G-c3n4 Structure
James Gillock
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A facile In Situ growth method was presented here for the preparation of graphitic carbon nitride (g-C3N4)/graphene composites, in which the direct growth and deposition of g-C3N4 nanosheets from organic N and C sources on the graphene surfaces was achieved to form the 3D contacted structure. The resulting 3D architecture possessed multilevel porous structure and efficient g-C3N4/graphene interfaces, which facilitated the fast electron transfer at the interfaces. Photoluminescence spectra showed that the recombination of photogenerated electrons and holes in the g-C3N4/graphene composites was greatly inhibited by the introduction of graphene, indicating the more efficient separation of electrons and hole in the g-C3N4/graphene composites than in pure g-C3N4. The catalytic activity of g-C3N4/graphene composite photocatalyst was enhanced by over two fold compared to pure g-C3N4 for removal of Rhodamine B under simulated sun light irradiation. This work indicates that the metal-free g-C3N4/graphene composite photocatalyst is a promising nanomaterial for further applications in water treatment.
Graphite carbon nitride (g-C3N4) is well known as one of the most promising materials for photocatalytic activities, such as CO2 reduction and water splitting, and environmental remediation through the removal of organic pollutants. On the other hand, carbon nitride also pose outstanding properties and extensive application forecasts in the aspect of field emission properties. In this mini review, the novel structure, synthesis and preparation techniques of full-bodied g-C3N4-based composite and films were revealed. This mini review discussed contemporary advancement in the structure, synthesis, and diverse methods used for preparing g-C3N4 nanostructured materials. The present study gives an account of full knowledge of the use of the exceptional structural and properties, and the preparation techniques of graphite carbon nitride (g-C3N4) and its applications.
Predominantly, wastewater is the major source of pollution, specifically, wastewater produced due to chemical industrialization, because this wastewater contains pronounced concentration of large organic fragments which are tremendously poisonous and carcinogenic in nature [3]. Previously, the environmental remediation technology (which comprises of adsorption, biological oxidation, chemical oxidation, and incineration) has been used in the treatment of all types of organic and toxic wastewater and also has its effective application in solar energy utilization, environmental treatment, and biomedical and sensing applications. Fujishima and Honda revealed the exceptional knowledge about the photochemical splitting of water into hydrogen and oxygen in the presence of TiO2 in 1972; research interest has been focused in heterogeneous photocatalysis [3,4,5]. The speeding up of photoreaction in the existence of a catalyst is described as photocatalysis. Photocatalysis reaction is best known to be carried out in media such as gas phase, pure organic liquid phases, or aqueous solutions. Also, in most chemical degradation methods, photocatalytic degradation vis--vis photons and a catalyst is often identified as the best in controlling of organic wastewater, solar energy utilization, environmental treatment, and biomedical and sensing applications [3, 5]. Hence, the utmost technology used for the treatment of organic wastewater and related applications is attributed to the evolving solar light-driven photocatalysts [3].
Semiconductor photocatalysts can be used for the removal of ambient concentrations of organic and inorganic species from aqueous or gas phase systems in drinking water treatment, environmental tidying, and industrial and health applications. This is due to the massive ability of these semiconductors (g-C3N4, TiO2- and ZnO) to oxidize organic and inorganic substrates in air and water through redox processes for its effective application in solar energy utilization, wastewater, and environmental treatment, biomedical and sensing applications without any second pollution.
Due to these outstanding properties of g-C3N4, the use of this promising g-C3N4 in water splitting, CO2 photo reduction, organic contaminants purification, catalytic organic synthesis, and fuel cells is more efficient and effective [6]. The number of admirable researches and reviews on g-C3N4 structure and preparation in the last few years has increased tremendously [10]. Authors mainly laid emphasis on the most contemporary advances on the structure, synthesis, and preparation techniques of g-C3N4 and carbon nitride (CNx) films vividly in this concise mini review. The unique structure and the novel synthesis and preparation techniques of g-C3N4, and CNX films are nicely presented, and the enlightened concepts on extending the preparation of g-C3N4 in this mini review are then emphasized. Also, the authors discussed the applications on g-C3N4, and the perspectives in future researches were also advocated.
