Controlling the Size and Morphology of Au@Pd Core–Shell Nanocrystals by Manipulating the Kinetics of Seeded Growth

This article reports a systematic study of the seed‐mediated growth of Au@Pd core–shell nanocrystals with a variety of controlled sizes and morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by tuning a set of reaction parameters, including the type and concentration of capping agent, the amount of ascorbic acid used as the reducing agent, and the injection rate used for the precursor solution. Starting from Au nanospheres of 11 nm in diameter as the seeds, Au@Pd core–shell nanocrystals with a number of morphologies, including octahedra, concave octahedra, rectangular bars, cubes, concave cubes, and dendrites, could all be obtained by simply altering the reaction rate. For the first time, it was possible to generate Au@Pd nanocrystals with concave structures on the surfaces while their sizes were kept below 20 nm. In addition, the as‐prepared Au@Pd nanocubes can be used as seeds to generate Au@Pd@Au and Au@Pd@Au@Pd nanocrystals with multishelled structures.     

Aqueous‐Phase Synthesis of Single‐Crystal Pd Seeds 3 nm in Diameter and Their Use for the Growth of Pd Nanocrystals with Different Shapes

This article describes an aqueous method for the synthesis of Pd seeds with a single‐crystal structure and a uniform diameter of 3 nm and their use for the growth of Pd nanocrystals with a variety of shapes. We have also investigated the effects of a number of parameters, including the temperature, reducing power of the reductant, and capping agent on the reduction rate of a Pd precursor, and thus the final size, size distribution, and morphology of the Pd seeds. By taking advantage of the coordination effect of Br^? ions with Pd²⁺ ions and their selective adsorption on the Pd(100) surface, Pd nanocrystals with a number of distinct shapes could be conveniently produced by varying the concentration of KBr added into the growth solution. This work provides a general and facile method for the green synthesis of Pd nanocrystals with controlled shapes, especially for the preparation of Pd nanocrystals with sizes in the sub‐10 nm regime.     

Controlling the size and morphology of Au@Pd core-shell nanocrystals by manipulating the kinetics of seeded growth

This article reports a systematic study of the seed-mediated growth of Au@Pd core-shell nanocrystals with a variety of controlled sizes and morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by tuning a set of reaction parameters, including the type and concentration of capping agent, the amount of ascorbic acid used as the reducing agent, and the injection rate used for the precursor solution. Starting from Au nanospheres of 11?nm in diameter as the seeds, Au@Pd core-shell nanocrystals with a number of morphologies, including octahedra, concave octahedra, rectangular bars, cubes, concave cubes, and dendrites, could all be obtained by simply altering the reaction rate. For the first time, it was possible to generate Au@Pd nanocrystals with concave structures on the surfaces while their sizes were kept below 20?nm. In addition, the as-prepared Au@Pd nanocubes can be used as seeds to generate Au@Pd@Au and Au@Pd@Au@Pd nanocrystals with multishelled structures.     

Low‐Temperature Facile Template Synthesis of Crystalline Inorganic Composite Hollow Spheres

This report presents a facile approach for the low‐temperature synthesis of crystalline inorganic‐oxide composite hollow spheres by employing the bulk controlled synthesis of inorganic‐oxide nanocrystals with polymer spheres as templates. The sulfonated polystyrene gel layer can adsorb the target precursor and induce inorganic nanocrystals to grow on the template in situ. The crystalline phase and morphology of the composite shell is tunable. By simply adjusting the acidity of the titania sol, crystalline titania composite hollow spheres with tunable crystalline phases of anatase, rutile, or a mixture of both were achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate) composite hollow spheres. The traditional thermal treatment for crystallite transformation is not required, thus intact shells can be guaranteed. The combination of oxide properties such as high refractive index, high dielectric constant, and catalytic ability with the cavity of the hollow spheres is promising for applications such as opacifiers, photonic crystals, high‐κ‐gate dielectrics, and photocatalysis.     

