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Graphitic Carbon Nitride “ Chem Soc Rev View Article Online REVIEW ARTICLE View Journal | View Issue Graphitic carbon nitride ‘‘reloaded’’: emerging applications beyond (photo)catalysis Cite this: Chem. Soc. Rev., 2016, 45,2308 Jian Liu,*ab Hongqiang Wang*cd and Markus Antoniettia Despite being one of the oldest materials described in the chemical literature, graphitic carbon nitride (g-C3N4) has just recently experienced a renaissance as a highly active photocatalyst, and the metal-free polymer was shown to be able to generate hydrogen under visible light. The semiconductor nature of g-C3N4 has triggered tremendous endeavors on its structural manipulation for enhanced photo(electro)chemical performance, aiming at an affordable clean energy future. While pursuing the stem of g-C3N4 related catalysis (photocatalysis, electrocatalysis and photoelectrocatalysis), a number of emerging intrinsic properties of g-C3N4 are certainly interesting, but less well covered, and we believe that these novel applications outside of conventional catalysis can be favorably exploited as well. Thanks to the general efforts devoted to the exploration and enrichment of g-C3N4 based chemistry, the boundaries of this area have Creative Commons Attribution 3.0 Unported Licence. been possibly pushed far beyond what people could imagine in the beginning. This review strives to cover the achievements of g-C3N4 related materials in these unconventional application fields for depicting the broader future of these metal-free and fully stable semiconductors. This review starts with Received 13th October 2015 the general protocols to engineer g-C3N4 micro/nanostructures for practical use, and then discusses the DOI: 10.1039/c5cs00767d newly disclosed applications in sensing, bioimaging, novel solar energy exploitation including photocatalytic coenzyme regeneration, templating, and carbon nitride based devices. Finally, we attempt www.rsc.org/chemsocrev an outlook on possible further developments in g-C3N4 based research. This article is licensed under a 1. Introduction The tri-s-triazine ring structure and the high degree of condensa- tion provide the polymer with high stability with respect to thermal Carbon nitride oligomers and polymers have a pretty long (up to 600 1C in air) and chemical attack (for example, acid, base, history. The first example in the carbon nitride family could and organic solvents), and an appealing electronic structure, i.e. Open Access Article. Published on 11 February 2016. Downloaded 10/3/2021 1:43:53 PM. be traced back to the 1830s, when Berzelius and Liebig, being a medium-bandgap, indirect semiconductor. These features respectively, reported the general formula (C3N3H)n and coined principally already allow its direct use in sustainable chemistry as a the notation ‘‘melon’’.1,2 Since 1989, work has been inspired by multifunctional heterogeneous metal-free catalyst. Liu and Cohen’s theoretical prediction that the b-polymorph of However, g-C3N4 was not used as a metal-free heterogeneous 3 hydrogen-free C3N4 wouldbeasuperhardmaterial. Meanwhile, catalyst until 2006 when a mesoporous version was used for 4 graphitic carbon nitride (g-C3N4) has attracted much attention, as it catalyzing Friedel–Crafts reaction. The subsequent discovery is the most stable allotrope. Being structurally similar to graphite, of visible-light-driven photocatalytic activity of g-C3N4 for hydrogen g-C3N4 bears strong covalent C–N bonds instead of C–C bonds in evolution by the same group in 2009 disclosed g-C3N4 as a new each layer, while the layers are bound by van der Waals forces, only. generation of metal-free polymeric photocatalysts.5 Since then, The framework topology identified in most ‘‘real-world’’ g-C3N4- the number of studies on the catalytic, electrocatalytic, and photo- substances is a defect-rich, N-bridged ‘‘poly(tri-s-triazine)’’. catalytic performance of graphitic carbon nitride has been steadily increasing.4,5 Future energy and environmental issues by devel- oping facile and economic visible-light-driven photocatalysts a Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, 14424 Potsdam, Germany for environment remediation and energy conversion have been b Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA. addressed, such as photocatalytic H2 evolution from water, photo- E-mail: [email protected] degradation of organic pollutants, photoelectric conversion, CO2 c Center for Nano Energy Materials, State Key Laboratory of Solidification activation, and other important catalytic reactions. Selecting Processing, School of Materials Science and Engineering, Northwestern ‘‘graphitic carbon nitride’’ as a topic in the search engine Polytechnical University, Xi’an, 710072, P. R. China d Department of