Sustainable CQDs/ZnO Nanocomposite for Multifaceted Applications in Detection of Pb 2+ and Degradation of RhB Dye

Sustainable CQDs/ZnO Nanocomposite for Multifaceted Applications in Detection of Pb 2+ and Degradation of RhB Dye | 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 Sustainable CQDs/ZnO Nanocomposite for Multifaceted Applications in Detection of Pb 2+ and Degradation of RhB Dye Laila Alkhtabi, Mohammad Mujahid This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6261982/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In this study, carbon quantum dots (CQDs) were synthesized from apple peel waste using a one-step hydrothermal process and incorporated into a ZnO nanocomposite. The synthesized product was characterized using various analytical techniques, including FTIR, XRD, SEM, and TEM. FTIR analysis revealed the presence of functional groups such as -COOH, C-O-C, and Zn-O, while XRD analysis confirmed the wurtzite crystalline structure of the nanocomposite. The CQDs/ZnO nanocomposite exhibited UV-Vis absorption peaks at 280 nm and 330 nm, attributed to the π-π* and n-π* transitions, respectively, indicating its optical activity. The calculated bandgap of 3.87 eV suggests the involvement of ZnO in its wurtzite phase, known for its wide bandgap properties. Adsorption studies showed that the CQDs/ZnO nanocomposite followed pseudo-first-order kinetics, demonstrating its efficiency in the adsorption process. Moreover, the fluorescence intensity of the nanocomposite significantly decreased in the presence of Pb²⁺ ions, enabling selective detection of Pb²⁺ over other metal ions. The fluorescence probe exhibited a linear response in the concentration range of 0–300 µM, with a detection threshold (DT) of 0.21 µM, highlighting its high sensitivity for Pb²⁺ detection. Additionally, the CQDs/ZnO nanocomposite was successfully applied to detect Pb²⁺ ions in real water samples, demonstrating its practical applicability. Hydrothermal Process Photocatalytic efficiency Fluorescence quenching Sensing of Pb2+ Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Water pollution remains a significant environmental and public health challenge, with heavy metals and synthetic dyes being two major contributors. Among these, lead (Pb²⁺) ions and Rhodamine B (RhB) dye stand out due to their widespread use, persistence, and severe ecological and health impacts[ 1 ]. The increasing presence of these pollutants in water sources, primarily from industrial and agricultural activities, poses serious risks to aquatic ecosystems and human populations, necessitating urgent remediation measures[ 2 ]. Lead contamination is a pressing issue, resulting from industrial processes such as mining, smelting, battery manufacturing, and the improper disposal of lead-based products. Pb²⁺ ions are highly toxic, even at trace levels, and can accumulate in living organisms, disrupting vital biological functions[ 3 ]. Chronic exposure to lead affects the nervous, reproductive, and hematopoietic systems, with children being particularly vulnerable to its neurotoxic effects[ 4 ]. The World Health Organization (WHO) and the United States Environmental Protection Agency (EPA) have set stringent limits on lead concentrations in drinking water, underscoring the critical need for effective detection and removal strategies[ 4 ]. Traditional methods for Pb²⁺ detection, including atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and electrochemical techniques, offer high sensitivity but are expensive, labor-intensive, and require sophisticated instrumentation.[ 5 ] These limitations have driven the development of alternative approaches, such as nanotechnology-based sensors and adsorbents, which provide cost-effective, efficient, and sustainable solutions for lead remediation[ 6 ]. Rhodamine B (RhB) is a synthetic xanthene dye extensively used in textiles, printing, paper, and food industries[ 7 ]. Despite its widespread applications, the improper discharge of RhB into water bodies has raised significant environmental concerns. RhB is known for its high chemical stability, making it resistant to natural degradation processes. Its persistence in water can lead to ecological imbalances and harm aquatic life. RhB is not only a pollutant but also poses serious health risks to humans[ 8 ]. Prolonged exposure to RhB can cause skin irritation, respiratory problems, and potential carcinogenic effects. Therefore, the removal of RhB from water sources is crucial for ensuring environmental sustainability and public health safety[ 9 ]. The remediation of water contaminated with Pb²⁺ ions and RhB dye is challenging due to their distinct chemical properties and the need for selective and efficient treatment methods[ 10 ]. Conventional treatment techniques, such as coagulation, filtration, and adsorption, are often ineffective or economically unfeasible when applied to these pollutants. Advanced oxidation processes and photocatalytic methods have shown promise but require the development of high-performance materials that are both cost-effective and environmentally friendly[ 11 ]. Nanotechnology has emerged as a transformative tool for addressing complex water pollution issues. Nanomaterials, particularly carbon-based nanomaterials like carbon quantum dots (CQDs), have garnered significant attention for their unique physicochemical properties, including high surface area, tunable fluorescence, and ease of functionalization. These properties make CQDs ideal for applications in sensing, adsorption, and photocatalysis.[ 12 – 14 ] The integration of CQDs with other materials, such as metal oxides, can further enhance their performance. Zinc oxide (ZnO), a widely studied metal oxide, is known for its excellent photocatalytic and adsorption properties. ZnO’s wide bandgap and ability to generate reactive oxygen species under UV irradiation make it a promising candidate for dye degradation and heavy metal removal. When combined with CQDs, the resulting nanocomposites exhibit synergistic effects, improving their optical, electronic, and catalytic performance[ 15 – 17 ]. This study focuses on the synthesis of a CQDs/ZnO nanocomposite derived from apple peel waste, a sustainable and eco-friendly carbon source. The nanocomposite aims to address the dual challenge of Pb²⁺ ion and RhB dye contamination in water. By leveraging the optical and adsorption properties of CQDs and the photocatalytic capabilities of ZnO, the CQDs/ZnO nanocomposite is expected to provide an efficient, cost-effective, and environmentally sustainable solution. The dual functionality of the CQDs/ZnO nanocomposite for Pb²⁺ ion detection and RhB dye degradation highlights its potential as a versatile material for water purification. Its fluorescence-based sensing mechanism enables selective and sensitive detection of Pb²⁺ ions, while its photocatalytic activity ensures effective degradation of RhB dye under visible-light irradiation. The use of apple peel waste as a carbon source not only reduces production costs but also aligns with the principles of green chemistry and waste valorization. In addition to addressing water pollution, the insights gained from this study contribute to the broader field of nanotechnology-based environmental remediation. The development of multifunctional nanocomposites can pave the way for innovative solutions to combat other emerging pollutants, ensuring clean and safe water for future generations. 