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1.
The nanoparticle microreactor (NPMR) is a new concept that we have introduced to describe a very small-scale system capable of converting an aerosol precursor to solid particles. The liquid precursor of about 1 µl is injected by a syringe through a septum into a tubular evaporator of 1.0 cm3 in volume with stopcocks at both ends. The evaporator has been preheated by a heating tape to a temperature sufficiently high for vaporization to occur in half a minute. By opening the stopcocks, the vaporized precursor is transported by a carrier gas stream into a quartz tube which is mounted along the axis of a tubular furnace. The nanoparticle aggregates produced in the reactor are sampled by deposition on an electron micrograph grid at the reactor exit. The NPMR was applied first to the synthesis of TiO2 particles by thermal decomposition of titanium tetraisopropoxide (TTIP) in a nitrogen carrier gas, with TTIP concentrations varying from 1.0 to 7.0 mol% or 2.35×10–6 to 1.65×10–5 in TiO2 volume loading, and decomposition temperatures from 300°C to 1000°C. Studies were made with a 2 mm reaction tube and a 4 mm tube with sheath gas. With the 2 mm tube, a considerable fraction of the TTIP precursor was consumed at the wall by surface reaction, resulting in very small particles. With the 4 mm tube, the primary particle size was comparable to that reported in the literature for steady flow experiments using a 22.2 mm tube. Primary particle sizes ranged from 200 to 400 nm. Depending on TTIP concentration and reactor temperature, the particles exhibited a bimodal size distribution, probably due to a two-stage nucleation. A fourfold increase in the gas flow rate had little effect on particle size, indicating that particle growth ended early, within one-fourth the tube length. Residence time in the reactor was between 0.35 and 1.4 s, and total run time about 1 min. The NPMR has potential for rapid assembly of large databases and is adaptable to combinatorial discovery of nanoparticles with novel properties. Design requirements for an ideal aerosol microreactor are discussed briefly. 相似文献
2.
Ju-Won Jeon 《Journal of Physics and Chemistry of Solids》2010,71(4):608-169
N-doped titania was prepared continuously by one-step synthetic method under supercritical and subcritical water conditions using titanium(IV)tetraisopropoxide (TTIP) and nitric acid as a titania precursor and nitrogen source, respectively. The synthesized N-doped titania particles were characterized by XRD, N2-adsorption, TEM, XPS, UV-vis diffuse reflectance spectroscopy. N-doped titania was successfully synthesized and its crystalline structure was homogenous anatase phase with high surface area. The absorption edge of synthesized N-doped titania shifted into the visible light region compared with commercial titania P25. All synthesized N-doped titania have higher photocatalytic activity than P25 under visible light irradiation. The photocatalytic activity of N-doped titania synthesized under supercritical water condition was the highest for the degradation of methyl orange under visible light due to the larger crystallite size compared with the N-doped titania synthesized under subcritical water condition. 相似文献
3.
Titanium dioxide (titania) particles were prepared by a water-in-oil emulsion system, and studied for the photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane or octane, and surfactant, such as polyoxyethylene (10) octylphenyl ether (TX-100), polyoxyethylene lauryl ether, or bis (2-ethylhexyl) sodium sulfosuccinate. Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then titania particles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. It was found that ME could be classified to the reversed micelle (RM) region and the swelling reversed micelle (SM) region according to the water content. The water droplets in RM were almost monodispersed, where the water content was small. On the other hand, the water droplets in SM had a size distribution, although most of the water molecules associated with surfactant molecules. The size of the particles prepared in the RM region was smaller than the ME size. In contrast, the size of the particles formed in the SM region was larger than the ME size, and coagulation of the particles was observed within a few hours. The smallest diameter of the particles was 2 nm in the system of cyclohexane with TX-100 surfactant when the molar ratio of water to surfactant was 2. Titania particles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 500 K, which is lower than the ordinal phase transition temperature. These anatase phase titania particles only showed a significant photodecomposition of methylene blue by illumination with a Xenon lamp. 相似文献
4.
