Microcrystalline Particles Research Articles

Postsynthetic Ligand and Cation Exchange in Robust Metal–Organic Frameworks

Postsynthetic ligand and metal ion exchange (PSE) processes are shown to readily occur in several "inert" metal-organic frameworks (MOFs), including zeolitic imidazolate frameworks (ZIFs). Ligand exchange can occur between solid samples, as was demonstrated under relatively mild conditions with two robust, topologically distinct MOFs, MIL-53(Al) and MIL-68(In). Interestingly, ligand PSE is not observed with MIL-101(Cr), which is attributed to the kinetic inertness of the Cr(III) ion. In addition to ligand exchange, metal ion (cation) PSE was also studied between intact MOF microcrystalline particles. Metal ion transfer between MIL-53(Al) and MIL-53(Fe) was readily observed. These PSE reactions were monitored and the products characterized by a number of techniques, including aerosol time-of-flight mass spectrometry, which permits single-particle compositional analysis. To show the potential synthetic utility of this approach, the PSE process was used to prepare the first Ti(IV) analogue of the robust UiO-66(Zr) framework. Finally, experiments to rule out mechanisms other than PSE (i.e., aggregation, dissolution/recrystallization) were performed. The results demonstrate that PSE, of either ligands or cations, is common even with highly robust MOFs such as UiO-66(Zr), MILs, and ZIFs. Furthermore, it is shown that PSE is useful in preparing novel materials that cannot be obtained via other synthetic methods.

Morphology-controlled electrodeposition of Cu2O microcrystalline particle films for application in photocatalysis under sunlight

Morphology-controlled Cu2O microcrystalline particle films had been successfully electrodeposited on tin-doped indium oxide glass substrates in CuSO4 solutions containing different amounts of polyethylene glycol (PEG) additives. With an increase of PEG, microcrystals gradually changed from irregular shapes to cubes, octahedrons, and spherical shapes. Sizes increasingly became smaller with an increase of PEG under the same deposition time. These films had been first used as recyclable photocatalysts and showed excellent and photocatalytic activities in photodegradation of methylene blue (MB) under sunlight. Activities were regularly varied relative to the morphologies of films controlled by the amount of PEG and could be further enhanced by adding a little amount of hydrogen peroxide in the MB solution. The method for controllable preparation of Cu2O microcrystals with photocatalytic activities was simple and inexpensive. The as-prepared particle films could also be used in photodegradation of many other pollutants under sunlight.

The inclusion of density fluctuations in the theory of adsorption of laterally interacting molecules on microcrystalline particles

Equations for the isotherms of adsorption of pure substances on small inhomogeneous crystalline particles with taking into account density fluctuations and intermolecular interactions in the quasi-chemical approximation were obtained for the first time.

On the ultraviolet light induced oxidation of amorphous As2S3 film

Illumination of amorphous As2S3 film by ultraviolet light with an overall light intensity on the sample surface of around 10Wcm−2 leads to extensive film oxidation. After 2min of illumination most of As2S3 film of an original thickness at around 0.425μm was converted into a cubic form of As2O3-arsenolite. A considerable amount of arsenolite microcrystals were found at a height of around 2μm and more which indicated a growth of As2O3 microcrystalline particles from the vapor phase.

Single‐Jet Precipitation of Silver Nanocrystals in the Presence of Poly(acrylic) Acid

AbstractPrecipitation of silver nanocrystals was carried out in a poly(acrylic) acid (PAA) solution by using a single‐jet crystallizer. The influence of the feeding rate, the injection position and the PAA dosage on the crystal size distribution (CSD) was clarified. The precipitated silver nanocrystals agglomerate with each other, forming an agglomerated microcrystal. In the presented case, smaller feeding rates caused smaller crystal sizes and narrower CSD widths. PAA, which is a water‐soluble polyelectrolyte, successfully inhibited agglomeration and crystal growth, and decreased the crystal size and the CSD width. Thus, this idea may also facilitate the production of other nano‐/microcrystalline particles.

