Study of the effect of rutile/anatase TiO2 nanoparticles synthesized by hydrothermal route in electrospun PVA/TiO2 nanocomposites

Mixed rutile–anatase TiO₂ nanoparticles were synthesized by hydrothermal treatment under acidic conditions and incorporated into poly(vinyl alcohol) (PVA). These nanocomposites were electrospun to produce nanofibers of PVA/TiO₂, which were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The photocatalytic degradation of Rhodamine B and degradation of the polymer by UV‐C lamps were also investigated. The results showed that TiO₂ nanoparticles did not change the morphology and thermal behavior of the nanofiber polymer, but were effective in modifying the UV absorption of PVA without reducing its stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced photocatalytic degradation of rutile/anatase TiO2 heterojunction nanoflowers

Rutile/anatase TiO₂ heterojunction nanoflowers were prepared via a facile one-step hydrothermal approach using titanium tetrachloride and urea as the raw materials, cetyl trimethyl ammonium bromide (CTAB) as the template. The prepared TiO₂ nanoflowers were characterized by XRD, SEM, TEM and BET analyses. The photocatalytic performance of the as-prepared TiO₂ samples for methyl blue degradation under simulated solar light was investigated. TiO₂ heterojunction nanoflowers with mixed rutile/anatase phase (prepared with 3 mmol CTAB) give the highest photocatalytic activity. In addition, TiO₂ nanoflowers show excellent stability after 9 cycles under the same conditions. These results suggested that the mixed phase anatase/rutile TiO₂ heterojunction nanoflowers have great potential for the future photodegradation of real dye waste water.     

Tunable TiO2 (anatase and rutile) materials manufactured by mechanical means

Anatase and rutile are two naturally found titanium dioxide phases with attractive dielectric, catalytic, and photo-catalytic characteristics. Anatase and rutile are photo-catalytically active in the UV region, since their band gaps are 3.2 eV and 3.75 eV, respectively. In this work is proposed a cost-effective, easy to launch methodology for modification of the TiO₂ bandgap. Such modifications will make the oxides photo-catalytically active in a wider optical range from the visible wavelengths to an extended UV spectrum. The proposed methodology is based on mechanical means such as mixing and milling. Various ratios of anatase:rutile were investigated and milled from 0 (mixing only) to 50 h using high energy mills. The results on mixing and milling show that it is possible to modify the bandgap of the TiO₂ from 2.53 eV to 4.04 eV. The characterization was conducted by means of X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, and optical spectroscopy.     

The critical size mechanism for the anatase to rutile transformation in TiO2 and doped-TiO2

A series of titania and doped titania materials have been prepared from sol–gel methods using a titanium isopropoxide precursor. Powder X-ray diffraction (PXRD) and secondary electron microscopy (SEM) have been used to follow the anatase to rutile transformation (ART) phase change in this system. PXRD was used to estimate the relative amounts of each phase and the average particle size at a series of temperatures. Importantly, very careful choice of reaction precursors were made so that a wide range of similar samples could be compared, thus removing effects due to preparation. It was found that doping with Si, Zr, Al and tertiary mixtures of these produced an elevated ART temperature whilst Co, Mn and V had the opposite effect. The most likely explanation for the elevation in the ART temperature is the presence of dopant strain fields, which limit mass transport in the system. Lowering of the ART temperature is probably related to creation defect sites, which provide low energy mass transport routes. It was also found that in the majority of samples, the mechanism for phase change was related to attaining a critical particle size. This was measured at around 450 Å independent of the dopant used. Results are discussed in terms of previous work.     

Characteristics and catalytic properties of Co/TiO2 for various rutile:anatase ratios

This present study revealed a dependence of rutile:anatase ratios in titania on the characteristics and catalytic properties of Co/TiO₂ catalysts during CO hydrogenation. In this study, Co/TiO₂ catalysts were prepared using various titania supports consisting of various rutile:anatase ratios of titania. In order to identify the characteristics, all catalyst materials were characterized using XRD, SEM/EDX, TPR, and hydrogen chemisorption. CO hydrogenation (H₂/CO = 10/1) was also performed to determine the overall activity and selectivity. It was found that both activity and selectivity were altered by changing the rutile:anatase ratios in the titania support.     

