Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals

Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals | 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 Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals Lisandra Eda Fusinato Zin, Jéssica Mulinari, Carolina Elisa Demaman Oro, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3813500/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 Agrochemicals have become essential to meet the increasing demand for food and other commodities, but they can contaminate the environment, especially water resources, if not properly managed. Advanced Oxidation Processes (AOP), such as Fenton’s process, are a quick alternative to remove these toxic compounds from water and wastewater. Previous studies suggest that carboxylic acids can promote the Fenton reaction by accelerating the degradation rate of H 2 O 2 and the formation of hydroxyl radicals. In this study, formic and acetic acids were applied in a heterogeneous Fenton system to degrade imidacloprid (C 9 H 10 N 5 ClO 2 ), a model agrochemical molecule. Activated limonite and steel wool were used as low-cost heterogeneous iron precursors. The activated limonite was produced by reducing limonite’s iron under H 2 flow at 200 and 300°C. The Fenton process with 300°C-activated limonite showed a reaction rate approximately 8-fold higher than the test using natural limonite and 2-fold higher than the one with limonite activated at 200°C. Adding acetic acid to the Fenton process using the 300°C-activated limonite increased the reaction rate by more than 2-fold. When steel wool was used as the iron precursor, the addition of acetic acid resulted in the complete degradation of imidacloprid within one minute of reaction. Acetic acid exhibited a higher promoting activity than formic acid, and the degradation rate increased with increasing concentrations of both carboxylic acids. This study indicates that carboxylic acids can serve as Fenton promoters to increase the degradation rate of agrochemicals, such as imidacloprid, present in water and wastewater. Heterogeneous Fenton Imidacloprid Pesticide Advanced Oxidation Processes. Fenton promoter Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction Fenton and Fenton-like processes can efficiently oxidize a wide range of organic compounds in water and wastewater (Ghime and Ghosh, 2021 ; Paterlini and Nogueira, 2005 ; Usman et al., 2022 ; Walling et al., 2021 ). These processes are based on the reaction between a transition metal ion, such as copper and nickel, but mostly iron (Fe 2+ ), and hydrogen peroxide (H 2 O 2 ). The ferrous ions catalyze the decomposition of H 2 O 2 generating hydroxyl radicals (•OH), which react with the organic compounds present in the aqueous media resulting in their mineralization (Kitajima et al., 1978 ). Among organic contaminants in water and soil are agrochemicals. Most of the used pesticides end up reaching the soil and water due to application drift, washing of treated leaves, leaching, erosion, direct application in water to control disease vectors, waste from empty packaging, washing of application equipment, and wastewater from pesticide industries (Sandanayake et al., 2022 ). Some pesticides are persistent organic pollutants that cause highly detrimental effects on the ecosystem and are extremely toxic to living organisms, even at low concentrations (Katsikantami et al., 2019 ; Zekkaoui et al., 2021 ). Several studies evaluated the potential of Fenton reactions for the degradation of agrochemicals: Zekkaoui et al. ( 2021 ) investigated the degradation of the organophosphate pesticide diazinon with Fenton and photo-Fenton reactions and achieved up to 96% of removal; Vasseghian et al. ( 2022 ) evaluated the degradation of Malathion using Fenton, photo-Fenton and sono-photo-Fenton processes and obtained up to 99% removal efficiencies; and Boonrattanakij, Kruthom and Lu ( 2022 ) studied the degradation of imidacloprid by fluidized-bed Fenton process, reaching 97% of removal. Different configurations and hybrid processes using Fenton reactions have been investigated for the degradation of several pesticides, but none studied the use of chemical promoters to enhance the reaction rate. Carboxylic acids have been applied in Fenton processes to promote the radical decomposition of H 2 O 2 . Ferraz et al. ( 2007 ) demonstrated that carboxylic acids could promote the degradation of dyes in heterogeneous Fenton systems using supported Fe (III). Adding formic acid increased the dye degradation rate from 30–100% in 5 minutes of reaction. Density functional theory (DFT) calculations showed that the carboxylic acid and the H 2 O 2 interact, forming a complex that generates stronger •OH radicals than the H 2 O 2 alone. The energy of the •OH radical generated from the H 2 O 2 //carboxylic acid complex is approximately three times higher than that produced from H 2 O 2 decomposition (Ferraz et al., 2007 ). Baba et al. ( 2015 ) also studied the effect of carboxylic acids on iron redox cycling in Fenton processes. They concluded that oxalic and citric acid accelerated the iron redox cycle and the •OH generation by 18% and 8%, respectively. According to the authors, carboxylic acids form complexes with Fe 2+ that change the reaction rates of the iron redox cycle (Baba et al., 2015 ). Jiang et al. ( 2019 ) applied the Fenton process promoted by formic acid and citric acid to the degradation of chlorinated hydrocarbons, and both enhanced the removal of the contaminant. The generation of highly reactive radicals is a critical step to turning Fenton processes into potential alternatives for water and wastewater treatment since the oxidation and, mainly, mineralization of most organic molecules is desired to be quick and non-selective (WANG and XU, 2012 ). Therefore, based on the possibility of promoting the radical decomposition of H 2 O 2 in Fenton processes, this study aims to apply different carboxylic acids (formic and acetic) in a heterogeneous Fenton system for the degradation of agrochemicals. Imidacloprid (C 9 H 10 N 5 ClO 2 ) was used as the model molecule since it is an insecticide with a broad spectrum of applications characterized by its high solubility in water and stability in aqueous media (Ding et al., 2011 ). Activated limonite and steel wool were applied as low-cost heterogeneous iron precursors. No study was found in the literature regarding the use of carboxylic acids to promote the Fenton degradation of pesticides. Once proven, the potential of this methodology can be extended to other pesticides and the degradation of numerous bio-persistent organic compounds. 2 Materials and Methods 2.1 Chemicals and materials Imidacloprid was used as a model pesticide molecule. Limonite and steel wool were used as heterogeneous iron precursors since limonite is natural clay, and commercial steel wool is available in every supermarket. Hydrogen peroxide, formic acid, acetic acid, and sulfuric acid were all analytical grade (P.A.). 2.2 Limonite activation Natural limonite contains approximately 45 wt.% of iron in its composition. Considering that the most active form of iron for the Fenton reactions is the reduced form, the limonite was activated using H 2 at 200 and 300°C for 1 h - the activation aimed at reducing Fe 3+ to Fe 2+ . After being cooled to room temperature, the activated limonite was kept in an amber vial with an H 2 atmosphere. Both 200 and 300°C activated limonite were used in the Fenton process to analyze the degradation of imidacloprid. 