2. Experiment 2.1. Material Apple peel was collected from the kitchen waste. ZnO and Rhodamine dye were purchased from Fisher scientific, India and Sigma Aldrich, India. All chemicals and reagents were used as received without further treatment. Double distilled water (DDW) is used for washing and dilution purposes 2.2. Preparation of CQDs CQDs were synthesized from Apple peel waste using a one-step hydrothermal method. Apple peels were ground and dried at 65°C for 24 hours in a hot air oven. The dried powder was mixed with 100 mL of distilled water and stirred for 45 minutes. The mixture was then heated in a hydrothermal autoclave at 200°C for 8 hours and cooled to room temperature. Large particles were removed, and the suspension was filtered through 0.45 µm filter paper and centrifuged at 3500 rpm for 15 minutes. Finally, the brown suspension was dried at 60°C, and the CQDs were stored at 4°C (as shown in Fig. 1 )[ 18 , 19 ]. 2.3. Preparation of CQDs/ZnO nanocomposite The CQDs/ZnO nanocomposite was synthesized by dispersing 2 g of ZnO powder into 10 mL of CQDs solution (as shown in Fig. 1 ). The mixture was stirred for 45 minutes at 300 rpm to ensure uniform dispersion and interaction. Subsequently, the solution was dried in an oven at 60°C for 24 hours to obtain the composite. During the process, functional groups on CQDs, such as hydroxyl (-OH) and carboxyl (-COOH), chemically interact with the ZnO surface; forming bonds like hydrogen bonds or ester linkages. These interactions enhance interfacial compatibility and improve the composite's photocatalytic and electronic properties[ 19 ]. 2.4. Characterization techniques Fourier Transform Infrared Spectroscopy (FTIR) was performed using a PerkinElmer Spectrometer version 10.4 to identify the functional groups present on the surface of the carbon quantum dots. X-ray diffraction (XRD) analysis was conducted with a Rigaku TTRAX III diffractometer to determine the crystallinity and amorphous nature of the composite. The morphological and textural properties of the composite, along with elemental distribution, were examined using transmission electron microscopy (TEM), and scanning electron microscopy (SEM) with JEOL-JEM 2100, Zeiss Gemini 300, and JEOL-JSM 6510 instruments. The optical properties of the composites were analyzed using Photoluminescence (PL) spectroscopy (Horiba DeltaFlex01-DD) and UV-Vis spectroscopy (Hitachi U3900). 2.5. Degradation experiment 0.1g of Rhodamine B was dissolved in 100mL of DDW for the preparation of 1000ppm standard solution and then diluted to 5mg/L concentrations. The photocatalytic degradation of r hodamine B in aqueous solution was studied under various experimental conditions using 1.5mg CQDs/ZnO under visible light irradiation (500W tungsten halogen lamp)[ 11 ]. The samples were taken at different intervals, and the UV-visible spectrophotometer was used to measure the dye absorbance at λ max = 270nm in order to evaluate the degradation performance of the produced materials. Using Eq. ( 1 ), the drug's percentage of degradation was calculated. $$\:\%\:Degradation=\frac{{A}_{0}-{A}_{t}}{{A}_{0}}\times\:100$$ 1 Where A 0 and A t are the absorbance values of drug at 0 and t time. The relationship between absorbance and concentration of drug obtained from the standard curve is given in Eq. 2 . $$\:Concentration\:\left(\frac{mg}{L}\right)=\frac{A+0.0494}{0.0158}\:\:$$ 2 2.6. Kinetics The photocatalytic degradation rate of dye was determined using the pseudo-order kinetics models Eq. ( 3 ). $$\:{r}_{t}=\frac{{-dC}_{t}}{dt}={k}_{n}{C}_{t}^{n}$$ 3 where, r t denotes Rhodamine B degradation rate, C t denotes drug concentration in aqueous medium at time t, k n denotes rate constant, and n is the reaction order ranges between 0 to 1[ 20 ]. The pseudo-first-order kinetic model means n = 1, can be obtained by integrating Eq. ( 3 ) which reduces to obtain Eq. ( 4 ) $$\:ln\frac{{C}_{t}}{{C}_{o}}=-{k}_{app}t$$ 4 2.7. Detection of Pb 2+ The as-synthesized nanocomposite were adjusted to the concentration of 300 µg mL − 1 in solutions containing different metal ions (Bi 2+ , Ca 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 3+ , Hg 2+ , Mg 2+ , Na + , Cd 2+ , Pb 2+ , Zn 2+ ) was investigated. After allowing the reaction to proceed for 10 min, the fluorescence emission spectra were recorded. The sensitivity and selectivity were measured in triplicate. To determine the detection range of Pb 2+ , 1 mL of an aqueous solution of CQDs/ZnO (100 µg mL − 1 ) was added to 1000 µL of saline phosphate buffer (PBS, pH = 7.4). Subsequently, varying concentrations of Pb 2+ (standard solution) were added. The fluorescence intensity at the excitation wavelength of 330 nm was recorded after 15 min[ 21 ]. 3. Results and Discussion 3.1. FTIR and XRD analysis The FTIR spectrum of CQDs/ZnO demonstrates significant functional groups indicative of the material's chemical structure. The broad band at 3455 cm⁻¹ corresponds to the stretching vibrations of hydroxyl (-OH) groups, confirming the presence of surface functionalities. The peak at 946 cm⁻¹ is associated with C–OH stretching and O–H bending, highlighting alcohol or phenol groups. Bands at 1445 cm⁻¹ and 1616 cm⁻¹ correspond to C = C and C = O vibrations, indicating the presence of aromatic rings and carbonyl groups, respectively. Additionally, peaks at 765 cm⁻¹ and in the range of 2858–2905 cm⁻¹ represent stretching vibrations of C-H bonds, typical in sp² and sp³ hybridized carbons (as shown Fig. 2 A). These findings collectively suggest the carbonization of starch, where decomposition and reorganization of organic precursors result in CQDs with abundant oxygen-containing groups. These functional groups enhance the interaction between CQDs and ZnO, improving their photocatalytic and electronic properties[ 19 , 22 , 23 ]. The XRD pattern of the CQDs/ZnO nanocomposite displays peaks at (002), (220), (311), (400), and (420) planes, corresponding to 2θ values of 24.7°, 38.5°, 47.87°, 55°, and 64.5°. The (002) peak is attributed to the graphitic structure of CQDs, indicating their crystalline nature (as shown Fig. 2 B). The remaining peaks correspond to the Hexagonal Wurtzite phase of ZnO, confirming its crystallinity and phase composition. These reflections validate the successful integration of CQDs with ZnO, forming a hybrid material. This combination enhances the composite's structural, optical, and electronic properties, making it suitable for photocatalytic and environmental remediation applications[ 16 , 24 ]. 3.2. Morphological studies techniques SEM of the CQDs/ZnO nanocomposite (as shown in Fig. 3 A) typically reveals an agglomerated structure. The ZnO nanoparticles are seen as small, uniformly distributed clusters, while CQDs appear as smaller, embedded particles on the ZnO surface. The interaction between CQDs and ZnO forms a rough, interconnected network, enhancing surface area and light absorption[ 25 ]. TEM (as shown in Fig. 3 B) provides high-resolution insights, showing ZnO nanoparticles as crystalline structures, with lattice fringes confirming their phase (anatase/rutile). CQDs are ultra-small, nearly spherical particles forms cluster like structure, uniformly dispersed on the ZnO surface. This homogeneous distribution indicates strong interfacial bonding, crucial for efficient electron transfer and photocatalytic activity[ 19 ]. 