Mesoporous spinel CoFe2O4 as an efficient adsorbent for arsenite removal from water: high efficiency via control of the particle assemblage configuration

Abstract

A 3D mesoporous network of ∼6 nm cobalt ferrite (CoFe2O4) nanoparticles (NPs), synthesized through a polymer-assisted aggregation self-assembly method, is presented. The single-phase crystallinity and high porosity of the obtained material were confirmed with X-ray diffraction, transition electron microscopy, Raman and N2 porosimetry studies. Porous CoFe2O4 assemblies, obtained after heat treatment of the hybrid networks, possess an open-pore structure with a BET surface area of 160 m2 g−1 and pores with an average size of ∼5.7 nm. Owing to its 3D network assemblage, this mesoporous CoFe2O4 exhibits an exceptional AsIII uptake capacity of 252.8 mg g−1, which is much higher than those of random CoFe2O4 NP aggregates (47.3 mg g−1) and bulk-like CoFe2O4 microparticles (43.6 mg g−1). A comprehensive surface complexation model is presented, allowing a quantitative description of the AsIII adsorption on Fe- and Co-sites. Our results indicate that the AsIII uptake can be attributed to specific FeOH and CoOH sites located on the outer surface and interior pore voids of the material. Confinement inside the pores is found to be responsible for strong lateral interactions among the adsorbed [H3AsO3] species. The AsIII uptake of the present CoFe2O4 material is 3 to 10-fold higher than those of other high-performance adsorbents, such as graphite oxide, ZVI/activated carbon and CoFe2O4 and NiFe2O4 nanostructures. This exemplifies that, apart from surface chemistry, fine tuning of the spatial arrangement of NPs can offer advantageous tools towards highly-efficient AsIII adsorbents.