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?

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

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

Solar driven catalysis on semiconductors to produce clean chemical fuels, such as hydrogen, is widely considered as a promising route to mitigate environmental issues caused by the combustion of fossil fuels and to meet increasing worldwide demands for energy. The major limiting factors affecting the efficiency of solar fuel synthesis include; (i) light absorption, (ii) charge separation and transport and (iii) surface chemical reaction; therefore substantial efforts have been put into solving these problems. In particular, the loading of co-catalysts or secondary semiconductors that can act as either electron or hole acceptors for improved charge separation is a promising strategy, leading to the adaptation of a junction architecture. Research related to semiconductor junction photocatalysts has developed very rapidly and there are a few comprehensive reviews in which the strategy is discussed (A. Kudo and Y. Miseki, Chemical Society Reviews, 2009, 38, 253–278, K. Li, D. Martin, and J. Tang, Chinese Journal of Catalysis, 2011, 32, 879–890, R. Marschall, Advanced Functional Materials, 2014, 24, 2421–2440). This critical review seeks to give an overview of the concept of heterojunction construction and more importantly, the current state-of-the art for the efficient, visible-light driven junction water splitting photo(electro)catalysts reported over the past ten years. For water splitting, these include BiVO4, Fe2O3, Cu2O and C3N4, which have attracted increasing attention. Experimental observations of the proposed charge transfer mechanism across the semiconductor/semiconductor/metal junctions and the resultant activity enhancement are discussed. In parallel, recent successes in the theoretical modelling of semiconductor electronic structures at interfaces and how these explain the functionality of the junction structures is highlighted.

/pdf/visible-light-driven-heterojunction-photocatalysts-for-water-33q4busijg.pdf

Visible-light driven heterojunction photocatalysts for water splitting – a critical review

Novel CdS quantum dot (QD)-coupled graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a chemical impregnation method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different CdS loadings using platinum as a cocatalyst in methanol aqueous solutions. The synergistic effect of g-C3N4 and CdS QDs leads to efficient separation of the photogenerated charge carriers and, consequently, enhances the visible light photocatalytic H2 production activity of the materials. The optimal CdS QD content is determined to be 30 wt %, and the corresponding H2 evolution rate was 17.27 μmol·h–1 under visible light irradiation, ∼9 times that of pure g-C3N4. A possible photocatalytic mechanism of the CdS/g-C3N4 comp...

Synthesis and Efficient Visible Light Photocatalytic Hydrogen Evolution of Polymeric g-C3N4 Coupled with CdS Quantum Dots

A hybrid WO3 /C3 N4 /CoOx system exhibits excellent photoelectrochemical activity for water oxidation. The system comprises a novel three-dimensionally branched WO3 nanosheet array coated with a layer of C3 N4 heterojunctions that are further decorated with CoOx nanoparticles. The photoelectrochemical activity arises from the effective light harvesting due to the 3D structure and "window effect," the excellent charge separation and transport in the heterojunction, and the fast interfacial charge collection and surface reactions due to the large surface area.

Branched WO3 nanosheet array with layered C3 N4 heterojunctions and CoOx nanoparticles as a flexible photoanode for efficient photoelectrochemical water oxidation.

pH-responsive polymer poly(4-vinyl pyridine) is coated on mesoporous silica through the facile “grafting to” method. The grafted polymer nanoshell can work as a pH-sensitive barrier to control the release of trapped molecules from mesoporous silica.

Responsive polymer-coated mesoporous silica as a pH-sensitive nanocarrier for controlled release.

A novel dopant-free TiO(2) photocatalyst (V(o)(.)-TiO(2)), which is self-modified by a large number of paramagnetic (single-electron-trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO(2) precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO(2) precursor, imidazole, and hydrochloric acid are all necessary for the formation of V(o)(.)-TiO(2). Although the synthesis of V(o)(.)-TiO(2) originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X-ray diffraction, XPS, and EPR spectroscopy reveal that the V(o)(.)-TiO(2) material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse-reflectance spectroscopy and photoelectrochemical measurement demonstrate that V(o)(.)-TiO(2) is a stable visible-light-responsive material with photogenerated charge separation efficiency higher than N-TiO(2) and P25 under visible-light irradiation. The V(o)(.)-TiO(2) material exhibits not only satisfactory thermal- and photostability, but also superior photocatalytic activity for H(2) evolution (115 μmol h(-1) g(-1)) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO(2) precursor) and calcination time on the photocatalytic activity and the microstructure of V(o)(.)-TiO(2) were elucidated.

Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

Solar-powered photocatalytic and photoelectrochemical(PEC) water splitting provide two promising strategies toproduce hydrogen for future energy needs. Currently, mostphotocatalytic or PEC water-splitting materials are based ontransition metal oxide, (oxy)nitride, or (oxy)sulfide semi-conductors with suitable band gaps and band positions.

Jikai Liu

Papers

Synthesis and Efficient Visible Light Photocatalytic Hydrogen Evolution of Polymeric g-C3N4 Coupled with CdS Quantum Dots

Branched WO3 nanosheet array with layered C3 N4 heterojunctions and CoOx nanoparticles as a flexible photoanode for efficient photoelectrochemical water oxidation.

Responsive polymer-coated mesoporous silica as a pH-sensitive nanocarrier for controlled release.

Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

Boron carbides as efficient, metal-free, visible-light-responsive photocatalysts.