Troubleshooting the influence of trace chemical impurities on nanoparticle growth kinetics electrochemical measurements.

Reproducibility issues resulting from particle growth solutions made with cetyltrimethylammonium bromide (CTAB) surfactant from different lots and product lines in a newly developed synthesis of monometallic palladium (Pd) tetrahexahedra (THH) nanoparticles are investigated a multi-pronged approach. Time-resolved electrochemical measurements of solution potential, variation of chemical parameters in colloidal synthesis, and correlation to electrodeposition syntheses are used together to uncover the effects of the unknown contaminants on the chemical reducing environment during nanoparticle growth. Iodide-a known impurity in commercial CTAB-is identified as one of the required components for equalizing the reducing environment across multiple CTAB sources.

Nanomaterials Synthesis Discovery via Parallel Electrochemical Deposition.

Electrodeposition of nanoparticles is investigated with a multichannel potentiostat in electrochemical and chemical arrays. deposition and shape control of palladium nanoparticles are explored in arrays with a two-stage strategy. Initial conditions for electrodeposition of materials are discovered in a first stage and then used in a second stage to logically expand chemical and electrochemical parameters.

Bridging Colloidal and Electrochemical Nanoparticle Growth with Electrochemical Measurements.

ConspectusProspective applications involving the electrification of industrial chemical processes and electrical energy to chemical fuels interconversion as part of the energy transition to renewable energy sources have led to an increasing need for highly tailored nanostructures immobilized on electrode surfaces. Control of surface facet structure across material compositions is of particular importance for ensuring performance in such applications. Colloidal methods for producing shaped nanoparticles in solution are abundant, particularly for noble metals.

An Integrated Electrochemistry Approach to the Design and Synthesis of Polyhedral Noble Metal Nanoparticles.

The synthesis of shaped metal nanoparticles to meet the precise needs of emerging applications requires intentional synthetic design directed by fundamental chemical principles. We report an integrated electrochemistry approach to nanoparticle synthetic design that couples current-driven growth of metal nanoparticles on an electrode surface-in close analogy to standard colloidal synthesis-with electrochemical measurements of both electrochemical and colloidal nanoparticle growth. A simple chronopotentiometry method was used to translate an existing colloidal synthesis for corrugated palladium (Pd) nanoparticles to electrochemical growth on a glassy carbon electrode, with minimal modification to the growth solution.

Halide-assisted metal ion reduction: emergent effects of dilute chloride, bromide, and iodide in nanoparticle synthesis.

Understanding the competing effects of growth-directing additives, such as halide ions, on particle formation in solution phase metal nanoparticle syntheses is an ongoing challenge. Further, trace halide impurities are known to have a drastic impact on particle morphology as well as reproducibility. Herein, we employ a "halide-free" platform as an analogue to commonly used halide-containing surfactants and metal precursors to isolate and study the effects of micromolar concentrations of halide ions (chloride, bromide, and iodide) on the rate of metal ion reduction.

Defects by design: synthesis of palladium nanoparticles with extended twin defects and corrugated surfaces.

Recent catalytic work has highlighted the importance of grain boundaries in the design of highly active catalyst materials due to the high energy of atoms at strained defect sites. In addition, undercoordinated atoms have long been known to contribute to the catalytic performance of metal nanoparticles. In this work, we describe a method for deliberately increasing the coverage of defect boundaries and undercoordinated atoms at the surfaces of well-defined, symmetric palladium nanoparticles.

Catalyst design for enhanced sustainability through fundamental surface chemistry.

Decreasing energy consumption in the production of platform chemicals is necessary to improve the sustainability of the chemical industry, which is the largest consumer of delivered energy. The majority of industrial chemical transformations rely on catalysts, and therefore designing new materials that catalyse the production of important chemicals via more selective and energy-efficient processes is a promising pathway to reducing energy use by the chemical industry. Efficiently designing new catalysts benefits from an integrated approach involving fundamental experimental studies and theoretical modelling in addition to evaluation of materials under working catalytic conditions.

The surface structure of silver-coated gold nanocrystals and its influence on shape control.