3.3. Optical study The CQDs/ZnO nanocomposite exhibits a UV-Vis absorption peak at 280 nm and 330nm, attributed to the π-π* and n- π* transitions in CQDs/ZnO, signifying their optical activity as shown in Fig. 4 A[ 26 ]. The bandgap value of 3.87 eV suggests ZnO's contribution, likely in its anatase phase, which has a wide bandgap. The fluorescence spectra as shown in Fig. 4 B, with excitation at 350 nm, show the highest intensity for pure CQDs due to their strong emission from surface defects and oxygen-containing groups. In the composite, the fluorescence intensity is reduced, indicating efficient charge transfer between CQDs and ZnO. This quenching implies that CQDs facilitate electron transfer to ZnO, suppressing recombination of charge carriers. The very low fluorescence intensity for pure ZnO confirms its limited emission ability. The integration of CQDs enhances the light absorption range and charge separation, making the nanocomposite suitable for photocatalytic and optoelectronic applications, leveraging CQDs' photoluminescence and ZnO's stability[ 27 , 28 ]. 3.4. Photocatalytic Study Before initiating the photodegradation process, equilibrium between adsorption and desorption was achieved by stirring the Rhodamine solution with the photocatalyst in the dark for 30 minutes. The UV-Vis absorption spectra (Fig. 5 A) of the nanocomposite solution show a significant decrease in absorption intensity as irradiation time increases. After 50 minutes of visible-light irradiation, approximately 98.1% of rhodamine was degraded, indicating the high photocatalytic efficiency of the CQDs/ZnO nanocomposite. Without a catalyst, Rhodamine B exhibited negligible self-degradation (4–5%), demonstrating its stability under direct photolysis[ 29 ]. In contrast, the presence of the nanocomposite significantly enhanced degradation, monitored regularly throughout the process (Fig. 5 B). The strong light absorption, high surface area, and efficient electron transport properties of CQDs/ZnO enable rapid degradation of organic pollutants. Surface modification of CQDs further enhances their photocatalytic activity, making them a sustainable choice for water treatment technologies[ 18 ]. Figure 5 C reveals that the degradation follows pseudo-first-order kinetics and different rate constant value of different catalyst and maximum value shown by CQDs/ZnO nanocomposite, while Fig. 5 D compares catalyst efficiencies, showing the order Blank < ZnO < CQDs < CQDs/ZnO[ 27 ]. 3.5. Sensing of heavy metal ions using CDs The fluorescence quenching impact of several metal ions (concentration: 300µM) on CDs (10 mg/ L) (Bi 2+ , Ca 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 3+ , Hg 2+ , Mg 2+ , Na + , Cd 2+ , Sr 2+ , Zn 2+ ) was investigated[ 30 , 31 ]. Figure 6 (A) shows that Cd 2+ ions dampened CQDs/ZnO PL intensity more selectively than other metal ions. Pb 2+ had the most quenching impact on CQDs/ZnO of all the metal cations examined, indicating the possible use of CQDs/ZnO as a selective indication sensor for Pb 2+ ion[ 32 , 33 ]. Chelation or coordination interactions between Pb 2+ ions and functional groups (-COOH, -OH, C-O, etc.) on the surface of CQDs/ZnO were identified as the quenching process. The adsorption of Pb 2+ ions on the nanocomposite surface and their interaction with -OH groups at the nanocomposite edges promote electron transport from the excited state of the nanocomposite to the vacant 4d orbital of Pb 2+ ions in this process. Consequently, the separation of charge carriers leads to fluorescence quenching. Figure 6 (B) illustrates the potential quenching mechanism[ 11 , 34 , 35 ]. Figure 6 (C) shows the dimming of CQDs/ZnO fluorescence at different Pb 2+ ion concentrations. The coordination contact between Pb 2+ ions and the carboxyl group of CQDs/ZnO gets stronger as the concentration of Pb 2+ ions rises. This enhances the non-radiative recombination of charge carriers and causes quenching as a consequence. Notably, at greater doses of Pb 2+ ions (300µM), no discernible impact was seen. Therefore, it is vital to detect Pb 2+ using the visible fluorescence approach[ 6 ]. A significant linear connection between fluorescence intensity (F o /F) and rising Pb 2+ ion concentration (0.02 to 70µM, R 2 = 0.993) can be seen in the Stern-Volmer plot of CQDs/ZnO. Plotting nonlinearly throughout the whole concentration range of 0.02 to 300 µM indicates that the system may be experiencing both dynamic and static quenching[ 21 ]. The following formula was used to get the quenching efficiency: where F 0 and F stand for the fluorescence intensity of CQDs/ZnO at excitation and emission wavelengths of 330 and 420 nm in the presence and absence of Pb 2+ , respectively, and K sv and Q stand for the Stern-Volmer quenching constant and the concentration of Pb 2+ . The calculated DT values, which was found to be 0.21 µM (S/N = 3, where S is the standard deviation and N is the slope), was found to be significantly lower than previously reported values. These findings suggest that the berry CQDs/ZnO have been innovatively developed as an efficient fluorescent probe for achieving the lowest detection threshold and sensitive detection of Pb 2+ over a range of concentration [ 6 , 36 ]. 3.6. Detection of Pb 2+ in the environmental samples It was shown that CQDs/ZnO was applicable to the environment by examining the amounts of Pb 2+ in actual water samples. Several water samples were subjected to conventional addition tests in order to confirm this methodology. Filtration and centrifugation were used on all samples to get rid of suspended constituents[ 36 – 39 ]. The fluorescence intensity of the CQDs/ZnO declined when standard solutions were added to the samples. At different concentrations, fluorescence responses were seen with the addition of Pb 2+ . The recoveries of every sample were calculated using the following formula. The concentration of Pb 2+ added to the ambient samples is represented by C 0 , while the concentrations of Pb 2+ in the samples in the presence and absence of a standard Pb 2+ solution are shown by C 1 and C 2 , respectively. All of the samples had recovery values between 98 and 106.4%, while the relative standard deviation (RSD) values varied from 0.77 to 0.89%. As Table 1 summarizes, these data show how accurate the suggested strategy is. Table 1 Determination of Pb 2+ in real sample Samples No. Added (µM) Found (µM) Recovery % RSD% (n = 4) River water 1 0 72 - 0.75 2 2 75.43 106.5 0.78 3 3 78.1 98 0.70 4 5 80.27 100 0.78 Tap water 1 0 55.63 98 0.88 2 2 62.78 99.5 0.92 3 3 60.12 105.4 0.86 4 5 66.03 101.2 0.87 Conclusion Carbon quantum dots (CQDs) were synthesized from apple peel waste using a one-step hydrothermal method and subsequently combined with zinc oxide (ZnO) to form a nanocomposite. The synthesized CQDs/ZnO nanocomposite was analyzed using various analytical techniques. FTIR confirmed the presence of functional groups, XRD identified the crystalline nature, SEM and TEM revealed the morphology, and UV-Vis spectroscopy and fluorescence analysis showed prominent peaks indicative of the material's optical properties. The nanocomposite achieved 98.1% degradation of Rhodamine B (RhB) dye, demonstrating excellent photocatalytic performance. Additionally, the CQDs/ZnO acted as an efficient fluorescent sensor for the selective and sensitive detection of Pb²⁺ ions, achieving a detection limit of 0.21 µM. Its practical applicability was further validated by successfully detecting Pb²⁺ ions in environmental water samples, underscoring its potential as a sustainable and effective solution for water pollution remediation. Declarations Funding Declaration There is no funding associated with this manuscript. 