UV Light-Induced degradation of food dyes in the presence of humic substances-coated iron oxide nanoparticles

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Rosales Vierma, María Luciana Montes, Mariela A. Fernández, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8722014/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 This study investigated the photodegradation of amaranth red (AR), sunset yellow (SY), and brilliant blue (BB) food dyes in aqueous solution under UV-A radiation with a maximum wavelength of 350 nm. The synergistic effect of humic substance-coated iron oxide nanoparticles (HS-FeOx) and hydrogen peroxide (H 2 O 2 ) was evaluated. While direct irradiation alone was ineffective, the addition of H 2 O 2 at a concentration of 0.1 M to the aqueous solution, led to minimal degradation (< 12%). The incorporation of HS-FeOx nanoparticles significantly enhanced the process, particularly for the azo dyes AR and SY. The most effective treatment combined HS-FeOx with H 2 O 2 , achieving high degradation percentages of (96.0 ± 0.6) %, (63.3 ± 0.6) % and (46.4 ± 0.1) % for AR, SY, and BB, respectively, after 60 minutes. Control experiments confirmed the oxidative degradation pathway and that Fenton-like reactions occurred even in darkness, though irradiation markedly improved efficiency. The degradation kinetics for all dyes followed a first-order model under the tested conditions. photodegradation UV Light food dyes iron oxides nanoparticles humic substances Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Dyes are extensively used in the textile, food, and plastic industries to enhance the aesthetic appeal of products. However, their widespread application contributes significantly to water pollution, with the textile sector being the primary source (Popli & Patel, 2015 ). A substantial number of these synthetic dyes are environmentally persistent and can pose risks to ecosystems and human health. In particular, azo dyes (-N = N-) and acid dyes have been proven to cause toxic effects in aquatic organisms and mammals (Hashem et al., 2011 ; Jiang et al., 2020 ). The treatment of wastewater containing these compounds presents still a considerable challenge due to their high chemical stability. The molecular structure of dyes, which commonly features benzene rings and resonant configurations, confers resistance to conventional biological and physico-chemical degradation processes (EFSA, 2015). While adsorption onto various materials has been widely employed as a non-conventional method for dye removal (Ncibi et al., 2007 ), this technique merely transfers the pollutant from the liquid to a solid phase, generating secondary waste that requires further disposal. In this context, Advanced Oxidation Processes (AOPs) are considered a cleaner alternative. AOPs are based on the in-situ generation of highly reactive species in solution, with or without irradiation, which can effectively degrade and, in some cases, mineralize target pollutants without producing significant solid waste (Deng & Zhao, 2015 ). The most well-established AOPs for water treatment are Fenton and photo-Fenton processes. In the classic Fenton reaction, highly oxidizing hydroxyl radicals ( ∙ OH, standard oxidation-reduction potential E° = 2.80 V) are generated through the reaction between ferrous ions (Fe²⁺) and hydrogen peroxide (H 2 O 2 ) (Pereira et al., 2012 ). The photo-Fenton process enhances this system by using electromagnetic energy to photoreduce Fe³⁺ back to Fe²⁺, facilitating a catalytic cycle that sustains the production of ∙OH radicals (Minella et al., 2014 ). Furthermore, humic substances (HS), a class of heterogeneous, polydisperse, dark-colored organic compounds prevalent in soils, natural waters, and sediments (Li & Shang, 2005; Zavarzina et al., 2021 ), have been shown to possess the capacity to generate reactive oxygen species in solution (Paciolla et al., 2002 ). The application of photo-Fenton-like processes mediated by iron oxides (FeOx) in the presence of humic substances may lead to a synergistic effect, enhancing the overall efficiency of contaminant degradation. The application of iron oxide nanomaterials functionalized with humic substances is a topic of study in the development of aquatic remediation technologies. For example, Carlos et al. (2011) have reported that humic acids, even when supported on iron oxide nanoparticles, can generate reactive oxygen species (ROS) under irradiation, suggesting their usefulness in oxidative degradation processes. This photocatalytic capacity is reinforced by work such as Arce et al. ( 2018 ), who demonstrated that fulvic acid-coated magnetite nanoparticles are optimal for the photosensitized reduction of Cr(VI). This work investigates the photodegradation of the food dyes Amaranth Red (AR), Sunset Yellow (SY), and Brilliant Blue (BB) in aqueous solution. The process was driven by irradiation at a maximum wavelength of 350 nm and utilized additives consisting of humic substances-coated magnetic nanoparticles in an oxidizing medium (0.1 M H 2 O 2 ). The study aims to evaluate the synergistic potential of this combined system for the effective remediation of dye-laden wastewater. Experimental Section Materials Iron (III) chloride hexahydrate (FeCl 3 ·6H 2 O), iron (II) sulfate heptahydrate (FeSO 4 ·7H 2 O), and hydrogen peroxide (30% w/w, H 2 O 2 ) were purchased from Anedra; sodium hydroxide (NaOH) from J.T. Baker; and ammonium hydroxide (30% w/w, NH 4 OH) from Sigma-Aldrich. All reagents were used without further purification. Bertinat Organic Compost was used as the source of humic substances. Deionized water (resistivity >18 MΩ·cm, total organic carbon <20 ppb) was obtained from a Millipore system. The E123 Amaranth Red (AR), E133 Brilliant Blue FCF (BB) and E110 Sunset Yellow (SY) food dyes were provided by the Saporiti company. The chemical structures of the dyes are shown in Fig. 1 . Extraction of humic substances The commercial compost used in this study was composed of various aquatic plant residues, black and blonde peat, forest litter, pine needles, vermicompost, aged manure, and perlite. These components were mixed and left to mature for six months to undergo the composting process. Humic substances (HS) were extracted from compost by suspending 100 g of pre-sieved compost in 300 mL of ultrapure water, adjusting the pH to 10 with NaOH, and stirring for 4 hours (David Gara et al., 2011). After standing overnight, the mixture was centrifuged to separate the liquid phase, then evaporated to dryness in a rotary evaporator under reduced pressure at 40°C. The resulting solid was dried at 60°C overnight and reserved for nanomaterial synthesis. Synthesis and characterization of nanoparticles A modification of the procedure reported by Arce et al. (2018) for the synthesis of nanoparticles was used here to prepare iron oxide magnetic nanoparticles (FeOx) with HS capping (HS-FeOx). Briefly, 6.1731 g FeCl 3· 6H 2 O and 4.0683 g FeSO 4· 7H 2 O were dissolved in water and heated to 90 °C. Then, two aqueous solutions were rapidly and sequentially added: (1) 10 mL of 25% ammonium hydroxide and (2) 50 mL of 1.0% w/v HS. The mixture was stirred at 90 °C for 30 min and then cooled to room temperature. The product was filtered, washed with water and ethanol, then dried overnight at 60 °C in a drying oven. The brown precipitate obtained was stored at room temperature as a dry brown powder prior to use in the experiments. The same procedure was conducted without the addition of HS to obtain uncapped nanomaterials. The FeOx and HS-FeOx nanoparticles were characterized by Scanning electron microscopy (SEM), UV-visible and fluorescence spectroscopies, X-Ray diffraction (XRD), zeta potential (ζ), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM) and Mössbauer spectroscopy. A Gemini Crossbeam 340 equipment was used for the measurements of images by Scanning Electron Microscope (SEM). Then ImageJ software was used to analyze the images and determine the particle size distribution of the formed Fe oxides nanoparticles. Absorption spectra were measured on a Shimadzu UV-1650PC at room temperature in quartz cells with 1.0 cm optical path length, between 200 and 900 nm. The fluorescence spectra were measured on air-equilibrated aqueous solutions or suspensions using a Shimadzu RF-5301PC, in a 1 cm length quartz cells at room temperature. Fluorescence Excitation–Emission Matrix (FEEM) were generated by collecting the data of successive emission spectra from 230 to 600 nm at excitation wavelengths that ranged from 220 to 450 nm, with 5 nm incremental steps. Diffraction patterns (3 o - 70 o , 10 s/step and a step size of 0.02 o (2θ)) were measured by a Philips PW 1710 diffractometer using CuKα radiation. Diffraction patterns of standard materials were considered to identify the present crystalline phases. Thermogravimetric measurements (TGA) were performed using Rigaku 8121 equipment, with alumina as reference material. For that, the sample was placed on alumina crucibles and heated from 24 °C to 1000 °C, in an air atmosphere, increasing the temperature at a rate of 10 °C/min. The TGA first-order derivative (DTGA) was calculated. The ζ-potential was determined using a Zeta Potential Analyzer (Brookhaven 90Plus/Bi, MA, USA) instrument on electrophoretic mobility function at room temperature. The ζ-potential range was set from 100 to 50 mV and the electrophoretic