纳米二氧化钛粉体的多晶型制备及形成机理

本文分别以四氯化钛、硫酸钛和钛酸丁酯为前驱物,研究了水热条件下二氧化钛微晶粉体的结晶晶型、晶粒形貌和晶粒度.采用XRD和TEM等分析手段分别对产物的晶相和晶粒形貌进行表征.实验结果表明:对于200℃水热反应,以四氯化钛为前驱物,通过加入氢氧化钠调节反应介质酸碱度,当溶液pH值小于1时,有利于形成金红石型粉体;当溶液pH值大于3并小于7时,有利于形成锐钛矿型粉体;当溶液ph值大于7时,有利于形成板钛矿型粉体.以硫酸钛为前驱物,通过控制胶体制备工艺及反应温度,制备得到锐钛矿型和板钛矿型粉体.金红石型粉体呈长条柱状,锐钛矿呈菱形或双锥状,板钛矿呈板块状.经过较为系统的实验研究,获得了金红石、锐钛矿、板钛矿三种晶相的粉体,并可通过控制前驱物的种类及酸碱度和水热反应条件随意地制备出以上三种晶相中的单晶相粉体.从结晶学出发,解释了二氧化钛纳米粉体的结晶形貌,并从晶体生长过程及生长机理的角度讨论了二氧化钛同质变体的形成机理.     

二氧化钛纳米棒的制备及其晶体生长机理分析

采用溶剂热法合成具有高结晶性与单分散性的TiO₂纳米棒. 采用TEM、XRD、HRTEM等对样品的微观结构进行表征, 并考察了TiO₂纳米棒对亚甲基蓝的光催化性能. 通过控制反应时间、反应温度, 研究纳米棒的形貌演变规律.结果表明, 可以通过“奥斯特瓦尔德熟化”和“取向接触”两种晶体生长过程制备出棒状TiO₂纳米晶, 降低纳米晶的表面能是晶体生长与形貌演变的主要驱动力; 高结晶性的TiO₂纳米棒具有高于P25的光催化能力.     

胶体纳米晶合成与形貌控制策略及机理EI北大核心CSCD

胶体纳米晶合成与控制策略主要从动力学方面考虑,一般要结合液相胶体成核生长理论和晶体生长理论来分析。本文首先从成核阶段、生长阶段和熟化阶段的控制方面阐述了胶体纳米晶形貌合成与控制。然后对于经典晶体学理论解释不了的现象,阐述了选择吸附机理、有效单体机理、取向连接机理等用来解释胶体纳米晶的合成机理。本文还对近年来发展的其他一些合成纳米材料的新机理或多种机理共同作用做了简要介绍。最后,对纳米晶合成与形貌控制的前景作了概述,认为定量和精准结构控制是纳米晶形貌合成与控制面临的巨大挑战和发展趋势。     

水热法制备纳米VO2及其相变机理的研究进展

VO_2是一种具有极大应用价值的功能材料,其潜在的应用产品有智能窗、热敏电阻、锂离子电池电极等,但纳米VO_2的大批量制备技术成了制约其应用的关键因素。水热合成法反应条件温和、对环境的污染小、能耗低、价格便宜;易控制化学价态、晶相、产物纯度较高;反应无需煅烧晶化,可以减少煅烧过程中产生的团聚,可获得通常条件下难以得到的纳米粉体,粉体粒径分布较窄、晶型和形貌可控,有望用于VO_2纳米结构的大量合成。聚焦于水热合成法制备纳米VO_2及其相变机理的研究进展,着重介绍了不同形貌与物相的纳米VO_2的水热合成制备方法、物相转换及机理、水热过程中VO_2的生长机制。最后,指出了水热法制备VO_2所面临的一些问题,并展望了未来的发展方向。     

