Unique Ordered TiO2 Superstructures with Tunable Morphology and Crystalline Phase for Improved Lithium Storage Properties

Unique ordered TiO₂ superstructures with tunable morphology and crystalline phase were successfully prepared by the use of different counterions. Dumbbell‐shaped rutile TiO₂ and nanorod‐like rutile mesocrystals constructed from ultrathin nanowires, and quasi‐octahedral anatase TiO₂ 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 TiO₂ superstructures with different morphologies and crystalline phases are also proposed based on a series of experimental results. The obtained TiO₂ 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 TiO₂ superstructures, which have a single‐crystal‐like and porous nature.     

Oxygen-Deficient Dumbbell-Shaped Anatase TiO2−x Mesocrystals with Nearly 100 % Exposed {101} Facets: Synthesis,Growth Mechanism,and Photocatalytic Performance

The development of hierarchical TiO₂ superstructures with new morphologies and intriguing photoelectric properties for utilizing solar energy is known to be an effective approach to alleviate the serious problems of environmental pollution. Herein, unique oxygen-deficient dumbbell-shaped anatase TiO_2−x mesocrystals (DTMCs) enclosed by nearly 100 % {101} facets were readily synthesized by mesoscale transformation in TiCl₃/acetic acid (HAc) mixed solution, followed by calcination under vacuum. These mesocrystals exhibited much higher photoreactivity toward removing the model pollutants methyl orange and Cr^VI than truncated tetragonal bipyramidal anatase nanocrystals (TNCs), anatase mesocrystals built from truncated tetragonal bipyramidal anatase nanocrystals (TTMCs), and anatase mesocrystals constructed by anatase nanocrystals with nearly 100 % exposed {101} facets (TMCs), revealing that both the oxidation and reduction abilities of anatase TiO₂ were simultaneously enhanced upon fabricating an oxygen-deficient mesocrystalline architecture with about 100 % exposed {101} facets. Further characterization illustrated that such an enhancement of photoreactivity was mainly due to the strengthened light absorption, boosted charge carrier separation, and nearly 100 % exposed {101} facets of the oxygen-deficient dumbbell-shaped anatase mesocrystals. This work will be useful for guiding the synthesis of oxygen-deficient ordered superstructures of metal oxides with desired morphologies and exposed facets for promising applications in environmental remediation.     

Preparation of controllable crystalline titania and study on the photocatalytic properties

Nanocrystalline TiO(2) catalysts with different anatase/rutile ratios and high surface area (113-169 m(2)/g) have been prepared at low temperature by the microemulsion-mediated hydrothermal method. The samples were characterized by x-ray diffraction (XRD), Fourier transform (FT)-IR spectra, UV-vis diffuse reflectance spectra, and nitrogen adsorption-desorption methods. The contents of anatase and rutile phases in the TiO(2) powders have been successfully controlled by simply changing the proportion of Cl(-) and SO(4)(2-) in the aqueous phase of the microemulsion. A proposed mechanism involving bidentately chelated sulfate is discussed to explain the variation of the crystalline phase in the TiO(2) powder. The photodegradation of methyl orange (MO) in water has been investigated over titanium dioxide consisting of different anatase/rutile ratios. The catalyst containing 74.2% anatase showed the highest photocatalytic activity, which is due to a synergistic effect between anatase and rutile. The synergism was also found for the photodegradation of MO with physically mixed anatase and rutile as catalysts.     

水热法合成掺杂铁离子的小管径TiO_2纳米管

碳纳米管这种一维结构的新材料的发现为物理、化学、材料科学和纳米科学开辟了全新的研究领域。近年来,非碳无机类富勒烯(InorganicFullerene-like,简称IF)纳米管也受到人们的广泛关注。迄今为止报道的无机类富勒烯纳米管主要有:过渡金属硫化物(MS2,M=W,Mo,Nb)犤1～3犦、V2O5犤4犦、Al2O3犤5犦纳米管等。其中金属氧化物纳米管在催化、吸附、单电子晶体管等方面有着潜在的应用前景。TiO2纳米粉体和纳米膜材料在太阳能的存储与利用、光电转换、光致变色及光催化降解大气和水中的污染物等方面具有广泛的应用。为了提高其光催化活性和对…     

Effect of TiO2 crystalline phase composition on the physicochemical and catalytic properties of Pd/TiO(2) in selective acetylene hydrogenation

