Yuan Na Zhu

Synthesis and Properties of Au Nanoparticles with Various Sizes

Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.

Preparation and Photoluminescence of Hybrid SiO2-Coated CdTe Nanocrystals

Novel hybrid SiO2-coated CdTe core-shell nanocrystals (NCs) were fabricated by re-dispersing green-emitting CdTe NCs in a solution of Cd2+ ions, thioglycolic acid (TGA), tetraethyl orthosilicate and ammonia with a sol-gel reaction at room temperature and a further reflux procedure. The hybrid NCs consisted of a CdTe core and a hybrid SiO2 shell with CdS-like clusters. The clusters created by the reaction of Cd2+ and S2- generated by the decomposition of TGA during reflux. The hybrid NCs exhibited tunable photoluminescence (PL) color from green to red and high PL quantum yield (PLQY). The CdS-like clusters play an important role for the hybrid NCs with numerous PL properties. Compared with initial CdTe NCs, the PLQY of the hybrid NCs increased from 18% to 47% together with a red-shifted PL peak wavelength of 61 nm. The average lifetime of the hybrid NCs (39 ns) is longer than that of initial CdTe NCs (25 ns). The high PLQY and the hybrid shell make CdTe NCs an important application for biological technique.

Photoluminescent Properties of TGA-Capped CdTe Quantum Dots

An environmentally friendly synthesis was developed to fabricate aqueous CdTe quantum dots (QDs) using thilglycolic acid (TGA) as a capping agent. Optimal preparation conditions including pH (11.2) and TGA/Cd molar ratio (1.5:1) resulted in CdTe QDs with high photoluminescence (PL) quantum yield up to 56%. The TGA-capped CdTe QDs exhibited tunable PL from green to red. Lifetime measurement indicated that the average lifetime of the TGA-capped QDs increased with increasing their sizes (27.5 and 37.2 ns for the QDs with PL peak wavelength of 607 and 636 nm, respectively). The PL of the QDs revealed the dependence of temperature, in which the QDs exhibited a red-shifted PL peak with increasing temperature. Such PL behavior depended strongly on the QD sizes.

Determination of Trace Copper with Sulfophenylazo Rhodanine by Catalytic Dynamic Spectrofluorimetry

Series new methods were established which were based on the research of determination of trace copper with four sulfophenylazo rhodanine derivatives by catalytic dynamic spectrofluorimetry under the optimum conditions. This proposed method was applied to the determination of copper in real samples with satisfactory results. According to experiment results, the influences of different active groups and substitution positions on fluorescent property of rhodanine derivatives were investigated and the relationship between molecule structure and fluorescent property was explored.

Effect of MoO3 on the Clinkers Formation of Portland Cement

The effects of MoO3 additives on the clinkers mineral formation of portland cement were investigated by X-ray diffraction,scanning electron microscopy. One reference mixture and others modified mixtures, prepared by mixing the blank sample with chemical grade MoO3 were studied. Based on experimental result, MoO3 shows the less positive effect, MoO3 added less than 1wt% was benefit for f-CaO absorbtion, but when more than 1wt% MoO3 was added, with the temperature increasing, increasing the free CaO (f-CaO) content compared with the pure sample,which cound not promote the formation of 3CaO·SiO4. MoO3 can stabilizes crystalline structure of β-2CaO·SiO4. The analysis results for the microstructure indicate that grain size of C3S in the samples with MoO3 is larger than that of only -portland clinker.

Synthesis and Characterization of Nanocrystalline Mg4Nb2O9 by the Modified Sol-Gel Method

Nanosized and highly reactive magnesium niobate Mg4Nb2O9 were successfully synthesized by a sol-gel method as potential candidates for use in microwave applications as a low-temperature co-fired ceramic (LTCC). The Nb-Mg-citric acid solution was evaporated resulting in a dry gel that was calcined in the temperature ranging from 550°C to 850°C for crystallization in air atmosphere. The crystallization process from the gel to the crystalline Mg4Nb2O9 was followed by thermal analysis and during calcinations phase evolution of the powders was studied using X-ray diffraction (XRD) technique. Particle size and morphology were examined by high resolution scanning electron microscopy (HR-SEM). At 850°C the corundum-like phase of magnesium niobate was obtained in air atmosphere with an average particle diameter of 80 nm approximately calculated from the HR-SEM images.

Synthesis and Properties of CdSe/CdXZn1-XS Quantum Dots

Highly luminescent CdSe/CdxZn1-xS core-shell quantum dots (QDs) were synthesized using CdSe cores with the size range of 2 to 5 nm in diameter through a facile organic route. The CdSe cores were prepared by using trioctylphosphine oxide and hexadecylamine as capping agents for the purpose of getting spherical morphology. The cores were coated with an alloy shell to decrease the lattice mismatch between the core and the shell through a facile organic approach. The QDs exhibited tunable photoluminescence (PL) up to 654 nm, narrow PL spectra (less than 40 nm for full width at half maximum) and high PL efficiency. Such properties make the core-shell QDs as a good candidate for further applications.

Facile Synthesis and Properties of CdxZn1-xSe Alloy Nanocrystals

CdxZn1-xSe alloy nanocrystals (NCs) were successfully synthesized by an organic route using oleic acid as a capping agent. The molar ratio of Cd/Zn strongly impact on the PL properties of the alloy NCs. The PL peak wavelength of the alloy NCs was 565 nm at the Cd/Zn molar ratio of 0.05 while their wavelength became 621 nm in the case of the molar ratio of 1. The average lifetime of the alloy NCs increased with increasing the Cd/Zn molar ratios (26 ns for a ratio of 0.05 and 45 ns for a ratio of 1). The X-ray diffraction analysis indicated that the alloy NCs revealed a cubic structure. The Cd/Zn molar ratio drastically affected the crystal structure of the alloy NCs which located between those of ZnSe and CdSe NCs.

SiO2 Beads with Quantum Dots: Synthesis and Bioapplication

Aqueous CdTe and organic CdSe/ZnS quantum dots (QDs) were encapsulated into SiO2 beads using various controlled sol-gel processes. Ligand exchange is a key to adjust the QD number in each bead and get a high photoluminescence (PL). Namely, partial ligand exchange from thioglycolic acid to 3-mercaptopropyotrimethoxysilane (MPS) on the CdTe QDs enables retention of the initial PL efficiency of the QDs in water, while the simultaneous addition of a poor solvent (ethanol) resulted in regulated assembly of the QDs through condensation of hydrolyzed MPS. SiO2 beads thus prepared had, for example, a diameter of 17 nm and contained 3 QDs each. The PL efficiency of these beads was 30%, while the initial PL efficiency was 38% in a colloidal solution. In addition, a method including surface silanization, phase transfer and self-assembly, and SiO2 shell growth has been developed to incorporate multiple hydrophobic CdSe/ZnS QDs into SiO2 beads where they are well suited for bio-application due to their high brightness, less-cytotoxic, and non-blinking nature. To investigate the potential use for labeling in bio-applications, SiO2 beads with multiple QDs were conjugated with IgG using streptavidin-maleimide as linkers. This preparation method is an important step towards fabricating intensely emitting biocompatible SiO2 beads impregnated with semiconductor QDs.