TiO2-based photocatalysts for emerging gaseous pollutants removal: From photocatalysts to reactors design

Air pollution is becoming a growing concern and the most significant universal issue in recent decades, which detrimentally impacts both human health and the ecological environment. Among the array of strategies for mitigating gaseous pollutants under ambient conditions, the photocatalytic oxidation process is one of the most effective and promising approaches for the removal of gaseous pollutants. Solar-driven photocatalytic oxidation has broad-spectrum activity against diverse organic and inorganic pollutants without severe conditions, indicating its immense potential in the realm of air purification. However, the commercial implementation of this approach remains constrained by challenges such as visible light utilization, photocatalyst deactivation, and intricate reaction mechanisms. Currently, there is a substantial gap between fundamental research and commercial use in the field of photocatalytic air purification. This review mainly focuses on three main significant issues for enhancing the commercial purpose of photocatalytic gaseous pollutants removal: (i) Innovative designing strategies of TiO2-based photocatalysts, (ii) Influencing factors on gaseous pollutants removal and (iii) Optimized photocatalytic reactor designs. This review comprehensively summarizes the recent progress of TiO2-based photocatalysts in strategies to enhance photocatalysis, especially on the practical challenges. It also delves into real-world scenarios of air purification, shedding light on the intricacy of this field. Moreover, the review scrutinizes the progress and difficulties of certain conventional photocatalytic reactor designs like annular, flat plate, monolith, fixed-bed, and microreactors, which are discussed and distinguished. We explored and highlighted some simulations-based scale-up reactors and pilot-scale reactor testing for commercial purposes of the removal of gaseous pollutants over TiO2-based photocatalysts. Finally, the existing limitations and problems of the current studies on photocatalytic oxidation are critically reviewed, and suggestions for future research on the air purification of gaseous pollutants for commercialization are proposed. The core objective of this work is to provide a repository of contemporary research and scientific concepts to underpin the practical deployment of TiO2-based photocatalysts for air purification of gaseous pollutants in the foreseeable future.