Nanocrystalline TiO2 Powders Research Articles

Zn掺杂TiO<sub>2</sub>的光催化性能研究

以钛酸四丁酯为钛源，醋酸锌为锌源用溶胶凝胶法制备了不同比例Zn掺杂TiO2纳米颗粒，掺杂比例为0 at%~10 at%。用X射线衍射(XRD)、透射电镜(TEM)、能谱分析(EDS)、紫外可见光谱(UV-Vis)等研究手段对所制备的Zn掺杂TiO2纳米颗粒进行分析，并对样品的光催化活性进行了研究。结果显示400℃退火的样品均为锐钛矿相TiO2，没有ZnO的衍射峰出现，EDS分析结果显示Zn离子存在于TiO2中，说明Zn离子成功掺杂进入TiO2晶格。通过TEM图像和谢乐公式计算可知，Zn掺杂TiO2的平均晶粒尺寸为6~7 nm，掺杂比例为1%的样品光催化降解亚甲基蓝染料效果最好。 TiO2 nanocrystalline powders with various Zn doping levels from 0 at% to 10 at% were synthesized via sol-gel method with Tetrabutyl orthotitanate (TBOT) and zinc acetate as Ti and Zn source. The samples were characterized by XRD, TEM, EDS and diffuse absorption spectrum. The effect of Zn doping on optical and photocatalytical properties of TiO2 was systematically investigated. XRD results show that all the prepared powders were Anatase TiO2, no ZnO was found when the samples were annealed at 400˚C. EDS analysis confirmed the existence of Zn in the samples. It suggests that Zn was successfully doped into TiO2. Average particle size of the prepared Zn-TiO2 powders was about 6 - 7 nm obtained from TEM measurement and Scherer Equation calculation. The nano size powders were used to catalytically decompose methylene blue, and the sample doped with 1 at% Zn showed the best photocatalytic activity, better than that of pure TiO2.

Photocatalytic air-cleaning using TiO2 nanoparticles in porous silica substrate

AbstractFor air-cleaning, TiO2 photocatalysis represents one of the very efficient advanced oxidation processes (AOPs) that can decompose chemically and microbiologically stable volatile organic compounds (VOCs). However, the photocatalytic activity of nanocrystalline TiO2 powders can be significantly suppressed due to TiO2’s poor adsorption characteristics for organic compounds and its relatively low surface area. The present study sought to solve this problem by immobilising nanocrystalline TiO2 in the porous silicate substrate. Two titania sources were used in an aqueous solution form: a suspension from a TiO2 producer in Slovenia, Cinkarna Celje (CC-40) and a TiO2 sol, prepared by a low-temperature synthesis developed at the University of Nova Gorica (TiO2-UNG). Two different types of mesoporous silica were used: SBA-15 with an ordered hexagonal pore arrangement and KIL-2 with disordered inter-particle mesoporosity. The structural characteristics, adsorption properties and photocatalytic activity of catalysts deposited on aluminium plates as thin films were investigated. CC-40 exhibited higher adsorption and photocatalytic activity than TiO2-UNG due to the greater quantity of Ti-OH groups on its surface. The addition of mesoporous silica led to higher adsorption and catalytic activity for both TiO2 sources. SBA-15 was more efficient than KIL-2.

Photohole Trapping Induced Platinum Cluster Nucleation on the Surface of TiO2Nanoparticles

The photocurrent response of TiO2 nanoparticles synthesized via the sol–gel process was studied in the presence of methanol, ethanol, and isopropanol. The nanocrystalline nature of photoelectrodes showed an important photocurrent in the presence of alcohol following the order methanol ≈ ethanol > isopropanol > H2O. This process mimics the photoelectrochemical response, and therefore a correlation of the photodeposition process of platinum nanoclusters on TiO2 particles in the presence of alcohol molecules was devised. The photodeposition mechanism of platinum nanoislands at the surface of a nanocrystalline TiO2 powder is discussed in the light of the photoelectrochemical results.

