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?

A review on g-C3N4-based photocatalysts

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Engineering heterogeneous semiconductors for solar water splitting

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

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Graphene in Photocatalysis: A Review

Semiconductor polymeric graphitic carbon nitride (g-C3N4) photocatalysts have attracted dramatically growing attention in the field of the visible-light-induced hydrogen evolution reaction (HER) because of their facile synthesis, easy functionalization, attractive electronic band structure, high physicochemical stability and photocatalytic activity. This review article presents a panorama of the latest advancements in the rational design and development of g-C3N4 and g-C3N4-based composite photocatalysts for HER application. Concretely, the review starts with the development history, synthetic strategy, electronic structure and physicochemical characteristics of g-C3N4 materials, followed by the rational design and engineering of various nanostructured g-C3N4 (e.g. thinner, highly crystalline, doped, and porous g-C3N4) photocatalysts for HER application. Then a series of highly efficient g-C3N4 (e.g., metal/g-C3N4, semiconductor/g-C3N4, metal organic framework/g-C3N4, carbon/g-C3N4, conducting polymer/g-C3N4, sensitizer/g-C3N4) composite photocatalysts are exemplified. Lastly, this review provides a comprehensive summary and outlook on the major challenges, opportunities, and inspiring perspectives for future research in this hot area on the basis of pioneering works. It is believed that the emerging g-C3N4-based photocatalysts will act as the “holy grail” for highly efficient photocatalytic HER under visible-light irradiation.

Semiconductor polymeric graphitic carbon nitride photocatalysts: the “holy grail” for the photocatalytic hydrogen evolution reaction under visible light

Novel p-n junction photocatalysts nitrogen doped graphene quantum dots (NGQDs)-BiOI/MnNb2O6 have been prepared via hydrothermal method for the environmental remediation. The photocatalytic activity of as-prepared photocatalysts was evaluated by the degradation of different antibiotics such as tetracycline (TC), oxytetracyline, ciprofloxacin and doxycycline. Compared with single MnNb2O6 and BiOI, the hybrid materials (NGQDs-BiOI/MnNb2O6) could significantly enhance photocatalytic activity. Meanwhile, both the BiOI/MnNb2O6 ratio (Bi/Mn ratio) and the amount of NGQDs displayed important influence on the antibiotics degradation. In addition, the 5%NGQDs-Bi/Mn sample performed the optimum photocatalytic degradation toward TC (87.2%) within 60 min. By further studies based on the electron spin resonance (ESR) and active species trapping experiments, this enhanced photocatalytic property could be ascribed to high charge carrier mobility of NGQDs and the p-n junction photocatalytic systems, which greatly promoted efficient separation of charge carriers.

Fabrication of nitrogen doped graphene quantum dots-BiOI/MnNb2O6 p-n junction photocatalysts with enhanced visible light efficiency in photocatalytic degradation of antibiotics

Promoting visible-light-induced photocatalytic degradation of tetracycline by an efficient and stable beta-Bi2O3@g-C3N4 core/shell nanocomposite

In-situ construction of hierarchical CdS/MoS2 microboxes for enhanced visible-light photocatalytic H2 production

The development of efficient visible-light-driven photocatalysts for water splitting has drawn much attention. Herein, we demonstrated a novel H2-producing photocatalytic system that employed nitrogen doped graphene quantum dots (NGQDs)-ZnNb2O6/g-C3N4 heterostructures as the hydrogen evolving catalysts. The as-prepared NGQDs-ZnNb2O6/g-C3N4 heterostructures were favorable for light harvesting and charge separation, and showed highly efficient photocatalytic performance for water splitting into hydrogen. Results showed that both the ZnNb2O6/g-C3N4 (Zn/CN) mole ratio and the amount of NGQDs displayed important influence for H2 production. Moreover, the optimum synthesis conditions of the Zn/CN mole ratio (1/7) and the amount of NGQDs (5%) were both obtained, and the corresponding 5%NGQDs-Zn/7CN sample performed a much higher hydrogen-evolution rate of 340.9 μmol h−1 g−1. By the further studies, the enhanced photocatalytic activity could be ascribed to the crucial roles of NGQDs and heterojunction photocatalytic system, which resulted in an efficient charge separation and the largely enhanced photocatalytic activity. Meanwhile, the possible photocatalytic mechanism of NGQDs-ZnNb2O6/g-C3N4 was also proposed. We envision that this work creates new opportunities for constructing and designing efficient visible-light-driven photocatalysts for hydrogen evolution reaction.

Constructing nitrogen doped graphene quantum dots-ZnNb2O6/g-C3N4 catalysts for hydrogen production under visible light

Development of high-efficiency photocatalysts for photocatalysis research has been a hotspot in recent years. In this study, an effective nitrogen-doped graphene quantum dots (NGQDs)-BiVO4/g-C3N4 Z-scheme heterojunction has been successfully prepared for environmental remediation. Antibiotics (tetracycline (TC), oxytetracycline (OTC) and ciprofloxacin (CIP)) were chosen as target pollutants to explore the photocatalytic performance. Results showed that both the BiVO4/g-C3N4 ratio (Bi/CN ratio) and NGQDs amount have an important influence on the antibiotics degradation. Under our experimental conditions, the optimum Bi/CN ratio was 1 : 2 and optimum NGQDs addition amount was 5 wt%, with the corresponding 5% NGQDs-Bi/2CN sample showing the highest photocatalytic efficiency (91.5% in 30 min with TC). By further study based on electron spin resonance (ESR) and active species trapping experiments, the enhanced photocatalytic property could be ascribed to the crucial role of NGQDs and Z-scheme photocatalytic system, which not only accelerated the separation of the charge carriers but also exhibited a strong oxidation and reduction ability for efficient degradation of organic pollutants.

Construction of nitrogen-doped graphene quantum dots-BiVO4/g-C3N4Z-scheme photocatalyst and enhanced photocatalytic degradation of antibiotics under visible light

Wei Gu

Papers

Fabrication of nitrogen doped graphene quantum dots-BiOI/MnNb2O6 p-n junction photocatalysts with enhanced visible light efficiency in photocatalytic degradation of antibiotics

Promoting visible-light-induced photocatalytic degradation of tetracycline by an efficient and stable beta-Bi2O3@g-C3N4 core/shell nanocomposite

In-situ construction of hierarchical CdS/MoS2 microboxes for enhanced visible-light photocatalytic H2 production

Constructing nitrogen doped graphene quantum dots-ZnNb2O6/g-C3N4 catalysts for hydrogen production under visible light

Construction of nitrogen-doped graphene quantum dots-BiVO4/g-C3N4Z-scheme photocatalyst and enhanced photocatalytic degradation of antibiotics under visible light