Phase transition between nanostructures of titanate and titanium dioxides via simple wet-chemical reactions

Titanate nanofibers of various sizes and layered structure were prepared from inorganic titanium compounds by hydrothermal reactions. These fibers are different from "refractory" mineral substances because of their dimension, morphology, and significant large ratio of surface to volume, and, surprisingly, they are highly reactive. We found, for the first time, that phase transitions from the titanate nanostructures to TiO(2) polymorphs take place readily in simple wet-chemical processes at temperatures close to ambient temperature. In acidic aqueous dispersions, the fibers transform to anatase and rutile nanoparticles, respectively, but via different mechanisms. The titanate fibers prepared at lower hydrothermal temperatures transform to TiO(2) polymorphs at correspondingly lower temperatures because they are thinner, possess a larger surface area and more defects, and possess a less rigid crystal structure, resulting in lower stability. The transformations are reversible: in this case, the obtained TiO(2) nanocrystals reacted with concentrate NaOH solution, yielding hollow titanate nanotubes. Consequently, there are reversible transformation pathways for transitions between the titanates and the titanium dioxide polymorphs, via wet-chemical reactions at moderate temperatures. The significance of these findings arises because such transitions can be engineered to produce numerous delicate nanostructures under moderate conditions. To demonstrate the commercial application potential of these processes, we also report titanate and TiO(2) nanostructures synthesized directly from rutile minerals and industrial-grade rutiles by a new scheme of hydrometallurgical reactions.     

Synthesis of TiO2 nanocoral structures in ever-changing aqueous reaction systems

A far-from-equilibrium strategy is developed to synthesize coral-like nanostructures of TiO(2) on a variety of surfaces. TiO(2) nanocoral structures consist of anatase base film and rutile nanowire layers, and they are continuously formed on substrates immersed in aqueous TiOSO(4)-H(2)O(2). The sequential deposition of TiO(2) starts with hydrolysis and condensation reactions of titanium peroxocomplexes in the aqueous phase, resulting in deposition of amorphous film. The film serves as adhesive interface on which succeeding growth of rutile nanowires to occur. This initial deposition reaction is accompanied by shift in pH of the reaction media, which is favorable condition for the growth of rutile nanocrystals. During the growth of rutile nanocoral layers, the amorphous base films are transformed to anatase phase. These sequential deposition reactions occur at temperatures as low as 80 °C, and the mild synthetic condition allows the use of a wide range of substrates such as ITO (indium tin oxide), glass, and even organic polymer films. The thickness of nanocoral layer is controllable by repeating the growth reaction of rutile nanocorals. TiO(2) nanocorals show photocatalytic activity as demonstrated by site-specific reduction of Ag(I) ions, which proceeds preferentially on the rutile nanowire layer. The rutile nanowire layer also shows photocatalytic decomposition of acetaldehyde, which is promoted upon increase of the thickness of the nanowire layer. The use of temporally transforming reaction media allows the formation of biphasic TiO(2) nanocoral structures, and the concept of nonequilibrium synthetic approach would be widely applicable to developing structurally graded inorganic nanointerfaces.     

TiO2纳米粒子包覆聚苯乙烯球的结晶性能与表面光电压特性

TiO2具有很高的光催化活性，同时TiO2纳米粒子具有耐酸碱和耐光化学腐蚀、低成本、无毒等性质，在许多领域引起广泛关注．据报道，TiO2的锐钛矿晶型比金红石晶型具有更好的光催化活性．由于金红石是TiO2的热力学稳定相，而锐钛矿是亚稳相，通常锐钛矿相在550-800℃温度范围内形成金红石相，从而降低其催化活性，限制了其应用．     