Chemistry, Stephenson Institute for Renewable Energy, of Web of Science, over 1900 publications could be found, University of Liverpool, Peach Street, Liverpool, L69 7ZF, UK. indicating the enormous interest in g-C3N4. Meanwhile and by E-mail: [email protected] all these joint efforts, a bunch of breakthrough studies have 2308 | Chem. Soc. Rev., 2016, 45, 2308--2326 This journal is © The Royal Society of Chemistry 2016 View Article Online Review Article Chem Soc Rev appeared on the stage, for instance, the quantum efficiency of development of nanosheet based sensors with a superior detection 13,14 g-C3N4 based photocatalytic hydrogen evolution with a sacrificial limit for different targets. Coupling with other substances agent now exceeds 7%;6,7 the graphitic carbon nitride based com- (graphene, semiconductors, metals, etc.)couldboostthesensing posite (with polypyrrole and carbon quantum dots, respectively) capabilities, and importantly, bringoutanewsensingmechanism. revealed the potential for accomplishing overall water splitting.8 While structuring plays important roles in the development of An electrocatalyst composed of graphenes and carbon nitrides, g-C3N4 based sensing, progress in discovering the novel intrinsic only, can potentially replace platinum catalysts in electrochemical properties of g-C3N4, such as its suitability for two-photon absor- 9–11 15 hydrogen evolution. The future practical application of g-C3N4 for bance, is becoming a key to understand this material in a broader sustainable chemistry is thus coming closer and becoming visible. context. For instance, an alternative for traditional fluorescence The rediscovery of g-C3N4 spurred the interest in other sensing has been developed based on a new electrochemical 16 versatile applications also. This can be exemplified by intensive phenomenon of g-C3N4, i.e. electrogenerated chemiluminescence. interest in the investigation of its sensing properties.12 Usually, The facile structural manipulation and amazing phenomena structuring of g-C3N4 into controlled morphologies, especially recently discovered have extended g-C3N4 based research from its shaped nanosheets, substantially helps the enhancement of sensing to bioimaging, solar cells, nanoarchitecture processes, response and consequently the sensitivity, leading to the rapid and nonvolatile memory devices.17–20 The advantageous features of g-C3N4 (simple composition, facile synthesis, low cost, and rich chemistry) have therefore stimulated researchers in a broader range, however inspiring Jian Liu received his PhD degree reviews so far have mainly focused on graphitic carbon nitride in Physical Chemistry with Prof. for (photo)catalysis.21–23 In the present review article, we intend Yanlin Song from Institute of to close this gap and target a relatively comprehensive and Chemistry, Chinese Academy updated review on its emerging applications beyond catalysis. of Sciences in 2011. In January Creative Commons Attribution 3.0 Unported Licence. As many of these novel applications and modifications come with of 2012, he joined Prof. Markus inherent features also useful for photocatalysis, we expect that Antonietti’s group at the Max- with the new properties of g-C3N4 being continually discovered, Planck Institute of Colloids and scientists with different research backgrounds will inspire each Interfaces with an Alexander von other, thus enabling faster, further progress of carbon nitride Humboldt Research Postdoctoral and other related research studies. Fellowship. After two and half years stay in the Department of Jian Liu Colloid Chemistry, he moved to 2. g-C3N4 family with diverse micro-/ This article is licensed under a Prof. Mercouri G. Kanatzidis’s nanostructures group at Northwestern University (Evanston, US) for further studying. His current scientific interest is mainly focused on the The intense recent studies led to the generation of a g-C3N4 synthesis of bio-inspired functional materials for solar energy and family with abundant micro-/nanostructures and morphol- Open Access Article. Published on 11 February 2016. Downloaded 10/3/2021 1:43:53 PM. environmental science. ogies, which are still being extended every day. Synthetic routes, Hongqiang Wang received his Markus Antonietti is a Director of PhD in Condensed Matter the Max Planck Institute of Physics at the Institute of Solid Colloids and Interfaces and has State Physics, Chinese Academy recently focused on sustainable of Sciences, in 2008. He then materials for the energy change. worked, respectively, as a He has written about 650 original Postdoctoral Researcher, an papers and is well cited in the Alexander von Humboldt Fellow field of functional polymers, and a Marie Curie Intra- porous materials, heterogeneous European
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