mobility was converted into ζ-potential values using the Smoluchowski equation. For each determination 100 µl of the NPs suspensions were dispersed in 1.0 ml of milli-Q water before measurements were taken. A LakeShore 7404 sample vibrating magnetometer was employed for the measurement of hysteresis loops (room temperature, magnetic field varying between ±1.9 T). For that, each sample was placed in a diamagnetic holder with negligible magnetic response. The high field magnetization, x hifi , the coercive field, Hc , the remanent magnetization, Mr , and the saturation magnetization, Ms , were extracted for the hysteresis loops. Mössbauer spectra were measured in transmission geometry using a conventional constant-acceleration spectrometer (room temperature, ±12 mm/s, gamma ray source of 57CoRh, 512 channels multichannel scaler). Each sample was properly mounted on a plastic holder and measured a long enough time to attain a well-defined spectrum. The Mössbauer spectrum of a α-Fe foil was used to calibrate the spectrometer. All the isomer shifts obtained from the fit are referred to this standard, and each spectrum was analyzed using hyperfine magnetic fields and quadrupole splitting distributions. Steady-State Irradiation Experiments Photolysis experiments of aqueous dye solutions were conducted in a reactor equipped with eight lamps emitting at λ max = 350 nm. Aqueous solutions of the three dyes were irradiated for 60 min using consistent initial concentration. The experiments were conducted using both coated (HS-FeOx) and bare (FeOx) nanoparticles, both in the presence and absence of H 2 O 2 . The degradation process was monitored at regular intervals via UV-Vis spectroscopy. All experiments were conducted at room temperature. The monitoring of dye concentrations was carried out by analyzing the absorption spectra and observing the changes in their main absorption bands at 522 nm, 630 nm, and 482 nm for AR, BB, and SY, respectively. The initial dye concentration was 2×10 -5 M in all cases. Control experiments were performed for all conditions. Results and Discussion Characterization of HS and HS-FeOx HS-FeOx SEM image ( Fig. 2a ) revealed aggregates of nanoparticles, although several free nanoparticles can be identified and considered to build-up their size distribution, presented, together with its fits in Fig. 2b . An almost cubic geomorphology is observed, with mean side of 16.9±0.7 nm, in agreement data reported for similar particles (Arce et al. 2018). Additionally, the UV-Vis extinction spectra for both samples, HS and HS-FeOx, are shown in the insets of Fig. 3a and 3b , respectively. Regarding the bare HS, a widely employed parameter in the characterization of humic substances is the E 4 /E 6 ratio, defined as the extinction ratio at 465 nm to 665 nm. Shirshova et al. (2006) proposed that the E 4 /E 6 ratio is indicative of the molecular size, degree of condensation, and aromaticity in HS. In this work, an E 4 /E 6 value of 1.275 was obtained for the extracted HS, which is consistent with values reported for other humic substances (Filcheva et al., 2018; Zalba et al., 2016). This specific value suggests a material with a relatively high molecular weight and a significant degree of condensation. The inset of Fig. 3b shows the extinction spectrum of HS-FeOx suspension at the same concentration employed in the degradation assays. The spectrum exhibits notable light scattering attributable to the nanoparticles. Notably, the characteristic intense extinction below 250 nm associated with HS is almost completely suppressed in the HS-FeOx system. This attenuation can be attributed to interactions between HS and iron oxide species, which promote the coordination of functional groups -predominantly carboxylic and phenolic moieties- to the nanoparticle surface. Such interactions modify the electronic environment of these chromophoric groups, diminishing their ability to absorb in the deep UV region (Niu et al., 2011). This spectroscopic change provides evidence for successful surface functionalization of the iron oxide nanoparticles with humic substances. The diffraction patterns of FeOx and HS-FeOx samples are shown in Fig. 4a . In both cases, the patterns are consistent with those expected for magnetite (Mg)/maghemite (Mh). The expected relative intensity for each phase is indicated at each peak (Gabbasov et al., 2015). In addition to the identification of the same peak positions, no significant differences are observed between the peak width, indicating that the presence of the HS does not affect the structural characteristics of the formed nanoparticles. The pH dependence of the zeta potential (ζ) of HS-FeOx dispersions in 1×10 -3 M KCl aqueous solutions shows a pH of zero-point charge (pHPZC) of 3.83 Fig. 4b , indicating that at this pH value the net charge of the particles is neutral. From this point onward, the deprotonation of acidic groups present in the humic substances begins as the pH increases. This process results in an increase in the net negative charge of the molecules, which leads to enhanced electrostatic repulsion between them. Consequently, the stability of the suspended particles against aggregation increases at pH values above 4. According to Klučáková & Kalina, (2015) the decrease in zeta potential may result from two simultaneous processes: the dissociation of acidic functional groups and the disaggregation of humic aggregates. The DTA-TGA curves corresponding to the NPs are shown in Fig. 4c . In the TGA curve, a mass loss is observed from room temperature to 800 °C. A slight endothermic valley is observed at 78 °C, associated with a 4.99% mass loss, which is attributed to the desorption of physically adsorbed water. From that point on, an exothermic trend begins in the DTA curve, accompanied by additional mass losses up to 400 °C, totaling 13.97%. These losses are associated with the oxidation of both labile and recalcitrant fractions of humic substances. Finally, the exothermic peak near 600 °C is assigned to a possible magnetite–hematite phase transition (Zheng et al., 2021; Chen et al., 2013) or a possible reduction of Fe 3 O 4 to FeO (Kim et al., 2000). The samples were also analyzed using a vibrating sample magnetometer (VSM), from which the hysteresis loop for each sample was obtained ( Fig. 5a ). Both samples exhibited a combined paramagnetic–superparamagnetic behavior (absence of coercivity, Hc , and remanent magnetization, Mr ). The absence of hysteresis is expected for the nanoparticles with the determined size. The paramagnetic contribution was similar for both samples ( x hifi = 1.41x10 -6 m 3 /kg FeOx; 1.33 x10 -6 m 3 /kg HS-FeOx), while the saturation magnetization ( Ms ) was higher for FeOx ( Ms = 25.4±0.1 Am 2 /kg) than for HS-FeOx ( Ms = 16.5±0.1 Am 2 /kg), as expected due to the presence of HS coating the material surface. Additionally, the FeOx sample showed a low Ms value compared to the expected values for bulk of magnetite or maghemite. This reduction could indicate the formation of Fe oxide with defects. To analyze this fact, Mössbauer spectra were measured ( Fig. 5b ). For both materials the spectrum only reveals the presence of doublets, corroborating the formation of nanometric particles. In addition, a wider signal, paramagnetic relaxation, must be included to attain a good enough fit, indicating a disorder caused by the incomplete formation of the oxides, which also explain the relatively low determined Ms . The absence of magnetic hyperfine splitting prevents the identification of whether magnetite, maghemite, or the determination of their relative proportions in a mixture of them. Irradiation Experiments After 60 minutes of irradiation of solution containing only the dyes, no significant degradation of the compounds was observed. Therefore, hydrogen peroxide (H 2 O 2 ) was added at a concentration of 0.1 M to promote oxidative conditions during irradiation. Under these conditions, degradation percentages of (10.3±0.6) % for AR, (7.0±0.6) % for SY, and (11.6±0.1) % for BB were achieved. Althouhgh the oxidative environment improved dye degradation, the determined percentages resulted relatively low and then the inclusion of HS-FeOx nanoparticles in the process was proposed. Upon the addition of 500 ppm of nanoparticles in a new assay, the degradation percentages under irradiation reached (60.2±0.7) % for AR, (26.1±0.8) % for SY, and (8.2±0.1) % for BB. These results indicate that the presence of the nanoparticles enhanced the degradation rate of AR and SY azo dyes. Different experimental conditions were tested under both irradiation and dark conditions to evaluate the synergistic effect, including FeOx in the presence and absence of H 2 O 2 , as well as HS-FeOx combined with H 2 O 2 . The combined use of HS-FeOx and H 2 O 2 (0.1 M) led to degradation percentages of (96.0±0.6) % for AR, (63.3±0.6) % for SY, and (46.4±0.1) % for BB after one hour of irradiation. The results obtained for AR under the different conditions are shown in Fig. 6 a , excluding dark controls. Similar behavior was observed for SY and BB. Control experiments using FeOx and H 2 O 2 nanoparticles under both irradiation and dark conditions yielded degradation values of (86.8±0.6) % for AR, (54.9±0.8) % for SY, and (35.9±0.1) % for BB under irradiation, and (60.1±0.6) % for AR, (41.1±0.9) % for SY, and (16.2±0.1) % for BB in the dark. These results suggest