光电化学水氧化用多孔单晶金红石TiO2纳米棒阵列光阳极的设计和构建

光电化学电池(如染料敏化太阳能电池、量子点敏化太阳能电池以及光电化学水分解电池)是实现太阳能转化及存储的有效手段之一.其中,光电极是光电化学电池的核心组成部分,它集光吸收、光生电荷输运及转移等决定光转化效率的关键过程于一身,因此构筑高活性半导体光电极以实现高效太阳能转化利用引起研究者广泛关注.多孔TiO2纳米颗粒堆垛薄膜光阳极因具有大的比表面积,可提供更多的染料(量子点)担载和反应活性位点,在光电化学电池中表现出优异活性而被广泛研究.然而, TiO2纳米颗粒间大量存在的晶界对光生电荷有较强的散射作用,降低了光生电荷的收集效率.英国牛津大学Snaith研究小组利用模板辅助水热过程首次获得了(001)晶面占优的多孔单晶锐钛矿TiO2微米颗粒,这种多孔单晶TiO2微米颗粒在具有大比表面积的同时,其单晶结构还能有效去除晶界对电荷的散射作用,因而具有优异的电荷输运特性.利用这种多孔单晶TiO2微米颗粒组建的光阳极用于染料敏化太阳能电池中,展现出优异的太阳能光电转化性能.受该工作启发,各种形貌的多孔单晶TiO2微米颗粒作为光催化剂和光电化学分解水用光阳极材料被广泛研究,并表现出优异活性.在单晶微米颗粒堆垛成的薄膜光电极中,虽然单个单晶微米颗粒中晶界对电荷的散射作用被有效抑制,但是单晶颗粒间的晶界仍然存在并影响光生电荷的收集效率.为了彻底抑制晶界对光生电荷的散射作用,每个单晶颗粒都应该贯穿整个薄膜,例如一维TiO2纳米棒单晶阵列薄膜.虽然一维单晶阵列薄膜能够有效提高光生电荷的收集效率,但相对于多孔薄膜具有较小的比表面积,限制了担载染料(量子点)和反应位点的数量.为了增大TiO2单晶纳米棒阵列薄膜的比表面积,目前主要的手段包括调控纳米棒长径比、表面修饰TiO2纳米颗粒以及二次生长构建TiO2枝晶阵列.本文首次提出通过制备多孔单晶TiO2纳米棒单晶阵列薄膜来获得高比表面积和高光生电荷收集效率的光阳极,提高光电化学电池的效率.在透明导电薄膜(FTO)表面利用水热生长TiO2纳米棒阵列薄膜之前,预先在FTO基体上沉积一层SiO2球密堆模板, TiO2纳米棒单晶阵列在从FTO表面向上生长过程中,会将SiO2球模板包裹进TiO2纳米棒中,再通过碱溶液将SiO2球模板溶解,首次在FTO基体上原位生长出多孔单晶TiO2纳米棒阵列薄膜.将所得多孔单晶金红石TiO2纳米棒阵列薄膜作为光电化学分解水电池光阳极,其光电化学分解水活性相对于实心单晶金红石TiO2纳米棒阵列提高了2.6倍.多孔单晶金红石TiO2纳米棒阵列光阳极性能的提升可归因于：(1)多孔结构赋予多孔单晶金红石TiO2纳米棒阵列薄膜更大的比表面积,可提供更多的反应活性位点;(2)多孔结构能够有效缩短单晶金红石TiO2纳米棒中光生电荷体相输运距离,提高光生电荷的收集效率;(3)多孔结构通过对光多次反射吸收可有效增强光吸收,产生更多光生电荷参与水分解反应;(4)在制备过程中引入Si掺杂,导致多孔单晶金红石TiO2纳米棒带隙扩大了0.1 eV,带隙增大归因于导带位置负移0.1 eV,光生电子具有更强的还原能力,光电流起始电位相应负移约0.1 V.     

高效一体化脱硫脱硝催化剂

热电厂燃煤锅炉排放的烟道气中含有 SO2、 NO等有害气体 ,它们是大气污染的主要污染源之一 ,其对自然生态、环境的破坏及造成的巨大经济损失已毋庸置疑 .因此国内外投入大量人力财力开展消除 SO2和 NO的研究 .NO的消除 (deNO_x)已开发成功用 NH3为还原剂的选择催化还原过程 (简称 SCR过程 ),在德日等国家已实现了工业化 .消除 SO2(deSO_x)工业上采用石灰乳喷射吸收法 .现在国外兴起所谓 deSO_x- deNO_x一体化方案 ,实际上它只是 deSO_x过程和 deNO_x过程的简单组合 .例如石灰乳吸收法和 SCRdeNO_x法的组合, SCRdeNO_x和…     

Chlorate ion mediated rutile to anatase reverse phase transformation in the TiO2 nanosystem

Rutile TiO(2) nanoneedles (8 nm × 100 nm) synthesized at room temperature by anodization in perchloric acid (pH < 1) are shown to undergo an interesting reverse phase transformation to anatase nanoparticles (8 nm) at 300 °C only if the chlorate ions are maintained in the ambient medium. When chlorate ions are removed by multiple washing, the rutile phase and the needle morphology are maintained. The mechanism of formation of the ion-stabilized solid and its thermal evolution is discussed.     