Optimisation of process parameters for fabrication of nanocrystalline TiO2–hydoxyapatite based scaffold using response surface methodology

The present study focuses on the application of central composite design of response surface methodology for optimisation of process parameters to develop a hybrid mechanically stable biocompatible porous scaffold. The scaffolds are developed by varying the composition of fish scale derived HAp and nanocrystalline TiO2 powders. The effects of sintering temperature, dwell time on the porosity and compressive strength of the scaffolds are investigated. Various diagnostic tools (e.g. thermogravimetric/differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy /energy dispersive X-ray spectroscopy) are used for composition, phase conformity and microstructure evaluation of green as well as sintered materials. The desirability function optimisation study reveals that at 60∶40 (TiO2∶HAp) concentration with sintering temperature of 1100°C for 90 min provides the maximum compressive strength of 78·5 MPa and maximum porosity of 33·5%.

Influence of pH on the formulation of TiO2 nano-crystalline powders with high photocatalytic activity

This paper describes the effect of synthesis conditions on the formation of anatase and rutile crystalline phases and photocatalytic activity of synthesised TiO2 phase. The synthesised powders were characterised by X-ray diffraction, Raman microscopy, Scanning Electron Microscopy and UV–Vis spectroscopy. Using these characterisation techniques, the structural, morphological and optical properties as a function of formulation pH were determined. Since photocatalysis is a surface process, the mass surface charge of the powders was also measured using a Faraday Cage connected to an electrometer. The structural, morphological, optical and surface properties were correlated with the photocatalytic activity of the formulated TiO2 powders.The influence of synthesis condition on the photocatalytic activity of TiO2 powders was determined by the degradation of Methylene Blue dye under both UV-A and visible light.

Room temperature photoluminescence of anatase and rutile TiO2 powders

The optical absorption and photoluminescence of anatase and rutile TiO2 were studied at room temperature. TiO2 nanocrystalline powders were synthesized in the form of pure anatase or rutile. The samples were characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL) methods. The PL spectra were studied under the intensive UV (3.68eV) laser excitation. Some interesting features in the PL spectra including the well-resolved peaks of excitonic and band–band transitions in TiO2 were observed, to our knowledge, for the first time. It is shown that PL bands including peaks at 2.71–2.81eV and its phonon replicas in anatase and rutile TiO2 arise from the excitonic e−−h+ recombination via oxygen vacancies. The excitonic peak at 2.91eV is attributed to the recombination of self-trapped excitons in anatase or free excitons in rutile TiO2. The PL peaks within 3.0–3.3eV in anatase TiO2 are ascribed to indirect allowed transitions due to the band–band e−−h+ recombination. The peaks at 3.03eV and 3.26eV are attributed to the free exciton emission near the fundamental band edge of rutile and anatase TiO2, respectively. The influence of TiO2 crystal structure and calcination temperature on the PL spectra is discussed.

Synthesis of Nanocrystalline TiO2 by NH4F-Assisted Low Temperature Hydrolysis Method and its Photocatalytic Ability for Rhodamine B

Nanocrystalline TiO2 powders were obtained at a low temperature between 50 and 80 °C by a hydrolysis of TiCl4 in a mixed solution of distilled water and alcohol. The as-synthesized TiO2 powders were characterized by X-ray diffraction analysis, transmission electron microscopy, and UVvisible absorption spectroscopy. Effects of the reaction temperature and the NH4F concentration on the formation of the nanocrystalline TiO2 powders were investigated. Results indicate that the reaction temperature greatly affects the particle size of the as-synthesized samples, and the NH4F concentration has a great effect on the phase structure of the as-synthesized samples. In addition, the photocatalytic activities of the as-synthesized samples for rhodamine B were also measured, and it is found that the sample synthesized from the NH4F concentration of 30 mM exhibits a higher photocatalytic activity than the P25 powder due to a high surface area and a pure anatase phase.

