Synthesis of Y2O3:(Li,Eu) films using phosphor powders coated with SiO2 nano particles

Y_1.9−xLi_0.1Eu_xO₃ (x=0.02, 0.05, 0.08, and 0.12) films were fabricated by spin-coating method. A colloidal silica suspension with Y_1.9−xLi_0.1Eu_xO₃ phosphor powder was exploited to obtain the highly stable and effective luminescent films onto the glass substrate. After heating as-prepared Y_1.9−xLi_0.1Eu_xO₃ films at 700 °C for 1 h, the phosphor films exhibit a high luminescent brightness as well as a strong adhesiveness on the glass substrate. The emission spectra of spin-coated and pulse-laser deposited Y_1.82Li_0.1Eu_0.08O₃ films were compared. The cathodoluminescence of the phosphor films was carried out at the anode voltage 1 kV.     

Incorporation of clay nano-particles in aqueous foams

During the process of crude oil/gasoline loading and storage, significant amounts of volatile organic compounds (VOCs) can be emitted to the environment. Stable aqueous foams can be spread as a flexible blanket on the top of the oil to control the VOC emission by providing a mass transfer barrier during the loading process. In this work, novel aqueous foams have been formulated by incorporating clay nano-particles in an aqueous solution of surfactants and polymers. The stability and mass transfer resistance of these foams were investigated at temperatures up to 125 F. In the presence of VOC, clay decreases the rate at which the liquid is drained out of the foam lamellae and increases the foam drainage half-life. These foams were found to be very stable in the presence of gasoline and crude oil and can last much longer than one day at the room temperature. The use of clay in the foam formulation reduces vapor diffusion through the lamellae and vapor emission through the foam column significantly for the first 10 h. Increase in temperature increases the rate of foam breakage due to higher water evaporation and lower liquid viscosity. In spite of this increase, the 0.5% polymer and 0.5% clay foam suppresses vapor emission from a gasoline longer than 3600, 1500 and 1100 min at 75 F, 105 F and 125 F, respectively. This foam also suppresses vapor emission from a crude oil longer than 4200, 2000 and 700 min at 75 F, 105 F and 125 F, respectively.     

Oxidation of CO on Fe2O3 model surfaces

Using first principles calculations based on a gradient corrected density functional formalism we show that Fe₂O₃ nano-particles with (1 0 0) and (0 0 0 1) surface orientations can oxidize CO to form CO₂ with or without the presence of O₂. However, depending on the surface orientation, the oxidation occurs through differing sequences. On the (1 0 0) surface, in the absence of O₂, two CO molecules are required for one CO oxidation in a concerted reaction while on a oxygen terminated (0 0 0 1) surface, a single CO molecule itself, without the aid of a second CO, can react with the lattice oxygen atoms to form CO₂. In the presence of O₂, the O vacancies created by an initial oxidation through lattice oxygen act as the favored sites for O₂ adsorption which can subsequently oxidize the incoming CO. Detailed reaction paths and the corresponding energetics for the proposed mechanisms are also studied.     

Computer simulations of the effect of atomic structure and coordination on the stabilities and melting behaviour of copper surfaces and nano-particles

We have studied the structures and stabilities of copper nano-particles and the melting properties of copper surfaces using interatomic potential-based molecular dynamics simulations, where the (1 1 1) surface has been shown to be the most stable in terms of surface energy and melting behaviour. Low energy shapes of nano-particles are influenced by the surfaces present and therefore have a higher proportion of (1 1 1) surface. The effect of surface structure on stability becomes less marked as the size of the nano-particle is increased. Melting is observed to occur below the bulk melting temperature in all the surfaces investigated, at increasingly lower temperatures from the (1 1 1), (1 0 0), (1 1 0) down to the (2 1 0) surface, confirming their order of decreasing stability. The melting processes of defective close-packed copper surfaces were also simulated. Steps, kinks, and facets were all shown to accelerate the melting of the surfaces. The melting is shown to initiate at the site of the defect and the results demonstrate that it is the low-coordinated atoms, at the step edge or kink, that are more mobile at lower temperatures. These features facilitate surface melting even further below the melting temperature than was observed for the perfect surfaces. Furthermore, facets of (1 0 0) surface were shown to be unstable even at moderate temperatures on the close-packed surface.     

Tuning of particle plasmon resonances in binary dielectric medium

Using light scattering spectroscopy, I demonstrate an approach to tune particle plasmon resonance in a binary dielectric media where silver nano-rods are embedded partially both in Anodic Aluminum Oxide (AAO) matrix and in air. A systematic experimental study under a controlled variation of the degree of embedding of nano-rods in AAO matrix has been presented. Experimental results have been interpreted based on the Drude model. Finite Difference Time Domain (FDTD) method has been employed to calculate the nature of the silver nano-rod resonance at the experimental conditions. Both the simulation results and theory corroborate the experimental findings.     