2.3 Limonite and steel wool characterization Mössbauer analysis was performed to verify the proportion of reduced phase obtained in each limonite activation temperature and to verify the oxidation state of the iron at the steel wool. Mössbauer spectra were collected at 298 K with a conventional constant acceleration transmission spectrometer using a 5 mCi 57 Co/Rh source. The samples contained approximately 10 mg·cm − 2 of iron. The isomer shift values were quoted relative to α-Fe. The data were numerically fitted using NORMOS® 90. 2.4 Imidacloprid degradation using Fenton reaction The tests were performed in batch mode at room temperature and constant agitation using a 250 mg·L − 1 imidacloprid solution at pH 3.0 (adjusted with H 2 SO 4 0.5 M). When limonite was used as the iron precursor, 1000 mg·L − 1 of H 2 O 2 and 750 mg·L − 1 of limonite were added to the imidacloprid solution. When the steel wool was used as the iron precursor, 430 mg·L − 1 of H 2 O 2 and 600 mg·L − 1 of steel wool were used. The degradation of imidacloprid was measured for 60 min by analyzing 3 mL samples in HPLC (Agilent) at 270 nm. An RP reverse phase C-18 column and a mobile phase of a 65:35 v/v solution of phosphoric acid 1 mM and acetonitrile were used. Before the analysis, the samples were passed through 0,45 µm PVDF filters and added to HPLC vials with 3 drops of sodium metabisulfite 1 M to stop the reaction. After 30 and 60 min of reaction, the total organic carbon content of the solution was measured by TOC-V CSH (Shimadzu) equipment and compared to the initial one. 2.5 Effect of carboxylic acids To evaluate the promoting effect of carboxylic acids, acetic acid (CH 3 COOH) was tested using limonite and steel wool as catalysts. The degradation of imidacloprid was analyzed by HPLC and total organic carbon measurements. Formic acid (HCOOH) was also tested using steel wool as the iron precursor to evaluate if different acids would have the same promoting effect. Different concentrations of acetic and formic acid (0.06 to 1.40 mL·L − 1 ) were tested. A 30 min kinetics was performed for the different acids at different concentrations. The quantity of iron leaching from the steel wool was also evaluated during the kinetics. 3 Results and Discussion 3.1 Limonite activation The iron (Fe 3+ ) naturally present in the limonite has low efficiency as an iron precursor in Fenton processes that generally uses Fe 2+ . That is why the limonite was reduced using a hydrogen flux at different temperatures. Natural limonite is mainly made of goethite (which presents a yellowish color) that, when reduced, is converted to magnetite (dark brown to black) (Bustamante et al., 2005; Palacios et al., 2011). Figure 1 shows the color change as limonite is reduced under different temperatures. Mössbauer analysis of the natural and reduced limonite (at 300 ºC) confirms that the treatment was effective in reducing the oxidation state of the limonite’s iron (Fig. 1 b). The presence of iron oxides or hydroxides (Fe 3+ ) in the form of small particles can be observed for the natural limonite (Fig. 1 ), which is evidenced by a strong central doublet due to the phenomenon of superparamagnetism (Veintemillas-Verdaguer et al., 2004; Bustamante et al., 2005). The formation of tetrahedral and octahedral sites can be observed for the thermal-treated limonite, which is characteristic of the formation of a magnetite phase containing both Fe 3+ and Fe 2+ . The Mössbauer analysis demonstrated that the thermal treatment in the H 2 atmosphere effectively reduced goethite to magnetite producing a cubic structure with many vacancies of cations and Fe 0 . 3.2 Steel wool characterization The Mössbauer analysis of the steel wool (Fig. 2 ) showed the presence of a prominent sextet with parameters identifying the presence of a single iron phase (Cornell and Schwertmann 2003). Two sub-spectra were observed, indicating the presence of metallic iron only, corresponding to more than 80% of the alpha species under ambient conditions. 3.3 Imidacloprid degradation using limonite as the iron precursor The limonite reduced at a higher temperature (300°C) presented a higher imidacloprid degradation during the Fenton process: approximately 60% after 60 min (Fig. 3 ). The use of natural limonite and reduced limonite at 200°C resulted in lower removals: 10 and 50% after 60 min. The increased degradation after reduction is due to the conversion of Fe 3+ to Fe 2+ and Fe 0 , which extension is directly proportional to the temperature used. The degradation of imidacloprid was also evaluated regarding the removal of total organic carbon (TOC) (Table 1 ). The tests with natural limonite (with and without H 2 O 2 ) showed TOC removals similar to those observed for imidacloprid determined by HPLC (approximately 10%). These results suggest that adsorption is the primary removal process, even with the presence of H2O2. Table 1 Total organic carbon (TOC) concentration of imidacloprid solutions treated by the Fenton process using natural and reduced limonite. Treatment TOC (mg· L − 1 ) Removal (%) Control 160 - Natural limonite 151 5.63 Natural limonite + H 2 O 2 148 7.50 Limonite reduced at 200°C + H 2 O 2 134 16.25 Limonite reduced at 300°C + H 2 O 2 71 55.63 For the Fenton processes using reduced limonite, the TOC removal is lower than the imidacloprid degradation measured by HPLC, mainly for the treatment using the 200°C-reduced limonite: HPLC results showed an imidacloprid degradation of approximately 50% and a TOC removal of only 17%. This fact suggests that the oxidative process is generating secondary species and not leading to the complete mineralization of the degraded imidacloprid. The effect of 2 mL·L − 1 of acetic acid on the Fenton process using the reduced limonite as the iron precursor was evaluated. The addition of the carboxylic acid promoted a higher degradation of imidacloprid in all the tests (Fig. 4 ). After 60 min, the test with limonite reduced at 300°C and acetic acid showed a removal of 80% of imidacloprid, approximately 25% higher than the 60% removal presented by the test without the carboxylic acid. To better visualize the acetic acid’s promoting effect, the results shown in Fig. 3 and Fig. 4 were linearized, and a pseudo-first-order kinetic model was adjusted to the data (Fig. 5 and Table 2 ). The reaction rate ( k ) increased with the increase in the limonite activation temperature. The Fenton process with limonite activated at 300°C showed a reaction rate approximately 8-fold higher than the test using natural limonite and 2-fold higher than the one with limonite activated at 200°C. When acetic acid was added to the Fenton processes, the reaction rate for the test using the 300°C-activated limonite more than doubled, and the test using the 200°C-activated limonite showed a more than 3-fold increase in the reaction rate. The increase in the reaction rate decreased the half-life of imidacloprid in the solution (Table 2 ). Table 2 Pseudo-first order reaction rate, calculated half-life, and regression coefficient for the removal of imidacloprid by Fenton reaction under different conditions using limonite as the iron precursor. Conditions k (min − 1 ) t 1/2 (min) R 2 Natural + H 2 O 2 0.0036 192.5 0.7853 Natural + H 2 O 2 + CH 3 COOH 0.0037 187.3 0.8137 200°C + H 2 O 2 0.0147 47.1 0.9071 200°C + H 2 O 2 + CH 3 COOH 0.0532 13.0 0.8922 300°C + H 2 O 2 0.0284 24.4 0.9959 300°C + H 2 O 2 + CH 3 COOH 0.0652 10.6 0.9898 It is important to highlight that the promoting effect was only observed in the tests using reduced limonite. The tests with natural limonite presented the same reaction kinetics regardless of the presence of acetic acid. These results suggest a relationship between the promoting activity of the carboxylic acid and the oxidation state of the iron ions used in the Fenton process. 