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

A copy of Guangbo jiemu bao [Broadcast Program Report] was being passed from hand to hand among a group of young people eager to be the first to read the article introducing the program "What Is Revolutionary Love?" It said: "… Young friends, you are certainly very concerned about this problem'. So, we would like you to meet the young women workers Meng Xiaoyu and Meng Yamei and the older cadre Miss Feng. They are the three leading characters in the short story ‘The Place of Love.’ Through the description of the love lives of these three, the story induces us to think deeply about two questions that merit further examination.

This is How the Discussion Started

A novel metal-free oxygen doped porous graphitic carbon nitride (OA-g-C3N4) was synthesized by condensation of oxalic acid and urea. The 40% OA-g-C3N4 catalyst can degrade bisphenol A (15 mg L−1) in 240 min with a mineralization rate as high as 56%. The markedly higher visible-light-driven oxidation activity of OA-g-C3N4 is attributed to the porous morphology and unique electrical structure. The porous structure of OA-g-C3N4 provides more active sites for adsorption and degradation of pollutants. Moreover, oxygen atoms in the tri-s-triazine units help to extend sufficient light absorption range up to 700 nm, improve the separation of charge-carriers and alter the position of valence band (VB) and conduction band (CB). The VB edge shifts from 1.95 eV to 2.46 eV due to the incorporation of O atoms, which leads to the change of active species in the photocatalytic reaction. Trapping experiment shows that superoxide radicals play the major role in the photocatalytic degradation of BPA on g-C3N4, while hydroxyl radical is the dominant active species in the photocatalytic degradation process over 40% OA-g-C3N4. This study presents a simple, economical and environment-friendly method to synthesized oxygen doped porous graphitic carbon nitride.

One step synthesis of oxygen doped porous graphitic carbon nitride with remarkable improvement of photo-oxidation activity: Role of oxygen on visible light photocatalytic activity

A g-C3N4–CdS composite catalyst with high visible-light-driven catalytic activity and photostability for methylene blue degradation

Visible light photocatalytic nitrogen fixation, as a low-cost and mild technology, needs efforts to explore an economical photocatalyst with high activity and stability. In this study, a metal-free black phosphorus (BP) nanosheets-decorated graphitic carbon nitride nanosheets photocatalyst (BPCNS) has been successfully synthesized. With BP acting as the cocatalyst, BPCNS shows excellent performance in both visible light nitrogen photofixation and pollutant reduction owing to the increased number of excited electrons and enhanced separation efficiency of charge carriers through formation of C P covalent bonds. Besides, the chemical structure of the BPCNS with optimal content of BP remains the same after exposure to air for 30 days or after five cycles of photocatalytic nitrogen fixation, since the occupation of the lone pairs on phosphorus atoms largely improves the chemical stability of BP.

Metal-free black phosphorus nanosheets-decorated graphitic carbon nitride nanosheets with CP bonds for excellent photocatalytic nitrogen fixation

Graphitic carbon nitride (g-C3N4) nanosheets were synthesized by exfoliating bulk g-C3N4 with a thermal treatment under H2 for the first time. The g-C3N4 nanosheets exhibited a 2D structure with a thickness of 2 nm, a high surface area and a low recombination rate of photogenerated electron–hole pairs, enhancing the visible light photocatalytic activity.

Fabrication of an exfoliated graphitic carbon nitride as a highly active visible light photocatalyst

Solar-driven distillation and desalination are promising technologies for large-scale water purification. Internal micro-channels are critical for the performance of a steam generation device in consideration of thermal management and water transportation. Here, we designed novel porous three-dimensional carbon foams (CFs) with unique interconnected channels and rough surfaces via alkali activation of naturally abundant wood. Promoted by the rough surface, the CFs can harvest more than 97% of the energy of the solar spectrum. The hydrophilic interconnected micro-channels of the CFs enhance water transportation and heat localization. Benefiting from these advantages, the highest steam generation efficiency of the CFs reaches 80.1% under 1 kW m−2. In addition, the CFs also show high stability under harsh conditions and high activity in desalination of seawater. With the unique interconnected micro-channels, this porous carbon device offers a scalable, cost-effective and efficient choice for solar steam generation.

Chenmin Xu

Papers

One step synthesis of oxygen doped porous graphitic carbon nitride with remarkable improvement of photo-oxidation activity: Role of oxygen on visible light photocatalytic activity

A g-C3N4–CdS composite catalyst with high visible-light-driven catalytic activity and photostability for methylene blue degradation

Metal-free black phosphorus nanosheets-decorated graphitic carbon nitride nanosheets with CP bonds for excellent photocatalytic nitrogen fixation

Fabrication of an exfoliated graphitic carbon nitride as a highly active visible light photocatalyst

Porous three-dimensional carbon foams with interconnected microchannels for high-efficiency solar-to-vapor conversion and desalination