“Role of Green Chemistry in Synthesizing Magnetite Nanoparticles for Efficient Arsenic Adsorption: A Comprehensive Review”

Abstract

This study investigates the adsorption behavior of arsenic species (As(III) and As(V)) over a broad pH range (2 to 13.7) and the efficacy of magnetite nanoparticles synthesized via green and conventional methods for arsenic removal from groundwater. Experimental results revealed distinct pH-dependent adsorption patterns for arsenic species: As(III) exhibited maximum adsorption near pH 8, whereas As(V) adsorbed predominantly around pH 4. At extremely low pH (2), both arsenic forms demonstrated minimal adsorption, while their conjugate base forms such as AsO3− and AsO43− showed enhanced adsorption at alkaline pH (13.5), indicating a strong influence of speciation and electrostatic interactions on removal efficiency. Ionic constituents in aqueous media, such as Cl−, HCO3−, H2PO4−, and SiO32−, facilitated adsorption, with cations like Na+, Mg2+, and Ca2+ further enhancing the process by altering surface charge dynamics of the adsorbents.

To develop cost-effective and sustainable adsorbents, magnetite nanoparticles were synthesized using onion peel (MNp-OP) and corn silk extract (MNp-CS), and compared with conventionally synthesized magnetite (MNp-CO). The green extracts were characterized for their antioxidant capacity using FRAP and DPPH assays, confirming high phenolic, flavonoid, and tannin content. Characterization of the nanoparticles through SEM/EDS, XRD, FTIR, and BET surface analysis demonstrated crystalline magnetite structure with high specific surface areas of 243 m²/g (MNp-OP) and 261 m²/g (MNp-CS). Adsorption experiments revealed that arsenic removal by these nanoparticles follows chemisorption, intraparticle diffusion, and external diffusion mechanisms. The maximal adsorption capacities for MNp-OP, MNp-CS, and MNp-CO were found to be 1.86, 2.79, and 1.30 mg/g, respectively, highlighting the superior performance of green-synthesized materials. These findings suggest that MNp-OP and MNp-CS are not only environmentally benign but also highly efficient adsorbents, offering a promising solution for mitigating arsenic contamination in groundwater.

Keywords: Arsenic adsorption, pH dependence, Magnetite nanoparticles, Green synthesis, Groundwater treatment