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Synthesis of Ligand-Capped Nanoparticles for Catalysis

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A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (31 May 2018) | Viewed by 24235

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Special Issue Editor

Prof. Dr. Young-Seok Shon

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Guest Editor

Department of Chemistry and Biochemistry and KEMP, California State University Long Beach, Long Beach, CA, USA
Interests: solution-phase synthesis and catalysis of metal nanoparticles and nanoparticle hybrids: selective catalysis and enzyme site mimics; micelle-like nanoparticles for green catalysis; liposome-encapsulated metal nanoparticles for biocatalysis; metal nanoparticle hybrids for photoenhanced catalysis
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Special Issue Information

Dear Colleagues,

Small and spherical organic ligand-capped nanoparticles are ideal candidates for enzyme site mimics due to their versatile ligand characteristics and overall shape. Many researchers have been working on fundamental research investigations, focusing on understanding how several factors, such as structure and functionality of the ligands, ligand density on the nanoparticle surface, size of the nanoparticles, and ligand conformational changes, determine the catalytic properties of the ligand-modified nanoparticles towards organic reactions including biologically important transformations. These studies have advanced the basic understanding of the relationship between the catalytic properties and the surface adsorbents of nanoparticles.

This Special Issue of Nanomaterials will attempt to cover the recent advancements in the ligand-capped nanoparticles for various catalysis applications.

Prof. Dr. Young-Seok Shon
Guest Editor

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Keywords

nanoparticles
clusters
catalysis
ligands
organic reactions
surface adsorbents

Published Papers (3 papers)

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Research

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13 pages, 2545 KiB

Open AccessArticle

Solution-Grown Dendritic Pt-Based Ternary Nanostructures for Enhanced Oxygen Reduction Reaction Functionality

by Gerard M. Leteba, David R. G. Mitchell, Pieter B. J. Levecque and Candace I. Lang

Nanomaterials 2018, 8(7), 462; https://doi.org/10.3390/nano8070462 - 26 Jun 2018

Cited by 14 | Viewed by 9126

Abstract

Nanoalloys with anisotropic morphologies of branched and porous internal structures show great promise in many applications as high performance materials. Reported synthetic approaches for branched alloy nanostructures are, however, limited by the synthesis using a seed-growth process. Here, we demonstrate a conveniently fast and one-pot solution-phase thermal reduction strategy yielding nanoalloys of Pt with various solute feed ratios, exhibiting hyperbranched morphologies and good dispersity. When Pt was alloyed with transition metals (Ni, Co, Fe), we observed well-defined dendritic nanostructures in PtNi, PtCo and Pt(NiCo), but not in PtFe, Pt(FeNi) or Pt(FeCo) due to the steric hindrance of the trivalent Fe(acac)₃ precursor used during synthesis. In the case of Pt-based nanoalloys containing Ni and Co, the dendritic morphological evolution observed was insensitive to large variations in solute concentration. The functionality of these nanoalloys towards the oxygen reduction reaction (ORR); however, was observed to be dependent on the composition, increasing with increasing solute content. Pt₃(NiCo)₂ exhibited superior catalytic activity, affording about a five- and 10-fold enhancement in area-specific and mass-specific catalytic activities, respectively, compared to the standard Pt/C nanocatalyst. This solution-based synthetic route offers a new approach for constructing dendritic Pt-based nanostructures with excellent product yield, monodispersity and high crystallinity. Full article

(This article belongs to the Special Issue Synthesis of Ligand-Capped Nanoparticles for Catalysis)

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12 pages, 1423 KiB

Open AccessArticle

pH-Responsive Mercaptoundecanoic Acid Functionalized Gold Nanoparticles and Applications in Catalysis

by Siyam M. Ansar, Saptarshi Chakraborty and Christopher L. Kitchens

Nanomaterials 2018, 8(5), 339; https://doi.org/10.3390/nano8050339 - 17 May 2018

Cited by 41 | Viewed by 8067

Abstract

Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pK_a of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium. The AuNP-MUA were investigated as a reusable catalyst in the catalytic reduction of 4-nitrophenol by borohydride—a model reaction for AuNPs. It was determined that 100% MUA surface coverage completely inhibits the catalytic activity of AuNPs. Decreasing the surface coverage was shown to increase catalytic activity, but this decrease also leads to decreased colloidal stability, recoverability, and reusability in subsequent reactions. At 60% MUA surface coverage, colloidal stability and catalytic activity were achieved, but the surface coverage was insufficient to enable redispersion following pH-induced recovery. A balance between AuNP colloidal stability, recoverability, and catalytic activity with reusability was achieved at 90% MUA surface coverage. The AuNP-MUA catalyst can also be recovered at different pH ranges depending on the recovery method employed. At pH ~4, protonation of the MUA results in reduced surface charge and aggregation. At pH ~9, ODA will form an ion-pair with the MUA and induce phase transfer into an immiscible organic phase. Both the pH-triggered aggregation/re-dispersion and aqueous/organic phase transfer methods were employed for catalyst recovery and reuse in subsequent reactions. The ability to recover and reuse the AuNP-MUA catalyst by two different methods and different pH regimes is significant, based on the fact that nanoparticle-catalyzed reactions may occur under different pH conditions. Full article

(This article belongs to the Special Issue Synthesis of Ligand-Capped Nanoparticles for Catalysis)

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Review

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21 pages, 4302 KiB

Open AccessReview

Synthesis of Alkanethiolate-Capped Metal Nanoparticles Using Alkyl Thiosulfate Ligand Precursors: A Method to Generate Promising Reagents for Selective Catalysis

by Khin Aye San and Young-Seok Shon

Nanomaterials 2018, 8(5), 346; https://doi.org/10.3390/nano8050346 - 18 May 2018

Cited by 31 | Viewed by 6417

Abstract

Evaluation of metal nanoparticle catalysts functionalized with well-defined thiolate ligands can be potentially important because such systems can provide a spatial control in the reactivity and selectivity of catalysts. A synthetic method utilizing Bunte salts (sodium S-alkylthiosulfates) allows the formation of metal nanoparticles (Au, Ag, Pd, Pt, and Ir) capped with alkanethiolate ligands. The catalysis studies on Pd nanoparticles show a strong correlation between the surface ligand structure/composition and the catalytic activity and selectivity for the hydrogenation/isomerization of alkenes, dienes, trienes, and allylic alcohols. The high selectivity of Pd nanoparticles is driven by the controlled electronic properties of the Pd surface limiting the formation of Pd–alkene adducts (or intermediates) necessary for (additional) hydrogenation. The synthesis of water soluble Pd nanoparticles using ω-carboxylate-S-alkanethiosulfate salts is successfully achieved and these Pd nanoparticles are examined for the hydrogenation of various unsaturated compounds in both homogeneous and heterogeneous environments. Alkanethiolate-capped Pt nanoparticles are also successfully synthesized and further investigated for the hydrogenation of various alkynes to understand their geometric and electronic surface properties. The high catalytic activity of activated terminal alkynes, but the significantly low activity of internal alkynes and unactivated terminal alkynes, are observed for Pt nanoparticles. Full article

(This article belongs to the Special Issue Synthesis of Ligand-Capped Nanoparticles for Catalysis)

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