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J Mater Chem C 1:4925–4932. https://doi.org/10.1039/C3TC30701H Atchudan R, Edison TNJI, Chakradhar D et al (2017) Facile green synthesis of nitrogen-doped carbon dots using Chionanthus retusus fruit extract and investigation of their suitability for metal ion sensing and biological applications. Sens Actuators B Chem 246:497–509. https://doi.org/10.1016/J.SNB.2017.02.119 Zhu Y, Li G, Li W et al (2023) Facile synthesis of efficient red-emissive carbon quantum dots as a multifunctional platform for biosensing and bioimaging. Dye Pigment 215:111303. https://doi.org/10.1016/J.DYEPIG.2023.111303 Wu X, Tian F, Wang W et al (2013) Fabrication of highly fluorescent graphene quantum dots using l-glutamic acid for in vitro/in vivo imaging and sensing. J Mater Chem C 1:4676–4684. https://doi.org/10.1039/C3TC30820K Ganguly S, Das P, Bose M et al (2017) Strongly blue-luminescent N-doped carbogenic dots as a tracer metal sensing probe in aqueous medium and its potential activity towards in situ Ag-nanoparticle synthesis. Sens Actuators B Chem 252:735–746. https://doi.org/10.1016/J.SNB.2017.06.068 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6261982","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":435635410,"identity":"3ac4b59a-1202-4bb7-ab25-930acfe58442","order_by":0,"name":"Laila Alkhtabi","email":"","orcid":"","institution":"King Abdulaziz University","correspondingAuthor":false,"prefix":"","firstName":"Laila","middleName":"","lastName":"Alkhtabi","suffix":""},{"id":435635411,"identity":"b7be3579-b036-4ca3-98d0-abbdeda39625","order_by":1,"name":"Mohammad Mujahid","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYJACA8YGCcZ+HjCbmQQtM3tI0cLA2MDAuOEMsVp0p50xKPi5w0J285nDzyQYKqwTG/gPP8Crxex2joFh7xkJ421n28wkGM6kJzZIpBkQ1GLA2yaRuO08g5kEY9thoBYGwloM/wK1bO5n/ybB+A+ohf/4B4JajEG2bODtAdrSANTCkEPIlrQCY9k2CeMZZ84UWyQcSzduk8gpIKAleZvh27Y62f6e9I03PtRYy/bzH9+AVwsQsCHckQDiElIPBMwPiFA0CkbBKBgFIxkAAIuSR6hl9Vc1AAAAAElFTkSuQmCC","orcid":"","institution":"King Abdulaziz University","correspondingAuthor":true,"prefix":"","firstName":"Mohammad","middleName":"","lastName":"Mujahid","suffix":""}],"badges":[],"createdAt":"2025-03-19 13:23:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6261982/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6261982/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":79668826,"identity":"9dbf0f43-d982-457f-9f73-83eba75c7595","added_by":"auto","created_at":"2025-04-01 10:47:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":228022,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme for synthesis of CQDs/ZnO\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/8b277ffdc7b55196c05560de.png"},{"id":79668827,"identity":"9b0b78dd-70a6-46d0-af72-363c9feb817f","added_by":"auto","created_at":"2025-04-01 10:47:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":124041,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA) FTIR B) XRD spectra of the synthesized CQDs/ZnO\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/e764e17dbaa8c67341130bd5.png"},{"id":79670302,"identity":"af5412c0-2f2e-40c4-888f-39322bc51b21","added_by":"auto","created_at":"2025-04-01 11:03:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":280395,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA) SEM image B) HRTEM images of the synthesized product.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/2cbfed5a0ced67b46b24b1bb.png"},{"id":79668830,"identity":"7d3bfa5b-1c36-446d-aa9f-4bfad2e97da1","added_by":"auto","created_at":"2025-04-01 10:47:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":119159,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA) UV-Vis spectra of CQDs/ZnO (Inset shows the bandgap) B) Fluorescence spectra of the different synthesized product.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/70aac5df73e52f9912cda2b9.png"},{"id":79669719,"identity":"fbbb65fa-f1b3-4105-a7a2-95c50e7b71bb","added_by":"auto","created_at":"2025-04-01 10:55:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":248903,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA) UV-Vis spectra of degradation of RhB dye B) Change in concentration of Rhodamine B by CQDs, ZnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e \u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eand CQDs/ZnO at different time interval under visible light source C) Pseudo-first order kinetics of the synthesized nanomaterial D) Degradation% by the different catalyst\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/9dedd815305d7361ecdaa2d5.png"},{"id":79668831,"identity":"ab0b5008-301d-438a-bacf-7c81a6e7eede","added_by":"auto","created_at":"2025-04-01 10:47:33","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":389455,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(A) Selectivity for various metal ions (1 µM) (B) FL spectra of the CQDs/ZnO response to Pb\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e ions with different concentrations (from top to bottom: 0.02-300 µM); [CQDs/ZnO] = 300.0 μg mL\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e−1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e; pH 7.0 of H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO; (C) Linear relationship between the concentration of Pb\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e and the degree of fluorescent quenching (F\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-F), F and F\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e0\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e were the fluorescence intensities of CQDs at 450 nm in the presence or absence of Pb\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/0fa456f4a287bc6434fff12d.png"},{"id":79934531,"identity":"68919860-efe4-401f-88a4-ceba8f19d49c","added_by":"auto","created_at":"2025-04-04 17:16:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2479345,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6261982/v1/0742db69-b0c9-45d3-99f6-cf8064a4a6a8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Sustainable CQDs/ZnO Nanocomposite for Multifaceted Applications in Detection of Pb 2+ and Degradation of RhB Dye","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWater pollution remains a significant environmental and public health challenge, with heavy metals and synthetic dyes being two major contributors. Among these, lead (Pb\u0026sup2;⁺) ions and Rhodamine B (RhB) dye stand out due to their widespread use, persistence, and severe ecological and health impacts[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The increasing presence of these pollutants in water sources, primarily from industrial and agricultural activities, poses serious risks to aquatic ecosystems and human populations, necessitating urgent remediation