Materials Science Forum Vol. 712

Abstract: The use of nanosized semiconductor particles in various forms for the photocatalytic degradation of pollutants has been discussed. The aim of this review is to provide a critical analysis of various reports on the degradation of pollutants by various semiconductor nanomaterials. It has been shown that self-organized one-dimensional nanotube matrix creates a better opportunity to remove pollutants more efficiently than the randomly oriented nanoparticles. The use of metal doping and mixed semiconductor systems has also been analyzed. Although large improvements in the present technology are required, the review points to focus on the advantages of nanomaterials compared to bulk materials in efficient purification of water.

Abstract: Tremendous amount of research work is going on Titanium dioxide (TiO₂) based materials. These materials have many useful applications in our scientific and daily life and it ranges from photovoltaics to photocatalysis to photo-electrochromics, sensors etc.. All these applications can be divided into two broad categories such as environmental (photocatalysis and sensing) and energy (photovoltaics, water splitting, photo-/electrochromics, and hydrogen storage). Synthesis of TiO₂ nanoparticles with specific size and structural phase is crucial, for solar sell application. Monodispersed spherical colloids with minimum size variation (5% or less) is essential for the fabrication of photonic crystals. When sensitized with organic dyes or inorganic narrow band gap semiconductors, TiO₂ can absorb light into the visible light region and convert solar energy into electrical energy for solar cell applications. TiO₂ nanomaterials also have been widely studied for water splitting and hydrogen production due to their suitable electronic band structure given the redox potential of water. Again nanostructured TiO₂ has extensively been studied for hydrogen storage with good storage capacity and easy releasing procedure. All these issues and related finding will be discussed in this review.

Abstract: Visible light-sensitive carbon doped titanium dioxide nanoparticles (C-TiO₂) were prepared by a sol-gel method. The carbon dopant was obtained from glucose. The dopant level incorporated into the TiO₂ lattice structure was varied by using different concentrations of the carbon source solution. The nanoparticles were characterized by X-ray diffraction (XRD), BET Surface area, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Scanning X-ray photoelectron spectroscopy (SXPS) and Diffuse reflectance spectroscopy (DRS). The presence of carbon in the TiO₂ lattice was determined by SXPS. The DRS results revealed that carbon doping reduced the band gap of TiO₂. Doping was also found to cause a reduction in the particle size of the TiO₂ nanoparticles and enhance anatase to rutile phase transformation. The photocatalytic activities of the prepared samples were evaluated by the photocatalytic degradation of methyl orange. The carbon doped TiO₂ showed a higher photocatalytic activity than degussa P25 and undoped TiO₂.

Abstract: Photocatalytically active TiO2 and silica doped TiO₂ (Si-TiO₂) synthesised using an aqueous sol-gel method and is characterised by particle size analysis, XRD, diffuse reflectance spectra and BET measurements. The photocatalytic analysis using methylene blue proved that the Si-TiO₂ possesses higher activity than pure TiO₂. This Si-TiO₂ having higher photo-catalytic activity was incorporated into white portland cement and this modified cement exhibited photo-catalytic activity as evaluated by using methylene blue degradation experiments. This novel work is considered to be useful for further development of self-cleaning cements. Moreover silica doped to TiO₂ improved surface area and thermal stability of anatase TiO₂ significantly. At 800 ^оC, 100 percentage anatase phase was obtained for Si-TiO₂ whereas pure TiO₂ showed 100 percentage rutile phase at the same temperature and surface aera of the Si-TiO₂ was 93 m²/g while pure TiO₂ showed only 2 m²/g.

Abstract: Bi₂O₃-TiO₂ nanocomposites were obtained by sol-gel method using tween 80 (T-80) or polyvinyl pyrrolidone-polyethylene glycol (PVP-PEG) as templating agent. The powder X-ray diffraction (XRD) patterns of both the composites reveal the crystal structure of Bi₂O₃ as primitive tetragonal and TiO₂ is in anatase phase. The energy dispersive X-ray (EDX) spectra provide the composition of Bi₂O₃ in Bi₂O₃-TiO₂ (T-80) and Bi₂O₃-TiO₂ (PVP-PEG) as 3.8 and 20.4 mol. %, respectively. The average crystallite sizes of Bi₂O₃-TiO₂ (T-80) and Bi₂O₃-TiO₂ (PVP-PEG), derived from XRD, are 9 and 17 nm, respectively. The scanning electron microscopic (SEM) images show the spherical shape of Bi₂O₃-TiO₂ (T-80) and the composites are polycrystalline. The diffuse reflectance spectra (DRS) of the composites display faint absorption of visible light and strong absorption in UV-A region. The photoluminescence (PL) spectra of both the composites are similar and the observed near band gap emission (NBE) and deep level emission (DLE) agree with those of TiO₂. The impedance spectra show that the charge-transfer resistances of the composites do not differ significantly. The visible light photoimpedance spectra display the photoconductance of Bi₂O₃-TiO₂ (PVP-PEG) but not that of Bi₂O₃-TiO₂ (T-80). Although the visible light-photocatalytic activities of the two nanocomposites to degrade dye do not differ significantly Bi₂O₃-TiO₂ (T-80) under UV-A light degrades dyes faster than Bi₂O₃-TiO₂ (PVP-PEG).

