A comprehensive review on N-metallic photocatalysts and photoreactor designs for enhanced photocatalytic reduction of carbon dioxide to value-added fuels

Sustainability is the key to achieving a cleaner environment by advancing renewable energy technologies, reducing carbon emissions, and creating a more resilient future. This goal has led to extensive research in the photocatalytic reduction of CO₂ to produce renewable solar fuels. The most essential requirements for efficient photocatalysis are the selection of an ideal photocatalyst and the design of an effective photoreactor. This review mainly focuses on N-metallic photocatalysts, which have become a viable strategy due to their synergistic, structural, and optical properties. Their composition, synthesis techniques such as post-synthetic modifications and in-synthetic modifications, and various metal combinations in enhancing charge separation, catalytic efficiency, and optimization of light absorption are discussed in detail. Additionally, photoreactors and their different designs, including two-phase and three-phase reactors such as fixed bed reactors, slurry reactors, microreactors, membrane reactors, and hybrid systems, are studied. The combination of multi-metallic photocatalysts with advanced reactors is analysed in detail, with its advantages and challenges to provide deep insights into the possibility for scalable and effective solar fuel conversion. Finally, the key challenges, and future directions in the development of efficient photocatalytic systems are discussed in order to provide a sustainable route toward solar fuels production by CO₂ utilization.