Hydrophilic/hydrophobic features of TiO2 nanoparticles as a function of crystal phase, surface area and coating, in relation to their potential toxicity in peripheral nervous system

The hydrophilic/hydrophobic properties of a variety of commercial TiO(2) nanoparticles (NP), to be employed as inorganic filters in sunscreen lotions, were investigated both as such (dry powders) and dispersed in aqueous media. Water uptake and the related interaction energy have been determined by means of adsorption microcalorimetry of H(2)O vapor, whereas dispersion features in aqueous solutions were investigated by dynamic light scattering and electrokinetic measurements (zeta potential). The optimized dispersions in cell culture medium were employed to assess the possible in vitro neuro-toxicological effect on dorsal root ganglion (DRG) cells upon exposure to TiO(2)-NP, as a function of crystal phase, surface area and coating. All investigated materials, with the only exception of the uncoated rutile, were found to induce apoptosis on DRG cells; the inorganic/organic surface coating was found not to protect against the TiO(2)-induced apoptosis. The risk profile for DRG cells, which varies for the uncoated samples in the same sequence as the photo-catalytic activity of the different polymorphs: anatase-rutile>anatase>rutile, was found not to be correlated with the surface hydrophilicity of the uncoated/coated specimens. Aggregates/agglomerates hydrodynamic diameter was comprised in the ~200-400 nm range, compatible with the internalization within DRG cells.     

Titanium dioxide anatase as matrix for matrix-assisted laser desorption/ionization analysis of small molecules

The use of inorganic species as assisting materials in matrix-assisted laser desorption/ionization (MALDI) analysis is an alternative approach to avoid interfering matrix ions in the low-mass region of the mass spectra. Reports of the application of inorganic species as matrices in MALDI analysis of small molecules are, however, scarce. Nevertheless, titanium dioxide (TiO(2)) powder has been reported to be a promising matrix medium. In this study we further explore the use of TiO(2) as a matrix for the MALDI analysis of low molecular weight compounds. We present results showing that nanosized TiO(2) anatase and TiO(2) rutile perform better as MALDI matrices than a commercial TiO(2) anatase/rutile mixture. Moreover, when using nanosized TiO(2) anatase as a matrix, high-quality mass spectra can be obtained with strong analyte signals and weak or non-existing matrix interference ions. Furthermore, our results show that the phase type plays an important role in the application of TiO(2) as a MALDI matrix.     

均相水解法制备金红石含量可控的纳米TiO2

用均相水解法通过调节对甲苯磺酸的添加量制备了金红石含量线性可控的纳米TiO2粒子,相同条件下,没有加入对甲苯磺酸时,制备的TiO02颗粒为纯锐钛矿晶型．制备的纳米TiO2颗粒,其单晶尺寸为19．5mm(金红石),13．5mm(锐钛矿),比表面积72．7m^2／g,通过公式计算得到了制备的TiO2纳米颗粒带隙能为2．83eV,比P25和纯锐钛矿纳米TiO2颗粒的带隙能均低．     

复合模板剂下有序介孔TiO2的制备研究

在复合模板剂聚氧乙烯十二烷基醚(Brij35）和聚乙二醇（PEG)下，制备出有序介孔TiO2.用XRD、HRTEM、SEM、FT-IR和N2吸附脱附等方法进行表征；并通过对反应过程中电导率和粘度的连续监测，分析有序介孔TiO2形成过程.研究表明,介孔TiO2为规整的六方排列结构，在低于400 ℃焙烧，有序结构稳定性高，比表面积达252 m2•g－1，孔径3.4 nm，晶型为锐钛矿；经500 ℃焙烧，有序介孔结构破坏，并开始出现金红石型晶相.有序介孔TiO2形成过程是基于在高极性介质中非极性的碳氢链聚集成为胶束，同时钛酸丁酯（TBOT）在已形成的胶束上聚集，在酸作用下不断水解缩聚而形成有序介孔结构，有效控制水解和聚合过程是控制介孔材料结构形成的关键.     

