High-efficiency simultaneous removal of Cr(VI) and As(V) by La-modified UiO-66: competition and synergy

Much research has focused on the removal of individual contaminants such as As(V) or Cr(VI) from wastewater. However, limited efforts have been devoted to their simultaneous removal in binary systems. This is largely due to the complexity of wastewater matrices and the similar chemical characteristics of As(V) and Cr(VI). In this study, La-modified UiO-66 was synthesized by a one-pot method and employed as a multifunctional adsorbent to simultaneously remove As(V) and Cr(VI) via batch experiments. Characterization results demonstrated that La was successfully grafted onto UiO-66 through Zr-ligand (O)-La and Zr-ligand (O)-Zr linkages, while the fcu structural topology and microporous nature of UiO-66 were well remained. For simultaneous uptake of As(V) and Cr(VI), a synergistic effect of Cr(VI) was observed on As(V) removal, whereas As(V) exhibited an inhibitory effect on Cr(VI) adsorption. Compared with the single component system, the adsorption capacity of As(V) in the binary system increased by approximately 26 %, while the adsorption capacity of Cr(VI) decreased by about 20 %. The enhanced uptake of As(V) was attributed to the formation of a new Cr As complex compound between adsorbed Cr(III) and As(V). In contrast, the inhibitory influence of As(V) on Cr(VI) adsorption was ascribed to the strong affinity of As(V) for the active adsorption sites. Overall, these results demonstrate that La-modified UiO-66 is a promising candidate for the simultaneous removal of As(V) and Cr(VI) in binary systems, particularly under conditions of elevated As(V) concentration.