Synthesis Strategies and Photocatalytic Efficiency of Bi2O3 based Nanostructures: A Comprehensive Review on Recent Progress and Applications in Dye Degradation, CO2 Reduction and Hydrogen Generation

Bismuth oxide (Bi2O3) based nanomaterials have emerged as promising visible light driven photocatalysts for different applications like wastewater treatment, CO2 reduction and hydrogen generation. This is possible due to their suitable band structure, strong visible light absorption and chemical stability. This review presents a critical assessment of recent advances in the synthesis, modification and photocatalytic applications of Bi2O3 nanostructures for the degradation of organic dyes, pharmaceutical residues and other emerging pollutants. Major synthesis routes, such as sol-gel, hydrothermal, solvothermal, chemical precipitation and green synthesis, are discussed in relation to their effects on crystal structure, morphology, surface properties and photocatalytic performance. Strategies to address the inherent limitations of pristine Bi2O3 are examined, with particular emphasis on elemental doping and heterojunction engineering. Recent developments in Bi2O3-based composites incorporating semiconductors such as TiO2, g-C3N4 and MoS2 are reviewed, with attention to interfacial charge transfer and improved charge-carrier separation. The fundamental aspects of photocatalysis, such as charge-carrier dynamics, reactive oxygen species formation and interfacial electron-transfer processes, are critically discussed. The scope of the review extends beyond pollutant degradation to the application of Bi2O3-based nanostructures in photocatalytic CO2 reduction and water splitting, with particular focus on solar-driven hydrogen generation, material modification and surface reaction pathways. The existing limitations in photocatalytic efficiency, structural stability and practical applicability are assessed, along with future research directions for the design of efficient, durable and scalable Bi2O3-based photocatalysts for environmental remediation and solar energy conversion.