溶胶-凝胶法制备的纳米TiO2结构相变及晶体生长动力学

讨论了采用溶胶-凝胶法经由先驱物钛酸四异丙脂水解而制备的纳米TiO₂粉末的 结构相变 ，并讨论了该纳米粉末的生长动力学机理.结果表明，水解pH值为0.9，当高压釜热处理温度 ＜503K时，粉末晶粒度增长较为缓慢，而当热处理温度＞503K时，粉末粒度明显长大.应用 相变理论计算出了纳米TiO₂颗粒的两阶段的生长激活能，分别是18.5kJ/mol和5 9.7kJ/mol .XRD物相分析表明，高压釜热处理温度达到503K时，样品就开始发生锐钛矿到金红石相的结 构相变，到543K就基本实现了这一结构相变，使得这一相变温度比其他文献中报道的又降低 了许多. 关键词： 2')" href="#">纳米TiO₂ 溶胶_凝胶法 结构相变 晶粒生长动力学     

Synthesis of titania/carbon nanocomposites by polymeric precursor method

Here we describe a single chemical route to obtain highly dispersed nanometric Ni particles embedded in titania/carbon matrixes (amorphous and crystalline). The synthesis of these nanocomposites is based on a polymeric precursor method. The metallic Ni nanoparticles (1-15 nm) were obtained in a single process. We also present the results of photocatalytic experiments involving a series of nanocrystalline composites based on TiO₂/carbon with embedded Ni nanoparticles as nanocatalysts for rhodamine 6G degradation in aqueous solution and investigate the effects of the structure and properties of the nanocomposites on their photocatalytic applications. The effect of the different annealing treatments on the formation of TiO₂ nanophases (anatase and/or rutile), the size of Ni particles and the role of the residual carbon phase on the final solid are also described.     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO₂结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO₂生长活化能在250℃以下和以上分别为(15.8±4.5)kJ/mol和(80.2±1.0)kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4)kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO₂生长速 关键词： 2')" href="#">纳米TiO₂ 锐钛矿 生长动力学 溶胶-凝胶法     

SnO$lt;sub$gt;2$lt;/sub$gt;纳米晶体的制备、结构与发光性质

使用软化学方法在碱性溶液中制备出了颗粒尺寸分布均匀的SnO₂纳米颗粒,使用透射电子显微镜（TEM）、X射线衍射（XRD）、光致发光谱（PL）和光吸收谱等方法分析与表征了SnO₂纳米颗粒的结构和光学性能.实验中通过表面活性剂的加入来控制纳米颗粒的结晶与凝聚.XRD,TEM的结果表明,原始制备出的SnO₂纳米颗粒的平均粒径小于4 nm,为完好的晶体状态.纳米颗粒经过400—1000 ℃退火后晶粒尺寸进一步增大.光吸收谱表明,相对于体材料,纳米颗粒的禁带宽度展宽并随颗粒尺寸增大而红移.光致发光谱测试表明,不同温度下退火的SnO₂纳米颗粒在350—750 nm有较强的发光,研究表明这是来源于颗粒表面的氧空位缺陷发光. 关键词： 氧化锡 表面活性剂 纳米颗粒 光致发光     

Temperature-resolved synchrotron X-ray diffraction of nanocrystalline titania in solvent: the effect of Cr–Sb and V–Sb doping

Nanocrystalline titania pigments were produced by high temperature-forced hydrolysis in a coordinating high-boiling solvent (and water for reference). The effect of synthesis conditions and co-doping with Cr–Sb and V–Sb on particle size and anatase-to-rutile transformation (A → R) was studied by temperature-resolved synchrotron X-ray diffraction. The experiments were performed directly on low concentration (3.5 vol.%) as-synthesized suspensions of titania nanoparticles (up to 230 °C) and on the corresponding dried powders (up to 950 °C). Crystallite size of as-synthesized nano-anatase is around 20 nm (glycol) or 70 nm (water); it exhibits a slow growth rate up to the onset temperature of the A → R. Phase composition and crystallite size are drastically influenced by both synthesis conditions and doping. Synthesis in water resulted in the simultaneous occurrence of anatase and brookite; transformation into rutile begins early but with a slower rate with respect to glycol-based samples. Doping affected the A → R, whose onset temperature in undoped titania (700 °C) was lowered to 650 °C (V–Sb) or prevented up to 950 °C (Cr–Sb). Both (V–Sb) and (Cr–Sb) dopings reduced the volume thermal expansion rate of anatase.     

Structural and thermoluminescence properties of undoped and Fe-doped-TiO<Subscript>2</Subscript> nanopowders processed by sol–gel method

In this study, we report on the nanocrystalline powders of TiO₂ and Fe-doped TiO₂ (anatase and rutile phases) prepared by sol–gel method. The X-ray diffraction and Raman spectroscopy measurements indicated the presence of anatase or rutile phase in nanopowders. TEM micrographs showed 10 and 112 nm average particle sizes for anatase and rutile, respectively. Furthermore, their thermoluminescence properties were analyzed.     

