Efficient and Durable Visible Light Photocatalytic Performance of Porous Carbon Nitride Nanosheets for Air Purification

Graphitic carbon nitride (g-C3N4) is an intriguing metal-free photocatalyst for pollution control. This research represents an efficient visible light photocatalytic removal of gaseous NO at 600 ppb level with porous g-C3N4 nanostructures synthesized by pyrolysis of thiourea. TG-DSC was employed to simulate the pyrolysis of thiourea, and the mechanistic formation process of g-C3N4 was revealed. The crystallinity, morphology, surface area, pore structures, band structure, and photocatalytic activity of g-C3N4 can be engineered by variation of pyrolysis temperature and time. A layer-by-layer coupled with layer-splitting process was proposed for the gradual reduction of layer thickness and size of g-C3N4 obtained at elevated temperature and prolonged time. The visible light photocatalytic activity of g-C3N4 nanosheets toward NO purification was significantly enhanced due to the enhanced crystallinity, nanosheet structure, large surface areas and pore volume and enlarged band gap as the pyrolysis temperature was increased and the pyrolysis time was prolonged. The optimized g-C3N4 nanosheets (CN-600 °C and CN-240 min) exhibited higher photocatalytic activity of 32.7% and 32.3% than C-doped TiO2 (21.8%) and BiOI (14.9%), which are also highly stable and can be used repeatedly without obvious deactivation under repeated irradiation, demonstrating their great potential for practical applications.