Preparation and Photoactivity of Nanocrystalline TiO2 Powders Obtained by Thermohydrolysis of TiOSO4

Nanocrystalline TiO2 photocatalysts were synthesized in mild conditions by thermohydrolysis of TiOSO4 in water at 100 °C and post-calcination treatment at various temperatures. The TiO2 powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area determinations, scanning electron microscopy and electron paramagnetic resonance measurements. The photoactivity of the samples was tested employing the photodegradation of 4-nitrophenol in liquid–solid regimen and the photooxidation of gaseous 2-propanol. The best results were obtained with the powder calcined at 600 °C for 10 h. Surprisingly, the not calcined sample was the most active for the abatement of NOx under irradiation. Time course of 4-nitrophenol degradation: (filled circle) as-prepared TiO2; (filled square) calcined at 600°C for 3 h; (filled triangle) Degussa P25; (filled diamond) calcined at 600°C for 10 h.

Preparation at Low-Temperature and Characterization of TiO<sub>2</sub> Film Used for Solar Cells

In this work, nanocrystalline TiO2 powder was prepared by the sol-gel method via tetrabutyl titanate as raw material, non-ion surfactant TO8 as a template. Then the nanocrystalline TiO2 thin film electrodes which were coated on FTO glass substrates via the slurry consiting of TiO2 powder prepared by us and the trabutyl titanate precursor were successfully prepared by using a simple and convenient hydrothermal method at low temperature. The structure and morphology of powders and films were characterized by X-ray diffraction, scanning electric microscopy. The influence factors on the samples were discussed. The photoelectric properties of cells assembled by the films were measured. The results show that, at 25°C and under 1000W/m2 light intensity，open voltage is 708mV, Jsc is 14.648mA/cm2, fill factor is 53.788, the conversion efficiency is 5.5988%.

Nanocrystalline TiO<sub>2</sub> Powder Materials Anticipates at Disinfect the Appliance in the Beaded Paint

Nanocrystalline TiO2 powder materials is a good use of the performance of paint additives , nano-TiO2 bactericidal coating made its added a new type of green paint , and has been applied in China's architectural coating industry and has achieved a good technical and economic effect.This article discusses some technical characteristics and production application prospects of nanoscale TiO2 powder.

Effects of NH 4 + and Cl− on the preparation of nanocrystalline TiO2 by hydrothermal method

Nanocrystalline TiO2 powders with different morphologies and grain sizes were successfully synthesized by the hydrothermal method. Different concentrations of hydrochloric acid (HCl), ammonium chloride (NH4Cl), ammonium sulfate [(NH4)2SO4], and ammonium carbonate [(NH4)2CO3] were used as additives in the hydrothermal process to investigate the effect of the concentration of ammonium (NH4+) and chloride ions (Cl−) on the phase compositions, morphologies, and grain sizes of the prepared TiO2. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy, Brunauer–Emmett–Teller analysis, and UV–Vis spectra. XRD results show that the as-synthesized powders are composed of anatase or a mixture of anatase and brookite. The grain size of the synthesized nano-TiO2 powder ranged from 5.0 to 11.3 nm, and the related BET specific surface area varied from 127.5 to 191.0 m2/g. The photocatalytic activities of the prepared TiO2 powders were evaluated by degradation of methylene blue (MB) in aqueous solution under UV light irradiation, and the results show that the photocatalytic performance of TiO2 powders synthesized with additives is improved compared with that of TiO2 prepared without any additives.

