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1.
This paper describes the equilibrium morphologies of zinc sulfide nanoparticles in the wurtzite phase as a function of size, determined using ab initio Density Functional Theory (DFT) simulations and a shape-dependent thermodynamic model predicting the Gibbs free energy of a nanoparticle. We investigate the relative stabilities of a variety of nanoparticle shapes based on the wurtzite structure and show how the aspect ratio of wurtzite nanorods moderates the size-dependent phase transformation to the zinc blende phase. We find that while wurtzite nanoparticles are thermodynamically unstable with respect to the low energy rhombic dodecahedron morphology in the zinc blende phase at all sizes, shape- and size-dependent phase transformations occur when other zinc blende morphologies are present. Despite popular synthesis of zinc sulphide nanoparticles in the wurtzite phase, an in-depth thermodynamic study relating to the relative stability of wurtzite shapes and comparison with the zinc blende phase does not exist. Therefore this is the first thermodynamic study describing how shape can determine the solid phase of zinc sulfide nanostructures, which will be of critical importance to experimental applications of nanostructured zinc sulfide, where phase and shape determines properties. 相似文献
2.
Three-dimensional, dendritic micrometer-scale spheres of alkali metal hydrogen titanate 1D nanostructures (i.e., nanowires and nanotubes) have been generated using a modified hydrothermal technique in the presence of hydrogen peroxide and an alkali metal hydroxide solution. Sea-urchin-like assemblies of these 1D nanostructures have been transformed into their hydrogen titanate analogues (lepidocrocite HxTi2-x/4squarex/4O4 (x approximately 0.7, square: vacancy)) by neutralization as well as into their corresponding anatase TiO2 nanostructured counterparts through a moderate high-temperature annealing dehydration process without destroying the 3D hierarchical structural motif. The as-prepared hollow spheres of titanate and titania 1D nanostructures have overall diameters, ranging from 0.8 to 1.2 microm, while the interior of these aggregates are vacuous with a diameter range of 100 to 200 nm. The constituent, component titanate and TiO2 1D nanostructures have a diameter range of 7+/-2 nm and lengths of up to several hundred nanometers. A proposed two-stage growth mechanism of these hollow micrometer-scale spheres was supported by time-dependent scanning electron microscopy, atomic force microscopy, and inductively coupled plasma atomic emission spectrometry data. We have also demonstrated that these assemblies are active photocatalysts for the degradation of synthetic Procion Red dye under UV light illumination. 相似文献
3.
Cassiers K Linssen T Meynen V Van der Voort P Cool P Vansant EF 《Chemical communications (Cambridge, England)》2003,(10):1178-1179
A new and generally applicable synthesis procedure is developed in order to synthesise micelle-templated mesoporous titania built up of nanosized anatase walls with thermal stability up to 600 degrees C. 相似文献
4.
Kotani H Hanazaki R Ohkubo K Yamada Y Fukuzumi S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(9):2777-2785
The catalytic activity of Pt nanoparticles (PtNPs) with different sizes and shapes was investigated in a photocatalytic hydrogen‐evolution system composed of the 9‐mesityl‐10‐methylacridinium ion (Acr+–Mes: photocatalyst) and dihydronicotinamide adenine dinucleotide (NADH: electron donor), based on rates of hydrogen evolution and electron transfer from one‐electron‐reduced species of Acr+–Mes (Acr.–Mes) to PtNPs. Cubic PtNPs with a diameter of (6.3±0.6) nm exhibited the maximum catalytic activity. The observed hydrogen‐evolution rate was virtually the same as the rate of electron transfer from Acr.–Mes to PtNPs. The rate constant of electron transfer (ket) increased linearly with increasing proton concentration. When H+ was replaced by D+, the inverse kinetic isotope effect was observed for the electron‐transfer rate constant (ket(H)/ket(D)=0.47). The linear dependence of ket on proton concentration together with the observed inverse kinetic isotope effect suggests that proton‐coupled electron transfer from Acr.–Mes to PtNPs to form the Pt? H bond is the rate‐determining step for catalytic hydrogen evolution. When FeNPs were used instead of PtNPs, hydrogen evolution was also observed, although the hydrogen‐evolution efficiency was significantly lower than that of PtNPs because of the much slower electron transfer from Acr.–Mes to FeNPs. 相似文献
5.
