Ti-Si mixed oxides prepared by polymer in situ sol-gel chemistry with the aid of CO2

A method to prepare titania-silica binary oxides is proposed in this work. In this route, inorganic precursors tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TIP) were simultaneously or sequentially impregnated into a polypropylene (PP) matrix using supercritical carbon dioxide as a swelling agent and carrier. Hydrolysis and condensation reaction of the precursors confined in a polymer network were induced by treating the composites in 1 mol.dm(-3) (1 M) HCl. Then the PP matrix was decomposed at higher temperature, and titania-silica binary oxides were obtained. The mixed oxides were characterized by X-ray diffraction and Raman, FTIR, and X-ray photoelectron spectroscopy. It was demonstrated that the structure of the oxides depended strongly on the procedure to impregnate the precursors. The simultaneous method, in which the TEOS and TIP were simultaneously impregnated into a PP matrix, resulted in mixed oxides with highly dispersed titanium oxide species in the SiO2 matrix, while the sequential method produced the mixed oxide with separate SiO2 and TiO2 phases which were connected by Ti-O-Si bands at the interface. The method described in this work provides a new route to control the texture of TiO2-SiO2 mixed oxide simply by the impregnation sequence.     

Large-scale synthesis of TiO2 nanorods via nonhydrolytic sol-gel ester elimination reaction and their application to photocatalytic inactivation of E. coli

A simple method of synthesizing a large quantity of TiO(2) nanorods was developed. A nonhydrolytic sol-gel reaction between titanium(IV) isopropoxide and oleic acid at 270 degrees C generated 3.4 nm (diameter) x 38 nm (length) sized TiO(2) nanocrystals. The transmission electron microscopic image showed that the particles have a uniform diameter distribution. X-ray diffraction and selected-area electron diffraction patterns combined with high-resolution transmission electron microscopic image showed that the TiO(2) nanorods are highly crystalline anatase crystal structure grown along the [001] direction. The diameters of the TiO(2) nanorods were controlled by adding 1-hexadecylamine to the reaction mixture as a cosurfactant. TiO(2) nanorods with average sizes of 2.7 nm x 28 nm, 2.2 nm x 32 nm, and 2.0 nm x 39 nm were obtained using 1, 5, and 10 mmol of 1-hexadecylamine, respectively. The optical absorption spectrum of the TiO(2) nanorods exhibited that the band gap of the nanorods was 3.33 eV at room temperature, which is 130 meV larger than that of bulk anatase (3.2 eV), demonstrating the quantum confinement effect. Oleic acid coordinated on the nanorod surface was removed by the reduction of the carboxyl group of oleic acid, and the Brunauer-Emmett-Teller surface area of the resulting naked TiO(2) nanorods was 198 m(2)/g. The naked TiO(2) nanorods exhibited higher photocatalytic activity than the P-25 photocatalyst for the photocatalytic inactivation of E. coli.     

Formation of titania nanofibers: a direct sol-gel route in supercritical CO2

In this letter, we present a new method to synthesize titania nanofibers with nanocrystallites via a sol-gel route in supercritical CO2. The nanofibers were formed by the esterification and condensation of titanium alkoxides using acetic acid as the polymerization agent in supercritical CO2 from 40 to 70 degrees C and 2500 to 8000 psia. The TiO2 nanofiber morphology was characterized by means of SEM and HRTEM, which indicated that the diameters ranged from 9 to 100 nm. N2 physisorption, and powder XRD showed that the nanofibers exhibited relatively high surface areas up to 400 m2/g and anatase and/or rutile nanocrystallites were formed after calcination.     

Effect of calcination temperature on the structure of a Pt/TiO2 (B) nanofiber and its photocatalytic activity in generating H2

Hydrogen trititanate (H 2Ti 3O 7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H 2Ti 3O 7 nanofibers at 573 K led to the formation of TiO 2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO 2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO 2 (B) and H 2Ti 3O 7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO 2 (B) nanofibers into a TiO 2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO 2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO 2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H 2 as did 1% Pt/P-25. TPR indicated that the calcination of 1% Pt/TiO 2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO 2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Pt (delta) sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO 2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity.     

