9.86 8.41 0 18 ZnO-MPE Trichoderma viridae 10.40 8.200 0 0 18 Trichosporon sp 16.31 15.66 13.35 0 22 Mucor sp 12.32 10.22 8.70 0 19 Aspergilus niger 11 10.22 8.62 0 18 ZnO-PPE Trichoderma viridae 8.96 0 0 0 18 Trichosporon sp 10.93 10.71 9.14 9.0 22 Mucor sp 7.9 7.47 0 0 19 Aspergilus niger 11.52 10.53 9.15 8.26 18 Two important parameters; MIC and MFC are significant in the study of antifungal activities of ZnONPs [ 36 ]. The lowest antimicrobial concentrations that, following an overnight incubation period, will prevent the growth of visible microorganisms are known as minimum inhibitory concentrations (MICs) [ 44 ]. On the other hand, MFC refers to the minimum concentration of the test sample that can eliminate the microbe. Alexander Fleming was the first to introduce the concept of minimum inhibitory concentration by measuring the antibacterial efficacy of medications using the turbidity of broth. The MIC and MFC of the ZnONPs is presented in (Table 3 ). The lowest MIC value of 62.5 µg/ml was recorded for ZnO-PPE against Trichosporon sp and Aspergilus niger , while the MFCs for all the samples were found to be > 500 µg/ml. These findings were found to be consistent with other reports [ 11 ]. Table 3 Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) of the synthesized ZnONPs (in µg/ml). Test Organisms ZnO-ppt MIC MFC ZnO-BPE MIC MFC ZnO-MPE MIC MFC ZnO-PPE MIC MFC Trichoderma viridae NT NT NT NT 250 > 500 250 > 500 Trichosporon sp 250 > 500 250 > 500 125 > 500 62.5 > 500 Mucor sp 125 > 500 NT NT 125 > 500 250 > 500 Aspergilus niger 125 > 500 125 > 500 125 > 500 62.5 > 500 KEY : NT = Not Tested 3.8 Photocatalytic Potentials of the synthesized ZnONPs To study the potential of the synthesized ZnONPs in photodegradation of MB under UV light irradiation, a 100 W mercury lamp, 10 ppm MB concentration, 100 mg catalyst loading and 15 minutes sampling intervals for 2 hours were used. Firstly, the adsorption-desorption equilibrium (dark reaction) and photolysis were carried out under constant stirring for 30 minutes. Both reactions showed insignificant (0–3%) removal of the methylene blue (MB) contaminant (results not shown here). Figure 6 ((A) and (B)) displays the absorption spectra of the MB degradation under UV light irradiation using ZnO-ppt and ZnO-MPE as photocatalysts, respectively. Reduction in absorption is evident from the intensity of the peaks around 615 and 664 nm, indicating that both samples are active photocatalysts driving the MB dye degradation process [ 38 ]. This approach made it possible to continuously observe and assess the degradation process at 15 min intervals for 120 minutes. Eq. (1) was used to calculate the MB degradation efficiency (D (%)) as reflected by (Fig. 6 (C) and (D)). Figure 9 (A) showed a gradual reduction of the UV absorption peak intensity for the ZnO-ppt sample. The photodegradation efficiency was low (8%) at the initial sampling point. From 30 minutes of reaction on stream, the degradation activity increased gradually up to 83% after 120 minutes (Fig. 9 (C)). The ZnO-MPE sample showed an initial MB degradation of 28%, a significant jump in degradation efficiency after 60 minutes, and gradually attaining the all high MB degradation of 91% after the 120 minutes reaction time (Fig. 9 (D)). Significant decolourization of the MB dye over the ZnO-MPE was observed, which is a testament to its high potential as a photocatalyst (Fig. 9 (E)). The higher photocatalytic potential of this sample can be attributed to its unique characteristics such as low band gap energy, high surface area, small crystallite sizes and peculiar morphology. The ZnO-BPE and ZnO-PPE samples showed initial phodegradation of 20 and 43%, respectively (supplementary information, Figure S6). The high initial degradation efficiency of the ZnO-PPE could be due to surface and structural defects in the samples, which serve as active sites for rapid generation of reactive oxygen species (ROSs) leading to higher initial photocatalytic efficiency of the sample. These defective sites are eventually blocked by the MB contaminant, resulting in slow degradation. After 120 minutes of reaction on stream, the ZnO-BPE attained 78% degradation while ZnO-PPE achieved only 73%. Thus, the decreasing order of MB photodegradation efficiency of the tested samples after 120 minutes of reaction follows; ZnO-MPE (91%) > ZnO-ppt (83%) > ZnO-BPE (78%) > ZnO-PPE (73%). The best performing catalyst, ZnO-MPE, was subjected to catalyst regeneration to check its stability and reusability. The used ZnO-MPE catalyst was extracted from the reaction mixture by centrifugation following each cycle of the reaction, and thoroughly washed with ethanol and double-distilled water to remove any adsorbed organic moieties from the MB dye before being used for subsequent cycles. Three regeneration cycles were carried out under similar experimental conditions, and the results are presented in (Fig. 10 ). The ZnO-MPE sample was seen to sustain its photodegradation efficiency after three regeneration cycles. To verify the structural and photostability changes in the used ZnO-MPE sample following reusability studies, the crystal structure and photoabsorption of the sample were verified by XRD and UV-visible spectroscopy, respectively. No significant shift in the XRD peaks was noted, and the Scherrer’s crystallite size is the same as in the fresh sample, confirming the structural stability of the used sample (Figure S7). Also based on the UV-vis DRS (Figure S8) of the sample post reusability studies, both the absorption spectrum and band gap energy of the sample remained the same as in the fresh sample, confirming its chemical and photostability. 3.9 Proposed Mechanism of the Photodegradation Process The widely proposed mechanism for photodegradation of MB dye using ZnO photocatalyst is based on the radical generation mechanism [ 50 ]. First, the dye is attacked by the extremely reactive radicals (.OH and .O 2 − ) produced in the dye solution, which eventually leads to the conversion of the MB into less hazardous products (water and carbon dioxide). Figure 11 provides an illustration of the proposed method of free radical generation and MB photodegradation using the ZnO-MPE as a model sample. When the ZnO-MPE nanoparticles are exposed to UV light, electrons (e − ) and holes (h + ) are created, which initiates the photocatalytic destruction process. In principle, when the sample surface is exposed to light with an energy greater than or equal to the band gap energy (E g ), a photoexcited electron (e − ) is moved from the valence band (VB) to the conduction band (CB), leaving behind a positive hole (h + ). Generally, a faster electron-hole pair formation is ensured by a smaller band gap, which makes the samples under investigation highly photoactive. The produced electron and hole go independently to the catalyst's surface and react with the O 2 and OH 2 , present in the MB solution to produce superoxide radical anions ( − O 2 .), hydroperoxyl radicals ( − OOH), and hydroxyl radicals ( − OH/.OH) (Fig. 11). The most potent oxidizing species among these radicals, referred to as reactive oxygen species (ROS) in photocatalytic oxidation processes, is the hydroxyl radicals, which can potentially degrade the MB contaminants in the vicinity of the photocatalyst surface. A significant issue in this mechanism is electron-hole pair recombination, which lowers the ROS formation efficiency and, hence, negatively affects the photodegradation process. However, it is stated in the literature that defects in the ZnONPs may potentially trap the generated electrons, preventing electron-hole pairs from recombining [ 51 ]. The biogenic synthesis proceeds via the formation of intermediate zinc complexes, resulting in the formation of defective ZnONPs after calcination treatment due to the combustion of the phytochemicals acting as ligands. Therefore, a significant level of ROS formation could be attributed to the existence of defects in the ZnONPs under study. Further, the size of the nanoparticles is an important factor that affects the photodegradation activity. Smaller particle samples have a greater surface-to-volume ratio, which provides more surface active sites for ROS generation. This, in turn, increases the interfacial charge carrier transfer for photodegradation of the MB dye contaminant. 4.0 Conclusion This work reported on biogenic synthesis of ZnONPs using banana (ZnO-BPE), mango (ZnO-MPE) and pineapple (ZnO-PPE) peel aqueous extracts. A reference sample (ZnO-ppt) was also prepared using simple precipitation method (without fruit extract) for comparison. These were characterized using various techniques. All the samples showed hexagonal wurtzite crystalline structure typical of ZnONPs while the type of the fruit peel extracts significantly influenced the properties of the samples. The ZnONPs showed Scherrer’s crystallite sizes of 21.80–38.00 nm, surface areas of 28.62–37.72 m 2 /g, sufficient UV light absorption and narrow bandgap of 2.41–2.85 eV. Different morphologies, ranging from spherical to flower-like, were observed as the fruit peel extract is varied. The potential of the samples as antifungal agents and as catalysts in photodegradation of MB yielded positive results. Highest antifungal potential was observed against Trichosporon sp for the ZnO-MPE at concentration of 250 µg/ml. All the samples showed good photocatalytic potential against MB degradation with highest degradation efficiency of 91% for the ZnO-MPE, which is sustained over three regeneration cycles. Compared to the other samples studied, the ZnO-MPE showed higher antifungal and photocatalytic potential, which was attributed to various factors including small particle size, large surface area, unique morphology and narrow bandgap. Declarations Funding : Partial funding (financial support) was received from the Tertiary Education Trust Fund, Nigeria (IBR2024). Employment : The authors are full-time faculty members of the Department of Chemistry, Federal University Lokoja Nigeria and Durban University of Technology South Africa, respectively. Competing Interests : The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article. Ethics and Consent to Participate : Not applicable. Consent to Publish : Not applicable. Authors’ Contribution : All the authors contributed significantly towards the completion of this research work. Dailami S.A Masokano : Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, Writing-original draft, Visualization. Jude E. Emurotu : Writing-review and editing, Supervision, Visualization. Usman O.A Shuaibu : Writing-review and editing, Supervision, Visualization. Pinkie Ntola : Resources, Validation, Writing-review and editing, Visualization. Acknowledgement The authors thank the Federal University Lokoja and the Tertiary Education Trust Fund (TETFUND-Nigeria) for the TETFUND-IBR research grant (2024). References Chavali MS, Nikolova MP. Metal oxide nanoparticles and their applications in nanotechnology. SN Appl Sci. 2019;1(6):607. Nair GM, Sajini T, Mathew B. ‘Advanced green approaches for metal and metal oxide nanoparticles synthesis and their environmental applications’, Talanta Open , vol. 5, p. 100080, 2022. Chaudhary RG, et al. Metal/metal oxide nanoparticles: toxicity, applications, and future prospects. 