Low‐Temperature Synthesis of Crystalline Inorganic/Metallic Nanocrystal‐Halloysite Composite Nanotubes

We have demonstrated a facile approach for the low‐temperature synthesis of crystalline inorganic/metallic nanocrystal‐halloysite composite nanotubes by employing the bulk controlled synthesis of inorganic/metallic nanocrystals on halloysite nanotubes. The halloysite clay nanotubes can adsorb the target precursor and induce inorganic/metallic nanocrystals to grow in situ. The crystalline phase and morphology of the composite clay nanotubes is tunable. By simply tuning the acidity of the titania sol, the crystalline titania‐clay nanotubes with tunable crystalline phases of anatase, a mixture of anatase and rutile or rutile are achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate)‐halloysite composite nanotubes. Metallic nickel nanocrystal can also be grown on the surface of halloysite nanotubes at low temperature. The traditional thermal treatment for crystallite transformation is not required, thus intact contour of halloysite nanotubes and the crystallinity structure of halloysite nanotubes can be guaranteed. The combined properties from inorganic/metallic nanocrystal (high refractive index, high dielectric constant and catalytic ability) and the halloysite clay nanotubes are promising for applications such as photonic crystals, high‐k‐gate dielectrics, photocatalysis and purification.     

Seed-mediated synthesis of gold octahedra in high purity and with well-controlled sizes and optical properties

We report a facile method for the synthesis of uniform Au octahedra with well-controlled sizes and optical properties by seed-mediated growth. Starting from single-crystal seeds of Au spheres with a uniform size, we could reproducibly obtain Au octahedra with a narrow size distribution (<7% in standard deviation) and in high purity (>90%). Moreover, the edge lengths of these Au octahedra could be readily tuned in a controllable fashion from 16 to 77 nm by varying the amount of seeds, the concentration of HAuCl(4) , or both. We have also investigated the effects of water and poly(vinyl pyrrolidone) (PVP) in the system, as well as the reaction temperature, on the evolution of octahedral shape.     

Facile Synthesis of Quasi‐One‐Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen‐Reduction Reaction

An intermediate‐template‐directed method has been developed for the synthesis of quasi‐one‐dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core–shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt₇Au PABNTs showed higher electrocatalytic activity and durability in the oxygen‐reduction reaction (ORR) in 0.1 M HClO₄ than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero‐nanostructures with controlled size and shape by utilizing an intermediate template.     

Quantitative Analysis of the Reduction Kinetics of a Pt(Ⅱ) Precursor in the Context of Pt Nanocrystal Synthesis?

In this letter, we report a quantitative analysis of how a Pt(Ⅱ) precursor is reduced to atoms at different temperatures for the formation of Pt nanocrystals with different morphologies and sizes. Our results suggest that in the early stage of a synthesis, the Pt(Ⅱ) precursor is reduced to atoms exclusively in the solution phase, followed by homogeneous nucleation to generate nuclei and then seeds. At a relatively low reaction temperature such as 22℃, the growth of the seeds is dominated by autocatalytic surface reduction that involves the adsorption and then reduction of the Pt(Ⅱ) precursor on the surface of the just-formed seeds. This particular growth pathway results in relatively large assemblies of Pt nanocrystals. When the reaction temperature is increased to 100℃, the dominant reduction pathway will be switched from surface to solution phase, producing much smaller assemblies of Pt nanocrystals. Our results also demonstrate that a similar trend applies to the seed-mediated growth of Pt nanocrystals in the presence of Pd nanocubes.     

A universal route with fine kinetic control to a family of penta-twinned gold nanocrystals

Some of the major difficulties hindering the synthesis of different types of colloidal nanocrystals are their complex synthetic methods and the lack of a universal growth mechanism in one system. Herein, we propose a general strategy of kinetically controlled seed-mediated growth to synthesize a family of penta-twinned gold nanocrystals. Specifically, different kinds of penta-twinned nanocrystals (truncated penta-twinned decahedra, truncated bipyramids, bipyramids, truncated bipyramids with tips, star-like penta-twinned nanocrystals, decahedra with concave edges, and decahedra) with tunable sizes and high purity were readily achieved in one system solely by tailoring the deposition kinetics of adatoms on different sites of decahedral seeds. The controllable deposition kinetics can be realized by changing the ratio of reductant/gold precursors (R), which dictates whether horizontal or vertical features along the 5-fold axis direction of Au decahedral seeds are produced. Additionally, the selective growth of a second metal (silver) on penta-twinned gold seeds can be reached through minor modification of R, which opens a new avenue for mechanistic investigation by visualizing the seed localization within the final particles. The present work demonstrates a general paradigm for the kinetic growth of penta-twinned crystals and would be extended to the synthesis of other families of nanocrystals.

