Carbon Nitride Oxide (g-C3N4)O and Heteroatomic N-Graphene (Azagraphene) as Perspective New Materials in CBRN Defense

Silenko²,

Solonin³

et al. 2019

The development of novel materials ensuring the use of solar radiation as an inexhaustible source of renewable and environmentally friendly energy is one of the actual problems of materials science. Scientific research towards of solving this important task showed the expediency of using photocatalytic processes with the participation of semiconductor systems. One of the most well-known catalyst titanium dioxide TiO 2 has photoactivity only in the ultraviolet region of the spectrum that significantly restricts its use. The application of based on undoped graphitelike carbon nitride g-C 3 N 4 or g-C 3 N 4 /TiO 2 composite catalysts allows using only part of the visible spectrum of solar radiation (with a wavelength of less than 460 nm). It is found that the doping of carbon nitride by oxygen significantly improves its photocatalytic properties to enhancing solar energy utilization. Therefore, to improve the photocatalytic activity of semiconductor photocatalyst, the coupling O-doped g-C 3 N 4 (O-g-C 3 N 4) with rutile TiO 2 is a good strategy. Novel composite material O-g-C 3 N 4 /TiO 2 was synthesized by gas phase method of deposition of O-doped g-C 3 N 4 on particles of rutile powder under the special reactionary conditions of the pyrolysis of melamine. Obtaining O-g-C 3 N 4 /TiO 2 binary composite was confirmed through various analytical techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS) methods. It is found that the absorption spectra of the O-g-C 3 N 4 /TiO 2 powders show a bathochromic shift of the long-wavelength edge of the fundamental absorption band (to 600 nm) relative to the absorption band of g-C 3 N 4 /TiO 2 (~ 460 nm). As a result, O-g-C 3 N 4 /TiO 2 photosensitivity is observed in the significant part of the visible region and the band gap of synthesized product is determined to be less than 2.4 eV versus 2.7 eV for undoped g-C 3 N 4 or g-C 3 N 4 /TiO 2. One stage constructing heterojunction structure of O-g-C 3 N 4 /TiO 2 composite may be used as a low-cost way to avoid the limitations of each component and realize a synergic effect in promoting the efficient generation and separation of charge carriers, thus boosting the photocatalytic activity to enhancing solar energy utilization.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesis O-g-C3N4/TiO2 rutile composite material for photocatalytic application

Silenko²,

Solonin³

et al. 2019

Synthesis of multilayer azagraphene and carbon nitride oxide

Silenko²,

Gubareni³

et al. 2018

As an one of the most promising materials of green energy as a photocatalyst for the production of hydrogen from renewable, natural sources (water, greenhouse gas) and environmental remediation through the degradation of toxic organic pollutants, graphite-like carbon nitride (characterized as a non-toxic and chemically highly resistant material) and its nanostructured and doped (especially by oxygen atoms) derivatives attract special attention. The actual task for expanding the scope of application of g-C 3 N 4 is to improve and optimize its catalytic, electronic and optical properties by increasing both the surface area of graphitic carbon nitride and the number of active centers of the carbon nitride network due to doping of carbon nitride. The use of a mixture of two different precursors ensures the creation of heterojunctions, and as a result, an improvement the photocatalytic characteristics of g-C 3 N 4. The oxygen-doped carbon nitride (O-g-C 3 N 4) and water-soluble carbon nitride oxide (g-C 3 N 4)O was simultaneously synthesized by the gas phase method under special reaction conditions of pyrolysis of cyanuric acid and urea mixture. Reduction by the hydroquinone of carbon nitride oxide (g-C 3 N 4)O yields nanostructured reduced carbon nitride (or reduced multilayer azagraphene). Obtained products were characterized by using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), chemical and X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM). According to the results of XPS and IR spectrometry the chemical bonds between atoms in a heteroatomic plane of reduced carbon nitride (RCN) correspond to the bonds in a synthesized carbon nitride (SCN). However, according to XRD results, reduced carbon nitride (RCN) probably consists of poorly connected heteroatomic azagraphene layers, because it has a significantly larger (on 0.09 nm) interplanar distance between the adjacent nitrogen-carbon layers than interplanar distance between the layers of synthesized carbon nitride (SCN). By SEM characterization it was found that the pyrolysis of a mixture of various precursors (cyanuric acid and urea) yielded a product with smaller crystalline domains (which can improve photocatalytic characteristics) than the pyrolysis of a single precursor (urea only).

Influence of the phase composition of the TiO2 matrix on the optical properties and morphology of deposited C3N4Ox nanoparticles

Silenko²,

Solonin³

et al. 2020

The use of oxygen modified graphite-like carbon nitride (C3N4Ox), photosensitive in the visible region of the optical spectrum, along with TiO2, photocatalytically active only in the ultraviolet region of the spectrum, in the C3N4Ox/TiO2 binary photocatalyst, opens a possibility of the use of sunlight energy. To increase opportunities of various kinds of photochemistry-related applications of C3N4Ox/TiO2 photocatalyst, the phase composition of the TiO2 matrix and morphology of nanoparticles of composite and their optical properties are very important. A novel composite material, C3N4Ox/TiO2, was synthesized in the present work in accordance with the approach developed in Frantsevich Institute for Problems of Materials Science of NASU for the synthesis of powdered oxygen-doped carbon nitride (C3N4Ox) by CVD method under the special reactionary conditions of the melamine pyrolysis, in particular, in the presence of a fixed air volume. Deposition of C3N4Ox carried out on the surface of a nanostructured powdered TiO2 matrix of different phase composition, rutile or anatase. The deposition of C3N4Ox (~5 % O) on both rutile and anatase nanopowders was confirmed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis-DRS) methods. SEM micrographs (recorded with a MIRA3 TESCAN scanning electron microscope) of nanoparticles of both C3N4Ox/TiO2 composites (anatase and rutile phases) demonstrate the arrangement of TiO2 as separate globular nanoparticles and clusters between the plates and in the channels of the porous scaly plates C3N4Ox. However, the anatase phase nanoparticles (synthesized in IPM NASU) have a higher dispersion, the average size of non-aggregated almost monodisperse particles is about 10 nm. Using UV/Vis spectroscopy, it has been found that a redshift of long-wavelength edge of the fundamental absorption band of the spectra is observed when going from TiO2 (anatase), TiO2 (rutile), C3N4, C3N4Ox/TiO2 (anatase), C3N4Ox/TiO2 (rutile) and, then, to C3N4Ox, and the band gap decreases from 3.2, 3.0, 2.6, 2.4, 2.25 to 2.1 eV in the above sequence of materials. In such a case, C3N4Ox/TiO2 (especially deposited on anatase phase) would absorb more visible light than g-C3N4 and TiO2, by generating more charges which favor the improvement in the photoactivity of the catalysts.