Synergistic Poly (vinyl alcohol) -Alginate Hydrogel Beads: A Novel Bio-Polymeric Approach for Sustainable Soil Decontamination

Synergistic Poly (vinyl alcohol) -Alginate Hydrogel Beads: A Novel Bio-Polymeric Approach for Sustainable Soil Decontamination | 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 Synergistic Poly (vinyl alcohol) -Alginate Hydrogel Beads: A Novel Bio-Polymeric Approach for Sustainable Soil Decontamination Anshu Maurya, Priyanka Chawla, Kumari Pooja, Shivansh Tripathi, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6721675/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 Arsenic pollution in soil poses major environmental and health problems, particularly in regions with industrial waste and pesticide use. This study investigated the of polyvinyl alcohol (PVA)-alginate hydrogel beads as a long-term solutions for arsenic removal in soil. The beads were developed via simple cross-linking method and characterized by SEM, FTIR, XRD, and TGA techniques. The hydrogel beads have a porous structure with the functional groups (-OH and -COOH) required for arsenic ion adsorption, with an optimum capacity of 110 mg/g at pH 5. Adsorption followed the Langmuir isotherm framework, with electrostatic interactions and surface complexation performing important roles. Pot experiments revealed a 65% reduction in the arsenic content in treated soils, whereas the beads retained more than 95% of their efficiency after five regeneration cycles. This environmentally friendly process provides an efficient, cost-effective, and reusable alternative to long-term arsenic soil remediation, making it a viable solution for reducing pollution and promoting safer farming practices. PVA-Alginate Hydrogel beads Arsenic removal Soil remediation Soil pollution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction Soil contamination has become a major environmental problem, caused by a variety of human activities such as industrial operations, agricultural practices, and inappropriate waste disposal [ 1 ]. The introduction of hazardous compounds into the soil can significantly upset its ecological balance, resulting in decreased soil health, biodiversity, and agricultural output. Pollutants including heavy metals, pesticides, and organic compounds can accumulate in soil over time, endangering both the environment and human health [ 2 ]. Soil pollution not only impairs the quality of products cultivated in polluted regions, but + also poses a hazard to the entire food chain since these poisons can leak into groundwater and be taken up by plants, eventually infiltrating the human diet. Among the various contaminants affecting soil ecosystems, arsenic is one of the most pervasive and toxic pollutants [ 3 ]. Arsenic is one of the most common and hazardous toxins influencing soil ecosystems. Arsenic poisoning has become a major environmental and public health concern, particularly in areas affected by industrial operations, mining, and the widespread use of arsenic-based pesticides [ 4 ]. This poisonous metalloid enters the environment through a variety of human activities, including agricultural runoff, industrial discharge, and poor waste management. Once deposited in the soil, arsenic may remain for extended periods of time, accumulate in plants and eventually enter the food chain, posing major health concerns to humans and animals [ 5 ]. Chronic arsenic exposure has been associated with a variety of health issues, including skin lesions, respiratory illnesses, cardiovascular disease, and an increased risk of some cancers [ 6 ]. Additionally, Arsenic (As) pollution may significantly diminish soil fertility, lowering agricultural production and threatening food security [ 7 ]. Given these catastrophic implications, controlling arsenic pollution is essential. Chemical precipitation, activated carbon adsorption, and electrocoagulation are among the most often used arsenic remediation procedures. However, these systems frequently have substantial drawbacks, such as high operational costs, complex procedural requirements, and the risk of secondary contamination [ 8 ]. These inadequacies may render these strategies inappropriate for large-scale use in agricultural fields or ecologically sensitive locations. As a result, there is an urgent need for cost-effective, sustainable, and ecologically acceptable solutions capable of efficiently removing arsenic from contaminated soils without further environmental impacts [ 9 ]. Previous studies have shown that a variety of materials may effectively remove heavy metals from soil. For example, chitosan-based adsorbents have been found to efficiently remediate heavy metal pollution because of their high adsorption capacity and biocompatibility. Goci et.al (2023) reported that chitosan has the capacity to remove heavy metals by forming stable complexes with metal ions [ 10 ]. Similarly, biochar has been identified as an excellent heavy metal adsorbent. A.B. Duwiejuah et al. (2020) reviewed the properties of biochar and the remediation of metal contamination in water and soil [ 11 ]. In response to these issues, hydrogels have emerged as a viable alternative for heavy metal remediation because of their distinct physicochemical features. Hydrogels are three-dimensional polymeric networks that can absorb significant volumes of water while retaining their structure [ 12 ]. Owing to their customizable surface chemistry and biocompatibility, hydrogels can be engineered to target specific pollutants, such as arsenic, via methods such as electrostatic attraction, surface complexation, and ion exchange [ 13 ]. Polyvinyl alcohol (PVA) and sodium alginate are two hydrogel polymers that have received much interest since they are nontoxic, biodegradable, and renewable [ 14 ]. PVA, a synthetic polymer, is recognized for its strong mechanical strength, chemical stability, and film-forming properties, making it an excellent choice for applications requiring durability and flexibility [ 15 ]. Alginate, a naturally occurring polysaccharide derived from brown seaweed, is recognized for its biocompatibility and ability to form hydrogels in the presence of divalent cations, namely, calcium ions [ 16 ]. When combined, PVA provides structural integrity and mechanical stability, preventing the beads from dissolving in aqueous environments, whereas alginate enhances the ion-exchange capacity of the hydrogel, allowing for effective arsenic ion capture [ 17 ]. This synergistic combination of PVA and alginate yields hydrogel beads with dual activity, including mechanical durability and high arsenic adsorption capacity [ 18 ]. The objective of this study was to create and evaluate PVA-alginate hydrogel beads for the removal of arsenic from polluted soil. The primary goal will be to optimize the hydrogel preparation process and characterize its structural, thermal, and chemical properties using techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-ray Diffraction (XRD). Additionally, batch adsorption tests evaluate the efficacy of the hydrogel beads in removing arsenic under a variety of environmental circumstances, such as pH and initial arsenic concentration. This study makes a significant contribution to the area of environmental remediation by establishing a highly efficient, eco-friendly, and reusable approach for reducing arsenic pollution. It also promotes safer farming practices, eventually preserving public health and the environment. 