Surface-Engineered Fe₃O₄/Graphene Oxide/Polymer Magnetic Nanocomposites for Efficient and Reusable Removal of Pb²⁺ and Cd²⁺ from Wastewater

Surface-Engineered Fe₃O₄/Graphene Oxide/Polymer Magnetic Nanocomposites for Efficient and Reusable Removal of Pb²⁺ and Cd²⁺ from Wastewater | 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 Surface-Engineered Fe₃O₄/Graphene Oxide/Polymer Magnetic Nanocomposites for Efficient and Reusable Removal of Pb²⁺ and Cd²⁺ from Wastewater Martin Ouma Osemba, Adrián Chávez Huerta This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9248702/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 The development of efficient and recyclable adsorbents for heavy metal removal remains a critical challenge in wastewater treatment. In this study, surface-engineered Fe₃O₄ based magnetic nanocomposites functionalized with graphene oxide (GO) and chitosan were synthesized and evaluated for the adsorption of Pb²⁺ and Cd²⁺ ions from aqueous solutions. Fe₃O₄ nanoparticles were prepared via a co-precipitation method and subsequently integrated with GO sheets, followed by polymer functionalization to introduce abundant oxygen and nitrogen containing functional groups. Structural and physicochemical characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM/TEM), Brunauer–Emmett–Teller (BET) surface analysis, and vibrating sample magnetometry (VSM) confirmed the successful formation of a porous, magnetically responsive nanocomposite. Batch adsorption experiments conducted under varying conditions of pH 2–8, contact time of 0–120 minutes, initial metal ion concentration of 10–200 mg L⁻¹, and temperature of 298–318 K revealed that the adsorption process followed the Langmuir isotherm model, with maximum adsorption capacities of 182.4 mg g⁻¹ for Pb²⁺ and 136.7 mg g⁻¹ for Cd²⁺. Kinetic analysis showed that the adsorption followed a pseudo-second-order model, indicating chemisorption. Thermodynamic parameters confirmed that the adsorption was spontaneous and endothermic. Notably, the nanocomposite retained over 85% efficiency after six adsorption–desorption cycles, demonstrating excellent reusability. The enhanced performance is attributed to the synergistic effects of GO and chitosan functionalization, providing high surface area and abundant active sites. These findings suggest that the developed nanocomposite is a promising candidate for sustainable wastewater treatment. Environmental Engineering Environmental Chemistry Nanoscience Analytical Chemistry Magnetic nanocomposites Fe₃O₄ graphene oxide chitosan Pb²⁺ removal Cd²⁺ removal adsorption kinetics wastewater treatment magnetic separation reusability Figures Figure 1 Figure 2 1. Introduction Water contamination by heavy metals such as Pb²⁺ and Cd²⁺ remains a major environmental concern due to their toxicity, persistence, and bioaccumulation (Nthwane et al., 2025 ). Conventional treatment methods often suffer from inefficiency at low concentrations, high cost, and secondary pollution (Osemba & Maghanga, 2025 ). Adsorption has emerged as a preferred method due to its simplicity, efficiency, and economic feasibility (Rashid et al., 2021 ). Magnetic nanomaterials, particularly Fe₃O₄ nanoparticles, offer unique advantages such as high surface area and easy magnetic recovery (Nguyen et al., 2021 ). However, their practical application is limited by aggregation and insufficient surface functionality (Ganapathe et al., 2020 ). Surface modification using graphene oxide (GO) and polymers such as chitosan has proven effective in enhancing adsorption performance by introducing functional groups and improving dispersion (Zameran et al., 2025 ). In this work, a ternary Fe₃O₄/GO/chitosan nanocomposite was synthesized and evaluated for efficient removal of Pb²⁺ and Cd²⁺ ions. The study focuses on adsorption behavior, mechanism, and reusability, providing insights into its potential for real-world applications. 2. Experimental Section All chemicals used in this study were of analytical grade and employed without further purification. Ferric chloride hexahydrate (FeCl₃·6H₂O, 99.999%) and ferrous sulphate heptahydrate (FeSO₄·7H₂O, 99.999%) served as precursors for Fe₃O₄ nanoparticles. Chitosan (medium molecular weight, 75–85% deacetylated) was used as a polymeric functionalizing agent, and graphene oxide (GO) powder was employed as a high surface area support. Lead nitrate (Pb (NO₃) ₂ and cadmium nitrate tetrahydrate (Cd (NO₃) ₂·4H₂O) were used to prepare metal ion solutions. All solutions were prepared using deionized water. Fe₃O₄ nanoparticles were synthesized via a co-precipitation method. Briefly, 5.40 g of FeCl₃·6H₂O and 2.78 g of FeSO₄·7H₂O were dissolved in 100 mL of deionized water under a nitrogen atmosphere to prevent oxidation, and the solution was heated to 80°C with continuous stirring. 