Synthesis and structural investigation of Pd/Ag bimetallic nanoparticles prepared by the solvothermal method

Pd/Ag bimetallic nanoparticles have been synthesized successfully by reducing PdCl₂ and AgNO₃ mixture in ethylene glycol solution using the solvothermal method. The prepared samples have been characterized by UV–vis, XRD, TEM, HRTEM, EDS, and XPS, respectively. Moreover, the bimetallic particles possess alloy and core-shell structure from the HRTEM images. Here, the lattice fringe spacing of Pd/Ag bimetallic nanoparticles corresponds to its (111) plane, which is between that of the Pd and Ag nanoparticles prepared under the same conditions. Furthermore, the possible formation mechanism and factors influencing the formation of Pd/Ag bimetallic nanoparticles, such as reaction temperature and time, have also been investigated.     

Synthesis and Reactivity of Magnetically Diverse Au@Ni Core–Shell Nanostructures

Core–shell bimetallic Au@Ni nanoparticles, with gold cores and thin nickel shells with overall size less than 10 nm, are synthesized and stabilized in pure cubic (fcc) and hexagonal (hcp) phase. Due to their unique crystal, electronic, and geometric structure, they show interesting magnetic and chemical properties. The Au@Ni_fcc is magnetic, whereas Au@Ni_hcp is non‐magnetic. Both the bimetallic nanostructures are stable to surface oxidation until 150 °C and show excellent catalytic activity for p‐nitrophenol reduction reaction.     

Sonication-Assisted Synthesis of Bimetallic Hg/Pd Alloy Nanoparticles for Catalytic Reduction of Nitrophenol and its Derivatives

In this article, we report a facile approach for the synthesis of an inexpensive catalyst of bimetallic Hg/Pd alloys comprising nanoparticles with various structures using a unique ultrasonic reaction that is conducted without the use of any reducing agent. The nanoparticles of Hg/Pd alloys (HgPd and Hg₂Pd₅) were achieved for the first time by sonicating an aqueous solution of Palladium (II) nitrate with metallic liquid mercury, as evidenced by XRD. EDS further confirmed the presence of Pd and Hg elements in the alloy. The surface morphology and structure of the nanoparticles have been systematically investigated by HRSEM, HRTEM and SAED pattern. In order to explore the catalytic activity of the as-synthesized nanoalloys, the catalytic reduction of 4-nitrophenol and a few other nitrophenol derivatives were investigated. Excellent catalytic activity was obtained for Hg/Pd (1:1) alloy, and the rate constant for the reduction of 4-NP with Hg/Pd at room temperature was found to be 58.4 × 10⁻³ s⁻¹, which is possibly the highest ever reported. The catalyst exhibited superior stability and reusability when compared with those reported in the literature for other catalysts based on noble metals.     

Photonic‐on‐a‐chip: a thermal actuated Mach‐Zehnder interferometer and a molecular thermometer based on a single di‐ureasil organic‐inorganic hybrid

An integrated photonic‐on‐a‐chip device based on a single organic‐inorganic di‐ureasil hybrid was fabricated for optical waveguide and temperature sensing. The device is composed by a thermal actuated Mach‐Zehnder (MZ) interferometer operating with a switching power of 0.011 W and a maximum temperature difference between branches of 0.89 ºC. The MZ interferometer is covered by a Eu³⁺/Tb³⁺ co‐doped di‐ureasil luminescent molecular thermometer with a temperature uncertainty of 0.1ºC and a spatial resolution of 13 µm. This is an uncommon example in which the same material (an organic‐inorganic hybrid) that is used to fabricate a particular device (a thermal‐actuated MZ interferometer) is also used to measure one of the device intrinsic properties (the operating temperature). The photonic‐on‐a‐chip example discussed here can be applied to sense temperature gradients with high resolution (10⁻³ ºC·µm⁻¹) in chip‐scale heat engines or refrigerators, magnetic nanocontacts and energy‐harvesting machines.     

