Uniform NH4TiOF3 mesocrystals prepared by an ambient temperature self-assembly process and their topotaxial conversion to anatase

For the first time, we describe a simple, room-temperature surfactant-mediated route to inorganic mesocrystals of NH(4)TiOF(3) and their remarkable topotaxial conversion by washing or annealing to TiO(2) as anatase mesocrystals.     

Nanoporous anatase TiO2 mesocrystals: additive-free synthesis, remarkable crystalline-phase stability, and improved lithium insertion behavior

Unique spindle-shaped nanoporous anatase TiO(2) mesocrystals with a single-crystal-like structure and tunable sizes were successfully fabricated on a large scale through mesoscale assembly in the tetrabutyl titanate-acetic acid system without any additives under solvothermal conditions. A complex mesoscale assembly process involving slow release of soluble species from metastable solid precursors for the continuous formation of nascent anatase nanocrystals, oriented aggregation of tiny anatase nanocrystals, and entrapment of in situ produced butyl acetate as a porogen was put forward for the formation of the anatase mesocrystals. It was revealed that the acetic acid molecules played multiple key roles during the nonhydrolytic processing of the [001]-oriented, single-crystal-like anatase mesocrystals. The obtained nanoporous anatase mesocrystals exhibited remarkable crystalline-phase stability (i.e., the pure phase of anatase can be retained after being annealed at 900 °C) and improved performance as anode materials for lithium ion batteries, which could be largely attributed to the intrinsic single-crystal-like nature as well as high porosity of the nanoporous mesocrystals.     

液相沉积法制备光催化活性TiO2薄膜和纳米粉体

采用液相沉积法，在35℃通过向六氟钛酸铵水溶液中添加硼酸和结晶诱导剂锐 铁矿型TiO2纳米晶，沉积出具有光催化活性的Ti02薄膜和纳米粉体．用XRD，AFM， 阶梯仪,UV-vis，BET法对Ti02薄膜和粉体的沉积条件、结构、厚度和性能进行了测 定和表征，并用亚甲兰的降解，评价了TiO2薄膜和纳米粉体的光催化活性．结果表 明，当反应物六氟钛酸铵与硼酸的摩尔比为1：2—1：4时，沉积的粉体和薄膜含有 锐钛矿相Ti02；经300℃热处理的Ti02薄膜和纳米粉体具有最高的光催化活性，它 的光催化活性是未经热处理前的5倍．本文还解释了经300℃热处理的薄膜和纳米粉 体具有最高光催化活性的原因．     

Photocatalytic water oxidation on F, N co-doped TiO2 with dominant exposed {001} facets under visible light

Visible-light-responsive anatase TiO(2) platelets with dominant {001} facets were prepared via a facile nitridation reaction from a TiOF(2) precursor. The in situ co-doping of N and F in the anatase TiO(2) nanoparticles leads to drastically enhanced absorption and excellent water oxidation performance in the visible light region.     

Unique Ordered TiO(2) Superstructures with Tunable Morphology and Crystalline Phase for Improved Lithium Storage Properties

Unique ordered TiO(2) superstructures with tunable morphology and crystalline phase were successfully prepared by the use of different counterions. Dumbbell-shaped rutile TiO(2) and nanorod-like rutile mesocrystals constructed from ultrathin nanowires, and quasi-octahedral anatase TiO(2) mesocrystals built from tiny nanoparticle subunits were achieved. Interestingly, the obtained anatase mesocrystals have a fine microporous structure and a large surface area. The influence of the counterions in the reaction system is discussed and possible mechanisms responsible for the formation of the unique ordered TiO(2) superstructures with different morphologies and crystalline phases are also proposed based on a series of experimental results. The obtained TiO(2) superstructures were used as anode materials in lithium ion batteries, and exhibited higher capacity and improved rate performance; this is attributed to the intrinsic characteristics of the mesoscopic TiO(2) superstructures, which have a single-crystal-like and porous nature.     