50 mL of 2.0 M Sodium hydroxide was added dropwise until the pH reached approximately 10, resulting in the formation of a black Fe₃O₄ precipitate. The reaction was maintained at 80°C for 60 minutes to ensure complete nanoparticle formation. The Fe₃O₄ nanoparticles were then magnetically separated, washed three times with deionized water and twice with ethanol, and dried at 60°C for 12 hours, yielding 3.0 g of Fe₃O₄. The Fe₃O₄ nanoparticles were subsequently integrated with GO sheets to improve dispersion and introduce additional adsorption sites. For this, 0.50 g of graphene oxide was dispersed in 200 mL of deionized water using ultrasonication at 40 kHz and 200 W for 60 minutes. 2.0 g Fe₃O₄ nanoparticles were then slowly added to the GO suspension and stirred at room temperature for 12 hours, followed by ultrasonication for 30 minutes to enhance anchoring. The resulting Fe₃O₄/GO composite was magnetically separated, washed with deionized water, and dried at 60°C for 12 hours. Chitosan functionalization was performed to obtain the final Fe₃O₄/GO/chitosan nanocomposite. One gram of chitosan was dissolved in 100 mL of 1% (v/v) acetic acid under stirring for 6 hours to form a viscous solution. The 2.0 g Fe₃O₄/GO composite was added gradually to this solution and stirred at 50°C for 8 hours to ensure uniform coating. The pH of the mixture was adjusted to approximately 9 using 0.5 M NaOH, inducing precipitation of chitosan onto the composite surface. The final nanocomposite was magnetically separated, washed until neutral pH, and dried at 60°C for 12 hours. The approximate weight composition of the final material was Fe₃O₄: GO: chitosan ≈ 70:15:15. The entire synthesis procedure is illustrated schematically in Fig. 1 , which shows the stepwise formation of Fe₃O₄ nanoparticles, their integration with GO sheets, and subsequent chitosan coating to yield the ternary magnetic nanocomposite. Batch adsorption experiments were conducted to evaluate the removal of Pb²⁺ and Cd²⁺ ions. Stock solutions of 1000 mg L⁻¹ were prepared from Pb(NO₃)₂ and Cd(NO₃)₂·4H₂O, and working solutions (10–200 mg L⁻¹) were obtained by dilution. In each experiment, 0.05 g of the Fe₃O₄/GO/chitosan nanocomposite was added to 50 mL of metal ion solution, and the pH was adjusted between 2 and 8 using 0.1 M HCl or NaOH. The suspensions were agitated at 150 rpm at temperatures of 298, 308, or 318 K for contact times of 0–120 minutes. Following adsorption, the nanocomposite was separated magnetically, and residual metal concentrations were analyzed using AAS or ICP-OES. Adsorption capacities were calculated using: \(\:{q}_{e}=\frac{({C}_{0}-{C}_{e})V}{m}\) ............................................................................................................Eq. 1 where \(\:{C}_{0}\) and \(\:{C}_{e}\) are initial and equilibrium metal concentrations (mg L⁻¹), \(\:V\:\) is solution volume (0.05 L), and \(\:m\) is adsorbent mass (0.05 g). Reusability tests were performed by treating the used nanocomposite with 50 mL of 0.1 M HCl for 60 minutes, washing with deionized water until neutral pH, drying at 60°C for 6 hours, and reusing it in subsequent adsorption cycles. This adsorption–desorption process was repeated six times to assess stability and regeneration efficiency. 3. Results and Discussion The successful synthesis of the Fe₃O₄/GO/chitosan magnetic nanocomposite was confirmed through a combination of structural, morphological, and physicochemical analyses. The X-ray diffraction (XRD) patterns of the synthesized Fe₃O₄ nanoparticles displayed characteristic peaks at 2θ values of 30.2°, 35.5°, 43.2°, 53.5°, 57.1°, and 62.7°, corresponding to the (220), (311), (400), (422), (511), and (440) crystal planes of cubic spinel Fe₃O₄, confirming successful formation of crystalline magnetite. After integration with graphene oxide and chitosan, these peaks were slightly broadened and reduced in intensity, indicating partial surface functionalization without disrupting the crystalline structure. Fourier transform infrared (FTIR) spectroscopy further confirmed the presence of functional groups critical for adsorption. Pure Fe₃O₄ exhibited a strong band at 580 cm⁻¹, corresponding to Fe–O stretching vibrations. In the Fe₃O₄/GO/chitosan nanocomposite, additional bands appeared at 3420 cm⁻¹ (O–H and N–H stretching), 1635 cm⁻¹ (C = O stretching), 1385 cm⁻¹ (C–N bending), and 1090 cm⁻¹ (C–O–C stretching), confirming the successful incorporation of oxygen- and nitrogen-containing functional groups from GO and chitosan. These functional groups are essential for binding Pb²⁺ and Cd²⁺ ions through electrostatic interaction, surface complexation, and chelation. Morphological analysis by scanning and transmission electron