3.4 Imidacloprid degradation using steel wool as the iron precursor The use of steel wool as the iron precursor for the Fenton degradation of imidacloprid was evaluated in the absence and presence of different concentrations of acetic and formic acid (Fig. 6 ). All reaction conditions presented the same tendency: an increase in imidacloprid’s degradation over time, especially in the first minutes of the reaction. Considering the first 3 min, an increase in the degradation of imidacloprid can be observed as the carboxylic acid concentration increases. The acetic acid promoted a higher imidacloprid degradation than the formic acid. To better visualize the effects, the results shown in Fig. 6 were linearized, and a pseudo-first-order kinetic model was adjusted to the data (Fig. 7 and Table 3 ). Table 3 Pseudo-first order reaction rate, calculated half-life, and regression coefficient for the removal of imidacloprid by Fenton reaction using steel wool as the iron precursor and different concentrations of acetic or formic acid Acid Concentration (mL·L − 1 ) k (min − 1 ) t 1/2 (min) R 2 Acetic 0.06 0.9131 0.76 0.9901 0.60 - - - 1.40 - - - Formic 0.06 0.4121 1.68 0.9571 0.60 1.0690 0.65 0.9604 1.40 1.1030 0.63 0.9910 - 0.00 0.1682 4.12 0.9613 For the tests conducted using acetic acid as a promoter in concentrations greater than 0.60 mL·L − 1 , it was not possible to calculate the reaction rate. With 1 min of reaction, the system already showed a 100% removal of imidacloprid. However, the results shown in Fig. 6 suggest an increase in the degradation rate with increased concentrations of acetic acid. The effect of the carboxylic acid could be better seen when formic acid was used as a promoter. The imidacloprid degradation rate increased from 0.41 to 1.10 min − 1 when the concentration of formic acid was increased from 0.06 to 1.40 mL·L − 1 . Among the evaluated carboxylic acids, acetic acid showed a more pronounced promoting effect than formic acid. The test conducted using 0.06 mL·L − 1 of acetic acid showed a reaction rate (0.91 min − 1 ) approximately twice the one observed for the test using the same concentration of formic acid (0.41 min − 1 ). For some assays, the content of soluble iron present in the solution was analyzed by atomic absorption spectroscopy. An increase in the soluble iron content is observed as a function of the reaction time in all evaluated conditions (Fig. 8 ). The soluble iron content increased proportionally with the volume of acidic promoter added to the solution. Higher soluble iron content was also observed when acetic acid was used as the Fenton promoter. Both trends are consistent with those observed for the imidacloprid removal rate, suggesting a link between the promoting effect of carboxylic acids and the ability to solubilize the iron present in the heterogeneous precursor. 4 Conclusions The Fenton process could degrade imidacloprid using low-cost iron precursors such as activated limonite and steel wool. Treatment of limonite under an H 2 atmosphere and 300°C reduced the iron ions from Fe 3+ to Fe 2+ , making the limonite more active during the Fenton reaction. The use of carboxylic acids, such as acetic and formic acid, showed to be a promising method to accelerate imidacloprid degradation. Imidacloprid was completely removed when using the steel wool and acetic acid during the Fenton process. Declarations Author Contribution Lisandra Eda Fusinato Zin: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data Curation, Writing – Original Draft, VisualizationJéssica Mulinari: Formal analysis, Data Curation, Writing – Original Draft, VisualizationCarolina Elisa Demaman Oro: Formal analysis, Data Curation, Writing – Original Draft, VisualizationMarco Di Luccio: Conceptualization, Methodology, Resources, Writing - Review & Editing, SupervisionRogério Dallago: Conceptualization, Methodology, Resources, Writing - Review & Editing, Supervision, Funding acquisition Acknowledgments The authors thank URI-Erechim, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil), and Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS, Brazil) for financial support and research infrastructure. References Baba, Y., Yatagai, T., Harada, T., Kawase, Y., 2015. 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Advanced Oxidation Processes for Wastewater Treatment: Formation of Hydroxyl Radical and Application. Critical Reviews in Environmental Science and Technology 42, 251–325. https://doi.org/10.1080/10643389.2010.507698 Zekkaoui, C., Berrama, T., Dumoulin, D., Billon, G., Kadmi, Y., 2021. Optimal degradation of organophosphorus pesticide at low levels in water using fenton and photo-fenton processes and identification of by-products by GC-MS/MS. Chemosphere 279, 130544. https://doi.org/10.1016/j.chemosphere.2021.130544 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. 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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-3813500","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":263885691,"identity":"6ce3deb2-c72d-41d1-95a4-1fd56eea9d77","order_by":0,"name":"Lisandra Eda Fusinato Zin","email":"","orcid":"","institution":"Universidade Regional Integrada do Alto Uruguai e das Missões (URI)","correspondingAuthor":false,"prefix":"","firstName":"Lisandra","middleName":"Eda Fusinato","lastName":"Zin","suffix":""},{"id":263885694,"identity":"5f8d51e3-b25e-4b09-b86f-dede3e401092","order_by":1,"name":"Jéssica 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Dallago","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA60lEQVRIie3RMYvCMBTA8ReEumhnM6hfocXVD9NQ0MndzSeCt9Sbz2/RD+DwSuBcwrkWnILg5KBbkQpGOXRLz024/Jc8Qn6EEACX6x2j2pTM0gFg+LsDXgVheCO914nA504F8dcZUnHuD9OtnB5PK+j4eeTtxhbClcBs8TkYpT9ixr/20ON5VA+VhQQkkJqJHKWKzWsNApGaWzjayEZjdknkMLiRkmBSTXKBslHI6E7M06OgivBco2zjIFwqNuMJtcygP0Ib8Tdxpg9lv+uruj4WZIZ1/K1t5B6bP8YWPP/UWvmHMy6Xy/V/uwI0JV2SYjtcUQAAAABJRU5ErkJggg==","orcid":"","institution":"Universidade Regional Integrada do Alto Uruguai e das Missões (URI)","correspondingAuthor":true,"prefix":"","firstName":"Rogério","middleName":"Marcos","lastName":"Dallago","suffix":""}],"badges":[],"createdAt":"2023-12-27 19:29:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3813500/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3813500/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49025062,"identity":"93cc7777-9f48-495d-82a4-929f87d11752","added_by":"auto","created_at":"2024-01-01 11:46:35","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":163441,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Images of the natural and reduced limonite; (b) Mössbauer spectra of the natural and limonite reduced at 300 °C.