Si-doped TiO2 Research Articles

Zirconium-doped and silicon-doped TiO 2 photocatalysts synthesis from ionic-liquid-like precursors

Nanocrystalline titania powders doped with either zirconium or silicon were synthesized at low temperature via destabilization of ionic-liquid-like precursors. Titania materials prepared at low temperature (85 °C) consisted of anatase nanocrystals of about 25 nm, according to powder X-ray diffraction and transmission electron microscopy. Dopant incorporation was evaluated using inductively coupled plasma-optical emission spectrometry, and it was found that dopant/titanium ratios in the powder (0.011 for Zr and 0.026 for Si) were lower than those in the precursor (0.11 for both). Low-temperature nitrogen adsorption–desorption isotherms displayed the characteristic hysteresis loop of mesoporous materials. Specific surface areas reached values of 130 and 155 m 2 g −1 for Zr-doped and Si-doped TiO 2, respectively. The photocatalytic activity of the synthesized nanopowders was tested using methyl orange and 4-chlorophenol as target pollutants.

Synthesis of nanocrystalline anatase TiO 2 by one-pot two-phase separated hydrolysis-solvothermal processes and its high activity for photocatalytic degradation of rhodamine B

Si-doped and un-doped nanocrystalline TiO 2 samples have been synthesized by simple one-pot water-organic two-phase separated hydrolysis-solvothermal (HST) processes, and characterized by XRD, BET, TEM, FT-IR, DRS and surface photovoltage techniques. The effects of the solvothermal temperature and Si doping on the anatase thermal stability, and on the photocatalytic activity for degrading rhodamine B were investigated in detail. The results show that, as the solvothermal temperature rises, the crystallinity and thermal stability of the resulting nano-sized anatase TiO 2 gradually increase. Noticeably, the as-prepared TiO 2 obtained at appropriate solvothermal temperature (160 °C) exhibits high photocatalytic activity. Moreover, although Si doping does not improve the photocatalytic activity of the as-prepared anatase TiO 2, it greatly enhances the anatase thermal stability and inhibits crystallite growth during the process of post-thermal treatment. Interestingly, the Si-doped TiO 2 post-treated at high temperature displays much higher photocatalytic activity than commercial P25 TiO 2. It is clearly demonstrated that the joint effects of high anatase crystallinity and large surface area lead to high photocatalytic activity. This work provides a simple and effective strategy for the synthesis of high-performance TiO 2-based functional nanomaterials.

Electrochemically assisted photocatalytic degradation of phenol using silicon-doped TiO 2 nanofilm electrode

Silicon-doped TiO 2 nanofilm was fabricated by chemical vapor deposition which can control the Si-doping amount well and obtain the rapid deposition of film. The results of X–ray diffraction (XRD) and X–ray photoelectron spectroscopy (XPS) analyses revealed that the introduced silicon might be incorporated into titania matrix. This incorporation helped to increase the thermal stability of titania, which was in favor of suppressing phase transformation from anatase to rutile and also inhibiting the growth of anatase crystallite at high calcination temperature. A significant blue-shift with enhanced absorption intensities was observed in the spectrum of UV absorption for Si-doped sample. The Si-doped sample with 5 mol % of silicon exhibited the best photoelectrochemical property, and its photocurrent density under UV light was 1.7 times that of TiO 2 nanofilm. The photocatalytic (PC) and electro-assisted photocatalytic (EAPC) activities were investigated using phenol as a probe substance. Compared with TiO 2 nanofilm, the Si-doped TiO 2 showed better PC and EAPC capabilities in the degradation of phenol under UV-light irradiation. The kinetic constants of phenol degradation for the 5 mol%-Si-doped TiO 2 in PC and EAPC processes under UV-light irradiation were 1.3 and 1.8 times as great as the values for the undoped TiO 2 nanofilm.

