Unfolding the significance of metal oxides for photocatalytic sustainable water splitting combined with organic pollutants

Impactful uses of nanomaterials are essential for addressing global energy and environmental issues, primarily via photocatalytic sustainable water splitting, which provides a sustainable pathway for the creation of hydrogen, and dye degradation, which breaks down hazardous dye wastewater pollutants. The scalable characteristics of nanomaterials, particularly their precise bandgap energy, increased surface area, and effective charge separation capability, have made them significant contributors. The present review examines four different kinds of nanocomposites that have shown enormous potential in water splitting and dye degradation: those based on zinc, iron, titanium, and cerium. Zinc oxide's photocatalytic activity shifted from the ultraviolet to the visible spectrum when dopants were added or when it was mixed with other oxides, such as copper. When combined with substances like graphene, iron oxide—which is well-known for producing hydroxyl radicals—becomes very efficient at water splitting and dye degradation. Despite being limited by UV light, titanium dioxide performs better when paired with reduced graphene oxide or silver particles, which boosts its effectiveness in both processes when exposed to visible light. Lastly, cerium oxide's distinct redox characteristics enable it to create efficient heterojunctions with substances like ZnO and TiO₂, improving charge transfer and lowering recombination. Moreover, this review provides attention to their dual use and guides how to optimize photocatalytic efficiency for environmental remediation and sustainable energy generation.