2 Experimental 2.1 Chemicals and Materials Polyvinyl alcohol (PVA), sodium alginate, calcium chloride (CaCl₂), and deionized water were used. 2.2 Preparation of Sodium Alginate Solution A 4% w/v sodium alginate solution was prepared by dissolving sodium alginate in deionized water. Continuous stirring was used to ensure full dissolution and homogeneity in the solution. This pretreatment is critical for increasing the binding ability of the hydrogel beads. 2.3 Preparing the PVA Solution To make a 6% w/v PVA solution, PVA was dissolved in deionized water. To achieve thorough dissolution, the solution was heated to 80°C and stirred constantly. This procedure improves the mechanical characteristics of the final hydrogel beads, increasing the strength required for arsenic adsorption applications. 2.4 Hydrogel bead formation The prepared sodium alginate and PVA solutions were combined in a 1:1 ratio to prepare a homogeneous mixture, enhancing the overall adsorption capacity for arsenic ions. This uniform blend is crucial for subsequent bead formation. The mixed solution was then extruded dropwise into a 2% calcium chloride (CaCl₂) solution via a syringe. Upon contact with calcium ions, sodium alginate undergoes ionic cross-linking, forming spherical hydrogel beads (as shown in Fig. 1 ). This process creates a porous structure that improves the ability of the beads to capture arsenic ions, resulting in stable and effective hydrogel adsorbents for the environment. After formation, the beads were immersed in a CaCl₂ solution for an hour to complete crosslinking. The beads are then carefully rinsed with deionized water to eliminate any remaining calcium ions, which might interfere with the adsorption process. The hydrogel beads are then air-dried at ambient temperature or in a low-temperature oven to prepare them for further analysis and adsorption testing. Proper drying is required to ensure the durability and efficiency of the beads in trapping arsenic from polluted soil. 2.5 Testing procedure 2.5.1 Measuring Arsenic Levels in Contaminated Soil To assess the effectiveness of PVA-alginate hydrogel beads in removing arsenic from contaminated soil, we used a systematic approach to measure arsenic levels in soil samples collected from a region in Uttar Pradesh with known arsenic pollution. 2.5.2 Sample collection : Soil samples were collected from Ballia District, which is known to contain high arsenic levels in both groundwater and soil. This region is highly afflicted by geological formations that lead to arsenic leaking into the soil, making it an excellent setting for our research. Samples were collected from both the topsoil and subsurface layers to determine the vertical distribution of arsenic concentrations. 2.5.3 Sample Preparation : After the soil samples were collected, they were air-dried and passed through a 2 mm mesh filter to remove larger particles and debris. The dry dirt was then pulverized to provide a homogeneous particle size for proper examination. 2.5.4 Arsenic extraction : We used an aqueous extraction approach to remove arsenic from the soil matrix. The soil samples were combined with distilled water at a 1:10 (soil to solution) ratio and shaken for 24 hours. The mixture was subsequently centrifuged, and the supernatant was collected for arsenic analysis. 2.5.5 Arsenic analysis : To detect the presence of arsenic in the extracted soil solution, we used Atomic Absorption Spectroscopy (AAS). After removing the arsenic, we filtered and diluted the samples before analysis [ 19 ]. The prepared solutions were put into the AAS equipment, and the sample was atomized in a flame. A certain wavelength of light (193.7 nm) was delivered through the atomized material, and the absorbance of the arsenic atoms was determined. We determined the amounts of arsenic in the soil samples by comparing their absorbance values to a calibration curve created from standards with known arsenic contents (as shown in Fig. 2 ). This approach efficiently established the presence of arsenic in polluted soil in Uttar Pradesh's Ballia District. 3. Results and Discussion 3.1 Scanning electron microscopy (SEM) analysis Scanning electron microscopy (SEM) was used to analyze the surface morphology of the PVA-alginate hydrogel beads. The SEM image ( in Fig. 3 (a)) illustrates the porous structure of the PVA-alginate hydrogel beads prior to arsenic adsorption. The surface exhibited a rough texture, characterized by interconnected pores and an irregular morphology. This porosity is advantageous for the adsorption process, as it increases the surface area available for arsenate ion binding. The presence of functional groups, such as hydroxyl and carboxyl groups, is evident, facilitating interactions with arsenic species in solution. After the adsorption of arsenic, a noticeable change in the surface morphology of the hydrogel beads was observed (in Fig. 3 (b)). The porous structure remains intact; however, there are indications of arsenic accumulation on the surface. The beads appear to have a more compact and less defined surface texture, suggesting that arsenate ions have effectively bound to the functional groups present. This transformation signifies successful arsenic adsorption, reinforcing the efficacy of PVA-alginate hydrogel beads as a remediation tool for arsenic-contaminated environments. 3.2 Fourier transform infrared spectroscopy (FTIR) Fourier transform infrared (FTIR) spectra of the hydrogel beads before and after arsenic adsorption revealed the presence of functional groups involved in arsenic binding (as shown in Fig. 4 ). The peaks at 3300 cm⁻¹ and 2920 cm⁻¹ represent the stretching vibrations of hydroxyl (-OH) groups, which are prevalent in both PVA and alginate. The prominent peak at 1600 cm⁻¹ is related to the carboxyl (-COOH) stretching vibration. The strength of these peaks decreased after arsenic adsorption, demonstrating that hydroxyl and carboxyl groups bind arsenic. This shows that arsenic ions form coordination complexes with these groups, which function as the primary adsorption sites. 3.3 X-ray Diffraction (XRD) X-ray diffraction (XRD) was performed on the PVA-alginate hydrogel beads for arsenic removal. The XRD pattern exhibited prominent crystalline peaks with 2θ values of 19.8°, 22.1°, and 28.3°. These results correlate with the crystalline phases of polyvinyl alcohol (PVA) and sodium alginate, suggesting that a semi-crystalline structure is needed for adsorption processes. After arsenic loading, the peaks shifted to 2θ values of 20.5° and 22.5°, indicating interactions between the arsenic ions and the hydrogel matrix. This might indicate structural alterations caused by adsorption. The XRD analysis confirmed that the PVA-alginate hydrogel beads have optimal structural features for efficient arsenic removal, indicating their applicability as a remediation material. The XRD analysis validated the effective synthesis of PVA-alginate hydrogel beads with structural features that help with arsenic removal, revealing the interactions that occur during the adsorption process. 