WO₃/TiO₂composite coatings on titanium: A comprehensive review of fabrication strategies and structure/property/performance correlations in visible-light photocatalysis

Visible-light-driven photocatalysis continues to face major limitations due to insufficient light absorption and rapid charge recombination in conventional TiO2-based systems. Integrating WO3 with TiO2 has emerged as a promising strategy to overcome these constraints by enhancing visible-light responsiveness and improving charge carrier dynamics. Accordingly, this review addresses the central research question: How do different fabrication routes of WO3/TiO2 composite coatings influence their structural features and, consequently, their photocatalytic performance under visible light? The review critically surveys recent studies on the manufacture of WO3/TiO2 composite coatings, with a special focus on how different preparation processes such as sol-gel, anodizing, plasma electrolytic oxidation (PEO), and hybrid routes affect their structures, optical properties, and photocatalytic activities. The formation of effective WO3/TiO2 heterojunctions improves carrier separation and extends light absorption, leading to significant degradation of organic pollutants or enhanced water-splitting performance. Particular attention is given to the role of morphological parameters, such as porosity, surface area, crystalline phase composition, and nanoparticle dispersion, in dictating photocatalytic activity. A comparative summary of structure-property-performance correlations is provided through examination of a broad range of experimental studies. It outlines the challenges that now exist in optimizing WO3/TiO2 systems in real-world environmental and energy applications. The findings presented here form the basis for rationalizing next-generation visible-light-responsive photocatalysts.