Granular Mg-Fe layered double hydroxide prepared using dual polymers: Insights into synergistic removal of As(III) and As(V)

Controlling the particle size and aggregation of nanosheet layers in layered double hydroxides (LDHs) is critical for their application. Herein, we report the preparation of Mg-Fe LDH through a co-precipitation method. The LDH was embedded using polyacrylamide (PAM) and polyvinyl alcohol (PVA; the LDH was designated as PAM/PVA-LDH) for As(III) and As(V) removal. We found that doping with 0.3 mL PVA (2 g L^-1) and 0.4 mL (20 g L^-1) PAM solution delaminated the nanosheet layers of 1 g of the LDH (PAM₄₀/PVA₃₀-LDH) and restructured the crystal phase from monoclinic to orthorhombic. This increased the surface area and pore volume. Furthermore, PAM₄₀/PVA₃₀-LDH exhibited higher affinity for As(III) and As(V) removal with maximum adsorption capacities of 14.1 and 22.8 mg g⁻¹, respectively, compared to LDH alone with adsorption capacities of 7.1 and 7.9 mg g⁻¹, respectively. It was found that the highest adsorption capacities of As(III) and As(V) using PAM₄₀/PVA₃₀-LDH occurred at pH ∼7 and pH 2.5, respectively. X-ray photoelectron spectroscopy analysis revealed that the removal of As(III) and As(V) on PAM₄₀/PVA₃₀-LDH was mainly attributable to ion exchange with intercalated SO₄^2-, hydrogen bonding, and complexation mechanisms. These findings illustrate that PAM₄₀/PVA₃₀-LDH would be an excellent adsorbent for the remediation of arsenic-polluted wastewater.