Ni控制掺杂TiO2薄膜的光电化学及光催化活性

采用溶胶-凝胶法通过分步控制工艺制备了镍离子不同掺杂方式的TiO₂薄膜。通过甲基橙的光催化降解动力学来表征其光催化活性。结果表明：镍离子非均匀掺杂在掺杂量0.5%时可以明显增强TiO₂的光催化活性，而均匀掺杂提高TiO₂的光催化活性较小。光电化学表征结果显示：镍离子非均匀掺杂TiO₂薄膜的瞬时光电流信号较强，说明其光生载流子易于生成且分离效果较好；循环伏安曲线表明，光照时Ni非均匀掺杂的TiO₂薄膜改变了体系的氧化还原电位，说明了薄膜内建电场的建立。基于半导体的P-N结原理探讨了镍离子非均匀掺杂TiO₂薄膜的光催化活性机理。     

总气压与Ar/O2流量比对直流对向靶磁控溅射TiO2薄膜光催化性能的影响

采用对向靶磁控溅射法在不同气压和Ar/O₂流量比条件下, 以氟化SnO₂ (FTO)导电玻璃为基底制备了多晶TiO₂薄膜. 台阶仪测量结果显示所制备TiO₂薄膜的平均厚度约为200 nm. 随着溅射气压的升高, TiO₂薄膜由锐钛矿与金红石混晶结构转变为纯锐钛矿结构. 分别采用场发射扫描电镜(FESEM)和原子力显微镜(AFM)分析了不同气压和Ar/O₂流量比对TiO₂薄膜表面形貌的影响, 结果显示TiO₂薄膜的表面粗糙度随溅射总气压和Ar/O₂流量比的增加而增大. 以初始浓度为100×10^-6 (体积分数)的异丙醇(IPA)气体为目标物检测所制备TiO₂薄膜的光催化性能, 并分析该气相光催化反应的机理, 在紫外照射条件下异丙醇先氧化为丙酮再被氧化为CO₂.当总溅射气压为2.0 Pa、Ar/O₂流量比为1:1时, 溅射所得TiO₂薄膜具备最优光催化活性并可在IPA降解反应中保持较高的催化活性和稳定性.     

Effect of dopant concentration on photocatalytic activity of TiO2 film doped by Mn non-uniformly

The thin films of TiO₂ doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO₂ films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO₂ films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO₂ thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO₂ films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO₂ films in terms of effective separation of the photon-generated carriers in the semiconductor.     

Fabrication of Ordered TiO2 Porous Thin Films by Sol-Dipping PS Template Method

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-drawing method from emulsion of PS and porous TiO₂ thin films were prepared by using sol-dipping template method to fill TiO₂ sol into the interstices among the close-packed PS templates and then annealing to remove the PS templates. The effects of TiO₂ precursor sol concentration and dipping time in sol on the porous structure of the thin films were studied. The results showed pore size of the ordered TiO₂ porous thin film depended mainly on PS size and partly on TiO₂ sol concentration. The shrinkage of pore diameter was about 10% for 0.2 M and 20% for 0.4 M TiO₂ sol concentrations. X-ray diffraction (XRD) spectra indicated the porous thin film was anatase structure. The transmittance spectrum showed that optical transmittance of the porous thin film kept above 70% beyond the wavelength of 430 nm. Optical band-gap of the porous TiO₂ thin film (fired at 550^∘;C) was 3.12 eV.     

Surface properties and photocatalytic activity of nanocrystalline titania films

In this work the efficiency and physicochemical details of a thin film produced by help of a microwave assisted sol gel technique is compared to different commercial powders (Degussa P25 and Hombikat UV100) deposited on glass substrates. Furthermore, a supercritical produced TiO₂ powder (SC 134) was included in the comparison.The prepared TiO₂ films were characterized using XRD, XPS, AFM, DSC and DLS. The photocatalytic activity was determined using stearic acid as a model compound. Investigation of the prepared films showed that the Degussa P25 film and the sol–gel film were the most photocatalytic active films. The activity of the films was found to be related to the crystallinity of the TiO₂ film and the amount of surface area and surface hydroxyl groups. Based on the XPS investigation of the films before and after UV irradiation it was suggested that the photocatalytic destruction of organic matter on TiO₂ films proceeds partly through formation of hydroxyl radicals which are formed from surface hydroxyl groups created by interactions between adsorbed water and vacancies on the TiO₂ surface. Furthermore a correlation between the amount of OH groups on the surface of the different TiO₂ films and the photocatalytic activity was found.     

Comparison of optical and structural properties of nanostructure TiO2 thin film doped by Sn and Nb

The thin films of TiO₂ doped by Sn or Nb were prepared by sol–gel method under process control. The effects of Sn and Nb doping on the structural, optical and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD) high resolution transmission electron microscopy and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy. XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO₂. Titania rutile phase formation in thin film was promoted by Sn⁴⁺ addition but was inhibited by Nb⁵⁺ doping. The activity of the photocatalyst was evaluated by photocatalytic degradation kinetics of aqueous methylene blue under UV and Visible radiation. The results show that the photocatalytic activity of the Sn-doped TiO₂ thin film have a larger degradation efficiency than Nb-doped TiO₂ under visible light, but under UV light photocatalytic activity of the Nb-doped TiO₂ thin film is better.     

