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

The current rapid industrial development causes the serious energy and environmental crises. Photocatalyts provide a potential strategy to solve these problems because these materials not only can directly convert solar energy into usable or storable energy resources but also can decompose organic pollutants under solar-light irradiation. However, the aforementioned applications require photocatalysts with a wide absorption range, long-term stability, high charge-separation efficiency and strong redox ability. Unfortunately, it is often difficult for a single-component photocatalyst to simultaneously fulfill all these requirements. The artificial heterogeneous Z-scheme photocatalytic systems, mimicking the natural photosynthesis process, overcome the drawbacks of single-component photocatalysts and satisfy those aforementioned requirements. Such multi-task systems have been extensively investigated in the past decade. Especially, the all-solid-state Z-scheme photocatalytic systems without redox pair have been widely used in the water splitting, solar cells, degradation of pollutants and CO2 conversion, which have a huge potential to solve the current energy and environmental crises facing the modern industrial development. Thus, this review gives a concise overview of the all-solid-state Z-scheme photocatalytic systems, including their composition, construction, optimization and applications.

All-Solid-State Z-Scheme Photocatalytic Systems

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

The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C 3 N 4 -WO 3 photocatalysts with different main parts of C 3 N 4 or WO 3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C 3 N 4 -WO 3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C 3 N 4 -WO 3 photocatalyst is WO 3 (namely g-C 3 N 4 /WO 3 ), the transport process of the photogenerated electrons and holes adopts the generic band–band transfer. Meanwhile, g-C 3 N 4 is covered by WO 3 powder, and the role of g-C 3 N 4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO 3 -g-C 3 N 4 photocatalyst is g-C 3 N 4 (namely WO 3 /g-C 3 N 4 ), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly.

Yingfei Hu

Papers

Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3

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

Ball milled h-BN: an efficient holes transfer promoter to enhance the photocatalytic performance of TiO2.

Preparation and characterization of direct Z-scheme photocatalyst Bi2O3/NaNbO3 and its reaction mechanism

Fabrication and characterization of novel Z-scheme photocatalyst WO3/g-C3N4 with high efficient visible light photocatalytic activity