Combustion synthesis, structural characterization, thermo and photoluminescence studies of CdSiO3:Dy3+ nanophosphor

CdSiO3:Dy3+ (1–9mol%) nanophosphors were prepared for the first time using the solution combustion method. The process of monoclinic phase formation was investigated by PXRD, TG–DTA and FTIR. The results show that the phase formation temperature of combustion-derived monoclinic CdSiO3 is found to be lower as compared to the powders prepared by solid-state and sol–gel methods. It was observed that the average crystallite size calculated by Debye–Scherrer's formula and Williamson–Hall (W–H) plot are well comparable and was found to be in the range of 35–70nm. Scanning electron micrographs indicate that there exist circular microcrystalline particles. It is observed that the optical energy gap is widened with the increase of Dy3+ ion dopant. The photoluminescence (PL) spectra exhibit characteristic transitions of Dy3+ due to 4F9/2→6H15/2 (blue) and 4F9/2→6H13/2 (yellow) regions. The thermoluminescence (TL) glow curve of CdSiO3:Dy3+ nano powder exposed to UV irradiation exhibited one main peak centered at 170°C. The intensity of the main peak increases up to the dose of 20min then it decreases. The glow curves were analyzed by the glow peak shape method and the estimated trap parameters are discussed.

Effect of equilibrium fluctuations on microcrystalline particles on adsorption isotherms and reaction rates

The effect of the finiteness of face areas and equilibrium fluctuations on the adsorption isotherms of binary molecular mixtures and the rate of surface processes occurring on nanosized particles is studied. The adsorption process is considered in the grand canonical ensemble; the rates of elementary stages are calculated in the kinetic mode. The surface region on the face is found to contain a number of adsorption centers ranging from 10 to 105. The effect of density fluctuations of adsorbed molecules on the partial adsorption isotherms and rate fluctuations is discussed. A calculation procedure for density fluctuations in heterogeneous microparticles with different faces and different binding energies of molecules with the surface is considered. It is shown that the greatest effect of density fluctuations is manifested at a low occupancy of each face of the particle.

Wavelength dependence of light propagation in a water suspension of anisotropic scatterers

We experimentally study the wavelength dependence of light propagation in a water suspension of lithium niobate microcrystalline particles. First, the ballistic transmission in the visible range of the suspension is measured. The nonlinear relationship is observed between the transport mean free path and the wavelength of the incident light. Secondly, we measure the coherent backscattering (CBS) of the sample at different wavelengths. The full width at half maximum of the CBS cone at 532 nm is about 1.24 times as large as that at 671 nm. The results indicate that the light with a long wavelength propagates further than the short wavelength light and the localization state of the short one is stronger. Finally, we investigate the light-controllable CBS experiments in the disordered materials of anisotropic scatterers, which show that the configuration of pump light with the longer wavelength and the probe light with the shorter wavelength performs better.

Foundations of the fluctuation theory of adsorption on microcrystalline particles

Fundamentals of the equilibrium fluctuation theory of adsorption of molecules on microcrystalline particles taking into account the atomic structure of nonuniform surfaces were developed. The importance of taking into account the discrete character of adsorption centers in constructing adsorption isotherm equations was demonstrated. This changes the type of the mathematical apparatus in the search for a maximum distribution function term in a grand canonical ensemble: instead of differential derivatives, symmetrized difference derivatives should be used. The fluctuation theory of adsorption was generalized to ideal multicomponent mixtures of molecules. Adsorption isotherm equations for multicomponent mixtures on uniform and nonuniform surfaces taking into account limited sizes of the surface of various microcrystal faces and fluctuation contributions were obtained. The equations describe the influence of equilibrium fluctuations on adsorption isotherms for adsorbent particles of all sizes, from nanometric to macroscopic. An analysis of the equations showed that the influence of fluctuations was strongest at low coverages for each microcrystal face. The simplest case of taking fluctuations into account in the presence of contributions of lateral interactions in the mean field approximation was discussed.