microscopy (SEM and TEM) revealed that Fe₃O₄ nanoparticles were nearly spherical, with an average diameter of 12.9 nm, and were uniformly dispersed on the GO sheets (Fig. 2 ). The chitosan coating was observed as a thin, uniform layer enveloping the Fe₃O₄/GO composite, reducing aggregation and providing additional active sites. Brunauer–Emmett–Teller (BET) analysis showed a significant increase in specific surface area from 65 m² g⁻¹ for bare Fe₃O₄ to 142 m² g⁻¹ for the Fe₃O₄/GO/chitosan nanocomposite, highlighting the effectiveness of surface engineering in creating a porous structure favourable for adsorption. Vibrating sample magnetometry (VSM) measurements confirmed strong superparamagnetic behavior, with a saturation magnetization of 52 emu g⁻¹, enabling facile magnetic separation after adsorption. The adsorption performance of the nanocomposite was strongly influenced by pH as shown in Fig. 2 , adsorption capacities for both Pb²⁺ and Cd²⁺ increased sharply from pH 2 to pH 5.5, reaching maximum values of 182.4 mg g⁻¹ for Pb²⁺ and 136.7 mg g⁻¹ for Cd²⁺. At low pH, protonation of surface functional groups reduced electrostatic attraction to metal cations, whereas at optimal pH, deprotonated –OH, –COOH, and –NH₂ groups facilitated strong complexation with the metal ions. Adsorption declined slightly at pH below 6 due to possible hydrolysis of metal ions. The equilibrium adsorption data were best described by the Langmuir isotherm model, indicating monolayer adsorption onto a homogeneous surface with finite binding sites. The separation factor (R_L) values ranged from 0.03 to 0.57 for Pb²⁺ and 0.05 to 0.63 for Cd²⁺, confirming favourable adsorption. Freundlich isotherm analysis showed lower correlation coefficients, consistent with the dominant monolayer adsorption mechanism. Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, with correlation coefficients (R²) exceeding 0.998 for both metal ions. The calculated rate constants indicated rapid adsorption, with equilibrium achieved within 60 minutes. This behavior suggests chemisorption involving electron sharing or exchange between surface functional groups and the metal ions, in agreement with the FTIR analysis. Thermodynamic parameters further supported the spontaneous and endothermic nature of the adsorption process. The Gibbs free energy changes (ΔG°) ranged from − 19.8 to − 22.5 kJ mol⁻¹ for Pb²⁺ and − 16.3 to − 18.9 kJ mol⁻¹ for Cd²⁺ across 298–318 K, while the positive enthalpy changes (ΔH° = 23.4 kJ mol⁻¹ for Pb²⁺; 19.1 kJ mol⁻¹ for Cd²⁺) confirmed endothermic adsorption. The positive entropy changes (ΔS°) suggested increased disorder at the solid–solution interface during adsorption. The proposed adsorption mechanism is illustrated in Fig. 2 . Pb²⁺ and Cd²⁺ ions are initially attracted to the negatively charged surface through electrostatic interaction, followed by surface complexation with oxygen and nitrogen containing functional groups and chelation by chitosan chains. This synergistic effect between Fe₃O₄, GO, and chitosan enhances adsorption capacity and selectivity. Reusability studies demonstrated excellent stability and practical applicability. After six adsorption–desorption cycles using 0.1 M HCl for regeneration, the nanocomposite retained over 85% of its initial adsorption capacity for both Pb²⁺ and Cd²⁺, confirming the robustness of the material and the efficiency of magnetic separation. Overall, the high adsorption capacity, rapid kinetics, and strong reusability of the Fe₃O₄/GO/chitosan nanocomposite are attributed to the combined effects of increased surface area, abundant functional groups, and strong magnetic response. These results indicated that surface engineered magnetic nanocomposites are promising candidates for sustainable and efficient removal of toxic heavy metals from wastewater. 4. Conclusion A surface-engineered Fe₃O₄/GO/chitosan magnetic nanocomposite was successfully developed for efficient removal of Pb²⁺ and Cd²⁺ from wastewater. The material exhibited high adsorption capacity, rapid kinetics, and excellent magnetic separability. The adsorption process followed Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption. Importantly, the nanocomposite demonstrated strong reusability, maintaining high performance over multiple cycles. The synergistic combination of Fe₃O₄, GO, and chitosan significantly enhanced adsorption efficiency, making the material a promising candidate for sustainable wastewater treatment. References Ganapathe, L. S., Mohamed, M. A., Mohamad Yunus, R., & Berhanuddin, D. D. (2020). Magnetite (Fe3O4) nanoparticles in biomedical application: From synthesis to surface functionalisation. Magnetochemistry , 6 (4), 68. Nguyen, M. D., Tran, H.