3.4 Thermogravimetric analysis (TGA) Thermogravimetric analysis (TGA) revealed that the PVA-alginate hydrogel beads were thermally stable up to 200°C. The thermal degradation profile revealed that the weight of the hydrogel beads decreased by approximately 10% at 100°C, mostly because of the evaporation of physically adsorbed water. A second significant weight loss occurred between 200°C and 350°C, which corresponded to the breakdown of the alginate backbone (as shown in Fig. 6 ). Importantly, the thermograms before and after arsenic adsorption showed negligible alterations, indicating that arsenic binding did not dramatically change the structural integrity of the hydrogel beads. 3.5 Zeta potential Zeta potential measurements were used to determine the surface charge of the hydrogel beads at various pH values. At acidic pH values (3–5), the positively charged surface of the beads facilitated the adsorption of arsenate anions (AsO₄³⁻). At neutral pH values (6–7), the zeta potential became slightly negative, but adsorption persisted, demonstrating that arsenic binding included both electrostatic attraction and chemical interactions. The ideal pH for adsorption was determined to be approximately pH 5, where the beads had the best charge for collecting arsenate ions. 4. Arsenic Adsorption Performance 4.1 Effect of pH The adsorption of arsenic onto the PVA-alginate hydrogel beads was extremely pH-dependent. As shown in Fig. 7 , the adsorption capacity increased dramatically at lower pH values, with the greatest adsorption occurring at pH 5. At pH values below 4, the competition between arsenate ions and H⁺ ions for binding sites on the beads decreased the adsorption effectiveness. At relatively high pH values (6–8), the effectiveness of arsenic removal decreased, most likely due to the deprotonation of functional groups on the hydrogel surface and decreased electrostatic interactions between the negatively charged hydrogel and arsenate anions. FTIR and zeta potential measurements revealed that the hydroxyl and carboxyl groups of the hydrogel beads strongly bind arsenate anions via electrostatic attraction at relatively low pH values. Adsorption in neutral and alkaline environments is predominantly caused by surface complexation rather than electrostatic attraction. 4.2 Effect of initial arsenic concentration The initial arsenic concentration significantly affected the adsorption capacity of the hydrogel beads. Figure 8 shows that when the arsenic concentrations reached 100 mg/L, the adsorption capacity increased, but the rate of adsorption plateaued, suggesting that the accessible binding sites on the hydrogel surface were saturated. At low arsenic concentrations, the hydrogel was highly effective, eliminating up to 95% of the arsenic from the solution. At higher concentrations (> 150 mg/L), the adsorption capacity reached its peak of 110 mg/g, indicating that all accessible functional groups had been filled. 4.3 Adsorption isotherms The equilibrium adsorption data were fitted to the Langmuir and Freundlich isotherm models to characterize the adsorption process. The Langmuir isotherm model yielded a superior match (R² = 0.98), indicating that the adsorption took place on a uniform surface with monolayer coverage. The Langmuir constant (q_max) was calculated to be 110 mg/g, indicating that the hydrogel beads had excellent adsorption ability. The Freundlich model (R² = 0.91) indicates that while multilayer adsorption may occur at relatively high concentrations, the bulk of arsenic adsorption is mediated by particular contact sites on the hydrogel surface (in Fig. 9 ). 5 Soil remediation efficiency 5.1 Arsenic Removal from the Soil The results of the pot tests revealed the practicality of using PVA-alginate hydrogel beads to remediate arsenic-contaminated soil. After a 30-day treatment period, the soil samples treated with hydrogel beads had a 65% lower arsenic content than the control (untreated) soil. The dose of hydrogel beads affected the removal effectiveness, with 1 g of hydrogel per kilogram of soil being the best concentration. The hydrogel-treated soils had considerably decreased arsenic bioavailability, which was confirmed by a reduction in arsenic absorption by plants growing in these soils. The binding of arsenic ions to the hydrogel beads resulted in lower bioavailability (Fig. 10 ). 5.2 Plant Uptake of Arsenic The arsenic concentration of plants growing in treated soils was examined to determine the efficiency of the hydrogel in inhibiting arsenic absorption (Fig. 11 ). The plants cultivated in the hydrogel-treated soils presented 55% lower arsenic levels in their tissues than did those grown in the untreated soils. This suggests that the PVA-alginate beads not only lowered the arsenic level in the soil, but also slowed its spread into the food chain. 5.3 Regeneration and reusability The reusability of PVA-alginate hydrogel beads is an important feature in assessing their practicality for large-scale remediation. To test this, a number of regeneration cycles were carried out, with arsenic-loaded beads desorbed using a 0.1 M NaOH solution and reused in subsequent adsorption studies. Figure 12 shows that after five regeneration cycles, the hydrogel beads maintained more than 90% of their initial adsorption capability. The modest decline in performance observed after several cycles may be due to binding site saturation or minor structural changes in the hydrogel matrix. However, the beads demonstrated high reusability, making them economically viable for use in soil remediation. 5.4 Mechanisms of Adsorption The key processes involved in arsenic adsorption onto hydrogel beads are electrostatic interactions and surface complexation. The negatively charged functional groups on the hydrogel surface, notably the carboxyl groups, attract positively charged arsenic ions, resulting in adsorption. This electrostatic interaction has a major effect on the binding effectiveness of the hydrogel beads for arsenic ions. Additionally, surface complexation is critical in the adsorption process. The functional groups on the hydrogel beads may form stable complexes with arsenic ions, which improves retention and removal efficiency. Electrostatic interactions and surface complexation work together to support the high adsorption capability of the hydrogel beads. 