Manipulating Oxidation States of Copper within Cu-BTC Using Na2S2O3 as a New Strategy for Enhanced Adsorption of Sulfide

Manipulation of the oxidation states of the metal species within metal–organic frameworks leads to compositional, structural, and surface property evolutions, which will impact their performance as sorbents in adsorptive separation processes. In this study, we propose a new low-cost postsynthesis strategy to modify the oxidation states of copper species within the copper-1,3,5-benzenetricarboxylic acid (Cu-BTC) structure employing Na2S2O3 as the reducing agent. The compositional and structural evolutions of the modified samples were thoroughly characterized by a series of methods, and the dimethyl disulfide (DMDS) adsorption performance was evaluated. Accurately controlled reduction of Cu(II) to Cu(I) and formation of nanopores in the modified Cu(I)/Cu(II)-BTC samples have been observed and confirmed experimentally. Specifically, the sample 0.46/Cu-BTC/24h with a Cu(I)/Cu(II) molar ratio of 1.79 exhibits both the highest DMDS adsorption capacity (146.66 mg-S/g) and fastest diffusion with D of 7.59 × 10–13 cm2/s at 298 K. Further density functional theory calculations reveal that the modified Cu(I)/Cu(II)-BTC structures exhibit much higher interaction energy, Ein, with DMDS (70.65 kJ/mol) than the parent Cu(II)-BTC (20.28 kJ/mol). Controllable reduction of Cu(II) to Cu(I) in Cu-BTC leads to significantly enhanced guest–host interactions as well as the formation of uniform nanoscale porosity leading to effect enhancement for the adsorption of DMDS using modified Cu-BTC materials.