Effect of pH on the Catalytic Degradation of Rhodamine B by Synthesized CDs/g-C3N4/Cu x O Composites

Yulian Guo; Chunsun Zhou; Lijuan Fang; Zhongda Liu; Wen Li; Miao Yang

doi:10.1021/acsomega.0c05915

Effect of pH on the Catalytic Degradation of Rhodamine B by Synthesized CDs/g-C₃N₄/Cu _x O Composites

ACS Omega. 2021 Mar 15;6(12):8119-8130. doi: 10.1021/acsomega.0c05915. eCollection 2021 Mar 30.

Authors

Yulian Guo¹, Chunsun Zhou¹, Lijuan Fang¹, Zhongda Liu¹, Wen Li¹, Miao Yang¹

Affiliation

¹ School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China.

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.