Oxygen assisted photoinduced changes in Ge 39Ga 2S 59 amorphous thin film

Annealing of the Ge 39Ga 2S 59 virgin amorphous thin film leads to the blue shift of the optical band gap owing to an increase of the film network order and to a decrease in the refractive index associated with both the film thickness expansion and a decrease in the mean molecular polarizability. Virgin film is only a little bleached by the illumination with the band gap or over band gap photons while the film annealed in the argon is practically insensitive to such illumination. Illumination by UV photons leads to significant changes in the surface topology of the virgin or annealed film. It is suggested that observed surface topology changes originate from the film oxidation, which is supported by: (i) Fourier transform infrared spectroscopy evidencing the presence of the broad absorption band in the region 750–900 cm −1 assigned to asymmetric stretching vibrations of the Ge–O–Ge bridge, (ii) the presence of the Raman feature at around 420 cm −1 assigned to symmetric stretching of bridging oxygen in O 3Ge–O–GeO 3 units and (iii) Atomic Force Microscopy indicating formation of some protrusions with entities reminiscent of isolated hexagonal particles which could be assigned to GeO 2 microcrystalline particles.

Synthesis and luminescence properties of YVO4:Eu3+ cobblestone - like microcrystalline phosphors obtained from the mixed solvent - thermal method

Abstract The mixed solvent-thermal method has been developed for the synthesis of YVO 4 :Eu 3+ luminescent materials in the N, N-dimethylformamide (DMF)/ de-ionized water (DIW) solution. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscope (TEM), UV/vis absorption and photoluminescence spectroscopies. The results demonstrate that we have obtained the uniform YVO 4 :Eu 3+ cobblestone - like microcrystalline phosphors in the mixed solution of DMF and DIW, which are different to the as-obtained YVO 4 :Eu 3+ nanoparticles in pure DIW. And the as - prepared YVO 4 :Eu 3+ microcrystalline particles are composed of numerous nanoparticles. The assembling phenomenon of the nanoparticles is strongly affected by the pH value of the solution and the volume ratio of DMF/DIW. Under UV excitation, the samples can emit the bright red light. While, the photoluminescence (PL) intensities of YVO 4 :Eu 3+ show some difference for samples obtained under the different reaction conditions. This is because that different microstructures of samples result in different combinative abilities between the surface and the adsorbed species so as to produce the different quenching abilities to the emission from Eu 3+ ions.

Synthesis, Processing and Solid State Excipient Interactions of Cucurbit[6]uril and Its Formulation into Tablets for Oral Drug Delivery

The synthesis, processing, and solid state excipient interactions of cucurbit[6]uril (CB[6]) and its formulation into oral tablets has been examined using a range of physical chemistry techniques. Rapid precipitation from HCl by the addition of water yields microcrystalline CB[6] with smaller and more consistent particle size (30-165 μm) compared with the sieved CB[6] (50-540 μm) produced from large crystals grown by slow evaporation from HCl. The microcrystalline particles also contain fewer water molecules in the crystal compared with the sieved particles: 10 and 16% respectively. Microcrystalline CB[6] can be formulated into tablets suitable for oral delivery with a CB[6] content of 1-50% w/w, with the other excipients including lactose, talc, Avicel, magnesium stearate and Ac-Di-Sol. In the solid state microcrystalline CB[6] does not interact significantly with the talc, Ac-Di-Sol or Avicel, but significant interactions are observed when mixed or ground with either magnesium stearate or lactose, resulting in the lowering of the melting points of both excipients. This work represents the first study of the physical processing and solid state chemistry of CB[n]s for pharmaceutical formulation and represents an important development step in the use of CB[n]s as drug delivery vehicles.

Light-controllable coherent backscattering from water suspension of lithium niobate microcrystalline particles

We experimentally study coherent backscattering of light for a water suspension of lithium niobate microcrystalline particles. Light-controllable weak localization of photons in a suspension is demonstrated for the first time to our knowledge. The effect is attributed to the reorientation of microcrystalline particles in the field of a linearly polarized pump beam. Thus the isotropic suspension becomes partially anisotropic.