that Fenton-like processes can occur even in the absence of HS and light (Pereira et al., 2012) with a significant difference observed between irradiation and dark conditions. Additional control experiments conducted for the three dyes under oxygen-free conditions confirmed that the observed degradation proceeded through an oxidative pathway, as significantly lower degradation percentages were obtained compared to those observed under aerobic environments. The kinetics of the degradation processes were studied using the pseudo-first-order reaction rate model, Equation 1 . The variation of ln(A/A₀) with time was examined for the three dyes, revealing pseudo-first-order kinetic behavior under the studied conditions, see Equation 1 . It is important to note that, in the case of the AR dye under irradiation in presence of HS-FeOx and H 2 O 2 , the kinetic fitting was performed only up to the 30-minute data point, since linearity was lost beyond this time. This deviation could be attributed to the formation of intermediate or degradation products that absorb in a spectral region close to that used for monitoring the dye. The resultant rate constants ( k ) are shown in Table 1 for three conditions: HS-FeOx in presence and absence of H 2 O 2 under irradiation, HS-FeOx and H 2 O 2 in dark. Table 1 . Pseudo-first-order rate constant for three conditions: HS-FeOx and H 2 O 2 under irradiation, HS-FeOx under irradiation HS-FeOx and H 2 O 2 in dark HS-FeOx/ H 2 O 2 (min -1 ) HS-FeOx (min -1 ) HS-FeOx/ H 2 O 2 (dark) (min -1 ) AR 0.078±0.003 0.018±0.002 0.0207±0.002 YS 0.0165±0.0004 0.0043±0.0004 0.0191±0.0007 BB 0.0104±0.0002 0.0013±0.0001 0.0023±0.0001 The differences observed in the pseudo-first order rate constants could be attributed to the structural features of the dyes. As shown in Table 1 , the reactivity toward decolorization is influenced by the electronic environment of the azo bond, which is susceptible to oxidative attack by reactive oxygen species (ROS) due to its high electron density. This susceptibility can be affected by the nature and positions of the adjacent substituents. In particular, aromatic rings usually stabilize the azo bond through electronic resonance effects. However, the presence of substituent groups with different electronic character can modify its reactivity. Such is the case with resonance electron-donating groups, like the hydroxyl group (-OH), which increase the electron density around the azo bond and, consequently, its susceptibility to oxidation, as observed in the results obtained for the AR and SY dyes compared to those obtained for BB, since a higher pseudo-first-order rate constant was obtained for AR and YS. Furthermore, the presence of an additional substituent in the meta position relative to the azo group, such as an electron-withdrawing sulfonic group (-SO 3 ), can additionally contribute to the degradative process. This effect can be attributed both to the partial destabilization of the aromatic system and to the increase in the dye solubility, which enhances the accessibility of the azo bond for oxidizing species. These combined effects would explain why the AR dye exhibits a higher reactivity towards oxidation compared to SY, despite both having azo structures, and why the BB dye is more stable, possibly due to greater electronic delocalization in its conjugated system. Previous investigations conducted by our group have demonstrated that irradiation of commercial compost-derived extracts (analogous to the humic extracts employed for NP coating in this work), results in the photochemical generation of diverse ROS (Bosio et al., 2008; David Gara et al., 2009). These studies identified the formation of both oxidizing species -including singlet oxygen ( 1 O 2 ), hydrogen peroxide (H 2 O 2 ), triplet-excited states of humic substances ( 3 HS * ), hydroxyl radicals ( • OH), superoxide anion radicals (O 2 • ⁻) - as well as reductive species (such as hydrated electrons, e⁻ aq ). Among these transient species, • OH and 1 O 2 were identified as the predominant contributors to contaminant degradation due to their high chemical reactivity and relatively significant steady-state concentrations (David Gara et al., 2009). The iron oxide nanoparticle core further enhances ROS production through heterogeneous Fenton and photo-Fenton processes. Hydroxyl radicals are known to react with a broad range of organic compounds in a diffusion-controlled kinetics, either by direct attack on the azo bond or by addition to the aromatic rings adjacent to this group (Dostanić et al, 2020). Singlet oxygen, while less reactive than • OH, exhibits selective reactivity toward electron-rich aromatic systems, heteroatoms, and unsaturated bonds, leading to the formation of endoperoxides, or other oxygenated products. In all these pathways, the loss of conjugation within the dye molecule results in chromophore disruption and, consequently, decolorization of the solution. Conclusions In this work, humic substance-coated iron oxide nanoparticles (HS-FeOx) were successfully synthesized by a coprecipitation method and thoroughly characterized. Physicochemical analyses confirmed that the nanocomposites consist of a magnetite/maghemite core with 14% HS surface coverage, preserving their inherent magnetic properties. The preservation of the magnetic nature of the iron oxide core confers an operational advantage, facilitating efficient separation and recovery of the catalyst from aqueous media using an external magnetic field. The performance of the HS-FeOx nanocomposites was evaluated in the photodegradation of food dyes using a system combining hydrogen peroxide and UV-A irradiation. The results demonstrated that HS-coated nanoparticles markedly enhance degradation efficiency compared to uncoated iron oxide nanoparticles under identical oxidative and irradiation conditions. The enhanced photodegradation efficiency can be attributed to the multifunctional role of the humic substances. Beyond improving colloidal stability, the HS layer acts as an effective photosensitizer, promoting the generation of reactive oxygen species under UV-A irradiation. This photochemical activity operates synergistically with the heterogeneous Fenton-like reactions occurring at the iron oxide surface, resulting in accelerated dye decolorization through an oxidative pathway. The necessity of light irradiation to fully activate this synergistic mechanism underscores the importance of photochemical processes in the overall degradation performance. The photochemical treatment developed in this study presents several practical advantages for environmental remediation. The use of UV-A radiation is particularly relevant, as it overlaps with the solar spectrum reaching the Earth’s surface, suggesting the potential use of sunlight as a sustainable and cost-effective energy source. Moreover, the magnetic recoverability and potential reusability of the HS-FeOx nanoparticles further enhance their applicability in water treatment systems. Overall, the incorporation of humic substances as a functional coating for iron oxide nanoparticles proved to be an effective strategy for designing an efficient hybrid catalyst for dye degradation in aqueous environments. By integrating catalytic and photochemical functionalities within a single nanomaterial, this approach represents a promising alternative within advanced oxidation processes and contributes to the development of sustainable technologies for the treatment of contaminated water. Declarations Author Contributions Lic. Janis G. Rosales Vierma : Synthesis and characterization of nanoparticles (equal), extraction and characterization of humic substances (equal), sample preparation (equal), irradiation experiments (equal), conceptualization (equal), investigation (equal), methodology (equal), validation (equal), visualization (equal), and writing - original draft (equal). Dr. María Luciana Montes : X-Ray diffraction (lead), Mössbauer spectroscopy (lead), formal analysis (equal), investigation (equal), methodology (equal). Dr. Mariela A. Fernandez : Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), zeta potential (ζ) (lead), formal analysis (equal), investigation (equal), methodology (equal). Dr. Pedro M. David Gara : Extraction and characterization of humic substances (equal), sample preparation (equal), irradiation experiments (equal), conceptualization (equal), formal analysis (equal), investigation (equal), methodology (equal), validation (equal), visualization (equal), and writing - original draft (equal), and writing - review & editing (equal). Dr. Valeria B. Arce : Extraction and characterization of humic substances (equal), irradiation experiments (equal), conceptualization (equal), formal analysis (equal), funding acquisition (lead), investigation (equal), resources (lead), visualization (equal), writing - original draft (equal), and writing - review & editing (equal). Acknowledgements J. G. Rosales Vierma is doctoral fellow of CONICET, Argentina. M. L. Montes and M. A. Fernández are research members of CONICET, Argentina. P. M. David Gara and V. B. Arce are research members of Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC-PBA). Ethical Approval "not applicable" Funding This research was funded by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT) PICT 2018-3451 and PICT APLICADOS 2021-0074. Availability of data and materials The data that support the findings of this study are available from the corresponding author upon reasonable request. References Arce, V. B., Mucci, C. R., Fernández Solarte, I., Torres Sánchez, R. M., & Mártire, D. O. (2018). Application of novel fulvic acid-coated magnetite nanoparticles for CO 2 - -mediated photoreduction of Cr(VI). Water, Air, & Soil Pollution, 229 , 39. https://doi.org/10.1007/s11270-018-3693-5 Bosio, G. N., Gara, P. D., Einschlag, F. S. G., Gonzalez, M. C., Del Panno, M. T., & Mártire, D. O. (2008). Photodegradation of soil organic matter and its effect on Gram-negative bacterial growth. Photochemistry and Photobiology, 84 (5), 1126–1132. https://doi.org/10.1111/j.1751-1097.2007.00274.x Carlos, L., Cipollone, M., Soria, D. B., Moreno, M. S., Ogilby, P. 