光催化活性TiO2薄膜的低温制备

在低温下,将基材浸渍在含配合物,F－离子捕获剂H3BO3,及加有结晶诱导剂锐钛矿TiO2纳米晶的过饱和水溶液中,在基材上沉积锐钛矿型TiO2薄膜.研究了水溶液的浓度、反应物和H3BO3的摩尔比、沉积时间、反应温度等对沉积TiO2薄膜的结构和性能的影响.并用UV Vis、XRD和SEM等对TiO2薄膜的透明性、厚度、物相和形貌等进行了表征.用亚甲蓝的光催化降解,评价了TiO2薄膜的光催化活性.     

The role of crystal phase in determining photocatalytic activity of nitrogen doped TiO2

Two series of nitrogen doped TiO(2) samples with different ratios of anatase to rutile phases were prepared by milling the mixture of P25 TiO(2) and C(6)H(12)N(4) in air and gaseous NH(3) atmosphere, respectively. Compared to air, NH(3) atmosphere plays an important role in delaying the crystallite transformation from anatase to rutile in the mechanochemical reaction of TiO(2) and C(6)H(12)N(4). In contrast to the previously reported results for pure TiO(2), it is found that nitrogen doped TiO(2) with higher content of rutile phase demonstrates higher photocatalytic activity in photodegrading pollutant Rhodamine B under both UV light and visible light irradiation (lambda>420 nm), and the amount of the surface-adsorbed water and hydroxyl groups on nitrogen doped TiO(2) have little correlations with their crystallite phases (anatase or rutile) and photocatalytic activity. The more abundant surface states characterized by photoluminescence spectroscopy together with the lowered valence band maximum of rutile TiO(2) by nitrogen doping are considered as the key factors for the higher activity of nitrogen doped TiO(2) with higher content of rutile phase.     

Solid state precursor strategy for synthesizing hollow TiO2 boxes with a high percentage of reactive {001} facets exposed

Three-dimensional, hollow, anatase TiO(2) boxes, each was enclosed by six single-crystalline TiO(2) plates exposed with highly reactive {001} facets, were facilely obtained by calcining a cubic TiOF(2) solid precursor at 500-600 °C. The formation of such particular nanostructures is attributed to the hard self-template restriction and the adsorption of F(-) ions from the TiOF(2).     

拓扑相变制备具有拓宽可见光响应范围的Ti3+自掺杂3D空盒状TiO2

TiO2广泛用作半导体光催化材料, 但由于自身对光利用率低(只吸收紫外光)、禁带宽度较大、光生载流子复合率极高, 限制了它在相关领域的应用. 为此, 设计了Ti3+离子自掺杂来克服TiO2半导体材料的上述缺点, 进而提高其光催化活性. 在不引入其他元素的情况下, 以TiOF2为原料, Zn粉为还原剂, 在水热条件下采用拓扑相变法原位制备了具有可见光响应的Ti3+自掺杂空盒状TiO2(记为Ti3+/TiO2)催化剂材料. 掺杂金属离子可以改变半导体TiO2的结晶度和产生晶格缺陷, 形成电子或空穴的捕获中心, 影响电子-空穴对的复合; 同时, 掺杂金属离子产生的晶格缺陷有利于Ti3+和氧空位的形成, 有利于提高TiO2的量子效率. Ti3+掺杂是一种既清洁又未引入其他金属离子的掺杂改性方法, 它能有效保持催化剂的结构和形貌不受其他金属离子的影响. 总之, 金属离子掺杂有效拓展了TiO2的光吸收范围, 并极大地提高了TiO2的光催化活性.本文研究了不同量的还原剂对催化剂空盒状TiO2结构形貌影响, 以及在可见光下光催化降解罗丹明B反应性能, 发现Ti3+/TiO2催化剂均拥有非常好的光催化活性, 其中R0.25催化剂在可见光下120 min, RhB降解率达到96%, 是TiO2的4倍多. 且可循环使用5次的光催化循环降解实验后, 表现出较高的稳定性. 催化剂经过Ti3+自掺杂后, 对催化剂自身的空盒状结构形貌并无很大的影响, 随着还原剂Zn粉的量增加, Ti4+还原形成Ti3+数量增加, 导致形成更多的氧空位. 皆为锐钛矿型TiO2,与未掺杂Ti3+的TiO2比较发现, 自掺杂Ti3+的TiO2的(105)XRD衍射峰越来越尖锐, (004)衍射峰越来越宽. 随着还原剂Zn粉质量的逐渐增加, 催化剂的光响应范围拓宽到可见光区, 且逐渐增强. 这说明Ti3+的掺杂不仅提高了TiO2在可见光的响应能力, 也提高了TiO2在紫外光范围的响应能力. 另外, 掺杂后的TiO2禁带宽度的减小, 使其价带上的电子更容易被可见光激发, 产生更多的电子-空穴对参与光催化反应, 从而提高TiO2的光催化效率.     

