In situ synthesis of hierarchical cobalt-aluminum layered double hydroxide on boehmite surface for efficient removal of arsenate from aqueous solutions: Effects of solution chemistry factors and sorption mechanism

A facile route is reported for the in situ formation of three-dimensionally structured hierarchical Co-Al layered double hydroxide (CoAl-LDH) crystals on a boehmite surface (CoAl-LDH@boehmite) via the dissolution of boehmite followed by the coprecipitation of Co and Al ions on the boehmite surface. The physicochemical properties of the as-prepared materials were characterized and tested for evaluating their sorption affinity toward arsenate (As(V)) in an aqueous solution. The characterization results confirmed that the plate-like CoAl-LDH nanocrystals were densely and uniformly formed on the boehmite surface with a three-dimensional hierarchical structure. Batch experiments were conducted systematically to evaluate the effects of the sorbent dosage, initial pH, competitive anions, and temperature on the sorption behavior of CoAl-LDH@boehmite. The sorption kinetics and isotherms studies indicated that the As(V) sorption processes could be well described by the pseudo-second-order and Sips isotherm models, respectively. The sorption mechanisms were confirmed by various solid phase analyses, including X-ray diffraction, Fourier transform infrared, transmission electron microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure. These findings suggest that the intercalation of As(V) into the interlayer region via anion exchange and bidentate-binuclear inner-sphere surface complexation due to ligand exchange were responsible for the removal of As(V) by CoAl-LDH@boehmite.