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 spec-troscopy 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.

Automated summary

With the rapid development of industry, large amounts of wastewater containing metal ions are generated and released into natural ecosystems. Removing heavy metal ions from these ecosystems efficiently is a major challenge. This review summarizes and discusses the sorption-catalytic reduction-immobilization of U(VI) and Cr(VI) by porous frameworks materials such as MOFs, COFs, and g-C3N4. The interaction mechanisms were studied through macroscopic batch sorption/column experiments, microscopic spectroscopy characterization, and molecular-level computational simulation. The porous frameworks materials with tunable pore sizes, active sites, and functional groups have high sorption capacity for U(VI) and Cr(VI), and can immobilize or extract them from complex systems. Doping/co-doping with metals/nonmetals and incorporating other nanomaterials/metal oxides can enhance catalytic activity. The challenges for real applications are also discussed in this review.