Efficiently Photocatalytic Activities of Novel Metal-free g-C₃N₄ Under Simulated Solar Irradiation: Removal Efficiency, Influence Factors, and Reaction Mechanism

Visible-light photocatalysis shows high removal efficiency and low cost. In this study, graphic carbon nitride (g-C₃N₄) was prepared via one-step pyrolysis from urea under 550 – 620 ℃ (namely T-g-C₃N₄). Of all T-g-C₃N₄, 600-g-C₃N₄ had a crystal structure, large surface area (85.21 m²·g⁻¹), and high content of periodic tri-s-triazine ring units. The conduction band energy and valence band energy of 600-g-C₃N₄ were estimated to be ‒1.11 and 1.56 eV. Rhodamine B (RhB) was selected as a representative refractory pollutant. With a RhB/600-g-C₃N₄ ratio of 0.1, the maximum RhB removal efficiency and mineralization efficiency reached 100% and 64%. O₂^•−, h⁺, ^•OH, and ¹O₂ were the reactive oxygen species. Low pH values favored the photocatalysis. The 600-g-C₃N₄/visible light system was not affected by the presence of Cl⁻, NO₃⁻, citric acid, and low-level humic acid but highly affected by NO₂⁻ and fulvic acid. The g-C₃N₄ kept high photocatalytic efficiencies in reuse of five times.