Abstract
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.
Highlights
The environmental pollution and energy crisis become an increasing threat to the development of human society
We focus on a study of the photocatalytic TiO2-based system associated with O-doped graphitic carbon nitride (C3N4Ox) [25], since the oxygen-modified graphitic carbon nitride samples synthesized in the IPM exhibit photosensitivity practically in the entire region of the visible spectrum
Synthesis of oxygen-doped carbon nitride (C3N4Ox) (~5 % O) on the surface of the nanostructured powdered TiO2 matrix of different phase composition, rutile or anatase, is confirmed through various analytical techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectra (UV-Vis-Diffuse reflectance spectra (DRS)) methods
Summary
The environmental pollution and energy crisis become an increasing threat to the development of human society. The authors [8] reported the remarkable hydrogen evolution rate under catalysis by oxygen modified C3N4 sample compared with undoped g-C3N4, that was attributed to the synergy between extended visible light response, better separation of the photogenerated charge carriers and the enlarged specific surface area It was assumed [12] that the significant enhancement of photocatalytic activity of O-doped carbon nitride could be ascribed to the synergistic effects of narrowed band gap and improved charge transfer efficiency. Synthesis of oxygen-doped carbon nitride (C3N4Ox) (~5 % O) on the surface of the nanostructured powdered TiO2 matrix of different phase composition, rutile or anatase, is confirmed through various analytical techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS) methods. The band gap energy was determined by plotting (αhν)1/2 νs photon energy
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