Direct fabrication of TiO2 nanoparticles deposited on hydroxyapatite crystals under mild hydrothermal conditions

TiO2 nanoparticles-deposited on hydroxyapatite (HAp) have been successfully synthesized by direct (single step) hydrothermal treatments of a CaCO3 suspension in a H3PO4 solution with 10 vol% TAS-FINE (titanium amine complex) at 150 degrees C for 6 h or 120 degrees C for 12-24 h under nearly neutral pH conditions. The obtained products were characterized by XRD, SEM-EDX, visible, Raman, and TEM. The XRD and Raman results showed the formation of HAp and TiO2 anatase phases under these hydrothermal conditions. SEM and TEM observations revealed that anatase TiO2 nanoparticles with the size of about 10 nm were deposited on the surfaces of the HAp crystals.     

Hydrothermal conversion of biomass into acetic acid

Hydrothermal process is one of the most promising processes for the conversion of biomass waste into resources among the several biomass conversion processes, because water of high temperature and high pressure has remarkable properties as a reaction medium. This paper described advances in our research involving overall reaction pathways for acetic acid production from biomass, mainly including (1) acetic acid production by controlling pathways of hydrothermal reaction, (2) acid-base behavior of water in the subcritical region and (3) effect of lignin on the acetic acid production in WO of lignocellulosic biomass.     

Hydrothermal synthesis of TiO2 nanofibres

TiO₂ nanofibres were synthesized by the hydrothermal method. The result shows that the growth of TiO₂ nanofibres is sensitive to the concentration of NaOH and the heating temperature.     

水热法制备锡掺杂氧化钛薄膜工艺因素研究

以Ti(SO4)2为前驱物,尿素为沉淀剂,SnCl4为掺杂剂,采用水热法制备出Sn-TiO2薄膜.利用XRD、SEM和UV-VIS等测试手段对薄膜的物相、表面形貌和吸光性等进行了表征.研究了Ti(SO4)2的浓度、SnCl4的掺入量、水热反应温度和保温时间对制备Sn-TiO2薄膜的影响.结果表明,在一定工艺条件下,可制备出均匀、致密,无可视缺陷,厚度约160 nm的Sn-TiO2薄膜.     

用TiO2、LiBH4和Mg低温制备TiB2纳米晶体

TiB2是一种超高温陶瓷材料,通常采用碳热、硼热法在1000℃以上的高温制备,其纳米晶体的制备一直是个难题.在本研究工作中,采用TiO2、LiBH4和Mg在600～800℃成功制备并分离提纯出了10～20 nm的TiB2纳米晶体.在反应中,LiBH4既作为硼源,又作为还原剂,而Mg则作为助还原剂.该反应使TiO2在60...     

Nanomaterials for adsorption and conversion of CO2 under gentle conditions

Global warming effect caused by excessive emission of greenhouse gases, such as CO₂ from modern industries, are emerging as serious environmental problem nowadays. Many strategies have been developed to address this issue, including solar energy utilization, green plants cultivation and coal desulfurization. These existing strategies always need sophisticated equipment and harsh reaction conditions, and are usually with limited efficiency. With the development of nanoscience and nanotechnology, it is becoming an effective strategy to directly capture and convert CO₂ with nanomaterials into valuable chemicals under gentle conditions. Herein, we summarize recent progress on nanomaterials for adsorption and conversion of CO₂ under gentle conditions, including various physical and chemical processes, and artificial photosynthesis. Future perspective and research direction of nanomaterials for CO₂ adsorption and conversion have been put forward on the basis of existing research works and our experimental experience.     

水热法制备TiO_2/g-C_3N_4及其光催化性能

采用水热法合成了可见光响应的TiO_2/g-C_3N_4复合催化剂,通过X射线衍射(XRD)、氮气吸附-脱附(BET)法、透射电子显微镜(TEM)、紫外-可见漫反射(UV-vis DRS)、荧光光谱(PL)、X射线光电子能谱(XPS)对样品进行了表征。并以亚甲基蓝为降解对象,考察了在可见光条件下不同催化剂对亚甲基蓝的降解能力。研究结果表明,锐钛矿型二氧化钛均匀地负载在石墨相氮化碳片层上,TiO_2/g-C_3N_4复合材料的光吸收带边扩展到470nm,具有优异的可见光催化效率,它对亚甲基蓝的光催化降解率达到99.0%。     

