Hybrid photocatalytic-ozonation for wastewater remediation: mechanisms and synergistic effects

Abstract

Hybrid photocatalytic ozonation (PC/O₃) has emerged as one of the most powerful advanced oxidation processes (AOPs) for degrading highly recalcitrant organic contaminants in industrial wastewater. By integrating semiconductor photocatalysis with ozone-driven oxidation, PC/O₃ systems unlock synergistic reaction pathways that significantly accelerate the production of hydroxyl radicals, suppress electron–hole recombination, and improve ozone utilization efficiency. This review presents a comprehensive and critical evaluation of recent advances in photocatalysis, ozonation, and their hybridization, with emphasis on mechanistic insights, catalyst engineering strategies, and operational factors governing PC/O₃ hybrid performance. State-of-the-art developments in the strategies designed to enhance photocatalysts' visible-light harvesting, prolong carrier lifetimes, and strengthen ozone activation have been summarized. Key process parameters, including catalyst dosage, ozone concentration, pH, light intensity, pollutant chemistry, and reactor configuration, are systematically analysed to demonstrate their influence on radical generation kinetics, mineralization efficiency, and reaction energetics. Reported PC/O₃ systems achieve 90–100% degradation and 60–90% TOC/COD mineralization for dyes, pharmaceuticals, and phenols, outperforming standalone AOPs in kinetics and stability. Reported PC/O₃ systems consistently demonstrate superior degradation rates, higher TOC and COD removal, and improved stability compared to individual photocatalysis or ozonation. Despite this progress, challenges persist in catalyst deactivation, scale-up, ozone management, and economic feasibility. Emerging solutions, including advanced reactor engineering, solar-driven operation, robust catalyst architectures, and intensified mass-transfer designs, are highlighted as promising pathways toward practical industrial implementation. Collectively, this review provides an up-to-date, mechanistic, and application-oriented framework for the rational design of next-generation PC/O₃ systems, offering a strategic pathway for translating laboratory innovations into sustainable industrial wastewater treatment technologies.