TiO2晶型转变(A→R)的影响因素

二氧化钛作为一种应用极广泛的陶瓷材料,其晶型不同所拥有的性质和功能不同。对影响二氧化钛晶型转变的因素进行了综述,总结了烧结温度、掺杂、颗粒尺寸、压应力以及烧结气氛等对二氧化钛晶型转变的影响,对相变机理进行分析,并就TiO_2的A→R相变的应用前景进行展望。     

金属离子掺杂对纳米TiO2晶型转变影响作用机制的研究进展

二氧化钛中引入金属杂质以提高二氧化钛的光催化活性受到了人们的广泛关注,对金属离子掺杂引起的二氧化钛晶型的转变进行了综述,总结了金属掺杂离子的熔点、离子半径、掺杂离子浓度、掺杂离子化合价等对TiO2晶型转变的影响,对TiO2晶型转变影响的作用机理进行了分析,并对TiO2光催化材料的金属离子掺杂改性研究的未来发展方向提出了建议.     

溶液络合法制备钙钛矿结构电子陶瓷粉体的合成与表征

采用溶液络合法合成了钙钛矿结构SrTiO3、PbTiO3和Bi2O3·3TiO2等电子陶瓷纳米粉体,用差热-热重分析(DTA/TG/DTG)、X光衍射分析(XRD)及扫描电镜(SEM)等手段对产物的热分解过程、晶型转变和粒径形貌进行了表征,并对由这些粉体烧成的电容器陶瓷的密度和介电性能进行了检测.实验结果表明,在600℃时,可以合成纯SrTiO3纳米粉体,而在400℃时,即有PbTiO3相生成.由这些粉体制备的电容器陶瓷显示出良好的烧结性能和介电性能.     

一种纯锐钛纳米二氧化钛粉体的研制及应用

对纳米二氧化钛粉体进行无机包膜和有机包覆改性,制备了一种高透明度和高效屏蔽紫外线的纯锐钛纳米二氧化钛粉体,分析了改性过程中有关纳米粉体的有机包覆效果的影响因素,通过测定粉体的光催化性,间接表征了它的包覆完整性,并用TEM、XRD、ICP-OES、紫外可见分光光度法表征了纳米粉体的粒径、内部形貌、晶型、重金属含量、屏蔽紫外线性能和透明度,结果表明,产品应用于防晒化妆品时,许多性能都得到明显提升。     

水热温度和酸洗浓度对水热法合成钛酸盐纳米管的影响

以P25纳米粉体和NaOH为原料,采用水热合成法制备出钛酸盐纳米管。通过TEM和XRD表征手段,研究了水热温度和酸洗浓度对钛酸盐纳米管微观形貌和晶型组成的影响。结果表明,用去离子水或低浓度的酸处理反应产物时,纳米管的结构清晰完整,其成分主要是H2Ti2O5.H2O;用高浓度的酸处理反应产物时会破坏纳米管结构,其成分主要是锐钛矿型TiO2。反应温度对产物的微观结构和晶型组成也有显著影响:水热温度90℃时的产物只能得到膜状物和少量纳米管,而水热温度从110℃升至190℃时,纳米管的长度逐渐增长,而管径基本不变;低温反应得到的产物晶型与原料类似,较高反应温度的产物为锐钛矿。     

形貌可控的TiO2纳米晶的溶胶凝胶-水热法组合制备

以四烷基氢氧化铵为结构导向剂,正丁醇为结构导向助剂,采用溶胶凝胶-水热法组合制备了不同形貌的二氧化钛纳米晶.通过TG/DTA、TEM、XRD、DLS等手段对产物进行了结构和形貌表征.研究表明,通过选择结构导向剂的烷基种类可分别得到四方型和纺锤型纳米晶,在一定范围内改变其浓度则可以控制晶体的晶化度、分散性和颗粒尺寸.     

