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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Preparation And Characterization Of 3 Nm Magnetic Niau Nanoparticles, Bethany Auten, Benjamin Hahn, Ganesh Vijayaraghavan, Keith Stevenson, Bert Chandler
Preparation And Characterization Of 3 Nm Magnetic Niau Nanoparticles, Bethany Auten, Benjamin Hahn, Ganesh Vijayaraghavan, Keith Stevenson, Bert Chandler
Bert D Chandler
Using PAMAM dendrimers as nanoparticle templates, a synthetic route to prepare 3 nm magnetic NiAu nanoparticles was developed. Aqueous solutions of hydroxyl-terminated generation 5 PAMAM dendrimers in 25 mM NaClO4 were shown to bind aqueous NiII. Coreduction of NiII and AuIII salts yielded bimetallic dendrimer stabilized nanoparticles, which were extracted into toluene with decanethiol. Characterization of the resulting monolayer protected clusters (MPCs) with transmission electron microscopy and UV-visible, atomic absorption, and X-ray photoelectron spectroscopies suggested that the MPCs had substantial surface enrichment in Au. Superconducting quantum interference device (SQUID) measurements at 5 K show the bimetallic MPCs to have low …
Synthesis And Characterization Of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles, Huifang Lang, Stephen Maldonado, Keith Stevenson, Bert Chandler
Synthesis And Characterization Of Dendrimer Templated Supported Bimetallic Pt-Au Nanoparticles, Huifang Lang, Stephen Maldonado, Keith Stevenson, Bert Chandler
Bert D Chandler
Bimetallic dendrimer-stabilized nanoparticles (DSNs) were used to prepare supported Pt-Au catalysts within the bulk miscibility gap for this binary system. Hydroxy-terminated generation 5 PAMAM dendrimers were used to prepare Cu0 nanoparticles (NPs). The Cu0 NPs were subsequently used to reduce K2PtCl4 and HAuCl4, preparing stabilized bimetallic Pt-Au NPs with a 1:1 stoichiometry. The stabilized NPs were adsorbed onto a high surface area silica support and thermally activated to remove the dendrimers. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and infrared spectroscopy of adsorbed CO showed that this preparation route resulted in NPs in which the two metals are intimately …
Adsorption Of Co On Supported Gold Nanoparticle Catalysts: A Comparative Study, Heather Hartshorn, Christopher Pursell, Bert Chandler
Adsorption Of Co On Supported Gold Nanoparticle Catalysts: A Comparative Study, Heather Hartshorn, Christopher Pursell, Bert Chandler
Bert D Chandler
The adsorption of CO on three different gold nanoparticle catalysts supported on high surface area TiO2 was studied using infrared transmission spectroscopy at room temperature and CO pressures typically used in CO oxidation reactions. The three, real-world catalysts were Au catalysts synthesized in our laboratory from thiol monolayer protected clusters (MPCs) and two commercial catalysts from the World Gold Council (WGC and AuTEK). Within experimental reproducibility, the adsorption data for the three catalysts are indistinguishable. While showing approximately Langmuir behavior, the adsorption data also show coverage dependence, as others have observed for many catalyst systems. Two approaches were used to …
Air And Water Free Solid-Phase Synthesis Of Thiol Stabilized Au Nanoparticles With Anchored, Recyclable Dendrimer Templates, John Gilbertson, Ganesh Vijayaraghavan, Keith Stevenson, Bert Chandler
Air And Water Free Solid-Phase Synthesis Of Thiol Stabilized Au Nanoparticles With Anchored, Recyclable Dendrimer Templates, John Gilbertson, Ganesh Vijayaraghavan, Keith Stevenson, Bert Chandler
Bert D Chandler
Solid-phase synthetic templates for Au nanoparticles were developed using Merrifield resins and polyamidoamine (PAMAM) dendrimers. This synthetic scheme affords the opportunity to prepare metal nanoparticles in the absence of air and water, and it does not necessitate phase transfer agents that can be difficult to remove in subsequent steps. Amine-terminated generation 5 PAMAM (G5NH2) dendrimers were grafted to anhydride functionalized polystyrene resin beads and alkylated with 1,2-epoxydodecane to produce G5C12anch. The anchored dendrimers bound both CoII and AuIII salts from toluene solutions at ratios comparable to those of solution phase alkyl-terminated PAMAM dendrimers. The encapsulated AuIII salts could be reduced …
Kinetic Evaluation Of Highly Active Supported Gold Catalysts Prepared From Monolayer-Protected Clusters: An Experimental Michaelis-Menten Approach For Determining The Oxygen Binding Constant During Co Oxidation Catalysis, Cormac Long, John Gilbertson, Ganesh Vijayaraghavan, Keith Stevenson, Christopher Pursell, Bert Chandler
Kinetic Evaluation Of Highly Active Supported Gold Catalysts Prepared From Monolayer-Protected Clusters: An Experimental Michaelis-Menten Approach For Determining The Oxygen Binding Constant During Co Oxidation Catalysis, Cormac Long, John Gilbertson, Ganesh Vijayaraghavan, Keith Stevenson, Christopher Pursell, Bert Chandler
