Application of COFs in capture/conversion of CO2 and elimination of organic/inorganic pollutants

Large amounts of various (in)organic pollutants and CO2 are released into the environment with the fast development of agriculture and industry, which results in the environmental pollution and climate change, thereby causes great threat to human society. The efficient capture and conversion of CO2 are critical to against the greenhouse effect, whereas the elimination of pollutants from environment is important to human health and ecosystem. The COFs (covalent organic frameworks) have attracted multidisciplinary research interests because of their outstanding physicochemical properties such as high surface areas, tunable porous structures, abundant active sites and functional groups. Herein the application of COFs in CO2 capture and conversion, the sorption-photocatalytic degradation of organic pollutants, and the sorption-catalytic reduction-solidification of heavy metals/radionuclides were reviewed and compared. The interaction mechanisms of COFs with the pollutant molecules were discussed from the macroscopic sorption results, microscopic spectroscopy analysis, and theoretical calculations. The adsorption capacity was mainly related to the surface areas, functional groups and active sites, whereas the photocatalytic activity was mainly dominated by •O2− and •OH active species. The COFs exhibited high sorption capacity and catalytic activity in CO2 capture and conversion, and removal of pollutants. However, there are still some main challenges of COFs in real applications: 1) the high and selective capture and conversion of CO2 with low cost and reusability; 2) the high visible light absorption and photocatalytic activity for organic molecule degradation; 3) the high sorption of target pollutants with high selectivity and reusability; 4) the high reduction ability for the in-situ solidification of target metals/radionuclides under complex conditions; and 5) the high selective extraction of radionuclides from complicated solutions such as seawater or salt lake. In the end, the perspectives and difficulties for COFs real applications were described.