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

Polymeric graphitic carbon nitride materials (for simplicity: g-C(3)N(4)) have attracted much attention in recent years because of their similarity to graphene. They are composed of C, N, and some minor H content only. In contrast to graphenes, g-C(3)N(4) is a medium-bandgap semiconductor and in that role an effective photocatalyst and chemical catalyst for a broad variety of reactions. In this Review, we describe the "polymer chemistry" of this structure, how band positions and bandgap can be varied by doping and copolymerization, and how the organic solid can be textured to make it an effective heterogenous catalyst. g-C(3)N(4) and its modifications have a high thermal and chemical stability and can catalyze a number of "dream reactions", such as photochemical splitting of water, mild and selective oxidation reactions, and--as a coactive catalytic support--superactive hydrogenation reactions. As carbon nitride is metal-free as such, it also tolerates functional groups and is therefore suited for multipurpose applications in biomass conversion and sustainable chemistry.

Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry

A review on g-C3N4-based photocatalysts

A facile synthetic strategy for nitrogen-deficient graphitic carbon nitride (g-C3 Nx ) is established, involving a simple alkali-assisted thermal polymerization of urea, melamine, or thiourea. In situ introduced nitrogen vacancies significantly redshift the absorption edge of g-C3 Nx , with the defect concentration depending on the alkali to nitrogen precursor ratio. The g-C3 Nx products show superior visible-light photocatalytic performance compared to pristine g-C3 N4 .

Alkali-Assisted Synthesis of Nitrogen Deficient Graphitic Carbon Nitride with Tunable Band Structures for Efficient Visible-Light-Driven Hydrogen Evolution.

Cyclohexanone is an important intermediate in the manufacture of polyamides in chemical industry, but direct selective hydrogenation of phenol to cyclohexanone under mild conditions is a challenge....

Highly selective hydrogenation of phenol and derivatives over a Pd@carbon nitride catalyst in aqueous media

Oxidation of hydrocarbons with clean oxidants is a crucial process for the development of products ranging from commodity chemicals to speciality pharmaceuticals. While selective oxidation is commonplace in nature and mainly occurs through a broad variety of cytochrome P450 enzymes, the synthetic catalysts that have been identified so far are relatively inactive with aliphatic C–H bonds. We present here a promising strategy for modifying polymeric graphitic carbon nitride by replacing the carbon atoms in the “melon” network using boron. 11B solid-state MAS NMR and XPS spectral studies confirmed the incorporation of the boron atoms in the polymeric g-C3N4 as well as the degree of doping, while X-ray diffraction and IR indicated that the characteristic structural properties of polymeric g-C3N4, such as the original graphitic structure, and the C–N heterocycle units were essentially retained. The boron-doped polymeric carbon nitride shows promising catalytic activity and high selectivity (≥87%) in the oxidation of benzylic aromatics. The use of this metal-free, organic, semiconducting polymer as an oxidation catalyst and H2O2 or O2 as oxidants makes the reactions interesting from both an economic and environmental point of view. It is also hoped that our findings will stimulate further investigation and will open new possibilities to form hybrid carbon nitride materials with new and probably exciting applications.

Synthesis of boron doped polymeric carbon nitride solids and their use as metal-free catalysts for aliphatic C–H bond oxidation

