Molten salt synthesis of a highly crystalline graphitic carbon nitride homojunction from a deep eutectic solvent for selective photocatalytic oxidation

Abstract

The construction of homojunctions in graphitic carbon nitride is regarded as an efficient approach to improve the charge separation and photocatalytic activity. However, the enhanced activity is still far from satisfactory due to the low crystalline bulk structure. Herein, a highly crystalline graphitic carbon nitride homojunction is synthesized by calcination of a mixture of NH₄SCN and urea, which forms a deep eutectic solvent using NaCl/KCl molten salts as the preparation medium. The homogeneity of the liquid precursor ensures an intimate homojunction interface, facilitating the charge separation, and the highly crystalline bulk structure builds a highway for rapidly transferring charge to the surface. Consequently, the bulk charge recombination is suppressed, and the spatial separation and transfer efficiency of charges are significantly improved. Compared to low crystalline homojunctions, this highly crystalline homojunction showed 15 times higher activity for the selective photocatalytic oxidation of benzyl alcohol to benzaldehyde. This work provides a simple strategy to construct a highly crystalline graphitic carbon nitride homojunction for solar energy conversion.