Bert D Chandler
Thiol monolayer-protected Au clusters (MPCs) were prepared using dendrimer templates, deposited onto a high-surface-area titania, and then the thiol stabilizers were removed under H2/N2. The resulting Au catalysts were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy of adsorbed CO. The Au catalysts prepared via this route displayed minimal particle agglomeration during the deposition and activation steps. Structural data obtained from the physical characterization of the Au catalysts were comparable to features exhibited from a traditionally prepared standard Au catalyst obtained from the World Gold Council (WGC). A differential kinetic study of CO oxidation catalysis by the …
Enhanced Oxygen Activation Over Supported Bimetallic Au-Ni Catalysts, Bert Chandler, Cormac Long, John Gilbertson, Christopher Pursell, Ganesh Vijayaraghavan, Keith Stevenson
Enhanced Oxygen Activation Over Supported Bimetallic Au-Ni Catalysts, Bert Chandler, Cormac Long, John Gilbertson, Christopher Pursell, Ganesh Vijayaraghavan, Keith Stevenson
Bert D Chandler
New bimetallic Ni-Au supported nanoparticle catalysts were prepared by using dendrimer templated nanoparticles. Amine-terminated generation 5 polyamidoamine (PAMAM) dendrimers were anchored to a commercial silica with a siloxane linked anhydride. The dendrimer was then alkylated and used to template Ni-Au nanoparticles, which were subsequently extracted into organic solution as thiol monolayer protected clusters (MPCs). Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) indicated bimetallic nanoparticles of about 2 nm in size. Nanoparticles were deposited onto P-25 TiO2, and the capping thiol ligands were removed under flowing H2. DRIFTS infrared spectra of adsorbed CO showed only Au on the catalyst …
Low-Temperature Activation Conditions For Pamam Dendrimer Templated Pt Nanoparticles, Anil Singh, Bert Chandler
Low-Temperature Activation Conditions For Pamam Dendrimer Templated Pt Nanoparticles, Anil Singh, Bert Chandler
Bert D Chandler
Surface immobilized polyamidoamine (PAMAM) dendrimer templated Pt nanoparticles were employed as precursors to heterogeneous catalysts. CO oxidation catalysis and in situ infrared spectroscopy were used to evaluate conditions for dendrimer removal. Infrared spectroscopy showed thatPAMAMdendrimer amide bonds begin decomposing at temperatures as low as 75 °C. Although the amide stretches are completely removed after 3 h of oxidation at 300 °C, 16 h were required to reach maximum catalytic activity. Further treatment under oxidizing or reducing atmospheres did not cause substantial changes in activity. Infrared spectroscopy of the activated materials indicated that organic residues, probably surface carboxylates, are formed during …
Origin Of Enantioselection In Chiral Alcohol Oxidation Catalyzed By Pd[(-)-Sparteine]Cl2, Jaime Mueller, Anne Cowell, Bert Chandler, Matthew Sigman
Origin Of Enantioselection In Chiral Alcohol Oxidation Catalyzed By Pd[(-)-Sparteine]Cl2, Jaime Mueller, Anne Cowell, Bert Chandler, Matthew Sigman
Bert D Chandler
A kinetic investigation into the origin of enantioselectivity for the Pd[(-)-sparteine]Cl2-catalyzed aerobic oxidative kinetic resolution (OKR) is reported. A mechanism to account for a newly discovered chloride dissociation from Pd[(-)-sparteine]Cl2 prior to alcohol binding is proposed. The mechanism includes (1) chloride dissociation from Pd[(-)-sparteine]Cl2 to form cationic Pd(-)-sparteine]Cl, (2) alcohol binding, (3) deprotonation of Pd-bound alcohol to form a Pd-alkoxide, and (4) â-hydride elimination of Pd-alkoxide to form ketone product and a Pd-hydride. Utilizing the addition of (-)-sparteine HCl to control the [Cl-] and [H+] and the resulting derived rate law, the key microscopic kinetic and thermodynamic constants were extracted …
Ultrafast Optical Study Of Small Gold Monolayer Protected Clusters: A Closer Look At Emission, Sung Hei Yau, Oleg Varnavski, John Gilbertson, Bert Chandler, Guda Ramakrishna, Theodore Goodson
Ultrafast Optical Study Of Small Gold Monolayer Protected Clusters: A Closer Look At Emission, Sung Hei Yau, Oleg Varnavski, John Gilbertson, Bert Chandler, Guda Ramakrishna, Theodore Goodson
Bert D Chandler
Monolayer-protected metal nanoclusters (MPCs) were investigated to probe their fundamental excitation and emission properties. In particular, gold MPCs were probed by steady-state and time-resolved spectroscopic measurements; the results were used to examine the mechanism of emission in relation to the excited states in these systems. In steady-state measurements, the photoluminescence of gold clusters in the range of 25 to 140 atoms was considerably stronger relative to larger particle analogues. The increase in emission efficiency (for Au25, Au55, and Au140 on the order of 10-5) over bulk gold may arise from a different mechanism of photoluminescence, as suggested by measurements on …