Amorphous metal-organic framework UiO-66-NO2 for removal of oxyanion pollutants: Towards improved performance and effective reusability

Abstract

Water pollution is one of the most significant environmental problems nowadays. The remediation of oxyanion pollutions is of great importance due to their recalcitrance and persistence in the environment as well as acute toxicities even at trace concentration levels. In this study, a water stable metal–organic framework (MOF), UiO-66-NO2, was prepared and deliberately amorphized in order that it will assume a more open and dynamic structure. The resulting amorphous UiO-66-NO2 (am-UiO-66-NO2) demonstrated a great efficacy in the removal of representative oxyanion pollutants in wastewater, i.e., arsenic, chromium and selenium species. It was found that the am-UiO-66-NO2 adsorbent exhibited enhanced adsorption capacities as well as an excellent reusability, which was less reported in literature. Notably, it was found that it could be effectively regenerated and reused whilst retaining more than 80% of its capacity after 8 cycles of applications. The amorphized MOF as well as its adsorption behaviors were thoroughly characterized and analyzed using X-ray photoelectron spectroscopy; the uptake of oxyanions was mainly due to the formation of Zr-O-M (M: oxyanions) complexes.