不锈钢丝网上薄膜TiO2光催化剂的Raman光谱研究

用Raman光谱方法来研究用Sol Gel法负载于金属丝网的薄膜TiO2 光催化剂的物相结构、厚度以及粒径大小。研究结果显示 ,薄膜达到一定厚度能够阻止基底Fe元素向薄膜表层的扩散 ;在 4 0 0℃下灼烧制得的薄膜TiO2 光催化剂具有锐钛矿晶型 ,而高于 4 0 0℃时 ,将出现金红石相TiO2 ;锐钛矿晶型TiO2 的Raman特征峰产生偏移 ,表明薄膜粒径的变化 ,通过计算表明 ,薄膜TiO2 的粒径为 10nm左右 ,TEM的分析结果也与之一致。     

High temperature stability of nanocrystalline anatase powders prepared by chemical vapour synthesis under varying process parameters

Systematic variation in the high temperature stability of nanocrystalline anatase powders prepared by chemical vapour synthesis (CVS) using titanium (IV) isopropoxide under varying flow rates of oxygen and helium was obtained by progressively shifting the decomposition product from C₃H₆ to CO₂. The as-synthesised powders were characterised by high temperature X-ray diffraction (HTXRD), simultaneous thermo-gravimetric analyses (STA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). It was observed that the anatase to rutile transformation temperature progressively increased for samples synthesised at higher O₂/He flow rate ratios. The improved anatase stability was attributed to the presence of incorporated carbon within the titania structure and confirmed by a high temperature carbon desorption peak.     

Type of lattice strain alteration,the reducing agent of activation energy of titania loading on the silica matrix than that of pure titania

Nanosized titania and silica-supported titania (SST) were prepared by the sol–gel method using titanium tetrachloride as a titania precursor. An opposite behavior was observed in the lattice strain of titania and SST before and after transition onset point (TOP). The effect of the changes of the lattice strain on the size of nanocrystallites, the TOP, and activation energy of phase transformation from anatase to rutile is investigated. It is shown that under identical synthesis conditions, the average size of nanocrystallites in SST was less than that of pure titania. Moreover, TOP of titania was lower in pure titania sample than that of SST due to the tensile strain of pure titania vs. the compressive strain of SST at low calcination temperature. However, the activation energy of pure titania due to the compressive strain and the exponential leap of the tensile strain of SST, after TOP, was higher than that of SST.     

The removal of sodium dodecylbenzene sulfonate surfactant from water using silica/titania nanorods/nanotubes composite membrane with photocatalytic capability

This paper reports experimental results on removal of sodium dodecylbenzene sulfonate (SDBS), using silica/titania nanorods/nanotubes composite membrane with photocatalytic capability. This multifunctional composite membrane has been successfully prepared from colloidal X-silica/titania sols (X denotes molar percent of silica) by the sol-gel technique. The prepared nanorods/nanotubes composite membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), scanning probe microscope (SPM) and UV-vis diffuse reflectance spectra (DRS). XRD patterns confirmed that the embedding of amorphous silica into nanophase titania matrix helped to increase the thermal stability of titania and control the size of titania particles. The small size titania particles with anatase phase played an important role in formation of silica/titania nanorods/nanotubes composite membranes with photocatalytic capability. The percentage of anatase phase titania reached 93% when 20%-silica/titania nanorods/nanotubes composite membrane calcined at 400 °C for 2 h. Most (95%) of the pore volume was located in mesopores of diameters ranging from 1.4 to 10 nm. The experimental results showed that the removal of SDBS achieved 89% after 100 min by combining the photocatalysis with membrane filtration techniques. Although the SDBS was not completely decomposed by photocatalysis, the degradation of the SDBS helped to enhance composite membrane flux and prevent membrane fouling. It was possible to treat successfully surfactant wastewater using multifunctional silica/titania nanorods/nanotubes composite membrane by means of a continuous process; this could be interesting for industrial applications.     

The influence of the substrate nature on the iron repartition in the titania matrix

Fe-doped titania films were deposited by RF sputtering onto different substrates (glass and ITO/glass) in the same deposition run. The rutile nanocrystalline structure of Fe-doped thin films deposited on glass substrates and anatase nanocrystalline structure of Fe-doped thin films deposited on ITO/glass substrates were evidenced by XRD. SEM investigations showed a smooth surface with a dense nanostructure. XPS study evidenced an almost stoichiometric composition with different iron contents. EPR and XPS studies evidenced that iron entered into TiO₂ lattice by substitution, as isolated and dimer species. In Fe-doped thin films deposited on ITO/glass substrates the iron content is ten times higher than in Fe-doped thin films deposited on glass substrates and that a part of them entered as Fe²⁺.     