Cheng-Yang WuBo-Sheng Chiang Springfield ChangDay-Shan Liu 《Applied Surface Science》2011,257(6):1893-1897
Hydro-oxygenated amorphous titanium oxide (a-TiOx:OH) films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using precursors of titanium tetraisopropoxide (TTIP) and oxygen. The influences of chemical states and crystal quality on the photocatalytic activity were systematically investigated in the as-deposited and post-annealed films. The degree of the photocatalytic activity was deeply correlated with the porosity related to the hydroxyl (OH) groups in the as-deposited amorphous film. The crystallized anatase structures was observed from the 200 °C-deposited a-TiOx:OH film after a post-annealing treatment at 400 °C. The photocatalytic activity related to the film with anatase structure was markedly superior to that of an amorphous film with porous structures. The larger the crystal size of the anatase structure, the higher the photocatalytic activity obtained. At elevated annealed temperatures, the inferior anatase structure due to the crystalline transformation led to a low photocatalytic activity. It was concluded that the photocatalytic activity of an amorphous TiOx film prepared using PECVD was determined by the porosity originating from the functional OH groups in the film, whereas the crystalline quality of anatase phase in the annealed poly-TiOx film was crucial to the photocatalytic activity. 相似文献
5.
The formation of submicron TiO2 smoke (a gas‐phase suspension) from titanium tetrachloride in a low‐pressure hydrolysis reaction in a simple reactor configuration has been studied. Particle size distribution, particle morphology and degree of crystallinity have been characterized as a function of reaction conditions. Highly crystalline anatase TiO2 particles with narrow size distribution and smaller particle size were formed at high reactor temperature, while larger, amorphous particles were found at lower reactor temperatures. These results are consistent with literature studies. At 817 °C, small (450 nm), spherical, unagglomerated particles could be produced. A gas‐phase dispersion of these particles is intended for use as seeds in subsequent kinetic studies of titanium dioxide formation reactions involving a rapid compression methodology. 相似文献
6.
Intermediate and high temperature proton conductors contain no structural protons. They only become proton conductors in water
vapor or hydrogen containing atmospheres. The reaction of these materials with the water from the atmosphere was first presented
by Wagner [1]. These reactions will be discussed in detail with doped earth alkaline cerates as an example.
Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994 相似文献
7.
Bin Zhao Kei Uchikawa John R. McCormick Chao Ying Ni Jingguang G. Chen Hai Wang 《Proceedings of the Combustion Institute》2005,30(2):2569-2576
Nano-sized titanium oxide particles were synthesized in a stationary, laminar, premixed, stagnation flame burning an ethylene–oxygen–argon mixture at an equivalence ratio of 0.36 under the atmospheric pressure. The titanium precursor, titanium tetraisopropoxide (TTIP), was fed into the flame by a carrier argon flow through a heated TTIP bath. Particles synthesized in this flame were characterized for their size distribution, morphology, phase purity, and crystal structure, by scanning mobility particle sizer, transmission electron microscopy, and X-ray diffraction. It was found that the mean diameter of the particles was highly controllable and ranged from 3 to 6 nm depending on TTIP loading. The particle size was nearly uniform, and particles appeared to be single crystals without excessive aggregation. XRD analyses show that particles directly synthesized in the flame are pure anatase. Upon sintering and size growth on the flame stabilizer, a notable portion of particles transformed into rutile with much larger crystal sizes. 相似文献
8.
Haiqing Li Lin Zhang Jung Kyu Jo Chang-Sik Ha Yury A. Shchipunov Il Kim 《Journal of nanoparticle research》2011,13(5):2117-2128
Titania/Hyperbranched polyglycidol (HBP) nanohybrids with tunable morphologies have been synthesized via a sol–gel process
at ambient temperature. One-shot addition of varied amounts of titanium precursor tetraisopropoxide (TTIP) yields spherical
titania/HBP solid particles with tunable size, while a controlled addition of TTIP results in spherical titania/HBP capsules.
