Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts
14 Oct 2008-Journal of Materials Chemistry (Royal Society of Chemistry)-Vol. 18, Iss: 41, pp 4893-4908
TL;DR: In this paper, high resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif of graphitic carbon nitride, and a new family of metal nitride nanostructures can also be accessed from the corresponding oxides.
Abstract: Graphitic carbon nitride, g-C3N4, can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.
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TL;DR: It is anticipated that this review can stimulate a new research doorway to facilitate the next generation of g-C3N4-based photocatalysts with ameliorated performances by harnessing the outstanding structural, electronic, and optical properties for the development of a sustainable future without environmental detriment.
Abstract: 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...
5,054 citations
TL;DR: The unique advances on ultrathin 2D nanomaterials are introduced, followed by the description of their composition and crystal structures, and the assortments of their synthetic methods are summarized.
Abstract: 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...
3,628 citations
TL;DR: The design and fabrication of a metal-free carbon nanodot–carbon nitride (C3N4) nanocomposite is reported and its impressive performance for photocatalytic solar water splitting is demonstrated.
Abstract: The use of solar energy to produce molecular hydrogen and oxygen (H2 and O2) from overall water splitting is a promising means of renewable energy storage. In the past 40 years, various inorganic and organic systems have been developed as photocatalysts for water splitting driven by visible light. These photocatalysts, however, still suffer from low quantum efficiency and/or poor stability. We report the design and fabrication of a metal-free carbon nanodot-carbon nitride (C3N4) nanocomposite and demonstrate its impressive performance for photocatalytic solar water splitting. We measured quantum efficiencies of 16% for wavelength λ = 420 ± 20 nanometers, 6.29% for λ = 580 ± 15 nanometers, and 4.42% for λ = 600 ± 10 nanometers, and determined an overall solar energy conversion efficiency of 2.0%. The catalyst comprises low-cost, Earth-abundant, environmentally friendly materials and shows excellent stability.
3,553 citations
TL;DR: In this article, a top-down thermal oxidation etching of bulk g-C3N4 in air has been shown to improve the photocatalytic activities of the material in terms of OH radical generation and hydrogen evolution.
Abstract: Graphitic (g)-C3N4 with a layered structure has the potential of forming graphene-like nanosheets with unusual physicochemical properties due to weak van der Waals forces between layers. Herein is shown that g-C3N4 nanosheets with a thickness of around 2 nm can be easily obtained by a simple top-down strategy, namely, thermal oxidation etching of bulk g-C3N4 in air. Compared to the bulk g-C3N4, the highly anisotropic 2D-nanosheets possess a high specific surface area of 306 m2 g-1, a larger bandgap (by 0.2 eV), improved electron transport ability along the in-plane direction, and increased lifetime of photoexcited charge carriers because of the quantum confinement effect. As a consequence, the photocatalytic activities of g-C3N4 nanosheets have been remarkably improved in terms of OH radical generation and photocatalytic hydrogen evolution.
2,900 citations
TL;DR: The "polymer chemistry" of g-C(3)N(4) is described, 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.
Abstract: 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.
2,735 citations
References
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TL;DR: The CASTEP program as mentioned in this paper is a computer program for first principles electro-Nic structure calculations, and some of its features and capabilities are described and near-future development plans outlined.
Abstract: CASTEP Computer program / Density functional theory / Pseudopotentials / ab initio study / Plane-wave method / Computational crystallography Abstract. The CASTEP code for first principles electro- nic structure calculations will be described. A brief, non- technical overview will be given and some of the features and capabilities highlighted. Some features which are un- ique to CASTEP will be described and near-future devel- opment plans outlined.
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TL;DR: The empirical model indicates that hypothetical covalent solids formed between carbon and nitrogen are good candidates for extreme hardness and first principles pseudopotential total energy calculation on the system shows that materials like the prototype can have bulk moduli comparable to or greater than diamond.
Abstract: An empirical model and an ab initio calculation of the bulk moduli for covalent solids are used to suggest possible new hard materials. The empirical model indicates that hypothetical covalent solids formed between carbon and nitrogen are good candidates for extreme hardness. A prototype system is chosen and a first principles pseudopotential total energy calculation on the system is performed. The results are consistent with the empirical model and show that materials like the prototype can have bulk moduli comparable to or greater than diamond. It may be possible to synthesize such materials in the laboratory.
2,364 citations
TL;DR: Ordered carbon molecular sieves exhibiting Bragg diffraction of X-ray lines have been synthesized for the first time, using mesoporous silica sieves as the template.
Abstract: Ordered carbon molecular sieves exhibiting Bragg diffraction of X-ray lines have been synthesized for the first time, using mesoporous silica molecular sieves as the template. Sucrose was converted to carbon inside the mesopores of the silica molecular sieves through a mild carbonization process using a sulfuric acid catalyst. The carbon molecular sieves were obtained after the removal of the silica framework using an aqueous solution of sodium hydroxide. The X-ray diffraction, transmission electron microscopy, and pore size analysis showed that the structure of the carbon molecular sieves consisted of a three-dimensional regular array of uniform mesopores 3 nm in diameter. The structure was not simply a negative replica of the used silica template, but the synthesis mechanism involved the unique transformation into a new ordered array that was triggered by the removal of the silica frameworks. The highly ordered mesoporous texture suggested its scientific and technological importance as a new shape-selec...
2,298 citations
TL;DR: Ordered mesoporous carbons have been synthesized using ordered mesopore silica templates as discussed by the authors, where the template needs to exhibit three-dimensional pore structure in order to be suitable for the ordered mesophorous carbon synthesis, otherwise disordered microporous carbon is formed.
Abstract: Ordered mesoporous carbons have recently been synthesized using ordered mesoporous silica templates. The synthesis procedure involves infiltration of the pores of the template with appropriate carbon precursor, its carbonization, and subsequent template removal. The template needs to exhibit three-dimensional pore structure in order to be suitable for the ordered mesoporous carbon synthesis, otherwise disordered microporous carbon is formed. MCM-48, SBA-1, and SBA-15 silicas were successfully used to synthesize carbons with cubic or hexagonal frameworks, narrow mesopore size distributions, high nitrogen Brunauer–Emmett–Teller (BET) specific surface areas (up to 1800 m2 g–1), and large pore volumes. Ordered mesoporous carbons are promising in many applications, including adsorption of large molecules, chromatography, and manufacturing of electrochemical double-layer capacitors.
1,467 citations
1,342 citations