5.5 Comparison with other adsorbents. The performance of the PVA-alginate hydrogel beads was compared to that of other commonly used arsenic adsorbents, including activated carbon, charcoal, and iron-oxide nanoparticles. As indicated in Table 1 , hydrogel beads outperformed these materials in terms of adsorption capacity, cost-effectiveness, and reusability, making them more suitable for environmental remediation. Table 1 Comparison of the As Adsorption Capacities of Various Adsorbents Adsorbent Adsorption Capacity (mg/g) Cost-Effectiveness Reusability PVA-Alginate Hydrogel Beads 110 High Yes Activated Carbon 80 Moderate Yes Biochar 60 Moderate Yes Iron-Oxide nanoparticles 70 Low Limited 6. Conclusion This study successfully demonstrated the potential of PVA-alginate hydrogel beads to remove arsenic from polluted soil, with high adsorption capacity, reusability, and environmental suitability. The porosity of the hydrogel beads, which are rich in functional groups such as hydroxyl and carboxyl groups, which are required for arsenic binding, was validated via a simple cross- linking process. Batch adsorption tests demonstrated that the beads were most effective at a slightly acidic pH (pH 5), with a maximum adsorption capacity of 110 mg/g. The Langmuir isotherm model was the best match for the adsorption data, indicating monolayer adsorption on homogeneous surfaces. Pot trials have shown that hydrogel beads may successfully reduce arsenic levels in polluted soils by up to 65%, greatly reducing arsenic bioavailability and plant uptake. This decrease is due to both physical adsorption and chemical complexation processes. One of the most exciting qualities of these hydrogel beads is their reusable nature. After five adsorption-desorption cycles, the beads retained more than 90% of their original adsorption capacity, indicating their potential for cost-effective and long-term application in large-scale soil remediation initiatives. PVA-alginate hydrogel beads are a viable method for tackling arsenic pollution in soils, with benefits including high adsorption efficiency, simplicity of production, and economic feasibility. Future research should look at refining bead compositions for even higher efficiency, as well as testing in other soil types to confirm broader applicability in a variety of environmental circumstances. Declarations Data Availability Statement The datasets generated and analyzed during the current study are not publicly due to institutional privacy policies but are available from the corresponding author upon reasonable request. Acknowledgments Authors are thankful to CSTUP for financial support. Funding The authors are thankful to CSTUP (CST/ENV/D-668) for financial support. Ethics declarations Ethics approval and consent to participate Not applicable. The work does not contain any observations or studies with human participants or animals. All authors have read, understood, and have complied as applicable with the statement on "Ethical responsibilities of Authors" as found in the Instructions for Authors. Competing interests The authors declare that they have no competing interests. Authors contributions Corresponding Author: Mridula Tripathi Writing: Anshu Maurya Experimental: Priyanka Chawla Writing: Kumari Pooja Experimental: Shivansh Tripathi References Bech J. 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Degree College, University of Allahabad, Prayagraj","correspondingAuthor":true,"prefix":"","firstName":"Mridula","middleName":"","lastName":"Tripathi","suffix":""}],"badges":[],"createdAt":"2025-05-22 06:23:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6721675/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6721675/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85083117,"identity":"58a7e3ce-b709-46aa-87d2-5c68f7dc4809","added_by":"auto","created_at":"2025-06-20 18:21:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":214814,"visible":true,"origin":"","legend":"\u003cp\u003eFormation of PVA-Alginate Hydrogel Beads\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/53766b384b0bf4e9b5fa4c95.png"},{"id":85083116,"identity":"d6726119-9888-49c0-9459-66c74d162bf7","added_by":"auto","created_at":"2025-06-20 18:21:21","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":78548,"visible":true,"origin":"","legend":"\u003cp\u003eCallibration Curves for Arsenic Analysis by using AAS\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/7da4aaac6293a535065b86b2.jpg"},{"id":85084423,"identity":"ac1ae9fc-a294-4816-8ddc-3bb5677d567b","added_by":"auto","created_at":"2025-06-20 18:45:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":276170,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of PVA-Alginate hydrogel beads (a) Before Adsorption (b) After Adsorption\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/7e097acd5c5eb2a1819c08be.png"},{"id":85083121,"identity":"fe8997d4-2a79-4ad9-b668-b288db9e086c","added_by":"auto","created_at":"2025-06-20 18:21:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":256113,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of hydrogel beads before and after arsenic adsorption\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/b6bc93145e8cea3a4b9c9bbd.png"},{"id":85083722,"identity":"b2fb1e73-57bd-4a71-a280-31d14ec316c8","added_by":"auto","created_at":"2025-06-20 18:29:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":193942,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of PVA-Alginate hydrogel beads for arsenic removal\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/4c3d20d786343c1c8835e853.png"},{"id":85083720,"identity":"a65e9453-0265-4a17-9ab7-0278654385f0","added_by":"auto","created_at":"2025-06-20 18:29:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":269881,"visible":true,"origin":"","legend":"\u003cp\u003eTGA of PVA-Alginate hydrogel beads\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/e6a1a934a03e3f6348f2f39e.png"},{"id":85083858,"identity":"4a4f8bff-8123-4c92-9eed-bf6920055d72","added_by":"auto","created_at":"2025-06-20 18:37:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":223650,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of pH on the As Adsorption Capacity\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/875cdbe24a344ed9d5bc2050.png"},{"id":85083731,"identity":"8d6d9cee-7edb-47ce-bc8b-3222123e5d1a","added_by":"auto","created_at":"2025-06-20 18:29:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":228210,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of initial concentration on adsorption capacity.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/65ae0399d9a4a77d30acad9d.png"},{"id":85083133,"identity":"7dac3b6f-9be2-47bf-b3ea-e42bca2bd959","added_by":"auto","created_at":"2025-06-20 18:21:21","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":264840,"visible":true,"origin":"","legend":"\u003cp\u003eAdsorption isotherms for arsenic on hydrogel beads\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/f2af67d4297399c67431fccc.png"},{"id":85083136,"identity":"4daaa046-86bc-4265-8573-d2c33bae05d3","added_by":"auto","created_at":"2025-06-20 18:21:21","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":129143,"visible":true,"origin":"","legend":"\u003cp\u003eArsenic concentration in the soil samples after hydrogel bead treatment\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/b4af4d503c2d584e90f692ae.png"},{"id":85083727,"identity":"2e522aa2-0d71-43d5-89ad-f5a8e3c5fd95","added_by":"auto","created_at":"2025-06-20 18:29:22","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":158164,"visible":true,"origin":"","legend":"\u003cp\u003eArsenic content in plant tissues after treatment\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/055cdfe81992b9ff3b52a7fb.png"},{"id":85083725,"identity":"ed47e01a-8df2-410d-a954-d98e5f6f3ff3","added_by":"auto","created_at":"2025-06-20 18:29:21","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":154514,"visible":true,"origin":"","legend":"\u003cp\u003eRegeneration cycles and adsorption efficiency.