The simplest field flow fractionation technique, which uses the earth's gravity as the external field is applied to isolate two populations, which differ in both shape and size, from a polydisperse sub-micron TiO2 powder of homogenous density. The fraction eluted first is spherical with an average diameter of 0.31 microm while the second fraction is ellipsoidal and can be associated with a 0.45 microm hydrodynamic diameter. Elution conditions appeared to be very sensitive to electrolyte and surfactant characteristics in the carrier phase as well as on the sample concentration. Using 25 microl (1%, w/w) sample suspension, separations of spherical from ovoid particles was performed in almost 2 h with a mobile phase of 0.001 M KNO3-0.01% (v/v) Fl-70 in water in a 0.025-cm thick channel made of polystyrene walls. 相似文献
6.
Pradeepan Periyat K. V. Baiju P. Mukundan P. Krishna Pillai K. G. K. Warrier 《Journal of Sol-Gel Science and Technology》2007,43(3):299-304
Nanocrystalline sol–gel derived titania doped with ceria (1, 2, 5 and 10-mole%) has been prepared from titanyl oxysulphate.
The titania doped with 5-mole% CeO2 after calcining to 500 °C, possesses specific surface area of 97 m2 g−1 and has anatase phase stability up to 900 °C. Moreover it retains a surface area of 37 m2 g−1 at 700 °C. In comparison, the undoped calcined material has anatase stability only up to 700 °C and specific surface area
only 48 m2 g-1 and 6 m2 g-1 at 500 °C and 700 °C, respectively. The diffuse reflectance spectra show that, as the cerium content increases, the absorption
undergoes a red shift and reaches the visible range. The exceptionally high phase stability, crystallinity and high surface
area are due to the extremely fine particle size and effective doping achieved by the specific synthesis method. The results
based on X-ray diffraction, specific surface area and diffuse reflectance spectra indicated that the maximum threshold limit
of doping is up to a value of 5-mole%. 相似文献
7.
8.
A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals. 相似文献
9.
Layered protonated titanates (LPTs), a class of interesting inorganic layered materials, have been widely studied because of their many unique properties and their use as precursors to many important TiO(2)-based functional materials. In this work, we have developed a facile solvothermal method to synthesize hierarchical spheres (HSs) assembled from ultrathin LPT nanosheets. These LPT hierarchical spheres possess a porous structure with a large specific surface area and high stability. Importantly, the size and morphology of the LPT hierarchical spheres are easily tunable by varying the synthesis conditions. These LPT HSs can be easily converted to anatase TiO(2) HSs without significant structural alteration. Depending on the calcination atmosphere of air or N(2), pure anatase TiO(2) HSs or carbon-supported TiO(2) HSs, respectively, can be obtained. Remarkably, both types of TiO(2) HSs manifest excellent cyclability and rate capability when evaluated as anode materials for high-power lithium-ion batteries. 相似文献
10.
McManus JS Cunningham PD Regan LB Dunne PW 《Chemical communications (Cambridge, England)》2012,48(60):7453-7455
Highly soluble anatase nanocrystals of 4 nm diameter have been prepared by the reaction of amorphous titania with trifluoroacetic acid. The solubility of the nanocrystals is a result of surface bound carboxylate groups, and enables the organic-inorganic hybrid material to be processed from solution to yield high quality coatings and thin-films. 相似文献
11.
Monodisperse anatase titania nanoparticles with controllable sizes (typically 10-300 nm) can be synthesized using an efficient and straightforward protocol via fine tuning of the ionic strength in the devised sol-gel methodology. 相似文献
12.
