Influence of the oxygen concentration on the formation of crystalline phases of TiO<Subscript>2</Subscript> during the low-pressure arc-discharge plasma synthesis

The synthesis of titanium dioxide (TiO₂) nanoparticles with different percentage of anatase and rutile phases is investigated. The synthesis is performed by controlling the oxygen percentage in the gas mixture in the plasmachemical evaporation–condensation process employing a low-pressure arc discharge. In all our experiments, the pressure in the plasmachemical reactor and the average size of particles remain constant and are 60 Pa and 6 nm, respectively. The crystal structure of synthesized TiO₂ is studied using X-ray diffraction; the morphology of the particles is analyzed employing transmission electron microscopy. Using X-ray phase analysis, it is established that the concentration of the TiO₂ anatase phase decreases upon a decrease in the oxygen concentration in the gas mixture. It is shown that the TiO₂ anatase phase is more efficient for photocatalytic decomposition of methylene blue than the rutile phase.     

Heterojunctions of TiO2 nanoparticle film and c-Si with different Fermi level positions

The photovoltaic properties of heterojunctions of titanium dioxide (TiO₂) nanoparticle films with single crystal silicon (c-Si) substrates with different Fermi level (E _f) positions were studied. The TiO₂ nanoparticles of rutile and anatase structures were studied without any sintering process. To clarify the photovoltaic properties, the characteristics of the heterojunction solar cells of TiO₂ nanoparticle films with p-Si and n-Si substrates were investigated, where several Si substrates with different resistivities were used. The I–V characteristics of p-Si/TiO₂ heterojunction showed the rectifying behavior and photovoltaic effect. The n-Si/TiO₂ heterojunction also showed good rectifying characteristics; however, the conversion efficiency was extremely lower than that of p-Si/TiO₂ heterojunction. The conversion efficiencies of various Si/TiO₂ (rutile) heterojunction solar cells against the Fermi level E _f of c-Si showed the maximum in the p-doped region. The photovoltaic properties of the Si/TiO₂ heterojunction also depended on the crystal structure of TiO₂, and the conversion efficiency of anatase is higher than that of rutile, which was attributed to the higher carrier mobility of anatase.     

Investigation on SERS of different phase structure TiO2 nanoparticles

In this paper, anatase and rutile TiO₂ nanoparticles as well as their mixed crystal phase structure TiO₂ nanoparticles were synthesized by a sol‐hydrothermal method, and were served as active substrates for surface‐enhanced Raman scattering (SERS) study. The results show that the 4‐mercaptobenzoic acid probe molecules exhibit different degree SERS enhancements on the surface of different phase structure TiO₂ nanoparticles. The mixed crystal structure TiO₂ with an appropriate proportion of anatase and rutile phase is favourable to SERS enhancement of adsorbed molecules. These are mainly attributed to the contributions of the TiO₂‐to‐molecule charge transfer mechanism and the mixed crystal effect. Copyright © 2015 John Wiley & Sons, Ltd.     

The preparation and characterization of nanoparticle TiO2/Ti films and their photocatalytic activity

Nanoparticle TiO₂/Ti films were prepared by a sol–gel process using Ti(OBu)₄ as raw material, the as-prepared film samples were also characterized by TG-DTA, XRD, TEM, SEM, XPS, DRS, PL, SPS and EFISPS testing techniques. TiO₂ nanoparticles experienced two processes of phase transition, i.e. amorphous to anatase and anatase to rutile at the calcining temperature range from 450 to 700 °C. TiO₂ nanoparticles calcined at 600 °C had similar composition, structure, morphology and particle size with the internationally commercial P-25 TiO₂ particles. Thus, the conclusion that 600 °C might be the most appropriate calcining temperature during the preparation process of nanoparticle TiO₂/Ti film photocatalysts could be made by considering the main factors such as the properties of TiO₂ nanoparticles, the adhesion of nanoparticle TiO₂ film to Ti substrate, the effects of calcining temperature on Ti substrate and the surface characteristics and morphology of nanoparticle TiO₂/Ti film for the practice view. The Ti element mainly existed on the nanoparticle TiO₂/Ti(3) film calcined at 600 °C as the chemical state of Ti⁴⁺, while O element mainly existed as three kinds of chemical states, i.e. crystal lattice oxygen, hydroxyl oxygen and adsorbed oxygen with increasing band energy. Its photoluminescence (PL) spectra with a peak at about 380 nm could be observed using 260 nm excitation, possibly resulting from the electron transition from the bottom of conduction band to the top of valence band. The PL peak position was nearly the same as the onset of its diffuse reflection spectra (DRS) and surface photovoltage spectroscopy (SPS), demonstrating that the effects of the quantum size on optical property were greater than that of the Coulomb and surface polarization. The PL spectra with two peaks related to the anatase and rutile, respectively, could be observed using the excited wavelength of 310 nm. Weak PL spectra could be observed using the excited wavelength of 450 nm, resulting from surface states. In addition, during the experimental process of the photocatalytic degradation phenol, the photocatalytic activity of nanoparticle TiO₂/Ti film with three layers calcined at 600 °C was the highest.     

