TiO2 and SnO2 based nanomaterials for photocatalysis: recent progress in synthesis, modification, and mechanisms

Titanium dioxide (TiO 2 ) and tin dioxide (SnO 2 ) have gained significant attention as photocatalytic materials due to their stability, abundance, and efficiency in degrading a wide range of organic pollutants. However, both semiconductors face intrinsic limitations, particularly rapid electron-hole recombination and limited visible-light absorption. To overcome these limitations, recent studies have focused on combining TiO 2 and SnO 2 and developing various modification strategies to enhance charge separation, extend light absorption, and improve photocatalytic performance. This review provides an overview of the structural and physicochemical properties of TiO 2 and SnO 2 and summarizes recent advances in their synthesis, modification, and photocatalytic applications. Particular attention is given to heterojunction engineering, doping, noble-metal incorporation, surface modification, and defect engineering, with emphasis on their effects on structure, charge-transfer behavior, and photocatalytic activity. The review also considers the distinction between pollutant removal and mineralization, catalyst stability and recyclability, performance in complex water matrices, and limitations related to scale-up and practical implementation. By considering TiO 2 and SnO 2 both individually and in coupled systems, this review relates synthesis and modification strategies to structure-property relationships, photocatalytic performance, and the challenges associated with their application in water treatment.