Abstract: nanosized titania catalyst and transition metal doped titania photocatalysts such as TiO₂/Ag, TiO₂/Cu and TiO₂/Ag/Cu were used for photocatalytic degradation of Amaranth. Doping of titania was done with impregnation method. Photocatalytic activity was checked in terms of percentages of decolorization, COD removal and TOC removal. It was found that TiO₂/Ag/Cu doped photocatalyst was more effective for Amaranth dye degradation under feasible treatment conditions. For decolorization, Amaranth took irradiation time of 210 min with UV/H₂O₂ but it took only 60 min with TiO₂/Ag/Cu doped photocatalyst. Only 29% COD and 49% TOC removal were achieved with homogeneous photodegradation, whereas with TiO₂/Ag/Cu heterogeneous photodegradation, 100% COD and 98% TOC removal was achieved in 9h for 50 ppm aqueous Amaranth solution. The relative electrical energy consumption per order of magnitude for photocatalytic degradation of Amaranth was considerably lower with TiO₂/Ag/Cu catalyst than that with UV/H₂O₂ and other combinations of doped photocatalyst. The photocatalysts were characterized using XRD and TEM analysis.

Abstract: The work presented in this paper is focused on the influence of dye sensitized TiO₂ for the elimination of a toxic dye intermediate J-acid (6-Amino naphthol-3-sulphonic acid). Effect of catalyst concentration, pH, initial concentration, H₂O₂ and ultrasound on the photocatalytic degradation of the dye intermediate was studied using an immersion well slurry reactor. A comparison of the catalytic activity of dye sensitized TiO₂ with UV 100 and ZnO photocatalysts under visible light illumination was also done.

Abstract: TiO₂ thin film enhanced by diethanolamine (DEA) and MCM-41 (D-TiO₂/MCM-41) was successfully synthesized by sol-gel dip coating technique on glass slides. The roles of DEA and MCM-41 on physical and photocatalytic characteristics of the films were studied using various techniques such as x-ray defraction (XRD), fourier transform infrared spectroscopy (FTIR), ultra violet-visible (UV-Vis) spectrometry, Brunauer, Emmett and Teller (BET) surface area analysis and field emission scanning electron microscope (FESEM). The XRD results showed that the thin film contained almost 100% anatase phase and the crystal size of TiO₂ was in the range of 4-8 nm. The FTIR spectra indicated the formation of Ti-O-Si and Si-O-Si linkages due to interaction of TiO₂ and MCM-41. The surface area of TiO₂ was increased significantly when MCM-41 was added. The use DEA and MCM-41 caused slight increase in visible light absorption but UV absorption was decreased. The photocatalytic reactivity of the thin film was tested by photocatalytic degradation of methylene blue under visible light. The addition of DEA as a nitrogen source was beneficial not only for obtaining stable/smooth surface of the thin film but also for enhancing photocatalysis of methylene blue by preventing charge carrier recombination. While MCM-41 played important functions in improving porosity and hydrophilicity of the film. The photodegradation of methylene blue was obtained up to 35% of its original concentration when 1M DEA and 0.3M MCM-41 were incorporated in TiO₂ thin film. The overall enhancement of photocatalytic activity of the film was a result of nitrogen doping, increased surface area as well as increased hydrophilicity provided by MCM-41.

Abstract: This study aims to provide the photocatalytic approach for treatment of some hazard air pollutants such as benzene, toluene, ethylbenzene and xylene (BTEX) under visible light. Silver doped titanium dioxide (Ag/TiO₂) thin films with various molar ratios (0.01, 0.05, 0.1 and 0.2 mol) were synthesized via sol-gel method and dipped on polyvinyl chloride (PVC) sheet before curing with UV lamp. The X-ray diffractograms showed the composite of TiO₂ anatase and nanosilver. The effect of silver doping on decreasing of band gap energy of TiO₂ was observed from the absorption edge shift to higher wave length, analyzed by UV-visible spectrometer. The results from hydrophilicity test indicated that hydrophilicity of TiO₂ thin film was increased by doping silver. The morphology of the Ag/TiO₂ thin film studied by Scanning Electron Microscope equipped with an Energy Dispersive Spectrometer revealed well dispersed nanosilver on the smooth thin film. The BTEX degradation was carried out in a batch reactor with the initial concentration of mixed BTEX gas [25 ppm]. The remaining BTEX was examined by Gas Chromatography equipped with flame ionization detector. Among Ag/TiO₂ thin films, the 0.1 Ag/TiO₂ thin films exhibited the best performance for gaseous BTEX degradation under visible light. The maximum degradation efficiency was belong to xylene (89%), followed by ethylbenzene (86%), toluene (83%) and benzene (79%).