A Comprehensive Review of Graphitic Carbon Nitride (g-C(3)N(4))–Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C(3)N(4) has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C(3)N(4), such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C(3)N(4)–metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C(3)N(4) and then, we discussed the combination of g-C(3)N(4) with various metal oxides such as TiO(2), ZnO, FeO, Fe(2)O(3), Fe(3)O(4), WO(3), SnO, SnO(2), etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO(2) reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C(3)N(4) to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C(3)N(4)–metal-oxide-based heterojunctions.