板式纳米碳纤维负载二氧化钛光催化复合材料的制备及降解甲基橙的研究

以板式纳米碳纤维为载体,采用酸性氧化法对载体进行预处理之后,使用钛酸异丙酯为钛源,高温水热法制备了二氧化钛/纳米碳纤维复合光催化剂,并考察了其对甲基橙的光催化去除能力及循环反应性能.复合材料中二氧化钛含量通过改变前驱体组成进行调节.材料的结构性能通过氮气吸附、X射线衍射(XRD)、能谱分析仪(EDS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、热重分析仪(TG-DSC)等测试技术进行了表征.结果表明,锐钛矿型的二氧化钛以纳米颗粒形式均匀分散在纳米碳纤维表面,从而形成了高度分散的二氧化钛/碳纤维纳米复合材料.另外,复合系统中中孔吸附作用的存在,与纳米二氧化钛的光催化产生协同作用,增强了复合材料在紫外光照射下对于水溶液中甲基橙的去除能力.在光照射下反应120 min时,不同担载量样品对甲基橙的去除率最高可达80.1%,不同煅烧温度样品最高可达79.2%.此外,光催化剂有着良好重复利用性能,3次循环反应后对甲基橙去除率仍可保持80.0%.     

Effect of acid on the crystalline phase of TiO2 prepared by hydrothermal treatment and its application in the oxidative steam reforming of methanol

Research on Chemical Intermediates - Titania (TiO2) supports with anatase (A), mixed, and rutile (R) crystalline phases were prepared via the hydrothermal treatment of titanium isopropoxide and...     

Stable hydrosols for TiO<Subscript>2</Subscript> coatings

The optimum processing parameters required to synthesize, by hydrolysis of titanium isopropoxide (TIP), highly stable hydrosols composed of nanoparticles of the smallest possible size, are deduced both from data available in literature and from our own experiments. The colloids prepared in these conditions are composed of aggregates of anatase (~90%) and brookite crystallites (5–6 nm). They are suitable for coatings and have long-term stability (more than one year) in terms of polymorphic composition, crystallite and agglomerate size. Stable sols composed solely of anatase crystallites (4 nm) can be prepared by partially complexing the TIP by acetylacetone before hydrolysis. It is not possible to produce porous films with these colloids because they are stabilized by electrostatic repulsion which causes the particles to organize themselves, during the drying step, to form materials with a close packed structure. However, coatings with controlled porosity can be prepared from these stable sols through the post addition of polymers, like PEG or block copolymers.     

羧基功能化离子液体表面修饰TiO2纳米微粒的制备及结构表征

本文用沉淀法制备了羧基功能化离子液体表面修饰半导体TiO2纳米颗粒, 并用FTIR, TEM, XRD和XPS对其结构进行了表征. 初步探讨了羧基功能化离子液体修饰TiO2纳米微粒的形成机理.     

SnO2/TiO2复合纳米纤维的制备及光催化性能

采用静电纺丝技术,以聚乙烯吡咯烷酮和钛酸正丁酯为前驱体,制得锐钛矿相TiO2纳米纤维。以TiO2纳米纤维为模板,通过水热合成法,制备了具有异质结构的SnO2/TiO2复合纳米纤维。利用扫描电镜(SEM)、X射线能量色散光谱（EDS）、透射电镜(TEM)和X射线衍射(XRD)等分析测试手段对其形貌和结构进行了表征,结果表明,SnO2纳米粒子均匀地生长在TiO2纳米纤维表面,形成了异质结构的SnO2/TiO2复合纳米纤维材料。通过改变反应物浓度,能有效地实现SnO2/TiO2复合纳米纤维的可控合成。以罗丹明B为模拟污染物,考察了SnO2/TiO2复合纳米纤维的光催化性能,与纯TiO2纳米纤维相比光催化活性明显提高,初步探讨了光催化反应机理。     