Preparation of Titanium Oxide Layer on Silica Glass Substrate with Titanium Naphthenate Precursor

Nanocrystalline TiO₂ thin films on silica glass substrates were prepared by using a naphthenic acid precursor. As-deposited thin films were heat treated at 500, 600, 700 and 800^∘C for 30 min in air. The TiO₂ thin films were analyzed by High Resolution X-ray diffraction, ultra violet—visible—near infrared spectrophotometer, field emission—scanning electron microscope and scanning probe microscope. After annealing at 600 and 700^∘C, the XRD patterns consist of only anatase peaks of TiO₂ film. Rutile(110) peak begins to appear at an annealing temperature of 800^∘C. Relative high transmittance at visible range was obtained for all films except the film annealed at 800^∘C. Optical band gap, E_g, is in the range between 3.53 and 3.78 eV except the TiO₂ film annealed at 500^∘C. The best hydrophilicity was achieved with a high-temperature annealing.     

Preparation of TiO2 Thin Film Photocatalysts by Dip Coating Using a Highly Viscous Solvent

TiO₂ thin film photocatalysts coated onto soda lime glass were prepared by a dip coating process using a highly viscous solvent. The source of the TiO₂ was tetraisopropyl orthotitanate, and -terpineol was used as the solvent. Two types of thin film preparation procedures based on dip coating (a sol-gel system and thermal decomposition system) were used to prepare the samples. TiO₂ thin films were obtained after calcination at 450°C for 1 hour. The film thickness obtained with a single dipping was proportional to the viscosity of the dip coating solutions. The obtained thin films were transparent with a thickness of 1 m. The crystal form of the obtained photocatalyst films was anatase alone. The thin films were formed with aggregated nano-sized TiO₂ single crystals (7–15 nm). The photocatalytic activity of the TiO₂ thin films, as evaluated by the photooxidation of NO (1 ppm) in dry air, was as high as our previous TiO₂ thin films prepared by the sol-gel method.     

Photocatalytic reduction of nitrate over TiO2 and Ag-modified TiO2

This research work presents the efficiency of the TiO₂ and Ag–TiO₂ thin films prepared by the sol–gel method and coated onto the surface of 304 stainless steel sheets used in the photocatalytic nitrate reduction processes. The Ag–TiO₂ thin films had the weight by weight (w/w) ratio of Ag⁺/TiO₂ of 0.1% as Ag atom. The XRD results showed that the crystalline phase structure of TiO₂ on the Ag–TiO₂ thin films was anatase. The optical band gaps of the TiO₂ and 0.1% Ag–TiO₂ thin films were respectively 3.27 and 2.70 eV, while the surface of the prepared catalysts was hydrophobic with the respective average water contact angles of 94.8° and 118.5° for the TiO₂ and 0.1% Ag–TiO₂ thin films. The net efficiencies of photocatalytic nitrate reduction of TiO₂ and 0.1% Ag–TiO₂ were 41.4% and 70.0%, respectively. The loading of Ag only influenced the nitrate removal efficiency without affecting the stoichiometric ratio of formate to nitrate. The net stoichiometric ratio of formate to nitrate of all experiments was 2.8:1.0, which is close to the stoichiometric ratio of 2.5:1.0 of the nitrate reduction to nitrite and then to nitrogen gas.     

掺杂钒和硅对TiO2薄膜超亲水性的影响

0引言 TiO2薄膜是众多氧化物半导体薄膜中研究最为广泛的一种材料．其表面的超亲水性和表面自清洁效应开辟了光催化薄膜功能材料的新的研究领域，已成为众多研究者研究的对象。但是如果薄膜仅由TiO2组成，当光照停止，水在TiO2薄膜表面的润湿角逐渐升高．并恢复原始状态。TiO2的禁带较宽，普通光线如太阳光等都不能将其激发．限制了其实际应用。因此如何使TiO2材料的光谱响应范围由紫外光反扩展到可见．光区一日如何更长时间地保持薄膜良好的亲水性是目前研究的重点。     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

The Effect of SiO2 Addition on the Grain Size and Photocatalytic Activity of TiO2 Thin Films

The uniform transparent TiO₂/SiO₂ nanometer composite thin films were prepared via sol-gel method on the soda lime glass substrates, and were characterized by X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy, UV-VIS spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET surface areas. It was found that the addition of SiO₂ to TiO₂ thin films could suppress the grain growth of TiO₂ crystal and increase the hydroxyl content of the surface of TiO₂ films. The photocatalytic activity of the as-prepared TiO₂/SiO₂ composite thin films increases for SiO₂ content of less than 5 mol%.     

Enhanced photo-catalytic activity of TiO2 nanostructured thin films under solar light by Sn and Nb co-doping

In this study, preparation of Sn and Nb co-doped TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of co-doping content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), field emission SEM (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy (XPS). XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO₂. Titania Rutile phase formation in thin film was promoted by Sn⁴⁺ addition but was inhibited by Nb⁵⁺ doping. The prepared co-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue (MB) solution under solar irradiation. Comparison with undoped and Sn or Nb-doped TiO₂, codoped TiO₂ shows an obviously higher catalytic activity under solar irradiation.     