N掺杂纳米TiO2可见光催化氧化丙烯的动力学行为

通过在不同温度的氨气气氛中处理纳米管钛酸(NTA)制得具有可见光响应的氮掺杂纳米二氧化钛. X射线衍射(XRD)谱表征结果显示, 当温度高于400 ℃时, 样品由正交晶系向锐钛矿相转变, 700 ℃处理得到的样品除了锐钛矿相TiO2外还有TiN 新相存在; 紫外-可见扩散漫反射(DRS)结果表明, 氮掺杂纳米TiO2在整个可见光区都有明显的吸收. 不同波长可见光及不同气体流速的光催化氧化丙烯动力学研究表明, 活性最好的N掺杂纳米TiO2催化剂(600 ℃ NH3处理)对可见光的利用范围可扩展至500 nm, 低浓度丙烯光催化氧化反应为一级反应.     

From titanium oxydifluoride (TiOF2) to titania (TiO2): phase transition and non-metal doping with enhanced photocatalytic hydrogen (H2) evolution properties

Single-crystalline TiOF(2) crystals with cubical morphology were prepared via a facile solvothermal method and their transformation to anatase TiO(2) under different calcination conditions such as pure argon, moist argon and pure hydrogen sulfide (H(2)S) was explored by using XRD/Raman/UV-Vis/SEM/TEM/SAED. The non-metal sulfur doping was successfully fulfilled and the doped TiO(2) microcubes showed the best photocatalytic H(2) evolution property.     

Monodisperse mesocrystals of YF3 and Ce3+/Ln3+ (Ln=Tb, Eu) co-activated YF3: shape control synthesis, luminescent properties, and biocompatibility

A family of monodisperse YF(3), YF(3):Ce(3+) and YF(3):Ce(3+)/Ln(3+) (Ln=Tb, Eu) mesocrystals with a morphology of a hollow spindle can be synthesized by a solvothermal process using yttrium nitrate and NH(4) F as precursors. The effects of reaction time, fluorine source, solvents, and reaction temperature on the synthesis of these mesocrystals have been studied in detail. The results demonstrate that the formation of a hollow spindle-like YF(3) can be ascribed to a nonclassical crystallization process by means of a particle-based reaction route in ethanol. It has been shown that the fluorine sources selected have a remarkable effect on the morphologies and crystalline phases of the final products. Moreover, the luminescent properties of Ln(3+)-doped and Ce(3+)/Ln(3+) -co-doped spindle-like YF(3) mesocrystals were also investigated. It turns out that Ce(3+) is an efficient sensitizer for Ln(3+) in the spindle-like YF(3) mesocrystals. Remarkable fluorescence enhancement was observed in Ce(3+)/Ln(3+) -co-doped YF(3) mesocrystals. The mechanism of the energy transfer and electronic transition between Ce(3+) and Ln(3+) in the host material of YF(3) mesocrystals was also explored. The cytotoxicity study revealed that these YF(3) -based nanocrystals are biocompatible for applications, such as cellular imaging.     

