Photocatalytic CO₂ Reduction with 100% CO Selectivity Using In₂O₃/CuO/g-C₃N₄ Ternary Composites

The key challenge in photocatalytic CO 2 reduction is to develop photocatalysts with high performance and ultrastability. Graphitic carbon nitride (g-C 3 N 4 ) is a promising semiconductor photocatalyst due to its low cost, simple preparation, and stability. However, bulk g-C 3 N 4 exhibits limitations such as low specific surface area, limited visible light absorption, and rapid recombination of photogenerated electron–hole pairs. Coupling multiple semiconductors enhances electron–hole separation, prolongs carrier lifetime, and improves interfacial charge transfer efficiency. Here, In 2 O 3 /CuO/g-C 3 N 4 ternary composites are synthesized via thermal polymerization and characterized by using XRD, TEM, XPS, and UV–vis spectroscopy. The ternary composite achieves superior photogenerated carrier separation compared with In 2 O 3 /g-C 3 N 4 and CuO/g-C 3 N 4 binary composites. In photocatalytic CO 2 reduction tests, In 2 O 3 /CuO/g-C 3 N 4 demonstrates higher catalytic activity with a CO yield of 890.50 μmol/g/h and a 100% CO selectivity.