Effect of annealing on TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by simple chemical precipitation method and annealed at different temperatures. The as-prepared TiO₂ are amorphous, and they transform into anatase phase on annealing at 450 °C, and rutile phase on annealing at 900 °C. The X-ray diffraction results showed that TiO₂ nanoparticles with grain size in the range of 21–24 nm for anatase phase and 69–74 nm for rutile phase have been obtained. FESEM images show the formation of TiO₂ nanoparticles with small size in structure. The FTIR and Raman spectra exhibited peaks corresponding to the anatase and rutile structure phases of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increase of annealing temperature.     

Effect of ambient pressure on the crystalline phase of nano TiO2 particles synthesized by a dc thermal plasma reactor

The synthesis of nanoparticles of titanium dioxide (TiO₂) with varying percentages of anatase and rutile phases is reported. This was achieved by controlling the operating pressure in a transferred-arc, direct current thermal plasma reactor in which titanium vapors are evaporated, and then exposed to ambient oxygen. The average particle size remained around 15 nm in each case. The crystalline structure of the as-synthesized nanoparticles of TiO₂ was studied with X-ray diffraction analysis; whereas the particle morphology was investigated with the help of transmission electron microscopy. The precursor species responsible for the growth of these nanoparticles was studied with the help of optical emission spectroscopy. As inferred from the X-ray diffraction analysis, the relative abundance of anatase TiO₂ was found to be dominant when synthesized at 760 Torr, and the same showed a decreasing trend with decreasing chamber pressure. The study also reveals that anatase TiO₂ is a more effective photocatalytic agent in degrading methylene blue by comparison to its rutile phase.     

热处理对爆轰合成的纳米TiO_2混晶的结构相变的影响

采用爆轰法制备了纳米TiO2混晶体,初步研究了不同煅烧温度(600℃和720℃)和不同煅烧时间(1 h,2 h,3.5 h和5 h)对其微结构和结构相变行为的影响,并应用热动力学理论讨论了从锐钛矿相到金红石相的结构相变过程和相变机理.研究表明:随着煅烧温度的升高和煅烧时间的增加,纳米TiO2的粒径逐渐增大,混晶中金红石相的含量逐渐提高.与常规方法制备的纳米TiO2不同的是,在相同煅烧温度和煅烧时间下金红石相的平均生长速率明显低于锐钛矿相.锐钛矿相完全相变为金红石的温度也明显低于常规方法报道的相变温度.该研究会对控制纳米TiO2晶体尺寸和批量合成提供一定的理论和实验指导.     

Estimation of contact area of nanoparticles in chains using continuum elastic contact mechanics