\u003c/p\u003e","description":"","filename":"floatimage6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/12d62006e1b56ef7b7373269.jpg"},{"id":49025246,"identity":"e2d07719-4956-4ec1-a2db-258317dc247c","added_by":"auto","created_at":"2024-01-01 11:54:35","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":148712,"visible":true,"origin":"","legend":"\u003cp\u003eMössbauer spectra of the steel wool.\u003c/p\u003e","description":"","filename":"floatimage7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/6b2b5d37d12ff7d8eedae168.jpg"},{"id":49025063,"identity":"4d6a183b-34ba-4481-8002-55294a4624d5","added_by":"auto","created_at":"2024-01-01 11:46:35","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":104388,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of the limonite reduction temperature in the degradation of imidacloprid over time.\u003c/p\u003e","description":"","filename":"floatimage8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/9b94abb9f9d1bab0aed25f1e.jpg"},{"id":49025069,"identity":"f594747d-a68f-496f-aedd-78a36dcd691c","added_by":"auto","created_at":"2024-01-01 11:46:36","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":105110,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of the addition of acetic acid in the degradation of imidacloprid by the Fenton process using reduced limonite (at 200 and 300 °C) as the iron precursor.\u003c/p\u003e","description":"","filename":"floatimage9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/36d3203336db85992c91aa34.jpg"},{"id":49025400,"identity":"3eb0d66e-8990-4723-84b3-ccec56538500","added_by":"auto","created_at":"2024-01-01 12:02:35","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":153344,"visible":true,"origin":"","legend":"\u003cp\u003ePseudo-first order kinetic mode adjusted to the imidacloprid degradation by the Fenton process using limonite as the iron precursor in different reaction conditions.\u003c/p\u003e","description":"","filename":"floatimage10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/e34880d96b8435ae98974069.jpg"},{"id":49025068,"identity":"cd7680c1-9837-4388-b00a-b8d4bd08282e","added_by":"auto","created_at":"2024-01-01 11:46:35","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":170071,"visible":true,"origin":"","legend":"\u003cp\u003eDegradation of imidacloprid over time using steel wool as the iron precursor and different concentrations of acetic and formic acid.\u003c/p\u003e","description":"","filename":"floatimage11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/ae4f54ed9432a31891ed2d03.jpg"},{"id":49025560,"identity":"895c694b-ae42-40b9-a6a0-aa3ff167fd9f","added_by":"auto","created_at":"2024-01-01 12:10:35","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":134635,"visible":true,"origin":"","legend":"\u003cp\u003ePseudo-first order kinetic model adjusted to the degradation of imidacloprid using steel wool as the iron precursor and different concentrations of carboxylic acids.\u003c/p\u003e","description":"","filename":"floatimage12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/e5de2e205b87cc040618a1a0.jpg"},{"id":49025067,"identity":"4b77ecf2-d66f-4c0a-9c64-cc2cf3437bf5","added_by":"auto","created_at":"2024-01-01 11:46:35","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":132309,"visible":true,"origin":"","legend":"\u003cp\u003eSoluble iron over time for the different carboxylic acids concentrations used in the Fenton reaction using steel wool as the iron precursor.\u003c/p\u003e","description":"","filename":"floatimage13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/1813f13b07fa4df957ad5e6c.jpg"},{"id":49278980,"identity":"b5256d63-a4dc-4edd-82ff-7495d92aa6ad","added_by":"auto","created_at":"2024-01-07 15:52:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":824464,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3813500/v1/e1e52bf3-5fbe-4cf5-8289-24e67ebee595.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eFenton and Fenton-like processes can efficiently oxidize a wide range of organic compounds in water and wastewater (Ghime and Ghosh, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Paterlini and Nogueira, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Usman et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Walling et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These processes are based on the reaction between a transition metal ion, such as copper and nickel, but mostly iron (Fe\u003csup\u003e2+\u003c/sup\u003e), and hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e). The ferrous ions catalyze the decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e generating hydroxyl radicals (\u0026bull;OH), which react with the organic compounds present in the aqueous media resulting in their mineralization (Kitajima et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1978\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong organic contaminants in water and soil are agrochemicals. Most of the used pesticides end up reaching the soil and water due to application drift, washing of treated leaves, leaching, erosion, direct application in water to control disease vectors, waste from empty packaging, washing of application equipment, and wastewater from pesticide industries (Sandanayake et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Some pesticides are persistent organic pollutants that cause highly detrimental effects on the ecosystem and are extremely toxic to living organisms, even at low concentrations (Katsikantami et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zekkaoui et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Several studies evaluated the potential of Fenton reactions for the degradation of agrochemicals: Zekkaoui et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) investigated the degradation of the organophosphate pesticide diazinon with Fenton and photo-Fenton reactions and achieved up to 96% of removal; Vasseghian et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) evaluated the degradation of Malathion using Fenton, photo-Fenton and sono-photo-Fenton processes and obtained up to 99% removal efficiencies; and Boonrattanakij, Kruthom and Lu (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) studied the degradation of imidacloprid by fluidized-bed Fenton process, reaching 97% of removal. Different configurations and hybrid processes using Fenton reactions have been investigated for the degradation of several pesticides, but none studied the use of chemical promoters to enhance the reaction rate.