Development Of Biochar-Hydrogel Composites And Fe3O4 Nanoparticles Functionalised Polyvinyl Alcohol/Chitosan Hydrogel Composites As Efficient And Low-Cost Materials To Remove Arsenic From Aqueous Solutions

Development Of Biochar-Hydrogel Composites And Fe3O4 Nanoparticles Functionalised Polyvinyl Alcohol/Chitosan Hydrogel Composites As Efficient And Low-Cost Materials To Remove Arsenic From Aqueous Solutions

As one of the most dangerous contaminants, arsenic (As) is responsible for serious, negative impacts on human health. Therefore, As-contaminated water and wastewater must be treated with effective As removal processes before being used for human consumption or release into the environment. In the last few years, hydrogel composites have attracted significant interest for application in environmental remediation, including water treatment. However, synthetic hydrogels have some disadvantages such as high production cost and latent toxicity. This study focused on developing two different hydrogel composites with natural, low-cost, non-toxic and biodegradable materials. In the first phase of the study, modified poly(acrylamide) hydrogels were developed by incorporating rice hull biochar (RHBC) and sugar cane bagasse biochar (SUBC). In the second phase, a modified chitosan-polyvinyl alcohol hydrogel was developed by incorporating Fe3O4 nanoparticles. As an extension of this material, a further modification was achieved with the integration of copper (ChFe-Cu hydrogel). Batch sorption experiments, regeneration and re-usable capacities were conducted for As removal. The highest arsenic (V) (As(V)) adsorption (15% for both RHBC and SUBC) was at the pH range of 6-7. Within this range, the protonated -NH2 and -CO groups in the hydrogels attracted As(V) oxyanions. The experimental kinetic and isotherm models predicted chemisorption and physisorption mechanisms. 0.1 M NaOH showed the best regeneration patterns and, because of this re-use capability, the As adsorption capacity was seen to be, not a single value from one adsorption cycle, but a cumulative value of several adsorption cycles. Considering arsenic (III) (As(III)), the optimum pH range was 6-7.5 for both the RHBC and SUBC hydrogels. The cumulative amount of As(III) adsorption was very low compared to the As(V) for both the RHBC and SUBC hydrogels. The limited functional group availability for As(III) adsorption was identified as the major reason for this result. The highest As(V) adsorption was achieved at pH range of 4-5 for both the ChFe (89%) and ChFe-Cu (99%) hydrogels. The kinetic and isotherm models predicted chemisorption mechanisms onto the ChFe and ChFe-Cu hydrogels. Electrostatic attractions with -NH3+ and -OH2+, ligand-exchange inner-sphere complexes formation and bidentate corner-sharing (2C), and bidentate edge-sharing (2E) trimetric surface complexes formation have been proposed as the adsorption mechanism of As(V). 0.1 M CH3COOH showed the best regeneration pattern and the cumulative adsorption capacities were 15.1 mg/g and 12.4 mg/g for ChFe and ChFe-Cu hydrogels respectively, along with four adsorption cycles.

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