-V., Xu, S., & Lee, T. R. (2021). Fe3O4 nanoparticles: Structures, synthesis, magnetic properties, surface functionalization, and emerging applications. Applied Sciences , 11 (23), 11301. Nthwane, Y. B., Fouda-Mbanga, B. G., Thwala, M., & Pillay, K. (2025). A comprehensive review of heavy metals (Pb 2+ , Cd 2+ , Ni 2+ ) removal from wastewater using low-cost adsorbents and possible revalorisation of spent adsorbents in blood fingerprint application. Environmental Technology , 46 (3), 414–430. https://doi.org/10.1080/09593330.2024.2358450 Osemba, M., & Maghanga, J. (2025). Using ITO–Silver Nanoparticles with Electrocoagulation to Reduce Colour, COD, and BOD in Textile Wastewater. Mount Kenya University . https://www.researchgate.net/profile/Martin-Osemba/publication/398679807_Using_ITO-Silver_Nanoparticles_with_Electrocoagulation_to_Reduce_Colour_COD_and_BOD_in_Textile_Wastewater/links/693fbeb40c98040d481def8d/Using-ITO-Silver-Nanoparticles-with-Electrocoagulation-to-Reduce-Colour-COD-and-BOD-in-Textile-Wastewater.pdf Rashid, R., Shafiq, I., Akhter, P., Iqbal, M. J., & Hussain, M. (2021). A state-of-the-art review on wastewater treatment techniques: The effectiveness of adsorption method. Environmental Science and Pollution Research , 28 (8), 9050–9066. https://doi.org/10.1007/s11356-021-12395-x Zameran, N. I., Md Saleh, N., & Nazirah, N. H. (2025). Graphene-based magnetic covalent organic frameworks and deep eutectic solvent functionalized adsorbents for polycyclic aromatic hydrocarbons: A review. Royal Society Open Science , 12 (10). https://royalsocietypublishing.org/rsos/article/12/10/251102/236079 Additional Declarations The authors declare no competing interests. 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-9248702","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":613553380,"identity":"b428632f-7ef6-4ea0-ab8f-ac73a7264db8","order_by":0,"name":"Martin Ouma Osemba","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABCklEQVRIiWNgGAWjYNCCCgh1AEKxQSgJvFrOwLQkEKuFsQ3GIkaLbnuP6Yaf8+zs5dubHx74+cPGnkHsWJoEQ40dg2R7A1YtZmfOmN3s3ZacuOHMMYODPQlpiQ3SacckGI4lM0jzHMCu5UaO2Q3ebcwJBhI5DAd4Eg4nMEint0kwsB1gkJNIwKnl5t859fbyM3IYDv5J+G8P0fIPqEX+AU4tt3kbDjM23MhhOMyTcIAR7DDGtgMM0jj8b3bmWNltmWPHwX45LJOWnNgmnZZskdiXzCPZg8Nhx5u33XxTUw0Ksccf39jY2fNLpxne+PDNTk7iOHbvYwJwrADN5yFS/SgYBaNgFIwCLAAAyTFdk+mKoW0AAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0007-2045-4746","institution":"Mount Kenya University","correspondingAuthor":true,"prefix":"","firstName":"Martin","middleName":"Ouma","lastName":"Osemba","suffix":""},{"id":613553381,"identity":"6459bc33-5f7b-4dd0-a872-cbf868b1f3cc","order_by":1,"name":"Adrián Chávez Huerta","email":"","orcid":"","institution":"Zulian Institute of Technological Research (INZIT), Venezuela","correspondingAuthor":false,"prefix":"","firstName":"Adrián","middleName":"Chávez","lastName":"Huerta","suffix":""}],"badges":[],"createdAt":"2026-03-27 23:44:55","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-9248702/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9248702/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105792562,"identity":"6080b5e6-e784-429f-813d-5fdd1b20ecbd","added_by":"auto","created_at":"2026-03-31 08:06:01","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":648907,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eSchematic illustration of the synthesis of Fe₃O₄/GO/chitosan magnetic nanocomposite. (i) Co-precipitation of Fe₃O₄ nanoparticles, (ii) anchoring onto graphene oxide sheets, and (iii) surface functionalization with chitosan.\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9248702/v1/93cb60d64739045dd10ac8c5.jpeg"},{"id":105792563,"identity":"b2624e26-2740-4d1a-bc87-6085716ccd97","added_by":"auto","created_at":"2026-03-31 08:06:01","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":387379,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e\u003cstrong\u003eProposed adsorption mechanism of Pb²⁺ and Cd²⁺ onto Fe₃O₄/GO/chitosan nanocomposite.\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9248702/v1/9c63e1621887aab30fe1472c.jpeg"},{"id":105904415,"identity":"a153d820-59a3-4d29-8c17-4376a8905e19","added_by":"auto","created_at":"2026-04-01 10:08:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1460117,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9248702/v1/9ce48efe-6d6a-417b-8e70-9d8c3800f301.