Keao Hu

The depolymerization mechanism of chitosan by hydrogen peroxide

Water-soluble chitosan with low molecular weight was prepared by the depolymerization of chitosan with aqueous H2O2 solution. The IR and 1H-NMR studies verify that depolymerization leads to the breakage of 1,4-β-D-glucoside bonds of chitosan. X-ray analysis shows the depolymerization takes place at the surface of the chitosan in crystal region by so called peeling-off process while the amorphous portion is depolymerized by penetrating pattern.

Tunable growth of nanodendritic silver by galvanic-cell mechanism on formed activated carbon

Well-defined silver dendritic nanostructures have been prepared in large quantities in an ambient environment using formed activated carbon (FAC) only. A reasonable mechanism (step 1: reduction by surface reductive groups; step 2: growing in the form of a galvanic cell) is suggested.

Formation of TiB2/TiN nanocomposite powder by high energy ball milling and subsequent heat treatment

Abstract TiB 2 /TiN nanocomposite powder was fabricated by high energy ball milling and subsequent heat treatment. The microstructure development of the powder mixtures was monitored by X-ray diffraction, differential scanning calorimeter, scanning electron microscopy and transmission electron microscopy. It was found that TiN formed within 30 h of milling. After 40 h of milling, the resulting powder mixture was composed of a small amount of nanosized TiN particles, nanocrystalline Ti and amorphous phase. The nanocrystalline Ti and amorphous phase were transformed into TiN and TiB 2 after subsequent heat treatment.

Green “planting” nanostructured single crystal silver

Design and fabrication of noble metal nanocrystals have attracted much attention due to their wide applications in catalysis, optical detection and biomedicine. However, it still remains a challenge to scale-up the production in a high-quality, low-cost and eco-friendly way. Here we show that single crystalline silver nanobelts grow abundantly on the surface of biomass-derived monolithic activated carbon (MAC), using [Ag(NH3)2]NO3 aqueous solution only. By varying the [Ag(NH3)2]NO3 concentration, silver nanoplates or nanoflowers can also be selectively obtained. The silver growth was illustrated using a galvanic-cell mechanism. The lowering of cell potential via using [Ag(NH3)2]+ precursor, together with the AgCl crystalline seed initiation, and the releasing of OH− in the reaction process, create a stable environment for the self-compensatory growth of silver nanocrystals. Our work revealed the great versatility of a new type of template-directed galvanic-cell reaction for the controlled growth of noble metal nanocrystals.

From crabshell to chitosan-hydroxyapatite composite material via a biomorphic mineralization synthesis method.

Hydroxyapatite–polymer composite materials, as biological bone tissue materials, have become an important research direction. In this paper, the calcium carbonate from the crabshells was transformed into hydroxyapatite by a hydrothermal process. According to the method that we called Biomorphic Mineralization synthesis, we obtained a novel kind of hydroxyapatite-chitosan composite materials which reserved the natural perfect structure of the original crabshells. Benefited from its fine micro-structure as the crabshells, this kind of materials held a high value of tensile modulus, which is expected to be promising bone tissue engineering applications.

Synthesis of 10 nanometric copper clusters in a polymer matrix by a solution‐reduction synthesis (SRS)

Nanometric metal clusters in a polymer host were synthesized by a solution-reduction route in a swelling cathode film (SCF) containing metal ions (such as Cu2+). The TEM results show that the scale of the clusters is about 10 nanometers and the distribution of their diameter is very narrow. The X-ray diffraction and the electron diffraction patterns confirm that the reduced clusters are the crystallites of metal (copper). The scale of nanometric clusters is affected by the electrochemical conditions in the reactions.