具有高光催化活性的介孔单晶TiO2薄膜的制备

光催化技术在常温下能够直接利用太阳能来驱动反应, 已成为一种理想的环境污染治理和洁净能源生产技术. 但是比较多的限制条件阻碍了光催化发展和实际应用, 如何有效解决这些限制因素成为光催化技术走向工业化应用必须解决的问题. 目前光催化材料研究存在的问题主要包括: (1)研究工作主要集中的粉体催化剂存在分离困难、难以重复利用的缺点, 开发与基底结合牢固的薄膜材料是十分必要的; (2)光催化材料本身的光响应范围影响光催化材料的应用, 拓宽催化剂材料的光吸收范围是亟待解决的; (3)光生电子和空穴的复合问题是影响光催化剂催化活性的主要因素之一, 很多方法被用来阻止电子-空穴对的复合, 如: 金属和非金属的掺杂、贵金属修饰、异质结、新型催化剂结构的设计等, 如何设计促进催化剂光生电子和空穴的分离成为光催化技术应用的重要问题.介孔单晶TiO2通过自组装的方法被制备, 成为TiO2的一种新结构材料. 介孔单晶TiO2结合了介孔材料的大比表面积、单晶材料的电荷传输快等优点, 对于光催化性能有了很大的提高. 目前介孔单晶TiO2主要是以粉体的形式存在, 但是粉体TiO2的应用受到多方面的影响, 如: 难回收不易重复利用, 与电催化结合难, 不能借助电催化提高电荷分离效率等. TiO2薄膜能够解决粉体的不足, 近年来, TiO2光催化薄膜得到广泛的研究, TiO2薄膜的制备方法很多, 主要有液相制备方法、物理气相沉积法、化学气相沉积法、电化学方法、溅射法等. TiO2薄膜主要是以纳米颗粒的形式沉积在基底上, 并且多为多晶和无定形. 而对于介孔单晶TiO2薄膜的制备和研究还没有报道. 我们通过直接焙烧一步法制备了介孔单晶TiO2薄膜, 并对TiO2薄膜的生长情况、表面结构、TiO2晶相和晶体完整程度的变化对性能的影响进行了研究. 通过调变Ti与F的比例和煅烧温度, 研究不同的制备条件对其性能的影响, 从而制备高活性TiO2薄膜. 为了进一步提高介孔单晶TiO2薄膜的活性和拓展其吸收光谱范围, 使用高温热解自组装技术一步法制备了贵金属Au负载的介孔单价TiO2薄膜, Au纳米颗粒跟TiO2有较好的结合度. 在可见光照射下, Au/TiO2异质结构中Au表面由等离子体共振效应产生的活泼电子会注入TiO2导带, 使光生电子和空穴得到分离; 同时Au具有特殊的可见光等离子体共振效应能显著改善TiO2类宽带隙半导体的可见光响应性能.实验用还原Cr(Ⅵ)作为探针反应, 考察不同Au含量对光催化性能的影响.     

Preparation of hollow capsule-stabilized gold nanoparticles through the encapsulation of the dendrimer

Nanocrystalline TiO2 powders were rapidly prepared by hydrolysis of Ti(OC4H9)4 under ultrasound irradiation. The influences of acids (HCl, HNO3, and H2SO4) and their corresponding salts (NaCl, KNO3, and Na2SO4) on the crystalline phase and morphology of products were investigated, respectively. Compared with NaCl and KNO3 that show no evident influence on the crystalline phase, HCl and HNO3 have a decisive influence on the crystalline phase of the products. However, both H2SO4 and Na2SO4 are favorable for the formation of anatase. By adjusting the concentration of SO2-(4) in the reaction medium, the contents of anatase and rutile phases in the TiO2 powders can be successfully controlled. The morphology of TiO2 crystallites are shown to be strongly related to the type of acid used in the reaction medium.     

由钛酸盐纳米带水热制备锐钛矿型TiO2纳米带

研究了水热处理具有层状结构的钛酸钠纳米带或钛酸纳米带转化为锐钛矿型TiO₂的制备过程、难易程度和相转化机理. 实验结果表明, 当水热反应温度和时间分别在160 ℃ 和24 h以内, 钛酸钠纳米带很难完全转化为锐钛矿型TiO₂, 若升高反应温度并延长反应时间, 则可制得纯的锐钛矿型TiO₂, 但纳米带形貌被严重破坏; 当水热反应温度和时间分别为160 ℃ 和16 h时, 1次酸洗的钛酸纳米带能够完全转化为锐钛矿型TiO₂, 若钛酸纳米带经过3次强酸浸泡, 则在160 ℃下相转化时间就会缩短到12 h, 所有钛酸纳米带在转化为TiO₂后的形貌仍为纳米带, 但经3次酸浸后生成的TiO₂纳米带表面更光滑. 讨论了钛酸钠纳米带或钛酸纳米带转化为锐钛矿型TiO₂的相转化机理.     