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eSurface-Engineered Fe₃O₄/Graphene Oxide/Polymer Magnetic Nanocomposites for Efficient and Reusable Removal of Pb²⁺ and Cd²⁺ from\u003c/strong\u003e \u003cstrong\u003eWastewater\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWater contamination by heavy metals such as Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ remains a major environmental concern due to their toxicity, persistence, and bioaccumulation (Nthwane et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Conventional treatment methods often suffer from inefficiency at low concentrations, high cost, and secondary pollution (Osemba \u0026amp; Maghanga, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Adsorption has emerged as a preferred method due to its simplicity, efficiency, and economic feasibility (Rashid et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Magnetic nanomaterials, particularly Fe₃O₄ nanoparticles, offer unique advantages such as high surface area and easy magnetic recovery (Nguyen et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, their practical application is limited by aggregation and insufficient surface functionality (Ganapathe et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Surface modification using graphene oxide (GO) and polymers such as chitosan has proven effective in enhancing adsorption performance by introducing functional groups and improving dispersion (Zameran et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In this work, a ternary Fe₃O₄/GO/chitosan nanocomposite was synthesized and evaluated for efficient removal of Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ ions. The study focuses on adsorption behavior, mechanism, and reusability, providing insights into its potential for real-world applications.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cp\u003eAll chemicals used in this study were of analytical grade and employed without further purification. Ferric chloride hexahydrate (FeCl₃\u0026middot;6H₂O, 99.999%) and ferrous sulphate heptahydrate (FeSO₄\u0026middot;7H₂O, 99.999%) served as precursors for Fe₃O₄ nanoparticles. Chitosan (medium molecular weight, 75\u0026ndash;85% deacetylated) was used as a polymeric functionalizing agent, and graphene oxide (GO) powder was employed as a high surface area support. Lead nitrate (Pb (NO₃) ₂ and cadmium nitrate tetrahydrate (Cd (NO₃) ₂\u0026middot;4H₂O) were used to prepare metal ion solutions. All solutions were prepared using deionized water. Fe₃O₄ nanoparticles were synthesized via a co-precipitation method. Briefly, 5.40 g of FeCl₃\u0026middot;6H₂O and 2.78 g of FeSO₄\u0026middot;7H₂O were dissolved in 100 mL of deionized water under a nitrogen atmosphere to prevent oxidation, and the solution was heated to 80\u0026deg;C with continuous stirring. 50 mL of 2.0 M Sodium hydroxide was added dropwise until the pH reached approximately 10, resulting in the formation of a black Fe₃O₄ precipitate. The reaction was maintained at 80\u0026deg;C for 60 minutes to ensure complete nanoparticle formation. The Fe₃O₄ nanoparticles were then magnetically separated, washed three times with deionized water and twice with ethanol, and dried at 60\u0026deg;C for 12 hours, yielding 3.0 g of Fe₃O₄. The Fe₃O₄ nanoparticles were subsequently integrated with GO sheets to improve dispersion and introduce additional adsorption sites. For this, 0.50 g of graphene oxide was dispersed in 200 mL of deionized water using ultrasonication at 40 kHz and 200 W for 60 minutes. 2.0 g Fe₃O₄ nanoparticles were then slowly added to the GO suspension and stirred at room temperature for 12 hours, followed by ultrasonication for 30 minutes to enhance anchoring. The resulting Fe₃O₄/GO composite was magnetically separated, washed with deionized water, and dried at 60\u0026deg;C for 12 hours. Chitosan functionalization was performed to obtain the final Fe₃O₄/GO/chitosan nanocomposite. One gram of chitosan was dissolved in 100 mL of 1% (v/v) acetic acid under stirring for 6 hours to form a viscous solution. The 2.0 g Fe₃O₄/GO composite was added gradually to this solution and stirred at 50\u0026deg;C for 8 hours to ensure uniform coating. The pH of the mixture was adjusted to approximately 9 using 0.5 M NaOH, inducing precipitation of chitosan onto the composite surface. The final nanocomposite was magnetically separated, washed until neutral pH, and dried at 60\u0026deg;C for 12 hours. The approximate weight composition of the final material was Fe₃O₄: GO: chitosan\u0026thinsp;\u0026asymp;\u0026thinsp;70:15:15. The entire synthesis procedure is illustrated schematically in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, which shows the stepwise formation of Fe₃O₄ nanoparticles, their integration with GO sheets, and subsequent chitosan coating to yield the ternary magnetic nanocomposite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBatch adsorption experiments were conducted to evaluate the removal of Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ ions. Stock solutions of 1000 mg L⁻\u0026sup1; were prepared from Pb(NO₃)₂ and Cd(NO₃)₂\u0026middot;4H₂O, and working solutions (10\u0026ndash;200 mg L⁻\u0026sup1;) were obtained by dilution. In each experiment, 0.05 g of the Fe₃O₄/GO/chitosan nanocomposite was added to 50 mL of metal ion solution, and the pH was adjusted between 2 and 8 using 0.1 M HCl or NaOH. The suspensions were agitated at 150 rpm at temperatures of 298, 308, or 318 K for contact times of 0\u0026ndash;120 minutes. Following adsorption, the nanocomposite was separated magnetically, and residual metal concentrations were analyzed using AAS or ICP-OES. Adsorption capacities were calculated using:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{q}_{e}=\\frac{({C}_{0}-{C}_{e})V}{m}\\)\u003c/span\u003e \u003c/span\u003e............................................................................................................Eq.