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(2000). Formation of a highly oriented FeO thin film by phase transition of Fe 3 O 4 and Fe nanocrystallines. Thin Solid Films, 360 (1–2), 118–121. https://doi.org/10.1016/S0040-6090(99)00562-3 Klučáková, M., & Kalina, M. (2015). Composition, particle size, charge, and colloidal stability of pH-fractionated humic acids. Journal of Soils and Sediments, 15 , 1900–1908. https://doi.org/10.1007/s11368-015-1142-2 Minella, M., Marchetti, G., De Laurentiis, E., Malandrino, M., Maurino, V., Minero, C., Vione, D., & Hanna, K. (2014). Photo-Fenton oxidation of phenol with magnetite as iron source. Applied Catalysis B: Environmental, 154–155 , 102–109. https://doi.org/10.1016/j.apcatb.2014.02.006 Morán Vieyra, F. E., Palazzi, V. I., Sanchez de Pinto, M. I., & Borsarelli, C. D. (2009). Combined UV–Vis absorbance and fluorescence properties of extracted humic substances-like for characterization of composting evolution of domestic solid wastes. Geoderma, 151 , 61–67. https://doi.org/10.1016/j.geoderma.2009.03.006 Ncibi, M. C., M’hjoub, B., & Seffen, M. (2007). Adsorptive removal of textile reactive dye using Posidonia oceanica (L.) fibrous biomass. International Journal of Environmental Science and Technology, 4 , 433–440. https://doi.org/10.1007/BF03325978 Niu, H., Zhang, D., Zhang, S., Zhang, X., Meng, Z., & Cai, Y. (2011). Humic acid coated Fe₃O₄ magnetic nanoparticles as highly efficient Fenton-like catalyst for complete mineralization of sulfathiazole. Journal of Hazardous Materials, 190 (1–3), 559–565. https://doi.org/10.1016/j.jhazmat.2011.03.086 Paciolla, M., Kolla, S., & Jansen, S. (2002). The reduction of dissolved iron species by humic acid and subsequent production of reactive oxygen species. Advances in Environmental Research, 7 , 169–178. https://doi.org/10.1016/S1093-0191(01)00129-0 Pereira, M., Oliveira, L., & Murad, E. (2012). Iron oxide catalysts: Fenton and Fenton-like reactions – A review. Clay Minerals, 47 (3). https://doi.org/10.1180/claymin.2012.047.3.01 Popli, S., & Patel, U. D. (2015). Destruction of azo dyes by anaerobic–aerobic sequential biological treatment: A review. International Journal of Environmental Science and Technology, 12 , 405–420. https://doi.org/10.1007/s13762-014-0499-x Shirshova, L. T., Ghabbour, E. A., & Davies, G. (2006). Spectroscopic characterization of humic acid fractions isolated from soil using different extraction procedures. Geoderma, 133 (3–4), 204–216. https://doi.org/10.1016/j.geoderma.2005.07.007 Xie, L., & Shang, C. (2005). Role of humic acid and quinone model compounds in bromate reduction by zerovalent iron. Environmental Science & Technology, 39 (4), 1092–1100. https://doi.org/10.1021/es049027z Zalba, P., Amiotti, N. M., Galantini, J. A., & Pistola, S. (2016). Soil humic and fulvic acids from different land-use systems evaluated by E4/E6 ratios. Communications in Soil Science and Plant Analysis, 47 (13–14), 1675–1679. https://doi.org/10.1080/00103624.2016.1206558 Zavarzina, A. G., Danchenko, N. N., Demin, V. V., Artemyeva, Z. S., & Kogut, B. M. (2021). Humic substances: Hypotheses and reality (a review). Eurasian Soil Science, 54 , 1826–1854. https://doi.org/10.1134/S1064229321120164 Zheng, H., Schenk, J., Spreitzer, D., Wolfinger, T., & Daghagheleh, O. (2021). Review on the oxidation behaviors and kinetics of magnetite in particle scale. Steel Research International, 92 , 2000687. https://doi.org/10.1002/srin.202000687 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8722014","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":611986044,"identity":"29933f81-bd0c-4256-a02e-8dcbdadbfc45","order_by":0,"name":"Janis G. Rosales Vierma","email":"","orcid":"","institution":"Centro de Investigaciones Ópticas (CIOp), (CONICET - CIC - UNLP)","correspondingAuthor":false,"prefix":"","firstName":"Janis","middleName":"G. Rosales","lastName":"Vierma","suffix":""},{"id":611986045,"identity":"72dea529-c454-4d83-b9d7-ba0e4ebae171","order_by":1,"name":"María Luciana Montes","email":"","orcid":"","institution":"Instituto de Física La Plata (IFLP), CCT-La Plata","correspondingAuthor":false,"prefix":"","firstName":"María","middleName":"Luciana","lastName":"Montes","suffix":""},{"id":611986046,"identity":"76a1f96a-35b3-41c7-af53-0cc5b86c0759","order_by":2,"name":"Mariela A. Fernández","email":"","orcid":"","institution":"Centro de Tecnología de recursos Minerales y Cerámica (CETMIC), (CIC-CONICET)","correspondingAuthor":false,"prefix":"","firstName":"Mariela","middleName":"A.","lastName":"Fernández","suffix":""},{"id":611986047,"identity":"100dc480-fbb5-4b05-9e9f-e04088e78521","order_by":3,"name":"Pedro M. David Gara","email":"","orcid":"","institution":"Centro de Investigaciones Ópticas (CIOp), (CONICET - CIC - UNLP)","correspondingAuthor":false,"prefix":"","firstName":"Pedro","middleName":"M. David","lastName":"Gara","suffix":""},{"id":611986049,"identity":"89d7cfc6-da96-4119-bcc1-6f33be70ab49","order_by":4,"name":"Valeria B. Arce","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA50lEQVRIiWNgGAWjYNCCCgYeCKMARCQQo+UMTIsBsVoY22AsYrQYHD/78MPHeXYy/NINbNIFBncY+NlzDBh+7sGj5Uy6seTMbck8knMOsEnPMHjGINnzxoCx5xluLZINaWzMvNsO8BjcSGCT5jE4zGBwA2gLzwE8WvqfsTH/nYOkxR6ohfEPHi38EkBbGBuQbZHIMWDGZwu/xDNmyZ5jIL8cbLbmMXjGI3HmWcFhGTxa2PjTGD/8qLGz55duPnibp+KOHH978saHb/BoQQAJxgYgeQAcp0RpAGphIEHxKBgFo2AUjCgAAH+GSAOVufgSAAAAAElFTkSuQmCC","orcid":"","institution":"Centro de Investigaciones Ópticas (CIOp), (CONICET - CIC - UNLP)","correspondingAuthor":true,"prefix":"","firstName":"Valeria","middleName":"B.","lastName":"Arce","suffix":""}],"badges":[],"createdAt":"2026-01-28 14:25:47","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8722014/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8722014/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105567397,"identity":"23dd8bb2-018c-4cc4-abe5-d380bd67f3cd","added_by":"auto","created_at":"2026-03-27 12:59:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":72428,"visible":true,"origin":"","legend":"\u003cp\u003eFood dyes chemical structures: a) amaranth red (AR); b) sunset yellow (SY); c) brilliant blue (BB).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/57645279153245854ee6e815.png"},{"id":105567306,"identity":"6fda9aab-084b-4810-989c-b88541ac340a","added_by":"auto","created_at":"2026-03-27 12:58:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":851890,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM image of HS-FeOx and (b) size distribution including the fit with log-normal function.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/18ea654821da72c86559ce1b.png"},{"id":105542730,"identity":"f64fad88-4108-4aa9-9931-78e36f966173","added_by":"auto","created_at":"2026-03-27 08:31:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":862765,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence Excitation-emission matrix of (a) HS (inset: HS UV-vis spectrum) and (b) HS-FeOx (inset: HS-FeOx UV-vis spectrum)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/08d27ed5b13c0b4ebba07fd9.png"},{"id":105542728,"identity":"e4183747-8ab4-49d3-81cf-baa776eb3879","added_by":"auto","created_at":"2026-03-27 08:31:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":495304,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Diffraction patterns of FeOx (top) and HS-FeOx (bottom) (b) pH-dependence of zeta potential (ζ) for HS-FeOx in 1×10\u003csup\u003e-3\u003c/sup\u003e M KCl medium. (c) DTA (dotted) and TGA (solid) curves obtained for HS-FeOx.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/73f9038b1bf8ae907864a033.png"},{"id":105542732,"identity":"798ffe49-ada6-4623-86ab-f5fa047f961f","added_by":"auto","created_at":"2026-03-27 08:31:48","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":683407,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Hysteresis loops and (b) Mössbauer spectra of FeOx and HS-FeOx\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/cd0aca7977e09be039c469f6.png"},{"id":105567005,"identity":"90ae3971-10f6-4e70-8d33-915a0c60af0a","added_by":"auto","created_at":"2026-03-27 12:58:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":707681,"visible":true,"origin":"","legend":"\u003cp\u003eAR degradation profiles under various conditions (a) and time-resolved spectra of AR under the most effective condition (b).