Hydrothermal synthesis of ZnO-graphene oxide microrod composites for photocatalytic degradation of methylene blue

Abstract Water pollution by organic dyes is a pressing environmental concern, as dye effluents from textile and other industries can severely contaminate natural water resources. Semiconductor photocatalysis has emerged as an effective advanced oxidation process for degrading such pollutants by generating highly reactive hydroxyl radicals under light irradiation. Zinc oxide (ZnO) is a widely studied photocatalyst due to its non-toxicity, abundance, and strong oxidative capabilities. However, pure ZnO is mainly UV-responsive (band gap ∼3.37 eV) and suffers from rapid charge carrier recombination, which limits its photocatalytic efficiency. Graphene oxide (GO) can serve as an excellent catalyst support to improve light harvesting and facilitate charge separation. In this work, ZnO microrods and GO–ZnO microrod composites were synthesized via a simple hydrothermal method. The materials were characterized by various spectroscopic and microscopic techniques. Photocatalytic activity was estimated by the degradation of methylene blue (MB) dye under simulated solar light. The ZnO-GO microrod composite exhibited enhanced visible-light absorption, more effective suppression of electron–hole recombination, and a higher MB degradation rate compared to pure ZnO. Nearly complete removal of MB was achieved with the composite within 1 h, whereas pure ZnO showed significantly lower efficiency. A mechanism is proposed wherein GO in the composite acts as a charge transport scaffold and adsorbent for dye molecules, leading to superior photocatalytic performance.