Reduced graphene oxide conjugated Cu2O nanowire mesocrystals for high-performance NO2 gas sensor

Reduced graphene oxide (rGO)-conjugated Cu(2)O nanowire mesocrystals were formed by nonclassical crystallization in the presence of GO and o-anisidine under hydrothermal conditions. The resultant mesocrystals are comprised of highly anisotropic nanowires as building blocks and possess a distinct octahedral morphology with eight {111} equivalent crystal faces. The mechanisms underlying the sequential formation of the mesocrystals are as follows: first, GO-promoted agglomeration of amorphous spherical Cu(2)O nanoparticles at the initial stage, leading to the transition of growth mechanism from conventional ion-by-ion growth to particle-mediated crystallization; second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals through mesoscale transformation, where Ostwald ripening is responsible for the growth of the nanowire building blocks; third, large-scale self-organization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, resulting in an integrated hybrid architecture where porous three-dimensional (3D) framework structures interspersed among two-dimensional (2D) rGO sheets. Interestingly, "super-mesocrystals" formed by 3D oriented attachment of mesocrystals are also formed judging from the voided Sierpinski polyhedrons observed. Furthermore, the interior nanowire architecture of these mesocrystals can be kinetically controlled by careful variation of growth conditions. Owing to high specific surface area and improved conductivity, the rGO-Cu(2)O mesocrystals achieved a higher sensitivity toward NO(2) at room temperature, surpassing the performance of standalone systems of Cu(2)O nanowires networks and rGO sheets. The unique characteristics of rGO-Cu(2)O mesocrystal point to its promising applications in ultrasensitive environmental sensors.     

Synthesis of uniform anatase TiO2 nanoparticles by the gel-sol method 2. Adsorption of OH- Ions to Ti(OH)4 gel and TiO2 particles

The pH value in the gel-sol system for the preparation of uniform anatase TiO2 nanoparticles, as a decisive factor for controlling the size and shape of the final product, was found to be significantly changed during the formation process of the anatase TiO2 particles from a condensed Ti(OH)4 gel. The dramatic evolution of pH with the progress of the synthetic process has clearly been explained in terms of the adsorption and desorption of a hydroxide ion (OH-) ora proton (H+) on the solids transforming with time. The adsorption and desorption of OH- or H+ were enhanced by the presence of an inert electrolyte such as NaClO4, as explained by its shielding effect on the electrical interactions between the electrically charged precipitates and free OH- and H+ ions. The electrolyte also hampered the phase transformation of Ti(OH)4 precipitate to anatase TiO2. This effect of electrolytes was explained in terms of the inhibited nucleation of anatase TiO2 by enhanced adsorption of OH- ions toTiO2 embryos. The points of zero charge (PZC) of the amorphous Ti(OH)4 precipitate and the anatase TiO2 particles at 25 degrees C were obtained from the change in pH associated with the adsorption and desorption of OH- or H+, i.e., 4.6 for Ti(OH)4 precipitate and 6.0 for anatase TiO2 in the presence of 0.1 mol dm(-3) NaClO4. The PZCof the Ti(OH)4 precipitate measured at 25 degrees C after additional aging at 100 degrees C for 30 min was shifted to 4.1, owing to the promoted adsorption of OH-.     

UV Raman spectroscopic study on TiO2. I. Phase transformation at the surface and in the bulk