The use of modeling in spray drying of emulsions and suspensions accelerates formulation and process development

In respiratory drug delivery, porous, lipid-based microparticles have shown performance advantages over microcrystalline particles ( Hirst et al., 2002). These engineered particles are manufactured by spray drying of emulsions or suspensions. The purpose of this work is to combine an understanding of underlying mechanisms with particle characterization data to develop models in support of a quality-by-design (QbD) approach to drug development. Powders were manufactured using a laboratory scale spray dryer. A thermodynamic model was developed for the spray drying process, allowing prediction of outlet temperature and powder residual water content. A stochastic model based on a Monte-Carlo simulator was developed to analyze the effects of relevant parameters on the aerodynamic size of the particles; modeled results were verified by comparison to measured aerodynamic size distributions of spray-dried powders. These modeling techniques allowed rank-ordering of the relative importance of formulation and process variables, and aided in developing an understanding of the drying unit operation.

Analysis of Compositionally and Structurally Graded Si:H and Si1−xGex:H Thin Films by Real Time Spectroscopic Ellipsometry

ABSTRACTSilicon-germanium (Si1−xGex:H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating intermediate and low H2-dilution material layers, which have been designed to produce predominately amorphous films with a controlled distribution of microcrystalline particles. The compositional evolution of alloy-graded a-Si1−xGex:H has been studied as well using similar methods. In each case, depth profiles of microcrystalline content, fμc, or Ge content, x, have been extracted. Additionally, real time spectroscopic ellipsometry has been used to monitor post-deposition exposure of a-Si:H, a-Si1−xGex:H, and a-Ge:H films to a hydrogen plasma in situ in order to determine sub-surface amorphous film modification similar to that which would occur when a highly H2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhanced performance of Si:H based solar cells, through controlled bandgap grading using compositionally graded amorphous binary alloys (a-Si1−xGex:H) or the incorporation of controlled fractions of microcrystallites into bulk amorphous i-layer materials, and by providing a fundamental understanding of the modification of component layers during the deposition of subsequent layers in multilayer stacks.

Studies of the diamond formation processes in glow → spark discharge

The formation of diamond microcrystalline particles of sizes 1.5 to 5 μm in the proceeding of a discharge at the direct current in the hydrogen atmosphere (100 Torr) is described. From the analysis of Raman spectra of the particles and their structures it has been found that they are diamonds of various habits. The particle growth rate (about 5 μm/s) is extremely high. It has been shown that the particles do not grow on a substrate and the hypothesis has been put forward that they form through the liquid phase of carbon. The particles have been revealed whose spectra exhibit new features at 819, 1063 and 1320 cm−1. A sharp intensive peak at 1320 cm−1 is a characteristic of an agglomerate of ultradispersed diamond.

Chemical co-precipitation synthesis and photoluminescence of Eu 3+ or Dy 3+ doped Zn 3Nb 2O 8 microcrystalline phosphors from hybrid precursors

Dy 3+, Eu 3+ activated Zn 3Nb 2O 8 phosphors were synthesized via a modified chemical co-precipitation technology with the different concentration. In order to obtain the hybrid precursors, the rare earth coordination polymers with salicylic acid were used as precursors and the polyethylene glycol (PEG) was used as dispersing media. Their microstructure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and scanning electronic microscope (SEM), which indicates that there exist some novel column-like microcrystalline particles with 0.5–5.0 μm sizes in dimension. The characteristic transition of Dy 3+ and Eu 3+ were identified in the emission spectra and the optimum concentration of activators in Zn 3Nb 2O 8 was found.

Wetting and Spreading of a Surfactant Film on Solid Particles: Influence of Sharp Edges and Surface Irregularities

