Reduction reactions by heterogeneous photocatalysis: From CO2 valorization to environmental remediation and valuable compounds synthesis

After a brief general presentation of strategies aimed at improving the efficiency of the photocatalytic process by modifying the photocatalyst and/or experimental reaction conditions, the attention will be focused on different photoreduction reactions where the reduction products are often of strategic and/or economic importance. These include the reduction of CO 2 in both the gas–solid and liquid–solid systems, the production of H 2 with its potential implications for clean energy generation (only briefly, given the vastness of the topic, which deserves a separate discussion), the reduction of NO 3 – to NO 2 – , nitrobenzenes to the corresponding anilines, and 4-nitrophenol to 4-aminophenol. Reactions that produce a less toxic and polluting product, such as the transformation of Cr(VI) to Cr(III), will also be highlighted. Notably, we emphasized the convenience in the contemporary occurrence of both oxidation and reduction processes by exploiting holes and electrons generated following the photocatalyst’s irradiation to valorize pollutants/waste products to valuable compounds.