Broccoli-shaped Cu-BTC/biochar composite with enhanced water stability for toluene adsorption: Influence of humid air aging

Insufficient water stability is an important problem restricting the practical application of metal–organic frameworks (MOFs) in the field of volatile organic compounds (VOCs) adsorption. In this work, a copper(II) benzene-1,3,5-tricarboxylate MOF (Cu-BTC)/biochar composite with improved water stability was obtained by a facile one-pot method for toluene adsorption applications. Different from the traditional regular octahedral configuration, Cu-BTC was scattered on biochar in the form of broccoli-shaped microspheres. The influence of humid air aging on the physiochemical and toluene adsorption properties of Cu-BTC and Cu-BTC/biochar composites under different periods were explored. The results show that the inner structure of Cu-BTC degrades with the micropores transformed into meso-macropores under the humid air aging. Moreover, the BET surface area was reduced by 63.2 % and 94.7 % after 3-month and 6-month aging, respectively, which could eventually lead to a serious decline (76.3 % and 96.5 %) in the adsorption capacities of toluene. It can also be found that compared to traditional octahedral Cu-BTC, the degradation process of broccoli-shaped Cu-BTC/biochar is effectively slowed down, which shows better moisture stability. The retention rates of toluene adsorption capacities for broccoli-shaped Cu-BTC/biochar were 57.7 % and 17.1 % after 3-month and 6-month aging, respectively. This study is helpful for better improving the water stability of MOFs materials used for VOCs adsorption.