Darkwah and Ao Nanoscale Research Letters (2018) 13:388 https://doi.org/10.1186/s11671-018-2702-3 NANO REVIEW Open Access Mini Review on the Structure and Properties (Photocatalysis), and Preparation Techniques of Graphitic Carbon Nitride Nano-Based Particle, and Its Applications Williams Kweku Darkwah and Yanhui Ao* Abstract 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. Keywords: Photocatalysis, Graphite carbon nitride (g-C3N4), Carbon nitride nano-based particle Introduction Predominantly, wastewater is the major source of pol- The central energy source elated from the extraterrestrial lution, specifically, wastewater produced due to chemical space, solar energy capacities to surpass the almanac industrialization, because this wastewater contains pro- world’s energy request by a large border [1]. Given the nounced concentration of large organic fragments which long forecast era of the Sun, solar energy is also consid- are tremendously poisonous and carcinogenic in nature ered the ultimate renewable source that can be harvested [3]. Previously, the environmental remediation technol- on the planet, Earth [2, 3]. The unending and discontinu- ogy (which comprises of adsorption, biological oxidation, ous nature of this energy source, however, presents key chemical oxidation, and incineration) has been used in challenges in relationships of harvesting, storage, and the treatment of all types of organic and toxic wastewa- utilization [4]. At the moment, there are a measure of ter and also has its effective application in solar energy technologies in place that may be used to face them. Solar utilization, environmental treatment, and biomedical energy can be flexibly gathered, transformed and kept in and sensing applications. Fujishima and Honda revealed the form of heat, which can either distribute heat to resi- the exceptional knowledge about the photochemical dence or be further converted into electricity, as well as splitting of water into hydrogen and oxygen in the pres- into other forms of energy [5]. The most innovative inves- ence of TiO2 in 1972; research interest has been focused tigated technologies concerning solar photon gaining may in heterogeneous photocatalysis [3–5]. The speeding up of be on those by the photocatalysis, as described by Edmond photoreaction in the existence of a catalyst is described as Becquerel, 1839 [5]. 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 * Correspondence: [email protected] degradation methods, photocatalytic degradation vis-à-vis Key Laboratory of Integrated Regulation and Resource Development on photons and a catalyst is often identified as the best in Shallow Lakes, Ministry of Education, Environmental Engineering controlling of organic wastewater, solar energy utilization, Department, College of Environment, Hohai University, Nanjing, China © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Darkwah and Ao Nanoscale Research Letters (2018) 13:388 Page 2 of 15 environmental treatment, and biomedical and sensing Review applications [3, 5]. Hence, the utmost technology used Graphitic Carbon Nitride and Photocatalysis for the treatment of organic wastewater and related ap- Photocatalysis is best referred to the acceleration of chem- plications is attributed to the evolving solar light-driven ical conversions (oxidations and reductions) brought photocatalysts [3]. about through the activation of a catalyst. This reaction Semiconductor photocatalysts can be used for the re- involves a semiconductor either alone or in combination moval of ambient concentrations of organic and inorganic with metal/organic/organometallic promoters, through species from aqueous or gas phase systems in drinking light absorption, following charge or energy transfer to be water treatment, environmental tidying, and industrial adsorbed which can lead to the photocatalytic transform- and health applications. This is due to the massive ability ation of a pollutant. During a photocatalysis mechanism, of these semiconductors (g-C3N4, TiO2- and ZnO) to there is a simultaneous occurrence of at least two main oxidize organic and inorganic substrates in air and water actions which aids a successful production of reactive oxi- through redox processes for its effective application in dizing species (Fig. 2). These reactions are oxidation of solar energy utilization, wastewater, and environmental dissociatively adsorbed H2O mostly generated by photo- treatment, biomedical and sensing applications without generated holes and reduction of an electron acceptor also any second pollution. created by photoexcited electrons (Fig. 2). Hence, these re- Polymeric graphitic carbon nitride (g-C3N4) has become actions produce a hydroxyl and superoxide radical anion, the prime center for consideration in photocatalysis re- respectively [11]. During photocatalysis reaction, it is obvi- search [6]. g-C3N4 is a visible-light-response element with ous that there is photon-assisted generation of catalytically band gap of 2.7 eV, and the energy location of CB and VB active species instead of the action of light as a catalyst in is at − 1.1 and 1.6 eV via normal hydrogen electrode areaction[12–15, 16]. Considerably, reaping of visible respectively [Wang et al. 2009]. In addition, g-C3N4 has light, mostly from sunlight, by catalyst (photocatalyst) to the ability to resist attacks from heat, strong acid, and initiate chemical transformations (Fig. 1) is described as strong alkaline solution [7]. g-C3N4 has a unique abil- photocatalysis. Application of C3N4 photocatalyst for itytobesimplypreparedbythermallypolycondensing wastewater treatment, solar energy utilization, environ- the cheap N-rich precursors, such as dicyanamide, mental treatment, and biomedical and sensing applica- cyanamide, melamine, melamine cyanurate, and urea, tions has been discussed in many areas of science. and this is unlike the other metal-containing photoca- Enlightenment of a semiconductor catalyst, such as talysts that require costly metal salts for preparation TiO2, ZnO, ZrO2, and CeO2, with photons carrying en- [6, 8]. Thermal condensation, solvothermal, chemical ergy equal or in excess of its band gap, creating an elec- vapor deposition, microwave-assisted, polymerization, tron hole pair similar to photo-induced electron transfer and hydrothermal synthesis are examples of prepara- and absorption of light promotes one electron into the tive strategies (Table 2) which have been commend- conduction band. The oxide may transfer its electron ably applied in the preparationofcarbonnitridefor (Fig. 2) to any adsorbed electron acceptor (thereby pro- distinctive purposes and analysis in the area of photo- moting its reduction), while the hole (or the electron va- catalysis and others [9]. cancy) may accept an electron from an adsorbed donor Due to these outstanding properties of g-C3N4,the (promoting its oxidation). g-C3N4 is capable of catalyz- use of this promising g-C3N4 in water splitting, CO2 ing hydrogen/oxygen evolution and CO2 reduction photo reduction, organic contaminants purification, under band gap excitation and in the presence of suit- catalytic organic synthesis, and fuel cells is more able co catalysts and/or sacrificial agents. efficient and effective [6]. The number of admirable researches and reviews on g-C3N4 structure and prep- aration in the last few years has increased tremen- Graphitic Carbon Nitride Nano-Based Particle dously [10]. Authors mainly laid emphasis on the most Materials with 1D nanostructures having distinct elec- contemporary advances on the structure, synthesis, tronic, chemical, and optical properties could have their and preparation techniques of g-C3N4 and carbon ni- size and morphology adjusted. This ability of the 1D tride (CNx) films vividly in this concise mini review. nanostructured materials has led to a novel advancement The unique structure and the novel synthesis and of diverse approaches to improve their photocatalytic ac- preparation techniques of g-C3N4,andCNX films are tivity [17]. In addition, there is guidance of electron nicely presented, and the enlightened concepts on movement in the axial direction and lateral confinement extending the preparation of g-C3N4 in this mini re- of electrons by these 1D nanostructures.