Crystalline carbon nitride for photocatalytic phenol degradation: effect of precursor and salt melt amounts

Abstract

Development of visible-light-active photocatalyst is an important approach to utilize solar energy in the future. The attempts to improve the crystallinity of photocatalyst have been the focus of the research. Recently, the use of potassium chloride-lithium chloride (KCl-LiCl) salt melt has been reported to increase the crystallinity of carbon nitride. In this work, precursor and salt melt amounts were varied to study the properties and the photocatalytic activity of the crystalline carbon nitride for phenol degradation. When the precursor amount was too low (1 g), no product was obtained due to the decomposition of precursor. When it was too high (4 g), the product showed the characters of amorphous CN. Optical properties also showed that when the precursor amount was 3-4 g, the incomplete condensation process occurred and defects were formed due to the excessive washing. The specific surface area also decreased with the increase of the precursor amount from 2 to 4. When the amount of salt melt was too low (2.5 g), the crystalline CN could not be obtained. However, when the amount of salt melt was increased to 7.5 g, impurities could not be avoided. Longer time and multiple washing processes were required in order to remove the impurities, which certainly affected the crystallinity. Photocatalytic activity test showed that the high activity was obtained on the sample prepared using the optimum amount of precursor (2 g) and salt melt (5 g), which would be due to the high crystallinity and large specific surface area.