Recent Advances of Graphitic Carbon Nitride-Based Structures and Applications in Catalyst, Sensing, Imaging, and LEDs

Abstract

The graphitic carbon nitride (g-C₃N₄) which is a two-dimensional conjugated polymer has drawn broad interdisciplinary attention as a low-cost, metal-free, and visible-light-responsive photocatalyst in the area of environmental remediation. The g-C₃N₄-based materials have excellent electronic band structures, electron-rich properties, basic surface functionalities, high physicochemical stabilities and are "earth-abundant." This review summarizes the latest progress related to the design and construction of g-C₃N₄-based materials and their applications including catalysis, sensing, imaging, and white-light-emitting diodes. An outlook on possible further developments in g-C₃N₄-based research for emerging properties and applications is also included.

Keywords: Catalysis; Graphitic carbon nitride (g-C3N4); Imaging; LED; Sensing.

Fig. 1

a Triazine and b tri-s-triazine (heptazine) structures of g-C₃N₄. Reprinted with permission from Ref. [40]. Copyright 2016 American Chemical Society

Fig. 2

Crystal structure and optical properties of graphitic carbon nitride. a Schematic diagram of a perfect graphitic carbon nitride sheet constructed from melem units. b Experimental XRD pattern of the polymeric carbon nitride, revealing a graphitic structure with an interplanar stacking distance of aromatic units of 0.326 nm. c UV-visible diffuse reflectance spectrum and image (inset) of g-C₃N₄. Reprinted with permission from Ref. [5]. Copyright 2009 Nature Publishing Group. Representation of the β-C₃N₄ (d), α-C₃N₄ (e), graphite-C₃N₄ (f), pseudocubic-C₃N₄ (g), and cubic-C₃N₄ (h). The carbon and nitrogen atoms are depicted as gray and blue spheres, respectively, from Ref. [4]. Copyright 1996 American Association for the Advancement of Science. (Color figure online)

Fig. 3

a Schematic 3D g-C₃N₄/Graphene structures. b, c SEM images of g-C₃N₄/graphene nanocomposites. Inset TEM image. d C 1s, e N 1s XPS and f UV–vis spectra of g-C₃N₄/graphene nanocomposites. Insets: photographs of the powder samples. Reprinted with permission from Ref. [66]. Copyright 2016 American Chemical Society

Fig. 4

a-c TEM images and d AFM image of g-C₃N₄ nanosheets. Inset of c SAED pattern. Reprinted with permission from Ref. [52]. Copyright 2014 John Wiley and Sons. e Schematic illustration of top-down and bottom-up synthetic strategies for g-C₃N₄ nanosheets. Reprinted with permission from Ref. [68]. Copyright 2015 The Royal Society of Chemistry. (Color figure online)

Fig. 5

1D g-C₃N₄ nanostructures. a SEM image of nanotubes [79]. b TEM image of nanotubes [83]. c TEM image of nanorods [81]. d TEM image of porous nanorods [82]. Inset: pore size distribution. e SEM image of nanofibers [30]. f SEM image of tubular structures [85]. Reprinted with permission from Ref. [79] (Copyright 2014 The Royal Society of Chemistry), with permission from Ref. [83] (Copyright 2016 American Chemical Society), with permission from Ref. [81] (Copyright 2014 American Chemical Society), with permission from Ref. [82] (Copyright 2012 The Royal Society of Chemistry), with permission from Ref. [30] (Copyright 2013 American Chemical Society), with permission from Ref. [85] (Copyright 2016 Wiley–VCH Verlag GmbH), respectively

Fig. 6

Morphology characterization of the HR-CN sample. a SEM, b TEM, and c, d corresponding elemental mapping images of g-C₃N₄. Reproduced from Ref. [80] by permission of the John Wiley & Sons Ltd. e A g-C₃N₄ layer and f A single g-C₃N₄ nanotube formed by rolling the g-C₃N₄ layer. Reproduced from Ref. [79] by permission of the Royal Society of Chemistry

Fig. 7

a HOMO-n and b LUMO + n orbitals of the single-layered g-C₃N₄, respectively. c HOMO-n and d LUMO + n orbitals of the double-layered g-C₃N₄, respectively. Reproduced from Ref. [87] by permission of John Wiley & Sons Ltd. e Schematic illustration of the controllable synthesis of g-C₃N₄ nanosheets, nanoribbons, and quantum dots. Reproduced from Ref. [86] by permission of the Royal Society of Chemistry

Fig. 8

a Typical H₂ and O₂ production from water under visible-light irradiation. b Wavelength-dependent QE (red dots) of water splitting by composite catalyst. c QE for different concentrations of carbon dots/g-C₃N₄ catalysts in a fixed mass of composite catalyst. d QE for different catalyst loads with a constant carbon dot concentration in 150 ml of ultra-pure water. Reproduced with permission from Ref. [95]. Copyright 2015 American Association for the Advancement of Science. (Color figure online)

Scheme 1

a Natural photosystem with green leafs, and the enlarged figure (right) depicts the light conversion in the stacked thylakoids. b Schematic illustration for the preparation of MSCN nanocapsules. Adapted with permission from Ref. [14]. Copyright 2017 American Chemical Society

Scheme 2

a Schematic representation of g-C₃N₄/MnO₂ nanocomposite for sensing of GSH. Reproduced with permission from Ref. [107]. Copyright 2014 American Chemical Society. b Schematic illustration of the dual-wavelength ratiometric ECL-RET biosensor configuration strategy. Reproduced with permission from Ref. [114]. Copyright 2016 American Chemical Society

Fig. 9

a In vivo tumor volume growth curves of mice in different groups after various treatments. b Body weight changes of Balb/c mice versus treated time under different conditions. c Photographs of excised tumors from representative Balb/c mice after 14 day treatment and d the corresponding digital photographs of mice in the control group and “UCNPs@g-C3N4 − PEG with 808 nm laser” group after 14 day treatment. e H&E stained tumor sections after 14 day treatment from different groups. Reproduced with permission from Ref. [118] Copyright 2016 American Chemical Society

Fig. 10

a Photoluminescence spectrum of the g-C₃N₄/silica gels excited at 365 nm displaying four peaks (430, 480, 580, and 627 nm) in the visible regime. b, c Photographs of a free-standing g-C₃N₄/silica-gel membrane, displaying both good transparency b and flexibility c. d CIE-1931 chromaticity diagram showing the emission from the typical g-C₃N₄/silica gels (marked by the black cross) excited at 365 nm. e FTIR spectra of AEATMS, g-C₃N₄-silica gels, and g-C₃N₄ particles. f Schematic drawing of an AEATMS-capped g-C₃N₄ particles in the g-C₃N₄/silica gels. Reproduced with permission from Ref. [119]. Copyright 2016 Wiley