Growth of Mg2TiO4 single crystals by the floating zone method

Single crystals of the peritectic compound Mg₂TiO₄ up to 8 mm diameter and 80 mm long along the [1 0 0] and [1 1 1] directions, were grown by the travelling solvent float zone (TSFZ) technique using a halogen lamp image furnace. The optimum conditions were as follows: sintering temperature of the charge rod, 1500° C, the growth rate, 2 mm h^–1 and the composition of the charge rod in molar ratio, MgOTiO₂=21.01. The chemical composition of the solvent zone was determined by application of the EPMA technique and the peritectic nature of Mg₂TiO₄ was proved. The refractive index of the grown crystal was 2.05.     

TiO2纳米管阵列薄膜的水热晶化

首先在KF和乙二醇的混合溶液中利用阳极氧化技术在钛基底表面制得了一层排列整齐、形貌均一的TiO₂纳米管阵列薄膜,然后将制得的薄膜进行水热处理,通过扫描电子显微镜、X射线衍射仪等表征手段研究了水热处理温度和时间对TiO₂纳米管阵列薄膜表面形貌、结晶度以及管状结构的影响。结果表明:水热处理即使在较短的时间内（如3 h）也可在较低温度下（如210℃）使TiO₂纳米管阵列薄膜由无定形转变为锐钛矿型结构;提高水热处理温度或延长水热处理时间均可提高薄膜的结晶度,但同时纳米管管壁结晶度增加会使管内径变小甚至堵塞,从而破坏管状结构。     

Cobalt nanoparticles as reusable catalysts for reduction of 4-nitrophenol under mild conditions

Facile reduction of p-nitrophenol to p-aminophenol by sodium borohydride catalysed by cobalt nanoparticles (CoNPs) has been discussed. A simple approach has been made to synthesize highly active and ordered structures of CoNPs. The air-stable nanoparticles were prepared from cobalt sulphate using tetrabutyl ammonium bromide as surfactant and sodium borohydride as reductant. The cobalt nanocolloids in aqueous medium were found to be efficient reusable catalysts for the p-nitrophenol reduction. Palladium nanoparticles prepared from palladium chloride and the same surfactant were found to reduce p-nitrophenol but lose their catalytic efficiency after recovery. Based on chemical and kinetic studies, an attempt has been made to elucidate the mechanism of p-nitrophenol reduction using these nanoclusters.     

Hydrothermal synthesis of highly pure brookite-type titanium oxide powder from aqueous sols of titanate nanosheets

Hydrothermal synthesis of brookite-type titanium dioxide was examined using aqueous sols of titanate nanosheets, which were prepared with Ti[OCH(CH₃)₂]₄ and N(CH₃)₄OH by a bottom-up process in aqueous solutions. Highly pure brookite powders were yielded at hydrothermal temperatures as low as 120 °C and N(CH₃)₄OH/Ti[OCH(CH₃)₂]₄ molar ratios greater than 2. Although titanate nanosheets are formed at N(CH₃)₄OH/Ti[OCH(CH₃)₂]₄ ≥ 0.4, the addition of excess N(CH₃)₄OH was critical in forming highly pure brookite powders. Excess N(CH₃)₄⁺ caused the precipitation of layered titanates, which were formed by stacking titanate nanosheets. Additionally, the crystal nucleation of brookite occurred in the precipitates. Then, the adsorption of titanate nanosheets on brookite particles caused the particles to transform into rod-like shapes elongated along the c-axis. The adsorbed titanate nanosheets were structurally converted into brookite under the influence of the underlying brookite crystal. Despite having a rough surface, the resulting brookite particles were single crystal-like. Moreover, the use of any tetraalkylammonium hydroxides other than N(CH₃)₄OH did not yield brookite. The addition of N(CH₃)₄OH to the reaction sols yielded precipitates of small titanate nanosheets. The morphology of the titanate nanosheets could have a significant influence on brookite crystallization.     