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Supplementary Files ArticleSI.docx Cite Share Download PDF Status: Published Journal Publication published 10 Nov, 2025 Read the published version in Discover Materials → Version 1 posted Editorial decision: Revision requested 07 Aug, 2025 Reviews received at journal 27 Jul, 2025 Reviews received at journal 22 Jul, 2025 Reviewers agreed at journal 17 Jul, 2025 Reviewers agreed at journal 17 Jul, 2025 Reviewers invited by journal 17 Jul, 2025 Editor assigned by journal 15 Jul, 2025 Editor invited by journal 14 Jul, 2025 Submission checks completed at journal 10 Jul, 2025 First submitted to journal 10 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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08:31:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27498,"visible":true,"origin":"","legend":"\u003cp\u003eTGA and DTG analysis (A) showing weight loss and (B) showing derivative weight loss of the synthesized ZnONPs\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/df9931cc7167d90f92c636c2.png"},{"id":87379850,"identity":"f87dbb4d-df44-4f71-be20-9ef822a6deb6","added_by":"auto","created_at":"2025-07-23 08:31:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":19283,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractogram of the synthesized ZnONPs (A) ZnO-ppt (B) ZnO-BPE (C) ZnO-MPE and (D) ZnO-PPE\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/65bbc9ea4a7bfb2788308e2a.png"},{"id":87379859,"identity":"92da1408-81fa-42cd-9257-9c316d172999","added_by":"auto","created_at":"2025-07-23 08:31:45","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":28982,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra of the synthesized ZnONPs (A) ZnO-ppt (B) ZnO-BPE (C) ZnO-MPE and (D) ZnO-PPE\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/b89c831abcc007614b7474ff.png"},{"id":87379841,"identity":"c4b721b3-51e0-4c72-aa91-9b6e8f2a2792","added_by":"auto","created_at":"2025-07-23 08:31:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":24083,"visible":true,"origin":"","legend":"\u003cp\u003eUV-visible spectra of the synthesized ZnONPs\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/bbd468dcfff76bb9e16e66dd.png"},{"id":87384206,"identity":"e5e482c7-306b-40f8-be09-42f993ecf99c","added_by":"auto","created_at":"2025-07-23 08:47:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":46934,"visible":true,"origin":"","legend":"\u003cp\u003eAdsorption-desorption isotherms of the synthesized ZnONPs (A) ZnO-ppt (B) ZnO-BPE (C) ZnO-MPE and (D) ZnO-PPE\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/9df5e4b5957e562cc17c47b9.png"},{"id":87378845,"identity":"5da1308e-7839-498d-b26b-8950281bc467","added_by":"auto","created_at":"2025-07-23 08:23:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":294697,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron micrograph and electron dispersive x-ray spectra of (A) ZnO-ppt and (B) ZnO-MPE, respectively\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/79890f6824863519fd6a3134.png"},{"id":87378893,"identity":"693d5230-d3ac-44dd-a14c-c7b238896fcf","added_by":"auto","created_at":"2025-07-23 08:23:45","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":198292,"visible":true,"origin":"","legend":"\u003cp\u003eInoculated plates showing the antifungal activities of (A) ZnO-ppt and (B) ZnO-MPE\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/5bdd51e8216f096f2130c633.png"},{"id":87378909,"identity":"b30518e6-a64a-4294-97a5-cff3128e6e6b","added_by":"auto","created_at":"2025-07-23 08:23:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":17914,"visible":true,"origin":"","legend":"\u003cp\u003eComparing the antifungal activities (zones of inhibition) of the samples against \u003cem\u003eTrichosporon sp \u003c/em\u003eat concentration of 250 µg/ml\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/f87ee7ec18c0bc71592f9983.png"},{"id":87378874,"identity":"f5bcdb01-0832-4825-8f11-d5870844ec82","added_by":"auto","created_at":"2025-07-23 08:23:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":165018,"visible":true,"origin":"","legend":"\u003cp\u003e(A) and (B) showing absorbance spectra of the MB dye degradation under UV light for ZnO-ppt and ZnO-MPE, respectively, (C) and (D) showing percentage degradation of the MB dye for ZnO-ppt and ZnO-MPE, respectively and (E) showing gradual decolouration of the MB dye over ZnO-MPE catalyst across 0-120 min reaction period\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/03a098bcb034397e5a043d07.png"},{"id":87378880,"identity":"bc5cdc95-cb25-4714-b25c-c82631a2c10d","added_by":"auto","created_at":"2025-07-23 08:23:44","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":10400,"visible":true,"origin":"","legend":"\u003cp\u003eRegeneration cycle of MB degradation over ZnO-MPE catalyst\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/5e9b0873effee90b490cd886.png"},{"id":87378813,"identity":"7ce3cfca-3d88-4db0-8a00-8efbf19a5e66","added_by":"auto","created_at":"2025-07-23 08:23:42","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":112663,"visible":true,"origin":"","legend":"\u003cp\u003eProposed Mechanism of the photodegradation of MB using ZnO-MPE\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/3c6e0359bbca1169385943fc.png"},{"id":96105246,"identity":"4e29400c-ac73-46fc-bfc2-71d639d74be7","added_by":"auto","created_at":"2025-11-17 16:10:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2212220,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/87de0e1e-82c9-4d26-928d-8c1ddb1d4172.pdf"},{"id":87378843,"identity":"bd97df8b-a29b-46d7-b6fd-b60eb44d46a3","added_by":"auto","created_at":"2025-07-23 08:23:44","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1265549,"visible":true,"origin":"","legend":"","description":"","filename":"ArticleSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-6965908/v1/c6a0a673f06ee6a98849b723.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eAntifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts \u003c/p\u003e","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eMetal oxide nanoparticles have continued to receive great attention due to a wide range of applications [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The tunable properties of metal oxide nanoparticles such as surface area, porosity, and morphology\u0026mdash;all associated with active surface phenomena\u0026mdash;have increased their effectiveness and expanded their range of uses. Biological and organic moieties can be used to alter or improve these properties to suit intended use in biological and environmental science [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. For instance, utilizing plant aqueous extracts as reducing/stabilizing agents sufficiently changed parameters such as particle size, crystallinity, surface area, porosity, morphology, and photoluminescence. But for many decades, there has been no universal method for synthesising and/or stabilizing metallic nanoparticles with the right surface modifications for a range of uses [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDue to their natural abundance, biocompatibility, non-toxicity, environmental friendliness, affordability, and chemical and thermal stability, zinc oxide nanoparticles (ZnONPs) is one of the few metal oxides that have drawn more attention [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. These are widely celebrated as potential photocatalysts due to their single oxidation state and suitable bandgap energy, and also as an antimicrobial agent, among numerous other applications [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. ZnO with n-type semiconducting properties has drawn a lot of interest because of its numerous uses in electronics, optics, and medicinal research [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Recently, its application in photocatalysis and as antifungal agent has been investigated explosively [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Interestingly, ZnONPs are generally considered non-toxic and harmless by various regulatory bodies including the U.S Department of Food and Drugs Administration (FDA, article number: 21CFR182.8991) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Furthermore, compared to other metal oxides, ZnONPs synthesized using a green approaches are potentially effective and beneficial for clinical and environmental applications. For example, ZnONPs are widely reported to show high potential in the photodegradation of organic dyes and for the treatment of various infectious diseases [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the last few decades, various researchers have put efforts to fine-tuning the properties of ZnONPs to enhance their activities by employing various synthesis approaches. Popular synthetic routes investigated in the literature include precipitation, sol-gel, microwave-assisted, hydrothermal, thermal decomposition, solution combustion, and biogenic (or phyto-assisted) synthesis methods [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The biogenic method is regarded as \"green\" since it does not use auxiliary solvents or generate harmful waste. Further, this method can be used to prepare a large sample in a single batch, and, hence, is readily scalable and cost-effective.