Nanoscale wetting controls reactive Pd ensembles in synthesis of dilute PdAu alloy catalysts.

The performance of bimetallic dilute alloy catalysts is largely determined by the size of minority metal ensembles on the nanoparticle surface. By analyzing the synthesis of catalysts comprising PdAu nanoparticles supported on silica using surface-sensitive techniques, we report that whether Pd overgrowth occurs before or after Au nanoparticle deposition onto the support controls the surface Pd ensemble size and abundance. These differences in Pd ensembles influence catalytic reactivity in H-D isotope exchange and benzaldehyde hydrogenation, which, in correlation with theoretical calculations, is used to elucidate the active site(s) in each reaction.

Vascular architecture-on-chip: engineering complex blood vessels for reproducing physiological and heterogeneous hemodynamics and endothelial function.

Human circulation exhibits significant diversity and heterogeneity of blood vessel shapes. The complex architecture of these vessels may be physiological or pathological resulting in unique hemodynamics and endothelial cell phenotypes that may determine the regulation and alteration of cell signaling pathways and vascular function. While human microphysiological systems of blood vessels (vessel-chips) have mimicked several aspects of vascular pathophysiology, engineering of these tools is still limited to the fabrication of homogeneous tubular structures, especially when living endothelial cell culture is also included.

Facilitating Hydrogen Dissociation over Dilute Nanoporous Ti-Cu Catalysts.

The dissociation of H is an essential elementary step in many industrial chemical transformations, typically requiring precious metals. Here, we report a hierarchical nanoporous Cu catalyst doped with small amounts of Ti (npTiCu) that increases the rate of H-D exchange by approximately one order of magnitude compared to the undoped nanoporous Cu (npCu) catalyst. The promotional effect of Ti was measured via steady-state H-D exchange reaction experiments under atmospheric pressure flow conditions in the temperature range of 300-573 K.

Synthesis and Characterization of Core-Shell Cu-Ru, Cu-Rh, and Cu-Ir Nanoparticles.

Optimizing the use of expensive precious metals is critical to developing sustainable and low-cost processes for heterogeneous catalysis or electrochemistry. Here, we report a synthesis method that yields core-shell Cu-Ru, Cu-Rh, and Cu-Ir nanoparticles with the platinum-group metals segregated on the surface. The synthesis of Cu-Ru, Cu-Rh, and Cu-Ir particles allows maximization of the surface area of these metals and improves catalytic performance.

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites.

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity.

Structural and Valence State Modification of Cobalt in CoPt Nanocatalysts in Redox Conditions.

Platinum is the primary catalyst for many chemical reactions in the field of heterogeneous catalysis. However, platinum is both expensive and rare. Therefore, it is advantageous to combine Pt with another metal to reduce cost while also enhancing stability.

Cluster-mining: an approach for determining core structures of metallic nanoparticles from atomic pair distribution function data.

A novel approach for finding and evaluating structural models of small metallic nanoparticles is presented. Rather than fitting a single model with many degrees of freedom, libraries of clusters from multiple structural motifs are built algorithmically and individually refined against experimental pair distribution functions. Each cluster fit is highly constrained.

Generalized Synthetic Strategy for Transition-Metal-Doped Brookite-Phase TiO Nanorods.

We report a generalized wet-chemical methodology for the synthesis of transition-metal (M)-doped brookite-phase TiO nanorods (NRs) with unprecedented wide-range tunability in dopant composition (M = V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.). These quadrangular NRs can selectively expose {210} surface facets, which is induced by their strong affinity for oleylamine stabilizer.

General Synthetic Route to High-Quality Colloidal III-V Semiconductor Quantum Dots Based on Pnictogen Chlorides.

The synthesis of colloidal III-V quantum dots (QDs), particularly of the arsenides and antimonides, has been limited by the lack of stable and available group V precursors. In this work, we exploit accessible InCl- and pnictogen chloride-oleylamine as precursors to synthesize III-V QDs. Through coreduction reactions of the precursors, we achieve size- and stoichiometry-tunable binary InAs and InSb as well as ternary alloy InAsSb QDs.

Tuning the Electrocatalytic Oxygen Reduction Reaction Activity of Pt-Co Nanocrystals by Cobalt Concentration with Atomic-Scale Understanding.

The development of a suitable catalyst for the oxygen reduction reaction (ORR), the cathode reaction of proton exchange membrane fuel cells (PEMFC), is necessary to push this technology toward widespread adoption. There have been substantial efforts to utilize bimetallic Pt-M alloys that adopt the ordered face-centered tetragonal (L1) phase in order to reduce the usage of precious metal, enhance the ORR performance, and improve catalyst stability. In this work, monodisperse Pt-Co nanocrystals (NCs) with well-defined size (4-5 nm) and cobalt composition (25-75 at%) were synthesized via colloidal synthesis.

Nanocrystal Core Size and Shape Substitutional Doping and Underlying Crystalline Order in Nanocrystal Superlattices.

Substitutional doping is a potentially powerful technique to control the properties of nanocrystal (NC) superlattices (SLs). However, not every NC can be substituted into any lattice, as the NCs have to be close in size and shape, limiting the application of substitutional doping. Here we show that this limitation can be overcome by employing ligands of various size.

Air-Stable CuInSe Nanocrystal Transistors and Circuits via Post-Deposition Cation Exchange.

Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films.

Improved Chemical and Colloidal Stability of Gold Nanoparticles through Dendron Capping.

Nanoparticle (NP) stability is imperative for commercialization of nanotechnology. In this study, we compare the stability of Au NPs with surfaces functionalized with oleylamine, dodecanethiol, and two dendritic ligands of different generations. Dendrimer ligands provide a significant increase in the chemical stability of Au NPs when analyzed by cyanide-induced NP decomposition as well as an investigation into their colloidal stability at ambient conditions.

Charge Transport Modulation in PbSe Nanocrystal Solids by Au Ag Nanoparticle Doping.

Nanocrystal (NC) solids are an exciting class of materials, whose physical properties are tunable by choice of the NCs as well as the strength of the interparticle coupling. One can consider these NCs as "artificial atoms" in analogy to the formation of condensed matter from atoms. Akin to atomic doping, the doping of a semiconducting NC solid with impurity NCs can drastically alter its electronic properties.

The dendritic effect and magnetic permeability in dendron coated nickel and manganese zinc ferrite nanoparticles.

The collective magnetic properties of nanoparticle (NP) solid films are greatly affected by inter-particle dipole-dipole interactions and therefore the proximity of the neighboring particles. In this study, a series of dendritic ligands (generations 0 to 3, G0-G3) have been designed and used to cover the surface of magnetic NPs to control the spacings between the NP components in single lattices. The dendrons of different generations introduced here were based on the 2,2-bis(hydroxymethyl)propionic acid (Bis-MPA) scaffold and equipped with an appropriate surface binding group at one end and several fatty acid segments at the other extremity.

Detection of adenosine 5'-triphosphate by fluorescence variation of oligonucleotide-templated silver nanoclusters.

Oligonucleotide-templated Ag nanoclusters (DNA-Ag NCs) prepared from AgNO3 using an oligonucleotide (5'-TAACCCCTAACCCCT-3') as a template and NaBH4 as a reducing agent have been used for sensing of adenosine 5'-triphosphate (ATP). The fluorescence intensity and emission wavelength of DNA-Ag NCs are dependent on the pH value and ATP concentration. At pH 3.