measures[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Lead contamination is a pressing issue, resulting from industrial processes such as mining, smelting, battery manufacturing, and the improper disposal of lead-based products. Pb\u0026sup2;⁺ ions are highly toxic, even at trace levels, and can accumulate in living organisms, disrupting vital biological functions[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Chronic exposure to lead affects the nervous, reproductive, and hematopoietic systems, with children being particularly vulnerable to its neurotoxic effects[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The World Health Organization (WHO) and the United States Environmental Protection Agency (EPA) have set stringent limits on lead concentrations in drinking water, underscoring the critical need for effective detection and removal strategies[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTraditional methods for Pb\u0026sup2;⁺ detection, including atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and electrochemical techniques, offer high sensitivity but are expensive, labor-intensive, and require sophisticated instrumentation.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] These limitations have driven the development of alternative approaches, such as nanotechnology-based sensors and adsorbents, which provide cost-effective, efficient, and sustainable solutions for lead remediation[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRhodamine B (RhB) is a synthetic xanthene dye extensively used in textiles, printing, paper, and food industries[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Despite its widespread applications, the improper discharge of RhB into water bodies has raised significant environmental concerns. RhB is known for its high chemical stability, making it resistant to natural degradation processes. Its persistence in water can lead to ecological imbalances and harm aquatic life. RhB is not only a pollutant but also poses serious health risks to humans[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Prolonged exposure to RhB can cause skin irritation, respiratory problems, and potential carcinogenic effects. Therefore, the removal of RhB from water sources is crucial for ensuring environmental sustainability and public health safety[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe remediation of water contaminated with Pb\u0026sup2;⁺ ions and RhB dye is challenging due to their distinct chemical properties and the need for selective and efficient treatment methods[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Conventional treatment techniques, such as coagulation, filtration, and adsorption, are often ineffective or economically unfeasible when applied to these pollutants. Advanced oxidation processes and photocatalytic methods have shown promise but require the development of high-performance materials that are both cost-effective and environmentally friendly[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Nanotechnology has emerged as a transformative tool for addressing complex water pollution issues. Nanomaterials, particularly carbon-based nanomaterials like carbon quantum dots (CQDs), have garnered significant attention for their unique physicochemical properties, including high surface area, tunable fluorescence, and ease of functionalization. These properties make CQDs ideal for applications in sensing, adsorption, and photocatalysis.[\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThe integration of CQDs with other materials, such as metal oxides, can further enhance their performance. Zinc oxide (ZnO), a widely studied metal oxide, is known for its excellent photocatalytic and adsorption properties. ZnO\u0026rsquo;s wide bandgap and ability to generate reactive oxygen species under UV irradiation make it a promising candidate for dye degradation and heavy metal removal. When combined with CQDs, the resulting nanocomposites exhibit synergistic effects, improving their optical, electronic, and catalytic performance[\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study focuses on the synthesis of a CQDs/ZnO nanocomposite derived from apple peel waste, a sustainable and eco-friendly carbon source. The nanocomposite aims to address the dual challenge of Pb\u0026sup2;⁺ ion and RhB dye contamination in water. By leveraging the optical and adsorption properties of CQDs and the photocatalytic capabilities of ZnO, the CQDs/ZnO nanocomposite is expected to provide an efficient, cost-effective, and environmentally sustainable solution. The dual functionality of the CQDs/ZnO nanocomposite for Pb\u0026sup2;⁺ ion detection and RhB dye degradation highlights its potential as a versatile material for water purification. Its fluorescence-based sensing mechanism enables selective and sensitive detection of Pb\u0026sup2;⁺ ions, while its photocatalytic activity ensures effective degradation of RhB dye under visible-light irradiation. The use of apple peel waste as a carbon source not only reduces production costs but also aligns with the principles of green chemistry and waste valorization.\u003c/p\u003e \u003cp\u003eIn addition to addressing water pollution, the insights gained from this study contribute to the broader field of nanotechnology-based environmental remediation. The development of multifunctional nanocomposites can pave the way for innovative solutions to combat other emerging pollutants, ensuring clean and safe water for future generations.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Material\u003c/h2\u003e \u003cp\u003eApple peel was collected from the kitchen waste. ZnO and Rhodamine dye were purchased from Fisher scientific, India and Sigma Aldrich, India. All chemicals and reagents were used as received without further treatment. Double distilled water (DDW) is used for washing and dilution purposes\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preparation of CQDs\u003c/h2\u003e \u003cp\u003eCQDs were synthesized from Apple peel waste using a one-step hydrothermal method. Apple peels were ground and dried at 65\u0026deg;C for 24 hours in a hot air oven. The dried powder was mixed with 100 mL of distilled water and stirred for 45 minutes. The mixture was then heated in a hydrothermal autoclave at 200\u0026deg;C for 8 hours and cooled to room temperature. Large particles were removed, and the suspension was filtered through 0.45 \u0026micro;m filter paper and centrifuged at 3500 rpm for 15 minutes. Finally, the brown suspension was dried at 60\u0026deg;C, and the CQDs were stored at 4\u0026deg;C (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Preparation of CQDs/ZnO nanocomposite\u003c/h2\u003e \u003cp\u003eThe CQDs/ZnO nanocomposite was synthesized by dispersing 2 g of ZnO powder into 10 mL of CQDs solution (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The mixture was stirred for 45 minutes at 300 rpm to ensure uniform dispersion and interaction. Subsequently, the solution was dried in an oven at 60\u0026deg;C for 24 hours to obtain the composite. During the process, functional groups on CQDs, such as hydroxyl (-OH) and carboxyl (-COOH), chemically interact with the ZnO surface; forming bonds like hydrogen bonds or ester linkages. These interactions enhance interfacial compatibility and improve the composite's photocatalytic and electronic properties[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Characterization techniques\u003c/h2\u003e \u003cp\u003eFourier Transform Infrared Spectroscopy (FTIR) was performed using a PerkinElmer Spectrometer version 10.4 to identify the functional groups present on the surface of the carbon quantum dots. X-ray diffraction (XRD) analysis was conducted with a Rigaku TTRAX III diffractometer to determine the crystallinity and amorphous nature of the composite. The morphological and textural properties of the composite, along with elemental distribution, were examined using transmission electron microscopy (TEM), and scanning electron microscopy (SEM) with JEOL-JEM 2100, Zeiss Gemini 300, and JEOL-JSM 6510 instruments. The optical properties of the composites were analyzed using Photoluminescence (PL) spectroscopy (Horiba DeltaFlex01-DD) and UV-Vis spectroscopy (Hitachi U3900).