Comparison of catalytic activity of graphitic carbon nitrides derived from different precursors for carbon dioxide conversion

The outrageous level of carbon dioxide (CO2) accumulation in the atmosphere due to persistent burning of fossil fuels is a serious problem to manhood, and there is upthrust growth in CO2 mitigation using various methodologies. In this regard, graphitic carbon nitride (GCN) based catalysts have been extensively used for CO2 conversion to cyclic carbonates. However, the catalytic activity and the product yields reported are different in different literature, which could be attributed mainly to the precursors used in the preparation of GCN. Hence, in this work, we have performed systematic investigations on GCN, derived from various commonly used precursors, including dicyandiamide, melamine, urea and thiourea, as a catalyst for CO2 conversion reaction involving its cycloaddition to epichlorohydrin to form cyclic carbonates. Suitable justifications were provided for superior activity of one over other. The results indicate that the amount of GCN obtained from different precursors follows the order as, dicyandiamide > melamine > thiourea > urea, using the same amount of initial precursor. Nevertheless, the urea-derived GCN possesses the highest surface area among all GCN and showed the best catalytic activity, giving 56% cyclic carbonate yield, which is almost 3 times higher of that obtained from GCN, derived from melamine. On the other hand, exfoliated GCN samples show a moderate decrease in catalytic activity, which could be attributed to a decrease in terminal amino groups, the active sites for catalyzing this reaction. This work provides some insightful findings for screening of best GCN precursor for catalytic CO2 cycloaddition to cyclic epoxides.