Si-doped mesoporous TiO 2 continuous fibers: Preparation by centrifugal spinning and photocatalytic properties

TiO 2 continuous fibers were prepared by a sol–gel method combined with centrifugal spinning without any template or binder polymer. The fibers were characterized using XRD, FT-IR, SEM, N 2 adsorption–desorption, and UV–vis DRS. The addition of silica was a crucial factor for obtaining long fibers because of the formation of Ti–O–Si networks. The effects of dopant contents and heat treatment temperatures were studied. It was found that the proper addition of silica into titania could improve the surface texture and enhance the thermal stability and crystal stability. When Si/Ti molar ratio was 0.15, mesoporous TiO 2 fibers with a BET surface area up to 127.7 m 2 g −1 were obtained after heat treatment at 700 °C. It displayed the highest photoactivity of all, and the degradation rate of X-3B in aqueous solution reached 99.6% after 75 min under UV irradiation. Furthermore, the degradation rate and the mineralization rate of X-3B were 94.7% and 58.9% after 3 h under solar irradiation, respectively. In addition, it was worthwhile to mention that the degradation efficiency was also more than 90% after 6 cycles.

Integration of separation and photocatalysis using an inorganic membrane modified with Si-doped TiO 2 for water purification

An unsymmetrical inorganic membrane with Si-doped TiO 2 layers was fabricated for the purpose of realizing filtration and photocatalysis in a single device in water purification process. Tetra- n-butyl titanate [Ti(OC 4H 9) 4, TBOT] and tetraethyl orthosilicate [Si(OC 2H 5) 4, TEOS] were used as precursors of TiO 2 and Si element source, and Si-doped TiO 2 photocatalytic layer was coated on a commercial Al 2O 3 membrane by sol–gel technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization demonstrated that the Si-doped TiO 2 thin layer possessed nanoporous membrane structure. The results of UV–vis diffuse reflectance spectra (DRS) and X-ray diffraction (XRD) pattern indicated that a strong UV absorption of as-prepared membrane surface was ascribed to anatase phase of TiO 2 materials. The thickness controllability of Si-doped TiO 2 layer was conducted by repeated-coating procedure, and water permeability and polyethylene glycol (PEG) retention of membrane were related with thickness of the TiO 2 layer. The removal efficiency of model pollutant, dye Reactive Red ED-2B (RR ED-2B), was improved obviously using the membrane under UV irradiation in comparison with photocatalysis or membrane separation alone, which demonstrated that the model pollutant was separated and degraded simultaneously. The multifunctional performance of composite membrane hints this unit may become more powerful in water purification process.

Si doping effects on the photocatalytic activity of TiO 2 nanotubes film prepared by an anodization process

In order to improve the quantum efficiency of TiO2 nanotube film, Si-doped TiO2 nanotubes were prepared by anodizing Ti in HF/Na2SiF6 solution. The experimental results show that the presence of Si can separate photogenerated electrons and holes effectively. It was found that the photocurrent density of Si-doped TiO2/Ti electrode is 2–3 times higher than that of undoped TiO2/Ti electrode, and the photoelectrocatalytic degradation rate of Si-doped TiO2/Ti electrode is increased by 76.6% over that of normal TiO2/Ti electrode at an applied potential of 1.5 V.

A silicon-doped TiO 2 nanotube arrays electrode with enhanced photoelectrocatalytic activity

Silicon-doped titania nanotube arrays were fabricated by electrochemical anodization on a Ti sheet, followed by chemical vapor deposition (CVD) treatment using tetraethylorthosilicate as silicon source. The highly ordered nanotube arrays obtained by anodization kept its nanotube-like structural integrity after CVD treatment. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results revealed that the introduced silicon might be incorporated into titania matrix. This incorporation helped to increase the thermal stability of titania, which was in favor of suppressing the phase transformation from anatase into rutile and also inhibiting the growth of anatase crystallite of titania at high calcination temperature. A significant blue-shift was observed in the spectrum of UV absorption. The surface of Si-doped TiO 2 nanotube arrays showed a super-hydrophilic behavior under UV illumination. For Si-doped TiO 2 nanotube electrode, the maximum photoconversion efficiencies of 31.8% under high-pressure mercury lamp irradiation and 16.5% using an optical filter (280–400 nm) under the same lamp irradiation were achieved, which were obviously higher than those of undoped one. The photoelectrocatalytic (PEC) activities were investigated using pentachlorophenol (PCP) as a probe substance. Compared with undoped TiO 2 nanotube electrode, the Si-doped TiO 2 showed better PEC capability in the degradation of PCP under high-pressure mercury lamp irradiation.

