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Junchao Huang

Publications and source records attributed to Junchao Huang.

6 recordsLinked to original sources
PubMed2005

Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell.

Nanosized Pt, PtRu, and Ru particles were prepared by a novel process, the hydrosilylation reaction. The hydrosilylation reaction is an effective method of preparation not only for Pt particles but also for other metal colloids, such as Ru. Vulcan XC-72 was selected as catalyst support for Pt, PtRu, and Ru colloids, and TEM investigations showed nanoscale particles and narrow size distribution for both supported and unsupported metals. All Pt and Pt-rich catalysts showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Ru and Ru-rich alloys were more typical of a hexagonal close-packed (hcp) structure. As evidenced by XPS, most Pt and Ru atoms in the nanoparticles were zerovalent, except a trace of oxidation-state metals. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results concluded that some alloy catalysts showed higher catalytic activities and better CO tolerance than the Pt-only catalyst; Pt56Ru44/C have displayed the best electrocatalytic performance among all carbon-supported catalysts.

Electrochemistry↗
PubMed2005

A DFT study of the amination of fullerenes and carbon nanotubes: reactivity and curvature.

The first principles density functional theory (DFT) approach (GGA-PW91/DNP) was used to study the addition reaction of methylamine to fullerenes C(50) and C(60) or single-walled carbon nanotubes (SWNTs) (5,5) and (10,0). To understand the relationship between reactivity and curvature, various addition sites have been investigated for comparisons. The DFT calculation results showed that the reaction energy of the addition of methylamine onto C(60) or the closed caps of (5,5) and (10,0) is rather low. Moreover, the reaction at a few sites even appears exothermic. However, the reaction on the perfect sidewall of the nanotubes is always endothermic, and the reaction energy is much higher than that on the caps. The energetically preferable addition sites are the carbon atoms located at the vertexes formed with five-, five-, six-membered rings on C(50) or five-, five-, seven-membered rings on defects of nanotubes. The systematic theoretical study revealed that the pyramidalization and pi-orbital misalignment could result in an increased reactivity of these pentagon-pentagon fusion sites. The reactivity depends on the pyramidalization angle, which is a quantitative measurement of the local curvature and strain of the reaction center.

Journal Article↗
PubMed2005

Platinum nanoparticles from the hydrosilylation reaction: capping agents, physical characterizations, and electrochemical properties.

Platinum nanoparticles synthesized by a unique synthetic approach, the hydrosilylation reaction, have been reported previously. However, the interaction between the underlying platinum nanosupport and the capping agents is poorly understood. Here we continue to investigate Pt nanoparticles from the hydrosilylation reaction to address this issue and present the characterization results of nuclear magnetic resonance, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. These characterization results conclude that two different modes of binding of the aliphatic capping agents with the platinum surface are attributed to the formation of Pt-C bonds under excess olefin concentration and Pt-Si bonds under excess hydrosilane concentration. Morphology and UV-vis spectra of the platinum nanoparticles were explored by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. Moreover, electrochemical properties of the platinum nanoparticles were also studied by cyclic voltammetry and chronoamperometry.

Journal Article↗
PubMed2004

Highly efficient luminescent organic clusters with quantum dot-like properties.

Organic clusters with uniform structure and size have been synthesized and studied. The quantum confinements on organic arms [chains shorter than exciton Bohr radii (aB)] have been confirmed by the discrete energy levels from PLE, narrow PL lines, size effect from UV, and spherical shape from TEM, as well as Raman peaks red-shifting and broadening. The results indicate the materials have QD-like properties.

Journal Article↗
PubMed2004

The effect of salt and pH on the phase-transition behaviors of temperature-sensitive copolymers based on N-isopropylacrylamide.

The salt and pH effects on the phase transition behaviors of temperature-sensitive hydrophilic and amphiphilic polymers containing copolymers of N-isopropylacrylamide as hydrophilic segments were investigated by UV and dynamic light scattering studies. The polymers used for this study include two hydrophilic polymers of HO-terminated poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (1) and HO-functionalized poly(N-isopropylacrylamide-co-N-hydroxylmethylacrylamide) (3), and their amphiphilic derivatives of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide) (2) and cholesteryl-grafted poly(N-isopropylacrylamide-co-N-hydroxylmethylacrylamide) (4). With the increase of NaCl concentration, significant salt effects on their phase transition behaviors were observed. (1) Significant decreases in the lower critical solution temperatures of all polymers were observed, the salt effects were also characterized by a newly defined 'phase transition salt concentration'; (2) time-course UV spectroscopic studies showed that the phase transitions became faster and more complete with the increase of NaCl concentration, which were demonstrated by a newly defined 'phase transition constant'; (3) the salt exerted stronger effects on phase transition behaviors of the amphiphilic polymers than that of the hydrophilic polymers, and on polymer 4 than polymer 2. In contrast, the phase transition behaviors of the polymers were less sensitive to pH. The present studies provide important information for the design and synthesis of temperature-sensitive polymers and polymeric micelles that are important drug delivery carriers for hydrophobic drugs.

Acrylamides↗