Xiujian Zhao

Tuning the Relative Concentration Ratio of Bulk Defects to Surface Defects in TiO2 Nanocrystals Leads to High Photocatalytic Efficiency

TiO(2) nanocrystals with tunable bulk/surface defects were synthesized and characterized with TEM, XRD, BET, positron annihilation, and photocurrent measurements. The effect of defects on photocatalytic activity was studied. It was found for the first time that decreasing the relative concentration ratio of bulk defects to surface defects in TiO(2) nanocrystals could significantly improve the separation efficiency of photogenerated electrons and holes, thus significantly enhancing the photocatalytic efficiency.

Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method

TiO2 thin films with different surface structures are prepared from alkoxide solutions containing polyethylene glycol (PEG) via the sol-gel method. The effects of PEG addition to the precursor solution on the surface structures and photocatalytic activity of the resultant thin films are studied. The larger the amount of PEG added to the precursor solution, the larger the size and number of pores produced in the resultant films when PEG added to the gel films decomposed completely during heat-treatment. The adsorbed hydroxyl content of such porous thin films is found to increase with increasing amount of PEG. However, the transmittance of the films decreases due to the scattering of light by pores of larger size and bigger number in the films. Photocatalytic degradation experiments show that methyl orange is efficiently decolorized in the presence of the TiO2 thin films by exposing its aqueous solution to ultraviolet light and the suitable surface structures remarkably enhance the photocatalytic activity of TiO2 films.

Photocatalytic activity of nanometer TiO2 thin films prepared by the sol-gel method

Abstract Transparent TiO2 nanometer thin films with high photocatalytic activity were prepared on soda-lime glass substrates via the sol–gel method using the TiO2 sol solution. The valency state of Ti element and the chemical compositions in TiO2 thin films were analyzed with X-ray photoelectron spectroscopy (XPS). Experimental results showed that besides Ti, O and C elements there is a small amount of Na and Ca elements diffused from the glass substrates and besides Ti(IV) there is a certain amount of Ti(III) and Ti(II) in TiO2 thin film. Heating temperature of 500°C may be adopted to convert TiO2 gel films into TiO2 (anatase) crystalline films and also the TiO2 (anatase) crystalline films show the highest photocatalytic activity. It was also found that the heat treatment for a suitable time at 500°C improves remarkably the photocatalytic activity of the TiO2 thin film, although for too long a time, rather deteriorates it. These results are explained on the basis of the changes in the surface structure and Ti3+ concentration with the heat treatment time.

Comparison of Dye Photodegradation and its Coupling with Light-to-Electricity Conversion over TiO2 and ZnO

Through comparing the photocatalytic performance of microscale ZnO, nano ZnO, and Degussa P25 titania (P25), it was found that the microscale ZnO exhibited 2.6-35.7 times higher photocatalytic activity for the photodegradation of various dye pollutants than P25 under both UV-visible and visible irradiation and showed much better photostability than the nano ZnO. The photocatalysts were characterized with XRD, Raman, BET, DRUV-vis, adsorption of dye, photoelectrochemical measurement, and PL. The much higher photocataltyic activity of the microscale ZnO than P25 under UV-visible irradiation is attributed to the higher efficiency of generation, mobility, and separation of photoinduced electrons and holes. The much higher visible photocataltyic activity of the microscale ZnO than P25 is due to the higher photosensitization efficiency of electron transfer from an excited dye to the conduction band of the microscale ZnO than that of P25. The much better photostability of the microscale ZnO than the nano ZnO is due to its better crystallinity and lower defects. The photostability of the microscale ZnO is greatly improved by the surface modification of ZnO with a small amount of TiO(2). On the basis of the excellent photocatalytic performance of the microscale ZnO and TiO(2)-modified ZnO, a novel device of coupling photodegradation with light-to-electricity conversion was developed, which is a promising candidate for the photocatalytic removal of dye pollutants and a renewable energy source.

Preparation and characterization of super-hydrophilic porous TiO2 coating films

In this study, the super-hydrophilic TiO2 coating films are prepared from alkoxide solutions containing polyethylene glycol (PEG) by the sol‐gel method on soda lime glass. The effects of PEG addition to the precursor solution on the super-hydrophilic property and microstructure of the resultant coating films are studied. The larger the amount and molecular weight of PEG, the larger are the size and numbers of pores produced in the resultant coating films on the decomposition of PEG during heat treatment. The adsorbed hydroxyl content of such porous coating films is found to increase due to the larger size and number of pores in the coating films. However, the transmittance of the coating film decreases due to the scattering by the larger size and number of pores. The contact angle for water of porous TiO2 coating film decreases with the increase of the adsorbed hydroxyl content, capillary force and roughness of the resultant coating films.

