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

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has been the hotspot in the materials science as a metal-free and visible-light-responsive photocatalyst. Pure g-C3N4 suffers from the insufficient sunlight absorption, low surface area and the fast recombination of photo-induced electron-hole pairs, resulting in low photocatalytic activity. Element doping is known to be an efficient method to tune the unique electronic structure and band gap of g-C3N4, which considerably broaden the light responsive range and enhance the charge separation. This review summarizes the recent progress in the development of efficient and low cost doped g-C3N4 systems in various realms such as photocatalytic hydrogen evolution, reduction of carbon dioxide, photocatalytic removal of contaminants in wastewater and gas phase. Typically, metal doping, nonmetal doping, co-doping and heterojunction based on doped g-C3N4 have been explored to simultaneously tune the crystallographic, textural and electronic structures for improving photocatalytic activity by enhancing the light absorption, facilitating the charge separation and transportation and prolonging the charge carrier lifetime. Finally, the current challenges and the crucial issues of element doped g-C3N4 photocatalysts that need to be addressed in future research are presented. This review presented herein can pave a novel avenue and add invaluable knowledge to the family of element doped g-C3N4 for the develop of more effective visible-light-driven photocatalysts.

Doping of graphitic carbon nitride for photocatalysis: A reveiw

Charge kinetics is highly critical in determining the quantum efficiency of solar-to-chemical conversion in photocatalysis, and this includes, but is not limited to, the separation of photoexcited electron–hole pairs, utilization of plasmonic hot carriers and delivery of photo-induced charges to reaction sites, as well as activation of reactants by energized charges. In this review, we highlight the recent progress on probing and steering charge kinetics toward designing highly efficient photocatalysts and elucidate the fundamentals behind the combinative use of controlled synthesis, characterization techniques (with a focus on spectroscopic characterizations) and theoretical simulations in photocatalysis studies. We first introduce the principles of various processes associated with charge kinetics that account for or may affect photocatalysis, from which a set of parameters that are critical to photocatalyst design can be summarized. We then outline the design rules for photocatalyst structures and their corresponding synthetic approaches. The implementation of characterization techniques and theoretical simulations in different steps of photocatalysis, together with the associated fundamentals and working mechanisms, are also presented. Finally, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

Steering charge kinetics in photocatalysis: intersection of materials syntheses, characterization techniques and theoretical simulations

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

Water splitting via two two-electron processes (the H2O first photocatalytically converted to H2 and H2O2 under visible light irradiation and then the H2O2 disproportionation to H2O and O2 by a thermal catalytic process) has attracted extensive attention recently.1,2 Contrary to these reports, we found that not only the photocatalytic H2 generation could be driven by visible light but also the two-electron H2O2 disproportionation to form H2O and O2 could also be photocatalyzed by visible light over g-C3N4 catalysts. Photocatalytic H2, O2 generation, and simultaneous H2O2 formation in Cu/C3N4 and Fe/C3N4 dispersions were confirmed, about 2.1 and 1.4 μmol of H2 and 0.8 and 0.5 μmol of O2 evolved over Cu/C3N4 and Fe/C3N4 in 12 h, respectively. To prove the photocatalytic process of H2O2 disproportionation, the H2O2 was added as a reagent in g-C3N4, Cu/C3N4, and Fe/C3N4 dispersions. The results showed that the activity of H2 evolution decreased with the increase of H2O2 concentration; the corresponding AQEs o...

Visible Photocatalytic Water Splitting and Photocatalytic Two-Electron Oxygen Formation over Cu- and Fe-Doped g-C3N4

In this work, a highly active H2 evolution NiSx catalyst decorated on graphene (NiSx/G) nanohybrid was prepared by an in situ chemical deposition method, in which nickel ion was first adsorbed onto graphene and subsequently reacted with sulfide ion to yield the NiSx/G nanohybrid. The NiSx/G catalyst exhibited activity for hydrogen generation 2-fold higher than that of pristine NiSx under visible light irradiation. The highest quantum efficiency of 32.5% was reached at 430 nm when Eosin Y was used as a photosensitizer. In this system, graphene not only provided a large area and two-dimensional substrate for the confined growth of NiSx but also greatly enhanced the transfer of photoelectrons from excited Eosin Y to the NiSx cocatalyst because of its promotion of charge separation, leading to the great enhancement of photocatalytic hydrogen evolution.

Chao Kong

Papers

Visible Photocatalytic Water Splitting and Photocatalytic Two-Electron Oxygen Formation over Cu- and Fe-Doped g-C3N4

Dye-Sensitized NiSx Catalyst Decorated on Graphene for Highly Efficient Reduction of Water to Hydrogen under Visible Light Irradiation

Robust Pt–Sn alloy decorated graphene nanohybrid cocatalyst for photocatalytic hydrogen evolution

Dye-sensitized cobalt catalysts for high efficient visible light hydrogen evolution

Super-paramagnetic nano-Fe3O4/graphene for visible-light-driven hydrogen evolution.