X-ray-absorption fine-structure spectroscopy study of the interactions between contaminant tetrahedral anions and self-assembled monolayers on mesoporous supports

Self-assembled monolayers on mesoporous supports (SAMMSs) have been found t o be superior sorbent materials for sequestering environmentally problemati c species. Coupling the rich coordination chemistry of transition metal com plexes with the SAMMS concept has afforded anion-specific sorbent materials with unprecedented anion binding capabilities. X-ray-absorption fine-struc ture (XAFS) spectroscopy is used to investigate the chemical interaction be tween an interfacially bound copper ethylenediamine complex (Cu(EDA)) and a rsenate and chromate anions within these nanoporous hybrid materials. The C u It-edge XAFS data indicate a structural change of Cu(EDA)(3) caused by th e anion bonding, consistent with a lock-and-key mechanism. The As and Cr It -edge features of the normalized absorption data signify As(V) and Cr(VI) i n the SAMMS samples. The Cr K-edge data show a distorted CrO4 tetrahedron w ith two short and two long oxygen distances, whereas the AsO4 tetrahedron i s symmetric. The average local structure about Cu, As, and Cr consistently indicate direct Cu-O bond formation, a monodentate linkage between the anio n and the Cu(II) cation, and a trigonal bipyramidal geometry of the Cu cent er in the adduct.