Papers by Keyword: Visible Light

Abstract: Mesoporous S-doped TiO₂ microspheres were synthesized via hydrothermal method using Ti (SO₄)₂ precursor and urea as homogeneous precipitate agent. The TiO₂-based catalyst samples were characterized by means of Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), N₂ adsorption/desorption and UV-vis diffuse reflectance spectra (UV-vis DRS). Photo-catalytic experiments were carried out by catalytic degradation of methylene blue aqueous solution under visible light. It was found that the S-doped TiO₂ microspheres gave better photo-catalytic performances. The higher absorbance in the visible region explained this phenomenon. There was an appropriate Ti (SO₄)₂ amount for the catalyst with better photo-catalytic degradation.

Abstract: Platinum doped Tungsten Oxide (WO₃/Pt) has been successfully coated on the glass substrate using spray deposition method. Doping of Pt on WO₃ was carried out by phodeposition method. The amount of Pt was varied by weight fraction of 0%, 1%, 2%, 4%. These films were characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). It is found that the crystal structure of WO₃ was not change with the Pt addition. However, the dominant plane orientation and the size of crystal were influenced by Pt addition. The crystal size increases with increasing the amount of Pt. After Pt addition, the film morphology showed the presence of pillar structure. The photocatalytic activity test resulted that WO₃/Pt photocatalyst has the ability for degradation of methylene blue (MB) under sunlight irradion. Significantly, the maximum efficiency of photodegradation was observed at 4% Pt doping amount in the WO₃ sample.

Abstract: The Ag₃PO₄ crystal with 200-600 nm in diameter was successfully synthesized using co-precipitation method with AgNO₃ and Na₂HPO₄^.12H₂O as starting materials. The product was characterized using XRD, DRS, FTIR and SEM. The photocatalytic activities were evaluated under blue light irradiation assisted by Fe²⁺. The 1 mL of Fe²⁺ aqueous solutions consisted of 1.00, 0.10, 0.01, 0.001 and 0.0001 mM Fe²⁺ was added into a 100 mL solution of Rhodamine B, and the photocatalytic oxidation of Rhodamine B was carried out under visible light irradiation. The highest photocatalytic activity was observed when 1 ml of 0.001 mM of Fe²⁺ aqueous solution was added in the Rhodamine B solution. The result inferred the possibility of in-situ peroxide generation during the photocatalysis reaction.

Abstract: The Bi₂O₃/Ag₃PO₄ composites consisting of the monoclinic α-Bi₂O₃ and body-centered cubic Ag₃PO₄ were successfully synthesized by grinding Ag₃PO₄ and Bi₂O₃ mixtures in ethanol using an agate mortar, followed by calcination at 500°C for 5 hours, where the Ag₃PO₄ was synthesized by co-precipitation method using AgNO₃ and NaH₂PO₄^.2H₂O as starting materials. The Bi₂O₃ content in the composite materials changed from 5 to 25 mol.%. The composites were characterized using XRD, DRS and BET specific surface area. The photocatalytic activities were evaluated using Rhodamin B degradation under visible light irradiation of blue LED (λ = 445 nm). The highest photocatalytic activities could be obtained at 5 mol.% Bi₂O₃ in Bi₂O₃/Ag₃PO₄ composite. The enhanced photocatalytic activity could be attributed to the effective separation of hole (h⁺) and electron (e^-) pairs in the Bi₂O₃/Ag₃PO₄ composite.

Abstract: In a single photoreactor, the degradation of rhodamine B (RhB) was studied on TiO₂ and Co-doped TiO₂ (Co-TiO₂) films under visible light. The results show that the degradation rate of RhB by photocatalytic (PC) and photosensitization (PS) on Co-TiO₂ films is quicker than that by PS degradation on TiO₂ film. However, a fast N-de-ethylation leads to the increase in degradation rate unsatisfactory. When a bias potential was applied onto Co-TiO₂ films, the degradation rate of RhB greatly increased. This can be attributed to the generation of more hydroxyl radicals on Co-TiO₂ anodes and cathode. These OH⋅ radicals attack the chromophoric structure of RhB. In addition, with the bias potential application, the optimal Co²⁺ dopant concentration increases from 0.02 % to 0.4%.

