Morphology-dependent structures and catalytic performances of Au nanostructures on Cu_2O nanocrystals synthesized by galvanic replacement reaction

Au nanostructures were prepared on uniform Cu2O octahedra and rhombic dodecahedra via the galvanic replacement reaction between HAuCl 4 and Cu2O. The compositions and structures were studied by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HRTEM), X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and in-situ DRIFTS spectroscopy of CO adsorption. Different from the formation of Au-Cu alloys on Cu2O cubes by the galvanic replacement reaction (ChemNanoMat 2 (2016) 861-865), metallic Au particles and positively-charged Au clusters form on Cu2O octahedra and rhombic dodecahedra at very small Au loadings and only metallic Au particles form at large Au loadings. Metallic Au particles on Cu2O octahedra and rhombic dodecahedra are more active in catalyzing the liquid phase aerobic oxidation reaction of benzyl alcohol than positively-charged Au clusters. These results demonstrate an obvious morphology effect of Cu2O nanocrystals on the liquid-solid interfacial reactions and prove oxide morphology as an effective strategy to tune the surface reactivity and catalytic performance. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells.In this work,a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires(PtTe NW)by using Te NW as an efficient sacrificial template.The existence of Te atoms separates the continuous Pt atoms,triggering a direct reaction pathway of formic acid electrooxidation reaction(FAEOR)at PtTe NW.The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg^(-1)/45.34 A m^(-2)at 0.643 V potential,which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles,respectively.Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms,which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR.This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

A novel PdNi/Al_2O_3 catalyst prepared by galvanic deposition for low temperature methane combustion

Galvanic deposition method was used to prepare the Pd/Ni-Al2O3-GD catalyst for the combustion of methane under lean conditions. The new catalyst and compared catalysts （Pd/Al2O3-IW, Pd-Ni/Al2O3-IW, Pd/Ni-Al2O3-IW） prepared by incipient wetness impregnation were characterized by N2-physisorption, XRD and TEM to clarify particle size and size distribution of palladium species. Combined O2-TPD and XPS results with the catalytic data, it shows that the surface palladium species with low valence exhibits better combustion performance due to their stronger interaction with support. The results indicate that the galvanic deposition method is an effective route to prepare efficient catalyst for methane combustion, and it also provides useful information for improving the present commercial catalyst.

Deep eutectic solvent-induced synthesis of Ni-Fe catalyst with excellent mass activity and stability for water oxidation

Ni-Fe bimetallic electrodes are currently recognized as a kind of benchmark transition metal-based oxygen evolution reaction(OER)electrocatalysts.Facile synthesis of Ni-Fe bimetallic electrode materials with excellent catalytic activity and satisfied stability by a simple and low-cost route is still a big challenge.Herein,well-defined Ni-Fe nanoparticles in-situ developed on a planar Fe substrate(Ni-Fe NPs/Fe)is fabricated via a facile one-step galvanic replacement reaction(GRR)carried out in an Ethaline-based deep eutectic solvent(DES).The prepared Ni-Fe NPs/Fe exhibits outstanding OER performance,which needs an overpotential of only 319 mV to drive a current density of 10 mA cm^(-2),with a small Tafel slope of 41.2 mV dec^(-1) in 1.0 mol L^(-1) KOH,high mass activity(up to 319.78 A g^(-1) at an overpotential of 300 mV)and robust durability for 200 h.Impressively,the Ni-Fe bimetallic oxygen-evolution electrode obtained from the Ethaline-based DES is catalytically more active and durable than that of its counterpart derived from the 4.2 mol L^(-1) NaCl aqueous solution.The reason for this is mainly related to the different morphology and surface state of the Ni-Fe catalysts obtained from these different solvent environments,particularly for the differences in phy-chemical properties,active species formed and deposition kinetics,offered by the Ethaline-based DES.

Triangular Au-Ag framework nanostructures prepared by multi-stage replacement and their spectral properties

Triangular Au-Ag framework nanostructures （TFN） were synthesized via a multi-step galvanic replacement reaction （MGRR） of single-crystalline triangular silver nanoplates in a chlorauric acid （HAuCl4） solution at room temperature. The morphological, compositional, and crystal structural changes involved with reaction steps were analyzed by using transmission electron microscopy（TEM）, energy-dispersive X-ray spectrometry （EDX）, and X-ray diffraction. TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. The in-plane dipolar surface plasmon resonance （SPR） absorption band of the Ag nanoplates locating initially at around 700 nm gradually redshifted to 1 100 nm via a multi-stage replacement manner after 7 stages. The adding amount of HAuCl4 per stage influenced the average redshift value per stage, thus enabled a fine tuning of the in-plane dipolar band. A proposed formation mechanism of the original Ag nanoplates developing pores while growing Au nanoparticles covering this underlying structure at more reaction steps was confirmed by exploiting surface-enhanced Raman scattering （SERS）.