Synthesis, characterization and microwave absorption properties of titania-coated barium ferrite composites

Anatase titania-coated barium ferrite composites were prepared by a heterogeneous precipitation method in the presence of barium ferrite particles. The obtained samples were characterized by ξ-pH, TEM, EDX and XRD. The complex permittivity and permeability were studied in the frequency range of 2-12 GHz. The structure and microwave response properties are investigated. The results show that the coverage of titania has a great influence on microwave response of barium ferrite. The formation of an anatase titania nano-layer on the surface of a barium ferrite particle changes the character of the frequency dispersion of the complex permittivity. Comparing the anatase titania-coated barium ferrite composites with the uncoated barium ferrite, the complex permittivity of the anatase titania-coated barium ferrite composites is higher than that of uncoated barium ferrite. The complex permeability of composites was found to decrease with an increase in frequency as well as with the molar ratio of Ti:Ba. The enhancement of the complex permittivity may be due to dipolar polarization and interfacial polarization. The maximum reflection loss was obtained at the Ti:Ba ratio of 1:10, and the peak of the maximum reflection loss shifts to a lower frequency value with increasing titania fraction. By changing the thickness of titania coverage, the frequency dependence of the complex permittivity could be adjusted, which provides us an opportunity for the synthesis of tailored particles.     

Deformation characteristics of nanocrystalline copper and nickel at low temperatures

Measurements were made of the deformation and fracture characteristics of nanocrystalline copper and nickel at temperatures between 4.2 and 300 K. It was observed that the flow stresses are sensitive to the sign of the load while deformation instability was observed at temperatures close to liquid-helium temperature. The temperature dependence of the yield stress was obtained. It was found that there is a range of a thermal deformation at low temperatures which extends to 60 K for nickel and 200 K for copper. Possible reasons for these characteristics in the deformation behavior of nanocrystalline materials are discussed, especially the role of quantum effects in the low-temperature deformation. Fiz. Tverd. Tela (St. Petersburg) 40, 1264–1267 (July 1998)     

Dynamic nucleation and growth of Ni nanoparticles on high-surface area titania

Nucleation and growth mechanisms of Ni nanoparticles synthesized via an incipient wetness technique on a high-surface area titania support (i.e., a mixture of anatase and rutile) are studied using environmental transmission electron microscope (ETEM). Most Ni nanoparticles are found to nucleate from the Ni precursor coated on the surface of the titania support. Even though both anatase and rutile supports are the nucleation sites for Ni nanoparticles, it was observed that the particles have different morphologies on the supports, i.e., a non-wetting morphology on the anatase support versus a wetting morphology on the rutile {1 0 1}. This is because the interfacial energy of Ni/rutile is lower than that of Ni/anatase. Titania clusters are found to nucleate on the surface of the Ni particles during in situ ETEM reduction, indicating that the presence of partial titania overlayers is directly related to the synthesis of the Ni/TiO₂ catalysts. The growth mode of the Ni nanoparticles on the titania support is three-dimensional, while that of the rutile cluster on the surface of the Ni is two-dimensional layer-by-layer.     

Observation of carbon‐facilitated phase transformation of titanium dioxide forming mixed‐phase titania by confocal Raman microscopy

Confocal Raman microscopy, a relatively new and advanced technique, is found to be suitable for imaging the chemical morphology below the submicrometer scale. It has been employed to probe the phase transformation of carbon‐containing titania (TiO₂) nanopowder and titania thin film subjected to laser annealing. The observation of phase transformation from the anatase phase to the rutile phase at high laser power annealing is attributed to carbon inclusion inside or on the surface of titania. Upon annealing, carbon could react with the oxygen of titania and create oxygen vacancies favoring the transformation from the anatase to the rutile phase. This study provides evidence for the carbon‐assisted phase transformation for creating carbon‐containing mixed‐phase titanium dioxide by laser annealing. We explicitly focus on the presence of carbon in the phase transformation of TiO₂ using confocal Raman microscopy. In all of the investigated samples, mixed anatase/rutile phases with carbon specifically was found at the rutile site. X‐ray diffraction (XRD), scanning electron microscopy (SEM) and energy‐dispersive spectroscopy (EDS) studies have been performed in addition to Raman mapping to verify the mixed‐phase titania formation. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermostable photocatalytically active TiO<Subscript>2</Subscript> anatase nanoparticles