The average outer and inner diameters of the resultant capsules are also controllable according to the amount of TTIP via
an Oswald ripening process. In addition, the modality of additional water supplied in the reaction systems can tune the morphologies
of the resulting titania/HBP particles from nanocapsules to nanotubes owing to the accelerated hydrolysis rate of TTIP. The
tunability in morphologies of the titania/HBP nanostructures ranging from solid spheres, capsules to tubes could be attributed
to the self-assembly of a large amount of titania/HBP aggregates in a rapid, controlled and anisotropic manner, respectively.
Surprisingly, by means of HBP contained in the resulting titania/HBP nanostructures, the gold nanoparticles are in situ generated
and encapsulated into titania/HBP matrix in the absence of additional reducing agent. The as-prepared gold nanoparticles functionalized
titania/HBP hybrids exhibit excellent catalytic function toward the reduction of 4-nitrophenol. This strategy demonstrates
a typical example for functionalizing the titania/HBP hybrids targeted to specific applications. 相似文献
9.
I. Banerjee Soumen Karmakar Naveen V. Kulkarni Ashok B. Nawale V. L. Mathe A. K. Das S. V. Bhoraskar 《Journal of nanoparticle research》2010,12(2):581-590
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. 相似文献
10.
Chien-Chon Chen Wen C. Say Sheng-Jen Hsieh Eric Wei-Guang Diau 《Applied Physics A: Materials Science & Processing》2009,95(3):889-898
We propose a mechanism for the growth of crystalline anodic titanium-oxide (ATO) nanochannel arrays based on thermodynamic
considerations and structural imperfections. Both amorphous and crystalline ATO films were obtained from the anodization of
a titanium foil. Amorphous ATO nanotubes have a single-layer form, which makes them inefficient for use in photo-catalytic
and solar-cell applications. Annealed ATO nanotubes are considered non-stoichiometric if the effect of oxygen partial pressure
on the composition is significant. The driving force behind growing crystalline ATO nanotubes is the drawing of oxygen from
the atmosphere to the oxygen site, which consequently decreases the concentration of oxygen vacancies in the anatase phase.
The small ionization energies of titanium ions produce the stoichiometric defects. A diagram showing Gibbs energy and Kroger–Vink
notation to indicate the strong influence of the non-stoichiometric ATO structure is deduced. 相似文献
11.
Effects of different annealing atmospheres on the surface and microstructural properties of ZnO thin films grown on Si (1 0 0) substrates were investigated. X-ray diffraction results showed that the crystallinity of the ZnO thin film annealed in an oxygen atmosphere was better than that annealed in a nitrogen atmosphere. Atomic force microscopy and transmission electron microscopy (TEM) images showed that the surfaces of the ZnO thin films annealed in a nitrogen atmosphere became very rough in contrast to those annealed in an oxygen atmosphere. High-resolution TEM images showed that many stacking faults and tilted grains could be observed in the ZnO thin films annealed in a nitrogen atmosphere in contrast to those annealed in an oxygen atmosphere. Surface morphology and microstructural property variations due to different annealing atmospheres in ZnO thin films are also described on the basis of the experimental results. 相似文献
12.
Kranthi K. Akurati Rainer Dittmann Andri Vital Ulrich Klotz Paul Hug Thomas Graule Markus Winterer 《Journal of nanoparticle research》2006,8(3-4):379-393
Binary TiO2/SiO2 and SnO2/SiO2 nanoparticles have been synthesized by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Si:Ti and Si:Sn ratios were produced at various flow rates of oxygen and the resulting powders were characterized by BET (Brunauer–Emmett–Teller) surface area analysis, XRD, TEM and Raman spectroscopy. In the Si–O–Ti system, mixed oxide composite particles exhibiting anatase segregation formed when the Si:Ti ratio exceeded 9.8:1, while at lower concentrations only mixed oxide single phase particles were found. Arrangement of the species and phases within the particles correspond to an intermediate equilibrium state at elevated temperature. This can be explained by rapid quenching of the particles in the flame and is in accordance with liquid phase solubility data of Ti in SiO2. In contrast, only composite particles formed in the Sn–O–Si system, with SnO2 nanoparticles predominantly found adhering to the surface of SiO2 substrate nanoparticles. Differences in the arrangement of phases and constituents within the particles were observed at constant precursor mixture concentration and the size of the resultant segregated phase was influenced by varying the flow rate of the oxidant. The above effect is due to the variation of the residence time and quenching rate experienced by the binary oxide nanoparticles when varying the oxygen flow rate and shows the flexibility of diffusion flame aerosol reactors. 相似文献
13.