\u003c/p\u003e\u003cp\u003ePlants contain an amazing variety of phytochemicals, such as alkaloids, flavonoids, saponins, steroids, tannins, phenolic acids, and other bioactive compounds, which are found in various parts including the fruits, flowers, leaves, roots, shoots, stems, bark, and seeds. Some of these naturally occurring secondary metabolites can function as stabilizing and reducing agent during the biogenic synthesis of ZnONPs [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In comparison to conventional physical and chemical processes, the biogenic synthesis of ZnONPs using plant aqueous extracts is conducted at room temperature (or a temperature below 100 \u0026ordm;C) and a neutral (or basic) pH, making it more cost-effective and environmentally benign [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Phytochemicals in aqueous extracts of various plant parts can affect ZnONPs' shape, surface area, porosity, particle size, and other electrical and surface characteristics. Common plant components parts such as leaves, flowers, fruits, and fruit peels are being extensively studied for the biogenic synthesis of ZnONPs. For example, leaf aqueous extracts of various medicinal plants such as \u003cem\u003eCyanometra ramiflora\u003c/em\u003e [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], \u003cem\u003eHibiscus rosasinensi\u003c/em\u003e [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], \u003cem\u003eCassia fistula\u003c/em\u003e and \u003cem\u003eMelia azedarach\u003c/em\u003e [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] and others have been used to synthesise ZnONPs for antimicrobial and photocatalytic applications.\u003c/p\u003e\u003cp\u003eFruit peels, often discarded as waste, hold a wealth of nutritional, medicinal, and environmental benefits. These outer layers of fruits, such as mangoes, oranges, lemons, bananas, etc., are rich in bioactive compounds such as flavonoids, phenolic acids, and dietary fibre. Generally, the dominant polar phytochemicals, flavonoids and phenolic acids, play a significant role in dictating the mechanism of the biogenic synthesis of ZnONPs, which include: (i) Reduction of the Zn\u003csup\u003e2+\u003c/sup\u003e ions in the metal salt solution, and (ii) Capping and stabilizing the ZnO nanoparticles formed, thereby preventing particle agglomeration. These mechanisms in turn influence the size, morphology and surface area, as well as the biological and photochemical properties of the synthesized ZnONPs [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn recent years, fruit peel aqueous extracts have been used to synthesise ZnONPs due to cost-effectiveness and environmental pros [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The most investigated fruit peels include \u003cem\u003eCitrus sinensis (L.)\u003c/em\u003e [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], \u003cem\u003eAnanas comosus (L.)\u003c/em\u003e [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], \u003cem\u003eCitrus limon (L.)\u003c/em\u003e [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], \u003cem\u003eMusa acuminate\u003c/em\u003e [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], \u003cem\u003eMangifera indica (L.)\u003c/em\u003e [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] and \u003cem\u003eMalus domestica\u003c/em\u003e [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Antimicrobial and photocatalytic applications of ZnONPs synthesized using fruit peel extracts has been well studied and documented [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. To the best of our knowledge, there was no report on the systematic study the antifungal and photocatalytic potentials of a series of ZnONPs synthesized using various fruit peel extracts under similar conditions. Thus, we report the biogenic synthesis of a series of ZnONPs using banana, mango and pineapple peel aqueous extracts as capping/reducing agents, and investigate how the particles\u0026rsquo; properties, such as size, surface area, morphology and bandgap, affect the antifungal and photocatalytic potentials of the synthesized ZnONPs.\u003c/p\u003e"},{"header":"2.0 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003eDouble distilled water was used as reaction medium throughout the study. Zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO) was supplied by MOLYCHEM India (98%, P. Code: 19982), while the methylene blue, sodium hydroxide and ethanol were supplied by Sigma Aldrich (98\u0026ndash;99%). All the chemicals were of high purity and used exactly as supplied, with no additional purification required. Banana (\u003cem\u003eMusa spp\u003c/em\u003e), mango (\u003cem\u003eMangifera indica\u003c/em\u003e) and pineapple (\u003cem\u003eAnanas comosos\u003c/em\u003e) peels were sourced from roadside fruit sellers within Lokoja metropolis, Kogi State, North-Central Nigeria.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Sample Preparation Methods\u003c/h2\u003e\u003cp\u003eThe fruit (banana, mango and pineapple) peels were obtained as waste materials from roadside fruit sellers within Lokoja metropolis, Nigeria. These waste materials were washed thoroughly with tap water to remove debris and any fleshy part of the fruits, cut into smaller pieces, rinsed thoroughly with distilled water, and dried under sunlight for five (5) days. The dried samples were then oven dried at 60 \u0026ordm;C for two days, crushed into powder using mortar and pestle and sieved through a 200 micron stainless steel laboratory mesh. The fine powders were stored in a desiccator for further use.\u003c/p\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 Preparation of the fruit peel aqueous extracts\u003c/h2\u003e\u003cp\u003eIn each case, the aqueous extracts of the respective fruit peels (banana, mango and pineapple) were prepared by weighing 10 g of the peel powder in a 500 ml beaker to which 200 ml distilled water was added. The mixture was then stirred on a hot magnetic stirrer at 80 \u0026ordm;C for two (2) hours. The mixture was then cooled to room temperature and allowed to stand for 10 minutes, filtered through a muslin cloth to get a clear supernatant, followed by proper filtration through a Whatman No. 1 filter paper with pores of 25 \u0026micro;m. The clear aqueous extracts of the banana, mango and pineapple peels were labelled as BPE, MPE and PPE, respectively, and kept in a refrigerator for further use.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Biogenic synthesis of the ZnONPs\u003c/h2\u003e\u003cp\u003eThe fruit peel aqueous extracts (BPE, MPE and PPE) were used for the biogenic synthesis of the ZnONPs. In each case, 100 mL of the aqueous extract was mixed with 0.25 M of zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO; 98%, P. Code: 19982) dissolved in 100 mL distilled water. The pH of the mixture was then adjusted to 12 using 0.25 M NaOH. The mixture was stirred on a magnetic stirrer at 80\u0026deg;C for 2 hrs, and then cooled in an ice bath to allow complete precipitation. Centrifugation was used to separate the precipitates at 5000 rpm for 5 minutes. The recovered solids were further washed with distilled water and ethanol to remove both organic and inorganic impurities, and the centrifugation was repeated five times under similar conditions. The recovered solids were then placed in a crucible dried overnight in an oven at 90\u0026deg;C, and calcined for 2 hours at 500\u0026deg;C to obtain the biosynthesized ZnONPs. These were labelled as ZnO-BPE, ZnO-MPE and ZnO-PPE, respectively, and stored in a desiccator for further use.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3 Precipitation synthesis of ZnO NPs\u003c/h2\u003e\u003cp\u003eA reference sample was prepared (without any fruit peel extract) using a simple precipitation method. Exactly 100 mL of 0.25 M solution of NaOH was added gradually to 100 mL of 0.25M zinc nitrate hexahydrate (Zn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO; 98%, P. Code: 19982) until precipitation was complete. The mixture was continuously stirred at 80 \u0026ordm;C for 2 hours, cooled to room temperature, and the precipitates formed were filtered, rinsed severally with distilled water, dried overnight in an oven at 90\u0026deg;C, and then calcined at 500\u0026deg;C for 2 hours. This sample was labelled as ZnO-ppt and stored in the desiccator for further use.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterization of the synthesized ZnONPs\u003c/h2\u003e\u003cp\u003eThermal analysis (TGA/DTG) of the synthesized ZnONPs was carried out using a thermo-balance (STA 6000, PerkinElmer) by heating the samples from 50 to 1000 \u0026ordm;C at a heating rate of 2 \u0026ordm;C/min under continuous flow of air.