\u003c/p\u003e \u003cp\u003eCarboxylic acids have been applied in Fenton processes to promote the radical decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. Ferraz et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) demonstrated that carboxylic acids could promote the degradation of dyes in heterogeneous Fenton systems using supported Fe (III). Adding formic acid increased the dye degradation rate from 30\u0026ndash;100% in 5 minutes of reaction. Density functional theory (DFT) calculations showed that the carboxylic acid and the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e interact, forming a complex that generates stronger \u0026bull;OH radicals than the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e alone. The energy of the \u0026bull;OH radical generated from the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e//carboxylic acid complex is approximately three times higher than that produced from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposition (Ferraz et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBaba et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) also studied the effect of carboxylic acids on iron redox cycling in Fenton processes. They concluded that oxalic and citric acid accelerated the iron redox cycle and the \u0026bull;OH generation by 18% and 8%, respectively. According to the authors, carboxylic acids form complexes with Fe\u003csup\u003e2+\u003c/sup\u003e that change the reaction rates of the iron redox cycle (Baba et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Jiang et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) applied the Fenton process promoted by formic acid and citric acid to the degradation of chlorinated hydrocarbons, and both enhanced the removal of the contaminant.\u003c/p\u003e \u003cp\u003eThe generation of highly reactive radicals is a critical step to turning Fenton processes into potential alternatives for water and wastewater treatment since the oxidation and, mainly, mineralization of most organic molecules is desired to be quick and non-selective (WANG and XU, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Therefore, based on the possibility of promoting the radical decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in Fenton processes, this study aims to apply different carboxylic acids (formic and acetic) in a heterogeneous Fenton system for the degradation of agrochemicals. Imidacloprid (C\u003csub\u003e9\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eN\u003csub\u003e5\u003c/sub\u003eClO\u003csub\u003e2\u003c/sub\u003e) was used as the model molecule since it is an insecticide with a broad spectrum of applications characterized by its high solubility in water and stability in aqueous media (Ding et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Activated limonite and steel wool were applied as low-cost heterogeneous iron precursors.\u003c/p\u003e \u003cp\u003eNo study was found in the literature regarding the use of carboxylic acids to promote the Fenton degradation of pesticides. Once proven, the potential of this methodology can be extended to other pesticides and the degradation of numerous bio-persistent organic compounds.\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals and materials\u003c/h2\u003e \u003cp\u003eImidacloprid was used as a model pesticide molecule. Limonite and steel wool were used as heterogeneous iron precursors since limonite is natural clay, and commercial steel wool is available in every supermarket. Hydrogen peroxide, formic acid, acetic acid, and sulfuric acid were all analytical grade (P.A.).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Limonite activation\u003c/h2\u003e \u003cp\u003eNatural limonite contains approximately 45 wt.% of iron in its composition. Considering that the most active form of iron for the Fenton reactions is the reduced form, the limonite was activated using H\u003csub\u003e2\u003c/sub\u003e at 200 and 300\u0026deg;C for 1 h - the activation aimed at reducing Fe\u003csup\u003e3+\u003c/sup\u003e to Fe\u003csup\u003e2+\u003c/sup\u003e. After being cooled to room temperature, the activated limonite was kept in an amber vial with an H\u003csub\u003e2\u003c/sub\u003e atmosphere. Both 200 and 300\u0026deg;C activated limonite were used in the Fenton process to analyze the degradation of imidacloprid.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Limonite and steel wool characterization\u003c/h2\u003e \u003cp\u003eM\u0026ouml;ssbauer analysis was performed to verify the proportion of reduced phase obtained in each limonite activation temperature and to verify the oxidation state of the iron at the steel wool. M\u0026ouml;ssbauer spectra were collected at 298 K with a conventional constant acceleration transmission spectrometer using a 5 mCi \u003csup\u003e57\u003c/sup\u003eCo/Rh source. The samples contained approximately 10 mg\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e of iron. The isomer shift values were quoted relative to α-Fe. The data were numerically fitted using NORMOS\u0026reg; 90.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Imidacloprid degradation using Fenton reaction\u003c/h2\u003e \u003cp\u003eThe tests were performed in batch mode at room temperature and constant agitation using a 250 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e imidacloprid solution at pH 3.0 (adjusted with H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e 0.5 M). When limonite was used as the iron precursor, 1000 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and 750 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of limonite were added to the imidacloprid solution. When the steel wool was used as the iron precursor, 430 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and 600 mg\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of steel wool were used.\u003c/p\u003e \u003cp\u003eThe degradation of imidacloprid was measured for 60 min by analyzing 3 mL samples in HPLC (Agilent) at 270 nm. An RP reverse phase C-18 column and a mobile phase of a 65:35 v/v solution of phosphoric acid 1 mM and acetonitrile were used. Before the analysis, the samples were passed through 0,45 \u0026micro;m PVDF filters and added to HPLC vials with 3 drops of sodium metabisulfite 1 M to stop the reaction. After 30 and 60 min of reaction, the total organic carbon content of the solution was measured by TOC-V CSH (Shimadzu) equipment and compared to the initial one.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Effect of carboxylic acids\u003c/h2\u003e \u003cp\u003eTo evaluate the promoting effect of carboxylic acids, acetic acid (CH\u003csub\u003e3\u003c/sub\u003eCOOH) was tested using limonite and steel wool as catalysts. The degradation of imidacloprid was analyzed by HPLC and total organic carbon measurements. Formic acid (HCOOH) was also tested using steel wool as the iron precursor to evaluate if different acids would have the same promoting effect. Different concentrations of acetic and formic acid (0.06 to 1.40 mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were tested. A 30 min kinetics was performed for the different acids at different concentrations. The quantity of iron leaching from the steel wool was also evaluated during the kinetics.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Limonite activation\u003c/h2\u003e \u003cp\u003eThe iron (Fe\u003csup\u003e3+\u003c/sup\u003e) naturally present in the limonite has low efficiency as an iron precursor in Fenton processes that generally uses Fe\u003csup\u003e2+\u003c/sup\u003e. That is why the limonite was reduced using a hydrogen flux at different temperatures. Natural limonite is mainly made of goethite (which presents a yellowish color) that, when reduced, is converted to magnetite (dark brown to black) (Bustamante et al., 2005; Palacios et al., 2011). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the color change as limonite is reduced under different temperatures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eM\u0026ouml;ssbauer analysis of the natural and reduced limonite (at 300 \u0026ordm;C) confirms that the treatment was effective in reducing the oxidation state of the limonite\u0026rsquo;s iron (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The presence of iron oxides or hydroxides (Fe\u003csup\u003e3+\u003c/sup\u003e) in the form of small particles can be observed for the natural limonite (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which is evidenced by a strong central doublet due to the phenomenon of superparamagnetism (Veintemillas-Verdaguer et al., 2004; Bustamante et al., 2005). The formation of tetrahedral and octahedral sites can be observed for the thermal-treated limonite, which is characteristic of the formation of a magnetite phase containing both Fe\u003csup\u003e3+\u003c/sup\u003e and Fe\u003csup\u003e2+\u003c/sup\u003e. The M\u0026ouml;ssbauer analysis demonstrated that the thermal treatment in the H\u003csub\u003e2\u003c/sub\u003e atmosphere effectively reduced goethite to magnetite producing a cubic structure with many vacancies of cations and Fe\u003csup\u003e0\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Steel wool characterization\u003c/h2\u003e \u003cp\u003eThe M\u0026ouml;ssbauer analysis of the steel wool (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) showed the presence of a prominent sextet with parameters identifying the presence of a single iron phase (Cornell and Schwertmann 2003). Two sub-spectra were observed, indicating the presence of metallic iron only, corresponding to more than 80% of the alpha species under ambient conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Imidacloprid degradation using limonite as the iron precursor\u003c/h2\u003e \u003cp\u003eThe limonite reduced at a higher temperature (300\u0026deg;C) presented a higher imidacloprid degradation during the Fenton process: approximately 60% after 60 min (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The use of natural limonite and reduced limonite at 200\u0026deg;C resulted in lower removals: 10 and 50% after 60 min. The increased degradation after reduction is due to the conversion of Fe\u003csup\u003e3+\u003c/sup\u003e to Fe\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e0\u003c/sup\u003e, which extension is directly proportional to the temperature used.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe degradation of imidacloprid was also evaluated regarding the removal of total organic carbon (TOC) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The tests with natural limonite (with and without H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) showed TOC removals similar to those observed for imidacloprid determined by HPLC (approximately 10%). These results suggest that adsorption is the primary removal process, even with the presence of H2O2.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\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\u003eTotal organic carbon (TOC) concentration of imidacloprid solutions treated by the Fenton process using natural and reduced limonite.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTOC (mg\u0026middot; L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRemoval (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eControl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNatural limonite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e151\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNatural limonite\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e148\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLimonite reduced at 200\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLimonite reduced at 300\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor the Fenton processes using reduced limonite, the TOC removal is lower than the imidacloprid degradation measured by HPLC, mainly for the treatment using the 200\u0026deg;C-reduced limonite: HPLC results showed an imidacloprid degradation of approximately 50% and a TOC removal of only 17%. This fact suggests that the oxidative process is generating secondary species and not leading to the complete mineralization of the degraded imidacloprid.\u003c/p\u003e \u003cp\u003eThe effect of 2 mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of acetic acid on the Fenton process using the reduced limonite as the iron precursor was evaluated. The addition of the carboxylic acid promoted a higher degradation of imidacloprid in all the tests (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). After 60 min, the test with limonite reduced at 300\u0026deg;C and acetic acid showed a removal of 80% of imidacloprid, approximately 25% higher than the 60% removal presented by the test without the carboxylic acid.\u003c/p\u003e \u003cp\u003eTo better visualize the acetic acid\u0026rsquo;s promoting effect, the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e were linearized, and a pseudo-first-order kinetic model was adjusted to the data (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The reaction rate (\u003cem\u003ek\u003c/em\u003e) increased with the increase in the limonite activation temperature. The Fenton process with limonite activated at 300\u0026deg;C showed a reaction rate approximately 8-fold higher than the test using natural limonite and 2-fold higher than the one with limonite activated at 200\u0026deg;C. When acetic acid was added to the Fenton processes, the reaction rate for the test using the 300\u0026deg;C-activated limonite more than doubled, and the test using the 200\u0026deg;C-activated limonite showed a more than 3-fold increase in the reaction rate. The increase in the reaction rate decreased the half-life of imidacloprid in the solution (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePseudo-first order reaction rate, calculated half-life, and regression coefficient for the removal of imidacloprid by Fenton reaction under different conditions using limonite as the iron precursor.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConditions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003ek\u003c/em\u003e (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003et\u003csub\u003e1/2\u003c/sub\u003e (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNatural\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e192.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.7853\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNatural\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;CH\u003csub\u003e3\u003c/sub\u003eCOOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e187.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.8137\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e200\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e47.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.9071\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e200\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;CH\u003csub\u003e3\u003c/sub\u003eCOOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0532\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.8922\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e300\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0284\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e24.