Study on the essential features for MOFs to reversible adsorption of H2S at room temperature

Metal-organic frameworks (MOFs) have been extensively studied for hydrogen sulfide (H2S) capture. However, reversible adsorption of H2S by MOFs materials, which allow the adsorbents to be repeatedly used, remains challenging. To get a rational insight into the reversible H2S adsorption on MOFs, eight MOFs with different features were selected as representatives, and their behaviors of adsorption and desorption for H2S in three cycles were investigated in a fixed-bed reactor. X-ray diffraction and nitrogen adsorption-desorption characterization were used to confirm the reversibility based on the alterations in MOFs’ physical and chemical properties before and after H2S adsorption. The results indicated that only UiO-66, MOF-801, and Mg-MOF-74 exhibited reversibility among these selected MOFs. Nevertheless, their highest H2S capacity is only 3.81 mg/g, far away from the practical application. Calculation results of adsorption sites, the density of states, adsorption distance, and the heat of adsorption show that a weak interaction between MOFs and H2S, which is afforded by metal centers or/and organic ligands, is needed for reversible adsorption. However, it is difficult to get a satisfactory H2S removal capacity in such a situation. Introducing new adsorption sites into structurally stable MOFs is considered an efficient strategy for increasing their reversible adsorption capacity.