Photocatalysis is best referred to the acceleration of chemical conversions (oxidations and reductions) brought about through the activation of a catalyst. This reaction involves a semiconductor either alone or in combination with metal/organic/organometallic promoters, through light absorption, following charge or energy transfer to be adsorbed which can lead to the photocatalytic transformation of a pollutant. During a photocatalysis mechanism, there is a simultaneous occurrence of at least two main actions which aids a successful production of reactive oxidizing species (Fig. 2). These reactions are oxidation of dissociatively adsorbed H2O mostly generated by photogenerated holes and reduction of an electron acceptor also created by photoexcited electrons (Fig. 2). Hence, these reactions produce a hydroxyl and superoxide radical anion, respectively [11]. During photocatalysis reaction, it is obvious that there is photon-assisted generation of catalytically active species instead of the action of light as a catalyst in a reaction [12,13,14,15, 16]. Considerably, reaping of visible light, mostly from sunlight, by catalyst (photocatalyst) to initiate chemical transformations (Fig. 1) is described as photocatalysis. Application of C3N4 photocatalyst for wastewater treatment, solar energy utilization, environmental treatment, and biomedical and sensing applications has been discussed in many areas of science.
Enlightenment of a semiconductor catalyst, such as TiO2, ZnO, ZrO2, and CeO2, with photons carrying energy equal or in excess of its band gap, creating an electron hole pair similar to photo-induced electron transfer and absorption of light promotes one electron into the conduction band. The oxide may transfer its electron (Fig. 2) to any adsorbed electron acceptor (thereby promoting its reduction), while the hole (or the electron vacancy) may accept an electron from an adsorbed donor (promoting its oxidation). g-C3N4 is capable of catalyzing hydrogen/oxygen evolution and CO2 reduction under band gap excitation and in the presence of suitable co catalysts and/or sacrificial agents.
Materials with 1D nanostructures having distinct electronic, chemical, and optical properties could have their size and morphology adjusted. This ability of the 1D nanostructured materials has led to a novel advancement of diverse approaches to improve their photocatalytic activity [17]. In addition, there is guidance of electron movement in the axial direction and lateral confinement of electrons by these 1D nanostructures. There has been advancement of 2D materials from graphene to metal oxide and metal chalcogenide nanosheets and then to 2D covalent organic frameworks (g-C3N4).
The appropriate means of selection of precursors and condensation methods had led to two main types of g-C3N4 structural polymorphs and this includes, firstly, the g-C3N4 consist of a condensed s-triazine units (ring of C3N3) with a periodic array of single-carbon vacancies. The second type of g-C3N4 consists of the condensed tri-s-triazine (tri-ring of C6N7) subunits coupled through planar tertiary amino groups, and this has greater periodic vacancies in the lattice. The g-C3N4 networks mainly consists of melon-based segments (the second type structure; this consists of the tri-s-triazine unit, Fig. 3a) which is thermodynamically more stable compared to the melamine-based arrangements (the first type structure; this compose of the s-triazine, Fig. 3b) as described by the functional theory (DFT) calculations [18]. Hence, it is broadly believed that the tri-s-triazine nucleus is the fundamental building blocks for the formation of the g-C3N4 network.
Currently, g-C3N4 is considered as a new-generation photocatalyst to recover the photocatalytic activity of traditional photocatalysts like TiO2, ZnO, and WO3. g-C3N4 is assumed to have a graphitic-like structure [26,27,28, 29, 30]. Thermal polycondensation method is generally used to prepare g-C3N4 and, hence, to investigate the electronic structure of g-C3N4.
The α-C3N4 is earlier found by Yu and coworkers [24]. These scientists used the calculation procedure of quantum mechanics clusters model and developed α-C3N4 by optimization the electronic structure of g-C3N4 for photocatalysis and others. In the structure of alpha-C3N4, C and N atoms linked by sp3 key was to used design the tetrahedron structure of g-C3N4. Liu and Cohen anticipated the existence of beta-C3N4 by means of band concept of first principles and prepared beta-C3N4 based on β-Si3N4 electronic structure. Liu and Cohen then revealed that the structure of β-C3N4 was hexagonal encompassing 14 atoms for each unit cell.
The outstanding prediction anticipated by Liu and Cohen in 1989 that the b-polymorph C3N4 would have exceptional high hardness values in comparison with diamond has enthused scientific research to date [26]. In 1993, C3N4 thin films via magnetron snorting of a graphite target on Si (100) and polycrystalline Zr substrates under a pure nitrogen ambience and consideration of the structure of C3N4 with analytical electron microscopy and Raman spectroscopy were synthesized by Chen and co-authors [27, 31]. Scientists, Teter and Hemley [28], foretold that alpha-C3N4, beta-C3N4, cubic-C3N4, pseudo cubic-C3N4, and graphite C3N4 show pronounced hardness approaching that of diamond in their experiment which they performed 3 years later as already described in accordance with first-principle calculations of the relative stability, structure, and physical properties of carbon nitride polymorphs.
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