同轴静电纺丝法在纳米中空TiO2纤维中填充Ag的应用

以聚乙烯吡咯烷酮(PVP)溶胶/钛酸四正丁酯和PVP溶胶/银颗粒为前驱体, 以共轴静电纺丝法制备了银填充的TiO2中空纳米纤维. 将双组分纤维在200 ℃下热处理去除乙醇与表面吸附水后, 继而在空气气氛中焙烧至600 ℃, 可以得到在内表面上沉积银颗粒的TiO2纳米管, 银颗粒的直径为5-40 nm, TiO2纳米管的外径150-300 nm, 管臂厚10-20 nm. 用红外吸收光谱(IR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等测试手段对超细纤维进行了表征. 中空纤维的直径和管壁可以通过改变电纺参数来调节. 与Ag-TiO2纳米纤维、TiO2纳米中空纤维、TiO2纳米纤维及TiO2纳米粉体相比较, Ag颗粒填充的TiO2纳米中空纤维在光分解亚甲基蓝上表现出了更好的光催化性能.     

Synthesis of TiO2 photocatalysts in supercritical CO2 via a non-hydrolytic route

Nanoscaled TiO2 powders with narrow size dispersion were prepared in supercritical carbon dioxide via non-hydrolytic acylation/deacylation of titanium alkoxide precursors with or without tris-fluorination. The microstructures of these powders were characterized by spectroscopic (FTIR, TGA, and XRD), microscopic (SEM or TEM), and surface area (BET) measurements. Photocatalytic oxidation of 1-octanol on these calcined TiO2 powders and on commercial T805 TiO2 suspended in aerated supercritical carbon dioxide revealed relative reactivity controlled by the powder microstructures. Calcined TiO2 prepared from titanium(IV) isopropoxide and trifluoroacetic anhydride was effectively dispersed in aerated supercritical carbon dioxide under stirring and exhibited high photocatalytic oxidation activity.     

Electrospun nanofibers of TiO2/CdS heteroarchitectures with enhanced photocatalytic activity by visible light

Herein, we have demonstrated that the electrospun nanofibers of TiO(2)/CdS heteroarchitectures could be fabricated through combining electrospinning technique with hydrothermal process. The configuration, crystal structure, and element composition of the as-prepared TiO(2)/CdS heteroarchitectures were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), resonant Raman spectrometer, X-ray photoelectron spectroscopy (XPS). The results indicated that the high-density hexagonal wurtzite CdS crystalline particles of ca. 6-40 nm in diameter were uniformly and closely grown on anatase TiO(2) nanofibers. Especially, the light-absorption properties as well as photocatalytic characteristics of pure TiO(2) nanofibers and TiO(2)/CdS heteroarchitectures with different amount loading of CdS were also investigated. The absorption of TiO(2)/CdS heteroarchitectures was extended to the visible due to effective immobilization of sensitizing agent CdS on TiO(2). In contrast with the pure TiO(2) nanofibers, the TiO(2)/CdS heteroarchitectures showed excellent photocatalytic activity by using rhodamine B dye as a model organic substrate under visible-light irradiation. It was worth noting that the cooperative photocatalytic mechanism of the TiO(2)/CdS heteroarchitectures was also discussed.     

Synthesis of monodisperse mesoporous TiO2 spheres with tunable sizes between 0.6 and 3.1 μm and effects of reaction temperature, Ti source purity, and type of alkylamine on size and monodispersity

We report a novel method for synthesizing monodisperse mesoporous TiO(2) spheres (sizes = 0.6-3.1 μm) by hydrolysis of titanium isopropoxide (TIP) in a mixture of C(8)-C(16)n-alkylamine, water, and ethanol. The size increases with decreasing temperature, TIP concentration, and water concentration, and upon purifying TIP. n-Dodecylamine gives the highest monodispersity.     