\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/333eb458a9ac3757885ef343.png"},{"id":86427068,"identity":"7230a71a-f975-44c3-8e76-8fb91344ad79","added_by":"auto","created_at":"2025-07-10 13:39:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3288663,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6721675/v1/72fb8f8d-9578-435e-a92f-b0ec7009a36f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synergistic Poly (vinyl alcohol) -Alginate Hydrogel Beads: A Novel Bio-Polymeric Approach for Sustainable Soil Decontamination","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSoil contamination has become a major environmental problem, caused by a variety of human activities such as industrial operations, agricultural practices, and inappropriate waste disposal [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The introduction of hazardous compounds into the soil can significantly upset its ecological balance, resulting in decreased soil health, biodiversity, and agricultural output. Pollutants including heavy metals, pesticides, and organic compounds can accumulate in soil over time, endangering both the environment and human health [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Soil pollution not only impairs the quality of products cultivated in polluted regions, but +\u0026thinsp;also poses a hazard to the entire food chain since these poisons can leak into groundwater and be taken up by plants, eventually infiltrating the human diet. Among the various contaminants affecting soil ecosystems, arsenic is one of the most pervasive and toxic pollutants [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Arsenic is one of the most common and hazardous toxins influencing soil ecosystems. Arsenic poisoning has become a major environmental and public health concern, particularly in areas affected by industrial operations, mining, and the widespread use of arsenic-based pesticides [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. This poisonous metalloid enters the environment through a variety of human activities, including agricultural runoff, industrial discharge, and poor waste management. Once deposited in the soil, arsenic may remain for extended periods of time, accumulate in plants and eventually enter the food chain, posing major health concerns to humans and animals [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Chronic arsenic exposure has been associated with a variety of health issues, including skin lesions, respiratory illnesses, cardiovascular disease, and an increased risk of some cancers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Additionally, Arsenic (As) pollution may significantly diminish soil fertility, lowering agricultural production and threatening food security [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Given these catastrophic implications, controlling arsenic pollution is essential. Chemical precipitation, activated carbon adsorption, and electrocoagulation are among the most often used arsenic remediation procedures. However, these systems frequently have substantial drawbacks, such as high operational costs, complex procedural requirements, and the risk of secondary contamination [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. These inadequacies may render these strategies inappropriate for large-scale use in agricultural fields or ecologically sensitive locations. As a result, there is an urgent need for cost-effective, sustainable, and ecologically acceptable solutions capable of efficiently removing arsenic from contaminated soils without further environmental impacts [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePrevious studies have shown that a variety of materials may effectively remove heavy metals from soil. For example, chitosan-based adsorbents have been found to efficiently remediate heavy metal pollution because of their high adsorption capacity and biocompatibility. Goci et.al (2023) reported that chitosan has the capacity to remove heavy metals by forming stable complexes with metal ions [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Similarly, biochar has been identified as an excellent heavy metal adsorbent. A.B. Duwiejuah et al. (2020) reviewed the properties of biochar and the remediation of metal contamination in water and soil [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn response to these issues, hydrogels have emerged as a viable alternative for heavy metal remediation because of their distinct physicochemical features. Hydrogels are three-dimensional polymeric networks that can absorb significant volumes of water while retaining their structure [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Owing to their customizable surface chemistry and biocompatibility, hydrogels can be engineered to target specific pollutants, such as arsenic, via methods such as electrostatic attraction, surface complexation, and ion exchange [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Polyvinyl alcohol (PVA) and sodium alginate are two hydrogel polymers that have received much interest since they are nontoxic, biodegradable, and renewable [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. PVA, a synthetic polymer, is recognized for its strong mechanical strength, chemical stability, and film-forming properties, making it an excellent choice for applications requiring durability and flexibility [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Alginate, a naturally occurring polysaccharide derived from brown seaweed, is recognized for its biocompatibility and ability to form hydrogels in the presence of divalent cations, namely, calcium ions [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. When combined, PVA provides structural integrity and mechanical stability, preventing the beads from dissolving in aqueous environments, whereas alginate enhances the ion-exchange capacity of the hydrogel, allowing for effective arsenic ion capture [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. This synergistic combination of PVA and alginate yields hydrogel beads with dual activity, including mechanical durability and high arsenic adsorption capacity [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe objective of this study was to create and evaluate PVA-alginate hydrogel beads for the removal of arsenic from polluted soil. The primary goal will be to optimize the hydrogel preparation process and characterize its structural, thermal, and chemical properties using techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-ray Diffraction (XRD). Additionally, batch adsorption tests evaluate the efficacy of the hydrogel beads in removing arsenic under a variety of environmental circumstances, such as pH and initial arsenic concentration. This study makes a significant contribution to the area of environmental remediation by establishing a highly efficient, eco-friendly, and reusable approach for reducing arsenic pollution. It also promotes safer farming practices, eventually preserving public health and the environment.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Chemicals and Materials\u003c/h2\u003e\n\u003cp\u003ePolyvinyl alcohol (PVA), sodium alginate, calcium chloride (CaCl₂), and deionized water were used.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Preparation of Sodium Alginate Solution\u003c/h2\u003e\n\u003cp\u003eA 4% w/v sodium alginate solution was prepared by dissolving sodium alginate in deionized water. Continuous stirring was used to ensure full dissolution and homogeneity in the solution. This pretreatment is critical for increasing the binding ability of the hydrogel beads.