A current review of TiO2 thin films: synthesis and modification effect to the mechanism and photocatalytic activity

Photocatalysts in the form of thin films such as TiO₂ show great potential for various applications due to their ease of separation after use and their diverse synthesis processes. However, pure TiO₂ has some intrinsic limitations, such as a wide bandgap (∼3.2 eV) which lowers its visible-light absorption and fast recombination of electrons and holes. Thus, it is necessary to modify TiO₂ thin film to increase its photocatalysis efficiency and overcome these problems. This review examines reports over the past 10 years on TiO₂ thin-film modification strategies using metal and non-metal modifiers with detailed possible mechanisms of modified TiO₂ thin-film including optical modification and heterostructure formation. Recent advancements indicate that modifications can reduce the band gap 0.14–0.85 eV lower compared to pure TiO₂ and several modified photocatalysts can degrade >90 % of pollutant molecules. This review also highlights the effect of synthesis methods such as sol-gel, hydrothermal, magnetron sputtering, atomic layer, and chemical vapor deposition on the film properties. The different methods lead to different properties including morphology, defects, optical properties, crystal structure, and roughness. This review aims to provide a comprehensive understanding of synthesis methods, mechanisms, and performance enhancements, offering insights into the future design of high-efficiency TiO₂ thin film-based photocatalysts.