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/2a278fca26da14858e16841b.png"},{"id":106414880,"identity":"b728dc18-6f0c-44bd-a645-a8917025c90b","added_by":"auto","created_at":"2026-04-08 10:29:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3623781,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8722014/v1/f27f5375-c4b8-4e6b-beef-75d8b7e8e9c8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"UV Light-Induced degradation of food dyes in the presence of humic substances-coated iron oxide nanoparticles","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDyes are extensively used in the textile, food, and plastic industries to enhance the aesthetic appeal of products. However, their widespread application contributes significantly to water pollution, with the textile sector being the primary source (Popli \u0026amp; Patel, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). A substantial number of these synthetic dyes are environmentally persistent and can pose risks to ecosystems and human health. In particular, azo dyes (-N\u0026thinsp;=\u0026thinsp;N-) and acid dyes have been proven to cause toxic effects in aquatic organisms and mammals (Hashem et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Jiang et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The treatment of wastewater containing these compounds presents still a considerable challenge due to their high chemical stability. The molecular structure of dyes, which commonly features benzene rings and resonant configurations, confers resistance to conventional biological and physico-chemical degradation processes (EFSA, 2015). While adsorption onto various materials has been widely employed as a non-conventional method for dye removal (Ncibi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), this technique merely transfers the pollutant from the liquid to a solid phase, generating secondary waste that requires further disposal. In this context, Advanced Oxidation Processes (AOPs) are considered a cleaner alternative. AOPs are based on the in-situ generation of highly reactive species in solution, with or without irradiation, which can effectively degrade and, in some cases, mineralize target pollutants without producing significant solid waste (Deng \u0026amp; Zhao, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The most well-established AOPs for water treatment are Fenton and photo-Fenton processes. In the classic Fenton reaction, highly oxidizing hydroxyl radicals (\u003csup\u003e\u003cb\u003e∙\u003c/b\u003e\u003c/sup\u003eOH, standard oxidation-reduction potential E\u0026deg; = 2.80 V) are generated through the reaction between ferrous ions (Fe\u0026sup2;⁺) and hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) (Pereira et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The photo-Fenton process enhances this system by using electromagnetic energy to photoreduce Fe\u0026sup3;⁺ back to Fe\u0026sup2;⁺, facilitating a catalytic cycle that sustains the production of ∙OH radicals (Minella et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Furthermore, humic substances (HS), a class of heterogeneous, polydisperse, dark-colored organic compounds prevalent in soils, natural waters, and sediments (Li \u0026amp; Shang, 2005; Zavarzina et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), have been shown to possess the capacity to generate reactive oxygen species in solution (Paciolla et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The application of photo-Fenton-like processes mediated by iron oxides (FeOx) in the presence of humic substances may lead to a synergistic effect, enhancing the overall efficiency of contaminant degradation.\u003c/p\u003e \u003cp\u003eThe application of iron oxide nanomaterials functionalized with humic substances is a topic of study in the development of aquatic remediation technologies. For example, Carlos et al. (2011) have reported that humic acids, even when supported on iron oxide nanoparticles, can generate reactive oxygen species (ROS) under irradiation, suggesting their usefulness in oxidative degradation processes. This photocatalytic capacity is reinforced by work such as Arce et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), who demonstrated that fulvic acid-coated magnetite nanoparticles are optimal for the photosensitized reduction of Cr(VI).\u003c/p\u003e \u003cp\u003eThis work investigates the photodegradation of the food dyes Amaranth Red (AR), Sunset Yellow (SY), and Brilliant Blue (BB) in aqueous solution. The process was driven by irradiation at a maximum wavelength of 350 nm and utilized additives consisting of humic substances-coated magnetic nanoparticles in an oxidizing medium (0.1 M H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e). The study aims to evaluate the synergistic potential of this combined system for the effective remediation of dye-laden wastewater.\u003c/p\u003e"},{"header":"Experimental Section","content":"\u003ch1\u003eMaterials\u003c/h1\u003e\n\u003cp\u003eIron (III) chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), iron (II) sulfate heptahydrate (FeSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;7H\u003csub\u003e2\u003c/sub\u003eO), and hydrogen peroxide (30% w/w, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) were purchased from Anedra; sodium hydroxide (NaOH) from J.T. Baker; and ammonium hydroxide (30% w/w, NH\u003csub\u003e4\u003c/sub\u003eOH) from Sigma-Aldrich. All reagents were used without further purification. Bertinat Organic Compost was used as the source of humic substances. Deionized water (resistivity \u0026gt;18 M\u0026Omega;\u0026middot;cm, total organic carbon \u0026lt;20 ppb) was obtained from a Millipore system. The E123 Amaranth Red (AR), E133 Brilliant Blue FCF (BB) and E110 Sunset Yellow (SY) food dyes were provided by the Saporiti company.\u003c/p\u003e\n\u003cp\u003eThe chemical structures of the dyes are shown in \u003cstrong\u003eFig. 1\u003c/strong\u003e. \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eExtraction of humic substances\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe commercial compost used in this study was composed of various aquatic plant residues, black and blonde peat, forest litter, pine needles, vermicompost, aged manure, and perlite. These components were mixed and left to mature for six months to undergo the composting process. Humic substances (HS) were extracted from compost by suspending 100 g of pre-sieved compost in 300 mL of ultrapure water, adjusting the pH to 10 with NaOH, and stirring for 4 hours (David Gara et al., 2011). After standing overnight, the mixture was centrifuged to separate the liquid phase, then evaporated to dryness in a rotary evaporator under reduced pressure at 40\u0026deg;C. The resulting solid was dried at 60\u0026deg;C overnight and reserved for nanomaterial synthesis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis and characterization of nanoparticles\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA modification of the procedure reported by Arce et al. (2018) \u0026nbsp;for the synthesis of nanoparticles was used here to prepare iron oxide magnetic nanoparticles (FeOx) with HS capping (HS-FeOx). Briefly, 6.1731 g FeCl\u003csub\u003e3\u0026middot;\u003c/sub\u003e6H\u003csub\u003e2\u003c/sub\u003eO and 4.0683 g FeSO\u003csub\u003e4\u0026middot;\u003c/sub\u003e7H\u003csub\u003e2\u003c/sub\u003eO were dissolved in water and heated to 90 \u0026deg;C. Then, two aqueous solutions were rapidly and sequentially added: (1) 10 mL of 25% ammonium hydroxide and (2) 50 mL of 1.0% w/v HS. The mixture was stirred at 90 \u0026deg;C for 30 min and then cooled to room temperature. The product was filtered, washed with water and ethanol, then dried overnight at 60 \u0026deg;C in a drying oven. The brown precipitate obtained was stored at room temperature as a dry brown powder prior to use in the experiments. The same procedure was conducted without the addition of HS to obtain uncapped nanomaterials. The FeOx and HS-FeOx nanoparticles were characterized by Scanning electron microscopy (SEM), UV-visible and fluorescence spectroscopies,\u0026nbsp;X-Ray diffraction (XRD), zeta potential (\u0026zeta;), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM) and M\u0026ouml;ssbauer spectroscopy.\u003c/p\u003e\n\u003cp\u003eA Gemini Crossbeam 340 equipment was used for the measurements of images by Scanning Electron Microscope (SEM). Then ImageJ software was used to analyze the images and determine the particle size distribution of the formed Fe oxides nanoparticles.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAbsorption spectra were measured on a Shimadzu UV-1650PC at room temperature in quartz cells with 1.0 cm optical path length, between 200 and 900 nm.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe fluorescence spectra were measured on air-equilibrated aqueous solutions or suspensions using a Shimadzu RF-5301PC, in a 1 cm length quartz cells at room temperature.\u0026nbsp;Fluorescence Excitation\u0026ndash;Emission Matrix (FEEM) were generated by collecting the data of successive emission spectra from 230 to 600 nm at excitation wavelengths that ranged from 220 to 450 nm, with 5 nm incremental steps.\u003c/p\u003e\n\u003cp\u003eDiffraction patterns (3\u003csup\u003eo\u003c/sup\u003e - 70\u003csup\u003eo\u003c/sup\u003e, 10 s/step and a step size of 0.02\u003csup\u003eo\u003c/sup\u003e (2\u0026theta;)) were measured by a Philips PW 1710 diffractometer using CuK\u0026alpha; radiation. Diffraction patterns of standard materials were considered to identify the present crystalline phases. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThermogravimetric measurements (TGA) were performed using Rigaku 8121 equipment, with alumina as reference material. For that, the sample was placed on alumina crucibles and heated from 24 \u0026deg;C to 1000 \u0026deg;C, in an air atmosphere, increasing the temperature at a rate of 10 \u0026deg;C/min. The TGA first-order derivative (DTGA) was calculated.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe \u0026zeta;-potential was determined using a Zeta Potential Analyzer (Brookhaven 90Plus/Bi, MA, USA) instrument on electrophoretic mobility function at room temperature. The \u0026zeta;-potential range was set from 100 to 50 mV and the electrophoretic mobility was converted into \u0026zeta;-potential values using the Smoluchowski equation. For each determination 100 \u0026micro;l of the NPs suspensions were dispersed in 1.0 ml of milli-Q water before measurements were taken.\u003c/p\u003e\n\u003cp\u003eA LakeShore 7404 sample vibrating magnetometer was employed for the measurement of hysteresis loops (room temperature, magnetic field varying between \u0026plusmn;1.9 T). For that, each sample was placed in a diamagnetic holder with negligible magnetic response. The high field magnetization, \u003cem\u003ex\u003csub\u003ehifi\u003c/sub\u003e\u003c/em\u003e, the coercive field, \u003cem\u003eHc\u003c/em\u003e, the remanent magnetization, \u003cem\u003eMr\u003c/em\u003e, and the saturation magnetization, \u003cem\u003eMs\u003c/em\u003e, were extracted for the hysteresis loops.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eM\u0026ouml;ssbauer spectra were measured in transmission geometry using a conventional constant-acceleration spectrometer (room temperature, \u0026plusmn;12 mm/s, gamma ray source of 57CoRh, 512 channels multichannel scaler). Each sample was properly mounted on a plastic holder and measured a long enough time to attain a well-defined spectrum. The M\u0026ouml;ssbauer spectrum of a \u0026alpha;-Fe foil was used to calibrate the spectrometer. All the isomer shifts obtained from the fit are referred to this standard, and each spectrum was analyzed using hyperfine magnetic fields and quadrupole splitting distributions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSteady-State Irradiation Experiments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePhotolysis experiments of aqueous dye solutions were conducted in a reactor equipped with eight lamps emitting at \u003cem\u003e\u0026lambda;\u003c/em\u003e\u003cem\u003e\u003csub\u003emax\u003c/sub\u003e\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e= 350 nm. Aqueous solutions of the three dyes were irradiated for 60 min using consistent initial concentration. The experiments were conducted using both coated (HS-FeOx) and bare (FeOx) nanoparticles, both in the presence and absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The degradation process was monitored at regular intervals via UV-Vis spectroscopy.\u003c/p\u003e\n\u003cp\u003eAll experiments were conducted at room temperature. The monitoring of dye concentrations was carried out by analyzing the absorption spectra and observing the changes in their main absorption bands at 522 nm, 630 nm, and 482 nm for AR, BB, and SY, respectively. The initial dye concentration was 2\u0026times;10\u003csup\u003e-5\u003c/sup\u003e M in all cases. Control experiments were performed for all conditions.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eCharacterization of HS and HS-FeOx\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHS-FeOx SEM image (\u003cstrong\u003eFig. 2a\u003c/strong\u003e) revealed aggregates of nanoparticles, although several free nanoparticles can be identified and considered to build-up their size distribution, presented, together with its fits in \u003cstrong\u003eFig. 2b\u003c/strong\u003e. An almost cubic geomorphology is observed, with mean side of 16.9\u0026plusmn;0.7 nm, in agreement data reported for similar particles (Arce et al. 2018). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAdditionally, the UV-Vis extinction spectra for both samples, HS and HS-FeOx, are shown in the insets of \u003cstrong\u003eFig. 3a\u003c/strong\u003e and \u003cstrong\u003e3b\u003c/strong\u003e, respectively. Regarding the bare HS, a widely employed parameter in the characterization of humic substances is the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e ratio, defined as the extinction ratio at 465 nm to 665 nm. Shirshova et al. (2006) proposed that the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e ratio is indicative of the molecular size, degree of condensation, and aromaticity in HS. In this work, an E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value of 1.275 was obtained for the extracted HS, which is consistent with values reported for other humic substances (Filcheva et al., 2018; Zalba et al., 2016). This specific value suggests a material with a relatively high molecular weight and a significant degree of condensation.\u003c/p\u003e\n\u003cp\u003eThe inset of \u003cstrong\u003eFig. 3b\u003c/strong\u003e shows the extinction spectrum of HS-FeOx suspension at the same concentration employed in the degradation assays. The spectrum exhibits notable light scattering attributable to the nanoparticles. Notably, the characteristic intense extinction below 250 nm associated with HS is almost completely suppressed in the HS-FeOx system. This attenuation can be attributed to interactions between HS and iron oxide species, which promote the coordination of functional groups -predominantly carboxylic and phenolic moieties- to the nanoparticle surface. Such interactions modify the electronic environment of these chromophoric groups, diminishing their ability to absorb in the deep UV region (Niu et al., 2011). This spectroscopic change provides evidence for successful surface functionalization of the iron oxide nanoparticles with humic substances.\u003c/p\u003e\n\u003cp\u003eThe diffraction patterns of FeOx and HS-FeOx samples are shown in \u003cstrong\u003eFig. 4a\u003c/strong\u003e. In both cases, the patterns are consistent with those expected for magnetite (Mg)/maghemite (Mh). The expected relative intensity for each phase is indicated at each peak (Gabbasov et al., 2015). In addition to the identification of the same peak positions, no significant differences are observed between the peak width, indicating that the presence of the HS does not affect the structural characteristics of the formed nanoparticles.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe pH dependence of the zeta potential (\u0026zeta;) of HS-FeOx dispersions in 1\u0026times;10\u003csup\u003e-3\u003c/sup\u003e M KCl aqueous solutions shows a pH of zero-point charge (pHPZC) of 3.83 \u003cstrong\u003eFig. 4b\u003c/strong\u003e, indicating that at this pH value the net charge of the particles is neutral. From this point onward, the deprotonation of acidic groups present in the humic substances begins as the pH increases. This process results in an increase in the net negative charge of the molecules, which leads to enhanced electrostatic repulsion between them. Consequently, the stability of the suspended particles against aggregation increases at pH values above 4. According to Kluč\u0026aacute;kov\u0026aacute; \u0026amp; Kalina, (2015) the decrease in zeta potential may result from two simultaneous processes: the dissociation of acidic functional groups and the disaggregation of humic aggregates.\u003c/p\u003e\n\u003cp\u003eThe DTA-TGA curves corresponding to the NPs are shown in \u003cstrong\u003eFig. 4c\u003c/strong\u003e. In the TGA curve, a mass loss is observed from room temperature to 800 \u0026deg;C. A slight endothermic valley is observed at 78 \u0026deg;C, associated with a 4.99% mass loss, which is attributed to the desorption of physically adsorbed water. From that point on, an exothermic trend begins in the DTA curve, accompanied by additional mass losses up to 400 \u0026deg;C, totaling 13.97%. These losses are associated with the oxidation of both labile and recalcitrant fractions of humic substances. Finally, the exothermic peak near 600 \u0026deg;C is assigned to a possible magnetite\u0026ndash;hematite phase transition (Zheng et al., 2021; Chen et al., 2013) or a possible reduction of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e to FeO (Kim et al., 2000).\u003c/p\u003e\n\u003cp\u003eThe samples were also analyzed using a vibrating sample magnetometer (VSM), from which the hysteresis loop for each sample was obtained (\u003cstrong\u003eFig. 5a\u003c/strong\u003e). Both samples exhibited a combined paramagnetic\u0026ndash;superparamagnetic behavior (absence of coercivity, \u003cem\u003eHc\u003c/em\u003e, and remanent magnetization, \u003cem\u003eMr\u003c/em\u003e). The absence of hysteresis is expected for the nanoparticles with the determined size. The paramagnetic contribution was similar for both samples (\u003cem\u003ex\u003csub\u003ehifi\u003c/sub\u003e\u003c/em\u003e = 1.41x10\u003csup\u003e-6\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e/kg FeOx; 1.33 x10\u003csup\u003e-6\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e/kg HS-FeOx), while the saturation magnetization (\u003cem\u003eMs\u003c/em\u003e) was higher for FeOx (\u003cem\u003eMs\u003c/em\u003e = 25.4\u0026plusmn;0.1 Am\u003csup\u003e2\u003c/sup\u003e/kg) than for HS-FeOx (\u003cem\u003eMs\u003c/em\u003e = 16.5\u0026plusmn;0.1 Am\u003csup\u003e2\u003c/sup\u003e/kg), as expected due to the presence of HS coating the material surface. Additionally, the FeOx sample showed a low \u003cem\u003eMs\u003c/em\u003e value compared to the expected values for bulk of magnetite or maghemite. This reduction could indicate the formation of Fe oxide with defects. To analyze this fact, M\u0026ouml;ssbauer spectra were measured (\u003cstrong\u003eFig. 5b\u003c/strong\u003e). For both materials the spectrum only reveals the presence of doublets, corroborating the formation of nanometric particles. In addition, a wider signal, paramagnetic relaxation, must be included to attain a good enough fit, indicating a disorder caused by the incomplete formation of the oxides, which also explain the relatively low determined \u003cem\u003eMs\u003c/em\u003e. \u0026nbsp;The absence of magnetic hyperfine splitting prevents the identification of whether magnetite, maghemite, or the determination of their relative proportions in a mixture of them.