Photocatalytic reduction of NO with NH 3 using Si-doped TiO 2 prepared by hydrothermal method

A series of Si-doped TiO 2 (Si/TiO 2) photocatalysts supported on woven glass fabric were prepared by hydrothermal method for photocatalytic reduction of NO with NH 3. The photocatalytic activity tests were carried out in a continuous Pyrex reactor with the flow rate of 2000 mL/min under UV irradiation (luminous flux: 1.1 × 10 4 lm, irradiated catalyst area: 160 cm 2). The photocatalysts were characterized by X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrophotometer, transmission electron microscopy (TEM), photoluminescence (PL) and temperature-programmed desorption (TPD). The experiment results showed that NO conversion on Si/TiO 2 at 323 K could exceed 60%, which was about 50% higher than that on Degussa P25 and pure TiO 2. With the doping of Si, photocatalysts with smaller crystal size, larger surface area and larger pore volume were obtained. It was also found that Ti–O–Si bands were formed on the surface of Si/TiO 2 and that the surface hydroxyl concentration was greatly increased. As a result, total acidity and NH 3 chemisorption amount were enhanced for Si/TiO 2 leading to its photocatalytic activity improvement.

First-principles calculations for geometrical structures and electronic properties of Si-doped TiO2

Abstract We studied the geometrical structures and electronic properties of Si-doped TiO 2 using spin-polarized density functional theory calculations. Our results show that the valence band maximum has a little raise in substitutional Si to O-doped TiO 2 , and the Fermi level is pinned in the conduction band edge, indicating typical n-type characteristic. In substitutional Si to Ti-doped TiO 2 , the electron transition energy from the valence band to the conduction band has a decrease about 0.25 and 0.2 eV in anatase and rutile TiO 2 , respectively, which may be responsible for the experimental redshift of optical absorption edge.

Preparation, characterization and photocatalytic activity of Si-doped and rare earth-doped TiO2 from mesoporous precursors

Si-doped and rare earth-doped TiO2 with large specific surface area were prepared by the hydrothermal method and sol–gel route, respectively, using C18H37NH2 as template. The samples were characterized by XRD, FT-IR, low-temperature N2 adsorption–desorption measurement, XPS and solid state UV–vis diffuse reflectance spectroscopy. The pore size for Si-doped TiO2 exhibits both mesoporous and microporous distribution, and that for rare earth-doped TiO2 exhibits a sharp and narrow distribution in microporous range. The photocatalytic activities were investigated with the degradation of phenol as probe reaction. Compared with pure TiO2, the conversion of phenol and selectivity to CO2 increases when adding rare earth elements, and the substitution of Si for Ti in an appropriate range also increases the conversion of phenol.

Effect of additives on photocatalytic activity of titanium dioxide powders synthesized by thermal plasma

TiO 2 nanopowder was synthesized from titanium tetrachloride in a thermal plasma reactor. To improve photocatalytic activity, silicon tetrachloride and iron(III) acetylacetonate were added to the plasma reactor. The photocatalytic activity of prepared pure TiO 2 (T-powder), Si-doped TiO 2 (ST) and Fe-doped TiO 2 (FT) powder was evaluated by photodegradation of acetaldehyde. Decomposition efficiency of T-powder under UV-light was increased with the content of anatase. A small amount of Si-dopant improved the photocatalytic activity, while excessive Si-dopant over 2% decreased the photocatalytic activity of ST-powder because of the reduction of active sites on the catalyst. FT-powder was tested for the photocatalytic activity under visible light and UV-light. Decomposition efficiency increased with the addition of Fe-dopant because of suppression of electron–holes recombination. However, excessive Fe-dopant by over 15% inhibited the crystallization of anatase and acted as recombination center, leading to decrease the decomposition efficiency.

Influence of the surface composition of TiO 2 on the electrical conductivity of CuBr–TiO 2 composites

Surface area and composition of nominally pure, Al- and Si-doped TiO 2 (anatase) nanoparticles were investigated. There is a clear evidence for Si segregation in pure and Si-doped TiO 2; the data for Al-doped samples can be interpreted by cosegregation of Al and Si. The electrical conductivity of CuBr–TiO 2 (20 vol%) composites using pure, Al- and Si-doped TiO 2 was investigated by impedance spectroscopy. The observed conductivity modifications can be related to the phase boundary chemistry, especially to the interactions between Cu + ions and OH surface groups of TiO 2.