\u003c/p\u003e\u003cp\u003eX-ray diffractograms of the ZnONPs were obtained using a D8-Advance multipurpose X-ray diffractometer from Bruker with Cu-K\u003csub\u003eα\u003c/sub\u003e radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) generated at 40kV and 45mA. The measurements were run within a range of 2 ϴ = 5\u0026ndash;70\u0026deg; with a step size of 0.034\u0026deg;. Data were background subtracted such that the phase analysis was carried out for a diffraction pattern with zero background. Phases were identified from the match of the calculated peaks with the measured ones until all phases were identified within the limits of the resolution of the results. Results were interpreted using the ICDD: PDF database 1999 and evaluated using EVA software from BRUKER.\u003c/p\u003e\u003cp\u003eFT-IR spectra of the samples were recorded using a Perkin Elmer model \u0026lsquo;Spectrum 100\u0026rsquo; spectrometer in the wavenumber range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. About 20 mg of each sample was analysed after a background scan was run prior to the characterization of each sample.\u003c/p\u003e\u003cp\u003eUV-visible diffuse reflectance spectra (UV-vis. DRS) of the samples were recorded on a Cary 5000 UV-Vis-NIR spectrophotometer from Agilent. Samples were prepared in a metallic sample holder and BaSO\u003csub\u003e4\u003c/sub\u003e was used as standard and diluent. About 200 mg of each sample was mixed with an equal amount of BaSO\u003csub\u003e4\u003c/sub\u003e, ground thoroughly into fine powder and placed in the metallic sample holder. Measurements were carried out at ambient temperature in the wavelength scan range of 200\u0026ndash;700 nm.\u003c/p\u003e\u003cp\u003eThe textural properties of the samples were studied using N\u003csub\u003e2\u003c/sub\u003e-physisorption at -196 \u0026ordm;C. The N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption isotherms were recorded on a Tristar II 3020 instrument from Micromeritics. Prior to analysis, samples were degassed at 200 \u0026ordm;C for 12 hours under a constant flow of nitrogen gas. Specific surface areas (S\u003csub\u003eBET\u003c/sub\u003e) were determined from the BET equation in the pressure range 0.05\u0026thinsp;\u0026lt;\u0026thinsp;P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.30. The average pore diameters were calculated from the BJH desorption isotherms. The cumulative pore volume was obtained from the desorption isotherms at P/P\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;~\u0026thinsp;1.0.\u003c/p\u003e\u003cp\u003eField emission gun scanning electron microscopy (FEGSEM) and transmission electron microscopy (TEM) techniques were used for the microscopy study, using a Zeiss Ultra Plus model FEGSEM and JOEL 2100 model TEM instruments, respectively. SEM samples were placed on a copper grid coated with carbon tape. The TEM samples were prepared by sonication in ethanol for 10 min, placed on a copper grid coated with a carbon film and then dried under a UV lamp.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Antifungal study of the synthesized ZnONPs\u003c/h2\u003e\u003cp\u003eAntifungal study was carried out using the disc diffusion method [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Four fungal isolates (\u003cem\u003eTrichoderma viridae, Trichosporon sp, Mucor sp\u003c/em\u003e and \u003cem\u003eAspergilus niger\u003c/em\u003e) were employed for this study. To prepare the inocula plates, 20 mL of sterile Potato Dextrose Agar (PDA) were poured into Petri dishes and allowed to solidify, and then 24 hours prepared test cultures were swabbed on the solidified PDA media and allowed to dry for 10 minutes. Discs (made using Whatman No. 1 filter paper) of 7 mm size impregnated with four different concentrations (500, 250, and 125 and 62.5 \u0026micro;g/ml) of the ZnONPs suspension in deionized water (DI) were then placed aseptically on the prepared culture plates, and allowed to sit at room temperature for 30 minutes for compound diffusion. The plates were then incubated for 24 hours at 37 \u0026ordm;C. Antifungal activity was measured based on the zones (in mm) surrounding the discs that show clear growth inhibition on the agar plates.\u003c/p\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.4.1 Determination of minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC)\u003c/h2\u003e\u003cp\u003eTo determine the MIC and MFC of the synthesized ZnONPs, sterile 96-well plates and Potato Dextrose Broth (PDB) were used. Four different concentrations (500, 250, and 125 and 62.5 \u0026micro;g/ml) of the ZnONPs suspensions were prepared by micro tube dilution method [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. In a total volume of 2 mL, about 0.1 mL of the standardized fungal inoculum was added followed by incubation at room temperature for 2 days. Results were checked for the tubes that shows visible growth or turbidity. The tube with minimum concentration that shows no visible growth or turbidity is considered as the MIC for that sample against a given fungal isolate. All tubes that show no visible growth were sub-cultured on a PDA plate and incubated for another 2 days at room temperature. The plates were observed for visible growth. The least concentration that shows no visible growth is recorded as the MFC for that sample against a given fungal isolate.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e2.5 \u003cb\u003ePhotodegradation of Methylene Blue\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eThe synthesized ZnONPs were applied for the photodegradation of methylene blue (MB) under UV light irradiation. Reaction was performed at ambient temperature and pressure for a total period of 120 minutes using a round bottomed flask as reactor, 100 W mercury lamp as UV light source, 10 ppm MB dye concentration and 100 mg catalyst loading. In each case, a 100 mg of the synthesised ZnONPs was added to 100 ml of the 10 ppm MB dye solution and this was continuously stirred 30 minutes under dark to achieve adsorption-desorption equilibrium before UV irradiation. Samples were taken at 15 minutes interval for 120 minutes. The ZnONPs in the sample were first separated by centrifugation at 10,000 rpm for 5 minutes, and the clear supernatants were analysed by UV visible spectrophotometer in the wavelength range of 200\u0026ndash;800 nm. The percentage of MB dye degradation (D) was calculated using the the following equation:\u003c/p\u003e\u003cp\u003eDegradation Efficiency, D (%) = [(A\u003csub\u003e0\u003c/sub\u003e-A\u003csub\u003et\u003c/sub\u003e)/A\u003csub\u003e0\u003c/sub\u003e] *100 \u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;.. (1)\u003c/p\u003e\u003cp\u003eWhere A\u003csub\u003e0\u003c/sub\u003e and A\u003csub\u003et\u003c/sub\u003e represents the absorbance of the MB solution at t\u0026thinsp;=\u0026thinsp;0 minutes and at sampling time (t), respectively.\u003c/p\u003e\u003c/div\u003e"},{"header":"3.0 Results and Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 TGA and DTG analysis of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eThe thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) curves of the synthesized ZnONPs before and after calcination at 500 \u0026ordm;C are presented in (supplementary information, Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e; Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The analysis was carried out under airflow within the temperature range of 50 to 1000 \u0026ordm;C with a ramp rate of 2 \u0026ordm;C/min. Prior to calcination treatment, all the samples showed significant weight loss (25\u0026ndash;45 wt%). Three distinct phases of significant weight loss were noted in the biogenic synthesized samples (supplementary information, Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). First, below 200\u0026deg;C, water evaporation and removal of volatile organic molecules was observed based on the DTG curve (Figure \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). This accounted for about 10% weight loss in the early stage of the TGA curve.\u003c/p\u003e\n \u003cp\u003eSecond, the rise in temperature between 200 to 450 \u0026ordm;C led to an increase in the skeletal disruption and breakdown of organic molecule/biomolecules (which served as stabilizing/capping agent for the biogenic synthesis of the ZnONPs) was observed resulting in a significant weight loss of 20 to 30%. This temperature range is responsible for the nucleation and crystal growth of the ZnO nanoparticles [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThird, a weight loss of about 5%, as the temperature was increased above 450 \u0026ordm;C, was observed in all the samples. This higher temperature weight loss could be attributed to the degradation of carbon residues from the volarization of biomolecules in the second stage, as well as other inorganic impurities [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. The ZnO-ppt sample showed a smooth continuous weight loss below 500 \u0026ordm;C, which could be attributed to the removal of water molecules, surface hydroxyl groups and nitrate groups from the substrates used during the precipitation synthesis of the sample. The observed weight loss (TGA) correlates well with the respective derivate weight (DTG) for all the analysed samples.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the TGA and DTG plots of the samples after calcination at 500 \u0026ordm;C. The TGA/DTG characterization was carried out to determine the thermal and chemical stability of the samples post calcination treatment. The TGA curve (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(A)) showed a negligible weight loss of 1.0 wt% for the ZnO-MPE sample due to the removal of adsorbed moisture from the nanoparticles\u0026apos; surface [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. The corresponding DTG curve (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(B)) showed two exothermic peaks below 200 \u0026ordm;C, which strongly suggests the removal of surface adsorbed water molecules and/ or total dehydration of the sample. The DTG of the ZnO-ppt sample showed similar behaviour as the ZnO-MPE, but with higher total weight loss of 4.1%.