Thermally stimulated transformations of sol-gel derived TiO2/MoO3 composites

We have studied the distinctive features of the reaction between titania and molybdenum trioxide in the sol-gel synthesis of TiO₂/MoO₃ composite materials (1–10 mol % MoO₃). The results demonstrate that interactions between phases, which depend on MoO₃ concentration in the composites and are stronger at higher heat-treatment temperatures, lead to suppression of titania crystallization, inhibit the anatase-to-rutile phase transition, and influence the morphology and structural perfection of the oxide phase.     

Quartz–titania composites for the photocatalytical modification of construction materials

In this paper the synthesis of photocatalytically modified core–shell composites is reported. The synthesis was realized by hydrolysis and condensation of tetrapropylorthotitanate on ground quartz, which is used as an additive in mortar and concrete. This allowed a controlled growth of titania layers on the particles with different thicknesses. The efficiency of the coating process was studied by interpretation of XRF results. The morphology of the composites was analyzed via SEM. Photoactivity of the particles was studied by analyzing the titania crystal phases of the shell (XRD) and calculating the photonic efficiency of NO-degradation measurements. Moreover methylene blue degradation was performed to reflect the self cleaning properties of the composite materials.     

Fabrication of titanate nanowires with different dimensions

Titanate nanowires were fabricated by the reaction of titania particles in a highly concentrated KOH aqueous solution at 150 °C for more than 20 h followed by the rinsing of the resultant compound with a 0.1 M HCl aqueous solution and purified water. The diameter and length of the titanate nanowires can be controlled by using titania powders with different crystalline phases and particle sizes. The crystalline phase in the titanate nanowire was considered to be a hydrated titanate.     

纳米二氧化钛粉体晶相控制实验研究

在水解－沉淀法制备纳米TiO2粉体的过程中，使用不同的沉淀剂获得了晶相不同的纳米TiO2粉体，使用混合沉淀剂，通过控制沉淀剂的比例，制备了晶相组成（金红石与锐钛矿比例）不同的纳米TiO2多晶粉体，采用相同的粉体制备工艺，不同的后续处理工艺，探讨了锐钛矿向金红石转变的相变温度，经分析研究后认为，水解－沉淀法制备的纳米粉体中的锐钛矿向金红石红转变的温度为500－800℃，完全转变的温度在800℃以上；纳米TiO2多晶粉体的晶相组成不仅与沉淀剂的种类，混合沉淀剂中沉淀剂的比例和粉体的煅烧温度有关，而且与粉体的后续处理工艺和粉体表面界面相的稳定性有关。     

Secondary phases in natural magnesite sintered with addition of titania, ilmenite and zirconia

The detail microstructures of sintered natural magnesite with addition of titania, zirconia and ilmenite mineralisers were studied using scanning electron microscopy (SEM) with special emphasis on energy dispersive X-ray analyses (EDXA). The study was directed towards the determination of secondary phase composition in sintered magnesite with different mineraliser addition. In order to evaluate the secondary phases with addition of transition metal oxides, keeping titania (TiO₂) as a reference mineraliser, a natural analog of titania containing iron i.e., Ilmenite (Fe₂O₃ · TiO₂) and pure Zirconia (ZrO₂) were added to magnesite which was then sintered up to 1700 °C. The relative behaviour of these pure and mixed oxide mineralisers during the sintering of magnesite has been evaluated with respect to their microstructure and secondary phase composition. The present paper showed that titania addition to natural magnesites resulted in the formation of calcium titanate in the secondary phase upon sintering. Zirconia, on the other hand, did not show any reaction product in the secondary phase. The addition of titania in the form of mixed oxide, ilmenite, also gave rise to calcium titanate formation, providing a similar microstructure, specially with reference to spatial distribution of phases in the secondary phase.     

