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

Engineering photocatalytic materials for renewable energy generation and environmental decontamination has always been a very exciting prospect to counter the global energy demands and pollution challenges. Graphitic carbon nitride (g-C 3 N 4 ), a polymeric, metal-free semiconductor with a mild band gap (2.7 eV) has become hot-spot in various scientific exploits such as environmental pollution mitigation, energy generation and storage, organic synthesis, sensors, etc. These applications exploit the interesting properties of g-C 3 N 4 such as good visible light absorption, graphene-like structure, good thermal and chemical stability and photocatalytic properties. In this review we begin with an overview of the fundamental aspects of photocatalysis as a pollution remediation strategy. This is followed by an introduction to graphitic carbon nitride as a photocatalyst, preparation strategies and its properties. Subsequently, a comprehensive and critical discussion of the various most recent developments towards enhancing the visible light photocatalytic properties of g-C 3 N 4 for pollution alleviation, selected results and important photocatalytic degradation mechanisms, is given. Summary remarks and future perspective conclude the review.

Graphitic carbon nitride (g-C3N4) nanocomposites: A new and exciting generation of visible light driven photocatalysts for environmental pollution remediation

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

Review on the criteria anticipated for the fabrication of highly efficient ZnO-based visible-light-driven photocatalysts

A novel plasmonic photocatalyst, Au/Pt/g-C3N4, was prepared by a facile calcination-photodeposition technique. The samples were characterized by X-ray diffraction, energy-dispersive spectroscopy, transmission electron microscopy, and UV–vis diffuse reflectance spectroscopy, and the results demonstrated that the Au and Pt nanoparticles (7–15 nm) were well-dispersed on the surfaces of g-C3N4. The Au/Pt codecorated g-C3N4 heterostructure displayed enhanced photocatalytic activity for antibiotic tetracycline hydrochloride (TC-HCl) degradation, and the degradation rate was 3.4 times higher than that of pure g-C3N4 under visible light irradiation. The enhancement of photocatalytic activity could be attributed to the surface plasmon resonance effect of Au and electron-sink function of Pt nanoparticles, which improve the optical absorption property and photogenerated charge carriers separation of g-C3N4, synergistically facilitating the photocatalysis process. Finally, a possible photocatalytic mechanism for degr...

Facile Photochemical Synthesis of Au/Pt/g-C3N4 with Plasmon-Enhanced Photocatalytic Activity for Antibiotic Degradation

ZnO/Ag2O heterostructures were successfully synthesized via a simple one-step photochemical route. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Photocatalytic activity toward degradation of a methylene blue (MB) aqueous solution under ultraviolet (UV) and visible light was investigated. The results showed that the as-prepared ZnO/Ag2O heterostructures significantly enhanced the UV and visible photocatalytic activity compared with pure ZnO and Ag2O. In particular, the rates of degradation using the as-prepared ZnO/Ag2O heterostructures were 27.4 and 15.6 times faster than that using bare ZnO nanoparticles under UV and visible light irradiation, respectively. Furthermore, the as-prepared ZnO/Ag2O heterostructures could be easily recycled in UV and visible photocatalytic applications due to the low concentration of surface defects. Moreover, the ZnO/Ag2O heterostructures could also degrade MB dye with high efficiency in various water types such as Changjiang river water, tap water, and deionized water, which will greatly promote their application in the area of environmental remediation.

Photochemical synthesis of ZnO/Ag2O heterostructures with enhanced ultraviolet and visible photocatalytic activity