We report the synthesis of linear ADPr oligomers of defined length up to a pentamer using an improved solid phase method. Binding study with human oncogenic helicase ALC1 shows that ADPr oligomers bind to ALC1 in a length-dependent manner.     

Seed‐Mediated Growth of Silver Nanocubes in Aqueous Solution with Tunable Size and Their Conversion to Au Nanocages with Efficient Photothermal Property

Two seed‐mediated approaches for the growth of silver nanocubes in aqueous solution have been developed. Addition of a silver‐seed solution to a mixture of cetyltrimethylammonium chloride (CTAC), silver trifluoroacetate, and ascorbic acid and heating the solution at 60 °C for 1.5 h produces uniform Ag nanocubes with tunable sizes from 23 to 60 nm by simply adjusting the volume of silver‐seed solution introduced. Alternatively, the silver‐seed solution can be injected into a mixture of cetyltrimethylammonium bromide (CTAB), silver nitrate, copper sulfate, and ascorbic acid and heated to 80 °C for 2 h to generate 46 nm silver nanocubes. Plate‐like Ag nanocrystals exposing {111} surfaces can be synthesized by reducing Ag(NH₃)₂⁺ with ascorbic acid in a CTAC solution. Relatively large Ag nanocubes were converted to cuboctahedral Au/Ag and Au nanocages and nanoframes with empty {111} faces through a galvanic replacement reaction. The nanocages showed a progressive plasmonic band red‐shift with increasing Au content. The nanocages exhibited high and stable photothermal efficiency with solution temperatures quickly reaching beyond 100 °C when irradiated with an 808 nm laser for large heat and water vapor generation.     

Continuous‐Flow Synthesis of CdSe Quantum Dots: A Size‐Tunable and Scalable Approach

In recent years, continuous‐flow/microreactor processing for the preparation of colloidal nanocrystals has received considerable attention. The intrinsic advantages of microfluidic reactors have opened new opportunities for the size‐controlled synthesis of nanocrystals either in the laboratory or on a large scale. Herein, an experimentally simple protocol for the size‐tunable continuous‐flow synthesis of rather monodisperse CdSe quantum dots (QDs) is presented. CdSe QDs are manufactured by using cadmium oleate as cadmium source, selenium dioxide as selenium precursor, and 1‐octadecene as solvent. Exploiting selenium dioxide as selenium source and 1‐octadecene as solvent allows execution of the complete process in open air without any requirement for air‐free manipulations using a glove box or Schlenk line. Continuous‐flow processing is performed with a stainless steel coil of 1.0 mm inner diameter pumping the combined precursor solution through the reactor by applying a standard HPLC pump. The effect of different reaction parameters, such as temperature, residence time, and flow rate, on the properties of the resulting CdSe QDs was investigated. A temperature increase from 240 to 260 °C or an extension of the residence time from 2 to 20 min affords larger nanocrystals (range 3–6 nm) whereas the size distribution does not change significantly. Longer reaction times and higher temperatures result in QDs with lower quantum yields (range 11–28 %). The quality of the synthesized CdSe QDs was confirmed by UV/Vis and photoluminescence spectroscopy, small‐angle X‐ray scattering, and high‐resolution transmission electron microscopy. Finally, the potential of this protocol for large‐scale manufacturing was evaluated and by operating the continuous‐flow process for 87 min it was possible to produce 167 mg of CdSe QDs (with a mean diameter of 4 nm) with a quantum yield of 28 %.     

One‐Pot Solvothermal Synthesis of Highly Water‐Dispersible Size‐Tunable Functionalized Magnetite Nanocrystal Clusters for Lipase Immobilization

A facile one‐pot synthesis of highly water‐dispersible size‐tunable magnetite (Fe₃O₄) nanocrystal clusters (MNCs) end‐functionalized with amino or carboxyl groups by a modified solvothermal reduction reaction has been developed. Dopamine and 3,4‐dihydroxyhydroxycinnamic acid were used for the first time as both a surfactant and interparticle linker in a polylol process for economical and environment‐friendly purposes. Morphology, chemical composition, and magnetic properties of the prepared particles were investigated by several methods, including FESEM, TEM, XRD, XPS, Raman, FTIR, TGA, zeta potential, and VSM. The sizes of the particles could be easily tuned over a wide range from 175 to 500 nm by varying the surfactant concentration. Moreover, ethylene glycol/diethylene glycol (EG/DEG) solvent mixtures with different ratios could be used as reductants to obtain the particles with smaller sizes. The XRD data demonstrated that the surfactants restrained the crystal growth of the grains. The nanoparticles showed superior magnetic properties and high colloidal stability in water. The cytotoxicity results indicated the feasibility of using the synthesized nanocrystals in biology‐related fields. To estimate the applicability of the obtained MNCs in biotechnology, Candida rugosa lipase was selected for the enzyme immobilization process. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with the free enzyme. This novel strategy would simplify the reaction protocol and improve the efficiency of materials functionalization, thus offering new potential applications in biotechnology and organocatalysis.     

