Graphitic Carbon Nitride‐Based Low‐Dimensional Heterostructures for Photocatalytic Applications

Abstract

Low‐dimensional materials and heterostructure photocatalysts are distinct research topics in artificial photocatalysis. The rational design of photocatalysts considering both aspects has established significant importance due to the fascinating advantages of superior charge carrier transport/transfer and photocatalytic performances. Graphitic carbon nitride (g‐C3N4), a captivating metal‐free and visible light‐active photocatalyst, has drawn interdisciplinary attention in the field of solar energy conversion and pollutant degradation because of its appropriate electronic band structure, excellent physicochemical stability, facile synthesis, and unique layered structure. The g‐C3N4‐based low‐dimensional heterostructures demonstrate various mechanisms for photogenerated charge carrier transfer including type I heterojunction, type II heterojunction, p–n heterojunction, Z‐scheme heterojunction, Schottky junction, and surface plasmon resonance (SPR) effect. Herein, the state‐of‐the‐art g‐C3N4‐based low‐dimensional heterostructure photocatalysts are analyzed to provide an insightful outlook with respect to doping and defect engineering, band structures tuning, and charged carrier dynamics to realize enhanced visible light absorption, improved photoinduced charge carrier transport/transfer, and spatially separated electron–hole pairs for improved photocatalytic performances. Furthermore, the potential application of g‐C3N4‐based low‐dimensional heterostructures for water splitting, CO2 reduction, and pollutant degradation is also presented. Finally, conclusion and invigorating perspective about challenges and opportunities for advanced design of g‐C3N4‐based low‐dimensional heterostructures are briefed.

One‐Step Realization of Crystallization and Cyano‐Group Generation for g‐C3N4 Photocatalysts with Improved H2 Production

“…With increasing calcination temperature, the absorption band at 1200–1600 cm −1 (CN heterocycle) is obviously strengthened and the absorption peaks among 3000–3500 cm −1 (N–H) gradually weaken because DCDA gradually denitrifies and polymerizes into g‐C 3 N 4 (Figure 2D), consistent with the reported results. [ 40,41 ] In addition, the cyano‐group peak (2180 cm −1 ) [ 42 ] first disappears from 200 to 300 °C (Figure 2C), suggesting the effective polymerization of DCDA molecules (with cyano‐groups) into melamine molecules (without cyano‐groups), consistent with the earlier results. With increasing temperature to 550 °C, the cyano‐group peak gradually appears again and then becomes stronger, clearly indicating that Na 2 CO 3 can effectively accelerate the pyrolysis of s‐triazine units, causing the generation of cyano‐groups on the resultant g‐C 3 N 4 surface (Figure 2D).…”

Recent Progress on Carbon Nitride and Its Hybrid Photocatalysts for CO2 Reduction

“…In other words, the band edges of both components are staggered. [ 17,114 ] Under irradiation, both semiconductors can potentially generate electron–hole pairs. Electrons and holes generated at either side of the heterojunction would flow, respectively, to semiconductors B and A. Spatial separation of the photogenerated electron–hole pairs can reduce recombination and increase carrier lifetimes significantly.…”

“…[ 132–137 ] The studies of g‐C 3 N 4 ‐based Z‐scheme heterojunction mainly focuses on 1) electron mediator‐assisted Z‐scheme heterojunction and 2) direct Z‐scheme heterojunction. [ 114 ] Table 1 shows the summary of recently reported g‐C 3 N 4 ‐based photocatalysts with Z‐scheme heterojunction.…”

The Active Sites Engineering of Catalysts for CO2 Activation and Conversion

“…[ 80,81 ] The sufficient electrons around the defect sites have a tendency to be transferred to CO 2 molecules and resulted in the activation of CO 2 by their electron interactions. [ 82,83 ] Defect sites are generally constituted by anion defect sites (O, C, N, and S defect sites), cation defect sites (Zn, Bi, etc.) and even dual defects (ZnO, BiO, etc.).…”