Pd/TiO(2) catalysts have been prepared using TiO(2) supports consisting of various rutile/anatase crystalline phase compositions. Increasing percentages of rutile phase in the TiO(2) resulted in a decrease in Brunauer-Emmett-Teller surface areas, fewer Ti(3+) sites, and lower Pd dispersion. While acetylene conversions were found to be merely dependent on Pd dispersion, ethylene selectivity appeared to be strongly affected by the presence of Ti(3+) in the TiO(2) samples. When TiO(2) samples with 0-44% rutile were used, high ethylene selectivities (58-93%) were obtained whereas ethylene losses occurred for those supported on TiO(2) with 85% or 100% rutile phase. X-ray photoelectron spectroscopy and electron spin resonance experiments revealed that a significant amount of Ti(3+) existed in the TiO(2) samples composed of 0-44% rutile. The presence of Ti(3+) in contact with Pd can probably lower the adsorption strength of ethylene resulting in an ethylene gain. Among the five catalysts used in this study, the results for Pd/TiO(2)-R44 suggest an optimum anatase/rutile composition of the TiO(2) used to obtain high selectivity of ethylene in selective acetylene hydrogenation.     

A facile synthesis of uniform NH4TiOF3 mesocrystals and their conversion to TiO2 mesocrystals

Uniform mesocrystals of TiO2 (anatase) have been prepared from mesocrystals of NH4TiOF3. NH4TiOF3 was synthesized from an aqueous solution containing (NH4)2TiF6 and H3BO3 in the presence of a nonionic surfactant Brij 56, Brij 58, or Brij 700, at low temperatures. The exterior shapes of NH4TiOF3 mesocrystals can be tuned by adjusting the reagent concentration, reaction time, reaction temperature, and rate of stirring. The formation of the NH4TiOF3 mesocrystals proceeds via a self-assembly process involving nonclassical crystal growth. By sintering in air at 450 degrees C, or washing with H3BO3 solution at ambient temperatures, the NH4TiOF3 mesocrystals can be converted to mesocrystals of TiO2 (anatase), and the original architecture is retained.     

Relationship Between Photocatalytic Activity and Structure of TiO2 Thin Film

TiO2 thin films with different crystalline structures were prepared by the CVD method. The relationship between photocatalytic activity of a TiO2 thin film and its crystalline type was investigated. These films were characterized by XRD and AFM. Their photocatalytic properties were tested by the degradation of NO2-. The results showed that the crystalline structures of TiO2 thin films are primary anatase and/or rutile when the preparation temperatures were less than 573 K and higher than 773 K respectively. When the preparation temperature was around 623 K, the structures of TiO2 thin films were mixed crystalline structure, which showed the highest catalytic activity. When the ratio of rutile to anatase in TiO2 thin films fell between 0.5 and 0.7, the highest catalytic activity for the degradation of NO2- was found.     

Influence of Sn4+ on the structural and electronic properties of Ti1-xSnxO2 nanoparticles used as photocatalysts

Ti(1-x)Sn(x)O(2) nanocrystalline materials employed for photocatalysis have been characterised by means of X-ray diffraction, Raman, X-ray absorption (XANES and EXAFS) and UV-Vis spectroscopy and high resolution transmission electron microscopy. Single-phase samples with anatase or rutile type structures and similar tin contents permitted a separate study of the effect of Sn(4+) ions on these crystalline forms, whereas materials composed of anatase and rutile mixtures were used to investigate the distribution of the dopant cations when both phases coexist. The results obtained from the single-phase doped TiO(2) samples indicate that the presence of tin causes a different effect when doping anatase or rutile in both their structural and electronic properties. While a random substitution of Sn(4+) for Ti(4+) seems plausible for the rutile phase, some kind of gradient in Sn(4+) concentration is possible in anatase. On the other hand, when anatase and rutile coexist, effects of doping are visible in both phases. Regarding chemical composition, a homogeneous distribution of tin was found in both calcined and hydrothermal multiphase samples. Photocatalytic experiments show that both tin-doping and coexistence of different phases have a beneficial effect on the activity of the catalysts.     

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.     