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIrradiation Experiments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter 60 minutes of irradiation of solution containing only the dyes, no significant degradation of the compounds was observed. Therefore, hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) was added at a concentration of 0.1 M to promote oxidative conditions during irradiation. Under these conditions, degradation percentages of (10.3\u0026plusmn;0.6) % for AR, (7.0\u0026plusmn;0.6) % for SY, and (11.6\u0026plusmn;0.1) % for BB were achieved.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthouhgh the oxidative environment improved dye degradation, the determined percentages resulted relatively low and then the inclusion of HS-FeOx nanoparticles in the process was proposed. Upon the addition of 500 ppm of nanoparticles in a new assay, the degradation percentages under irradiation reached (60.2\u0026plusmn;0.7) % for AR, (26.1\u0026plusmn;0.8) % for SY, and (8.2\u0026plusmn;0.1) % for BB. These results indicate that the presence of the nanoparticles enhanced the degradation rate of AR and SY azo dyes.\u003c/p\u003e\n\u003cp\u003eDifferent experimental conditions were tested under both irradiation and dark conditions to evaluate the synergistic effect, including FeOx in the presence and absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, as well as HS-FeOx combined with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. The combined use of HS-FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (0.1 M) led to degradation percentages of (96.0\u0026plusmn;0.6) % for AR, (63.3\u0026plusmn;0.6) % for SY, and (46.4\u0026plusmn;0.1) % for BB after one hour of irradiation. The results obtained for AR under the different conditions are shown in \u003cstrong\u003eFig. 6\u003c/strong\u003e\u003cstrong\u003ea\u003c/strong\u003e, excluding dark controls. Similar behavior was observed for SY and BB.\u003c/p\u003e\n\u003cp\u003eControl experiments using FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e nanoparticles under both irradiation and dark conditions yielded degradation values of (86.8\u0026plusmn;0.6) % for AR, (54.9\u0026plusmn;0.8) % for SY, and (35.9\u0026plusmn;0.1) % for BB under irradiation, and (60.1\u0026plusmn;0.6) % for AR, (41.1\u0026plusmn;0.9) % for SY, and (16.2\u0026plusmn;0.1) % for BB in the dark. These results suggest that Fenton-like processes can occur even in the absence of HS and light (Pereira et al., 2012) with a significant difference observed between irradiation and dark conditions. Additional control experiments conducted for the three dyes under oxygen-free conditions confirmed that the observed degradation proceeded through an oxidative pathway, as significantly lower degradation percentages were obtained compared to those observed under aerobic environments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe kinetics of the degradation processes were studied using the pseudo-first-order reaction rate model, \u003cstrong\u003eEquation 1\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1774599787.png\" width=\"906\" height=\"181\"\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe variation of ln(A/A₀) with time was examined for the three dyes, revealing pseudo-first-order kinetic behavior under the studied conditions, see \u003cstrong\u003eEquation 1\u003c/strong\u003e. It is important to note that, in the case of the AR dye under irradiation in presence of HS-FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the kinetic fitting was performed only up to the 30-minute data point, since linearity was lost beyond this time. This deviation could be attributed to the formation of intermediate or degradation products that absorb in a spectral region close to that used for monitoring the dye. The resultant rate constants (\u003cem\u003ek\u003c/em\u003e) are shown in \u003cstrong\u003eTable 1\u003c/strong\u003e for three conditions: HS-FeOx in presence and absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e under irradiation, HS-FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in dark.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003ePseudo-first-order rate constant for three conditions: HS-FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e under irradiation, HS-FeOx under irradiation HS-FeOx and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in dark\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable style=\"width: 3.5e+2pt;\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd nowrap=\"\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003eHS-FeOx/ H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(min\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003eHS-FeOx\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(min\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eHS-FeOx/ H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(dark) (min\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003eAR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.078\u0026plusmn;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.018\u0026plusmn;0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.0207\u0026plusmn;0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003eYS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.0165\u0026plusmn;0.0004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.0043\u0026plusmn;0.0004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.0191\u0026plusmn;0.0007\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003eBB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.0104\u0026plusmn;0.0002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd nowrap=\"\"\u003e\n \u003cp\u003e0.0013\u0026plusmn;0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.0023\u0026plusmn;0.0001\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\u003eThe differences observed in the pseudo-first order rate constants could be attributed to the structural features of the dyes. As shown in \u003cstrong\u003eTable 1\u003c/strong\u003e, the reactivity toward decolorization is influenced by the electronic environment of the azo bond, which is susceptible to oxidative attack by reactive oxygen species (ROS) due to its high electron density. This susceptibility can be affected by the nature and positions of the adjacent substituents. In particular, aromatic rings usually stabilize the azo bond through electronic resonance effects. However, the presence of substituent groups with different electronic character can modify its reactivity. Such is the case with resonance electron-donating groups, like the hydroxyl group (-OH), which increase the electron density around the azo bond and, consequently, its susceptibility to oxidation, as observed in the results obtained for the AR and SY dyes compared to those obtained for BB, since a higher pseudo-first-order \u0026nbsp;rate constant was obtained for AR and YS.\u003c/p\u003e\n\u003cp\u003eFurthermore, the presence of an additional substituent in the meta position relative to the azo group, such as an electron-withdrawing sulfonic group (-SO\u003csub\u003e3\u003c/sub\u003e), can additionally contribute to the degradative process. This effect can be attributed both to the partial destabilization of the aromatic system and to the increase in the dye solubility, which enhances the accessibility of the azo bond for oxidizing species. These combined effects would explain why the AR dye exhibits a higher reactivity towards oxidation compared to SY, despite both having azo structures, and why the BB dye is more stable, possibly due to greater electronic delocalization in its conjugated system.