Synthesis of highly active crystalline carbon nitride prepared in various salt melts for photocatalytic degradation of phenol

Abstract

Crystallinity could have a decisive influence on photocatalytic performance. In this study, the synthesis of crystalline carbon nitride (CN) was studied via an ionic melt polycondensation of urea precursor in the presence of various salt melts, which were KCl-LiCl, KCl-NaCl, and KCl-ZnCl 2 . While all the salt melts helped to improve the optical properties of the CN, only KCl-LiCl salt melt could form crystalline CN as evidenced by its X-ray diffraction pattern. Furthermore, the specific surface area of CN (72 m 2 /g) was maintained when using KCl-LiCl (73 m 2 /g), but it was decreased in the presence of KCl-NaCl (22 m 2 /g) or KCl-ZnCl 2 (17 m 2 /g). The CN prepared without the salt melt only showed 10% phenol degradation under the light of a solar simulator, while the use of KCl-LiCl significantly improved the activity to 24%. On the other hand, the CN prepared in the presence of KCl-NaCl and KCl-ZnCl 2 gave phenol degradation of 14% and 7%, respectively. This work demonstrated that the crystallinity, improved absorption in the visible light region, and maintained large specific surface area of the CN were crucial to achieve the high activity.