In addition to particle size and surface chemistry, the shape of particles plays an important role in their wetting and displacement by the surfactant film in the lung. The role of particle shape was the subject of our investigations using a model system consisting of a modified Langmuir-Wilhelmy surface balance. We measured the influence of sharp edges (lines) and other highly curved surfaces, including sharp corners or spikes, of different particles on the spreading of a dipalmitoylphosphatidyl (DPPC) film. The edges of cylindrical sapphire plates (circular curved edges, 1.65 mm radius) were wetted at a surface tension of 10.7 mJ/m2 (standard error (SE) = 0.45, n = 20) compared with that of 13.8 mJ/m2 (SE = 0.20, n = 20) for cubic sapphire plates (straight linear edges, edge length 3 mm) (p < 0.05). The top surfaces of the sapphire plates (cubic and cylindrical) were wetted at 8.4 mJ/m2 (SE = 0.54, n = 20) and 9.1 mJ/m2 (SE = 0.50, n = 20), respectively, but the difference was not significant (p > 0.05). The surfaces of the plates showed significantly higher resistance to spreading compared to that of the edges, as substantially lower surface tensions were required to initiate wetting (p < 0.05). Similar results were found for talc particles, were the edges of macro- and microcrystalline particles were wetted at 7.2 mJ/m2 (SE = 0.52, n = 20) and 8.2 mJ/m2 (SE = 0.30, n = 20) (p > 0.05), respectively, whereas the surfaces were wetted at 3.8 mJ/m2 (SE = 0.89, n = 20) and 5.8 mJ/m2 (SE = 0.52, n = 20) (p < 0.05), respectively. Further experiments with pollen of malvaceae and maize (spiky and fine knobbly surfaces) were wetted at 10.0 mJ/m2 (SE = 0.52, n = 10) and 22.75 mJ/m2 (SE = 0.81, n = 10), respectively (p < 0.05). These results show that resistance to spreading of a DPPC film on various surfaces is dependent on the extent these surfaces are curved. This is seen with cubic sapphire plates which have at their corners a radius of curvature of about 0.75 microm, spiky malvaceae pollen with an even smaller radius on top of their spikes, or talc with various highly curved surfaces. These highly curved surfaces resisted wetting by the DPPC film to a higher degree than more moderately curved surfaces such as those of cylindrical sapphire plates, maize pollens, or polystyrene spheres, which have a surface free energy similar to that of talc but a smooth surface. The macroscopic plane surfaces of the particles demonstrated the greatest resistance to spreading. This was explained by the extremely fine grooves in the nanometer range, as revealed by electron microscopy. In summary, to understand the effects of airborne particles retained on the surfaces of the respiratory tract, and ultimately their pathological potential, not only the particle size and surface chemistry but also the particle shape should be taken in consideration.

Matrix-inducing synthesis and luminescence of microcrystalline red phosphors YVO4:Pb2+,Eu3+ derived from the in situ coprecipitation of hybrid precursors

Using rare-earth coordination polymers with o-hydroxylbenzoate as a precursor, composing with polyvinyl alcohol as a dispersing medium, a novel red-emitting material of YVO4:xPb2+, yEu3+ (x=0, 1.0, 1.2, 1.5, 1.8, 2.0, and 5.0 mol %; y=5 mol %) was synthesized by an in situ coprecipitation process. Its microstructure and micromorphology have been analyzed by x-ray powder diffraction and scanning electronic microscopy, which indicates that there exist some novel cobblestone-like microcrystalline particles. With Pb2+ as a sensitizer, these materials all exhibit strong red emission near 618 nm due to the 5D0 → 7F2 transition of Eu3+ ions. At x=1.5, YVO4:Pb2+, Eu3+ shows the strongest emission intensity, which indicates an efficient energy transfer from Pb2+ to Eu3+.

In situ chemical co-precipitation synthesis of YVO4:RE (RE = Dy3+, Sm3+, Er3+) phosphors by assembling hybrid precursors

YVO4:RE (RE=Dy3+, Sm3+, Er3+) were prepared via an in situ chemical co-precipitation technology, and the assembly process of hybrid precursors was as follows: using rare earth coordination polymers with salicylic acid as precursors and composing with the polyvinyl alcohol (PVA) as dispersing media. Their microstructure and micromorphology have been analyzed by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), which indicate that there exist some novel cobblestone-like microcrystalline particles. All the doped rare earth ions showed their characteristic emissions in YVO4 hosts. The concentration quenching all appeared of the three dopant ions and the optimum concentrations for Dy3+, Er3+, Sm3+ were determined to be 2, 3, 1mol% in yttrium vanadate particles, respectively.