Synthesis of Crystalline Nanosized Titanium Dioxide via a Reverse Micelle Method at Room Temperature

Crystalline TiO2 nanoparticles were synthesized by hydrolysis of titanium tetrabutoxide in the presence of hydrochloric acid in Np-5(lgepal CO-520)/ cyclohexane reverse micelle solution at room temperature.Pure rutile nanoparticles were obtained at an appropriate acid concentration.The influences of various reaction conditions such as the concentration of acids,water content value (2=[H2O]/[Np-5]) on the formation,erystal phase,morphology,and size of the TiO2 particles were investigated.     

Sn4+掺杂TiO2中空纤维材料的制备及光催化性能

以Ti(OCH2CH2CH2CH3)4为钛源,脱脂棉花纤维为模板,利用浸渍-热转化两步法制备了具有中空结构的Sn4+掺杂TiO2光催化纤维材料(Sn4+/TiO2),利用X-射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见光谱(UV-vis)等技术对其晶体结构、形貌、尺寸、光吸收特性等进行了表征.以亚甲基蓝(MB)溶液的脱色降解为模型反应,考察了样品Sn4+/TiO,在太阳光下的光催化性能.结果表明:利用该法制得的Sn4+/TiO2材料具有中空纤维结构;煅烧温度影响材料Sn4+/TiO2的相结构、组成、尺寸、形貌以及催化性能;Sn4+的掺入能够显著改善TiO2在太阳光条件下的催化性能,600℃煅烧2h所得的Sn4+掺杂量x=0.29％的TiO2中空纤维材料具有最佳的光催化活性,太阳光下2h即可使MB溶液的脱色降解率达97.28％;重复使用5次仍可使MB溶液的脱色降解率保持在90％以上,且该催化剂材料易于离心分离去除.     

TiO2纳米晶光催化降解铬酸根离子的研究

以二氧化钛为光催化剂,研究了溶液的ｐＨ值、铬酸根离子的初始浓度、通入的气体种类、氧化钛的载量等因素对铬酸根离子降解率的影响。同时合成了粒径小于１０ｎｍ的锐钛矿相和金红石相氧化钛纳米晶来考察晶相和尺寸效应对降解率的影响。结果表明,锐钛矿的催化活性高于金红石相,两者的催化活性均大大高于市售的氧化钛微粉。     

Hollowing Sn-doped TiO2 nanospheres via ostwald ripening

The well-known physical phenomenon Ostwald ripening in crystal growth has been widely employed in template-free fabrication of hollow inorganic nanostructures in recent years. Nevertheless, all reported works so far are limited only to stoichiometric phase-pure solids. In this work we describe the first investigation of doped (nonstoichiometric) materials using Ostwald ripening as a means of creating interior space. In particular, we chose the xSnO2-(1 - x)TiO2 binary system to establish preparative principles for this approach in synthesis of structurally and compositionally complex nanomaterials. In this study, uniform Sn-doped TiO2 nanospheres with hollow interiors in 100% morphological yield have been prepared with an aqueous inorganic route under hydrothermal conditions. Furthermore, our structural and surface analyses indicate that Sn4+ ions can be introduced linearly into TiO2, and preferred structural phase(s) can also be attained (e.g., either anatase or rutile, or their mixtures). Fluoride anions of starting reagents are adsorbed on the surface sites of oxygen. The resultant anion overlayer may contribute to stabilization of surface and creation of repulsive interaction among the freestanding nanospheres. On the basis of these findings, we demonstrate that Ostwald ripening can now be employed as a general hollowing approach to architect interior spaces for both simple and complex nanostructures.     

