As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

A review on g-C3N4-based photocatalysts

Photocatalysis is considered as one of the promising routes to solve the energy and environmental crises by utilizing solar energy. Graphitic carbon nitride (g-C3N4) has attracted worldwide attention due to its visible-light activity, facile synthesis from low-cost materials, chemical stability, and unique layered structure. However, the pure g-C3N4 photocatalyst still suffers from its low separation efficiency of photogenerated charge carriers, which results in unsatisfactory photocatalytic activity. Recently, g-C3N4-based heterostructures have become research hotspots for their greatly enhanced charge carrier separation efficiency and photocatalytic performance. According to the different transfer mechanisms of photogenerated charge carriers between g-C3N4 and the coupled components, the g-C3N4-based heterostructured photocatalysts can be divided into the following categories: g-C3N4-based conventional type II heterojunction, g-C3N4-based Z-scheme heterojunction, g-C3N4-based p–n heterojunction, g-C3N4/metal heterostructure, and g-C3N4/carbon heterostructure. This review summarizes the recent significant progress on the design of g-C3N4-based heterostructured photocatalysts and their special separation/transfer mechanisms of photogenerated charge carriers. Moreover, their applications in environmental and energy fields, e.g., water splitting, carbon dioxide reduction, and degradation of pollutants, are also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced g-C3N4-based heterostructured photocatalysts are presented.

g-C3N4-Based Heterostructured Photocatalysts

S-Scheme Heterojunction Photocatalyst

Nowadays, the increasing CO2 emissions have attracted widespread attentions and it is necessary to reduce CO2 emissions to solve the global warming problem. So photocatalytic reduction of CO2 into chemical fuels is a promising strategy. Here, a Z-scheme porous g-C3N4/Sn2S3-diethylenetriamine (Pg-C3N4/Sn2S3-DETA) composite without an electron intermediary is designed. Photocatalytic performance of the as-fabricated samples is investigated on the basis of photocatalytic CO2 reduction (PCR) to form CH4 and CH3OH. We find that the Z-scheme heterostructure photocatalysts show a higher PCR performance than Pg-C3N4 and Sn2S3-DETA. An optimized Pg-C3N4/Sn2S3-DETA heterostructure sample displays high CH4 production rate of 4.84 μmol h−1 g−1 and CH3OH-production rate of 1.35 μmol h−1 g−1 with 5% Pg-C3N4 content. The superior PCR performance could be ascribed to the special structure of a direct Z-scheme Pg-C3N4/Sn2S3-DETA photocatalyst, which is beneficial to efficient separation of electron-hole pairs. Density functional theory (DFT) calculation further confirms the presence of direct Z-scheme mechanism. This Z-scheme heterostructure photocatalyst with superior performance may inaugurate the perspective on a new promising hierarchy of materials on CO2 photoreduction.

All-solid-state artificial Z-scheme porous g-C3N4/Sn2S3-DETA heterostructure photocatalyst with enhanced performance in photocatalytic CO2 reduction

Design of a direct Z-scheme photocatalyst: Preparation and characterization of Bi2O3/g-C3N4 with high visible light activity

Step-scheme (S-scheme) photocatalytic system has been considered as an effective method for solar energy conversion by utilizing broadband solar energy, realizing easy separation of photoexcited carriers and strong redox ability. Herein, the novel ternary Ni2P cocatalysted two-dimensional (2D)/2D SnNb2O6/CdS-diethylenetriamine (SNO/CdS-D) system was designed and fabricated. The S-scheme SNO/CdS-D heterostructure gives photocatalytic hydrogen production of 7808 μmol g−1 h−1, which is about 130.13 and 2.35 times stronger than that of SNO and CdS-D. Further, noble-metal-free Ni2P cocatalyst is decorated into SNO/CdS-D heterostructure, the photocatalytic hydrogen evolution performance could be enhanced to 11,992 μmol g−1 h−1. Additionally, XPS analysis and DFT calculation revealed the carriers moves from CdS-D to SNO and then to Ni2P in the Ni2P-SNO/CdS-D nanocomposite. This work will give a reliable and clear insight into the interface and surface design of the 2D catalysts and offer a broadband photocatalytic hydrogen evolution process without noble metal cocatalysts.

Noble-metal-free Ni2P modified step-scheme SnNb2O6/CdS-diethylenetriamine for photocatalytic hydrogen production under broadband light irradiation

The poor utilization of visible light and the speedy recombination of photoexcited carriers limit the further development of carbon nitride polymer (CN) photocatalysts. It is a valid means for enhancing the photocatalytic ability to ameliorate the electronic and physicochemical properties via modifying the structure of CN. The sulfur- and chlorine-codoped graphite CN (S/Cl-CN) was successfully fabricated with low-cost ammonium chloride and thiourea as precursors. The introduction of Cl atoms will establish interlayer channels to promote interlayer charge migration and up-shifted conduction-band level. S atom is appropriate to be incorporated into the CN framework to replace N atom, which is beneficial to adjust the band gap. Then, inorganic-organic CdSe-diethylenetriamine (D) grown in situ are employed to fabricate a S/Cl-CN/CdSe-D heterojunction. S/Cl-CN/CdSe-D heterojunction exhibits greater hydrogen evolution activity compared to CN, S-CN, Cl-CN, S/Cl-CN, CdSe-D and CN/CdSe-D. Finally, Step-scheme (S-scheme) photocatalytic mechanism based on S/Cl-CN/CdSe-D heterostructure was proposed.

Two-dimensional sulfur- and chlorine-codoped g-C3N4/CdSe-amine heterostructures nanocomposite with effective interfacial charge transfer and mechanism insight

Jinfeng Zhang

Papers

All-solid-state artificial Z-scheme porous g-C3N4/Sn2S3-DETA heterostructure photocatalyst with enhanced performance in photocatalytic CO2 reduction

Design of a direct Z-scheme photocatalyst: Preparation and characterization of Bi2O3/g-C3N4 with high visible light activity

Noble-metal-free Ni2P modified step-scheme SnNb2O6/CdS-diethylenetriamine for photocatalytic hydrogen production under broadband light irradiation

Two-dimensional sulfur- and chlorine-codoped g-C3N4/CdSe-amine heterostructures nanocomposite with effective interfacial charge transfer and mechanism insight

Step-scheme porous g-C3N4/Zn0.2Cd0.8S-DETA composites for efficient and stable photocatalytic H2 production