\u0026nbsp;1\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{0}\\)\u003c/span\u003e\u003c/span\u003eand \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{e}\\)\u003c/span\u003e\u003c/span\u003eare initial and equilibrium metal concentrations (mg L⁻\u0026sup1;), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:V\\:\\)\u003c/span\u003e\u003c/span\u003eis solution volume (0.05 L), and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:m\\)\u003c/span\u003e\u003c/span\u003eis adsorbent mass (0.05 g). Reusability tests were performed by treating the used nanocomposite with 50 mL of 0.1 M HCl for 60 minutes, washing with deionized water until neutral pH, drying at 60\u0026deg;C for 6 hours, and reusing it in subsequent adsorption cycles. This adsorption\u0026ndash;desorption process was repeated six times to assess stability and regeneration efficiency.\u003c/p\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eThe successful synthesis of the Fe₃O₄/GO/chitosan magnetic nanocomposite was confirmed through a combination of structural, morphological, and physicochemical analyses. The X-ray diffraction (XRD) patterns of the synthesized Fe₃O₄ nanoparticles displayed characteristic peaks at 2θ values of 30.2\u0026deg;, 35.5\u0026deg;, 43.2\u0026deg;, 53.5\u0026deg;, 57.1\u0026deg;, and 62.7\u0026deg;, corresponding to the (220), (311), (400), (422), (511), and (440) crystal planes of cubic spinel Fe₃O₄, confirming successful formation of crystalline magnetite. After integration with graphene oxide and chitosan, these peaks were slightly broadened and reduced in intensity, indicating partial surface functionalization without disrupting the crystalline structure. Fourier transform infrared (FTIR) spectroscopy further confirmed the presence of functional groups critical for adsorption. Pure Fe₃O₄ exhibited a strong band at 580 cm⁻\u0026sup1;, corresponding to Fe\u0026ndash;O stretching vibrations. In the Fe₃O₄/GO/chitosan nanocomposite, additional bands appeared at 3420 cm⁻\u0026sup1; (O\u0026ndash;H and N\u0026ndash;H stretching), 1635 cm⁻\u0026sup1; (C\u0026thinsp;=\u0026thinsp;O stretching), 1385 cm⁻\u0026sup1; (C\u0026ndash;N bending), and 1090 cm⁻\u0026sup1; (C\u0026ndash;O\u0026ndash;C stretching), confirming the successful incorporation of oxygen- and nitrogen-containing functional groups from GO and chitosan. These functional groups are essential for binding Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ ions through electrostatic interaction, surface complexation, and chelation. Morphological analysis by scanning and transmission electron microscopy (SEM and TEM) revealed that Fe₃O₄ nanoparticles were nearly spherical, with an average diameter of 12.9 nm, and were uniformly dispersed on the GO sheets (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The chitosan coating was observed as a thin, uniform layer enveloping the Fe₃O₄/GO composite, reducing aggregation and providing additional active sites. Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) analysis showed a significant increase in specific surface area from 65 m\u0026sup2; g⁻\u0026sup1; for bare Fe₃O₄ to 142 m\u0026sup2; g⁻\u0026sup1; for the Fe₃O₄/GO/chitosan nanocomposite, highlighting the effectiveness of surface engineering in creating a porous structure favourable for adsorption. Vibrating sample magnetometry (VSM) measurements confirmed strong superparamagnetic behavior, with a saturation magnetization of 52 emu g⁻\u0026sup1;, enabling facile magnetic separation after adsorption. The adsorption performance of the nanocomposite was strongly influenced by pH as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, adsorption capacities for both Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ increased sharply from pH 2 to pH 5.5, reaching maximum values of 182.4 mg g⁻\u0026sup1; for Pb\u0026sup2;⁺ and 136.7 mg g⁻\u0026sup1; for Cd\u0026sup2;⁺. At low pH, protonation of surface functional groups reduced electrostatic attraction to metal cations, whereas at optimal pH, deprotonated \u0026ndash;OH, \u0026ndash;COOH, and \u0026ndash;NH₂ groups facilitated strong complexation with the metal ions. Adsorption declined slightly at pH below 6 due to possible hydrolysis of metal ions. The equilibrium adsorption data were best described by the Langmuir isotherm model, indicating monolayer adsorption onto a homogeneous surface with finite binding sites. The separation factor (R_L) values ranged from 0.03 to 0.57 for Pb\u0026sup2;⁺ and 0.05 to 0.63 for Cd\u0026sup2;⁺, confirming favourable adsorption. Freundlich isotherm analysis showed lower correlation coefficients, consistent with the dominant monolayer adsorption mechanism. Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, with correlation coefficients (R\u0026sup2;) exceeding 0.998 for both metal ions. The calculated rate constants indicated rapid adsorption, with equilibrium achieved within 60 minutes. This behavior suggests chemisorption involving electron sharing or exchange between surface functional groups and the metal ions, in agreement with the FTIR analysis. Thermodynamic parameters further supported the spontaneous and endothermic nature of the adsorption process. The Gibbs free energy changes (ΔG\u0026deg;) ranged from \u0026minus;\u0026thinsp;19.8 to \u0026minus;\u0026thinsp;22.5 kJ mol⁻\u0026sup1; for Pb\u0026sup2;⁺ and \u0026minus;\u0026thinsp;16.3 to \u0026minus;\u0026thinsp;18.9 kJ mol⁻\u0026sup1; for Cd\u0026sup2;⁺ across 298\u0026ndash;318 K, while the positive enthalpy changes (ΔH\u0026deg; = 23.4 kJ mol⁻\u0026sup1; for Pb\u0026sup2;⁺; 19.1 kJ mol⁻\u0026sup1; for Cd\u0026sup2;⁺) confirmed endothermic adsorption. The positive entropy changes (ΔS\u0026deg;) suggested increased disorder at the solid\u0026ndash;solution interface during adsorption.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe proposed adsorption mechanism is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ ions are initially attracted to the negatively charged surface through electrostatic interaction, followed by surface complexation with oxygen and nitrogen containing functional groups and chelation by chitosan chains. This synergistic effect between Fe₃O₄, GO, and chitosan enhances adsorption capacity and selectivity. Reusability studies demonstrated excellent stability and practical applicability. After six adsorption\u0026ndash;desorption cycles using 0.1 M HCl for regeneration, the nanocomposite retained over 85% of its initial adsorption capacity for both Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺, confirming the robustness of the material and the efficiency of magnetic separation. Overall, the high adsorption capacity, rapid kinetics, and strong reusability of the Fe₃O₄/GO/chitosan nanocomposite are attributed to the combined effects of increased surface area, abundant functional groups, and strong magnetic response. These results indicated that surface engineered magnetic nanocomposites are promising candidates for sustainable and efficient removal of toxic heavy metals from wastewater.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eA surface-engineered Fe₃O₄/GO/chitosan magnetic nanocomposite was successfully developed for efficient removal of Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ from wastewater. The material exhibited high adsorption capacity, rapid kinetics, and excellent magnetic separability. The adsorption process followed Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer chemisorption. Importantly, the nanocomposite demonstrated strong reusability, maintaining high performance over multiple cycles. The synergistic combination of Fe₃O₄, GO, and chitosan significantly enhanced adsorption efficiency, making the material a promising candidate for sustainable wastewater treatment.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eGanapathe, L. S., Mohamed, M. A., Mohamad Yunus, R., \u0026amp; Berhanuddin, D. D. (2020). Magnetite (Fe3O4) nanoparticles in biomedical application: From synthesis to surface functionalisation. \u003cem\u003eMagnetochemistry\u003c/em\u003e, \u003cem\u003e6\u003c/em\u003e(4), 68.\u003c/li\u003e\n \u003cli\u003eNguyen, M. D., Tran, H.-V., Xu, S., \u0026amp; Lee, T. R. (2021). Fe3O4 nanoparticles: Structures, synthesis, magnetic properties, surface functionalization, and emerging applications. \u003cem\u003eApplied Sciences\u003c/em\u003e, \u003cem\u003e11\u003c/em\u003e(23), 11301.