Microorganism-mediated synthesis of chemically difficult-to-synthesize Au nanohorns with excellent optical properties in the presence of hexadecyltrimethylammonium chloride

Fundamental Research Funds for Central Universities [2010121051]; NSFC [21106117, 21036004]Closely packed, size-controllable and stable Au nanohorns (AuNHs) that are difficult to synthesize through pure chemical reduction are facilely synthesized using a microorganism-mediated method in the presence of hexadecyltrimethylammonium chloride (CTAC). The results showed that the size of the as-synthesized AuNHs could be tuned by adjusting the dosage of the Pichia pastoris cells (PPCs). The initial concentrations of CTAC, ascorbic acid (AA) and tetrachloroaurate trihydrate (HAuCl4 center dot 3H(2)O) significantly affected the formation of the AuNHs. Increasing the diameters of AuNHs led to a red shift of the absorbance bands around 700 nm in their UV-vis-NIR spectra. Interestingly, the AuNH/PPC composites exhibited excellent Raman enhancement such that rhodamine 6G with concentration as low as (10(-9) M) could be effectively detected. The formation process of the AuNHs involved the initial binding of the Au ions onto the PPCs with subsequent reduction by AA to form supported Au nanoparticles (AuNPs) based on preferential nucleation and initial anisotropic growth on the platform of the PPCs. The anisotropic growth of these AuNPs, which was influenced by CTAC and PPCs, resulted in the formation of growing AuNHs, while the secondary nucleation beyond the PPCs produced small AuNPs that were subsequently consumed through Ostwald ripening during the aging of the AuNHs. This work exemplifies the fabrication of novel gold nanostructures and stable bio-Au nanocomposites with excellent optical properties by combining microorganisms and a surfactant

Fabrication of Au/Pd alloy nanoparticle/Pichia pastoris composites: a microorganism-mediated approach

Fundamental Research Funds for Central Universities [2010121051]; NSFC projects [21106117, 21036004]Synthesis of metal nanoparticles (NPs) is in the limelight in modern nanotechnology. In this present study, bimetallic Au/Pd NP/Pichia pastoris composites were successfully fabricated through a one-pot microbial reduction of aqueous HAuCl4 and PdCl2 in the presence of H-2 as an electron donor. Interestingly, flower-like alloy Au/Pd NP/Pichia pastoris composites were obtained under the following conditions, NaCl concentration 0.9% (w/v), molar ratio of Au/Pd (1 : 2) and the time for pre-adsorption of Au(III) and Pd(II) ions 15 min, through fresh yeast reduction. The mapping results from scanning transmission electron microscopy (STEM) with a high-angle annular dark field detector confirmed that the Au/Pd NPs on the surface of the yeast were indeed alloy. Furthermore, the energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements showed that the composition of the bimetallic NPs were consistent with the initial molar ratio of the precursors

Microorganism-mediated synthesis of chemically difficult-to-synthesize Au nanohorns with excellent optical properties in the presence of hexadecyltrimethylammonium chloride

Fundamental Research Funds for Central Universities [2010121051]; NSFC [21106117, 21036004]Closely packed, size-controllable and stable Au nanohorns (AuNHs) that are difficult to synthesize through pure chemical reduction are facilely synthesized using a microorganism-mediated method in the presence of hexadecyltrimethylammonium chloride (CTAC). The results showed that the size of the as-synthesized AuNHs could be tuned by adjusting the dosage of the Pichia pastoris cells (PPCs). The initial concentrations of CTAC, ascorbic acid (AA) and tetrachloroaurate trihydrate (HAuCl4 center dot 3H(2)O) significantly affected the formation of the AuNHs. Increasing the diameters of AuNHs led to a red shift of the absorbance bands around 700 nm in their UV-vis-NIR spectra. Interestingly, the AuNH/PPC composites exhibited excellent Raman enhancement such that rhodamine 6G with concentration as low as (10(-9) M) could be effectively detected. The formation process of the AuNHs involved the initial binding of the Au ions onto the PPCs with subsequent reduction by AA to form supported Au nanoparticles (AuNPs) based on preferential nucleation and initial anisotropic growth on the platform of the PPCs. The anisotropic growth of these AuNPs, which was influenced by CTAC and PPCs, resulted in the formation of growing AuNHs, while the secondary nucleation beyond the PPCs produced small AuNPs that were subsequently consumed through Ostwald ripening during the aging of the AuNHs. This work exemplifies the fabrication of novel gold nanostructures and stable bio-Au nanocomposites with excellent optical properties by combining microorganisms and a surfactant

Simple Method for Synthesizing Aluminum-Yttrium Garnet (Nd:YAG) Nanopowders by Flushing (Bubbling) with Ammonia