Anatase is the low-temperature (300–550 °C) crystalline polymorph of TiO₂ and it transforms to rutile upon heating. For applications utilizing the photocatalytic properties of nanoscale anatase at elevated temperatures (over 600 °C) the issue of phase stabilisation is of major interest. In this study, binary TiO₂/SiO₂ particles were synthesized by a flame aerosol process with TiCl₄ and SiCl₄ as precursors. The theoretical Si/Ti ratio was varied in the range of 0.7–1.3 mol/mol. The synthesized TiO₂/SiO₂ samples were heat treated at 900 and 1,000 °C for 3 h to determine the thermostability of anatase. Pyrogenic TiO₂ P25 (from Evonik/Degussa, Germany) widely applied as photocatalyst was used as non-thermostabilized reference material for comparison of photocatalytic activity of powders. Both the non-calcinated and calcinated powders were characterized by means of XRD, TEM and BET. Photocatalytic activity was examined with dichloroacetic acid (DCA) chosen as a model compound. It was found that SiO₂ stabilized the material retarding the collapse of catalyst surface area during calcination. The weighted anatase content of 85% remains completely unchanged even after calcination at 1,000 °C. The presence of SiO₂ layer/bridge as spacer between TiO₂ particles freezes the grain growth: the average crystallite size increased negligibly from 17 to 18 nm even during the calcination at 1,000 °C. Due to the stabilizing effect of SiO₂ the titania nanoparticles calcinated at 900 and 1,000 °C show significant photocatalytic activity. Furthermore, the increase in photocatalytic activity with calcination temperature indicates that the titania surface becomes more accessible either due to intensified cracking of the SiO₂ layer or due to enhanced transport of SiO₂ into the necks thus releasing additional titania surface.     

Study of coatings based on titanium oxides and oxynitrides using a set of methods

A set of methods has been applied to study the properties of titanium oxide and oxynitride coatings on steel. It is established that the coatings consist of two phases with a nanocrystalline and an amorphous structure with a high proportion (～50 %) of grain boundaries; anatase is the dominant crystalline phase. The obtained results can be applied in the development of coatings for stents as well as for manufacturing hydrogen accumulators.     

Modeling the structure and spectral properties of sensitizing black dye for nanocrystalline TiO<Subscript>2</Subscript> solar cells

Spectral and electronic properties of a sensitizing black dye; a 4,4′,4′′-tricarboxy-2,2′:6′,2′-terpyridine)tris(isocyanato) ruthenium(II) complex; for nanocrystalline TiO₂ solar cells have been investigated by modern methods of quantum chemistry. The light absorption mechanism in the lowest excited triplet states of the dye was studied. The efficiency of electron injection into nanocrystalline TiO₂ is shown to depend on both the nature of charge-transfer states and asymmetric deformation of an excited triplet term of the black dye.     

Properties of mesoporous tungstosilicic acid/titania composites prepared by sol-gel method

The tungstosilicic acid/titania composites were prepared by the sol-gel method. Titanium isopropoxide was used as titania precursor, and urea as a low-cost template. The tungstosilicic acid (TSA) was added in the same step as that in which titania hydrogel is formed. The TSA-modified samples only showed the characteristic peaks of anatase phase of titanium oxide in the XRD patterns, indicating that the presence of TSA retarded the crystallization of the anatase phase and its transformation into the rutile phase. Spherical particles with sizes between 200 and 700 nm, formed by aggregation of nanoparticle aggregates (4-50 nm in size), were observed. The particle size increased when the TSA content was raised and also increased slightly with the thermal treatment temperature. Mesoporous materials were obtained, with a mean pore diameter higher than 3.1 nm. Both the increase of the TSA concentration in the solid and the calcination temperature led to a decrease in the specific surface area of the samples. The main heteropolyoxometallate species present in the composites is the [SiW₁₂O₄₀]⁴⁻ anion for the composites calcined up to 500 °C. The band gap energy decreased as a result of the introduction of TSA into the titania matrix, though it remained almost constant with the calcination temperature increase.     

Supersonic cluster beam deposition of nanostructured titania

Nanostructured titanium dioxide films have been deposited by supersonic cluster beam deposition (CBD). Nanoparticles are produced by a pulsed microplasma cluster source (PMCS) and selected by aerodynamic separation effects. The as-deposited film is a complex mixture where amorphous material coexists, at the nanoscale, with anatase and rutile crystal phases. The nanocrystalline fraction of the film is characterized by crystal size ranging from 100 nm to less than 5 nm. We have characterized the film structure by transmission electron microscopy, Raman spectromicroscopy, X-ray diffraction, and UV-visible spectroscopy showing that correlations exist between cluster size and film properties. In particular if very small clusters are deposited, the film shows a predominant rutile phase whereas larger clusters form films with mainly anatase structure. Our observations suggest that phonon confinement effects are responsible for a significant shift and broadening observed for the Raman peaks. In addition, optical gap tuning is provided by mass selection: large clusters assembling generates a film with 3.22 eV optical gap, while smallest clusters 3.52 eV.