Controlled Synthesis of Kinked Ultrathin ZnS Nanorods/Nanowires Triggered by Chloride Ions: A Case Study

Colloidal synthesis of kinked ultrathin ZnS nanorods/nanowires with mixed phases using tiny Ag₂S nanocrystals as catalysts is reported. It is found that chloride ions can induce the controlled morphology transition from straight to kinking. The synthetic parameters modulating the growth of kinked ZnS nanorods/nanowires are systematically investigated. Chloride ions introduced in the reaction can generate more proportion of wurtzite phase by slowing the nucleation and growth rates during the growth of one‐dimensional (1D) ZnS nanorods/nanowires. The formation of kinked morphology is responsible for the increased domains of mixed stacking and twinning in single 1D nanostructures. The present recipe on controlled synthesis of 1D kinked nanorods/nanowires provides a model of crystal growth control, and these unique 1D nanostructures may also offer new opportunities to fabricate nanodevices with special functions.     

Syntheses, characterization and properties of novel nanostructures consisting of Ni/titanate and Ni/titania

Ni/titanate one-dimensional nanostructures and Ni/titania nanocrystal composites were produced by a facile synthetic procedure using protonic titanate nanotubes as the precursor templates. The formation mechanisms for the nanostructures were proposed. The nickel ions first enter into the titanate matrix through three approaches, ion-exchanges reaction with the interlayered hydrogen ions, capillary forces from the microcavities, and electrostatic adsorptions due to the negatively charged outer surface of the titanate nanotubes. The following metallic nickel nucleation and growth may have occurred for these three kinds of the nickel ions reduced under hydrogen gas flow at elevated temperatures. The supports' titanate nanotubes may phase transform into the anatase titania nanocrystals and further into the mixture of anatase and rutile titania along with the increases of temperature. The Ni/titanate nanocomposites demonstrate paramagnetic behaviors and the Ni/titania nanocrystals display typical ferromagnetic behaviors. The Ni/titania sample reduced at 550 °C containing 14.5% rutile has higher photocatalytic activities than the sample reduced at 350 °C containing pure anatase, which is ascribed to a synergistic effect between anatase and rutile. The ferromagnetic characteristics of the Ni/titania products make them available as magnetically separable photocatalysts, which can be separated and recovered quickly by applying an external magnetic field.     

Recent progress in mesoporous titania materials: adjusting morphology for innovative applications

Abstract

This review article summarizes recent developments in mesoporous titania materials, particularly in the fields of morphology control and applications. We first briefly introduce the history of mesoporous titania materials and then review several synthesis approaches. Currently, mesoporous titania nanoparticles (MTNs) have attracted much attention in various fields, such as medicine, catalysis, separation and optics. Compared with bulk mesoporous titania materials, which are above a micrometer in size, nanometer-sized MTNs have additional properties, such as fast mass transport, strong adhesion to substrates and good dispersion in solution. However, it has generally been known that the successful synthesis of MTNs is very difficult owing to the rapid hydrolysis of titanium-containing precursors and the crystallization of titania upon thermal treatment. Finally, we review four emerging fields including photocatalysis, photovoltaic devices, sensing and biomedical applications of mesoporous titania materials. Because of its high surface area, controlled porous structure, suitable morphology and semiconducting behavior, mesoporous titania is expected to be used in innovative applications.     

无模板法可控合成多层次结构二氧化钛微球

以1,4-二氧六环为溶剂,采用溶剂热法成功实现无模板法可控合成二氧化钛多层次结构微球。通过系统改变反应体系中浓盐酸与四异丙醇钛(TTIP)相对物质的量比能够有效调控二氧化钛形貌。当浓盐酸与TTIP物质的量比控制在0(或0.7或0.9)、1.8、3.6与5.7时,所得产物分别为纳米颗粒构建二氧化钛微球、纳米棒修饰二氧化钛微球、纳米棒花菜结构以及纳米棒海胆结构。在成功进行形貌调控的基础上,进一步探讨了二氧化钛多种结构的形成机理,并对其光催化产氢性能进行了表征。研究发现,在这4种结构中,纳米棒修饰二氧化钛微球具有最佳的光催化性能,这可能是由于同时存在金红石和锐钛矿两种晶型而形成异质结结构所导致。