\u003c/p\u003e\n\u003cp\u003ePrevious investigations conducted by our group have demonstrated that irradiation of commercial compost-derived extracts (analogous to the humic extracts employed for NP coating in this work), results in the photochemical generation of diverse ROS (Bosio et al., 2008; David Gara et al., 2009). These studies identified the formation of both oxidizing species -including singlet oxygen (\u003csup\u003e1\u003c/sup\u003eO\u003csub\u003e2\u003c/sub\u003e), hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e), triplet-excited states of humic substances (\u003csup\u003e3\u003c/sup\u003eHS\u003csup\u003e*\u003c/sup\u003e), hydroxyl radicals (\u003csup\u003e\u0026bull;\u003c/sup\u003eOH), superoxide anion radicals (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull;\u003c/sup\u003e⁻) - as well as reductive species (such as hydrated electrons, e⁻\u003csub\u003eaq\u003c/sub\u003e). Among these transient species, \u003csup\u003e\u0026bull;\u003c/sup\u003eOH and \u003csup\u003e1\u003c/sup\u003eO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ewere identified as the predominant contributors to contaminant degradation due to their high chemical reactivity and relatively significant steady-state concentrations (David Gara et al., 2009). The iron oxide nanoparticle core further enhances ROS production through heterogeneous Fenton and photo-Fenton processes. Hydroxyl radicals are known to react with a broad range of organic compounds in a diffusion-controlled kinetics, either by direct attack on the azo bond or by addition to the aromatic rings adjacent to this group (Dostanić et al, 2020). Singlet oxygen, while less reactive than \u003csup\u003e\u0026bull;\u003c/sup\u003eOH, exhibits selective reactivity toward electron-rich aromatic systems, heteroatoms, and unsaturated bonds, leading to the formation of endoperoxides, or other oxygenated products. In all these pathways, the loss of conjugation within the dye molecule results in chromophore disruption and, consequently, decolorization of the solution.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this work, humic substance-coated iron oxide nanoparticles (HS-FeOx) were successfully synthesized by a coprecipitation method and thoroughly characterized. Physicochemical analyses confirmed that the nanocomposites consist of a magnetite/maghemite core with 14% HS surface coverage, preserving their inherent magnetic properties. The preservation of the magnetic nature of the iron oxide core confers an operational advantage, facilitating efficient separation and recovery of the catalyst from aqueous media using an external magnetic field.\u003c/p\u003e \u003cp\u003eThe performance of the HS-FeOx nanocomposites was evaluated in the photodegradation of food dyes using a system combining hydrogen peroxide and UV-A irradiation. The results demonstrated that HS-coated nanoparticles markedly enhance degradation efficiency compared to uncoated iron oxide nanoparticles under identical oxidative and irradiation conditions. The enhanced photodegradation efficiency can be attributed to the multifunctional role of the humic substances. Beyond improving colloidal stability, the HS layer acts as an effective photosensitizer, promoting the generation of reactive oxygen species under UV-A irradiation. This photochemical activity operates synergistically with the heterogeneous Fenton-like reactions occurring at the iron oxide surface, resulting in accelerated dye decolorization through an oxidative pathway. The necessity of light irradiation to fully activate this synergistic mechanism underscores the importance of photochemical processes in the overall degradation performance.\u003c/p\u003e \u003cp\u003eThe photochemical treatment developed in this study presents several practical advantages for environmental remediation. The use of UV-A radiation is particularly relevant, as it overlaps with the solar spectrum reaching the Earth\u0026rsquo;s surface, suggesting the potential use of sunlight as a sustainable and cost-effective energy source. Moreover, the magnetic recoverability and potential reusability of the HS-FeOx nanoparticles further enhance their applicability in water treatment systems.\u003c/p\u003e \u003cp\u003eOverall, the incorporation of humic substances as a functional coating for iron oxide nanoparticles proved to be an effective strategy for designing an efficient hybrid catalyst for dye degradation in aqueous environments. By integrating catalytic and photochemical functionalities within a single nanomaterial, this approach represents a promising alternative within advanced oxidation processes and contributes to the development of sustainable technologies for the treatment of contaminated water.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLic. Janis G. Rosales Vierma\u003c/strong\u003e: Synthesis and characterization of nanoparticles (equal), extraction and characterization of humic substances\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e(equal), sample preparation (equal), irradiation experiments (equal), conceptualization (equal), investigation (equal), methodology (equal), validation (equal), visualization (equal), and writing - original draft (equal). \u003cstrong\u003eDr. Mar\u0026iacute;a Luciana Montes\u003c/strong\u003e: X-Ray diffraction (lead), M\u0026ouml;ssbauer spectroscopy (lead), formal analysis (equal), investigation (equal), methodology (equal). \u003cstrong\u003eDr. Mariela A. Fernandez\u003c/strong\u003e: Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), zeta potential (\u0026zeta;) (lead), formal analysis (equal), investigation (equal), methodology (equal). \u003cstrong\u003eDr. Pedro M. David Gara\u003c/strong\u003e: Extraction and characterization of humic substances\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e(equal), sample preparation (equal), irradiation experiments (equal), conceptualization (equal), formal analysis (equal), investigation (equal), methodology (equal), validation (equal), visualization (equal), and writing - original draft (equal), and writing - review \u0026amp; editing (equal). \u003cstrong\u003eDr. Valeria B. Arce\u003c/strong\u003e: Extraction and characterization of humic substances\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e(equal), irradiation experiments (equal), conceptualization (equal), formal analysis (equal), funding acquisition (lead), investigation (equal), resources (lead), visualization (equal), writing - original draft (equal), and writing - review \u0026amp; editing (equal).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ. G. Rosales Vierma is doctoral fellow of CONICET, Argentina. M. L. Montes and M. A. Fern\u0026aacute;ndez\u003csup\u003e\u0026nbsp;\u003c/sup\u003eare research members of CONICET, Argentina. P. M. David Gara and V. B. Arce are research members of Comisi\u0026oacute;n de Investigaciones Cient\u0026iacute;ficas de la Provincia de Buenos Aires (CIC-PBA).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026quot;not applicable\u0026quot; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded by Agencia Nacional de Promoci\u0026oacute;n Cient\u0026iacute;fica y Tecnol\u0026oacute;gica (ANPCyT) PICT 2018-3451 and PICT APLICADOS 2021-0074. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eArce, V. B., Mucci, C. 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S., \u0026amp; Kogut, B. M. (2021). Humic substances: Hypotheses and reality (a review). \u003cem\u003eEurasian Soil Science, 54\u003c/em\u003e, 1826\u0026ndash;1854. https://doi.org/10.1134/S1064229321120164\u003c/li\u003e\n \u003cli\u003eZheng, H., Schenk, J., Spreitzer, D., Wolfinger, T., \u0026amp; Daghagheleh, O. (2021). Review on the oxidation behaviors and kinetics of magnetite in particle scale. \u003cem\u003eSteel Research International, 92\u003c/em\u003e, 2000687. https://doi.org/10.1002/srin.202000687\u003c/li\u003e\n\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":"photodegradation, UV Light, food dyes, iron oxides nanoparticles, humic substances","lastPublishedDoi":"10.21203/rs.3.rs-8722014/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8722014/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated the photodegradation of amaranth red (AR), sunset yellow (SY), and brilliant blue (BB) food dyes in aqueous solution under UV-A radiation with a maximum wavelength of 350 nm. The synergistic effect of humic substance-coated iron oxide nanoparticles (HS-FeOx) and hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) was evaluated. While direct irradiation alone was ineffective, the addition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at a concentration of 0.1 M to the aqueous solution, led to minimal degradation (\u0026lt;\u0026thinsp;12%). The incorporation of HS-FeOx nanoparticles significantly enhanced the process, particularly for the azo dyes AR and SY. The most effective treatment combined HS-FeOx with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, achieving high degradation percentages of (96.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6) %, (63.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6) % and (46.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1) % for AR, SY, and BB, respectively, after 60 minutes. Control experiments confirmed the oxidative degradation pathway and that Fenton-like reactions occurred even in darkness, though irradiation markedly improved efficiency. The degradation kinetics for all dyes followed a first-order model under the tested conditions.\u003c/p\u003e","manuscriptTitle":"UV Light-Induced degradation of food dyes in the presence of humic substances-coated iron oxide nanoparticles","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-27 08:31:43","doi":"10.21203/rs.3.rs-8722014/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":"4fdd3e4d-b910-44d1-bfe4-7b5fe539ab05","owner":[],"postedDate":"March 27th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-27T08:31:43+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-27 08:31:43","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8722014","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8722014","identity":"rs-8722014","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}