The Synthesis Of Visible-light Photo-catalysis Nitrogen-carbon-doped Nano-TiO₂ Film By Sol-gel Method

Photoinduced oxidation and reduction reactions at the surface of TiO2 particles orthin films have been attracting much attention in view of their possible applicationsranging from photo electrochemical splitting of water into hydrogen and oxygenand wet solar cells to photocatalysis. Its unique photocatalytic properties make itsuitable for the oxidation of organic pollutants and other contaminants fromwastewater or drinking water supplies. TiO2 has a serious disadvantage in that itcan absorb only UV light, therefore, it is widely recognized that the development ofphotocatalysts should allow the main part of the solar spectrum, and even poorillumination of interior lighting, to be used.Recently, the major goal in the development of TiO₂-based materials is to extendthe photoactivity from 3.2eV into the range of visible light in order to utilize solarlight more efficiently. One approach was to dope transition metals into TiO2, andanother was to form reduced TiOx photocatalysts. Recently, doping ofpolycrystalline powders and films of TiO2 with anion impurities such as nitrogencarbonand sulfur has been shown to be effective in lowering the threshold energyfor photochemistry on the TiO₂ surface. Asahi et al. have accomplished N-dopingby reactive sputtering of TiO₂ film targets in N₂/Ar gas mixtures, byhigh-temperature treatment of TiO₂ powders in NH3/Ar atmospheres, and byoxidative annealing of TiN powder. In these cases, a noticeable new absorptionrange for light at energies less than the band gap energy of 3.0 eV has beenobserved and the films and powders of TiO2-xNx showed a dramatic improvementover pure titanium oxide under visible light in their optical absorption and the levelof photocatalytic activity. ShahedThe research of the nano-film synthesis was followed:1.Visible-light Photocatalysis in Nitrogen-carbon-doped TiO2 Film by HeatingTiO2 Gel-Film Using the Ionized N2: Recently, doping of polycrystalline powdersand films of TiO2 with anion impurities such as nitrogen, carbon, and sulfur hasbeen shown to be effective in lowering the threshold energy for photochemistry onthe TiO2 surface. Asahi et al. have accomplished N-doping by reactive sputtering ofTiO2 film targets in N2/Ar gas mixtures, by high-temperature treatment of TiO2powders in NH3/Ar atmospheres. The research for the N-doped TiO2 has found thatit can absorb the light between 400-520nm of the Visible-light and realize thecatalysis of the TiO2.We sought a photocatalyst with high reactivity under visible light. Nitrogen andcarbon doping TiO2 films were obtained by heating the TiO2 gel in an ionized N2gas. Films of TiO2-x-yNxCy have revealed an improvement over titanium dioxide(TiO2) under visible light in optical absorption and photocatalytic activity such asphotodegradation of methyl orange. The result of FE-SEM showed that the TNCfilm has more homogeneous particle size than s-s film. The UV-visible absorptionmeasurements indicates that the TiO2-x-yNxCy films noticeably absorb the light atthe range of visible light and have high absorbance, whereas the absorbance of s-sfilm was much lower. The N (1s) core levels (figure 1a) of TNC film revealed threepeak structures at binding energies of 402.4eV, 399.2eV, and 396.3eV. Thenitrogen peak at 396.3eV was assigned to the N-Ti bonds. The C (1s) core levels ofTNC film revealed four peak structures at binding energies of 288.1eV, 286.3eV,284.6eV and 282.9eV. the carbon peak at 282.9eV was attributed to the C-Tibinding which represented that carbon was doped into substitutional sites of O inTiO2. Thus, the observed changes in the XPS spectra are providing consistentstructural information for O-Ti-N and O-Ti-C formation, the substitutional dopingof nitrogen and carbon for oxygen, which leads to the enhanced photocatalyticactivity in TNC film.The process of the oxygen atom substituted by nitrogen and carbon wasdiscussed. Oxygen vacancy induced by the formation of Ti3+ species and nitrogenand carbon doped into substitution sites of TiO2 have been proven to beindispensable for the better photocatalytic activity, as assessed by UV-VisSpectroscopy and X-ray photoemission spectroscopy.2.Nitrogen and carbon doping TiO2-x-yNxCy films were calcined at 450 oC for 2hto discuss the thermal stability of the films. The TTNC films have revealed animprovement over the TiO2 films under visible light in optical absorption andphotocatalytic activity such as photodegradation of methyl orange. X-rayPhotoemission Spectroscopy, Infrared spectrum and UV-Visible Spectroscopy wereused to find the difference of two kinds of films. There is a new N-O with thebinding energy at 400.1eV which assigned to (N2O2)2-responsible for theimprovement of the photo-catalysis of the films. This also proves the thermalstability of the TNC films.The nitrogen-carbon-doped TiO2 film by heating TiO2 gel-Film using the ionizedN2 increase the visible-light photocatalysis of TiO2 film on glass. After TNC filmswere calcined at 450 oC for 2h to discuss the thermal stability of the films, wefound the improved photo catalysis of TiO2 films.