Graphitic Carbon Nitride Modified with Zr-Thiamine Complex for Efficient Photocatalytic CO₂ Insertion to Epoxide: Comparison with Traditional Thermal Catalysis

CO2 conversion to valuable chemicals and fuels at ambient temperature and atmospheric pressure using a sustainable energy source is an attractive but challenging task. Herein, Zr-thiamine is pyrolyzed with urea under N2 atmosphere to prepare Zr-thiamine modified carbon nitride (Zr-Thia/g-CN) catalyst. The catalyst exhibits optimum Lewis acidity and basicity to produce excellent cyclic carbonate yields by the insertion reaction of CO2 into epoxide on a large scale under neat conditions in the absence of any cocatalyst under traditional thermal catalysis in 6 h. The catalyst exhibits similar cyclic carbonate yield under simulated light (250 W Hg lamp, λ > 360 nm) in 24 h and, most importantly, under sunlight in 12 h in the presence of a low amount of cocatalyst (2.5 mol % with respect to epoxide) under ambient temperature, 1 bar pressure, and neat conditions. The catalyst is efficiently recycled up to 5 cycles in traditional thermal catalysis and photocatalytic conditions. The structure–activity relationship is established, and the reaction mechanism is proposed with the help of CO2 adsorption, CO2 temperature-programmed desorption techniques, acidity–basicity measurements, optoelectronic properties, control reactions, and catalytic activity data. The development of a single catalyst for catalyzing the same reaction under traditional thermal catalytic and sustainable photocatalytic conditions will attract researchers of different disciplines.