This article reports the successful synthesis of mesoporous hydroxyapatite, Ca10(PO4)6(OH)2
(denoted HA) using cationic surfactant as the template. The wide-angle (2θ > 10°) diffraction data revealed characteristic peaks of HA, where a hexagonal lattice structure can be deduced. The lattice structure is found in space group P63/m, the parameters of which are in excellent agreement with reference data; i.e.a
=
b
= 0.9418 nm, c
= 0.6884 nm. For small angle diffraction (2θ < 10°), the characteristic peaks occur at 2θ values of 3.30, 5.75, 7.25 and 8.30°, indicating the presence of atomic planes with a periodical spacing of 2.677 nm. Nitrogen adsorption indicated a pore size distribution of approximately 3 nm, and a corresponding pore volume of 0.0113 cm3 g−1, hence the volume ratio of the mesopores was found to be ∼0.036. SEM micrographs reveal a rod-like structure of HA, possessing a thickness of about 50–100 nm and length ranging from 500 to 1000 nm, while TEM micrographs revealed that nano-channels are formed within the rod-like structure. These nano-channels align in a lengthwise direction within the rods, consistent with the cavities being generated by the removal of “organic” CTAB templating structure during calcination. The channels have dimensions of around 3.5 nm and the spaces between the nano-channels are filled with an ordered crystalline HA structure. Comparing the pore size and the spacing between neighboring channels, the pore volume ratio of each rod was calculated to be ∼0.029, which is in agreement with the result from gas adsorption. A probable mechanism is that CTAB–PO43− mixtures form rod-like micelles, which contain many PO43− groups on the surface, and in the presence of Ca2+, Ca9(PO4)6 clusters are preferentially condensed on the rod-shaped micellar surface due to the conformation compatibility between the identical hexagonal shapes of the micelles and Ca9(PO4)6 clusters. The micelles act as nucleating points for the growth of HA crystals. During the thermal incubation stage, CTAB–HA complexes are produced and they coalesce to form a stable three-dimensional rod-like structure. The morphology of the final product shows about 10 layers of HA crystal grows on one micelle during the reaction in water.

Hydroxyapatite nanostructure material derived using cationic surfactant as a template

Graphitic carbon nitride (g-C 3 N 4 ) and N-hydroxy compounds can function as a non-metal photocatalytic system to activate O 2 for the selective allylic oxidation under mild conditions, avoiding the employment of any metal derivative or organic oxidizing agents. Interestingly, the novel photocatalytic system affords a remarkably high selectivity towards the formation of aldehydes, especially in the oxidation of toluene. By combining the unique nature of g-C 3 N 4 (surface basicity, semiconductor features, high stability) and the remarkable catalytic oxidation reactivity of nitroxyl radicals, this photocatalytic system opens up a mild and efficent access for C―H bond activation.

Visible‐Light‐Induced Metal‐Free Allylic Oxidation Utilizing a Coupled Photocatalytic System of g‐C3N4 and N‐Hydroxy Compounds

Hydrothermal carbonization (HTC) of carbohydrates is an economic and sustainable technique for the synthesis of carbon materials. However, the assembly of carbohydrates with soft templates is susceptible to hydrolysis, degradation, and relatively high HTC temperature. Thus, it is still challenging to control the HTC/soft templating of carbohydrates and prepare mesoporous carbon with specific properties. Herein, a simple and effective self-transformation strategy is proposed to improve the HTC/soft templating, which introduces an insoluble melamine sulfate into the formation processes. Mechanism studies indicate that the assembly of d-fructose with soft templates is greatly promoted by coassembling with the gradually released melamine sulfate. As a result, carbonaceous composites with a flower-like structure and N-doping were synthesized. Further, ordered mesoporous carbons with N-doping are obtained after calcination. The obtained carbons exhibit outstanding ability for heavy metal adsorption and supercap...

Jia Yao

Papers

Highly selective hydrogenation of phenol and derivatives over a Pd@carbon nitride catalyst in aqueous media

Synthesis of boron doped polymeric carbon nitride solids and their use as metal-free catalysts for aliphatic C–H bond oxidation

Hydroxyapatite nanostructure material derived using cationic surfactant as a template

Visible‐Light‐Induced Metal‐Free Allylic Oxidation Utilizing a Coupled Photocatalytic System of g‐C3N4 and N‐Hydroxy Compounds

Controlled Synthesis of Ordered Mesoporous Carbohydrate-Derived Carbons with Flower-like Structure and N-Doping by Self-Transformation