New insight on the adsorption capacity of metallogels for antimonite and antimonate removal: From experimental to theoretical study

Development of high capacity material for antimonite (Sb(III)) and antimonate (Sb(V)) removal is the key to solving water antimony contamination. Three-dimensional Cu(II)-specific metallogels (Cu-MG), which are considered to have high density adsorption sites for antimony (Sb), were first applied to adsorb Sb(III) and Sb(V). Batch assays resulted in adsorption capacities of Cu-MG for Sb(III) and Sb(V) at 102.4 mg/g and 264.1 mg/g, respectively. In addition, the adsorption capacity for Sb(III) was up to 225.7 mg/g using in situ oxidation. Kinetic assays resulted in more than 90% removal of Sb in 30 min. X-ray photoelectron spectroscopy (XPS) revealed the adsorption of Sb depended mainly on coordination interactions of vacant orbitals of the Cu atom with the lone-pairs of the O atom of Sb(OH)₃ or Sb(OH)₆^-. Adsorption energy based on density functional theory (DFT) confirmed that Sb(III) adsorbed as a single layer whereas Sb(V) adsorbed as a multi-layer. These findings are consistent with experimental results. In addition, DFT calculations revealed that the Cu-MG theoretical capacity for Sb(V) adsorption is higher than for Sb(III). Cu-MG is a new and promising class of adsorbents for the removal of Sb(III) and Sb(V) from contaminated water.