Fabrication and synergistic effect of nitrogen defective crystalline carbon nitride for enhanced photocatalytic selective oxidation of benzyl alcohol under blue LED irradiation

Abstract

Exploring efficient visible-light-catalytic systems for benzyl alcohol selective oxidation is highly desirable in sustainable and green chemistry. Herein, nitrogen-defective crystalline polymeric carbon nitride (g-C₃N₄) was successfully synthesized by a molten salt method. The equilibrium between crystallization and defective structure was controlled by the proper addition of KOH. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), fluorescence spectroscopy and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). Experimental investigations indicate that the increase of crystallinity and appropriate nitrogen defects can both promote the photo-generated electron transfer efficiency of g-C₃N₄. The nitrogen defective crystalline g-C₃N₄ exhibits good photocatalytic performance for benzyl alcohol oxidation, with 97.3% conversion and 87.7% selectivity under blue LED irradiation with air as an oxidant for 12 h, which is about 1.25 and 3.15 times that of crystalline g-C₃N₄ and bulk g-C₃N₄. Our work provides a simple method for synthesizing nitrogen defective crystalline g-C₃N₄, while also pioneering a new strategy to enhance the performance of semiconductors through the trade-off between defects and crystallinity.