Characterisation of Sonochemically Produced PdO Nanoparticles by X‐ray Absorption Near Edge Structure Spectroscopy

Brij‐35 [polyoxyethylene(23) lauryl ether] stabilised palladium nanoparticles, obtained on attempted sonochemical reduction of PdCl₂ by sodium sulfite in water under Argon, instantaneously oxidized to PdO. The particles obtained were stable and have narrow size distribution with an average size of 10 nm diameter. PdO nanoparticles were reduced to Pd nanoparticles in an autoclave by treatment with 50 bar hydrogen at 140 °C. The catalytic behaviour of Pd nanoparticles, thus obtained, is unusual in comparison with conventional Pd catalysts. The nanoparticles were characterized by UV‐Vis spectroscopy, TEM and their X‐ray Absorption Near Edge Structure (XANES) at the Pd‐L‐III edge.     

On‐line surface enhanced Raman spectroscopic detection in a recyclable Au@SiO2 modified glass capillary

A facile method was developed to fabricate a high sensitive, reproducible and recyclable surface enhanced Raman spectroscopy (SERS) active glass capillary. The Au nanoparticles were synthesized through a seed‐mediated growth approach and then self‐assembled onto the inner wall of glass capillaries. The attached Au nanoparticles were homogeneously coated with thin silica shell by using the silane coupling agent to functionalize the Au surface. By using thiophenol (TP) as SERS probe molecules, the substrate exhibited robust SERS effects. The adsorbed SERS probe molecules could be rapidly and completely removed away by flowing sodium borohydride solution and thus to obtain a refresh Au@SiO₂ film‐coated substrate for the cyclic detection on different species. The on‐line detection of TP and malachite green (MG) with different concentrations was performed in the flowing system. The intensities of SERS signals were dependent on concentrations of the detected molecules. The results indicated that the SERS‐active substrate has potential applications on the on‐line qualitative and quasi‐quantitative analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Adsorption of 2‐amino‐5‐cyanopyridine on a gold surface as probed by surface‐enhanced Raman spectroscopy

The adsorption of 2‐amino‐5‐cyanopyridine (2‐ACP) was investigated in solution at different pH values by i n situ surface‐enhanced Raman scattering (SERS) spectroscopy combined with the electrochemical method. The assignments of the main bands were first performed on the basis of the spectral features of similar compounds and with the help of density functional theory calculations. The results revealed that the adsorption and the interfacial structure of 2‐ACP on the Au electrode depended on the applied potential and the pH values of the solution. In the natural solution, 2‐ACP was adsorbed on the surface with a vertical orientation by the CN group from − 0.4 to − 1.0 V, whereas in the − 0.4 to 0.8 V range, the N atom of the pyridine ring was bound to the surface. A transition region for the reorientation of the two adsorption modes was observed from − 0.8 to − 0.4 V. A flat configuration was preferred at an extremely negative potential. A similar surface adsorption behavior was observed in the alkali environment, while the Stark effect slope decreased because of the adsorption of OH⁻. Due to the protonation of N atom in the acidic solution, the potential region for the coexistence of two configurations ranged from − 0.4 to 0.2 V. Additionally, a similar adsorption configuration was proposed on the Au colloids at various pH values. The results revealed that the adsorption behavior became more complex on colloidal surfaces than that on a rigid electrode surface. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization of Pd/Y multilayers with B4C barrier layers using GIXR and X‐ray standing wave enhanced HAXPES

Pd/Y multilayers are high‐reflectance mirrors designed to work in the 7.5–11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B₄C barrier layers located at the interfaces of the Pd and Y layers to reduce interdiffusion, which is expected from calculating the mixing enthalpy of Pd and Y. Grazing‐incident X‐ray reflectometry is used to characterize these multilayers. B₄C barrier layers are found to be effective in reducing Pd–Y interdiffusion. Details of the composition of the multilayers are revealed by hard X‐ray photoemission spectroscopy with X‐ray standing wave effects. This consists of measuring the photoemission intensity from the samples by performing an angular scan in the region corresponding to the multilayer period and an incident photon energy according to Bragg's law. The experimental results indicate that Pd does not chemically react with B nor C at the Pd–B₄C interface while Y does react at the Y–B₄C interface. The formation of Y–B or Y–C chemical compounds could be the reason why the interfaces are stabilized. By comparing the experimentally obtained angular variation of the characteristic photoemission with theoretical calculations, the depth distribution of each component element can be interpreted.     