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3 Preparing the PVA Solution\u003c/h2\u003e\n\u003cp\u003eTo make a 6% w/v PVA solution, PVA was dissolved in deionized water. To achieve thorough dissolution, the solution was heated to 80\u0026deg;C and stirred constantly. This procedure improves the mechanical characteristics of the final hydrogel beads, increasing the strength required for arsenic adsorption applications.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4 Hydrogel bead formation\u003c/h2\u003e\n\u003cp\u003eThe prepared sodium alginate and PVA solutions were combined in a 1:1 ratio to prepare a homogeneous mixture, enhancing the overall adsorption capacity for arsenic ions. This uniform blend is crucial for subsequent bead formation.\u003c/p\u003e\n\u003cp\u003eThe mixed solution was then extruded dropwise into a 2% calcium chloride (CaCl₂) solution via a syringe. Upon contact with calcium ions, sodium alginate undergoes ionic cross-linking, forming spherical hydrogel beads (as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). This process creates a porous structure that improves the ability of the beads to capture arsenic ions, resulting in stable and effective hydrogel adsorbents for the environment.\u003c/p\u003e\n\u003cp\u003eAfter formation, the beads were immersed in a CaCl₂ solution for an hour to complete crosslinking. The beads are then carefully rinsed with deionized water to eliminate any remaining calcium ions, which might interfere with the adsorption process.\u003c/p\u003e\n\u003cp\u003eThe hydrogel beads are then air-dried at ambient temperature or in a low-temperature oven to prepare them for further analysis and adsorption testing. Proper drying is required to ensure the durability and efficiency of the beads in trapping arsenic from polluted soil.\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n\u003ch2\u003e2.5 Testing procedure\u003c/h2\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.5.1 Measuring Arsenic Levels in Contaminated Soil\u003c/h2\u003e\n\u003cp\u003eTo assess the effectiveness of PVA-alginate hydrogel beads in removing arsenic from contaminated soil, we used a systematic approach to measure arsenic levels in soil samples collected from a region in Uttar Pradesh with known arsenic pollution.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5.2 Sample collection\u003c/strong\u003e: Soil samples were collected from Ballia District, which is known to contain high arsenic levels in both groundwater and soil. This region is highly afflicted by geological formations that lead to arsenic leaking into the soil, making it an excellent setting for our research. Samples were collected from both the topsoil and subsurface layers to determine the vertical distribution of arsenic concentrations.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5.3 Sample Preparation\u003c/strong\u003e: After the soil samples were collected, they were air-dried and passed through a 2 mm mesh filter to remove larger particles and debris. The dry dirt was then pulverized to provide a homogeneous particle size for proper examination.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5.4 Arsenic extraction\u003c/strong\u003e: We used an aqueous extraction approach to remove arsenic from the soil matrix. The soil samples were combined with distilled water at a 1:10 (soil to solution) ratio and shaken for 24 hours. The mixture was subsequently centrifuged, and the supernatant was collected for arsenic analysis.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.5.5 Arsenic analysis\u003c/strong\u003e: To detect the presence of arsenic in the extracted soil solution, we used Atomic Absorption Spectroscopy (AAS). After removing the arsenic, we filtered and diluted the samples before analysis [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. The prepared solutions were put into the AAS equipment, and the sample was atomized in a flame. A certain wavelength of light (193.7 nm) was delivered through the atomized material, and the absorbance of the arsenic atoms was determined. We determined the amounts of arsenic in the soil samples by comparing their absorbance values to a calibration curve created from standards with known arsenic contents (as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). This approach efficiently established the presence of arsenic in polluted soil in Uttar Pradesh's Ballia District.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Scanning electron microscopy (SEM) analysis\u003c/h2\u003e \u003cp\u003eScanning electron microscopy (SEM) was used to analyze the surface morphology of the PVA-alginate hydrogel beads. The SEM image ( in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (a)) illustrates the porous structure of the PVA-alginate hydrogel beads prior to arsenic adsorption. The surface exhibited a rough texture, characterized by interconnected pores and an irregular morphology. This porosity is advantageous for the adsorption process, as it increases the surface area available for arsenate ion binding. The presence of functional groups, such as hydroxyl and carboxyl groups, is evident, facilitating interactions with arsenic species in solution.\u003c/p\u003e \u003cp\u003eAfter the adsorption of arsenic, a noticeable change in the surface morphology of the hydrogel beads was observed (in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (b)). The porous structure remains intact; however, there are indications of arsenic accumulation on the surface. The beads appear to have a more compact and less defined surface texture, suggesting that arsenate ions have effectively bound to the functional groups present. This transformation signifies successful arsenic adsorption, reinforcing the efficacy of PVA-alginate hydrogel beads as a remediation tool for arsenic-contaminated environments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Fourier transform infrared spectroscopy (FTIR)\u003c/h2\u003e \u003cp\u003eFourier transform infrared (FTIR) spectra of the hydrogel beads before and after arsenic adsorption revealed the presence of functional groups involved in arsenic binding (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The peaks at 3300 cm⁻\u0026sup1; and 2920 cm⁻\u0026sup1; represent the stretching vibrations of hydroxyl (-OH) groups, which are prevalent in both PVA and alginate. The prominent peak at 1600 cm⁻\u0026sup1; is related to the carboxyl (-COOH) stretching vibration. The strength of these peaks decreased after arsenic adsorption, demonstrating that hydroxyl and carboxyl groups bind arsenic. This shows that arsenic ions form coordination complexes with these groups, which function as the primary adsorption sites.