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.9959\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e300\u0026deg;C\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;CH\u003csub\u003e3\u003c/sub\u003eCOOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0652\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.9898\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIt is important to highlight that the promoting effect was only observed in the tests using reduced limonite. The tests with natural limonite presented the same reaction kinetics regardless of the presence of acetic acid. These results suggest a relationship between the promoting activity of the carboxylic acid and the oxidation state of the iron ions used in the Fenton process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Imidacloprid degradation using steel wool as the iron precursor\u003c/h2\u003e \u003cp\u003eThe use of steel wool as the iron precursor for the Fenton degradation of imidacloprid was evaluated in the absence and presence of different concentrations of acetic and formic acid (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAll reaction conditions presented the same tendency: an increase in imidacloprid\u0026rsquo;s degradation over time, especially in the first minutes of the reaction. Considering the first 3 min, an increase in the degradation of imidacloprid can be observed as the carboxylic acid concentration increases. The acetic acid promoted a higher imidacloprid degradation than the formic acid. To better visualize the effects, the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e were linearized, and a pseudo-first-order kinetic model was adjusted to the data (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePseudo-first order reaction rate, calculated half-life, and regression coefficient for the removal of imidacloprid by Fenton reaction using steel wool as the iron precursor and different concentrations of acetic or formic acid\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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=\"left\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAcid\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConcentration (mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003ek\u003c/em\u003e (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003et\u003csub\u003e1/2\u003c/sub\u003e (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAcetic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.9131\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9901\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\u003e0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\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\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFormic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.4121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9571\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\u003e0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.0690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9604\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\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.1030\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9910\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1682\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9613\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor the tests conducted using acetic acid as a promoter in concentrations greater than 0.60 mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, it was not possible to calculate the reaction rate. With 1 min of reaction, the system already showed a 100% removal of imidacloprid. However, the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e suggest an increase in the degradation rate with increased concentrations of acetic acid. The effect of the carboxylic acid could be better seen when formic acid was used as a promoter. The imidacloprid degradation rate increased from 0.41 to 1.10 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e when the concentration of formic acid was increased from 0.06 to 1.40 mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAmong the evaluated carboxylic acids, acetic acid showed a more pronounced promoting effect than formic acid. The test conducted using 0.06 mL\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of acetic acid showed a reaction rate (0.91 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) approximately twice the one observed for the test using the same concentration of formic acid (0.41 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eFor some assays, the content of soluble iron present in the solution was analyzed by atomic absorption spectroscopy. An increase in the soluble iron content is observed as a function of the reaction time in all evaluated conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The soluble iron content increased proportionally with the volume of acidic promoter added to the solution. Higher soluble iron content was also observed when acetic acid was used as the Fenton promoter. Both trends are consistent with those observed for the imidacloprid removal rate, suggesting a link between the promoting effect of carboxylic acids and the ability to solubilize the iron present in the heterogeneous precursor.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThe Fenton process could degrade imidacloprid using low-cost iron precursors such as activated limonite and steel wool. Treatment of limonite under an H\u003csub\u003e2\u003c/sub\u003e atmosphere and 300\u0026deg;C reduced the iron ions from Fe\u003csup\u003e3+\u003c/sup\u003e to Fe\u003csup\u003e2+\u003c/sup\u003e, making the limonite more active during the Fenton reaction. The use of carboxylic acids, such as acetic and formic acid, showed to be a promising method to accelerate imidacloprid degradation. Imidacloprid was completely removed when using the steel wool and acetic acid during the Fenton process.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eLisandra Eda Fusinato Zin: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data Curation, Writing \u0026ndash; Original Draft, VisualizationJ\u0026eacute;ssica Mulinari: Formal analysis, Data Curation, Writing \u0026ndash; Original Draft, VisualizationCarolina Elisa Demaman Oro: Formal analysis, Data Curation, Writing \u0026ndash; Original Draft, VisualizationMarco Di Luccio: Conceptualization, Methodology, Resources, Writing - Review \u0026amp; Editing, SupervisionRog\u0026eacute;rio Dallago: Conceptualization, Methodology, Resources, Writing - Review \u0026amp; Editing, Supervision, Funding acquisition\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors thank URI-Erechim, Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico (CNPq, Brazil), Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior (CAPES, Brazil), and Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado do Rio Grande do Sul (FAPERGS, Brazil) for financial support and research infrastructure.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBaba, Y., Yatagai, T., Harada, T., Kawase, Y., 2015. Hydroxyl radical generation in the photo-Fenton process: Effects of carboxylic acids on iron redox cycling. Chemical Engineering Journal 277, 229\u0026ndash;241. https://doi.org/10.1016/j.cej.2015.04.103\u003c/li\u003e\n \u003cli\u003eBoonrattanakij, N., Kruthom, S., Lu, M.