Mg掺杂锐钛矿相TiO_2的第一性原理计算

利用基于密度泛函理论的第一性原理对不同浓度Mg掺杂锐钛矿相TiO2的电子结构和光学特性进行理论计算。结果表明,随着Mg掺杂浓度的增大,锐钛矿相TiO2的晶格膨胀程度越大,带隙宽度增大并且吸收边蓝移;不同掺杂浓度下Mg的3s和2p轨道对锐钛矿相TiO2的价带和导带组成贡献较小;在波长约为200⁵95、595595、595⁸00 nm的光区内,Mg掺杂锐钛矿相TiO2的光吸收能力分别减弱和增强。     

Hydrothermal corrosion behavior of iron aluminide under SCWO conditions

Fe₃Al based iron aluminide was tested under supercritical water oxidation (SCWO) conditions to explore its possible use as a reactor material for hydrothermal processes. Degradation resistance of the material were evaluated in distilled water at 450 °C and 300 atm in a closed reactor. The results of the kinetics studies, metallographic observations as well as phase and chemical analysis of the corrosion products indicated limited applicability of iron aluminide in SCWO conditions.     

Enhanced densification and microwave dielectric properties of Mg2TiO4 ceramics added with CeO2 nanoparticles

We report the study of the effects of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of MTO–CeO₂ (x wt.%) ceramics with x = 0, 0.5, 1.0 and 1.5 prepared by solid-state reaction method by adding CeO₂ nanoparticles as a sintering aid. The pure Mg₂TiO₄ ceramics were not densifiable below 1450 °C. However, when CeO₂ nanoparticles were added to MTO, the densification achieved at 1300 °C along with the increase in average grain size with the uniform microstructure and improved microwave dielectric properties. This is mainly driven by the large surface energy of CeO₂ nanoparticles and their defect energy during the sintering process. While the addition of CeO₂ nanoparticles in MTO ceramics does not change the dielectric constant (?_r), the unloaded quality factor (Q_u) was altered significantly. MTO–CeO₂ (1.5 wt.%) ceramics sintered at 1300 °C exhibit superior microwave dielectric properties (?_r ～ 14.6, Q × f₀ ～ 167 THz), as compared to the pure Mg₂TiO₄ ceramics. The observed results are correlated to the enhancement in density and the development of uniform microstructure with the enhanced grain size.     

水热法制备钛酸盐纳米管的研究进展

作为一种有诱人前景的新材料,钛酸盐纳米管的研制开发正在国内外展开.介绍了钛酸盐纳米管的微观结构和形成机理;综述了目前最为常见的钛酸盐纳米管的合成方法--水热法以及水热法制备钛酸盐纳米管的诸多影响因素:NaOH的浓度、反应时间和反应温度等;简要介绍了钛酸盐纳米管的应用.     

水热法制备过程中TiO2纳米纤维成形机理研究

采用水热法制备出φ20～30nm, 长度达微米级的TiO2纳米纤维, 以XRD、TEM、IR等手段对不同工艺条件下获得的产物晶型结构、微观形貌以及化学组成进行了表征, 对TiO₂纳米纤维成形机理进行探讨, 并就洗涤过程中pH值对纤维结构的影响进行分析. 结果表明, TiO₂纳米纤维的形成机理可能是锐钛矿型TiO₂纳米颗粒在强碱作用下生成K₂Ti₆O₁₃颗粒, 小颗粒沿一定晶轴生长, 遵循溶解-生长机理, 逐渐长成纳米纤维. 清洗溶液的pH值对产物的成分和结构有较大影响, 通过控制清洗溶液的pH值和热处理温度, 可以获得组成分别为K₂Ti₆O₁₃、H₂Ti₃O₇和TiO₂的纳米纤维. 在pH=7、80℃烘干条件下得到的主要是H₂Ti₃O₇纳米纤维, 400℃煅烧后转变为TiO₂纳米纤维.     

热液法低温制备锐钛矿型二氧化钛纳米粉体

以钛酸四丁酯为前驱体,采用热液法在低于100℃的条件下制备了纳米晶TiO2粉体。运用DSC、XRD和HRTEM对所获得的TiO2粉体进行表征。XRD结果表明：所得到的TiO2粉体都是锐钛矿相,颗粒大小随着热液处理温度（60～100℃）的升高而增大,由Scherrer公式计算,其粒径介于4.8～6.9nm。同时,研究了所获TiO2粉体在紫外光下降解亚甲基蓝的性质。