Deep eutectic solvent-functionalized ZIF-67: A novel bifunctional heterogeneous catalyst for chemical fixation of CO2 into cyclic carbonates

Background

CO₂ is one of the dominant greenhouse gases that causes global warming and a series of serious environmental problems. The catalytic chemical conversion of CO₂ into value-added products is one of the attractive approaches.

Methods

A novel zeolitic imidazolate framework (ZIF-67) has been successfully synthesized by incorporating choline chloride and thiosemicarbazide-based deep eutectic solvent onto the surface of ZIF-67, denoted as ChTSC@ZIF-67. The material's textural and physical characteristics were analyzed using powder XRD, TGA, zeta potential, SEM, and BET surface area measurements.

Significant Findings

The utilization of ChTSC@ZIF-67 as a catalyst for the conversion of epoxides and carbon dioxide into cyclic carbonates, in the absence of a co-catalyst or solvent, was investigated under various experimental conditions. Optimum conditions (3 mg catalyst, 4.0 bar CO₂ pressure, 80 °C, and 3 h reaction time) led to the production of diverse cyclic carbonates with excellent yield and selectivity. The synergistic effect between the active site in ZIF-67 and the deep eutectic solvent may be the main reason for the high catalytic activity. Furthermore, the catalyst retains its heterogeneous nature for more than six cycles, exhibiting no substantial decline in yield.