\u003c/p\u003e\n \u003cp\u003eBoth ZnO-BPE and ZnO-PPE showed similar profiles with broad DTG peaks below 400 \u0026ordm;C and total weight loss of about 5.2%. The broadness of the DTG peaks in these samples could be due to the removal of strongly adsorbed water molecules within the pores of the nanoparticles. All the samples showed smooth continuous weight loss, which strongly suggests the absence of organic molecules or carbon deposits on the surface of the calcined samples. Further, the TGA and DTG results for the biogenic synthesized samples suggest the potential of the phytochemicals in banana, mango and pineapple peels to serve as capping/reducing agents to biofabricate ZnONPs, and results in materials with different thermal and chemical stability.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 XRD of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eXRD was used to analyze the crystal structure and particle sizes of the synthesized ZnONPs (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The samples showed similar diffraction peaks typical of hexagonal wurtzite crystalline structure of ZnO at 2\u0026theta; values and crystal planes (\u003cem\u003ehkl\u003c/em\u003e) of ca. 31.95\u0026ordm; (100), 34.54\u0026ordm; (002), 36.38\u0026ordm; (101), 47.64\u0026ordm; (102), 56.78\u0026ordm; (110), 62.96\u0026ordm; (103), 68.20\u0026ordm; (112) and 69.36\u0026ordm; (201) respectively, consistent with the joint committee on powder diffraction standards (JCPDS file number: 36-1451) [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. Few low intensity peaks outside the standard ZnO crystal structure could be due to baseline calibration error or minor impurities in the samples. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows crystallite sizes of the samples calculated using the Debye-Scherrer\u0026rsquo;s method (Eq. (1)) by measuring the full width at half maxima (FWHM) of the most intense peak (2\u0026theta;\u0026thinsp;=\u0026thinsp;ca. 36.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 (101)).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eBulk and surface properties of the synthesized ZnONPs\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZnO-ppt\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZnO-BPE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZnO-MPE\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZnO-PPE\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eXRD ref. peak (2\u0026theta;/degrees)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eFWHM\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrystallite size (nm)\u003c/strong\u003e \u003csup\u003e\u003cstrong\u003ea\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e30.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBand gap energy (eV)\u003c/strong\u003e \u003csup\u003e\u003cstrong\u003eb\u003c/strong\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBET surface area (m\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e/g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e29.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eBJH Pore diameter (nm)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eCummulative pore volume (cm\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e/g)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e\u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Calculated/obtained from XRD using Debye-Scherrer equation\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;Calculated/obtained from Tauc Plot using the UV-vis spectral data\u003c/p\u003e\n \u003cp\u003eCrystallite size, \u003cem\u003eL = (k\u0026lambda;)/\u0026beta; cos\u0026theta;\u003c/em\u003e \u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;.. (1)\u003c/p\u003e\n \u003cp\u003eWhere \u003cem\u003eL\u003c/em\u003e is the crystallite size (in nm), \u003cem\u003ek\u003c/em\u003e is constant (usually 0.89 for a Cu-k\u0026alpha; radiation source), \u003cem\u003e\u0026lambda;\u003c/em\u003e is the wavelength of x-ray radiation (usually 0.154 nm for a Cu-k\u0026alpha; radiation source), \u003cem\u003e\u0026beta;\u003c/em\u003e is full width at half maximum of the reference peak (in radians), and \u003cem\u003e\u0026theta;\u003c/em\u003e is the reference Bragg\u0026rsquo;s angle (in degrees) [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eA significant change in the particle sizes was observed, with ZnO-MPE showing a smaller particle size of 21.80 nm. The decreasing order of crystallite sizes was as follows; ZnO-ppt\u0026thinsp;=\u0026thinsp;38.00 nm\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-PPE\u0026thinsp;=\u0026thinsp;30.10 nm\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-BPE\u0026thinsp;=\u0026thinsp;25.20 nm\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-MPE\u0026thinsp;=\u0026thinsp;21.80 nm (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). This trend is in direct agreement with the intensity of the XRD peaks. One of the major advantages of the biogenic synthesis of NPs is nanosizing [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. Thus, varying the fruit peel extracts resulted in the decrease in crystallite sizes of the synthesized ZnONPs, hence, validating part of the hypothesis of this research work. A similar observation was reported in the literature when different plant parts were investigated [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 FT-IR spectra of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e presents the FT-IR spectra of the synthesized ZnONPs. A vibration frequency at about 521 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was attributed to Zn-O vibration modes of the ZnONPs, while peaks at 1380 and 1635 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were assigned to stretching vibrations of the H\u003csub\u003e2\u003c/sub\u003eO and C\u0026thinsp;=\u0026thinsp;C/C\u0026thinsp;=\u0026thinsp;O bonds, respectively [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. It is believed that the peaks at 1380 and 1635 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e observed in all the samples are due to adsorbed water and CO\u003csub\u003e2\u003c/sub\u003e molecules from the atmosphere. The low intensity broad peaks at 3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are due to bending/stretching vibrations of hydroxyl groups in adsorbed moisture on the surface of the samples.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 UV-visible spectra of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eTo determine the absorption property and, consequently, the bandgap energy (\u003cem\u003eE\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e) of the synthesized ZnONPs, UV-visible diffuse reflectance (UV-vis. DRS) spectroscopy was utilized. The samples were examined within the wavelength range of 200\u0026ndash;700 nm, and the Tauc method was used to compute the band gap energies (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). A typical wurzite crystal phase of ZnO has a broad UV-vis absorption spectrum with maximum around 364 nm, which results in O\u003csub\u003e2p\u003c/sub\u003e Zn\u003csub\u003e3d\u003c/sub\u003e (\u0026pi;-\u0026pi;*) electronic excitation from the VB to the CB, leading to photocatalytic activity [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e showed the UV-vis. DRS spectra of the synthesized ZnONPs. Broad absorption bands in the range of 200\u0026ndash;400 nm (UV-region) appeared in all the samples. ZnO-ppt and ZnO-MPE showed slightly broader spectra extending into the visible region, which could lead to enhanced optical properties of the samples.\u003c/p\u003e\n \u003cp\u003eAnother crucial factor that must be taken into account in photocatalytic investigations is bandgap energy (E\u003csub\u003eg\u003c/sub\u003e). Typical bandgap energy of bulk ZnO is 3.37 eV, but this work reported ZnONPs with narrow (indirect) bandgap energies in the range of 2.41\u0026ndash;2.85 eV, elucidated based on the Tauc method (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e; supplementary information, Figure S2). Similar bandgap energies are reported elsewhere [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. The bandgap typically lowers as particle size rises; this is due to the quantum size effect, which causes the bandgap to eventually decrease as particle size increases. However, the claim that the bandgap solely depends on the particle size factor is not always accurate. Numerous other parameters, including the synthesis method, morphology, lattice strain, particle size, crystal defect, and surface roughness, can also cause the decrease in the bandgap of the ZnONPs [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eAlthough it is challenging to identify the precise variables that have altered the optical bandgap in the synthesized samples, it may be one or a combination of the previously listed factors. Additionally, the absorption spectrum\u0026apos;s broad peaks (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) and presence of multiple peaks indicates that the synthesised samples have structural defects capable of influencing the photabsorption and excitation energy (E\u003csub\u003eg\u003c/sub\u003e) of the materials. It is therefore understood that the lower bandgap observed in the synthesized ZnONPs could be due to confinement effects arising from the biogenic synthesis method employed [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e], since this synthesis approach is known to generate surface defects. Overall, the low bandgap energy (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) reflects a low energy requirement to excite electron from the valence band (VB) to the conduction band (CB), which could lead to better antifungal and photocatalytic performance of the samples.