Selective adsorption of sulphur dioxide and hydrogen sulphide by metal–organic frameworks

The removal of highly toxic gasses such as SO2 and H2S is important in various industrial and environmental applications. Metal organic frameworks (MOFs) are promising candidates for the capture of toxic gases owing to their favorable properties such as high selectivity, moisture stability, thermostability, acid gas resistance, high sorption capacity, and low-cost regenerability. In this study, we perform first principles density functional theory (DFT) and grand-canonical Monte Carlo (GCMC) simulations to investigate the capture of highly toxic gases, SO2 and H2S, by the recently designed ZTF and MAF-66 MOFs. Our results indicate that ZTF and MAF-66 show good adsorption performances for SO2 and H2S capture. The nature of the interactions between H2S or SO2 and the pore surface cavities was examined at the microscopic level. SO2 is adsorbed on the pore surface through two types of hydrogen bonds, either between O of SO2 with the closest H of the triazole 5-membred ring or between O of SO2 with the hydrogen of the amino group. For H2S inside the pores, the principal interactions between H2S and surface pores are due to a relatively strong hydrogen bonds established between the nitrogens of the organic part of MOFs and H2S. Also, we found that these interactions depend on the orientation of SO2/H2S inside the pores. Moreover, we have studied the influence of the presence of water and CO2 on H2S and SO2 capture by the ZTF MOF. The present GCMC simulations reveal that the addition of H2O molecules at low pressure leads to an enhancement of the H2S adsorption, in agreement with experimental findings. However, the presence of water molecules decreases the adsorption of SO2 irrespective of the pressure used. Besides, SO2 adsorption is increased in the presence of a small number of CO2 molecules, whereas the presence of carbon dioxide in ZTF pores has an unfavorable effect on the capture of H2S.