Effect of graphene type in Cu-BTC/graphene hybrid adsorbents with ultra-low graphene content for hydrogen sulfide removal

Hybrid adsorbents based on metal-organic frameworks (MOFs) are promising for selective removal of acid gases. Here, three graphene-integrated Cu-BTC hybrid adsorbents with ultra-low content (0.5wt%) of graphene oxide (GO), few-layer graphene (FLG), and thermally reduced graphene (TRG), respectively, were in-situ grown and tested for adsorptive removal of H2S. The structure, surface chemistry, morphology, and thermal and textural properties of the developed MOF hybrids were assessed and correlated with the H2S removal efficiency, which was evaluated by breakthrough experiments using pure and mixed H2S/CH4 gases under various conditions. Graphene integration was found to enhance the pore volume of the hybrids, while GO increased microporosity and surface area, and FLG and TRG introduced mesopores to the structures. At 298 and 423K, breakthrough capacities of 28.7 and 24.2mgg-1, 44.6 and 53.7mgg-1, and 44.2 and 26.8mgg-1 were evidenced for the GO, FLG, and TRG hybrid adsorbents, respectively, which were higher than in pure MOF (22.1 and 21.6mgg-1). Cu-BTC/GO exhibited the highest H2S/CH4 selectivity of 266 at 423K and 1bar corresponding to a 40% increase compared to parent MOF (190). Physicochemical and morphological investigation of the adsorbents post H2S exposure was also carried out indicating that the interaction mechanism of H2S with the materials is based on the combination of both physical and reactive adsorption, which is distinctive for each hybrid in relation to the nature of the incorporated graphene counterpart and the resulting structural configuration.