-C., 2022. Degradation of imidacloprid by fluidized-bed Fenton process. Journal of Environmental Chemical Engineering 10, 108193. https://doi.org/10.1016/j.jece.2022.108193\u003c/li\u003e\n \u003cli\u003eDing, T., Jacobs, D., Lavine, B.K., 2011. Liquid chromatography-mass spectrometry identification of imidacloprid photolysis products.\u0026nbsp;Microchemical Journal 99, 535\u0026ndash;541. https://doi.org/10.1016/j.microc.2011.07.005\u003c/li\u003e\n \u003cli\u003eFerraz, W., Oliveira, L.C.A., Dallago, R., Concei\u0026ccedil;\u0026atilde;o, L. da, 2007.\u0026nbsp;Effect of organic acid to enhance the oxidative power of the fenton-like system: Computational and empirical evidences. Catalysis Communications 8, 131\u0026ndash;134. https://doi.org/10.1016/j.catcom.2006.05.038\u003c/li\u003e\n \u003cli\u003eGhime, D., Ghosh, P., 2021. 19 - Fenton and Fenton-like processes for improving the dewaterability of refractory organic compounds, in: Pal, K., Banerjee, I., Sarkar, P., Bit, A., Kim, D., Anis, A., Maji, S. (Eds.), Food, Medical, and Environmental Applications of Polysaccharides. Elsevier, pp. 555\u0026ndash;580. https://doi.org/10.1016/B978-0-12-819239-9.00010-5\u003c/li\u003e\n \u003cli\u003eJiang, W., Tang, P., Lyu, S., Brusseau, M.L., Xue, Y., Zhang, X., Qiu, Z., Sui, Q., 2019. Enhanced redox degradation of chlorinated hydrocarbons by the Fe(II)-catalyzed calcium peroxide system in the presence of formic acid and citric acid. Journal of Hazardous Materials 368, 506\u0026ndash;513. https://doi.org/10.1016/j.jhazmat.2019.01.057\u003c/li\u003e\n \u003cli\u003eKatsikantami, I., Colosio, C., Alegakis, A., Tzatzarakis, M.N., Vakonaki, E., Rizos, A.K., Sarigiannis, D.A., Tsatsakis, A.M., 2019. Estimation of daily intake and risk assessment of organophosphorus pesticides based on biomonitoring data \u0026ndash; The internal exposure approach. Food and Chemical Toxicology 123, 57\u0026ndash;71. https://doi.org/10.1016/j.fct.2018.10.047\u003c/li\u003e\n \u003cli\u003eKitajima, N., Fukuzumi, S., Ono, Y., 1978. Formation of superoxide ion during the decomposition of hydrogen peroxide on supported metal oxides. J. Phys. Chem. 82, 1505\u0026ndash;1509. https://doi.org/10.1021/j100502a009\u003c/li\u003e\n \u003cli\u003ePaterlini, W.C., Nogueira, R.F.P., 2005. Multivariate analysis of photo-Fenton degradation of the herbicides tebuthiuron, diuron and 2,4-D. Chemosphere 58, 1107\u0026ndash;1116. https://doi.org/10.1016/j.chemosphere.2004.09.068\u003c/li\u003e\n \u003cli\u003eSandanayake, S., Hettithanthri, O., Buddhinie, P.K.C., Vithanage, M., 2022. Plant Uptake of Pesticide Residues from Agricultural Soils, in: Rodr\u0026iacute;guez-Cruz, M.S., S\u0026aacute;nchez-Mart\u0026iacute;n, M.J. (Eds.), Pesticides in Soils: Occurrence, Fate, Control and Remediation, The Handbook of Environmental Chemistry. Springer International Publishing, Cham, pp. 197\u0026ndash;223. https://doi.org/10.1007/698_2021_806\u003c/li\u003e\n \u003cli\u003eUsman, M., Jellali, S., Anastopoulos, I., Charabi, Y., Hameed, B.H., Hanna, K., 2022. Fenton oxidation for soil remediation: A critical review of observations in historically contaminated soils. Journal of Hazardous Materials 424, 127670. https://doi.org/10.1016/j.jhazmat.2021.127670\u003c/li\u003e\n \u003cli\u003eVasseghian, Y., Almomani, F., Le, V.T., Moradi, M., Dragoi, E.-N., 2022. Decontamination of toxic Malathion pesticide in aqueous solutions by Fenton-based processes: Degradation pathway, toxicity assessment and health risk assessment. Journal of Hazardous Materials 423, 127016. https://doi.org/10.1016/j.jhazmat.2021.127016\u003c/li\u003e\n \u003cli\u003eWalling, S.A., Um, W., Corkhill, C.L., Hyatt, N.C., 2021. Fenton and Fenton-like wet oxidation for degradation and destruction of organic radioactive wastes. npj Mater Degrad 5, 1\u0026ndash;20. https://doi.org/10.1038/s41529-021-00192-3\u003c/li\u003e\n \u003cli\u003eWang, J.L., Xu, L.J., 2012. Advanced Oxidation Processes for Wastewater Treatment: Formation of Hydroxyl Radical and Application. Critical Reviews in Environmental Science and Technology 42, 251\u0026ndash;325. https://doi.org/10.1080/10643389.2010.507698\u003c/li\u003e\n \u003cli\u003eZekkaoui, C., Berrama, T., Dumoulin, D., Billon, G., Kadmi, Y., 2021. Optimal degradation of organophosphorus pesticide at low levels in water using fenton and photo-fenton processes and identification of by-products by GC-MS/MS. Chemosphere 279, 130544. https://doi.org/10.1016/j.chemosphere.2021.130544\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":"Heterogeneous Fenton, Imidacloprid, Pesticide, Advanced Oxidation Processes., Fenton promoter","lastPublishedDoi":"10.21203/rs.3.rs-3813500/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3813500/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAgrochemicals have become essential to meet the increasing demand for food and other commodities, but they can contaminate the environment, especially water resources, if not properly managed. Advanced Oxidation Processes (AOP), such as Fenton\u0026rsquo;s process, are a quick alternative to remove these toxic compounds from water and wastewater. Previous studies suggest that carboxylic acids can promote the Fenton reaction by accelerating the degradation rate of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and the formation of hydroxyl radicals. In this study, formic and acetic acids were applied in a heterogeneous Fenton system to degrade imidacloprid (C\u003csub\u003e9\u003c/sub\u003eH\u003csub\u003e10\u003c/sub\u003eN\u003csub\u003e5\u003c/sub\u003eClO\u003csub\u003e2\u003c/sub\u003e), a model agrochemical molecule. Activated limonite and steel wool were used as low-cost heterogeneous iron precursors. The activated limonite was produced by reducing limonite\u0026rsquo;s iron under H\u003csub\u003e2\u003c/sub\u003e flow at 200 and 300\u0026deg;C. The Fenton process with 300\u0026deg;C-activated limonite showed a reaction rate approximately 8-fold higher than the test using natural limonite and 2-fold higher than the one with limonite activated at 200\u0026deg;C. Adding acetic acid to the Fenton process using the 300\u0026deg;C-activated limonite increased the reaction rate by more than 2-fold. When steel wool was used as the iron precursor, the addition of acetic acid resulted in the complete degradation of imidacloprid within one minute of reaction. Acetic acid exhibited a higher promoting activity than formic acid, and the degradation rate increased with increasing concentrations of both carboxylic acids. This study indicates that carboxylic acids can serve as Fenton promoters to increase the degradation rate of agrochemicals, such as imidacloprid, present in water and wastewater.\u003c/p\u003e","manuscriptTitle":"Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-01 11:46:31","doi":"10.21203/rs.3.rs-3813500/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":"067ff775-c039-48e7-b0f9-e0cb5a8a0653","owner":[],"postedDate":"January 1st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-01-07T15:44:19+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-01 11:46:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3813500","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3813500","identity":"rs-3813500","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}