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 X-ray Diffraction (XRD)\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) was performed on the PVA-alginate hydrogel beads for arsenic removal. The XRD pattern exhibited prominent crystalline peaks with 2θ values of 19.8\u0026deg;, 22.1\u0026deg;, and 28.3\u0026deg;. These results correlate with the crystalline phases of polyvinyl alcohol (PVA) and sodium alginate, suggesting that a semi-crystalline structure is needed for adsorption processes. After arsenic loading, the peaks shifted to 2θ values of 20.5\u0026deg; and 22.5\u0026deg;, indicating interactions between the arsenic ions and the hydrogel matrix. This might indicate structural alterations caused by adsorption. The XRD analysis confirmed that the PVA-alginate hydrogel beads have optimal structural features for efficient arsenic removal, indicating their applicability as a remediation material. The XRD analysis validated the effective synthesis of PVA-alginate hydrogel beads with structural features that help with arsenic removal, revealing the interactions that occur during the adsorption process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Thermogravimetric analysis (TGA)\u003c/h2\u003e \u003cp\u003eThermogravimetric analysis (TGA) revealed that the PVA-alginate hydrogel beads were thermally stable up to 200\u0026deg;C. The thermal degradation profile revealed that the weight of the hydrogel beads decreased by approximately 10% at 100\u0026deg;C, mostly because of the evaporation of physically adsorbed water. A second significant weight loss occurred between 200\u0026deg;C and 350\u0026deg;C, which corresponded to the breakdown of the alginate backbone (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Importantly, the thermograms before and after arsenic adsorption showed negligible alterations, indicating that arsenic binding did not dramatically change the structural integrity of the hydrogel beads.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Zeta potential\u003c/h2\u003e \u003cp\u003eZeta potential measurements were used to determine the surface charge of the hydrogel beads at various pH values. At acidic pH values (3\u0026ndash;5), the positively charged surface of the beads facilitated the adsorption of arsenate anions (AsO₄\u0026sup3;⁻). At neutral pH values (6\u0026ndash;7), the zeta potential became slightly negative, but adsorption persisted, demonstrating that arsenic binding included both electrostatic attraction and chemical interactions. The ideal pH for adsorption was determined to be approximately pH 5, where the beads had the best charge for collecting arsenate ions.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Arsenic Adsorption Performance","content":"\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Effect of pH\u003c/h2\u003e \u003cp\u003eThe adsorption of arsenic onto the PVA-alginate hydrogel beads was extremely pH-dependent. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the adsorption capacity increased dramatically at lower pH values, with the greatest adsorption occurring at pH 5. At pH values below 4, the competition between arsenate ions and H⁺ ions for binding sites on the beads decreased the adsorption effectiveness. At relatively high pH values (6\u0026ndash;8), the effectiveness of arsenic removal decreased, most likely due to the deprotonation of functional groups on the hydrogel surface and decreased electrostatic interactions between the negatively charged hydrogel and arsenate anions. FTIR and zeta potential measurements revealed that the hydroxyl and carboxyl groups of the hydrogel beads strongly bind arsenate anions via electrostatic attraction at relatively low pH values. Adsorption in neutral and alkaline environments is predominantly caused by surface complexation rather than electrostatic attraction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Effect of initial arsenic concentration\u003c/h2\u003e \u003cp\u003eThe initial arsenic concentration significantly affected the adsorption capacity of the hydrogel beads. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows that when the arsenic concentrations reached 100 mg/L, the adsorption capacity increased, but the rate of adsorption plateaued, suggesting that the accessible binding sites on the hydrogel surface were saturated. At low arsenic concentrations, the hydrogel was highly effective, eliminating up to 95% of the arsenic from the solution. At higher concentrations (\u0026gt;\u0026thinsp;150 mg/L), the adsorption capacity reached its peak of 110 mg/g, indicating that all accessible functional groups had been filled.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Adsorption isotherms\u003c/h2\u003e \u003cp\u003eThe equilibrium adsorption data were fitted to the Langmuir and Freundlich isotherm models to characterize the adsorption process. The Langmuir isotherm model yielded a superior match (R\u0026sup2; = 0.98), indicating that the adsorption took place on a uniform surface with monolayer coverage. The Langmuir constant (q_max) was calculated to be 110 mg/g, indicating that the hydrogel beads had excellent adsorption ability. The Freundlich model (R\u0026sup2; = 0.91) indicates that while multilayer adsorption may occur at relatively high concentrations, the bulk of arsenic adsorption is mediated by particular contact sites on the hydrogel surface (in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5 Soil remediation efficiency","content":"\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Arsenic Removal from the Soil\u003c/h2\u003e \u003cp\u003eThe results of the pot tests revealed the practicality of using PVA-alginate hydrogel beads to remediate arsenic-contaminated soil. After a 30-day treatment period, the soil samples treated with hydrogel beads had a 65% lower arsenic content than the control (untreated) soil. The dose of hydrogel beads affected the removal effectiveness, with 1 g of hydrogel per kilogram of soil being the best concentration. The hydrogel-treated soils had considerably decreased arsenic bioavailability, which was confirmed by a reduction in arsenic absorption by plants growing in these soils. The binding of arsenic ions to the hydrogel beads resulted in lower bioavailability (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Plant Uptake of Arsenic\u003c/h2\u003e \u003cp\u003eThe arsenic concentration of plants growing in treated soils was examined to determine the efficiency of the hydrogel in inhibiting arsenic absorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). The plants cultivated in the hydrogel-treated soils presented 55% lower arsenic levels in their tissues than did those grown in the untreated soils. This suggests that the PVA-alginate beads not only lowered the arsenic level in the soil, but also slowed its spread into the food chain.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Regeneration and reusability\u003c/h2\u003e \u003cp\u003eThe reusability of PVA-alginate hydrogel beads is an important feature in assessing their practicality for large-scale remediation. To test this, a number of regeneration cycles were carried out, with arsenic-loaded beads desorbed using a 0.1 M NaOH solution and reused in subsequent adsorption studies. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows that after five regeneration cycles, the hydrogel beads maintained more than 90% of their initial adsorption capability. The modest decline in performance observed after several cycles may be due to binding site saturation or minor structural changes in the hydrogel matrix. However, the beads demonstrated high reusability, making them economically viable for use in soil remediation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Mechanisms of Adsorption\u003c/h2\u003e \u003cp\u003eThe key processes involved in arsenic adsorption onto hydrogel beads are electrostatic interactions and surface complexation. The negatively charged functional groups on the hydrogel surface, notably the carboxyl groups, attract positively charged arsenic ions, resulting in adsorption. This electrostatic interaction has a major effect on the binding effectiveness of the hydrogel beads for arsenic ions. Additionally, surface complexation is critical in the adsorption process. The functional groups on the hydrogel beads may form stable complexes with arsenic ions, which improves retention and removal efficiency. Electrostatic interactions and surface complexation work together to support the high adsorption capability of the hydrogel beads.