Highly Efficient Visible-Light-Induced Photocatalytic Activity of Nanostructured AgI/TiO2 Photocatalyst

Nanostructured AgI/TiO(2) photocatalyst was synthesized by a feasible approach with AgNO(3), LiI, and Ti(OBu)(4) and characterized by X-ray diffraction, transmission electron microscopy, angle-dependent X-ray photoelectron spectroscopy, diffusive reflectance UV-vis spectroscopy, Raman spectroscopy, photoluminescence, and the Brunauer-Emmett-Teller technique. The results of characterization reveal that the nanostructured AgI/TiO(2) has a novel core/shell/shell nanostructure of AgI/Ag-I(2)/TiO(2). Compared with TiO(2) (P25) supported AgI, the formation of the nanostructure results in substantial shifting of the absorption edge of AgI to red, enhancement of the absorption intensity, and the appearance of a strong tail absorption above 490 nm, which is assigned to the absorption of I(2) and Ag. Photocatalytic tests show that the nanostructured AgI/TiO(2) photocatalyst exhibited very high visible-light-induced photocatalytic activity for the photodegradation of crystal violet and 4-chlorophenol, which is 4 and 6 times higher than that of P25 titania supported AgI, respectively. The highly efficient visible-light-induced photocatalytic activity of the nanostructured AgI/TiO(2) is attributed to its strong absorption in the visible region and low recombination rate of the electron-hole pair due to the synergetic effect among the components of AgI, Ag, I(20, and TiO(2) in the nanostructured AgI/TiO(2).

Effect of substrates on the photocatalytic activity of nanometer TiO2 thin films

Abstract Transparent anatase TiO 2 nanometer thin films with photocatalytic activity were prepared via the sol-gel method on soda-lime glass, fused quartz, and soda-lime glass precoated with a SiO 2 layer. The resulting thin films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The photocatalytic activity of the various TiO 2 films was evaluated by the photocatalytic decolorization of aqueous methyl orange. The diffusion of sodium and calcium ions from the soda-lime glass into the nascent TiO 2 films was found to be detrimental to the photocatalytic activity of the resulting TiO 2 films. Sodium and calcium diffusion into nascent TiO 2 films was effectively retarded by a 0.3 μm SiO 2 interfacial layer formed on the soda-lime glass.

Effect of surface treatment on the photocatalytic activity and hydrophilic property of the sol-gel derived TiO2 thin films

Transparent anatase TiO2 nanometer thin films were prepared via the sol-gel method on soda-lime glass, and then the as-prepared TiO2 films were treated in HCl solution. The TiO 2 films before and after treatment were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and UV-visible spectrophotometer. The photocatalytic activity and hydrophilic property of the various TiO2 films were evaluated by the photocatalytic decolorization of aqueous methyl orange and examining the contact angle for water of TiO2 films, respectively. The concentration of sodium and calcium in nascent TiO2 films was effectively reduced and the adsorbed hydroxyl content on the surface of TiO 2 films was found to increase by soaking the as-prepared TiO 2 films in HCl solution. The deleterious effect of sodium and calcium ions from the soda-lime glass on the photocatalytic activity of the nascent TiO2 films was prevented by surface acid treatment. At the same time, hydrophilic property of the treated TiO2 films was enhanced.

Preparation, Microstructure and Photocatalytic Activity of the Porous TiO2 Anatase Coating by Sol-Gel Processing

In this study the porous TiO2 anatase coatings are prepared from alkoxide solutions containing polyethylene glycol (PEG) by a dip-coating technique. The effects of PEG addition to the precursor solution on the photocatalytic activity and microstructure of the resultant coatings are studied. The larger amount and the larger molecular weight of PEG, the larger size and more pores produced in the resultant coatings on the decomposition of PEG during heat-treatment. The adsorbed hydroxyl content of such porous coatings is found to increase due to the larger size and more pores in the coatings. However, the transmittance of the coatings decreases due to the scattering by the larger size and more pores. Photocatalytic degradation experiments show that organophosphorous insecticide, dimethyl-2,2-dichlorovinyl phosphate (DDVP), was efficiently degraded in the presence of the porous TiO2 coatings by exposing the DDVP solution to sunlight. Photocatalytic degradation rate was related to the adsorbed hydroxyl content, transmittance and morphology of the resultant coatings.

Low temperature fabrication of V-doped TiO2 nanoparticles, structure and photocatalytic studies

V-doped TiO(2)nanoparticles were synthesized at low temperature and characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and photoluminescence (PL) spectroscopy, respectively. It is found the nanoparticle shape changed from needle, to short stick and then to cubic with the increase of doped V concentration, which was also accompanied by the improvement of crystallinity. The specific surface area (S(BET)) decreased with increasing V content. It is confirmed that V ions can be doped in TiO(2) by substituting Ti(4+) ions, which suppressed the CB --> VB and surface recombination of photoinduced electrons and holes, and a relation was found between the PL spectra and the UV photocatalytic activity. There was an optimum V content for the V-doped TiO(2) to present the best UV-light induced photoactivity, but they were visible-inactive. At last, the effect of the doping V as trapping centers on photocatalysis was investigated in detail, and used to explain the difference between the photocatalysis under the illumination of UV light and visible light.