Design of Semiconductor-Based Photocatalysts for CO2 Reduction and Green Hydrogen Production to Advance Environmental Sustainability

The global energy crisis and climate change constitute immense challenges, largely due to rising CO2 emissions and dependence on fossil fuels. Transitioning to low-carbon, renewable technologies is crucial for the long-term security of energy and achieving climate goals. Thus, photocatalytic CO2 reduction and production of hydrogen (H2) have emerged as solutions, providing dual advantages of mitigating greenhouse gases (GHG) and generating sustainable solar fuels. Semiconductor-based photocatalysts are vital, facilitating light-driven redox reactions that convert carbon dioxide into useful chemicals and split water to produce hydrogen. Various material classes emerge from recent advances, with traditional oxides such as ZnO and TiO2 and advanced systems such as graphitic carbon nitride, perovskites, and metal- organic frameworks, including emerging nanostructures ranging from single-atom catalysts to quantum dots, among others. Design strategies, namely heterostructure formation, band gap engineering, and co-catalyst integration, have improved charge separation, light harvesting, and product selectivity. Evidence from literature also demonstrates significant progress in the enhancement of photocatalytic activity and stability, as efficiencies approach practical thresholds in certain systems. Yet, some challenges remain, such as limited long-term durability, rapid charge recombination, barriers to large-scale implementation, and competing side reactions. Future perspectives also emphasize the importance of integrating artificial photosynthesis, machine learning-driven catalyst discovery, earth-abundant materials, and techno-economic & life-cycle analyses to ensure industrial and environmental viability. Semiconductor- based photocatalysis generally presents a pathway for achieving carbon-neutral energy, as long as ongoing research strives to bridge the gap between laboratory practices and scalable applications in different industries.