Sorption-catalytic reduction/extraction of hexavalent Cr(VI) and U(VI) by porous frameworks materials

Large amounts of wastewater containing metal ions are generated and inevitably released into the natural ecosystems with the fast development of industry. The efficient elimination of the heavy metal ions from the ecosystems is the main challenge to decrease the metal ions’ toxicity. In this review, the sorption-catalytic reduction-immobilization of U(VI) to UIVO2 and Cr(VI) to CrIII(OH)3 or other possible precipitates by porous frameworks materials (metal–organic frameworks (MOFs), covalent organic frameworks (COFs) and graphite carbon nitride (g-C3N4)) was summarized and discussed. The interaction mechanism was discussed from macroscopic studies of batch sorption/column experimental results, microscopic analysis of advanced spectroscopy characterization and the computational simulation at the molecular level. The porous frameworks materials with tunable pore sizes, abundant active sites and functional groups could adsorb U(VI) or Cr(VI) with high sorption capacity, and could reduce U(VI)/Cr(VI) to immobilize or to extract Cr(VI)/U(VI) from complex systems. The doping/co-doping of metals/nonmetals and incorporation with other nanomaterials/metal oxides could efficiently enhance the catalytic activity. In the end of this review, the possible challenges for the real applications were described.