5‐(2‐Mercaptoethyl)‐1H‐tetrazole: Facile Synthesis and Application for the Preparation of Water Soluble Nanocrystals and Their Gels

A facile method for the preparation of the novel capping ligand 5‐(2‐mercaptoethyl)‐1H‐tetrazole for the stabilization of water‐soluble nanocrystals was developed. This effective synthetic procedure is based on the cycloaddition of sodium azide to 3,3′‐dithiobis(propionitrile) followed by the reductive cleavage of a S?S bond with triphenylphosphine. The structure of the synthesized compound was confirmed by single‐crystal X‐ray analysis. A target tetrazole was successfully applied for the direct aqueous synthesis of CdTe and Au nanocrystals. CdTe nanocrystals capped with 5‐(2‐mercaptoethyl)‐1H‐tetrazole were found to reveal high photoluminescence efficiencies (up to 77 %). Nanocrystals capped with this tetrazole ligand are able to build 3D structures in a metal‐ion‐assisted gelation process in aqueous solution. Critical point drying of the as‐formed hydrogels allowed the preparation of the corresponding aerogels, while preserving the mesoporous structure.     

Controllable Synthesis of Nearly Monodisperse Spherical Aggregates of CeO2 Nanocrystals and Their Catalytic Activity for HCHO Oxidation

Herein, we report a facile surfactant‐assisted solvothermal synthetic method to prepare nearly monodisperse spherical CeO₂ nanocrystals. A good control of the size of CeO₂ nanocrystals in the range of 100–500 nm was achieved by simply varying the synthetic parameters such as reaction time, volume ratio of ethanol to water (R), molar ratio of PVP, and concentration of Ce(NO₃)₃?6 H₂O in solution. A possible mechanism for the growth of spherical CeO₂ nanocrystals is proposed. The obtained CeO₂ nanocrystals with a surface area of up to 47 m²g^?1 were then employed as a catalyst support. By loading Au‐Pd nanoparticles (about 3 wt. %) onto the CeO₂ support, an Au‐Pd/CeO₂ catalyst was prepared that exhibited high catalytic activity for HCHO oxidation. At the low temperature of 50 °C, the percentage of HCHO conversion was 100 %, suggesting potential applications in preferential oxidation and other catalytic reactions. These Au‐Pd/CeO₂ catalysts may also find applications in indoor formaldehyde decontamination and industrial catalysis. The facile solvothermal method can be extended to the preparation of other metal oxide nanocrystals and provides guidance for size‐ and morphology‐controlled synthesis.     

Wurtzite Cu2GeS3 Nanocrystals: Phase‐ and Shape‐Controlled Colloidal Synthesis

The first colloidal synthesis of Cu₂GeS₃ (CGS) nanocrystals with a thermodynamically metastable wurtzite crystal phase is reported. As a benefit of the sulfur precursors used in the synthesis, the shape of the as‐synthesized wurtzite CGS nanocrystals can be controlled in the form of spherical nanoparticles, nanorectangles, and hollow nanorectangles. A detailed investigation into the effects of reaction conditions necessary to obtain phase‐pure wurtzite CGS nanocrystals is presented. The choice of sulfur precursor and precursor injection temperature play a significant role in determining the crystal phase of the CGS nanocrystals. The band gap of the new wurtzite phase CGS was measured to be 1.76 eV and the CGS nanocrystals exhibited a good electrochemical photoresponse, which was indicative of their potential application as an active layer in the field of solar cells.     