Simultaneous phase- and size-controlled synthesis of TiO(2) nanorods via non-hydrolytic sol-gel reaction of syringe pump delivered precursors

The simultaneous phase- and size-controlled synthesis of TiO(2) nanorods was achieved via the non-hydrolytic sol-gel reaction of continuously delivered two titanium precursors using two separate syringe pumps. As the injection rate was decreased, the length of the TiO(2) nanorods was increased and their crystalline phase was simultaneously transformed from anatase to rutile. When the reaction was performed by injecting titanium precursors contained in two separate syringes into a hot oleylamine surfactant solution with an injection rate of 30 mL/h, anatase TiO(2) nanorods with dimensions of 6 nm (thickness) x 50 nm (length) were produced. When the injection rate was decreased to 2.5 mL/h, star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 200 nm and a small fraction of rod-shaped anatase TiO(2) nanorods with dimensions of 9 nm x 100 nm were synthesized. Pure star-shaped rutile TiO(2) nanorods with dimensions of 25 nm x 450 nm were synthesized when the injection rate was further decreased to 1.25 mL/h. The simultaneous phase transformation and length elongation of the TiO(2) nanorods were achieved. Under optimized reaction conditions, as much as 3.5 g of TiO(2) nanorods were produced. The TiO(2) nanorods were used to produce dye-sensitized solar cells, and the photoconversion efficiency of the mixture composed of star-shaped rutile TiO(2) nanorods and a small fraction of anatase nanorods were comparable to that of Degussa P-25.     

Dispersion behaviors of molybdena on titania (rutile and/or anatase)

Raman and FT-IR spectra were employed to investigate the dispersion of molybdena on mixed TiO2 (rutile and anatase, signed as R and A) with different BET surface ratios of rutile/TiO2(R + A). The results showed that (1) molybdena would preferentially disperse on the rutile surface in mixed TiO2; (2) for MoO3/rutile with low molybdena loading (e.g., 0.20 mmol/100 m2 rutile), a dispersed molybdena species existed on the rutile surface in an isolated tetrahedral coordination environment, while for MoO3/rutile with high molybdena loading (e.g. 0.82 mmol/100 m2 rutile), a polymeric molybdena species could be detected on the rutile surface; (3) for the MoO3/anatase sample, a dispersed molybdena species existed on the anatase surface in a polymeric coordination environment; and (4) the formation of the Bronsted acid site on the surface of rutile and anatase should be related to the polymeric molybdena species. All these results have been discussed via the interaction between OH groups of molybdena and OH groups of rutile and anatase, and it seems reasonable to suggest that, for the lower molybdena loading, the different states of the dispersed molybdena species should result from the different dehydration orders of OH groups of the molybdena and surface OH groups of rutile and anatase.     

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.     

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。     

Versatile biomimetic dendrimer templates used in the formation of TiO2 and GeO2

Biomimetic synthesis is emerging as an advantageous alternative to the harsh synthetic conditions traditionally used in metal oxide syntheses techniques. Silaffins, proteins from the C. fusiformis diatom, form silica in an aqueous environment under benign conditions. Amine terminated PAMAM and PPI dendrimers are effective mimics of silaffins and other silica precipitating polyamines. We have expanded the scope of dendrimer mediated metal oxide formation to include titanium dioxide, a photocatalyst, and germanium dioxide, a blue photoluminescent material. The nanoparticles were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (IR), and X-ray diffraction patterns (XRD). A variable temperature XRD analysis of TiO(2) nanoparticles was conducted to study the transition from anatase to rutile. TiO(2) nanoparticles synthesized in phosphate buffer showed a 200 degrees C decrease in the anatase to rutile transition temperature relative to TiO(2) templated in water. XRD analysis of GeO(2) nanoparticles in either water or phosphate buffer reveal crystalline alpha-phase germanium oxide. To our knowledge, this is the first report of the synthesis of crystalline GeO(2) under ambient conditions.     

二氧化钛系列光催化剂的拉曼光谱

采用溶胶-凝胶法制备了TiO₂粉体和薄膜光催化剂.使用FT-Raman光谱和激光共聚焦拉曼光谱研究了粉体和薄膜的拉曼光谱,探讨了热处理条件、Fe³⁺掺杂和以硅胶为载体的薄膜化所引起的TiO₂结构变化.结果表明,TiO₂在350℃存在由无定形向锐钛矿相的转变,600℃下存在锐钛矿相向金红石相的转变,750℃下完全转变为金红石相;掺杂会引起TiO₂的晶格畸变,导致拉曼谱峰宽化;以硅胶为载体的TiO₂负载薄膜的部分拉曼谱峰与粉体相比,有一定的位移和宽化.     

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.     

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。     

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...     

Y掺杂纳米TiO2的合成及晶型转变过程

溶胶-凝胶;锐钛型;金红石型;Y掺杂纳米TiO2的合成及晶型转变过程     

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.