Photocatalytic inactivation of Gram-positive and Gram-negative bacteria by reactive plasma processed nanocrystalline TiO2 powder

Nanocrystalline TiO2 powder is synthesized using a novel reactive plasma process in which the precursor TiH2 powder is oxidized through thermal plasma in-flight route to generate nanocrystalline TiO2 powder. The synthesized powder consists of nano-sized TiO2 particles, both anatase and rutile phases, in which anatase is the predominant phase. An additional feature of the plasma synthesized TiO2 powder is the higher surface concentration of Ti3+ state and hydroxyl group that enhance its photocatalytic activity. The photocatalytic inactivation of Gram-positive Enterococcus and Gram-negative Klebsiella bacteria is studied using the plasma synthesized TiO2 nanopowder with 365 nm ultraviolet (UV) light. The mechanism behind the photocatalytic disinfection of bacteria is discussed. The plasma synthesized TiO2 nanopowder catalyst is found effective in killing Enterococcus and Klebsiella. The results corroborated that the plasma synthesized TiO2 powder can be used for waste water treatment and water purification.

A Simple and Rapid Synthetic Route to Nanocrystalline TiO<sub>2</sub> by Microwave Irradiation

Well-dispersed nanocrystalline TiO2 powders with the average size of about 4 nm have been synthesized by a simple and rapid microwave irradiation method. The as-obtained TiO2 nanoparticles displayed obvious quantum size effects characterized by Raman spectroscopy.

Effects of I-doping content on the structural, optical and photocatalytic activity of TiO2 nanocrystalline powders

I-doping TiO2 nanocrystalline powders were synthesised by a simple co-precipitation method. After heat treatment at 500 °C, an anatase crystalline phase has been stabilised. The structural and optical properties of the nanostructured powders were investigated by X-ray diffraction, Raman and UV–vis spectrometry. With an increase of the iodine dopant quantity the crystallites size tends to decrease and there is an increase in the structure deformation. A decrease of the energy band gap was observed with an increase of the iodine amount. An increase of the photocatalytic activity of the I-doped TiO2 nanostructured powders with the increase of the iodine content was also observed due to the decrease of the energy bad gap.

Low-Temperature Fabrication of TiO2 Electrodes for Flexible Dye-Sensitized Solar Cells Using an Electrospray Process

Hierarchically structured TiO2 (HS-TiO2) was prepared on a flexible ITO-PEN (polyethylene naphthalate) substrate via electrospray deposition using a commercially available TiO2 nanocrystalline powder in order to fabricate flexible DSSCs under low-temperature (<150 °C) conditions. The cell efficiency increased when using flexible ITO-PEN substrates post-treated by either a mechanical compression treatment or a chemical sintering treatment using titanium n-tetrabutoxide (TTB). The mechanical compression treatment reduced the surface area and porosity of the HS-TiO2; however, this treatment improved the interparticle connectivity and physical adhesion between the HS-TiO2 and ITO-PEN substrate, which increased the photocurrent density of the as-pressed HS-TiO2 cells. The electron diffusion coefficients of the as-pressed HS-TiO2 improved upon compression treatment, whereas the recombination lifetimes remained unchanged. An additional chemical sintering post-treatment involving TTB was tested for its effects on DSSC efficiency. The freshly coated TiO2 submitted to TTB hydrolysis in water at 100 °C yielded an anatase phase. TTB treatment of the HS-TiO2 cell after compression treatment yielded faster electron diffusion, providing an efficiency of 5.57% under 100 mW cm(-2), AM 1.5 global illumination.

Synthesis and characterization of CdS doped TiO2 nanocrystalline powder: A spectroscopic study

This report aimed to study the effect of CdS doping in TiO2 on the phase transformation of TiO2 from anatase to rutile using X-ray diffraction (XRD) and Raman spectroscopy. CdS-doped TiO2 nanocomposites have been prepared and characterized using Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). We have observed that contrary to bare TiO2, phase transformation of TiO2 from anatase to rutile is hindered when doped with CdS at high temperature. Raman spectroscopy is found to be more sensitive for detection of the surface of TiO2 as compared to XRD.