Facile Synthesis of Gd(OH)3‐Doped Fe3O4 Nanoparticles for Dual‐Mode T1‐ and T2‐Weighted Magnetic Resonance Imaging Applications

The facile hydrothermal synthesis of polyethyleneimine (PEI)‐coated iron oxide (Fe₃O₄) nanoparticles (NPs) doped with Gd(OH)₃ (Fe₃O₄‐Gd(OH)₃‐PEI NPs) for dual mode T₁‐ and T₂‐weighted magnetic resonance (MR) imaging applications is reported. In this approach, Fe₃O₄‐Gd(OH)₃‐PEI NPs are synthesized via a hydrothermal method in the presence of branched PEI and Gd(III) ions. The PEI coating onto the particle surfaces enables further modification of poly(ethylene glycol) (PEG) in order to render the particles with good water dispersibility and improved biocompatibility. The formed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs have a Gd/Fe molar ratio of 0.25:1 and a mean particle size of 14.4 nm and display a relatively high r₂ (151.37 × 10^?3m ^?1 s^?1) and r₁ (5.63 × 10^?3m ^?1 s^?1) relaxivity, affording their uses as a unique contrast agent for T₁‐ and T₂‐weighted MR imaging of rat livers after mesenteric vein injection of the particles and the mouse liver after intravenous injection of the particles, respectively. The developed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs may hold great promise to be used as a contrast agent for dual mode T₁‐ and T₂‐weighted self‐confirmation MR imaging of different biological systems.     

Synthesis of Self‐Stabilized Poly(N‐(3‐Amidino)‐Aniline) Particles and their CO2‐Responsive Properties

Novel CO₂‐responsive conductive polymer particles based on poly(N‐(3‐amidino)‐aniline) (or PNAAN) are reported in this work. A CO₂‐responsive N‐(3‐amidino)‐aniline (NAAN) monomer is firstly synthesized with the pendant amidine group at the meta‐position of aniline (AN) and subsequently polymerized into the PNAAN polymer by chemical oxidation. Self‐assembly of PNAAN in turn forms the polymer particles. In the strong or weak acid media, the amidine group protonates into cationic amidinium and self‐stabilizes the PNAAN particles without the use of any stabilizers. The reaction media are found to affect the polymerization rate and self‐assembly of particles, and hence the size and size distribution of the resultant particles. The particles synthesized in strong basic media show CO₂‐responsvie properties since the H⁺ released by dissolved CO₂ (dCO₂) can protonate the amidine group into hydrophilic amidinium group and result in swelling of the PNAAN particles. Zeta‐potential measurements show the reversible change of particle surface charges in the presence and absence of dCO₂. Dynamic light scattering (DLS) measurements show the particle size linearly changed with dCO₂ concentration in the range of 5 × 10^?4 and 2.5 × 10^?2 atm. This is the first reported CO₂‐responsive polyaniline (PANI) particles for dCO₂ sensing or reversible fixation of CO₂.     

Chromatographic paper embedded with silver nanostructure as a disposable substrate for surface‐enhanced Raman spectroscopy and catalytic reactor

The high cost of regular diagnostic kits severely impeded its uses for routine clinical assay and fieldworks. A cost‐effective chromatography paper is chemically modified with Ag nanostructures using the simple electroless silver deposition, producing a scalable and disposable substrate for surface‐enhanced Raman spectroscopy, as well as a large scale of catalytic active sites over many chemical reactions. Synergetic measurement including surface‐enhanced Raman spectroscopy and laser desorption ionization‐mass spectrometry is performed on Ag decorated filter paper using a thiol containing compound as indicator, allowing for the acquisition of spatially correlated spectroscopy in the tandem mode. In addition, hydrophilic porous cellulose network that contains a certain amount of liquid naturally served as a chemical reactor for molecular transport and reaction. Positive results from catalytic reaction on metallized paper convincingly demonstrated that total microanalysis system on paper (μ‐TASoP), as a compelling alternative would find a wide breadth of applications in developing disposable medical devices and customary laboratory assays. Copyright © 2015 John Wiley & Sons, Ltd.     

