Revealing the contribution of Cu(II) and Cu(I) inherent in MOF-199 for efficient thiophene removal at room temperature

Abstract

Thiophene (C4H4S) removal from coke oven gas is critical to its subsequent high valuable utilization but remains a challenge. MOF-199 was considered as a promising candidate for C4H4S adsorption removal owing to its nature of enriched opened Cu sites. However, the presence of mixed valence of Cu(II) and Cu(I) in MOF-199 makes it puzzling to their respective contribution to the removal of C4H4S. Herein, a series of MOF-199 with different Cu(I) contents were synthesized using different methods, including hydrothermal, solution diffusion, and ultrasonic, and their C4H4S adsorption performance were investigated. The respective contributions of Cu(II) and Cu(I) to the C4H4S removal was systematically discussed. The collected results indicated that although the samples prepared with different methods present a remarkable difference in textural characters, the latter was found to have a negligible influence on the C4H4S removal owing to MOF-199(H) affording an inferior surface area and pore volumes but performing the best C4H4S removal capacity of 53.7 mg S/g. The co-adsorption results of CH3SCH3 and C4H4S indicated that the excellent performance of MOF-199(H) mainly attributed to the presence of Cu(I), which provides active sites for C4H4S adsorption through π complex coordination. Cu(II) species was also found to the C4H4S adsorption via soft-acid-base coordinated interaction, but its contribution is 8.3 mg S/g, only accounting for 15.5 %. Additionally, the adsorption of C4H4S on MOF-199(H) was found to follow the intra-particle diffusion model and the Langmuir models. Moreover, MOF-199(H) also exhibited an excellent regeneration performance due to the weak interaction between C4H4S and their opened Cu sites, the C4H4S adsorption capacity still reaches 50.6 mg S/g after three regeneration cycles, about 94 % of its initial value. The results collected in this study will provide new insights for the manipulation of performance of C4H4S adsorption on the MOF-199.