Facet‐Dependent and Light‐Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold–Palladium Core–Shell Nanocatalysts

Au–Pd core–shell nanocrystals with tetrahexahedral (THH), cubic, and octahedral shapes and comparable sizes were synthesized. Similar‐sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen‐evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts. In particular, Au–Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3‐fold rate enhancement benefiting from lattice strain, modified surface electronic state, and a broader range of light absorption. Finite‐difference time‐domain (FDTD) simulations show a stronger electric field enhancement on Au–Pd core–shell THH than those on other Pd‐containing nanocrystals. Light‐assisted nitro reduction by ammonia borane on Au–Pd THH was also demonstrated. Au–Pd tetrahexahedra supported on activated carbon can act as a superior recyclable plasmonic photocatalyst for hydrogen evolution.     

A Facile Phosphine‐Free Method for Synthesizing PbSe Nanocrystals with Strong Optical Limiting Effects

PbSe semiconductor nanocrystals (NCs) have attracted ever‐growing interest owing to both their fundamental physics and potential applications in a diverse range of fields such as optoelectronic devices and nonlinear optics. The current fabrication strategy for colloidal PbSe NCs, however, frequently involves acutely toxic reagents and tedious reaction procedures, and is plagued by products with poorly controlled size and morphology. Herein, we report a facile, low‐cost, and phosphine‐free method for synthesizing PbSe NCs, which provides highly uniform NCs with tunable mid‐IR absorption, and they are promising for bio‐related applications. These high quality NCs were obtained by the reaction of elemental Se and PbCl₂ in oleylamine as both the ligand and reaction medium. The high flexibility and reproducibility of the method reported in this study allows us to synthesize monodispersed PbSe NCs with well‐controlled size and morphology. In addition, these products show strong optical limiting effects, and thus hold potential for developing nonlinear optical devices.     

Alkylaminosilane‐Assisted Simultaneous Etching and Growth Route to Synthesise Metal Nanoparticles Encapsulated by Silica Nanorattles

An efficient and facile method to synthesise silica nanorattles with multiple noble metal (Au and Pd) cores by a simultaneous etching and growth route has been developed. In this strategy, a dual‐functional alkylaminosilane was adopted to form the middle layer of solid organic–inorganic hybrid solid‐silica spheres (HSSSs), which enabled the selective etching of the middle hybrid layer of the HSSSs and the in situ growth of metal nanoparticles (NPs) inside the cavity in a one‐step hydrothermal reaction. By adjusting the pH values of the reaction system, the metal NPs could be grown exclusively inside the silica nanorattles, resulting in a high atomic utilisation of the noble metals. The size and number of Au cores were tunable by manipulating the initial concentration of HAuCl₄. The prepared silica nanorattles with Au cores were successfully applied to the catalytic reduction of 4‐nitrophenol and showed high catalytic activity and cycle stability. Catalysts with multiple gold cores exhibited superior catalytic activity to those with a single gold core, probably because they possess smaller Au cores with greater surface area.     

Facile synthesis of size-tunable ZIF-8 nanocrystals using reverse micelles as nanoreactors

This paper describes a robust method for the synthesis of high-quality ZIF-8 nanocrystals using reverse micelles as discrete nanoscale reactors.The precise size control of ZIF-8 nanocrystals is conveniently achieved by tuning the concentration of precursors,reaction temperatures,the amount of water,and the structure of surfactants.The as-synthesized ZIF-8 nanocrystals are of narrow distribution and tunable size.A size-dependent catalytic activity for Knoevenagel condensation reaction is further demonstrated by using ZIF-8 nanocrystals with different sizes as the catalysts.This facile method opens up a new opportunity in the synthesis of various ZIFs nanocrystals.     

Polyoxometalate‐Mediated One‐Pot Synthesis of Pd Nanocrystals with Controlled Morphologies for Efficient Chemical and Electrochemical Catalysis

Polyoxometalates (POMs), as inorganic ligands, can endow metal nanocrystals (NCs) with unique reactivities on account of their characteristic redox properties. In the present work, we present a facile POM‐mediated one‐pot aqueous synthesis method for the production of single‐crystalline Pd NCs with controlled shapes and sizes. The POMs could function as both reducing and stabilizing agents in the formation of NCs, and thus gave a fine control over the nucleation and growth kinetics of NCs. The prepared POM‐stabilized Pd NCs exhibited excellent catalytic activity and stability for electrocatalytic (formic acid oxidation) and catalytic (Suzuki coupling) reactions compared to Pd NCs prepared without the POMs. This shows that the POMs play a pivotal role in determining the catalytic performance, as well as the growth, of NCs. We envision that the present approach can offer a convenient way to develop efficient NC‐based catalyst systems.