Effects of Homogenization Scheme ofTiO2Screen-Printing Paste for Dye-Sensitized Solar Cells

TiO2porous electrodes have been fabricated for photoelectrodes in dye-sensitized solar cells (DSCs) using TiO2screen-printing paste from nanocrystalline TiO2powder dried from the synthesized sol. We prepared the TiO2screen-printing paste by two different methods to disperse the nanocrystalline TiO2powder: a “ball-milling route” and a “mortal-grinding route.” The TiO2ball-milling (TiO2-BM) route gave monodisperse TiO2nanoparticles, resulting in high photocurrent density (14.2 mA cm−2) and high photoconversion efficiency (8.27%). On the other hand, the TiO2mortal-grinding (TiO2-MG) route gave large aggregate of TiO2nanoparticles, resulting in low photocurrent density (11.5 mA cm−2) and low photoconversion efficiency (6.43%). To analyze the photovoltaic characteristics, we measured the incident photon-to-current efficiency, light absorption spectroscopy, and electrical impedance spectroscopy of DSCs.

Preparation of TiO&lt;sub&gt;2&lt;/sub&gt; Nanocrystalline Powder with High Specific Area Using Urea as the Template

TiO2 nanocrystalline powders with high specific area were prepared using urea as the template by the sol-gel method. The samples were characterized by X-ray diffraction, N2 adsorption isotherms, and transmission electron microscopy. Urea plays a key role in the preparation process of TiO2 nanocrystalline powders. Large amounts of small urea aggregates were formed in the sol-gel process and decomposed during the calcination process, which results in the formation of large amounts of mesopores. Urea also inhibits the agglomeration and growth of the TiO2 nanoparticle, which facilitates the preparation of a TiO2 powder with smaller nanocrystal size. The above effects of urea may be the main reason of the as-prepared sample with very high specific surface area.

Effect of Synthesis Conditions on Photocatalytic Activities of Nanoparticulate TiO&lt;sub&gt;2&lt;/sub&gt;

In the present study, design of experiments (Orthogonal experiment) was used to find an optimal combination for the factors, which affect the catalytic activity of nano-crystalline TiO2 powder synthesized by sol–gel method. Sixteen kinds of TiO2 powder were prepared by changing three material ratio at four levels. The effects of calcinations temperature on the catalyst activity of TiO2 were investigated by single factor experiments. TiO2 were characterized by XRD. The results of design of experiments are examined by the direct observation analysis. The preparation conditions have been optimized as material ratio nTi(OC4H9)4: nH2O: nHN(C2H5OH)2: nC2H5OH=1:2:2.5:20, mean 16.8 nm TiO2 nanoparticle with anatase structure obtained at 500°C calcination. The photodegradation efficiency of methylene blue in aqueous solution is 99 % under 1g/L catalyst.

The Effect of Microstructure on the Photocatalytic Properties of TiO&lt;sub&gt;2&lt;/sub&gt;

Titanium dioxide is a cheap, chemically stable and non-toxic material. However its photocatalytic properties are unstable and it is a modest semiconductor and a mediocre insulator. For several applications it would be interesting to make it either more insulating or more conducting. The goal of this work was to modify the photocatalytic properties of nano-crystalline TiO2 powders by wet chemical routes and hydrothermal methods to understand the mechanism leading to these modifications The principal factors that influence the photocatalytic properties are on the one hand the concentration and nature of the chemical and physical conditions in TiO2, and on the other hand the morphology of the powders. The study was split into two parts. The fist part describes the modifications of the material obtained by chemical preparation's parameters. Like: preparation method, pH., additives, surfactants, and temperature. The second part describes the modifications obtained by modifying the photo catalysis reactors. Several analysis techniques have been used to characterize the TiO2 samples. They are essentially divided in four categories. The chemical analyses included electron probe microanalyses. The structure and morphology analyses of powders were carried out with x-ray diffraction. The photo catalytically properties in batch or CRS mode were measured in room temperature. Finally optical transmission provided information on the electronic states and morphology of the samples. The results imply that powders with anatase 40% and rutile 60 % with 15nm crystallite size have the optimum properties.