Abstract: The graphitic carbon nitride (g-C₃N₄) materials have been synthesized from nitrogen rich precursors such as urea and thiourea by directly heating at 520 °C for 2 h. The as-synthesized carbon nitride samples were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) and particle size analysis. The photoelectrochemical measurements were performed using several on-off cycles under visible-light irradiation. The x-ray diffraction peak is broader which indicates the fine powder nature of the synthesized materials. The estimated crystallite size of carbon nitrides synthesized from urea (U-CN) and thiourea (T-CN) are 4.0 and 4.4 nm respectively. The particle size of U-CN and T-CN were analysed by particle size analyser and were found to be 57.3 and 273.3 nm respectively. The photocatalytic activity for the degradation of the textile dye namely, direct red-81 (DR81) using these carbon nitrides were carried out under visible light irradiation. In the present investigation, a comparison study on the carbon nitrides synthesized from cheap precursors such as urea and thiourea for the degradation of DR81 has been carried out. The results inferred that U-CN exhibited higher photocatalytic activity than T-CN. The photoelectrochemical studies confirmed that the (e^--h⁺) charge carrier separation is more efficient in U-CN than that of T-CN and therefore showed high photocatalytic degradation. Further, the smaller particle size of U-CN is also responsible for the observed degradation trend.

Abstract: Typha latifolia were successfully used as template to synthesize mesoporous titania and silica with efficient photocatalytic activity under solar and visible light. Both two titania and silica samples were characterized by a combination of various physicochemical techniques, such as, N₂ adsorption/ desorption isotherm, diffuse reflectance UV-vis, and X-ray diffraction. It was found that both two synthesized samples exhibited similar morphologies to the original templates. The presence of the residual carbon species of mesoporous titania and silica strongly affects their photocatalytic activity. The photoactivity of P25 TiO₂ could not almost exhibit while both mesoporous titania and silica samples exhibited varied photoactivities for dyes under visible light, due to the presence of the residual carbon species. Moreover, as a whole the titania sample enhanced the higher photocatalytic activity than the silica sample under both solar and visible light.

Abstract: Precision guided weapons played important roles in war. For disturbing the guidance of laser, thermal infrared and TV, the Interference camouflage smoke material covering the visible light, thermal infrared and millimeter wave band, was studied in this paper. Meanwhile, the effects of combustion’s multi-band interference camouflage were proved in the experiment. And based on the calculation model of TV guidance seeker range, the analysis of multiband smokescreen camouflage interference effect was provided.

Abstract: The effect of dopant concentration on N, Fe co-doped TiO2 for photodegradation of methylene blue under ordinary visible light was investigated. The photocatalyst samples were prepared using solgel method with titanium tetraisopropoxide as precursor of titania. The dopant concentrations were varied from 0.50% and 1.0% and the calcinations temperature was fixed at 600oC. The prepared photocatalysts were characterized using XRD and FTIR to determine their physical properties. The results from XRD proved that photocatalyst with dopant concentration of 1.0% N, 1.0% Fe-TiO₂ showing highly desirable properties in phase and crystal size. The results from FTIR revealed the presence of both the dopants in the samples. The effectivity of photocatalysts was tested by performing a standard batch photocatalytic degradation experiment with methylene blue as a model pollutant under ordinary visible light. The result showed that photocatalyst with high dopant concentration for both nitrogen and ferrum dopant (1.0 % N, 1.0% Fe-TiO₂) yielded a maximum of 80.50% methylene blue degraded within five hours of irradiation time.

Abstract: Yellow colored anatase Fe/N co-doped TiO₂ powders have been successfully synthesized by one step hydrothermal method at a lower temperature. The grain size was about 10 nm and the specific surface area of the powders ranged from 160 to 166 m²/g. The light absorption of Fe/N co-doped TiO₂ powders was enhanced in the visible light region of 400~500 nm and a new absorption peak at about 470 nm appeared when the Fe/Ti ratio exceeded 0.5%. The visible light photoactivity of Fe/N co-doped TiO₂ powders has been greatly improved than that of un-doped TiO₂ powders under visible light irradiation.