Photocatalytic Activity and Photo-Induced Wettability Conversion of TiO2 Thin Film Prepared by Sol-Gel Process on a Soda-Lime Glass

We have developed the transparent photoactive TiO₂ thin film coated on soda lime glass (SLG) by sol-gel process. Titanium dioxide thin films coated on SLG exhibit lower photocatalytic activity due to the thermal diffusion of Na ion from the SLG substrate. Thin SiO₂ film precoating is very effective to prevent the thermal diffusion of Na ion. We have evaluated the photocatalytic decomposition of gaseous acetaldehyde and the photo-induced surface wettability of TiO₂ films with and without SiO₂ precoating layer. As expected, the TiO₂ film on SiO₂/SLG is more photoactive to decompose acetaldehyde than that on SLG. However, as for wettability conversion, there was little difference in the conversion rate between TiO₂ film without SiO₂, and TiO₂ film with SiO₂. Different dependence of Na ion diffusion on two kinds of photo-induced reaction on TiO₂ is discussed based on the difference of the photo-induced reaction mechanism.     

Sol–gel derived silver-incorporated titania thin films on glass: bactericidal and photocatalytic activity

Titanium dioxide (TiO₂) and silver-containing TiO₂ (Ag-TiO₂) thin films were prepared on silica pre-coated float glass substrates by a sol–gel spin coating method. The bactericidal activity of the films was determined against Staphylococcus epidermidis under natural and ultraviolet (UV) illumination by four complementary methods; (1) the disk diffusion assay, (2) UV-induced bactericidal test, (3) qualitative Ag ion release in bacteria inoculated agar media and (4) surface topographical examination by laserscan profilometry. Photocatalytic activity of the films was measured through the degradation of stearic acid under UV, solar and visible light conditions. The chemical state and distribution of Ag nanoparticles, as well as the structure of the TiO₂ matrix, and hence the bactericidal and photocatalytic activity, is controlled by post-coating calcination treatment (100–650 °C). Additionally, under any given illumination condition the Ag-incorporated films were found to have superior bactericidal and photocataltyic activity performance compared to TiO₂ thin films. It is shown that with optimized thin film processing parameters, both TiO₂ and Ag-TiO₂ thin films calcined at 450 °C were bactericidal and photocatalytically active.     

Surface chemistry and optical property of TiO2 thin films treated by low-pressure plasma

The low temperature RF plasma treatment was used to control the surface chemistry and optical property of TiO₂ thin films deposited by RF magnetron sputtering with a very good uniformity at 300 °C substrate heating temperature. The XRD pattern indicates the crystalline structure of the film could be associated to amorphous structure of TiO₂ in thin film. The plasma treatment of TiO₂ film can increase the proportion of Ti³⁺ in Ti2p and decrease in carbon atoms as alcohol/ether group in C1s at the surface. The optical transmittance of the film was enhanced by 50% after the plasma treatment. The surface structure and morphology remain the same for untreated and low-pressure plasma-treated films. Therefore, increase in the optical transmission could be due to change in surface chemistry and surface cleaning by plasma treatment.     

Influence of High-energy electron-beam on photocatalytic activity of TiO2 films on carbon-fiber deposited by atomic layer deposition

High-energy electron-beam with energy of 1 MeV was used for modifying surface structure of TiO₂ thin films on carbon fiber prepared by using atomic layer deposition under atmospheric pressure. TiO₂ nanoparticles (∼20 nm) on carbon fiber underwent structural modification of the surface upon electron-beam treatment, resulting in enhanced photocatalytic activity. In contrast, a thicker film of TiO₂ did not show such changes in surface structure and photocatalytic activity by electron-beam treatment. We demonstrate that electron-beam can be used for modifying surface structure of photocatalysts consisting of nanoparticles for improvement of their activity.     

Preparation of the visible light responsive TiO2 thin film photocatalysts by the RF magnetron sputtering deposition method

TiO₂ thin film photocatalysts which could induce photoreactions under visible light irradiation were successfully developed in a single process by applying an ion engineering technique, i.e., the radio frequency (RF) magnetron sputtering deposition method. The TiO₂ thin films prepared at temperatures greater than 773 K showed the efficient absorption of visible light; on the other hand, the TiO₂ thin films prepared at around 573 K were highly transparent. This clearly means that the optical properties of TiO₂ thin films, which absorb not only UV but also visible light, can be controlled by the preparation temperatures of the RF magnetron sputtering deposition method. These visible light responsive TiO₂ thin films were found to exhibit effective photocatalytic reactivity under visible light irradiation (λ > 450 nm) at 275 K for the reductive decomposition of NO into N₂ and N₂O. From various characterizations, the orderly aligned columnar TiO₂ crystals could be observed only for the visible light responsive TiO₂ thin films. This unique structural factor is expected to modify the electronic properties of a TiO₂ semiconductor, enabling the efficient absorption of visible light.