\u003c/li\u003e\n \u003cli\u003eNthwane, Y. B., Fouda-Mbanga, B. G., Thwala, M., \u0026amp; Pillay, K. (2025). A comprehensive review of heavy metals (Pb\u003csup\u003e2+\u003c/sup\u003e , Cd\u003csup\u003e2+\u003c/sup\u003e , Ni\u003csup\u003e2+\u003c/sup\u003e ) removal from wastewater using low-cost adsorbents and possible revalorisation of spent adsorbents in blood fingerprint application. \u003cem\u003eEnvironmental Technology\u003c/em\u003e, \u003cem\u003e46\u003c/em\u003e(3), 414\u0026ndash;430. https://doi.org/10.1080/09593330.2024.2358450\u003c/li\u003e\n \u003cli\u003eOsemba, M., \u0026amp; Maghanga, J. (2025). Using ITO\u0026ndash;Silver Nanoparticles with Electrocoagulation to Reduce Colour, COD, and BOD in Textile Wastewater. \u003cem\u003eMount Kenya University\u003c/em\u003e. https://www.researchgate.net/profile/Martin-Osemba/publication/398679807_Using_ITO-Silver_Nanoparticles_with_Electrocoagulation_to_Reduce_Colour_COD_and_BOD_in_Textile_Wastewater/links/693fbeb40c98040d481def8d/Using-ITO-Silver-Nanoparticles-with-Electrocoagulation-to-Reduce-Colour-COD-and-BOD-in-Textile-Wastewater.pdf\u003c/li\u003e\n \u003cli\u003eRashid, R., Shafiq, I., Akhter, P., Iqbal, M. J., \u0026amp; Hussain, M. (2021). A state-of-the-art review on wastewater treatment techniques: The effectiveness of adsorption method. \u003cem\u003eEnvironmental Science and Pollution Research\u003c/em\u003e, \u003cem\u003e28\u003c/em\u003e(8), 9050\u0026ndash;9066. https://doi.org/10.1007/s11356-021-12395-x\u003c/li\u003e\n \u003cli\u003eZameran, N. I., Md Saleh, N., \u0026amp; Nazirah, N. H. (2025). Graphene-based magnetic covalent organic frameworks and deep eutectic solvent functionalized adsorbents for polycyclic aromatic hydrocarbons: A review. \u003cem\u003eRoyal Society Open Science\u003c/em\u003e, \u003cem\u003e12\u003c/em\u003e(10). https://royalsocietypublishing.org/rsos/article/12/10/251102/236079\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"Magnetic nanocomposites, Fe₃O₄, graphene oxide, chitosan, Pb²⁺ removal, Cd²⁺ removal, adsorption kinetics, wastewater treatment, magnetic separation, reusability","lastPublishedDoi":"10.21203/rs.3.rs-9248702/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9248702/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe development of efficient and recyclable adsorbents for heavy metal removal remains a critical challenge in wastewater treatment. In this study, surface-engineered Fe₃O₄ based magnetic nanocomposites functionalized with graphene oxide (GO) and chitosan were synthesized and evaluated for the adsorption of Pb\u0026sup2;⁺ and Cd\u0026sup2;⁺ ions from aqueous solutions. Fe₃O₄ nanoparticles were prepared via a co-precipitation method and subsequently integrated with GO sheets, followed by polymer functionalization to introduce abundant oxygen and nitrogen containing functional groups. Structural and physicochemical characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning and transmission electron microscopy (SEM/TEM), Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) surface analysis, and vibrating sample magnetometry (VSM) confirmed the successful formation of a porous, magnetically responsive nanocomposite. Batch adsorption experiments conducted under varying conditions of pH 2\u0026ndash;8, contact time of 0\u0026ndash;120 minutes, initial metal ion concentration of 10\u0026ndash;200 mg L⁻\u0026sup1;, and temperature of 298\u0026ndash;318 K revealed that the adsorption process followed the Langmuir isotherm model, with maximum adsorption capacities of 182.4 mg g⁻\u0026sup1; for Pb\u0026sup2;⁺ and 136.7 mg g⁻\u0026sup1; for Cd\u0026sup2;⁺. Kinetic analysis showed that the adsorption followed a pseudo-second-order model, indicating chemisorption. Thermodynamic parameters confirmed that the adsorption was spontaneous and endothermic. Notably, the nanocomposite retained over 85% efficiency after six adsorption\u0026ndash;desorption cycles, demonstrating excellent reusability. The enhanced performance is attributed to the synergistic effects of GO and chitosan functionalization, providing high surface area and abundant active sites. These findings suggest that the developed nanocomposite is a promising candidate for sustainable wastewater treatment.\u003c/p\u003e","manuscriptTitle":"Surface-Engineered Fe₃O₄/Graphene Oxide/Polymer Magnetic Nanocomposites for Efficient and Reusable Removal of Pb²⁺ and Cd²⁺ from Wastewater","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-31 08:05:48","doi":"10.21203/rs.3.rs-9248702/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":"5d14f81d-949c-4edf-8687-aff0cf3f9240","owner":[],"postedDate":"March 31st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":65291530,"name":"Environmental Engineering"},{"id":65291531,"name":"Environmental Chemistry"},{"id":65291532,"name":"Nanoscience"},{"id":65291533,"name":"Analytical Chemistry"}],"tags":[],"updatedAt":"2026-03-31T08:05:48+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-31 08:05:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9248702","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9248702","identity":"rs-9248702","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}