Comparative Photocatalytic Performance of Graphene-Modified Titanium Dioxide and ZincOxide Nanostructures for Solar-Driven Wastewater Remediation

Abstract

Increasing industrialization and urban wastewater discharge have intensified the global presence of persistent organic pollutants, pharmaceutical residues, dyes, and heavy-metal-associated contaminants within aquatic systems. Semiconductor photocatalysis has emerged as a promising sustainable remediation strategy because it enables solar-driven degradation of toxic compounds through advanced oxidation mechanisms. This study comparatively analyzes the photocatalytic performance of graphene-modified titanium dioxide (G–TiO2) and graphene-modified zinc oxide (G–ZnO) nanostructures for wastewater remediation under simulated solar irradiation. The article investigates how structural modification, electron-transfer dynamics, band-gap characteristics, reactive oxygen species generation, and physicochemical stability influence measurable remediation efficiency and environmental sustainability. Using comparative materials analysis, spectroscopy- based characterization evidence, computational interpretation, and peer-reviewed experimental literature, the study evaluates the mechanistic differences between TiO2- and ZnO-based photocatalytic systems. The findings indicate that graphene incorporation substantially improves charge separation efficiency, surface adsorption capacity, and visible-light responsiveness in both systems. However, G–TiO2 demonstrates greater long-term physicochemical stability and photocorrosion resistance, whereas G–ZnO exhibits higher short-term electron mobility and rapid degradation kinetics under optimized conditions. The comparative evidence further reveals that photocatalytic efficiency depends not solely on semiconductor composition but on nanoscale interface interactions, crystallographic structure, oxygen vacancy dynamics, and contaminant- specific reaction pathways. This article contributes to natural sciences scholarship by integrating nanomaterials science, environmental chemistry, photocatalytic physics, and sustainability-oriented engineering into a unified framework explaining solar-driven pollutant degradation mechanisms and technological scalability for environmental remediation systems.