Understanding the surface structure of metal nanocrystals with specific facet indices is important due to its impact on controlling nanocrystal shape and functionality. However, this is particularly challenging for halide-adsorbed nanocrystals due to the difficulty in analysing interactions between metals and light halides (for example, chloride). Here we uncover the surface structures of chloride-adsorbed, silver-coated gold nanocrystals with {111}, {110}, {310} and {720} indexed facets by X-ray absorption spectroscopy and density functional theory modelling.

Making sense of the mayhem behind shape control in the synthesis of gold nanoparticles.

The formation of anisotropic Au nanoparticles predominantly follows one of two growth pathways: (1) kinetic control or (2) selective surface passivation. This Perspective describes the mechanisms that control Au nanoparticle shape via these pathways in the context of three basic chemical parameters: metal complex reduction potential, metal ion availability, and adsorbate binding strength. These chemical parameters influence the crystallinity and surface facets of the Au nanoparticles, thus dictating particle shape.

Plasmon-mediated syntheses of metallic nanostructures.

The ability to prepare noble metal nanostructures of a desired composition, size, and shape enables their resulting properties to be exquisitely tailored, which has led to the use of these structures in numerous applications, ranging from medicine to electronics. The prospect of using light to guide nanoparticle reactions is extremely attractive since one can, in principle, regulate particle growth based on the ability of the nanostructures to absorb a specific excitation wavelength. Therefore, using the nature of light, one can generate a homogenous population of product nanoparticles from a heterogeneous starting population.

Anisotropic nanoparticles as shape-directing catalysts for the chemical etching of silicon.

Anisotropic Au nanoparticles have been used to create a library of complex features on silicon surfaces. The technique provides control over feature size, shape, and depth. Moreover, a detailed study of the etching rate as a function of the nanoparticle surface facet interfaced with the silicon substrate suggested that the etching is highly dependent upon the facet surface energy.

Centrifugal shape sorting and optical response of polyhedral gold nanoparticles.

A centrifugal route for separating small {110}-faceted gold nanostructures, namely rhombic dodecahedra (RD) and triangular bipyramids (BPs), which form simultaneously during synthesis and cannot be separated by means of conventional filtration methods, is presented. The centrifuged solution shows two distinct bands: i) RD and ii) BPs, as verified in the corresponding scanning electron microscopy images. The sorted BPs show a refractive index dependence 2.

Synthesis of gold hexagonal bipyramids directed by planar-twinned silver triangular nanoprisms.

The direct growth of planar-twinned Au nanoparticles (NPs) in high yield remains a challenge in shape-controlled NP synthesis largely because suitable planar-twinned seeds for Au NP growth have not been identified to date. Herein we describe the use of planar-twinned Ag triangular nanoprisms as a means to dictate Au NP twin structure. In a one-pot process, the Ag triangular nanoprisms first undergo oxidative Au replacement, forming Ag-Au alloy nanoframes and concomitantly releasing Ag(+) into solution, which then directs subsequent Au NP growth through an underpotential deposition process.

Plasmon-mediated synthesis of silver cubes with unusual twinning structures using short wavelength excitation.

The plasmon-mediated synthesis of silver nanoparticles is a versatile synthetic method which leverages the localized surface plasmon resonance (LSPR) of nanoscale silver to generate particles with non-spherical shapes and control over dimensions. Herein, a method is reported for controlling the twinning structure of silver nanoparticles, and consequently their shape, via the plasmon-mediated synthesis, solely by varying the excitation wavelength between 400, 450, and 500 nm, which modulates the rate of Ag⁺ reduction. Shorter, higher energy excitation wavelengths lead to faster rates of reaction, which in turn yield structures containing a greater number of twin boundaries.

Chemically isolating hot spots on concave nanocubes.

We report a simple and general strategy for selectively exposing and functionalizing the sharp corners of concave nanocubes, which are the SERS hot spots for such structures. This strategy takes advantage of the unique shape of the concave cubes by coating the particles with silica and then etching it away to expose only the corner regions, while maintaining the silica coating in the concave faces. These corner regions can then be selectively modified for improved enhancement and signal response with SERS.

Stepwise evolution of spherical seeds into 20-fold twinned icosahedra.