Boron-doped rutile TiO2/ anatase TiO2/ ZrTiO4 ternary heterojunction photocatalyst with optimized phase interface and band structure

To improve the photocatalytic performance of TiO₂-based heterostructures, Z-scheme/Ⅱ-type rutile TiO₂ (R)/anatase TiO₂ (A)/ZrTiO₄ ternary heterojunction photocatalyst was designed and prepared via a facile one-step calcining strategy. Phase interface and band structure of the materials were controlled and optimized by regulating R–TiO₂/A–TiO₂ mass ratio in the TiO₂ (A, R)/ZrTiO₄ structures using boron doping. The highest photocatalytic performance and excellent catalytic stability of Rhodamine B removal was observed from the heterojunction with a low R–TiO₂/A–TiO₂ mass ratio of 0.066, even after five testing cycles, accompanying with low photoluminescence intensity and electrochemical impedance, high photocurrent and charge carrier density (5.12 × 10²² cm⁻³), and a positive shift of valence band position (from +2.06 to + 2.16 eV). The increased photodegradation behaviour was due to the remarkably enhanced separation efficiency and improved redox ability of the photo-induced charge carriers as a result of the high content of oxygen vacancies and the formed anatase TiO₂/rutile TiO₂ Z-scheme heterojunction.     

Enhanced photocatalytic activity of electrospun TiO2/ZnO nanofibers with optimal anatase/rutile ratio

The photocatalytic characteristics of the TiO₂/ZnO nanofibers synthesized by electrospinning followed by calcinating at different temperatures to alter the anatase-to-rutile ratio are investigated. The results demonstrate that the photocatalytic activity of TiO₂/ZnO nanofibers is enhanced by optimizing the anatase/rutile ratio among the trade-off effects of the band-gap energy, the electron/hole recombination rate, and the surface area. When calcined at 650 °C, the TiO₂/ZnO nanofibers with optimal anatase/rutile ratio (48:52) balancing these trade-off effects have the highest photocatalytic efficiency both in the degradation of RhB in liquid and conversion of NO gas.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Kinetics of anatase transition to rutile TiO2 from titanium dioxide precursor powders synthesized by a sol-gel process

Kinetics of anatase transition to rutile TiO₂ from titanium dioxide precursor powders synthesized by a sol-gel process have been studied using differential thermal analysis (DTA), X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED) and high resolution TEM (HRTEM). The DTA result shows residual organic matter decomposed at 436 K. The transition temperature for amorphous precursor powders converted to anatase TiO₂ occurred at 739 K. Moreover, the full anatase transition to rutile TiO₂ occurred at 1001 K. The activation energy of anatase TiO₂ formation was 128.9 kJ/mol. On the other hand, the activation energy of anatase transition to rutile TiO₂ was 328.4 kJ/mol. Mesoporous structures can be observed in the TEM image.     

金红石型纳米二氧化钛的煅烧

纳米二氧化钛粉体的功能决定了产品的高附加值，而功能在很大程度上取决于产物的粒度和晶型。在金红石型纳米二氧化钛的生产过程中，煅烧方式是影响产品质量与产品应用的重要因素之一。比较了几种常用的干燥和煅烧方式，指出其存在的问题。提出了采用旋流动态煅烧炉和旋转闪蒸干燥器组合方式生产金红石型纳米二氧化钛的煅烧方案，给出了工艺流程、煅烧条件及要求、系统设备配套选型。     

Construction of quantum-scale catalytic regions on anatase TiO2 nanoparticles by loading TiO2 quantum dots for the photocatalytic degradation of VOCs

We constructed quantum-scale catalytic regions on the surfaces of TiO₂ nanoparticles by loading TiO₂ quantum dots (QDs) with a two-step method. The removal rate and mineralization efficiency of toluene were measured and then used in evaluating the oxidation performance of the prepared samples. A home-built atmospheric surface photovoltage spectrometer and X-ray photoelectron spectrometer were used in analyzing band alignment across the interface between TiO₂ QD and TiO₂ particle and the transfer of charge carriers at the surface. Results showed that an upward band bending formed from the TiO₂ particle to the TiO₂ QD and promoted the accumulation of holes at the QD side. Moreover, the QD and surrounding substrate TiO₂ formed a quantum-scale catalytic region, improving the reaction probability of electron-hole pairs and corresponding intermediates. The mineralization efficiency of toluene in QD-loaded TiO₂ reached 95.8%. The synthetic method is green and simple, showing potential in scale production and industrial application.     

Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO₂ nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO₂ thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.     

New kinetic models for the crystallization of anatase nanoparticles from amorphous titania (TiO2)

In this article, amorphous Titania (TiO₂) nanoparticles were crystallized both in a solution environment and by a dry heat treatment using new kinetic models with the capabilities of more accurately predicting the polymorphic transformation behavior of TiO₂. In these models, both the nucleation and growth processes were simultaneously taken into account. The results were indicative of the Surface Nucleation (SN) of anatase occurring in a hydrothermal treatment process through the phase transformation. Also, both the surface and interface nucleation processes were found to play significant roles in the phase transformation kinetics when dealing with dry heat treatments at low temperatures. The proposed models were advantageous to any other published models, in which the nucleation mechanisms had been incorporated with suitable growth expressions. In other words, no experimental data of a particle size were required to investigate the phase transformation kinetics of TiO₂ nanoparticles in the models presented in this article.     

