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

Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

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 series of composites of graphitic carbon nitride and in situ nitrogen-doped titanium dioxide (g-C3N4-N-TiO2) were prepared by a simple pyrolysis process of urea and Ti(OH)4. The obtained products were characterized by means of X-ray diffraction, FT-IR transmission spectroscopy, electron microscopy, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, etc. Compared with g-C3N4 and commercial P25, the as-prepared photocatalysts exhibit enhanced photocatalytic performance for photoreduction of CO2 in the presence of water vapor at room temperature. It was found that the mass ratios of urea to Ti(OH)4 in precursors play a role in formation of the composites, and the high ratios of urea to Ti(OH)4 result in the composites of g-C3N4 and N-doped TiO2, while low ratios only result in N-doped TiO2. An interesting selectivity of photocatalytic products displayed that N-doped TiO2 samples were related to CH4 and CO generation, while g-C3N4 and N-TiO2 composites were related to CO generation, and the product selectivity may originate from the formed g-C3N4. The highest amount of CO (14.73 μmol) was obtained on the optimized photocatalyst under 12 h light irradiation, which is four times of that over commercial P25. Based on these results, a possible mechanism for the enhanced photocatalytic performance was proposed.

Facile in situ synthesis of graphitic carbon nitride (g-C3N4)-N-TiO2 heterojunction as an efficient photocatalyst for the selective photoreduction of CO2 to CO

Desulfurization of dibenzothiophene by chemical oxidation and solvent extraction with Me3NCH2C6H5Cl·2ZnCl2 ionic liquid

Solution combustion synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl2O4 nanopowders

Preparation of Ca-doped LaFeO3 nanopowders in a reverse microemulsion and their visible light photocatalytic activity

A novel and highly efficient three-component Au@CdS/MIL-101 heterostructure was successfully synthesized. The MIL-101(Cr) with large surface area was introduced as a matrix for the well-dispersed growth of Au nanoparticles, and the CdS was selectively coated on the Au nanoparticles. Under visible light irradiation, the Au@CdS/MIL-101 heterostructure presents superior hydrogen evolution rate over the pure CdS, CdS/MIL-101 and Au/MIL-101 composites. The Au@CdS/MIL-101 heterostructure exhibits an unusual H2 production rate of 250 μmol h−1/10 mg, which is 2.6 times higher than that of pure CdS. The performance enhancement of Au@CdS/MIL-101 heterostructure can be attributed to the following reasons: (i) the large surface area of MIL-101(Cr) can effectively disperse the Au and CdS nanoparticles, resulting in more active adsorption sites and reaction centers. (ii) the strong surface plasmon resonance absorption of Au could accelerate the charge transfer and extend the light response spectrum of CdS. This three-component Au@CdS/MIL-101 heterostructure combining the large surface area of MOF and the surface plasmon resonance of Au into a single structure may provide a potential way to design highly efficient and solar-energy-harvesting photocatalysts.

Ying Liu

Papers

Facile in situ synthesis of graphitic carbon nitride (g-C3N4)-N-TiO2 heterojunction as an efficient photocatalyst for the selective photoreduction of CO2 to CO

Desulfurization of dibenzothiophene by chemical oxidation and solvent extraction with Me3NCH2C6H5Cl·2ZnCl2 ionic liquid

Solution combustion synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl2O4 nanopowders

Preparation of Ca-doped LaFeO3 nanopowders in a reverse microemulsion and their visible light photocatalytic activity

Controlled fabrication and enhanced visible-light photocatalytic hydrogen production of Au@CdS/MIL-101 heterostructure