TiO<Subscript>2</Subscript> nanofibers embedding single crystalline TiO<Subscript>2</Subscript> nanowires

Epitaxially grown titanium dioxide (TiO₂) nanofibers embedding single crystalline TiO₂ nanowires (NWs) were successfully fabricated by electropinning poly(vinyl pyrrolidone)/ethanol solutions mixed with hydrothermally synthesized TiO₂ NWs and titanium isopropoxide precursors and subsequently calcinating the electrospun nanofibers. Utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the morphologies of TiO₂ NWs and nanofibers were investigated. High resolution TEM (HR-TEM) and selected area electron diffraction (SAED) allowed us to indentify the fact that, during the calcination process under the optimized condition, titanium isopropoxide precursors were epitaxially crystallized on the surface of single crystalline TiO₂ NWs. Based on the X-ray diffraction (XRD) experiments, it was also realized that the crystalline structure of hydrothermally synthesized TiO₂ NWs and epitaxially crystallized TiO₂ nanofibers is anatase and that TiO₂ composite nanofibers embedding TiO₂ NWs exhibited a higher crystallinity than the pristine TiO₂ nanofibers. Additionally, ultraviolet visible (UV–Vis) spectra of nanofibers indicated that optical properties of TiO₂ nanofibers can be tuned by introducing the single crystalline TiO₂ NWs.     

Controlled synthesis of highly dispersed TiO2 nanoparticles using SBA-15 as hard template

Highly dispersed TiO2 nanoparticles were successfully synthesized by a wet impregnation method using SBA-15 as hard template for confining the growth of TiO2 nanocrystals, and then calcined at 550 degrees C in muffle furnace for 2 h. The as-synthesized samples were characterized with Fourier transform infrared spectra (FTIR), Raman spectroscopy, diffuse reflectance UV-visible spectroscopy (UV-vis), powder X-ray diffraction (XRD), small-angle X-ray diffraction (SAXRD), nitrogen adsorption, transmission electron microscopy (TEM) and photoluminescence spectra (PL). It was found that SBA-15 contained abundant silanol groups after removal of triblock copolymers by ethanol extraction and could easily adsorb a great number of titanium alkoxide via chemisorption. After subsequent hydrolysis of the anchored Ti complexes and calcination of the amorphous TiO2, anatase TiO2 nanocrystals with spherical shape and uniform particle diameter of about 6 nm were formed. A blue shift was observed in UV-vis absorption spectra due to the quantum size effect of TiO2 nanoparticles. Moreover, the as-prepared TiO2 nanoparticles showed a high PL intensity due to an increase in the recombination rate of photogenerated electrons and holes under UV light irradiation.     

氮和碳共掺杂TiO2纳米晶的制备及可见光催化性能

以钛酸四丁酯为钛源, 冰醋酸为抑制剂, 超细铵盐为固体载体, 采用新型溶胶-凝胶法制备了氮和碳共掺杂TiO2纳米晶(N-C-TiO2) 光催化剂. 透射电子显微镜(TEM)结果表明, N-C-TiO2样品颗粒均匀, 尺寸细小, 且分散性好; 热失重分析(TGA)、 X射线粉末衍射(XRD)和X射线光电子能谱(XPS)研究结果表明, 复合干凝胶经低温热处理, 使铵盐载体分解、 挥发去除, 样品为单一的锐钛矿相, N和C原子扩散进入晶格结点或间隙位置, 与TiO2化学键结合; 氮气等温吸附-脱附结果表明, 样品比表面积高达356 m2/g, 孔体积为0.27 mL/g. 以氙灯为可见光光源, 罗丹明B水溶液为模拟污染物, P25为参比催化剂, 在辐射强度为100 mW/cm2的可见光照射条件下, N-C-TiO2具有很高的光催化活性, 其可见光催化活性明显高于P25.     

