Ionic liquid-assisted growth of Cu3(BTC)2 nanocrystals on graphene oxide sheets: Towards both high capacity and high rate for CO2 adsorption

Abstract

Hierarchical porous metal organic framework (MOF) composites are highly demanded because they can keep the high activity and good transport property simultaneously. A novel method of ionic liquid-assisted growth of Cu3(BTC)2 on graphene oxide (GO) sheets was proposed and applied to improve both CO2 adsorption capacity and adsorption rate. Three ionic liquids (ILs) of triethylene tetramine acetate (TETA-Ac), triethylene tetramine tetrafluoroborate (TETA-BF4) and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) were used to investigate the effects of cations and anions of ILs on the structure of GO-IL/MOF composite. With amine or imidazole cations adsorbed at the surface of GO and the contrary anions closely attached, GO-ILs can provide a lot of active sites for the absorption of Cu2+ cations through the coordination. Just like a bridge, ILs assisted the initial growth of the first seed layer of Cu3(BTC)2 on the surface of GO. Among various GO-IL/MOF composites, GO-TAc/MOF-60 sample showed a superimposed structure, which lead to more accessible adsorption activity sites and shorten the transfer distance. Also, the GO sheets in GO-IL/MOF provide channels for faster transfer. It showed a high CO2 adsorption capability of 5.62mmol/g at 25°C and 100kPa, and a high CO2 kinetic separation performance as well. More importantly, the composite presented a quite good cyclic adsorption/desorption stability. The relations between the specific structures of the composites and the CO2 adsorption behaviors were tentatively demonstrated to reveal a convenient way for designing and fabricating hierarchical MOF composites.