Static and dynamic adsorption of arsenate from water by Fe³⁺ complexed with 3-aminopropyltriethoxysilane-modified carboxymethyl chitosan

Fe³⁺ complexed with 3-aminopropyltriethoxysilane (APTES)-modified carboxymethyl chitosan (CMC) named Fe-ACMC was synthesized by a one-step method at room temperature and pressure. The surface morphology and chemical structure of Fe-ACMC were characterized by SEM-EDS, XRD, BET, FT-IR, XPS, and ζ-potential. In batch adsorption, the optimum pH for arsenate [As(V)] adsorption onto Fe-ACMC was 3–9 with removal efficiency > 99%. The adsorption of As(V) could reach equilibrium within 25 min and the maximum adsorption capacity was 84.18 mg g^–1. The pseudo-second-order model fitted well the kinetic data (R² = 0.995), while the Freundlich model well described the adsorption isotherm of As(V) on Fe-ACMC (R² = 0.979). The co-existing anions (NO₃^–, CO₃^2–, and SO₄^2–) exhibited a slight impact on the As(V) adsorption efficiency, whereas PO₄^3– inhibited As(V) adsorption on Fe-ACMC. The real applicability of Fe-ACMC was achieved to remove ca. 10.0 mg L^–1 of As(V) from natural waters to below 0.05 mg L^–1. The regeneration and reuse of Fe-ACMC for As(V) adsorption were achieved by adding 0.2 mol L^–1 HCl. The main adsorption mechanism of As(V) on Fe-ACMC was attributed to electrostatic attraction and inner-sphere complexation between –NH₂···Fe³⁺ and As(V). In fixed-bed column adsorption, the Thomas model was the most suitable model to elucidate the dynamic adsorption behavior of As(V). The loading capacity of the Fe-ACMC packed column for As(V) was 47.04 mg g^–1 at pH 7 with an initial concentration of 60 mg L^–1, flow rate of 3 mL min^–1, and bed height of 0.6 cm.