Galvanic replacement reaction for in situ fabrication of litchi-shaped heterogeneous liquid metal-Au nano-composite for radio-photothermal cancer therapy

With tremendous research advances in biomedical application,liquid metals(LM)also offer fantastic chemistry for synthesis of novel nano-composites.Herein,as a pioneering trial,litchi-shaped heterogeneous eutectic gallium indium-Au nanoparticles(EGaIn-Au NPs),served as effective radiosensitizer and photothermal agent for radio-photothermal cancer therapy,have been successfully prepared using in situ interfacial galvanic replacement reaction.The enhanced photothermal conversion efficiency and boosted radio-sensitization effect could be achieved with the reduction of Au nanodots onto the eutectic gallium indium(EGaIn)NPs surface.Most importantly,the growth of tumor could be effectively inhibited under the combined radio-photothermal therapy mediated by EGaIn-Au NPs.Inspired by this approach,in situ interfacial galvanic replacement reaction may open a novel strategy to fabricate LM-based nano-composite with advanced multi-functionalities.

Preparation of a Pt-Ni_(2)P/NF catalyst for highly efficient hydrogen evolution using a magnetic field to promote Ni-Pt galvanic replacement

The noble metal Pt is an ideal catalyst for promoting the hydrogen evolution reaction(HER)during the electrolysis of water.However,Pt is also expensive and suffers from low utilization rates.In this work,a Pt-Ni_(2)P/NF nanorod catalyst with a low Pt loading was synthesized under different magnetic fields,and it was found that the application of a magnetic field can increase the rate of the galvanic replacement reaction.When the magnetic field strength increases from 0 to 600 mT,the chemical reaction rate increases gradually,and the utilization rate of Pt increased by 2.3 times under 600 mT.The mechanism of the magnetic field-induced magnetohydrodynamic(MHD)effect on the galvanic replacement reaction was revealed.In a 1 M KOH solution and at a current density of 10 mA cm^(-2),the overpotential of Pt-Ni_(2)P/NF prepared by applying a 600 mT magnetic field was as low as 15 mV and the Tafel slope was 37 mV dec^(-1),compared with values of 82 mV and 70 mV dec^(-1) for a specimen prepared without a magnetic field.Additionally,at an overpotential of 90 mV,the mass-based Pt activity of the former material was 12 times greater while its turnover frequency was 19 times greater.This work provides theoretical and technical knowledge expected to assist in the controllable preparation of materials in magnetic fields and the efficient utilization of metallic resources.

Nanostage Alloying of Metals in Liquid Phase

Alloying of metals is known from antiquity. Alloy making i.e., homogenizing metals started in a “hit-or-miss” way. The 1st alloy from copper (Cu) and tin (Sn) was produced around 2500 BC and from then Bronze Age began. Subsequently iron (Fe) age started after the Bronze Age. Aluminium (Al) alloying was discovered much later because pure Al could not be recovered easily even though Al is the most abundant metal in the earth’s crust. Refining of Al is a very difficult job because of its strong affinity towards oxygen. To ease alloying, melting points (mp) of the individual constituents and reactivity of metal towards oxygen were the hurdles. Now understanding the thermodynamics of metal mixing has paved alloying. Periodic properties of elements concerning size, electronegativity, crystal structure, valency, lattice spacing, etc. are considered for alloying. In this feature article, more emphasis is given to Hume-Rothery rules in which the necessary parameters for alloying have been illustrated. Importantly standard electrode potential (E0) values, eutectic, phase diagram, size-related strain in metals, etc. have been looked into in the present discussion. One elegant example is Sn-Pb alloy, known as soft solder. Soft solder was in use for many years to connect metals and in electric circuitry. Low melting, flowability, and conductivity of soft solder had placed Sn-Pb alloy a unique position in industries, laboratories and even in cottage industries. However, toxic Pb volatilizes during soldering and hence soft solder is banned almost in all countries. We felt the need for a viable alternative to obtain soldering material and then silver (Ag) based highly conducting, an eco-friendly alloy of Sn resulted in from a high boiling liquid. The discovery engenders not only a new conducting soldering alloy but also a new concept of melting metals together. Furthermore, new ideas of alloying have been generalized at their nanostages from a suitable high boiling solvent.