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Surface area and porosity of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the N\u003csub\u003e2\u003c/sub\u003e adsorption\u0026ndash;desorption isotherms for the synthesized ZnONPs. All the samples showed type IV isotherms typical of mesoporous materials. The ZnO-ppt sample showed H\u003csub\u003e2\u003c/sub\u003e-type hysteresis, while the biogenic synthesized samples showed H\u003csub\u003e3\u003c/sub\u003e-type hysteresis, in the relative pressure (P/P\u003csub\u003e0\u003c/sub\u003e) range of 0.4-1.0. These findings suggests the presence of mesopores in all the synthesized ZnONPs, which is in agreement with other report [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) surface area, and the Barrett\u0026ndash;Joyner\u0026ndash;Halenda (BJH) pore volume and pore diameter of the samples are presented in (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The biogenic synthesis was found to influence both the surface area and porosity of the materials. The ZnO-ppt showed the smallest surface area of 28.62 m\u003csup\u003e2\u003c/sup\u003e/g, while the surface area of the biogenic synthesized samples in decreasing order follows; 37.72 m\u003csup\u003e2\u003c/sup\u003e/g (ZnO-MPE)\u0026thinsp;\u0026gt;\u0026thinsp;31.85 m\u003csup\u003e2\u003c/sup\u003e/g (ZnO-BPE)\u0026thinsp;\u0026gt;\u0026thinsp;29.89 m\u003csup\u003e2\u003c/sup\u003e/g (ZnO-PPE). This trend is consistent with theory and also in good agreement with the particle sizes of the samples calculated based on the Scherer\u0026rsquo;s method (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). Average BJH pore diameter and cumulative pore volume were found to be in the ranges 8.92\u0026ndash;13.13 nm and 0.13\u0026ndash;0.26 cm\u003csup\u003e3\u003c/sup\u003e/g, respectively. These observations are comparable with the literature [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 Structural Morphology and Composition of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eThe structural morphology of the synthesized ZnONPs was examined using SEM and TEM, while the composition of the samples was ascertained using EDX spectroscopy. Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e presents the SEM images and the corresponding EDX spectra for ZnO-ppt and ZnO-MPE, respectively. The ZnO-ppt showed evenly distributed spherical shaped particles with little particle agglomeration, while the ZnO-MPE showed flower-like morphology. This remarkable change in morphology in the biogenic synthesized sample indicated the influence of the synthesis approach on the morphology of the nanoparticles. SEM of the ZnO-BPE and ZnO-PPE showed flakes-like and cloud-like morphology, respectively (supplementary information, Figure S3), with higher degree of agglomeration when compared to the previous samples. The EDX spectra of all the samples showed Zn and O as dominant peaks, at 0.5 KeV for O and 1.0, 8.4 and 9.0 KeV for Zn, confirming the formation of the ZnONPs [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. Other significant peaks include C at 0.2 KeV and two unlabelled Cu between 2.0 and 3.5 KeV, arising from the carbon coated copper grit used during sample preparation.\u003c/p\u003e\n \u003cp\u003eTEM images confirmed the morphologies obtained from SEM for all the samples (supplementary information, Figure S4). However, for the ZnO-ppt sample, hexagonal shaped particles were also observed at 50 nm magnification, in addition to the spherical shaped particles (supplementary information, Figure S5). It is widely argued that TEM provides a better means to study particle size of ZnONPs. This is undoubtedly true when dealing with particles of similar morphology. But in this study where samples with different morphologies are compared, XRD is considered more suitable. Nevertheless, both techniques can alternatively serve as a powerful tool for the determination of particle sizes of nanomaterials.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\n \u003ch2\u003e3.7 Antifungal Potentials of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eFour food-spoilage fungal isolates (\u003cem\u003eTrichoderma viridae, Trichosporon sp, Mucor sp\u003c/em\u003e and \u003cem\u003eAspergilus niger\u003c/em\u003e) were used to test the antimicrobial potential of the synthesized ZnONPs at different concentrations viz; 500, 250, 125 and 62.5 \u0026micro;g/ml using the disc diffusion method. Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the antifungal efficacy of the ZnO-ppt and ZnO-MPE against \u003cem\u003eTrichosporon sp\u003c/em\u003e at 250 \u0026micro;g/ml concentration. The zone of inhibition\u0026apos;s (ZI) diameter differed with fungal isolates and concentration of the ZnONPs (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Highest ZI values were recorded against \u003cem\u003eTrichosporon sp\u003c/em\u003e at 500 \u0026micro;g/ml for all the tested ZnONPs, and the values were seen to decline as the concentration decreases.\u003c/p\u003e\n \u003cp\u003eThe ZnONPs tested showed susceptibility against the fungal isolates at least at the high concentration (500 \u0026micro;g/ml), except for ZnO-ppt against \u003cem\u003eTrichoderma viridae\u003c/em\u003e and ZnO-BPE against \u003cem\u003eTrichoderma viridae\u003c/em\u003e and \u003cem\u003eMucor sp\u003c/em\u003e. All the tested samples were inactive at the lowest concentration (62.5 \u0026micro;g/ml), with the exception of the ZnO-PPE sample against \u003cem\u003eTrichosporon sp\u003c/em\u003e and \u003cem\u003eAspergilus niger\u003c/em\u003e. Overall, the samples were more effective against \u003cem\u003eTrichosporon sp\u003c/em\u003e and least active against \u003cem\u003eTrichoderma viridae\u003c/em\u003e. This observation can be explained based on physiological and biochemical differences between the two microbes. For example, \u003cem\u003eTrichoderma viridae\u003c/em\u003e grows optimally at 20\u0026ndash;25 \u0026ordm;C and wider pH range of 4\u0026ndash;9, while \u003cem\u003eTrichosporon sp\u003c/em\u003e prefers a more narrow temperature and pH range of 20\u0026ndash;25 \u0026ordm;C and 5\u0026ndash;7, respectively [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e]. Further, the cell wall of \u003cem\u003eTrichoderma viridae\u003c/em\u003e composed primarily of chitin and beta-glucans, which act as stronger defense system against external threat compared to the cell wall of \u003cem\u003eTrichosporon sp\u003c/em\u003e composed of mannans and beta-glucans, known to provide a much weaker defense. It is also reported that \u003cem\u003eTrichoderma viridae\u003c/em\u003e produce a wide range of enzymes such as celluloses, xylanases, and proteases, whereas \u003cem\u003eTrichosporon sp\u003c/em\u003e produces few enzymes such as lipases and amylases [\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. These enzymes may serve to defend the cells against external threats, thereby minimizing the effect of the tested ZnONPs on the fungal isolates.\u003c/p\u003e\n \u003cp\u003eThe exact method of interaction between nanoparticles and cell organelles that triggers antimicrobial activity is still unknown, despite several attempts to explain how they infiltrate microbial cells. In general, four methods of penetration have been established: (1) the nanoparticles attach to the cell membrane and disrupt it; (2) the Zn ions produce reactive oxygen species (ROS) that harm the microbial DNA; (3) the ionic forms of the nanoparticles interfere with ATP synthesis and DNA replication; and (4) the nanoparticles interact with amino acid and nucleic acid moieties of the cell membrane by forming thiols or phosphates [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e compares the antifungal potentials of the ZnONPs against \u003cem\u003eTrichosporon sp\u003c/em\u003e at a concentration of 250 \u0026micro;g/ml. Often than not, the antimicrobial properties of ZnONPs have been linked to particle size of the nanoparticles [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e], [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e]. Although a direct correlation between particle size and antifungal activity could not be established for this study, the smaller particle size of the ZnO-MPE could have contributed, in addition to other factors such as morphology and surface area, to its higher antifungal potential. In a recent study by Pariona and co-workers, the antifungal activity of ZnO was reported to be shape-dependent [\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e]. Thus, particle size and morphology play a crucial role on in the high antifungal potential of the ZnO-MPE sample.