Huixuan Wang

Biosynthesis of silver and gold nanoparticles by novel sundried Cinnamomum camphora leaf

The synthesis of nanocrystals is in the limelight in modern nanotechnology. Biosynthesis of nanoparticles by plant extracts is currently under exploitation. Not only could silver nanoparticles ranging from 55 to 80 nm in size be fabricated, but also triangular or spherical shaped gold nanoparticles could be easily modulated by reacting the novel sundried biomass of Cinnamomum camphora leaf with aqueous silver or gold precursors at ambient temperature. The marked difference of shape control between gold and silver nanoparticles was attributed to the comparative advantage of protective biomolecules and reductive biomolecules. The polyol components and the water-soluble heterocyclic components were mainly responsible for the reduction of silver ions or chloroaurate ions and the stabilization of the nanoparticles, respectively. The sundried leaf in this work was very suitable for simple synthesis of nanoparticles.

Rapid preparation process of silver nanoparticles by bioreduction and their characterizations

Abstract Bioreduction as a novel nanoparticle synthesizing technology attracts increasing attention. Dried cells of the bacterium Aeromonas sp. SH10 rapidly reduced [Ag(NH 3 ) 2 ] + to Ag 0 in the solution into which some amount of OH − was introduced. The surface plasmon resonance centered at 425 nm on the UV-vis spectra and five broad Bragg reflections on the XRD pattern showed that stable silver nanoparticles were formed during the bioreduction process. TEM and SEM observations suggested that the silver nanoparticles were uniform in size and well dispersed on the cells and in the solution. Therefore, silver nanoparticles could be prepared rapidly by this bioreduction technology.

Quantitative nucleation and growth kinetics of gold nanoparticles via model-assisted dynamic spectroscopic approach

Lacking of quantitative experimental data and/or kinetic models that could mathematically depict the redox chemistry and the crystallization issue, bottom-to-up formation kinetics of gold nanoparticles (GNPs) remains a challenge. We measured the dynamic regime of GNPs synthesized by l-ascorbic acid (representing a chemical approach) and/or foliar aqueous extract (a biogenic approach) via in situ spectroscopic characterization and established a redox-crystallization model which allows quantitative and separate parameterization of the nucleation and growth processes. The main results were simplified as the following aspects: (I) an efficient approach, i.e., the dynamic in situ spectroscopic characterization assisted with the redox-crystallization model, was established for quantitative analysis of the overall formation kinetics of GNPs in solution; (II) formation of GNPs by the chemical and the biogenic approaches experienced a slow nucleation stage followed by a growth stage which behaved as a mixed-order reaction, and different from the chemical approach, the biogenic method involved heterogeneous nucleation; (III) also, biosynthesis of flaky GNPs was a kinetic-controlled process favored by relatively slow redox chemistry; and (IV) though GNPs formation consists of two aspects, namely the redox chemistry and the crystallization issue, the latter was the rate-determining event that controls the dynamic regime of the whole physicochemical process.

Biosynthesized Ag/α-Al2O3 catalyst for ethylene epoxidation: the influence of silver precursors

Biosynthesized Ag/α-Al2O3 catalysts toward ethylene epoxidation were prepared with Cinnamomum camphoratrees (CC) extract using AgNO3, silver–ammonia complex ([Ag (NH3)2]+) and silver–ethylenediamine complex ([Ag(en)2]+) as the silver precursors. The catalyst from [Ag(en)2]+ demonstrated better activity compared to the catalysts from the other two precursors, 1.41% EO concentration with EO selectivity of 79.1% and 12.0% ethylene conversion were achieved at 250 °C. To investigate the influence of silver precursors on the catalytic performance, three catalysts were characterized by XRD, UV-Vis, XPS, SEM and O2-TPD techniques. The results indicated that [Ag(en)2]+ precursors could be reduced more effectively by CC extract, and Ag particles were successfully immobilized onto the α-Al2O3 support under mild conditions. Moreover, a silver defects surface on the Ag/α-Al2O3 catalyst from [Ag(en)2]+ precursors had the best oxygen activation ability, playing an important role in the generation of electrophilic oxygen species which were responsible for the epoxidation reaction of CC to EO.

Stable Silver Nanoparticles with Narrow Size Distribution Non-enzymatically Synthesized by Aeromonas sp SH10 Cells in the Presence of Hydroxyl Ions

Fundamental Research Funds for Central Universities [2010121051]; NSFC projects [21106117, 21036004, 20976146]; Research Fund for the Doctoral Program of Higher Education of China [20100121110032, 20110121120018]; NSF-Fujian projects [2010J05032]

Preparation of Ag/α-Al2O3 for ethylene epoxidation through thermal decomposition assisted by extract of Cinnamomum camphora

An Ag/α-Al2O3 catalyst designed for application in the epoxidation of ethylene was prepared through thermal decomposition assisted by extract of Cinnamomum camphora. The effects of the reaction parameters on the catalytic performance were evaluated, including the extract concentration, calcining temperature and calcining time. The results demonstrated that the thermal decomposition should be conducted at 600 °C in N2 for 60 min, assisted by 0.25 g mL−1Cinnamomum camphora extract. Compared with a simple thermal decomposition method, the sintering and aggregation of Ag particles and Ag loss during the reaction were alleviated by the presence of the catalyst that had been synthesized with the assistance of biomass.

Transfer of Biosynthesized Gold Nanoparticles from Water into an Ionic Liquid Using Alkyltrimethyl Ammonium Bromide: An Anion-Exchange Process

Biosynthesized gold nanoparticles (GNPs) were transferred from water to a hydrophobic ionic liquid (IL), [Bmim]PF(6), with the assistance of alkyl trimethyl ammonium bromide. The phase transfer mechanism was illustrated through the exemplification of cetyltrimethyl ammonium bromide (CTAB). Interaction between GNPs and CTAB was demonstrated through zeta potential analysis. Moreover, an anion-exchange process was discovered between CTAB and IL. During the process, the hydrophobic CTAPF(6) formed in situ on the GNPs led to the hydrophobization and thus phase transfer of the GNPs. The phase transfer efficiency was found to be size-dependent.