Cobalt and nickel nanoparticles were produced by hydrogen reduction reaction from cobalt or nickel chloride precursor vapour
in nitrogen carrier gas. This aerosol phase method to produce nanoparticles is a scalable one-step process. Two different
setups were introduced in particle production: a batch type reactor and a continuously operated reactor. Common feature in
these setups was hydrogen mixing in a vertical flow reactor. The process was monitored on-line for particle mass concentration
and for gas phase chemical reactions. Tapered element oscillating microbalance measured the particle mass concentration and
Fourier transform infrared spectroscopy was used to monitor relevant gas phase species. The produced cobalt and nickel particles
were characterised using transmission electron microscopy and x-ray diffraction. The produced cobalt and nickel particles
were crystalline with cubic fcc structure. Twinning was often observed in cobalt particles while nickel particles were mostly
single crystals. The cobalt particles formed typically long agglomerates. No significant neck growth between the primary particles
was observed. The primary particle size for cobalt and nickel was below 100 nm. 相似文献
14.
Photocatalytic oxidation of organic adsorbates on anatase TiO2 films has been examined in different atmospheres of humid air, dry air and vacuum. The photocatalytic oxidation was observed by IR absorption spectroscopy (IRAS) with a multiple-internal-reflection (MIR) geometry. The photocatalytic oxidation is the fastest in the air at a humidity of 70% where oxygen and water vapor are consuming to produce OH radicals and O2− anions on the TiO2 surface with the UV exposure. In the dry air, a rate of the photocatalytic oxidation is almost 30% of that in the humid air, where only O2− anions oxidize the organic adsorbates. In vacuum, on the other hand, it is negligible, which suggests that adsorbed H2O molecules do not play an important role in the photocatalytic reaction. It is suggested that an addition of the water vapor is necessary to achieve the higher catalytic activity. 相似文献
15.
Bimodally porous (2–4 and 20–100 nm) titania powders were prepared by hydrolysis of titanium tetraisopropoxide (TTIP), and the effect of hydrolysis temperature on the phase transformation and pore structure was investigated. The phase transformation was slightly retarded with increasing hydrolysis temperature, when the initial water concentration was small. The evolution of particle phase composition from amorphous to crystalline anatase and rutile was largely proportional to the calcination temperature and the initial water concentration. The pore size distribution was bimodal with fine intra-particle pores (2–4 nm in diameter) and larger inter-particle pores (20–100 nm). The intra-particle pores decreased in diameter at the hydrolysis temperature of 20°C. The specific surface area (SSA) of the dried powders ranged from 253 to 587 m2/g and the highest SSA was obtained at the hydrolysis temperature of 20°C. 相似文献
16.
