Abstract
The narrow pH range of Fenton oxidation restricts its applicability in water pollution treatment. In this work, a CDs/g-C3N4/Cu x O composite was synthesized via a stepwise thermal polymerization method using melamine, citric acid, and Cu2O. Adding H2O2 to form a heterogeneous Fenton system can degrade Rhodamine B (Rh B) under dark conditions. The synthesized composite was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption isotherms. The results showed that CDs, Cu2O, and CuO were successfully loaded on the surface of g-C3N4. By evaluating the catalytic activity on Rh B degradation in the presence of H2O2, the optimal contents of citric acid and Cu2O were 3 and 2.8%, respectively. In contrast to a typical Fenton reaction, which is favored in acidic conditions, the catalytic degradation of Rh B showed a strong pH-dependent relation when the pH is raised from 3 to 11, with the removal from 45 to 96%. Moreover, the recyclability of the composite was evaluated by the removal ratio of Rhodamine B (Rh B) after each cycle. Interestingly, recyclability is also favored in alkaline conditions and shows the best performance at pH 10, with the removal ratio of Rh B kept at 95% even after eight cycles. Through free radical trapping experiments and electron spin resonance (ESR) analysis, the hydroxyl radical (•OH) and the superoxide radical (•O2 -) were identified as the main reactive species. Overall, a mechanism is proposed, explaining that the higher catalytic performance in the basic solution is due to the dominating surface reaction and favored in alkaline conditions.