Relationship between structures of polyacrylonitrile (PAN)-copper gradient composite film and electrochemical-reaction conditions

In this article, the relationship between the morphological structure and electrochemical conditions, the crystal structure in the electrochemical deposited phase, and the thermal properties of polyacrylonitrile (PAN)-copper gradient composite films ( GCF ) were studied. The results showed that the morphology of the GCF depended very much on the electrochemical conditions used in the reactions. The percent area of the deposited phase on the cross section of the GCF decreases with increases of the predrying time of the solution coated on the cathode, the power voltage, and the temperature in the electrochemical reactor. According to the data of a differential scanning calorimeter and a scanning electronic microscope, PAN chains are physically crosslinked by a deposited phase. Under the electrochemical conditions used in this article, the components of PAN are not affected by the electrochemical reactions.

Synthesis, characterization and structural analysis of polylactide grafted onto water-soluble hydroxypropyl chitin as backbone

Brush-like polylactide grafted onto water-soluble hydroxylpropyl chitin as backbone is investigated. The copolymers are synthesized by ring-opening melting polymerization using stannous octoate as catalyst. The structure of the branched polymers is characterized by IR spectrometry and ~1H-NMR. The reaction is carried out fluently under the feeding ratio of hydroxylpropyl chitin to lactide being 5:1,8:1,10:1 1 respectively The length of the branched polylactide increases with the lactide content in the feed. The result of the ~1H-NMR demonstrates that the most length of the branched polylactide is about 5 or so.

Ce0.8M0.2O2−δ(M=Mn,Fe,Ni,Cu) as SOFC Anodes for Electrochemical Oxidation of Hydrogen and Methane

Oxide anodes such as doped ceria offer improved tolerance for nonidealities in anode environment such as redox cycles, sulfur and other poisons, and hydrocarbons. Mixed-valence transition element in ceria provides an additional redox couple besides Ce 4+ /Ce 3+ in reduced atmosphere, facilitating its electrocatalytic reaction for oxidation of fuels. This paper presents the electrochemical characteristics of Ce 0.8 M 0.2 Ο 2-δ (M =Mn,Fe,Ni,Cu) for oxidation of hydrogen and methane. Ce 0.8 M 0.2 O 2-δ was synthesized, and crystal phase analysis by X-ray diffraction was performed. Single-phase Ce 0.8 M 0.2 O 2-δ (M=Mn,Fe,Ni) were formed. A second phase, CuO, was found in the powders with the nominal composition of Ce 0.8 Cu 0.2 Ο 2-δ Ce 0.8 M 0.2 Ο 2-δ exhibited stability in reducing atmosphere. In comparison, similar microstructural characteristics were found for Ce 0.8 M 0.2 O 2-δ (M = Mn, Fe, Cu). However, Ce 0.8 Ni 0.2 O 2-δ exhibits poor microstructure with large cracks. The electrochemical oxidation of wet hydrogen and wet methane was investigated with impedance spectroscopy by using the three-electrode configuration. It was found that Ce 0.8 M 0.2 O 2-δ (M = Mn, Fe, Ni, Cu) demonstrates relatively low electrochemical activity in both hydrogen and methane. Regarding low n-type conductivity of transition metal cation-containing ceria, it was suggested that an oxide with a high electronic conductivity be added into the Ce 0.8 M 0.2 O 2-δ matrix for improvement of the electrode performance.

Thermal behaviors of mesocarbon microbeads and physical properties of carbon plates

Mesophase microbeads are a prominent precursor of carbon artifacts with high density and high strength since the powder has significant self-sintering ability. The formation of sintering bridges as a consequence of the liquid-phase sintering at approximately 535°C is inferred by thermal analysis. According to thermogravimetric and DSC analyses, the intensive pyrolysis of MCMBs occurs from about 600 to 800°C and releases volatiles thus resulting in remarkable volume shrinkage. In this work, carbonaceous plates without binder are prepared by cold molding from MCMBs with 2.1 of C/H mole ratio and about 12 μm of average particle size, sintered at three different temperatures of 800, 1150 and 1400°C. A relative higher bulk density of 1710 kg/m3, bending strength of 84 MPa and electrical conductivity of 2.4 S/m are obtained successfully after calcining the plate at 1400°C.