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAntifungal activity (Zones of Inhibition) of the synthesized ZnONPs\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTest Organisms\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eConcentration (\u0026micro;g/ml)/ Inhibition zone (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003cp\u003e(Ketaconazole (mg/ml))/\u003c/p\u003e\n \u003cp\u003eInhibition Zone (mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e500\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e62.5\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"6\"\u003e\n \u003cp\u003eZnO-ppt\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichoderma viridae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichosporon sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMucor sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAspergilus niger\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"6\"\u003e\n \u003cp\u003e\u003cstrong\u003eZnO-BPE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichoderma viridae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichosporon sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMucor sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAspergilus niger\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"6\"\u003e\n \u003cp\u003e\u003cstrong\u003eZnO-MPE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichoderma viridae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichosporon sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMucor sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAspergilus niger\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"6\"\u003e\n \u003cp\u003e\u003cstrong\u003eZnO-PPE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTrichoderma viridae\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTrichosporon sp\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMucor sp\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAspergilus niger\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTwo important parameters; MIC and MFC are significant in the study of antifungal activities of ZnONPs [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. The lowest antimicrobial concentrations that, following an overnight incubation period, will prevent the growth of visible microorganisms are known as minimum inhibitory concentrations (MICs) [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. On the other hand, MFC refers to the minimum concentration of the test sample that can eliminate the microbe. Alexander Fleming was the first to introduce the concept of minimum inhibitory concentration by measuring the antibacterial efficacy of medications using the turbidity of broth. The MIC and MFC of the ZnONPs is presented in (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The lowest MIC value of 62.5 \u0026micro;g/ml was recorded for ZnO-PPE against \u003cem\u003eTrichosporon sp\u003c/em\u003e and \u003cem\u003eAspergilus niger\u003c/em\u003e, while the MFCs for all the samples were found to be \u0026gt;\u0026thinsp;500 \u0026micro;g/ml. These findings were found to be consistent with other reports [\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMinimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) of the synthesized ZnONPs (in \u0026micro;g/ml).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTest Organisms\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eZnO-ppt\u003c/p\u003e\n \u003cp\u003eMIC MFC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eZnO-BPE\u003c/p\u003e\n \u003cp\u003eMIC MFC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eZnO-MPE\u003c/p\u003e\n \u003cp\u003eMIC MFC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eZnO-PPE\u003c/p\u003e\n \u003cp\u003eMIC MFC\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichoderma viridae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eTrichosporon sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMucor sp\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAspergilus niger\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003e\u003cstrong\u003eKEY\u003c/strong\u003e: NT\u0026thinsp;=\u0026thinsp;Not Tested\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\n \u003ch2\u003e3.8 Photocatalytic Potentials of the synthesized ZnONPs\u003c/h2\u003e\n \u003cp\u003eTo study the potential of the synthesized ZnONPs in photodegradation of MB under UV light irradiation, a 100 W mercury lamp, 10 ppm MB concentration, 100 mg catalyst loading and 15 minutes sampling intervals for 2 hours were used. Firstly, the adsorption-desorption equilibrium (dark reaction) and photolysis were carried out under constant stirring for 30 minutes. Both reactions showed insignificant (0\u0026ndash;3%) removal of the methylene blue (MB) contaminant (results not shown here). Figure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e ((A) and (B)) displays the absorption spectra of the MB degradation under UV light irradiation using ZnO-ppt and ZnO-MPE as photocatalysts, respectively. Reduction in absorption is evident from the intensity of the peaks around 615 and 664 nm, indicating that both samples are active photocatalysts driving the MB dye degradation process [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. This approach made it possible to continuously observe and assess the degradation process at 15 min intervals for 120 minutes. Eq. (1) was used to calculate the MB degradation efficiency (D (%)) as reflected by (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e (C) and (D)).\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e(A) showed a gradual reduction of the UV absorption peak intensity for the ZnO-ppt sample. The photodegradation efficiency was low (8%) at the initial sampling point. From 30 minutes of reaction on stream, the degradation activity increased gradually up to 83% after 120 minutes (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e(C)). The ZnO-MPE sample showed an initial MB degradation of 28%, a significant jump in degradation efficiency after 60 minutes, and gradually attaining the all high MB degradation of 91% after the 120 minutes reaction time (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e(D)). Significant decolourization of the MB dye over the ZnO-MPE was observed, which is a testament to its high potential as a photocatalyst (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e(E)). The higher photocatalytic potential of this sample can be attributed to its unique characteristics such as low band gap energy, high surface area, small crystallite sizes and peculiar morphology.\u003c/p\u003e\n \u003cp\u003eThe ZnO-BPE and ZnO-PPE samples showed initial phodegradation of 20 and 43%, respectively (supplementary information, Figure S6). The high initial degradation efficiency of the ZnO-PPE could be due to surface and structural defects in the samples, which serve as active sites for rapid generation of reactive oxygen species (ROSs) leading to higher initial photocatalytic efficiency of the sample. These defective sites are eventually blocked by the MB contaminant, resulting in slow degradation. After 120 minutes of reaction on stream, the ZnO-BPE attained 78% degradation while ZnO-PPE achieved only 73%. Thus, the decreasing order of MB photodegradation efficiency of the tested samples after 120 minutes of reaction follows; ZnO-MPE (91%)\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-ppt (83%)\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-BPE (78%)\u0026thinsp;\u0026gt;\u0026thinsp;ZnO-PPE (73%).\u003c/p\u003e\n \u003cp\u003eThe best performing catalyst, ZnO-MPE, was subjected to catalyst regeneration to check its stability and reusability. The used ZnO-MPE catalyst was extracted from the reaction mixture by centrifugation following each cycle of the reaction, and thoroughly washed with ethanol and double-distilled water to remove any adsorbed organic moieties from the MB dye before being used for subsequent cycles. Three regeneration cycles were carried out under similar experimental conditions, and the results are presented in (Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e). The ZnO-MPE sample was seen to sustain its photodegradation efficiency after three regeneration cycles.\u003c/p\u003e\n \u003cp\u003eTo verify the structural and photostability changes in the used ZnO-MPE sample following reusability studies, the crystal structure and photoabsorption of the sample were verified by XRD and UV-visible spectroscopy, respectively. No significant shift in the XRD peaks was noted, and the Scherrer\u0026rsquo;s crystallite size is the same as in the fresh sample, confirming the structural stability of the used sample (Figure S7). Also based on the UV-vis DRS (Figure S8) of the sample post reusability studies, both the absorption spectrum and band gap energy of the sample remained the same as in the fresh sample, confirming its chemical and photostability.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\n \u003ch2\u003e3.9 Proposed Mechanism of the Photodegradation Process\u003c/h2\u003e\n \u003cp\u003eThe widely proposed mechanism for photodegradation of MB dye using ZnO photocatalyst is based on the radical generation mechanism [\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e]. First, the dye is attacked by the extremely reactive radicals (.OH and .O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) produced in the dye solution, which eventually leads to the conversion of the MB into less hazardous products (water and carbon dioxide). Figure\u0026nbsp;11 provides an illustration of the proposed method of free radical generation and MB photodegradation using the ZnO-MPE as a model sample. When the ZnO-MPE nanoparticles are exposed to UV light, electrons (e\u003csup\u003e\u0026minus;\u003c/sup\u003e) and holes (h\u003csup\u003e+\u003c/sup\u003e) are created, which initiates the photocatalytic destruction process. In principle, when the sample surface is exposed to light with an energy greater than or equal to the band gap energy (E\u003csub\u003eg\u003c/sub\u003e), a photoexcited electron (e\u003csup\u003e\u0026minus;\u003c/sup\u003e) is moved from the valence band (VB) to the conduction band (CB), leaving behind a positive hole (h\u003csup\u003e+\u003c/sup\u003e).\u003c/p\u003e\n \u003cp\u003eGenerally, a faster electron-hole pair formation is ensured by a smaller band gap, which makes the samples under investigation highly photoactive. The produced electron and hole go independently to the catalyst\u0026apos;s surface and react with the O\u003csub\u003e2\u003c/sub\u003e and OH\u003csub\u003e2\u003c/sub\u003e, present in the MB solution to produce superoxide radical anions (\u003csup\u003e\u0026minus;\u003c/sup\u003eO\u003csub\u003e2\u003c/sub\u003e.), hydroperoxyl radicals (\u003csup\u003e\u0026minus;\u003c/sup\u003eOOH), and hydroxyl radicals (\u003csup\u003e\u0026minus;\u003c/sup\u003eOH/.OH) (Fig. 11). The most potent oxidizing species among these radicals, referred to as reactive oxygen species (ROS) in photocatalytic oxidation processes, is the hydroxyl radicals, which can potentially degrade the MB contaminants in the vicinity of the photocatalyst surface.