Bismuth-based photocatalysts for sustainable water remediation and solar hydrogen generation: State-of-the-art and future directions

The rapid increase in environmental pollution and global energy demand has intensified the search for sustainable technologies capable of simultaneously addressing wastewater contamination and clean fuel generation. Photocatalysis has emerged as a promising strategy because it utilizes solar energy to drive redox reactions under mild operating conditions. Among various photocatalytic materials, bismuth-based photocatalysts have attracted significant attention due to their narrow band gaps, excellent visible-light absorption, layered crystal structures, chemical stability, and tuneable electronic properties. The review discusses the structural and functional characteristics of major bismuth-based systems. Emphasis is placed on advanced modification strategies such as heterojunction construction, metal/non-metal doping, and oxygen-vacancy defect regulation, all of which significantly improve charge separation efficiency, light harvesting and surface reaction kinetics. Recent ternary and Z-scheme systems have demonstrated excellent capability for degrading organic pollutants while concurrently enhancing hydrogen production rates under visible-light irradiation. The review further analyzes the photocatalytic mechanisms governing reactive oxygen species generation, interfacial charge migration and proton reduction pathways. Despite major progress, several limitations remain, including photo-corrosion, charge recombination, low quantum efficiency and challenges in scaling laboratory results to practical reactors. Future perspectives highlight defect-controlled nanostructures, noble-metal-free cocatalysts, real wastewater applications and pilot-scale solar reactor development. Overall, bismuth-based photocatalysts offer strong potential as multifunctional materials for integrating environmental remediation with renewable hydrogen production, supporting the transition toward sustainable energy and water treatment technologies.