以纳米微晶纤维素为模板的酸催化水解法制备球形介孔TiO_2

以纳米微晶纤维素(NCC)为模板剂,采用酸催化水解法制备了球形介孔TiO2(SP-TiO2).并采用扫描电镜、透射电镜、X射线衍射、紫外-可见漫反射光谱和低温N2吸附-脱附等手段对其进行了表征.结果表明,所制SP-TiO2为直径100～200nm的规整球形颗粒,单个球形颗粒由粒径为10～20nm的TiO2小晶粒组成.其介孔孔径为8.2～13.5nm,且随焙烧温度的升高而增大.NCC长链结构之间羟基键合所形成的狭小空间构成的微反应器,可有效限制TiO2前驱体的生长和团聚,诱导其晶粒自组装成球形结构,并抑制由锐钛矿相向金红石相转变.600oC焙烧的SP-TiO2表现出最高的光催化活性,对苯酚降解率达89%.     

The different behavior of rutile and anatase nanoparticles in forming oxy radicals upon illumination with visible light: an EPR study

Photoexcited TiO(2) has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light-induced reactions of a suspension of titanium dioxide (TiO(2)) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin-trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O(2)(-)) radicals were detected in TiO(2) rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O(2)(-) radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O(2)(-) formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO(2) neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400-500 nm) was found to be responsible for the light-induced ROS in TiO(2) nanoparticles. The characterization of the mechanism of visible light-induced oxy radicals formation by TiO(2) nanoparticles could contribute to its use as a sterilization agent.     

Mechanism of titania deposition into cylindrical poly(styrene-block-4 vinyl pyridine) block copolymer templates

A simple and effective way for TiO(2) to be deposited on silicon or indium tin oxide (ITO) substrates has been achieved by using a poly(styrene-block-4-vinyl pyridine) (PS-b-P4VP) block copolymer template. In particular, a mechanism for the formation of TiO(2) within the P4VP phase was developed. Within this model, the TiO(2) deposition occurs by swelling of the protonated P4VP segments followed by transport of Ti precursor, probably protonated Ti(OH)(4) given the low pH conditions used, into the swollen P4VP followed by condensation into TiO(2) during the heating/plasma etch processes. TiO(2) nanostructure morphology is affected by pH and deposition temperatures, because these parameters affect the degree of protonation of P4VP segments and diffusion of the titanium(IV) bis(ammonium lactato)dihydroxide (TALH) precursor into the film. A pH range of 2.1-2.5 for silicon substrates and pH = 2.1 for ITO substrates gave the narrower TiO(2) nanostructures distributions, and deposition at 70 °C gave TiO(2) nanostructures with more regular arrangements and smoother surface than those deposited at room temperature. The use of 1,4-diiodobutane as a P4VP cross-linking compound is demonstrated to be a critical parameter for maintaining good cylindrical surface morphology for both the block copolymer template and the TiO(2) nanostructures.     

TiOCl2溶液合成异形TiO2纳米粉及形成机理研究

以TiOCl2溶液为前驱物,由室温至180℃直接反应均可获得TiO2纳米晶。当反应温度低于70℃,100℃和160℃时,沉淀粒子形貌分别为针形聚集体、球型和针形单晶。相应反应温度下所得沉淀的晶型分别为金红石型、混晶和金红石型。晶体的形貌和粒子的均一性强烈依赖于反应温度和成核与成长速率。详细讨论了TiOCl2溶液在各个温区的水解及TiO2粒子的形成机理。     

二氧化钛基固体超强酸的结构及其光催化氧化性能

采用溶胶－凝胶法制备了多孔性,大比表面积的ＳＯ４＾２－／ＴｉＯ２固体超强催化剂,运用ＸＲＤ,ＢＥＴ比表面积测定,ＸＰＳ和ＵＶ－Ｖｉｓ反射光谱等技术对该催化剂的结构,表面状态以及半导体特征进行了表征,并通过ＣＨ３Ｂｒ,Ｃ６Ｈ６和Ｃ２Ｈ４等典型有机物的气相光催化氧化反应。     

制备均一形貌的长二氧化钛纳米管

在温和的水热条件下,用碱溶液处理不同粒径的锐钛矿相和金红石相二氧化钛 纳米粉体,得到了不同形貌的二氧化钛纳米管,并用TEM,XRD,FT-Raman和BET等 对其进行了表征。金红石相的超细纳米晶有利于形成均一形貌的纳米管,用粒径仅 为7.2 nm的金红石相纳米粉体为前驱体得到了长度为500 nm的长二氧化钛纳米管。 用纳米晶反应活性对晶粒尺寸的依赖性及晶相稳定性解释了长纳米管的形成机理。