One-pot construction of highly active defective g-C3N4 via hydrogen bond of the biomass for the improvement of CO2 conversion

Abstract

Graphitic carbon nitride (g-C₃N₄) containing conjugated tri-s-triazine units has a high abundance of amine and guanidine groups, which are ideal for the application of CO₂ conversion. However, absolute g-C₃N₄ is inherently scarce in Lewis base sites, which leads to low catalytic activities. In this study, we present a simple and green method to in situ construct chrysanthemum stalk-derived porous carbon/ highly active defective g-C₃N₄ (PC/g-C₃N₄) through hydrogen bond, increasing the surface area and a high density of Lewis base sites. The chrysanthemum stalk contains cellulose, hemicellulose and lignin, which possess a significant number of hydroxyl functional groups and drain channels, thereby providing more hydrogen bonding for highly active defective g-C₃N₄. The XPS spectra revealed that, in comparison to PC/g-C₃N₄–1 and PC/ g-C₃N₄–2.5, PC/g-C₃N₄–2 exhibited a higher C-NH₂ content at the edge of the nitrogen element. PC/g-C₃N₄–2 had a high specific surface area to expose more active sites for absorbing CO₂. The quantification of the base sites is determined by the peak area of the thermal programmed desorption of CO₂ and is 229.6 μmol/g for PC/g-C₃N₄–2. PC/g-C₃N₄–2 demonstrated excellent catalytic activity in the cycloaddition with hierarchical pores. The yield of cyclic carbonate was up to 99% with a selectivity of 99% under mild solvent-free conditions. The mechanistic studies indicate that PC/g-C₃N₄–2 not only captured CO₂, but also provided hydrogen bonds to activate the oxygen atom of epichlorohydrin (ECH). It is our contention that the multifunctional organic-inorganic hybrid materials have considerable potential for the production of cyclic carbonate.