In this research, we have studied the doping behaviors of eight transition metal ion dopants on the crystal phase, particle sizes, XRD patterns, adsorption spectra, anatase fraction, and photoreactivity of TiO₂ nanoparticles. The pristine and ion-doped TiO₂ nanoparticles of 15.91-25.47 nm were prepared using sol–gel method. Test metal ion concentrations ranged from 0.00002 to 0.2 at.%. The absorption spectra of the TiO₂ nanoparticles were characterized using UV-Visible spectrometer. The wavelength of the absorption edge of TiO₂ was estimated using the spectra derivative-tangent method. The photoreactivities of pristine and ion-doped TiO₂ nanoparticles under UV irradiation were quantified by the decoloring rate of methyl orange. XRD patterns were recorded using a Rigaku D/MAX-2500 V diffractometer with Cu Kα radiation (50 kV and 250 mA), and particle size and anatase fraction were calculated. Results reveal that different ion doping exhibited complex effects on the studied characteristics of TiO₂ nanoparticles. In general, red shift occurred to ion-doped TiO₂ nanoparticles, but still with higher TiO₂ photoreactivities when doped with Fe³⁺ and Ni²⁺ ions. Among the ions investigated, Ni-doped TiO₂ nanoparticles have shown highest photoreactivity at the concentration of 0.002 at.%, about 1.9 times that of the pristine TiO₂. Ion doping was shown to reduce the diameter and influence the fraction of anatase. Data also indicated that the combination of anatase diameter and ion radius might play an important role in the photoreactivity of TiO₂ nanoparticles. This investigation contributes to the understanding of complex ion doping effects on TiO₂ nanoparticles, and provides references for enhancing their environmental application.     

Computational study on the structural and surface properties of amorphous hydroxylated TiO<Subscript>2</Subscript> spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO₂) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO₂ in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO₂ surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 ^o . The bulk system was developed using periodic boundary conditions. The TiO₂ nanoparticles were extracted by applying a spherical cut section in the bulk TiO₂ melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO₂ nanoparticles and bulk amorphous TiO₂, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO₂ nanoparticles are strongly size-dependent and different from those of the bulk TiO₂. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO₂ nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO₂ nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO₂ spherical nanoparticles is estimated to be around 8.1/nm ², which lies in the range of 8–16/nm ², found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.     

Size-controllable synthesis of functional heterostructured TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> core–shell nanoparticles

Mono and bicomponent TiO₂ and WO₃ nanoparticles were synthesized inside Vycor^® glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO₂ as anatase phase, while WO₃ is a mixture of the γ-WO₃ (monoclinic) and δ-WO₃ (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO₂ nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO₃ nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO₂ and WO₃ monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core–shell nanoparticles with tunable core sizes and shell thicknesses.     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO₂结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO₂生长活化能在250℃以下和以上分别为(15.8±4.5)kJ/mol和(80.2±1.0)kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4)kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO₂生长速 关键词： 2')" href="#">纳米TiO₂ 锐钛矿 生长动力学 溶胶-凝胶法     

TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC

利用自制TiO₂纳米粒子研究敏化染敏太阳能电池. 使用自制的旋转涂布加热平台装置将产出的TiO₂粒子均匀的涂布在ITO导电玻璃上形成薄膜,浸泡于N-719 染料中12小时以上作为DSSCs的光电极 元件,最后完成染料敏化太阳能电池的系统组装并进行光电转换效率测量. 实验结果表明,放电过程产出的TiO₂纳米粒子具有锐钛矿晶相,粒径尺寸可控制在20～70 nm,粒子表面电位约为-30 mV,是稳定的纳米悬浮夜. 添加0.5 mL 的Triton X-100在导电玻璃表面上,利用的旋转涂布加热到22 oC可以制得厚度均匀缜密的薄膜结构,不但粒子不受到热处理效应与介面活性剂的影响而发生晶相改变,并且薄膜也有良好的染料吸附效果. 较厚二氧化钛薄膜的光电极会提升敏化染敏太阳能电池的效率. 实验结果得知,以15 μm的二氧化钛薄膜组装DSSCs测得最高效率2.15%,但是当薄膜厚度超过15 μm 则会导致开路电压与充填因子逐渐下降,光电转换效率变差.     