Phase transformation of TiO2 from anatase to rutile is studied by UV Raman spectroscopy excited by 325 and 244 nm lasers, visible Raman spectroscopy excited by 532 nm laser, X-ray diffraction (XRD), and transmission electron microscopy (TEM). UV Raman spectroscopy is found to be more sensitive to the surface region of TiO2 than visible Raman spectroscopy and XRD because TiO2 strongly absorbs UV light. The anatase phase is detected by UV Raman spectroscopy for the sample calcined at higher temperatures than when it is detected by visible Raman spectroscopy and XRD. The inconsistency in the results from the above three techniques suggests that the anatase phase of TiO2 at the surface region can remain at relatively higher calcination temperatures than that in the bulk during the phase transformation. The TEM results show that small particles agglomerate into big particles when the TiO2 sample is calcined at elevated temperatures and the agglomeration of the TiO2 particles is along with the phase transformation from anatase to rutile. It is suggested that the rutile phase starts to form at the interfaces between the anatase particles in the agglomerated TiO2 particles; namely, the anatase phase in the inner region of the agglomerated TiO2 particles turns out to change into the rutile phase more easily than that in the outer surface region of the agglomerated TiO2 particles. When the anatase particles of TiO2 are covered with highly dispersed La2O3, the phase transformation in both the bulk and surface regions is significantly retarded, owing to avoiding direct contact of the anatase particles and occupying the surface defect sites of the anatase particles by La2O3.     

Morphosynthesis of alanine mesocrystals by pH control

Crystallization of DL-alanine is studied as a single polymorph model case to analyze the different modes of crystallization of polar organic molecules in absence of any structure directing additives. Depending on supersaturation, which is controlled either by temperature or by pH, and in the absence of additives, crystallization by mesoscale assembly of nanoparticles is found over a wide range of conditions, leading to so-called mesocrystals. This supplements the classical molecule-based crystallization mechanism, which is identified at lower supersaturations and at pH values away from the isoelectric point (IEP). The resulting alanine crystals are characterized by SEM, XRD, and single-crystal analysis. Time-resolved conductivity measurements and dynamic light scattering of the reaction solutions reveal information about precursor structures and reaction kinetics. A formation mechanism is proposed for the alanine mesocrystals.     

蛋氨酸改性TiO2空心纳米盒高效可见光催化RhB分解和NO氧化

由高能面 TiO2纳米片 (TiO2-NSs) 组装成的 TiO2空心纳米盒 (TiO2-HNBs)显示出比单独 TiO2-NSs 更强的光催化性能, 但是 TiO2-HNBs 依然属于紫外光催化剂, 无法充分利用太阳能. 因此, 开发具有可见光响应的由高能面 TiO2-NSs 组装而成的 TiO2-HNBs 具有重要意义. 本文将立方体 TiOF2与含有 N 和 S 元素的生物分子蛋氨酸混合, 通过一步焙烧制备了具有可见光响应活性的 N 和 S 元素共掺杂的 TiO2-HNBs(掺杂催化剂标记为 TMx, 未掺杂催化剂标记为 Tx, x 代表焙烧温度).由立方体 TiOF2到锐钛矿相 TiO2空心纳米盒的转变是一个自模板转化过程. 氟离子的存在降低了 TiO2高能面(001)面的表面能, 从而使得高能面 TiO2纳米片的形成变得可能. 因此, 热处理立方体 TiOF2可得到由高能面 TiO2纳米片组装的 TiO2空心纳米盒.本文系统研究了焙烧温度 (300-500 ℃) 对所制 TiO2-HNBs 结构与光催化性能的影响. 结果发现, 在 350 ℃下焙烧, TiOF2完全转化成锐钛矿相 TiO2-HNBs. 但是焙烧蛋氨酸与 TiOF2的混合物, 需 400 ℃才能完全实现 TiOF2到锐钛矿相TiO2-HNBs 的转变. 这说明蛋氨酸的加入阻碍了 TiOF2向锐钛矿相 TiO2-HNBs 的转变. XPS 结果显示, 经过 400 ℃焙烧的蛋氨酸改性样品 (TM400), N 和 S 元素成功掺入了 TiO2-HNBs 晶格, 使其产生可见光催化活性.相对于 400 ℃焙烧 TiOF2所得样品 T400, 蛋氨酸改性的 TM400 催化剂可见光降解罗丹明 B 染料 (RhB) 和 NO 氧化的性能分别提升了 1.55 倍和 2.0 倍, 这与其更强的可见光吸收性能和光生载流子分离效率有关. 400 ℃焙烧的蛋氨酸改性的 TM400 可见光催化活性稳定, 连续 5 次可见光催化 RhB 降解后, 其活性没有明显改变, 显示了潜在的应用前景.