Effect of Copper-Modification of g-C₃N₄ on the Visible-Light-Driven Photocatalytic Oxidation of Nitrophenols

Graphitic carbon nitride (g-C₃N₄) has proved to be a promising heterogeneous photocatalyst in the visible range. It can be used, among others, for the oxidative conversion of environmentally harmful nitrophenols occurring in wastewater. However, its photocatalytic activity needs to be enhanced, which can be achieved by modification with various dopants. In our work, copper-modified g-C₃N₄ was prepared by ultrasonic impregnation of the pristine g-C₃N₄ synthesized from thiourea. The morphology, microstructure, and optical properties of the photocatalysts were characterized by XRD, FT-IR, DRS, SEM, XPS, and TEM. DRS analysis indicated a slight change in both the CB and the VB energies of Cu/g-C₃N₄ compared to those of g-C₃N₄. The efficiency of the photocatalysts prepared was tested by the degradation of nitrophenols. Copper modification caused a sevenfold increase in the rate of 4-nitrophenol degradation in the presence of H₂O₂ at pH = 3. This dramatic enhancement can be attributed to the synergistic effect of copper and H₂O₂ in this photocatalytic system. A minor Fenton reaction role was also detected. The reusability of the Cu/g-C₃N₄ catalyst was demonstrated through five cycles. Copper-modified g-C₃N₄ with H₂O₂ proved to be applicable for efficient visible-light-driven photocatalytic oxidative degradation of nitrophenols.