《Ultrasonics sonochemistry》2014,21(2):681-691
Here, titanium dioxide nanoparticles (NPs) were sonosynthesized and loaded simultaneously onto the cotton fabric. Titanium tetra isopropoxide (TTIP) was used as precursor and ultrasonic irradiation was utilized as a tool for synthesis of TiO2 in low temperature with anatase structure and loading nanoparticles onto the cotton fabric. TiO2 loaded cotton fabric was characterized by XRD, FE-SEM, EDS, and XRF. Moreover, several properties of the treated cotton fabrics such as self-cleaning, UV protection, washing durability, and tensile strength were studied. The effect of variables, including TTIP concentration and sonication time, was investigated based on central composite design (CCD) and response surface methodology (RSM). The results confirmed formation of anatase TiO2 nanoparticles with 3–6 nm crystalline size loaded onto the cotton fabric at low temperature (75 °C) that led to good self-cleaning and UV-protection properties. The excellent UV-protection rating of the treated fabric maintained even after 25 home launderings indicating an excellent washing durability. Interestingly, sonochemical method had no negative influence on the cotton fabric structure. The statistical analysis indicated significant effect of both TTIP concentration and sonication time on the content of the loaded TiO2 on the fiber and self-cleaning properties of the fabric. 相似文献
17.
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. 相似文献
18.
The surface area of nanosized agglomerates is of great importance as the reactivity and health effects of such particles are
highly dependent on surface area. Changes in surface area through sintering during nanoparticle synthesis processes are also
of interest for precision control of synthesised particles. Unfortunately, information on particle surface area and surface
area dynamics is not readily obtainable through traditional particle mobility sizing techniques. In this study, we have experimentally
determined the mobility diameter of transition regime agglomerates with 3, 4, and 5 primary particles. Agglomerates were produced
by spray drying well-characterised polystyrene latex particles with diameters of 55, 67, 76, and 99 nm. Tandem differential
mobility analysis was used to determine agglomerate mobility diameter by selecting monodisperse agglomerates with the same
number of primary particles in the first DMA, and subsequently completely sintering the agglomerates in a furnace aerosol
reactor. The size distribution of the completely sintered particles was measured by an SMPS system, which allowed for the
determination of the number of primary particles in the agglomerates. A simple power law regression was used to express mobility
diameter as a function of primary particle size and the number of primary particles, and had an excellent correlation (R2 = 0.9971) with the experimental data. A scaling exponent was determined from the experimental data to relate measured mobility
diameter to surface area for agglomerates. Using this relationship, the sintering characteristics of agglomerates were also
examined for varying furnace temperatures and residence times. The sintering data agreed well with the geometric sintering
model (GSM) model proposed by Cho & Biswas (2006a) as well as with the model proposed Koch & Friedlander (1990) for sintering by viscous flow. 相似文献
19.
A novel method has been developed for the preparation of nano-sized TiO2 with anatase phase. Nanoparticles with diameter about 6 nm were prepared at a relatively low temperature (75 °C) and short time. The synthesis was carried out by the hydrolysis of titanium tetra-isopropoxide (TTIP) in the presence of water, ethanol, and dispersant under ultrasonic irradiation (500 kHz) at low intensity. The results show that variables such as water/ethanol ratio, irradiation time, and temperature have a great influence on the particle size and crystalline phases of TiO2 nanoparticles. Characterization of the product was carried out by different techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV–vis spectroscopy. 相似文献
20.
M. Salaün M. Audier M. Duneau F. Delyon 《Applied Physics A: Materials Science & Processing》2008,93(1):105-110
In 2000, Campbell et al. (Nature 404:53, 2000) have shown that three-dimensional periodic nanostructures can be obtained from UV laser interference irradiation of photoresist
for 6 nanosecond single pulse. We have developed a similar experiment for photolytic gas phase decomposition and for photopatternable
organic–inorganic hybrid resins.
Different steps in results, presently reported, were first to determine the characteristics of both the 3D interference pattern
and interferometer to be associated to a CVD reactor and second to verify the mechanical stability of the set up confirmed
with the structuration of a siloxane based methacrylic resins by UV polymerization and finally to grow periodic nanostructures
by photolytic gas phase decomposition of chromyl chloride. The experimental results obtained so far indicate that, depending
on the electromagnetic energy density, a vapor phase decomposition of chromyl chloride leads to periodic arrays of either
Cr–O amorphous or Cr2O3 particles on glass and (001)TiO2 substrates at room temperature. 相似文献