Advances in graphene oxide based multifunctional photocatalysts for the degradation of synthetic dyes: a review

The large-scale discharge of dye contaminated wastewater from textile and other industries poses a severe environmental challenge because of the high stability, toxicity, and poor biodegradability of synthetic dyes. The semiconductor-based photocatalysis has become a promising advanced oxidation process used in the dye remediation and enabling pollutant degradation by redox reactions under exposure to light irradiation. This review focuses on graphene oxide (GO) and reduced graphene oxide (rGO) based photocatalysts for the degradation of organic dyes in aqueous environments. Their structural, physicochemical characteristics, along with their role in improving the photocatalytic activity, are critically discussed. GO/rGO acts as an effective adsorbent, electron acceptor, and charge-transfer mediator due to the presence of abundant oxygen-containing functional groups, high surface area, and two-dimensional π-conjugated networks. These features suppress the electron-hole recombination and facilitate the generation of reactive oxygen species. GO-based semiconductor and metal oxide heterojunctions are fundamentally addressed in the context of enhanced utilization of visible-light, interface charge transfer, and degradation performance of cationic and anionic dyes. The key processes involved in photocatalysis include dye adsorption, separation of charges, and the oxidation routes of radicals, which are systematically discussed. Despite the high dye removal efficiencies regularly reported in laboratory studies, challenges related to catalyst recovery, stability, reusability, and reduced performance in complex wastewater remain significant. To overcome these limitations, by rational material design and enhanced integration processes are required to develop the advanced GO-based photocatalysis for wastewater treatment applications.