Scott P. Ahrenkiel

Interfacial Synthesis of Gold-Polyaniline Nanocomposite and Its Electrocatalytic Application.

Gold-polyaniline (Au-PANI) nanocomposite was prepared using a simple interfacial polymerization method, performed in an immiscible water/toluene biphasic system using tetrachloroaurate, AuCl4(-) as an oxidant. The formation of Au nanoparticles (AuNPs) or Au-PANI nanocomposite can be controlled to a certain degree by varying the ratio of initial Au(+) and aniline concentrations. Under optimal condition (HAuCl4/aniline ratio is 1:2), green dispersion of Au-PANI nanocomposite is produced in aqueous phase, whose morphology, structure and physicochemical properties are investigated in details. The nanocomposite shows granular morphology with mostly rodlike AuNPs embedded in polymer. It was found that polyaniline in the composite is in the conducting emeraldine salt form, containing high amount of Au (28.85 wt %). Furthermore, the electrical conductivity of the nanocomposite was found to be four-fold higher than that of the polymer itself. In addition, the nanocomposite powder, isolated from the as-prepared aqueous dispersion, can later be easily redispersed in water and further used for various applications. Moreover, the obtained Au-PANI nanocomposite showed excellent electrocatalytic performance toward the electrochemical oxygen reduction reaction (ORR), with high ORR onset potential and good selectivity. This makes it a promising candidate for a new class of Pt-free ORR catalyst.

Self-referenced luminescence thermometry with Sm3+ doped TiO2 nanoparticles

The performance of Sm(3+) doped TiO2 nanoparticles for luminescence temperature sensing was tested over a temperature range from room to 110 °C. The Sm(3+) ions were incorporated into TiO2 nanocrystals using hydrolytic sol-gel route. Microstructural characterization of the obtained material was performed using transmission electron microscopy and x-ray diffraction measurements. Luminescence emission spectra of Sm(3+) doped TiO2 nanoparticles consists of two distinct spectral regions: the high energy region associated with the trap emission of the TiO2 host, and the low energy region with well-resolved emission peaks of the Sm(3+) ions. The ratio between Sm(3+) emission and TiO2 trap emission shows strong temperature dependence, and is tested for temperature sensing. The relative sensor sensitivity was found to be higher than 1% °C(-1) over given temperature range with the maximum value of 10.54% °C(-1) at 57.5 °C. Lifetime data derived from the Sm(3+) emission decay revealed that time-resolved measurements provide comparable quality of temperature sensing as corresponding ratiometric measurements, with a maximum relative sensitivity of 10.14% °C(-1) at 66.5 °C.

The influence of reaction media on CdIn2S4 and ZnIn2S4 nanocrystallite formation and growth of mesocrystal structures

A hot-injection method for the synthesis of CdIn2S4 in three different compositions of organic media/solvents was studied. Nanosized CdIn2S4 is successfully synthesized in an oleic acid/oleylamine mixture of complexing/capping agents. The obtained mesocrystals of 20–30 nm in diameter are self-organized in marigold-like structures. The estimated band-gap of synthesized semiconductor is in the visible spectral region and has a value of about 2.1 eV. The potential of the band edges is calculated using an empirical equation. The as-prepared material was successfully transferred from organic to aqueous media by using 2-mercaptoethanol in a surface ligand exchange process. Using a similar synthetic procedure, ZnIn2S4 synthesis was performed. The obtained materials were characterized using UV/vis spectroscopy, XRD and TEM. Formation and growth mechanisms of the synthesized materials are proposed.

A Standards-Based Method for Compositional Analysis by Energy Dispersive X-Ray Spectrometry Using Multivariate Statistical Analysis: Application to Multicomponent Alloys

Given an unknown multicomponent alloy, and a set of standard compounds or alloys of known composition, can one improve upon popular standards-based methods for energy dispersive X-ray (EDX) spectrometry to quantify the elemental composition of the unknown specimen? A method is presented here for determining elemental composition of alloys using transmission electron microscopy-based EDX with appropriate standards. The method begins with a discrete set of related reference standards of known composition, applies multivariate statistical analysis to those spectra, and evaluates the compositions with a linear matrix algebra method to relate the spectra to elemental composition. By using associated standards, only limited assumptions about the physical origins of the EDX spectra are needed. Spectral absorption corrections can be performed by providing an estimate of the foil thickness of one or more reference standards. The technique was applied to III-V multicomponent alloy thin films: composition and foil thickness were determined for various III-V alloys. The results were then validated by comparing with X-ray diffraction and photoluminescence analysis, demonstrating accuracy of approximately 1% in atomic fraction.

Synthesis and Characterization of Electrospun Poly(vinyl pyrrolidone) (PVP) and Poly(vinyl alcohol) (PVA) Nanofibers with Au Nanoparticles

S. Mishra,* S. P. Ahrenkiel,* V. V. Vodnik,** Z. V. Saponjic,** and J. M. Nedeljkovic** * Nanoscience and Nanoengineering Ph.D. Program, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA ** Vinca Institute of Nuclear Sciences, P.O. Box 522, 11001 Belgrade, Serbia Electrospinning is an electrical, jet-based method of fabricating nanofibers that involves the application of a very high electrostatic force on the capillary containing the polymer solution or polymer-melt. The fibers are created by an electrically charged jet of the polymer solution, which can be collected on the surface of a grounded template. The incorporation of metal nanoparticles produces functional nanofibers. Among the noble metal nanoparticles, gold nanoparticles are promising because they have electronic, magnetic, optical and catalytic properties [1]. The solution for electrospinning poly(vinyl pyrrolidone) (PVP) nanofibers was prepared by mixing varying concentrations of 10 nm Au nanoparticles-colloidal solution and PVP (average M.W. 1,300,000) in isopropyl alcohol (IPA). The electrospinning was carried out at 15 kV to produce non-woven mats of fibers with diameters ranging from 85 nm to 1 µm. Using a Hitachi H-7000 FA TEM, we could confirm the presence of Au nanoparticles within the amorphous PVP matrix (Fig. 1A and 1B). The distribution of Au nanoparticles in the PVP fibers was completely random. Au/PVA nanocomposite films were prepared by using colloidal solution of Au nanoparticles and poly(vinyl alcohol) (PVA) (average M.W. 72,000) as precursors. A colloidal solution of 0.91 mM Au was prepared [2]. Direct mixing of 1 ml of 5 mass% aqueous PVA solution with 12 ml of 0.91 mM Au colloidal solution lead to formation of stable transparent PVA/Au dispersion. The mixture was placed in a Petri dish and dried in air. After solvent evaporation, a transparent, 4.1 wt% Au/PVA film was obtained. PVA nanofibers with Au nanoparticles were prepared by electrospinning a solution made by dissolving the PVA thin films containing Au nanoparticles, with average diameters ranging from 15 nm to 30 nm, in H

Lattice-Mismatched III-V Epilayers for High-Efficiency Photovoltaics

The project focused on development of new approaches and materials combinations to expand and improve the quality and versatility of lattice-mismatched (LMM) III-V semiconductor epilayers for use in high-efficiency multijunction photovoltaic (PV) devices. To address these goals, new capabilities for materials synthesis and characterization were established at SDSM&T that have applications in modern opto- and nano-electronics, including epitaxial crystal growth and transmission electron microscopy. Advances were made in analyzing and controlling the strain profiles and quality of compositional grades used for these technologies. In particular, quaternary compositional grades were demonstrated, and a quantitative method for characteristic X-ray analysis was developed. The project allowed enhanced collaboration between scientists at NREL and SDSM&T to address closely related research goals, including materials exchange and characterization.