Comparison of bulk g-C3N4 (left) and nanosheet g-C3N4 powders, 100 mg each.[1]
Graphitic carbon nitride (g-C3N4) is a family ofcarbon nitride compounds with a general formula near to C3N4 (albeit typically with non-zero amounts of hydrogen) and two major substructures based onheptazine and poly(triazine imide) units which, depending on reaction conditions, exhibit different degrees ofcondensation, properties andreactivities.
Graphitic carbon nitride can be made bypolymerization ofcyanamide,dicyandiamide ormelamine. The firstly formed polymeric C3N4 structure,melon, with pendantamino groups, is a highly orderedpolymer. Further reaction leads to more condensed and less defective C3N4 species, based ontri-s-triazine (C6N7) units as elementary building blocks.[2]
Well-crystallized graphitic carbon nitride nanocrystallites can also be prepared via benzene-thermal reaction betweenC3N3Cl3 andNaNH2 at 180–220 °C for 8–12 h.[4]
Recently, a new method of syntheses of graphitic carbon nitrides by heating at 400-600 °C of a mixture of melamine anduric acid in the presence ofalumina has been reported. Alumina favored the deposition of the graphitic carbon nitrides layers on the exposed surface. This method can be assimilated to an in situchemical vapor deposition (CVD).[5]
A commercial graphitic carbon nitride is available under the brand name Nicanite. In its micron-sized graphitic form, it can be used fortribological coatings, biocompatible medical coatings, chemically inert coatings, insulators and forenergy storage solutions.[6] Graphitic carbon nitride is reported as one of the best hydrogen storage materials.[7][8] It can also be used as a support for catalyticnanoparticles.[1]
Due to their properties (primarily large, tuneable band gaps and efficient intercalation of salts) graphitic carbon nitrides are under research for a variety of applications:
The significant resilience of carbon nitrides combined with surface and intralayer reactivities make them potentially useful catalysts relying on their labile protons and Lewis base functionalities. Modifications such as doping, protonation and molecular functionalisation can be exploited to improve selectivity and performance.[11]
Despite graphitic carbon nitride having some advantages, such as mild band gap (2.7 eV), absorption of visible light and flexibility, it still has limitations for practical applications due to low efficiency of visible light utilization, high recombination rate of the photo generated charge carriers, low electrical conductivity and small specific surface area (<10 m2g−1).[12] To modify these shortages, one of the most attractive approaches is doping graphitic carbon nitride with carbonnanomaterials, such as carbon nanotubes. First, carbon nanotubes have large specific surface area, so they can provide more sites to separate the charge carriers, then decrease the recombination rate of the charge carriers and further increase the activity of reduction reaction.[13] Second, carbon nanotubes show high electron conducting ability, which means they can improve graphitic carbon nitride with visible light response, efficient charge carrier separation and transfer, thereby improving its electronic properties.[14] Third, carbon nanotubes can be regarded as a kind of narrow band semiconductor material, also known as a photosensitizer, which can extend the range of the light absorption of semiconductor photocatalytic material, thereby enhancing its utilization of visible light.[15]
Energy Storage materials
Due to the intercalation of Li being able to occur to more sites than for graphite due to intra layer voids in addition to intercalation between layers, gCN can store a large amount of Li[16] making them potentially useful forrechargeable batteries.
^abThomas, A.; Fischer, A.; Goettmann, F.; Antonietti, M.; Müller, J.-O.; Schlögl, R.; Carlsson, J. M. (2008). "Graphitic Carbon Nitride Materials: Variation of Structure and Morphology and their Use as Metal-Free Catalysts".Journal of Materials Chemistry.18 (41):4893–4908.CiteSeerX10.1.1.529.6230.doi:10.1039/b800274f.S2CID53124927.
^abGuo, Q. X.; Xie, Y.; Wang, X. J.; Lv, S. C.; Hou, T.; Liu, X. M. (2003). "Characterization of Well-Crystallized Graphitic Carbon Nitride Nanocrystallites via a Benzene-Thermal Route at Low Temperatures".Chemical Physics Letters.380 (1–2):84–87.Bibcode:2003CPL...380...84G.doi:10.1016/j.cplett.2003.09.009.
^Dante, R. C.; Martín-Ramos, P.; Correa-Guimaraes, A.; Martín-Gil, J. (2011). "Synthesis of Graphitic Carbon Nitride by Reaction of Melamine and Uric Acid".Materials Chemistry and Physics.130 (3):1094–1102.doi:10.1016/j.matchemphys.2011.08.041.
^Nair, Asalatha A. S.; Sundara, Ramaprabhu; Anitha, N. (2015-03-02). "Hydrogen storage performance of palladium nanoparticles decorated graphitic carbon nitride".International Journal of Hydrogen Energy.40 (8):3259–3267.Bibcode:2015IJHE...40.3259N.doi:10.1016/j.ijhydene.2014.12.065.
^Nair, Asalatha A. S.; Sundara, Ramaprabhu (2016-05-12). "Palladium Cobalt Alloy Catalyst Nanoparticles Facilitated Enhanced Hydrogen Storage Performance of Graphitic Carbon Nitride".The Journal of Physical Chemistry C.120 (18):9612–9618.doi:10.1021/acs.jpcc.6b01850.
^Wang, Xinchen; Maeda, Kazuhiko; Thomas, Arne; Takanabe, Kazuhiro; Xin, Gang; Carlsson, Johan M.; Domen, Kazunari; Antonietti, Markus (2009). "A metal-free polymeric photocatalyst for hydrogen production from water under visible light".Nature Materials.8 (1):76–80.Bibcode:2009NatMa...8...76W.doi:10.1038/nmat2317.PMID18997776.S2CID205402078.
^Thomas, Arne; Fischer, Anna; Goettmann, Frederic; Antonietti, Markus; Müller, Jens-Oliver; Schlögl, Robert; Carlsson, Johan M. (2008-10-14). "Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts".Journal of Materials Chemistry.18 (41): 4893.CiteSeerX10.1.1.529.6230.doi:10.1039/b800274f.ISSN1364-5501.S2CID53124927.
^Niu P, Zhang L L, Liu G, Cheng H M et al. Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities[J]. Advanced Functional Materials, 2012, 22(22): 4763-4770.
^Zhang L Q, He X, Xu X W et al. Highly active TiO2/g-C3N4/G photocatalyst with extended spectralresponse towards selective reduction of nitrobenzene[J]. Applied Catalysis B: Environmental. 2017, 203:65-71.
^Dong F, Li Y H, Wang Z Y, Ho W K et al. Enhanced visible light photocatalytic activity and oxidation ability ofporous graphene-like g-C3N4nanosheets via thermal exfoliation[J]. Applied Surface Science, 2015, 358: 393–403.
^Mishra A K, Mamba G et al. Graphic carbon nitride nanocomposites: A new and exciting generation of visible light driven photocatalysts for environmental pollution remediation[J]. Applied Catalysis B, 2016, 21: 351-371.
^Wu, Menghao; Wang, Qian; Sun, Qiang; Jena, Puru (2013-03-28). "Functionalized Graphitic Carbon Nitride for Efficient Energy Storage".The Journal of Physical Chemistry C.117 (12):6055–6059.doi:10.1021/jp311972f.ISSN1932-7447.
