Layered g-C3N4/TiO2 nanocomposites for efficient photocatalytic water splitting and CO2 reduction: a review

Solar-driven photocatalysts for water splitting and CO2 reduction have been widely studied for dealing with environmental pollution and energy sustainability issues. Among the most promising semiconductor photocatalysts, graphitic carbon nitride (g-C3N4) and TiO2 (anatase) with band gaps of ∼2.7 and ∼3.2 eV, respectively, are investigated extensively. However, the high photogenerated carrier recombination efficiency of g-C3N4 and the relatively wide band gap of TiO2 (responsive to ultraviolet light only) are the factors that can lower the photocatalytic activities of the materials. Thus, one of the prevalent strategies is to construct g-C3N4/TiO2 nanocomposites to promote charge carrier separation and to improve photoabsorption in the visible region for attaining efficient utilization of solar energy in photocatalytic water splitting, CO2 reduction, and organic pollutant photodegradation. Here, a comprehensive overview is made on the exploitation of g-C3N4/TiO2 nanocomposites for photocatalytic applications, emphasizing layered heterostructures, for solar-driven H2 generation and CO2 reduction. Challenges in resolving various issues such as low efficiency, low stability, and noble metal cocatalyst dependency, as well as band gap narrowing accompanied reduction in redox ability of the g-C3N4/TiO2 nanocomposites, are discussed.