Barbara Filipowicz Marek Pruszyński Seweryn Krajewski Aleksander Bilewicz 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):889-895
Various types of sodium and potassium titanate nanostructures (nanotubes, nanofibers, nanoribbons, nanwires) were synthesized and characterized by X-ray diffraction, SEM and TEM, as well BET and BJH methods. Adsorption of radiotracer 137Cs+ ions from aqueous solutions on synthesized titanate nanostructures was investigated in batch technique as a function of contact time, concentration of sodium ions and pH of the solutions. It was found that among the studied nanostructures nanotubes shows the highest selectivity for 137Cs, which is related to a zeolitic character of Cs+ adsorption. The efficient adsorption of 137Cs was obtained in Na+ solutions with concentration below 10?2 M, at pH 7–9 and in contact time above 2 h. Moreover, nanotubes have the higher specific surface area than other nanostructures, which results in better availability of ion exchange groups and high ion exchange capacity. These properties of nanotubes indicate that they may be used for adsorption of 137Cs from various types of nuclear wastes. 相似文献
13.
Acar H Garifullin R Guler MO 《Langmuir : the ACS journal of surfaces and colloids》2011,27(3):1079-1084
Mineralized biological materials such as shells, skeleton, and teeth experience biomineralization. Biomimetic materials exploit the biomineralization process to form functional organic-inorganic hybrid nanostructures. In this work, we mimicked the biomineralization process by the de novo design of an amyloid-like peptide that self-assembles into nanofibers. Chemically active groups enhancing the affinity for metal ions were used to accumulate silicon and titanium precursors on the organic template. The self-assembly process and template effect were characterized by CD, FT-IR, UV-vis, fluorescence, rheology, TGA, SEM, and TEM. The self-assembled organic nanostructures were exploited as a template to form high-aspect-ratio 1-D silica and titania nanostructures by the addition of appropriate precursors. Herein, a new bottom-up approach was demonstrated to form silica and titania nanostructures that can yield wide opportunities to produce high-aspect-ratio inorganic nanostructures with high surface areas. The materials developed in this work have vast potential in the fields of catalysis and electronic materials. 相似文献
14.
The dipole polarizabilities of Co(n)Bz(m), (n, m = 1-4, m = n, n + 1) clusters are studied by means of an all-electron gradient-corrected density functional theory and finite field method. The dipole moments are relatively large for most of the clusters, implying their asymmetric structures. The total polarizability increases rapidly as cluster size, whereas the average polarizability shows "odd-even" oscillation with relatively large values at (n, n + 1). The polarizabilities exhibit clear shape-dependent variation, and the sandwich structures have systematically larger polarizability and anisotropy than the rice-ball isomers. The dipole polarizabilities are further analyzed in terms of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, ionization potential, and electron delocalization volume. We conclude that the polarizability variations are determined by the interplay between the geometrical and electronic properties of the clusters. 相似文献
15.
Gregory Mogilevsky Qiang Chen Alfred Kleinhammes Yue Wu 《Chemical physics letters》2008,460(4-6):517-520
We constructed a truly nanotubular structure model of titania nanotubes based on delaminated anatase with realistic dimensions replicating those observed in experiments. It is shown that this nanotubular structure based on delaminated anatase produces an XRD pattern in excellent agreement with the observed spectrum and that the tube axis is along the [0 1 0] direction of the anatase structure. Preserving the atomic registry of delaminated anatase between adjacent layers is essential along the tube axis but unnecessary along the circumference. These understandings provide detailed information on the structure and morphology of hydrothermally synthesized titania nanotubes. The findings will help discern the complex surface chemistry of these materials. 相似文献
16.