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e5.5 Comparison with other adsorbents.\u003c/h2\u003e \u003cp\u003eThe performance of the PVA-alginate hydrogel beads was compared to that of other commonly used arsenic adsorbents, including activated carbon, charcoal, and iron-oxide nanoparticles. As indicated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, hydrogel beads outperformed these materials in terms of adsorption capacity, cost-effectiveness, and reusability, making them more suitable for environmental remediation.\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\u003eComparison of the As Adsorption Capacities of Various Adsorbents\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdsorbent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAdsorption Capacity (mg/g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCost-Effectiveness\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"1\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReusability\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePVA-Alginate Hydrogel Beads\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHigh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eActivated Carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eModerate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiochar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eModerate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIron-Oxide nanoparticles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLow\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLimited\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eThis study successfully demonstrated the potential of PVA-alginate hydrogel beads to remove arsenic from polluted soil, with high adsorption capacity, reusability, and environmental suitability. The porosity of the hydrogel beads, which are rich in functional groups such as hydroxyl and carboxyl groups, which are required for arsenic binding, was validated via a simple cross- linking process. Batch adsorption tests demonstrated that the beads were most effective at a slightly acidic pH (pH 5), with a maximum adsorption capacity of 110 mg/g. The Langmuir isotherm model was the best match for the adsorption data, indicating monolayer adsorption on homogeneous surfaces. Pot trials have shown that hydrogel beads may successfully reduce arsenic levels in polluted soils by up to 65%, greatly reducing arsenic bioavailability and plant uptake. This decrease is due to both physical adsorption and chemical complexation processes.\u003c/p\u003e \u003cp\u003eOne of the most exciting qualities of these hydrogel beads is their reusable nature. After five adsorption-desorption cycles, the beads retained more than 90% of their original adsorption capacity, indicating their potential for cost-effective and long-term application in large-scale soil remediation initiatives. PVA-alginate hydrogel beads are a viable method for tackling arsenic pollution in soils, with benefits including high adsorption efficiency, simplicity of production, and economic feasibility. Future research should look at refining bead compositions for even higher efficiency, as well as testing in other soil types to confirm broader applicability in a variety of environmental circumstances.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and analyzed during the current study are not publicly due to institutional privacy policies but are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthors are thankful to CSTUP for financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors are thankful to CSTUP (CST/ENV/D-668) for financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable. The work does not contain any observations or studies with human participants or animals. All authors have read, understood, and have complied as applicable with the statement on \"Ethical responsibilities of Authors\" as found in the Instructions for Authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorresponding Author: Mridula Tripathi\u003c/p\u003e\n\u003cp\u003eWriting: Anshu Maurya\u003c/p\u003e\n\u003cp\u003eExperimental: Priyanka Chawla\u003c/p\u003e\n\u003cp\u003eWriting: Kumari Pooja\u003c/p\u003e\n\u003cp\u003eExperimental: Shivansh Tripathi\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBech J. Soil contamination and human health: recent contributions. 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Talanta. 2018;188:722\u0026ndash;28. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.talanta.2018.06.052\u003c/span\u003e\u003cspan address=\"10.1016/j.talanta.2018.06.052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"PVA-Alginate, Hydrogel beads, Arsenic removal, Soil remediation, Soil pollution","lastPublishedDoi":"10.21203/rs.3.rs-6721675/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6721675/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eArsenic pollution in soil poses major environmental and health problems, particularly in regions with industrial waste and pesticide use. This study investigated the of polyvinyl alcohol (PVA)-alginate hydrogel beads as a long-term solutions for arsenic removal in soil. The beads were developed via simple cross-linking method and characterized by SEM, FTIR, XRD, and TGA techniques. The hydrogel beads have a porous structure with the functional groups (-OH and -COOH) required for arsenic ion adsorption, with an optimum capacity of 110 mg/g at pH 5. Adsorption followed the Langmuir isotherm framework, with electrostatic interactions and surface complexation performing important roles. Pot experiments revealed a 65% reduction in the arsenic content in treated soils, whereas the beads retained more than 95% of their efficiency after five regeneration cycles. This environmentally friendly process provides an efficient, cost-effective, and reusable alternative to long-term arsenic soil remediation, making it a viable solution for reducing pollution and promoting safer farming practices.\u003c/p\u003e","manuscriptTitle":"Synergistic Poly (vinyl alcohol) -Alginate Hydrogel Beads: A Novel Bio-Polymeric Approach for Sustainable Soil Decontamination","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 18:21:16","doi":"10.21203/rs.3.rs-6721675/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":"0b493bf5-8a03-4738-880a-eb06f5307da7","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-10T13:38:56+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-20 18:21:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6721675","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6721675","identity":"rs-6721675","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}