Effects of the physicochemical properties of titanium dioxide nanoparticles, commonly used as sun protection agents, on microvascular endothelial cells

Until now, the potential effects of titanium dioxide (TiO₂) nanoparticles on endothelial cells are not well understood, despite their already wide usage. Therefore, the present work characterizes six TiO₂ nanoparticle samples in the size range of 19 × 17 to 87 × 13 nm, which are commonly present in sun protection agents with respect to their physicochemical properties (size, shape, ζ-potential, agglomeration, sedimentation, surface coating, and surface area), their interactions with serum proteins and biological impact on human microvascular endothelial cells (relative cellular dehydrogenase activity, adenosine triphosphate content, and monocyte chemoattractant protein-1 release). We observed no association of nanoparticle morphology with the agglomeration and sedimentation behavior and no variations of the ζ-potential (?14 to ?19 mV) in dependence on the surface coating. In general, the impact on endothelial cells was low and only detectable at concentrations of 100 μg/ml. Particles containing a rutile core and having rod-like shape had a stronger effect on cell metabolism than those with anatase core and elliptical shape (relative cellular dehydrogenase activity after 72 h: 60 vs. 90 %). Besides the morphology, the nanoparticle shell constitution was found to influence the metabolic activity of the cells. Upon cellular uptake, the nanoparticles were localized perinuclearly. Considering that in the in vivo situation endothelial cells would come in contact with considerably lower nanoparticle amounts than the lowest-observable adverse effects level (100 μg/ml), TiO₂ nanoparticles can be considered as rather harmless to humans under the investigated conditions.     

Effect of Particle Size and Phase Composition of Titanium Dioxide Nanoparticles on the Photocatalytic Properties

Titanium dioxide (TiO₂) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl₄) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO₂ nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO₂ nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO₂ nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.     

Toxicological consequences of TiO<Subscript>2</Subscript>, SiC nanoparticles and multi-walled carbon nanotubes exposure in several mammalian cell types: an in vitro study

The development of nanotechnologies may lead to dissemination of potentially toxic nanoparticles in the environment. Toxicology of these nano-sized particles is thus attracting attention of public and governments worldwide. Our research is focused on the in vitro response of eukaryotic cells to nanoparticles exposure. For this purpose, we used cellular models of primary target organs (lung: A549 alveolar epithelial cells), or secondary target organs (liver: WIF-B9, Can-10 and kidneys: NRK-52E, LLC-PK1 proximal cells), i.e., organs exposed if nanoparticles are translocated through epithelial barriers. These cells were exposed to TiO₂, SiC nanoparticles or multi-walled carbon nanotubes (MWCNT). The influence of nanoparticles physico-chemical characteristics on various toxicological endpoints (cytotoxicity, reactive oxygen species generation, genotoxicity) was specified. Our data demonstrate that nanoparticles toxicity depend on their size, morphology, and chemical composition, the finest, spherical shaped, and anatase TiO₂ nanoparticles being the more cytotoxic to NRK-52E cells, while SiC nanoparticles exert almost no cytotoxicity. MWCNT cytotoxicity neither depended on their length, nor on the presence of metal impurities. Nanoparticles cytotoxicity also depended on the exposed cell line. All the tested nanoparticles were uptaken by cells and caused intracellular reactive oxygen species generation. Relative to genotoxic effects, DNA strand breaks were detected in NRK-52E cells via the alkaline comet assay after exposure of cells to TiO₂ nanoparticles and to a lesser extent after exposure to MWCNT, but no double strand breaks were detected. The originality of this study lies on the panel of nanomaterials which were tested on a variety of cell lines. All these data may lead to a better understanding of nanomaterial toxicity and hazards for health.     

Effect of Nb doping on morphology,crystal structure,optical band gap energy of TiO2 thin films

Nb–TiO₂ nanofibers and thin films were prepared using a sol–gel derived electrospinning and spin coating, respectively, by varying the Nb/Ti molar ratios from 0 to 0.59 to investigate the effect of Nb doping on morphology, crystal structure, and optical band gap energy of Nb–TiO₂. XRD results indicated that Nb–TiO₂ is composed of anatase and rutile phases as a function of Nb/Ti molar ratio. As the Nb/Ti molar ratio rose, the anatase to rutile phase transformation and the reduction in crystallite size occurred. The band gap energy of Nb–TiO₂ was changed from 3.25 eV to 2.87 eV when the anatase phase was transformed to rutile phase with increasing the Nb doping. Experimental results indicated that the Nb doping was mainly attributed to the morphology, the crystal structure, the optical band gap energy of Nb–TiO₂, and the photocatalytic degradation of methylene blue.     