The effect of protonation on the surface acidic properties of titanate nanowires (TiONWs) was investigated. Nanowires were synthesized by the alkali hydrothermal method which resulted in one dimensional nanostructures of large external surface area and well-defined lamellar interlayer structure. The Na+/H+ ratio in the structure can be tuned by ion-exchange. Our aim was to characterize the morphology of the as-synthesized nanostructures by HRTEM and SEM measurements and assess their surface acidity using in situ infrared spectroscopic measurements and temperature programmed desorption. It was found that the numbers of Lewis and Brönsted acidic sites in the Na-form and the H-form of the TiONWs is different. The ratio and the nature of acidic sites can be tuned by the ion exchange process. The wire-like morphology and the tunable acidity are features of titanate nanowires that may render them a promising material in various heterogeneous catalytic applications. 相似文献
17.
Jinhua Jiang Qiuming Gao Zhi Chen 《Journal of molecular catalysis. A, Chemical》2008,280(1-2):233-239
Gold nanoparticles were first supported on protonic titanate nanotubes with the formation of Au/titanate nanocomposites. They were further transformed to Au/titania nanocomposites via an acetic acid treatment at 70 °C for 60 h. The porosity, crystal structure and morphology of those composites have been studied by X-ray diffraction (XRD), High-resolution transmission electron microscope (HRTEM), and low-temperature nitrogen adsorption. Catalytic tests for CO oxidation show that the Au/titanate nanocomposites had a promising activity with complete conversion of CO at 70 °C and that of Au/titania was at room temperature (25 °C). Both catalysts exhibited good thermal and long-term stabilities. The influence of the crystal vacancies and surface properties of the titanate and titania supports on the catalytic activities were evaluated. 相似文献
18.
Dongfang Zhang 《Colloid Journal》2012,74(4):456-462
This work reports the synthesis and studies on photocatalytic activity of a material based on titanium oxide doped with silver. Two kinds of Ag-deposited TiO2 were synthesized via soft chemical reduction (SCR) and photodeposition (PD) methods. The structure, composition and chemical properties of the obtained products were investigated by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence spectra and Fourier transformation infrared spectroscopy techniques. The photocatalytic oxidation activity in a course of removal and destruction of organic compounds such as methyl orange dye using Ag/TiO2 hybrid material was studied. The results suggest that SCR synthesized Ag/TiO2 exhibited better photocatalytic performance that that obtained by PD method. The relationship between the synthesis method and photocatalytic activity of synthesized Ag/TiO2 was analyzed with a focus on the plasmonic photocatalysis of silver. When compared to PD method, the SCR produced more homogeneous and smaller silver particles with a better dispersion than photodeposition that results in a relative increase of material activity in the photocatalytic degradation of dye pollutant. 相似文献
19.
The synthesis of anatase and rutile titania could be achieved in mixed organic media with the variation of alcohols in the media under mild conditions. Although a nonhydrolytic process cannot be excluded, it is suggested that the formation of titania in these systems is based mainly on the hydrolytic process initiated by the water generated as a result of an esterification reaction between the alcohols and acetic acid. It has been found that the phase of the TiO2 produced depends on the choice of alcohols and temperature. Partial morphology and size are also affected by these factors. It is proposed that the viscosity and pressure of the reaction media influence the particle size. X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and UV-visible adsorption spectroscopy were employed to characterize the final products. 相似文献
20.
Jan Perlich Mine Memesa Alexander Diethert Ezzeldin Metwalli Weinan Wang Stephan V. Roth Jochen S. Gutmann Peter Müller-Buschbaum 《Colloid and polymer science》2012,290(2):119-126
The fabrication of a functional multilayer system with a gradually hierarchical order formed by individual titania thin films
of different porosity is investigated. The porous or sponge-like nanostructures are fabricated using a diblock copolymer assisted
sol–gel process. The successive spin-coating of the sol–gel solution onto the silicon substrate deposits a thin polymer nanocomposite
film which is transformed to purely anatase titania nanostructures via calcination. In total, this procedure is repeated layer
by layer for three times. This layer-by-layer approach is monitored with grazing incidence small-angle X-ray scattering (GISAXS)
after each fabrication step. The GISAXS investigation is complemented in real space with a scanning electron microscopy characterization
of the respective preparation stages. From the characterization, a porous titania multilayer system with gradually structured
levels is clearly identified. 相似文献