Photocatalyst deactivation in gaseous VOCs photooxidation: Mechanisms, stability enhancement, and regeneration strategies

Air pollution from volatile organic compounds (VOCs) has raised interest in photocatalytic oxidation for air cleaning. However, photocatalysts often lose activity under real conditions. Unlike laboratory settings, real air contains many organic compounds. These can cause competitive adsorption, form reactive byproducts, and poison the surface. As a result, photocatalytic performance drops over time. This review explains the main reasons for deactivation in gas-phase systems. These include the buildup of carbon residues, formation of byproducts with nitrogen or sulfur, coke deposits, and damage to the material’s structure. We also discuss how surface defects, crystal structure, and particle shape affect both activity and durability. Different methods to restore activity are reviewed. These include heating, chemical cleaning, and light-based recovery. We also highlight recent advances in material design. Examples include single-site catalysts and porous structures such as metal organic frameworks. These materials can improve selectivity and resist deactivation. Machine learning is also gaining attention. It can help predict stability and guide the design of better photocatalysts. Although deactivation is widely studied, few reports focus on gas-phase systems with a clear mechanistic view. This review fills that gap. It combines experiments with analysis to support the design of stable and reusable photocatalysts for clean air. • Mechanisms of photocatalyst deactivation during VOCs oxidation. • Strategies to mitigate fouling, poisoning, and structural decay. • Advances in regeneration: thermal, chemical, and photo-assisted. • Emerging roles of single-atom catalysts and TiO₂–MOF hybrids. • Machine learning for predicting stability and guiding catalyst design.