\u003c/p\u003e\n \u003cp\u003eA significant issue in this mechanism is electron-hole pair recombination, which lowers the ROS formation efficiency and, hence, negatively affects the photodegradation process. However, it is stated in the literature that defects in the ZnONPs may potentially trap the generated electrons, preventing electron-hole pairs from recombining [\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e]. The biogenic synthesis proceeds via the formation of intermediate zinc complexes, resulting in the formation of defective ZnONPs after calcination treatment due to the combustion of the phytochemicals acting as ligands. Therefore, a significant level of ROS formation could be attributed to the existence of defects in the ZnONPs under study. Further, the size of the nanoparticles is an important factor that affects the photodegradation activity. Smaller particle samples have a greater surface-to-volume ratio, which provides more surface active sites for ROS generation. This, in turn, increases the interfacial charge carrier transfer for photodegradation of the MB dye contaminant.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4.0 Conclusion","content":"\u003cp\u003eThis work reported on biogenic synthesis of ZnONPs using banana (ZnO-BPE), mango (ZnO-MPE) and pineapple (ZnO-PPE) peel aqueous extracts. A reference sample (ZnO-ppt) was also prepared using simple precipitation method (without fruit extract) for comparison. These were characterized using various techniques. All the samples showed hexagonal wurtzite crystalline structure typical of ZnONPs while the type of the fruit peel extracts significantly influenced the properties of the samples. The ZnONPs showed Scherrer\u0026rsquo;s crystallite sizes of 21.80\u0026ndash;38.00 nm, surface areas of 28.62\u0026ndash;37.72 m\u003csup\u003e2\u003c/sup\u003e/g, sufficient UV light absorption and narrow bandgap of 2.41\u0026ndash;2.85 eV. Different morphologies, ranging from spherical to flower-like, were observed as the fruit peel extract is varied. The potential of the samples as antifungal agents and as catalysts in photodegradation of MB yielded positive results. Highest antifungal potential was observed against \u003cem\u003eTrichosporon sp\u003c/em\u003e for the ZnO-MPE at concentration of 250 \u0026micro;g/ml. All the samples showed good photocatalytic potential against MB degradation with highest degradation efficiency of 91% for the ZnO-MPE, which is sustained over three regeneration cycles. Compared to the other samples studied, the ZnO-MPE showed higher antifungal and photocatalytic potential, which was attributed to various factors including small particle size, large surface area, unique morphology and narrow bandgap.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: Partial funding (financial support) was received from the Tertiary Education Trust Fund, Nigeria (IBR2024).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEmployment\u003c/strong\u003e: The authors are full-time faculty members of the Department of Chemistry, Federal University Lokoja Nigeria and Durban University of Technology South Africa, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate\u003c/strong\u003e: Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e: Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contribution\u003c/strong\u003e: All the authors contributed significantly towards the completion of this research work. \u003cstrong\u003e\u003cem\u003eDailami S.A Masokano\u003c/em\u003e\u003c/strong\u003e: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, Writing-original draft, Visualization. \u003cstrong\u003e\u003cem\u003eJude E. Emurotu\u003c/em\u003e\u003c/strong\u003e: Writing-review and editing, Supervision, Visualization. \u003cstrong\u003e\u003cem\u003eUsman O.A Shuaibu\u003c/em\u003e\u003c/strong\u003e: Writing-review and editing, Supervision, Visualization. \u003cstrong\u003e\u003cem\u003ePinkie Ntola\u003c/em\u003e\u003c/strong\u003e: Resources, Validation, Writing-review and editing, Visualization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank the Federal University Lokoja and the Tertiary Education Trust Fund (TETFUND-Nigeria) for the \u003cstrong\u003eTETFUND-IBR\u003c/strong\u003e research grant (2024).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChavali MS, Nikolova MP. Metal oxide nanoparticles and their applications in nanotechnology. 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Int J Inorg Mater. 2001;3(7):643\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePariona N, Paraguay-Delgado F, Basurto-Cereceda S, Morales-Mendoza J, Hermida-Montero L. Mtz-Enriquez, \u0026lsquo;Shape-dependent antifungal activity of ZnO particles against phytopathogenic fungi\u0026rsquo;. Appl Nanosci. 2020;10:435\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHouas A, Lachheb H, Ksibi M, Elaloui E, Guillard C, Herrmann J-M. Photocatalytic degradation pathway of methylene blue in water. Appl Catal B Environ. 2001;31(2):145\u0026ndash;57.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStan M, Popa A, Toloman D, Dehelean A, Lung I, Katona G. Enhanced photocatalytic degradation properties of zinc oxide nanoparticles synthesized by using plant extracts. Mater Sci Semicond Process. 2015;39:23\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"dime","sideBox":"Learn more about [Discover Materials](https://www.springer.com/journal/43939)","snPcode":"","submissionUrl":"","title":"Discover Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Zinc oxide, Nanoparticles, Green synthesis, Catalyst, Methylene blue, Photodegradation, Antifungal","lastPublishedDoi":"10.21203/rs.3.rs-6965908/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6965908/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBanana (\u003cem\u003eMusa spp\u003c/em\u003e), mango (\u003cem\u003eMangifera indica\u003c/em\u003e) and pineapple (\u003cem\u003eAnanas comosos\u003c/em\u003e) peel aqueous extracts were employed to synthesize zinc oxide nanoparticles (ZnONPs), namely; ZnO-BPE, ZnO-MPE and ZnO-PPE, respectively. A reference sample, ZnO-ppt (without fruit peel extract) was also synthesized by simple precipitation. These were calcined at 500 ºC and characterized using x-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), UV-visible spectroscopy (UV-VIS), Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA/DTG), scanning electron microscopy-electron dispersive x-ray (SEM-EDX) and Transmission electron microscopy (TEM) techniques. The XRD of the samples revealed a hexagonal wurtzite crystalline structure typical of ZnONPs, with the Debye Scherrer’s crystallite sizes ranging from 21-38 nm. FTIR spectra of the samples showed Zn-O vibration bands at ~521 cm\u003csup\u003e-1\u003c/sup\u003e while the UV-vis showed a narrow band gap in the range of 2.41-2.85 eV, and good UV light absorption in all the samples. The SEM images showed significant differences in the morphology of the samples, including spherical-hexagonal shape for the ZnO-ppt sample, and flower-like shaped particles for the ZnO-MPE. Antifungal assay showed that all the samples are active against \u003cem\u003eTrichosporon sp\u003c/em\u003e and \u003cem\u003eAspergilus niger\u003c/em\u003e isolates.\u003cem\u003e \u003c/em\u003eHighest zones of inhibitions were obtained for the ZnO-MPE against \u003cem\u003eTrichosporon sp.\u003c/em\u003e, while the ZnO-PPE sample showed the lowest MIC of 62.5 µg/ml against \u003cem\u003eAspergilus niger\u003c/em\u003e.\u003cem\u003e \u0026nbsp;\u003c/em\u003ePhotodegradation potential of the samples against 10 ppm methylene blue solution showed 73-91 % degradation under UV-light irradiation. The best performing photocatalyst, ZnO-MPE, sustained its degradation efficiency over three regeneration cycles.\u0026nbsp;\u003c/p\u003e","manuscriptTitle":"Antifungal and Photocatalytic Potentials of Zinc Oxide Nanoparticles Synthesized Using Various Fruit Peel Aqueous Extracts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-23 08:23:15","doi":"10.21203/rs.3.rs-6965908/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-07T09:17:35+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-27T11:32:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-22T13:57:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"70445286069380083743886167861895183580","date":"2025-07-17T13:40:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"90345230284688986197765365047865826321","date":"2025-07-17T09:43:48+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-17T09:05:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-15T16:35:07+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-07-14T10:05:34+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-10T15:08:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Materials","date":"2025-07-10T14:42:44+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"dime","sideBox":"Learn more about [Discover Materials](https://www.springer.com/journal/43939)","snPcode":"","submissionUrl":"","title":"Discover Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"09ad4646-e8d7-4f52-841e-50560faf0e4d","owner":[],"postedDate":"July 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-11-17T16:05:47+00:00","versionOfRecord":{"articleIdentity":"rs-6965908","link":"https://doi.org/10.1007/s43939-025-00399-0","journal":{"identity":"discover-materials","isVorOnly":false,"title":"Discover Materials"},"publishedOn":"2025-11-10 15:58:01","publishedOnDateReadable":"November 10th, 2025"},"versionCreatedAt":"2025-07-23 08:23:15","video":"","vorDoi":"10.1007/s43939-025-00399-0","vorDoiUrl":"https://doi.org/10.1007/s43939-025-00399-0","workflowStages":[]},"version":"v1","identity":"rs-6965908","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6965908","identity":"rs-6965908","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}