Understanding the factors that influence the growth and final shape of noble metal nanostructures is important for controlling their properties. However, relative to their single-crystalline counterparts, the growth of nanoparticles that contain twin defects can be difficult to control because multiple competitive growth pathways can yield such structures. We used spherical, cubic, and octahedral single-crystalline gold nanoparticles as dual electron microscopy labels and plasmonic seeds to track the growth of multiply twinned silver nanostructures.

Defining rules for the shape evolution of gold nanoparticles.

The roles of silver ions and halides (chloride, bromide, and iodide) in the seed-mediated synthesis of gold nanostructures have been investigated, and their influence on the growth of 10 classes of nanoparticles that differ in shape has been determined. We systematically studied the effects that each chemical component has on the particle shape, on the rate of particle formation, and on the chemical composition of the particle surface. We demonstrate that halides can be used to (1) adjust the reduction potential of the gold ion species in solution and (2) passivate the gold nanoparticle surface, both of which control the reaction kinetics and thus enable the selective synthesis of a series of different particle shapes.

Shape control of gold nanoparticles by silver underpotential deposition.

Four different gold nanostructures: octahedra, rhombic dodecahedra, truncated ditetragonal prisms, and concave cubes, have been synthesized using a seed-mediated growth method by strategically varying the Ag(+) concentration in the reaction solution. Using X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy, we provide quantitative evidence that Ag underpotential deposition is responsible for stabilizing the various surface facets that enclose the above nanoparticles. Increasing concentrations of Ag(+) in the growth solution stabilize more open surface facets, and experimental values for Ag coverage on the surface of the particles fit well with a calculated monolayer coverage of Ag, as expected via underpotential deposition.

Bottom-up synthesis of gold octahedra with tailorable hollow features.

Gold octahedra with hollow features have been synthesized in high yield via the controlled overgrowth of preformed concave cube seeds. This Ag(+)-assisted, seed-mediated synthesis allows for the average edge length of the octahedra and the size of the hollow features to be independently controlled. We propose that a high concentration of Ag(+) stabilizes the {111} facets of the octahedra through underpotential deposition while the rate of Au(+) reduction controls the dimensions of the hollow features.

Synthesis and isolation of {110}-faceted gold bipyramids and rhombic dodecahedra.

Two {110}-faceted gold nanostructures--rhombic dodecahedra and obtuse triangular bipyramids--have been synthesized via a Ag-assisted, seed-mediated growth method. The combination of a Cl(-)-containing surfactant with a low concentration of Ag(+) plays a role in the stabilization of the {110} facets. To the best of our knowledge, this is the first reported synthesis of a {110}-faceted bipyramid structure.

Oxidation of a guanine derivative coordinated to a Pt(IV) complex initiated by intermolecular nucleophilic attacks.

In this study we report that fac-[Pt(IV)(dach)(9-EtG)Cl(3)](+) (dach = d,l-1,2-diaminocyclohexane, 9-EtG = 9-ethylguanine) in high pH (pH 12) or phosphate solution (pH 7.4) produces 8-oxo-9-EtG and Pt(II) species. The reaction in H(2)(18)O revealed that the oxygen atom in hydroxide or phosphate ends up at the C8 position of 8-oxo-G.

Concave cubic gold nanocrystals with high-index facets.

A new class of gold nanostructures, concave nanocubes, enclosed by 24 high-index {720} facets, have been prepared in a monodisperse fashion by a modified seed-mediated synthetic method. The Cl(-) counterion in the surfactant plays an essential role in controlling the concave morphology of the final product. The concave nanocubes exhibit higher chemical activities compared with low-index {111}-faceted octahedra.

Importance of platinum(II)-assisted platinum(IV) substitution for the oxidation of guanosine derivatives by platinum(IV) complexes.

Guanosine derivatives with a nucleophilic group at the 5' position (G-5') are oxidized by the Pt (IV) complex Pt( d, l)(1,2-(NH 2) 2C 6H 10)Cl 4 ([Pt (IV)(dach)Cl 4]). The overall redox reaction is autocatalytic, consisting of the Pt (II)-catalyzed Pt (IV) substitution and two-electron transfer between Pt (IV) and the bound G-5'. In this paper, we extend the study to improve understanding of the redox reaction, particularly the substitution step.