Facile construction Z-scheme anatase/rutile TiO2/g-C3N4 hybrid for efficient photocatalytic H2 evolution under visible-light irradiation

Z-scheme anatase/rutile TiO₂/g-C₃N₄ hybrids (denoted as LTARCN-x, x represents calcination temperature) were designed and synthesized by growing TiO₂ nanorods on the surface of g-C₃N₄ utilizing impregnation-calcination method. Furthermore, through the etched effect of hydrochloric acid and calcination treatment, the as-prepared LTARCN-x possessed abundant pore structure and larger surface area, and the surface area of LTARCN-425 was 8.5 times than that of bulk g-C₃N₄. Meanwhile, the g-C₃N₄ would play a role of carrier to prevent from the aggregation of TiO₂ nanorods. In addition, under visible light irradiation, the Z-scheme heterostructure would be constructed between the rutile TiO₂ nanorod and g-C₃N₄ nanosheet, respectively. The optimized photocatalyst LTARCN-425 exhibited a preferable activity, the photocatalytic hydrogen production rate of LTARCN-425 was about 1031 μmol g^?1 h^?1, and it was about 6.3 and 13.6 times than that of g-C₃N₄ and TiO₂, respectively. Moreover, the photocatalytic mechanism of the hydrogen production was studied intensively via designing fluorescent probe, Pt and PbO₂ deposition experiment, and the characterizations of EPR, TEM, HRTEM and XPS.     

金红石相纳米二氧化钛分散浆料制备及其复合电镀应用

以四氯化钛为原料低温水解 ,在液相中一步简单地制备了金红石相TiO2 ,并且原位制备了一定浓度的纳米TiO2 分散浆料。X射线衍射测试表明此TiO2 呈纯的金红石结构 ,透射电子显微镜观察发现此浆料分散性好 ,可直接在化学复合电镀中应用。采用常规的电镀过程在金属表面形成了TiO2 -Ni复合电镀层 ,比一般的镀镍层均匀、细致。     

铈硅包覆金红石型钛白粉及光催化性研究

采用溶胶-凝胶法,制备了铈硅包覆金红石型钛白粉,通过正交实验考察了浆液浓度、分散剂用量和两种包膜剂含量对铈硅包覆金红石型钛白粉性能的影响。采用Nano-ZS型粒度仪、扫描电镜（SEM）、透射电镜（TEM）和能谱（EDS）等测试手段,对金红石型钛白粉的Zeta电位、表面形貌和元素进行了表征。结果表明：在水浴温度为80 ℃左右、转速为600 r/min、浆液质量浓度为400 g/L、分散剂质量分数为0.1%、二氧化铈质量分数为3%、二氧化硅质量分数为4%的条件下,金红石型钛白粉表面包覆了两层均匀而致密的二氧化硅和二氧化铈膜;罗丹明B光催化降解实验证实,铈硅包覆明显改善了金红石型钛白粉的光催化屏蔽性。     

Facile fabrication of TiO2-SiO2-C composite with anatase/rutile heterostructure via sol-gel process and its enhanced photocatalytic activity in the presence of H2O2

Constructing anatase/rutile heterostructure in TiO₂ based materials is a quite powerful approach to enhance their photocatalytic activities. Herein, by simply annealing the sol-gel derived TiO₂-SiO₂ composite in N₂ atmosphere at 850 °C, TiO₂-SiO₂-C composite (CTS-850) with anatase/rutile heterostructure has been successfully prepared, while the counterpart prepared in air contains only anatase phase. It was proven that the residual organic groups in the sol-gel process were converted into carbon species upon N₂ annealing, during which TiO₂ in the composite was partially reduced, not only leaving lots of oxygen vacancies on its surface but also promoting the phase transformation. By turning the annealing temperature and atmosphere, a series of control products were further synthesized. Among these samples, the CTS-850 showed the best photocatalytic performance toward Rhodamine B degradation in the presence of H₂O₂, which was mainly due to its lowest band gap and the enhanced sensitization of H₂O₂ by oxygen vacancies. Moreover, the photocatalytic activity of CTS-850 remained unchanged after five cycles and a proper mechanism was also proposed.     

暴露高能晶面锐钛矿型TiO2研究进展

在总结TiO2晶体的形貌结构理论预测研究的基础上,全面且深入地评述了不同形貌的暴露高能晶面锐钛矿相TiO2材料的合成方法及其调控机制。在合成出微米级单晶的基础上,暴露高能晶面的锐钛矿型TiO2纳米晶以及由基本纳米结构单元构成的三维纳米结构聚集体被陆续被制备出来。此外,本文还介绍了暴露高能晶面锐钛矿型TiO2材料的掺杂改性研究,阐述了新合成出的暴露高能晶面锐钛矿型TiO2材料在光催化降解污染物和分解水、太阳电池以及锂离子电池等领域的应用性能。最后,指出了暴露高能晶面TiO2在制备和应用研究上存在的不足和今后的发展方向。