Probing the origin and stability of bivalency in copper based porous coordination network and its application for H₂S...

A bivalent Cu(I,II) metal-organic framework (MOF) based on the 4,4',4″-s-Triazine-2,4,6-triyl-tribenzoate linker was synthesized via a solvothermal method. The MOF possessed 43.8% of the Cu sites as Cu⁺ with a surface area of 1257 m² g^-1. The detailed spectroscopic analysis confirmed dimethylformamide (DMF) solvent as the reductant responsible for Cu⁺ sites in the synthesized MOF. The Cu⁺ sites were easily accessible and prone to oxidation in hot water or acidic gas environment. The MOF showed water-induced structural change, which could be partially recovered after soaking in DMF solvent. The synthesized MOF showed a high hydrogen sulfide (H₂S) uptake capacity of 4.3 mmol g^-1 at 298 K and an extremely low H₂S pressure of 0.0005 bar. The adsorption capacity was the highest among Cu-based MOFs with PCN-6-M being regenerable, which made it useful for deep desulfurization applications. The adsorbed H₂S was mineralized to sulfide, sulfur, and sulfates, mediated by the Cu⁺/Cu²⁺ redox cycle in the presence of adsorbed water and molecular oxygen. Thus, the study confirmed that DMF as a reductant is responsible for the origin of bivalency in PCN-6-M and possibly in other Cu-based MOFs reported in the literature. Also, the developed MOF could be a potential candidate for flue gas desulfurization and gas purification applications.