Reduced Graphene Oxide-Supported Copper(I) Oxide Composites for the Degradation of Methylene Blue: Exploring the Capacity of RGO as an Electron Capturer for Achieving Highly Stable Photocatalytic Activity

Abstract

Reduced graphene oxide (RGO)-modified copper(I) oxide (Cu₂O–RGO) is a high-performance composite and a low-cost photocatalyst for methylene blue (MB) degradation. To evaluate the effect of RGO on the photocatalytic performances of Cu₂O–x% RGO composites (where x is the loading amount of RGO) in MB degradation, Cu₂O was separately loaded with 10, 20, and 30 wt % RGO via a precipitation method. We synthesized a Cu₂O–30% RGO composite with a superior surface area (S_BET) of 43.701 m²/g, which provided a large active area for MB photodegradation. Cu₂O–30% RGO composite was significantly more effective as a catalyst than bare Cu₂O for MB photodegradation, as it degraded 99.2% MB in only 30 min under visible-light irradiation without oxidation agents as compared to the case of bare Cu₂O (17.5% MB degradation). Notably, the Cu₂O–30% RGO composite afforded the largest rate constant of 0.10193 L/min under visible-light irradiation, which was twice that of the Cu₂O–30% RGO composite without irradiation (0.0561 L/min). Electron (e^–) capture efficacy of RGO in suppressing electron (e^–)–hole (h⁺) pairs recombination was demonstrated, and a plausible mechanism was proposed to rationalize the high photocatalytic efficiency of Cu₂O–30% RGO. The RGO in Cu₂O–RGO composites played crucial roles, narrowing the band gap, extending the lifetime, and substantially enhancing the photocatalytic activity of Cu₂O. Durability and reusability of the catalysts were also examined, and MB degradation by the Cu₂O–30% RGO composite was maintained at 95% in the second decolorization cycle followed by a decline to 87% in the fifth decolorization cycle, rendering the Cu₂O–30% RGO composite appropriate for use in real-time environmental applications. This study provides an effective photocatalyst for the degradation of organic pollutants in wastewater and suggests its potential for future applications in related fields. Furthermore, herein, the role of RGO as an electron capturer in Cu₂O–RGO composites for MB degradation under visible-light irradiation is comprehensively analyzed for the first time.