含树枝状大分子PAMAM的苯乙烯乳液聚合

将树枝状大分子PAMAM (4 5代 )作为种子 ,以苯乙烯为代表性单体进行乳液聚合 .研究结果表明 ,加入树枝状大分子PAMAM时 ,所制得的聚合物乳液粒子平均粒径在 30～ 5 0nm之间 ,小于 10 0nm ,且大小分布均匀 ;所制备的聚合物在 16 70cm- 1 左右处出现酰胺的特征吸收峰 ,在 330 0cm- 1 左右处出现N—H伸缩振动特征峰 ;说明树枝状大分子PAMAM起到种子的作用 ,所制备的聚合物含树枝状大分子PAMAM .     

Synthesis and band-gap photoluminescence from cadmium phosphide nano-particles

Cadmium phosphide (Cd₃P₂) when synthesized from the direct reaction of cadmium metal salt and tri-octylphosphine (TOP) in presence of sodium metal showed band-gap emissions with engineered band-gap energy in between 2.85 and 2.75 eV. Optical studies showed pronounced quantum confinement effect from nano-particles so prepared. X-ray diffraction (XRD) pattern of black powders revealed hexagonal Cd₂P₃ crystal structure. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed mixed morphology of fluffy particles likely to be amorphous in nature. Far-infrared (far-IR) spectroscopy revealed peaks associated with (Cd₃P₂).     

Layered double hydroxides: a novel nano-sorbent for solid-phase extraction

The nickel–aluminum layered double hydroxide (Ni–Al LDH) was synthesized by a simple co-precipitation method with controlled pH and followed by hydrothermal treatment. The obtained nano-structured inorganic material was employed, for the first time, as a new solid-phase extraction (SPE) sorbent for the extraction and pre-concentration of trace levels of fluoride ions from aqueous solutions. An indirect method was used for monitoring of extracted fluoride ions. The method is based on the quenching effect of extracted fluoride ions upon the fluorescence intensity of Al–oxine complex via the forming of AlF₆³⁻, which was determined spectrofluorometrically at λ_em = 510 nm with excitation at λ_ex = 404 nm. The effect of several parameters such as type of interlayer anion in Ni–Al LDH structure, pH, sample flow rate, elution conditions, amount of nano-sorbent, sample volume and co-existing ions on the extraction efficiency of the analyte were investigated. The results showed that fluoride ions could be retained on the Ni–Al (NO₃⁻) LDH at pH 6.0 and stripped by 1.2 mL of 3.0 mol L⁻¹ NaOH. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 9.0 ng mL⁻¹ and 50, respectively. The optimized method was successfully applied to the determination of fluoride concentration in various water samples. The results obtained from the proposed method were successfully compared with those provided by standard SPADNS method.     

Synthesis of nano hydroxyapatite powder that simulate teeth particle morphology and composition

A simple sol–gel precipitation technique to synthesize nano hydroxyapatite (HA) particles (30 nm) that show similar morphology, size and crystallinity to HA crystals of human teeth is reported. Calcium nitrate tetrahydrate and potassium dihydrogenphosphate were used as calcium and phosphorus precursors, respectively. Double distilled water was used as a diluting media for HA sol preparation and ammonia was used to adjust the pH to 11. After aging, the HA gel was dried at 40 °C and calcined to different temperatures ranging from 200 to 600 °C. The dried and calcined powders were characterized for phase composition using X-ray diffractrometry, and Fourier transform infra-red spectroscopy. The particle size and morphology was studied using Transmission electron microscopy. The particle size distribution analysis of HA powders showed skewed distribution plot. The phase and particle characterization studied above showed that HA calcined at 600 °C simulate HA crystals of teeth.     

高分子单链的研究进展

随着纳米科技在高分子领域的不断升温,高分子单链凝聚态的研究引起了人们的广泛重视。高分子单链以纳米尺度的微粒孤立存在,不存在分子链之间的几何缠结。本文综述了近年来国内外高分子单链的研究进展。首先介绍了高分子单链的主要制备方法如喷雾法、冷冻干燥法、微乳液聚合法、反向沉淀法以及表面扩展膜法,接着详细介绍了高分子单链的表征技术及高分子链构象的计算机模拟技术,最后介绍了高分子单链及单分子胶束在制备金属纳米粒子领域的应用,并展望了高分子单链的研究领域和方向。