Nafion薄膜中单分散TiO2纳米晶体的合成

采用全氟化离子聚合物薄膜(钠型Nafion薄膜)作模板合成了平均直径为4.0nm的TiO₂晶体粒子。利用高分辨电子显微镜(HRTEM)、X-射线衍射仪(XRD)和紫外-可见光谱仪(UV-VIS)，对Nafion中TiO₂的含量、粒子大小分布、相变条件、纳米晶体微观型貌及其结构、Nafion薄膜结构和TiO₂粒子形成机理等进行了研究。研究结果表明，Nafion中Ti⁴⁺含量不仅与起始原料有关，还与起始物浓度有关。TiO₂在Nafion中的形成速度主要受控于水在膜中的扩散速度，而TiO₂晶体粒子的大小与分布则取决于Nafion的孔径，与起始原料种类以及晶化条件无关。文中还探索了无定型TiO₂转变成单分散晶体的各种途径，详细讨论了TiO₂晶体粒子合成的影响因素。     

Mechanical properties of titania nanofiber mats fabricated by electrospinning of sol–gel precursor

Flexible mats of titania fibers are prepared by calcination of electrospun polyvinylpyrrolidone fibers containing titanium isopropoxide precursor. Structural investigation of the calcinated nanofibers by X-ray diffraction (XRD) and electron diffraction (ED) combined with the morphologies by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the titania fibers, with an average diameter of 180 nm, were comprised of anatase and rutile crystals. The mechanical, chemical and thermal properties of the titania fiber mats are further investigated by the techniques of Instron mechanical tester, thermogravimetric analyzer (TGA), and Fourier transform infrared spectroscopy (FT-IR). The titania fiber mat prepared in this method exhibited a significant flexibility with 461 MPa Young’s modulus.     

Single-phase titania nanocrystallites and nanofibers from titanium tetrachloride in acetone and other ketones

Single-phase titania nanomaterials were prepared by autoclaving titanium tetrachloride in acetone at 80-140 degrees C. Depending on the molar ratio of TiCl4 to acetone (TiCl4/Ac), TiO2 materials with different phases and morphologies were obtained. When the TiCl4 concentration was no higher than TiCl4/Ac=1/15, single-phase anatase TiO2 nanocrystals in sizes ranging from 4 to 10 nm were prepared by tuning TiCl4/Ac ratios from 1/90 to 1/15. However, when the TiCl4 concentration was high enough (e.g., TiCl4/Ac>or=1/10), single-phase rutile TiO2 nanofibers were obtained selectively. The materials were characterized comprehensively using X-ray diffraction, transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and nitrogen adsorption measurements. With the aid of GC/MS analysis of organic products in the liquid phase, it is shown that the controlled hydrolysis of TiCl4 with water, which was in situ generated from the TiCl4-catalyzed aldol condensation reactions of acetones, played an important role in the formation of the titania nanomaterials. Some of the organic condensates may function to stabilize the phase and morphology of the materials. This mechanism was also supported by our success in using other ketones as alternatives to acetone in the synthesis.     

同轴静电纺丝法在纳米中空Ti02纤维中填充Ag的应用

以聚乙烯吡咯烷酮(PVP)溶胶,钛酸四正丁酯和PVP溶胶,银颗粒为前驱体,以共轴静电纺丝法制备了银填充的TiO2中空纳米纤维.将双组分纤维在200℃下热处理去除乙醇与表面吸附水后,继而在空气气氛中焙烧至600℃.可以得到在内表面上沉积银颗粒的TiO2纳米管,银颗粒的直径为5-40 nm,TiO2纳米管的外径150-300 nm.管臂厚10-20 nm.用红外吸收光谱(IR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等测试手段对超细纤维进行了表征.中空纤维的直径和管壁可以通过改变电纺参数来调节.与Ag-TiO2纳米纤维、TiO2纳米中空纤维、TiO2纳米纤维及TiO2纳米粉体相比较,Ag颗粒填充的TiO2纳米中空纤维在光分解亚甲基蓝上表现出了更好的光催化性能.