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Degradation experiment\u003c/h2\u003e \u003cp\u003e0.1g of \u003cem\u003eRhodamine B\u003c/em\u003e was dissolved in 100mL of DDW for the preparation of 1000ppm standard solution and then diluted to 5mg/L concentrations. The photocatalytic degradation of r\u003cem\u003ehodamine B\u003c/em\u003e in aqueous solution was studied under various experimental conditions using 1.5mg CQDs/ZnO under visible light irradiation (500W tungsten halogen lamp)[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The samples were taken at different intervals, and the UV-visible spectrophotometer was used to measure the dye absorbance at λ\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;270nm in order to evaluate the degradation performance of the produced materials. Using Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the drug's percentage of degradation was calculated.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\%\\:Degradation=\\frac{{A}_{0}-{A}_{t}}{{A}_{0}}\\times\\:100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere A\u003csub\u003e0\u003c/sub\u003e and A\u003csub\u003et\u003c/sub\u003e are the absorbance values of drug at 0 and t time. The relationship between absorbance and concentration of drug obtained from the standard curve is given in Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:Concentration\\:\\left(\\frac{mg}{L}\\right)=\\frac{A+0.0494}{0.0158}\\:\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Kinetics\u003c/h2\u003e \u003cp\u003eThe photocatalytic degradation rate of dye was determined using the pseudo-order kinetics models Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{r}_{t}=\\frac{{-dC}_{t}}{dt}={k}_{n}{C}_{t}^{n}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere, r\u003csub\u003et\u003c/sub\u003e denotes \u003cem\u003eRhodamine B\u003c/em\u003e degradation rate, C\u003csub\u003et\u003c/sub\u003e denotes drug concentration in aqueous medium at time t, k\u003csub\u003en\u003c/sub\u003e denotes rate constant, and n is the reaction order ranges between 0 to 1[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The pseudo-first-order kinetic model means n\u0026thinsp;=\u0026thinsp;1, can be obtained by integrating Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) which reduces to obtain Eq.\u0026nbsp;(\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e)\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:ln\\frac{{C}_{t}}{{C}_{o}}=-{k}_{app}t$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7. Detection of Pb\u003csup\u003e2+\u003c/sup\u003e\u003c/h2\u003e \u003cp\u003eThe as-synthesized nanocomposite were adjusted to the concentration of 300 \u0026micro;g mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in solutions containing different metal ions (Bi\u003csup\u003e2+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Hg\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, Pb\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e) was investigated. After allowing the reaction to proceed for 10 min, the fluorescence emission spectra were recorded. The sensitivity and selectivity were measured in triplicate. To determine the detection range of Pb\u003csup\u003e2+\u003c/sup\u003e, 1 mL of an aqueous solution of CQDs/ZnO (100 \u0026micro;g mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ) was added to 1000 \u0026micro;L of saline phosphate buffer (PBS, pH\u0026thinsp;=\u0026thinsp;7.4). Subsequently, varying concentrations of Pb\u003csup\u003e2+\u003c/sup\u003e (standard solution) were added. The fluorescence intensity at the excitation wavelength of 330 nm was recorded after 15 min[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.1. FTIR and XRD analysis\u003c/h2\u003e \u003cp\u003eThe FTIR spectrum of CQDs/ZnO demonstrates significant functional groups indicative of the material's chemical structure. The broad band at 3455 cm⁻¹ corresponds to the stretching vibrations of hydroxyl (-OH) groups, confirming the presence of surface functionalities. The peak at 946 cm⁻¹ is associated with C–OH stretching and O–H bending, highlighting alcohol or phenol groups. Bands at 1445 cm⁻¹ and 1616 cm⁻¹ correspond to C = C and C = O vibrations, indicating the presence of aromatic rings and carbonyl groups, respectively. Additionally, peaks at 765 cm⁻¹ and in the range of 2858–2905 cm⁻¹ represent stretching vibrations of C-H bonds, typical in sp² and sp³ hybridized carbons (as shown Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). These findings collectively suggest the carbonization of starch, where decomposition and reorganization of organic precursors result in CQDs with abundant oxygen-containing groups. These functional groups enhance the interaction between CQDs and ZnO, improving their photocatalytic and electronic properties[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe XRD pattern of the CQDs/ZnO nanocomposite displays peaks at (002), (220), (311), (400), and (420) planes, corresponding to 2θ values of 24.7°, 38.5°, 47.87°, 55°, and 64.5°. The (002) peak is attributed to the graphitic structure of CQDs, indicating their crystalline nature (as shown Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). The remaining peaks correspond to the Hexagonal Wurtzite phase of ZnO, confirming its crystallinity and phase composition. These reflections validate the successful integration of CQDs with ZnO, forming a hybrid material. This combination enhances the composite's structural, optical, and electronic properties, making it suitable for photocatalytic and environmental remediation applications[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Morphological studies techniques\u003c/h2\u003e \u003cp\u003eSEM of the CQDs/ZnO nanocomposite (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA) typically reveals an agglomerated structure. The ZnO nanoparticles are seen as small, uniformly distributed clusters, while CQDs appear as smaller, embedded particles on the ZnO surface. The interaction between CQDs and ZnO forms a rough, interconnected network, enhancing surface area and light absorption[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTEM (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB) provides high-resolution insights, showing ZnO nanoparticles as crystalline structures, with lattice fringes confirming their phase (anatase/rutile). CQDs are ultra-small, nearly spherical particles forms cluster like structure, uniformly dispersed on the ZnO surface. This homogeneous distribution indicates strong interfacial bonding, crucial for efficient electron transfer and photocatalytic activity[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Optical study\u003c/h2\u003e \u003cp\u003eThe CQDs/ZnO nanocomposite exhibits a UV-Vis absorption peak at 280 nm and 330nm, attributed to the π-π* and n- π* transitions in CQDs/ZnO, signifying their optical activity as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The bandgap value of 3.87 eV suggests ZnO's contribution, likely in its anatase phase, which has a wide bandgap. The fluorescence spectra as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB, with excitation at 350 nm, show the highest intensity for pure CQDs due to their strong emission from surface defects and oxygen-containing groups. In the composite, the fluorescence intensity is reduced, indicating efficient charge transfer between CQDs and ZnO. This quenching implies that CQDs facilitate electron transfer to ZnO, suppressing recombination of charge carriers. The very low fluorescence intensity for pure ZnO confirms its limited emission ability. The integration of CQDs enhances the light absorption range and charge separation, making the nanocomposite suitable for photocatalytic and optoelectronic applications, leveraging CQDs' photoluminescence and ZnO's stability[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Photocatalytic Study\u003c/h2\u003e \u003cp\u003eBefore initiating the photodegradation process, equilibrium between adsorption and desorption was achieved by stirring the Rhodamine solution with the photocatalyst in the dark for 30 minutes. The UV-Vis absorption spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA) of the nanocomposite solution show a significant decrease in absorption intensity as irradiation time increases. After 50 minutes of visible-light irradiation, approximately 98.1% of rhodamine was degraded, indicating the high photocatalytic efficiency of the CQDs/ZnO nanocomposite. Without a catalyst, Rhodamine B exhibited negligible self-degradation (4–5%), demonstrating its stability under direct photolysis[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn contrast, the presence of the nanocomposite significantly enhanced degradation, monitored regularly throughout the process (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). The strong light absorption, high surface area, and efficient electron transport properties of CQDs/ZnO enable rapid degradation of organic pollutants. Surface modification of CQDs further enhances their photocatalytic activity, making them a sustainable choice for water treatment technologies[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC reveals that the degradation follows pseudo-first-order kinetics and different rate constant value of different catalyst and maximum value shown by CQDs/ZnO nanocomposite, while Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD compares catalyst efficiencies, showing the order Blank \u0026lt; ZnO \u0026lt; CQDs \u0026lt; CQDs/ZnO[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Sensing of heavy metal ions using CDs\u003c/h2\u003e \u003cp\u003eThe fluorescence quenching impact of several metal ions (concentration: 300µM) on CDs (10 mg/ L) (Bi\u003csup\u003e2+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Hg\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e, Cd\u003csup\u003e2+\u003c/sup\u003e, Sr\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e) was investigated[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(A) shows that Cd\u003csup\u003e2+\u003c/sup\u003e ions dampened CQDs/ZnO PL intensity more selectively than other metal ions. Pb\u003csup\u003e2+\u003c/sup\u003e had the most quenching impact on CQDs/ZnO of all the metal cations examined, indicating the possible use of CQDs/ZnO as a selective indication sensor for Pb\u003csup\u003e2+\u003c/sup\u003e ion[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Chelation or coordination interactions between Pb\u003csup\u003e2+\u003c/sup\u003e ions and functional groups (-COOH, -OH, C-O, etc.) on the surface of CQDs/ZnO were identified as the quenching process. The adsorption of Pb\u003csup\u003e2+\u003c/sup\u003e ions on the nanocomposite surface and their interaction with -OH groups at the nanocomposite edges promote electron transport from the excited state of the nanocomposite to the vacant 4d orbital of Pb\u003csup\u003e2+\u003c/sup\u003e ions in this process. Consequently, the separation of charge carriers leads to fluorescence quenching. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(B) illustrates the potential quenching mechanism[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(C) shows the dimming of CQDs/ZnO fluorescence at different Pb\u003csup\u003e2+\u003c/sup\u003e ion concentrations. The coordination contact between Pb\u003csup\u003e2+\u003c/sup\u003e ions and the carboxyl group of CQDs/ZnO gets stronger as the concentration of Pb\u003csup\u003e2+\u003c/sup\u003e ions rises. This enhances the non-radiative recombination of charge carriers and causes quenching as a consequence. Notably, at greater doses of Pb\u003csup\u003e2+\u003c/sup\u003e ions (300µM), no discernible impact was seen. Therefore, it is vital to detect Pb\u003csup\u003e2+\u003c/sup\u003e using the visible fluorescence approach[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. A significant linear connection between fluorescence intensity (F\u003csub\u003eo\u003c/sub\u003e/F) and rising Pb\u003csup\u003e2+\u003c/sup\u003e ion concentration (0.02 to 70µM, R\u003csup\u003e2\u003c/sup\u003e = 0.993) can be seen in the Stern-Volmer plot of CQDs/ZnO. Plotting nonlinearly throughout the whole concentration range of 0.02 to 300 µM indicates that the system may be experiencing both dynamic and static quenching[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The following formula was used to get the quenching efficiency:\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"483\" height=\"71\"\u003e\u003c/p\u003e \u003cp\u003ewhere F\u003csub\u003e0\u003c/sub\u003e and F stand for the fluorescence intensity of CQDs/ZnO at excitation and emission wavelengths of 330 and 420 nm in the presence and absence of Pb\u003csup\u003e2+\u003c/sup\u003e, respectively, and K\u003csub\u003esv\u003c/sub\u003e and Q stand for the Stern-Volmer quenching constant and the concentration of Pb\u003csup\u003e2+\u003c/sup\u003e. The calculated DT values, which was found to be 0.21 µM (S/N = 3, where S is the standard deviation and N is the slope), was found to be significantly lower than previously reported values. These findings suggest that the berry CQDs/ZnO have been innovatively developed as an efficient fluorescent probe for achieving the lowest detection threshold and sensitive detection of Pb\u003csup\u003e2+\u003c/sup\u003e over a range of concentration [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Detection of Pb\u003csup\u003e2+\u003c/sup\u003e in the environmental samples\u003c/h2\u003e \u003cp\u003eIt was shown that CQDs/ZnO was applicable to the environment by examining the amounts of Pb\u003csup\u003e2+\u003c/sup\u003e in actual water samples. Several water samples were subjected to conventional addition tests in order to confirm this methodology. Filtration and centrifugation were used on all samples to get rid of suspended constituents[\u003cspan additionalcitationids=\"CR37 CR38\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e–\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The fluorescence intensity of the CQDs/ZnO declined when standard solutions were added to the samples. At different concentrations, fluorescence responses were seen with the addition of Pb\u003csup\u003e2+\u003c/sup\u003e. The recoveries of every sample were calculated using the following formula.