Chiral AuCu heterostructures with site-specific geometric control and tailored plasmonic chirality

Rational design and construction of chiral-achiral hybrid structures are of great importance to realize the multifunctional complex chiral structures toward emerging technological applications. However, significant challenges remain due to the lack of fine control over the heterostructure. Here, we have developed a general bottom-up synthetic strategy for the site-selective growth of Cu nanodomains on intrinsically chiral Au nanocrystals. Chiral AuCu heterostructures with three distinct architectures were achieved by controlling the overgrowth of Cu nanodomains in a site-specific manner. The geometry-dependent plasmonic chirality of the heterostructures was demonstrated experimentally by circular dichroism spectroscopy and theoretically through finite-difference time-domain simulations. The site-specific geometric control of chiral AuCu heterostructures was also extended to employ anisotropic chiral Au nanoplates and nanorods as the building blocks. By virtue of the galvanic replacement reactions between metal ions and Cu atoms, chiral heterostructures with increasing architectural complexity and compositional diversity can be further achieved. The current work not only opens up a promising strategy to synthesize complex chiral hybrid nanostructures but also provides an important knowledge framework that guides the rational design of multifunctional chiral hybrid nanostructures toward chiroptical applications.

Surface engineering on segmented copper-iron nanowires arrays

Surface engineering that could modulate the surface shape to be endowed with the high specific surface ratio,abundant chemical dangling bonds and improved defects exposure is highly desired and needs further exploring.Here,we report a facile strategy of surface engineering on decorating the controllable segmented copper-iron nanowires arrays(Cu-Fe NWs)with their respective hydroxides.Specifically,the pristine segmented Cu-Fe NWs are firstly synthesized via sequentially electrodepositing Cu NWs and Fe NWs inside the nanochannels of anode aluminum oxide(AAO)template.Subsequently,the surface and interface of Cu-Fe NWs are wet-chemically etched,in which the metallic Cu and Fe are partially converted into Cu(OH)_(x)nano-fibrous roots(NFRs)and FeO(OH)_(y)nanoparticles(NPs),and finally decorate around the respective outer-surface of Cu NWs and Fe NWs segments.As one case of the applications in hydrogen evolution reaction(HER),our surface-modified Cu-Fe NWs exhibit improved catalytic activity compared with Fe NWs.

Matryoshka-caged gold nanorods： Synthesis, plasmonic properties, and catalytic activity

Matryoshka-caged gold nanorods （mCGNRs） were successfully synthesized by alternating between a seed-mediated silver-coating method and galvanic replacement reactions （GRRs）. As the number of matryoshka layers of the mCGNRs increased, the plasmon resonance peak broadened and was red-shifted, and the catalytic activity towards the reduction of 4-nitrophenol （4-NTP） increased. When mCGNRs with 6 layers were used as nanocatalysts in the reduction of 4-nitrophenol, the reaction rate coefficient was 5.2- and 3.7-times higher than that of the gold-nanorod- and caged-gold-nanorod-catalyzed reductions of 4-nitrophenol, respectively. In addition, the surface-plasmon-resonance-based absorption of light enhanced the catalytic performance of the mCGNRs. With the support of a polyurethane foam, the mCGNRs synthesized in this study can be applied as recydable heterogeneous catalysts for the reduction of 4-nitrophenol.

Preparation of Large-area Controllable Patterned Silver Nanocrystals for High Sensitive and Stable Surface-enhanced Raman Spectroscopy

A novel and facile method for fabricating large-area pattemed silver nanocrystals was introduced and the investigation on the high sensitive and stable surface-enhanced Raman spectroscopy（SERS） of the nanocrystals was carried out. Nanostructured silicon substrate was processed by laser interference and used as a template for growing silver nanocrystals via galvanic battery reaction method. The substrate with large area for violent chemical reaction was tailored into a nanocell array. The limited reaction area hindered the growth of silver nanocrystals and made their size uniform and controllable. The size and gaps of the nanocrystals could be controlled by template period and ratio, which were easily reproduced by laser interference. Taking 10^-8 to 10^-11 mol/L RhoG for example, the optimized silver arrays exhibited great potential for ultrasensitive molecular sensing in terms of its high SERS enhancement ability, favorable stability, and excellent reproducibility.