A simple method is developed for synthesizing nanopowder of neodymium-doped yttrium aluminum garnet (Nd:YAG) by coprecipitation with flushing (bubbling) by ammonia. Different methods are used to study the specimens obtained, such as thermogravimetry/differential scanning calorimetry, X-ray powder diffraction, infrared spectroscopy based on a Fourier transform, scanning electron microscopy. Results show that stoichiometric Nd:YAG powders may be prepared by calcination of a precursor at 900°C for 2 h. In addition, it is detected that a slow ammonia supply rate (5 – 10 ml/min) is favorable for forming Nd:YAG powders with a good structure and with an average particle size of ~70 nm. The technology developed by us does not use manual titration for synthesizing multibasic oxides, as a result of which this technology may be readily used on an industrial scale. ? 2014, Springer Science+Business Media New York

Co-precipitation synthesis and two-step sintering of YAG powders for transparent ceramics

Natural Science Foundation of China [21206079, 21106117, 21036004]Yttrium aluminum garnet (Y3Al5O12, YAG) precursor was synthesized by the co-precipitation method with ammonium hydrogen carbonate as the precipitant. The influence of aging and calcination temperature on the precursor composition and transformation temperature of the YAG phase was investigated. On that basis, a two-step sintering (TSS) method (heating the sample up to 1800 C followed by holding it at 1600 C for 8 h) was used to fabricate bulk transparent YAG ceramics in vacuum (10(-3) Pa) in this communication. A variety of techniques, such as X-ray powder diffraction, infrared spectra, scanning electron microscopy and UV-vis-NIR spectrophotometry were adopted to characterize the resulting YAG powders and ceramics. The results showed that aging had a dramatic effect on the precursor composition, which in turn influenced the transformation temperature of the YAG phase. Loosely agglomerated YAG powders with a mean particle size of 50 nm were obtained by calcinating the precursor without aging at 1000 C. Finally, a transparent YAG ceramic specimen, achieving the in-line transmittance of 41% in the visible wavelength region and a nearly pore-free microstructure with uniform grains of about 4 mu m, was produced via the TSS technique. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Calcified Shrimp Waste Supported Pd NPs as an Efficient Catalyst toward Benzene Destruction

Shrimp waste (SW) was calcified to CaCO3 and CaO with variant morphologies by simple calcination in air and used as efficient support for Pd NPs (<7 nm) in benzene oxidation. A combination of in situ diffuse reflectance fourier transform (DRIFT), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were utilized to study the physicochemical properties and reveal the possible oxidation mechanism. The existence of both Pd2+ and Pd0 was essential for the oxidation activity. The 0.5-Pd/SW@600 catalyst with low activation energy (Ea = 50 kJ/mol) presented the best activity among the calcified SW supports. The observed performances correlated with the high Pd metal dispersion, the nature and morphology of the support, and the synergistic effect between the small Pd NPs and the SW support. In addition, the catalyst showed desirable stability and exceptional reusability, being highly resistant to CO2 and H2O vapor. Considering their green, high efficiency, but cost-effective nature, the biogenic Pd/SW catalysts are promising catalysts, and a million tons of SW can find application as support in benzene abatement. © 2019 American Chemical Society

Microorganism-mediated, CTAB-directed synthesis of hierarchically branched Au-nanowire/Escherichia coli nanocomposites with strong near-infrared absorbance

BACKGROUND: The facile use of microorganisms as green templates for shape-control of Au nanostructures can not only utilize their characteristic nanoscale dimensions and versatility, but also bridge the gap between bulk materials and Au nanostructures for technical applications. RESULTS: Using Escherichia coli cells (ECCs), closely packed, hierarchically branched, chemically difficult-to-synthesize and stable Au nanowires (AuNWs) were fabricated through a seedless microorganism-mediated, hexadecyltrimethylammonium bromides (CTAB)-directed method. The ECCs played dual roles in the biosorption of Au ions and acted as preferential nucleation sites for Au nanocrystals in the formation of the AuNWs. In addition, proper CTAB concentration and just a little excessive ascorbic acid were essential to the formation of the AuNWs. The preferential nucleation sites that were simultaneously mediated by adjacent cells favored branched growth. Random growth of the same nanowire with multiple branched points gave rise to hierarchically branched AuNWs. Interestingly, the AuNW/ECC nanocomposites exhibited a noticeable absorbance at around 1900 nm in the near-infrared (NIR) region. CONCLUSION: This study verifies the general strategy by combining a microorganism and CTAB for the fabrication of functional AuNW/microorganism nanocomposites. ? 2013 Society of Chemical Industry