\u003c/p\u003e \u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"498\" height=\"64\"\u003e\u003c/p\u003e\u003cp\u003eThe concentration of Pb\u003csup\u003e2+\u003c/sup\u003e added to the ambient samples is represented by C\u003csub\u003e0\u003c/sub\u003e, while the concentrations of Pb\u003csup\u003e2+\u003c/sup\u003e in the samples in the presence and absence of a standard Pb\u003csup\u003e2+\u003c/sup\u003e solution are shown by C\u003csub\u003e1\u003c/sub\u003e and C\u003csub\u003e2\u003c/sub\u003e, respectively. All of the samples had recovery values between 98 and 106.4%, while the relative standard deviation (RSD) values varied from 0.77 to 0.89%. As Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes, these data show how accurate the suggested strategy is.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetermination of Pb\u003csup\u003e2+\u003c/sup\u003e in real sample\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAdded (µM)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFound (µM)\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRecovery %\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRSD%\u003c/p\u003e \u003cp\u003e(n = 4)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRiver water\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.75\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e75.43\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e106.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e78.1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.70\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e80.27\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.78\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTap water\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e55.63\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e98\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.88\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e62.78\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e60.12\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e105.4\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e66.03\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e101.2\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eCarbon quantum dots (CQDs) were synthesized from apple peel waste using a one-step hydrothermal method and subsequently combined with zinc oxide (ZnO) to form a nanocomposite. The synthesized CQDs/ZnO nanocomposite was analyzed using various analytical techniques. FTIR confirmed the presence of functional groups, XRD identified the crystalline nature, SEM and TEM revealed the morphology, and UV-Vis spectroscopy and fluorescence analysis showed prominent peaks indicative of the material's optical properties.\u003c/p\u003e\u003cp\u003eThe nanocomposite achieved 98.1% degradation of Rhodamine B (RhB) dye, demonstrating excellent photocatalytic performance. Additionally, the CQDs/ZnO acted as an efficient fluorescent sensor for the selective and sensitive detection of Pb²⁺ ions, achieving a detection limit of 0.21 µM. Its practical applicability was further validated by successfully detecting Pb²⁺ ions in environmental water samples, underscoring its potential as a sustainable and effective solution for water pollution remediation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eFunding Declaration\u003c/strong\u003e \u003cp\u003eThere is no funding associated with this manuscript.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eThe Author Contribution\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cb\u003eLaila Alkhtabi: Experimental performance, graph plotting, writing\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eMohammad Mujahid: Editing, graph plotting, technical explanation and checking the whole manuscript.\u003c/b\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDutt MA, Hanif MA, Nadeem F, Bhatti HN (2020) A review of advances in engineered composite materials popular for wastewater treatment. 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Sens Actuators B Chem 252:735\u0026ndash;746. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/J.SNB.2017.06.068\u003c/span\u003e\u003cspan address=\"10.1016/J.SNB.2017.06.068\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hydrothermal Process, Photocatalytic efficiency, Fluorescence quenching, Sensing of Pb2+","lastPublishedDoi":"10.21203/rs.3.rs-6261982/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6261982/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, carbon quantum dots (CQDs) were synthesized from apple peel waste using a one-step hydrothermal process and incorporated into a ZnO nanocomposite. The synthesized product was characterized using various analytical techniques, including FTIR, XRD, SEM, and TEM. FTIR analysis revealed the presence of functional groups such as -COOH, C-O-C, and Zn-O, while XRD analysis confirmed the wurtzite crystalline structure of the nanocomposite. The CQDs/ZnO nanocomposite exhibited UV-Vis absorption peaks at 280 nm and 330 nm, attributed to the π-π* and n-π* transitions, respectively, indicating its optical activity. The calculated bandgap of 3.87 eV suggests the involvement of ZnO in its wurtzite phase, known for its wide bandgap properties. Adsorption studies showed that the CQDs/ZnO nanocomposite followed pseudo-first-order kinetics, demonstrating its efficiency in the adsorption process. Moreover, the fluorescence intensity of the nanocomposite significantly decreased in the presence of Pb\u0026sup2;⁺ ions, enabling selective detection of Pb\u0026sup2;⁺ over other metal ions. The fluorescence probe exhibited a linear response in the concentration range of 0\u0026ndash;300 \u0026micro;M, with a detection threshold (DT) of 0.21 \u0026micro;M, highlighting its high sensitivity for Pb\u0026sup2;⁺ detection. Additionally, the CQDs/ZnO nanocomposite was successfully applied to detect Pb\u0026sup2;⁺ ions in real water samples, demonstrating its practical applicability.\u003c/p\u003e","manuscriptTitle":"Sustainable CQDs/ZnO Nanocomposite for Multifaceted Applications in Detection of Pb 2+ and Degradation of RhB Dye","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-01 10:47:28","doi":"10.21203/rs.3.rs-6261982/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"54645adc-ccf6-4bad-87d4-03d0fb24a03a","owner":[],"postedDate":"April 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-04T17:08:32+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-01 10:47:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6261982","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6261982","identity":"rs-6261982","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}