Megan F Bornstein | University of Utah (original) (raw)
Uploads
Papers by Megan F Bornstein
ACS Catalysis, Jun 22, 2016
Much research has been done using polymer and silica particles as support materials for catalytic... more Much research has been done using polymer and silica particles as support materials for catalytically active noble metal nanoparticles, but these materials have limited stability in organic solvents or under extreme reaction conditions such as high pH. Here we present a robust and versatile composite polymer-diamond support for ultrasmall noble metal nanoparticles combining chemical and mechanical stability of diamond with the chemical versatility of a polymer. By exploiting the rich surface chemistry of nanodiamond and incorporating a reactive thiol−ene polymer, a thinly coated polymer-diamond composite was formed. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) confirmed the presence of the polymer. High resolution scanning transmission electron microscopy (S/TEM) analysis showed that in situ growth of gold, platinum and palladium nanoparticles produced high density coverage at the polymer-diamond support surface. Energy dispersive spectroscopy mapping and S/TEM imaging indicated spatial alignment of nanoparticles with chemical groups present in the polymer used for particle tethering. The polymer-diamond supported nanoparticles catalyze the NaBH 4 reduction of paranitrophenol to para-aminophenol and possess better stability than silica supports which dissolve at high pH resulting in nanoparticle aggregation. With the high robustness of the diamond and the ability to tailor the monomer combinations, this polymer-diamond support system may be expanded to a wide range of nanoparticle compositions suitable for various reaction conditions.
Chemcatchem, Jul 26, 2019
Silica nanoparticles carrying covalently bound dipyridylmethylene (dpm) ligands were treated with... more Silica nanoparticles carrying covalently bound dipyridylmethylene (dpm) ligands were treated with Pd(OAc)2 in acetone in an attempt to prepare a silica surface-immobilized Pd 2+dpm complex. However, instead of the expected tethered complexes, small, monodisperse and evenly distributed palladium nanoparticles (PdNPs) formed. We found that an organic impurity, most likely an alcohol, in reagent-grade acetone led to the reduction of Pd(OAc)2 to form PdNPs. The size and surface distribution of the PdNPs are affected by temperature, and formation of PdNPs can be inhibited by using high purity solvents and/or low temperature. The PdNPs supported on silica nanoparticles demonstrated catalytic activity in oxidation of benzyl alcohol to benzaldehyde, while silica nanoparticles with surface-immobilized Pd 2+-dpm complexes required an induction period in order to reach a similar level of catalytic activity. In all cases, PdNPs were observed after the catalytic reaction, providing evidence that the induction period exhibited by the materials carrying Pd 2+-dpm complexes may be related to a time-dependent PdNP formation process, with PdNPs rather than the immobilized complexes playing a central role in the catalytic reaction. Although nanoparticles are sometimes identified after carrying out catalytic reactions with supported molecular Pd complexes, our studies demonstrate the importance of identifying the species present in as-synthesized heterogeneous materials of supported transition metal complexes.
ACS Catalysis, Jun 22, 2016
Much research has been done using polymer and silica particles as support materials for catalytic... more Much research has been done using polymer and silica particles as support materials for catalytically active noble metal nanoparticles, but these materials have limited stability in organic solvents or under extreme reaction conditions such as high pH. Here we present a robust and versatile composite polymer-diamond support for ultrasmall noble metal nanoparticles combining chemical and mechanical stability of diamond with the chemical versatility of a polymer. By exploiting the rich surface chemistry of nanodiamond and incorporating a reactive thiol−ene polymer, a thinly coated polymer-diamond composite was formed. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) confirmed the presence of the polymer. High resolution scanning transmission electron microscopy (S/TEM) analysis showed that in situ growth of gold, platinum and palladium nanoparticles produced high density coverage at the polymer-diamond support surface. Energy dispersive spectroscopy mapping and S/TEM imaging indicated spatial alignment of nanoparticles with chemical groups present in the polymer used for particle tethering. The polymer-diamond supported nanoparticles catalyze the NaBH 4 reduction of paranitrophenol to para-aminophenol and possess better stability than silica supports which dissolve at high pH resulting in nanoparticle aggregation. With the high robustness of the diamond and the ability to tailor the monomer combinations, this polymer-diamond support system may be expanded to a wide range of nanoparticle compositions suitable for various reaction conditions.
Chemcatchem, Jul 26, 2019
Silica nanoparticles carrying covalently bound dipyridylmethylene (dpm) ligands were treated with... more Silica nanoparticles carrying covalently bound dipyridylmethylene (dpm) ligands were treated with Pd(OAc)2 in acetone in an attempt to prepare a silica surface-immobilized Pd 2+dpm complex. However, instead of the expected tethered complexes, small, monodisperse and evenly distributed palladium nanoparticles (PdNPs) formed. We found that an organic impurity, most likely an alcohol, in reagent-grade acetone led to the reduction of Pd(OAc)2 to form PdNPs. The size and surface distribution of the PdNPs are affected by temperature, and formation of PdNPs can be inhibited by using high purity solvents and/or low temperature. The PdNPs supported on silica nanoparticles demonstrated catalytic activity in oxidation of benzyl alcohol to benzaldehyde, while silica nanoparticles with surface-immobilized Pd 2+-dpm complexes required an induction period in order to reach a similar level of catalytic activity. In all cases, PdNPs were observed after the catalytic reaction, providing evidence that the induction period exhibited by the materials carrying Pd 2+-dpm complexes may be related to a time-dependent PdNP formation process, with PdNPs rather than the immobilized complexes playing a central role in the catalytic reaction. Although nanoparticles are sometimes identified after carrying out catalytic reactions with supported molecular Pd complexes, our studies demonstrate the importance of identifying the species present in as-synthesized heterogeneous materials of supported transition metal complexes.