Mixed-terminal MXenes react with SF₆ in aqueous solution: reaction mechanism and pathway

The search for an ecofriendly treatment for the strong greenhouse gas SF6 has become a global hot issue. Herein, the mixed-terminal Ti3C2Tx MXene catalyzing conversion of SF6 in aqueous solution was explored. The catalytic network on realistic Ti3C2Tx was constructed. By theoretical calculations, target products and the microscopic reaction mechanism were studied. Firstly, SF6 exhibited different degrees of chemisorption on the constructed Ti3C2Tx surfaces of three varying terminal proportions, with different terminals showing synergistic effects. Secondly, taking the effect of H2O and surface hydroxyl into account, the catalytic conversion system of SF6 on a Ti3C2(OH)(0.66)O-1.33 surface was constructed, containing 25 sub-reactions with H2S as one of the final products. SF6 went through successive defluorination on the Ti3C2(OH)(0.66)O-1.33 surface to form low-fluorine sulfide SFx (x = 5, 4, 3, 2, 1), with energy of 80.685 kcal mol(-1) released during the whole process. The energy barriers of all the SF6 decomposition sub-reactions were significantly lower than that in free space. Besides, O terminals were regarded as potential hydroxyl terminals in aqueous solution, which continuously provided active hydroxyl groups for the Ti3C2(OH)(0.66)O-1.33 surface. Thus, SF6 conversion in aqueous solution will not result in deactivation of Ti3C2Tx catalyst. This work provides a theoretical basis for MXene to catalyze SF6 decomposition in an efficient way.