A novel ternary plasmonic photocatalyst, Au-loaded porous graphitic C3N4/graphene layered composite (Au/pg-C3N4/GR), was fabricated by a facile sonication-photodeposition technique. In this hybrid structure, a polymeric semiconductor pg-C3N4 was immobilized on the surfaces of graphene sheets to form a layered composite with Au nanoparticles of sizes 10–15 nm uniformly deposited on it. The photocatalytic performance of the as-prepared Au/pg-C3N4/GR composite was evaluated by degradation of methylene blue (MB) and ciprofloxacin (CIP) as representative dye pollutant and antibiotic pollutant under visible light irradiation, respectively. The degradation rates of MB and CIP over the Au/pg-C3N4/GR photocatalyst were 4.34 and 3.05 times higher that of porous g-C3N4 (pg-C3N4), respectively, and even 7.42 and 6.09 times higher than that of pure g-C3N4, respectively. The results indicated that an improved photocatalytic efficiency was obtained when Au nanoparticles and graphene sheets co-incorporated in porous g-C3N4. The porous structure within the samples is advantageous to the adsorption capacity. The surface plasmon resonance (SPR) effect of Au and electron-acceptor role of graphene, which would improve the visible light harvesting ability, facilitate photogenerated charge carrier separation, as well as create more active reaction sites, and synergistically contribute to the enhancement of photocatalytic activity. Moreover, a possible photocatalytic mechanism was also tentatively proposed.

Au-loaded porous graphitic C3N4/graphene layered composite as a ternary plasmonic photocatalyst and its visible-light photocatalytic performance

Porous graphitic carbon nitride (pg-C3N4) synthetized by pyrolysis of urea was hybridized with Ag-doped Fe2O3 to form a visible-light-driven photocatalyst pg-C3N4/Ag/Fe2O3 via a simple chemical adsorption method. The obtained pg-C3N4/Ag/Fe2O3 composites with different Ag/Fe2O3 content were characterized in terms of composition, morphology, and optical properties by XRD, EDS, FT-IR, TEM and UV-vis DRS. The photocatalytic activities were evaluated by degradation of Rhodamine B (RhB) as a representative organic pollutant under visible light irradiation. The results showed Ag/Fe2O3 (5 wt%) modified pg-C3N4 exhibited excellent photocatalytic activity in the degradation of RhB and the degradation rate was 2.74 times higher than that of pure pg-C3N4. The heterostructured coupling of pg-C3N4 with a novel metal, Ag, and semiconductor, Fe2O3, in the aspect of energy level matching would effectively improve visible-light absorption capability and facilitate photogenerated electron–hole pairs separation, synergistically accounting for the enhancement of photocatalytic activity. A possible photocatalytic mechanism was also tentatively proposed.

Fabrication of porous g-C3N4/Ag/Fe2O3 composites with enhanced visible light photocatalysis performance

This manuscript describes the deposition of carbon on the surface of ZnO nanoparticles via a simple adsorption and calcination process. The prepared ZnO/C sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and thermogravimetric analysis (TGA); the results indicated that carbon was successfully doped on the surface of the ZnO nanoparticles. The photocatalytic activity and adsorption capacity were evaluated by photocatalytic decomposition and adsorption of the dye methylene blue (MB) in aqueous solution. The results showed that the obtained ZnO/C sample exhibited much higher photocatalytic properties and adsorption capacity for MB than pure ZnO and carbon because of the formation of heteroarchitectures, which might have improved the separation of photogenerated electrons and holes. In particular, the pseudo-first-order rate constant of the ZnO/C sample was 0.326 min−1, which was 10 times greater than that of pure ZnO. Moreover, the ZnO/C composites could remove dyes from different water sources like the Changjiang River water with high efficiency as well as from deionized water, greatly promoting their application in the area of environmental remediation.

Jinjuan Xue

Papers

Facile Photochemical Synthesis of Au/Pt/g-C3N4 with Plasmon-Enhanced Photocatalytic Activity for Antibiotic Degradation

Photochemical synthesis of ZnO/Ag2O heterostructures with enhanced ultraviolet and visible photocatalytic activity

Au-loaded porous graphitic C3N4/graphene layered composite as a ternary plasmonic photocatalyst and its visible-light photocatalytic performance

Fabrication of porous g-C3N4/Ag/Fe2O3 composites with enhanced visible light photocatalysis performance

A facile route for the preparation of ZnO/C composites with high photocatalytic activity and adsorption capacity