Optical properties of anatase and rutile titanium dioxide: Ab initio calculations for pure and anion-doped material

The optical properties of rutile and anatase titanium dioxide (TiO₂) are calculated from the imaginary part of the dielectric function using pseudopotential density functional method within its generalized gradient approximation (GGA) and a scissors approximation. The fundamental absorption edges calculated for the unit cell of both rutile and anatase are consistent with experimentally reported results of single crystal rutile and anatase TiO₂ and with previous theoretical calculations. A significant optical anisotropy is observed in the anatase structure which holds promise for investigating the band gap modification with better visible-light response and provides a reliable foundation for addressing the effect of impurities on the fundamental absorption edge/band gap of anatase TiO₂. Further calculations on the electronic structure and the optical properties of C-, N-, and S-doped anatase TiO₂ are performed. The results are analyzed and discussed in terms of optical anisotropy and scissors approximations.     

Nanotitania-coated multi-walled carbon nanotube composite by facile colloidal processing route for photocatalytic applications

Multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanocomposites (MWCNTs/TiO₂) were fabricated by a simple novel colloidal processing route and tested as a photocatalyst for degradation of methylene blue under UV irradiation. The novel idea behind this work is to make MWCNTs and TiO₂ nanoparticle suspensions separately highly oppositely charged and utilize the electrostatic force of attraction between two entities to deposit nanotitania onto MWCNTs surface. Particle charge detector, scanning electron microscopy, transmission electron microscope, energy dispersive X-rays, X-rays diffraction (XRD), and Raman spectroscopy were used to characterize the composite. XRD and Raman spectroscopic analysis showed the crystalline structure of deposited TiO₂ over MWCNTs surface structure as anatase phase. It was found that MWCNTs/TiO₂ composite structure have much higher photocatalytic activity compared to TiO₂ nanoparticles. The composite material developed may find potential applications in the degradation of organic pollutants in aqueous medium under UV irradiation.     

Integration of individual TiO2 nanotube on the chip: Nanodevice for hydrogen sensing

Titania (TiO₂) exists in several phases possessing different physical properties. In view of this fact, we report on three types of hydrogen sensors based on individual TiO₂ nanotubes (NTs) with three different structures consisting of amorphous, anatase or anatase/rutile mixed phases. Different phases of the NTs were produced by controlling the temperature of post‐anodization thermal treatment. Integration of individual TiO₂ nanotubes on the chip was performed by employing metal deposition function in the focused ion beam (FIB/SEM) instrument. Gas response was studied for devices made from an as‐grown individual nanotube with an amorphous structure, as well as from thermally annealed individual nanotubes exhibiting anatase crystalline phase or anatase/rutile heterogeneous structure. Based on electrical measurements using two Pt complex contacts deposited on a single TiO₂ nanotube, we show that an individual NT with an anatase/rutile crystal structure annealed at 650 °C has a higher gas response to hydrogen at room temperature than samples annealed at 450 °C and as‐grown. The obtained results demonstrate that the structural properties of the TiO₂ NTs make them a viable new gas sensing nanomaterial at room temperature. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

锐钛矿相和金红石相TiO2:Nb的光电性能研究

采用基于密度泛函理论的第一性原理计算了锐钛矿相和金红石相TiO₂:Nb的晶体结构、电子结构和光学性质. 结果表明, 在相等的摩尔掺杂浓度下(6.25%), 锐钛矿相TiO₂:Nb的导带底电子有效质量小于金红石相TiO₂:Nb, 且前者室温载流子浓度是后者的两倍左右, 即具有更大的施主杂质电离率, 从而解释了锐钛矿相TiO₂:Nb比金红石相TiO₂:Nb具有更优异电学性能的实验现象. 光学计算也表明锐钛矿相在可见光区有更大的透过率, 从而在理论上解释了锐钛矿相TiO₂:Nb比金红石相TiO₂:Nb更适于做透明导电材料的原因. 计算结果与实验数据能较好符合. 关键词： 2:Nb')" href="#">TiO₂:Nb 第一性原理 电子结构 光学性能