Ru(III), Os(VIII), Pd(II) and Pt(IV) catalysed oxidation of glycyl–glycine by sodium N‐chloro‐p‐toluenesulfonamide: comparative mechanistic aspects and kinetic modelling

The Ru(III)/Os(VIII)/Pd(II)/Pt(IV)‐catalysed kinetics of oxidation of glycyl–glycine (Gly‐Gly) by sodium N‐chloro‐p‐ toluenesulfonamide (chloramine‐T; CAT) in NaOH medium has been investigated at 308 K. The stoichiometry and oxidation products in each case were found to be the same but their kinetic patterns observed are different. Under comparable experimental conditions, the oxidation‐kinetics and mechanistic behaviour of Gly‐Gly with CAT in NaOH medium is different for each catalyst and obeys the underlying rate laws:

• Rate = k [CAT]_t [Gly‐Gly]⁰ [Ru(III)][OH^?]^x
• Rate = k [CAT]_t[Gly‐Gly]^x [Os(VIII)]^y[OH^?]^z
• Rate = k [CAT]_t[Gly‐Gly]^x [Pd(II)][OH^?]^y
• Rate = k [CAT]_t[Gly‐Gly]⁰ [Pt(IV)]^x[OH^?]^y

Here, and x, y, z < 1 in all the cases. The anion of CAT, CH₃C₆H₄SO₂NCl^?, has been postulated as the common reactive oxidising species in all the cases. Under comparable experimental conditions, the relative ability of these catalysts towards oxidation of Gly‐Gly by CAT are in the order: Os(VIII) > Ru(III) > Pt(IV) > Pd(II). This trend may be attributed to the different d‐electronic configuration of the catalysts. Further, the rates of oxidation of all the four catalysed reactions have been compared with uncatalysed reactions, under identical experimental conditions. It was found that the catalysed reaction rates are 7‐ to 24‐fold faster. Based on the observed experimental results, detailed mechanistic interpretation and the related kinetic modelling have been worked out for each catalyst. Copyright © 2008 John Wiley & Sons, Ltd.     

XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca

Klebsiella oxytoca BAS‐10 ferments citrate to acetic acid and CO₂, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS‐10, in the presence of palladium species, to increase the EPS secretion and improve Pd‐EPS yield. In this process, bi‐metallic (FePd‐EPS) biomaterials were produced for the first time. The morphology of bi‐metallic EPS, and the chemical state of the two metals in the FePd‐EPS, are investigated by transmission electron microscopy, Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence, and X‐ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono‐metallic Pd‐EPS and Fe‐EPS complexes. Iron in FePd‐EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe³⁺, with a small amount of Fe²⁺ in the structure, most probably a mixture of different nano‐crystalline iron oxides and hydroxides, as in mono‐metallic Fe‐EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face‐centred cubic structure in both bi‐metallic (FePd‐EPS) and mono‐metallic (Pd‐EPS) species. In bi‐metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi‐metallic species (FePd‐EPS) in a hydrodechlorination reaction is improved in comparison with mono‐metallic Pd‐EPS.     

Component‐Controlled Synthesis of Small‐Sized Pd‐Ag Bimetallic Alloy Nanocrystals and Their Application in a Non‐Enzymatic Glucose Biosensor

Small‐sized monodisperse Pd‐Ag alloy nanocrystals (NCs) are synthesized via a solid‐liquid and solid‐solid phase chemical route, i.e., sequential reduction of Pd(NO₃)₂ and AgNO₃ solid precursors in the liquid mixture of dodecylamine and 1‐octadecene, followed by fusion of formed Pd and Ag NCs at 250 °C. By controlling the addition sequence and molar ratio of the metallic precursors, a series of Pd‐Ag alloy NCs, including Pd₅Ag, Pd₂Ag, PdAg, PdAg₂, and PdAg₅, is obtained. The alloy NCs are highly crystallized and exhibit a strong atomic ensemble in addition to component‐dependent electronic effects. Pd₂Ag NCs have unique structure and electronic properties, showing a much faster electron transfer process at a modified glassy carbon electrode interface compared with that of other alloys. Therefore, the Pd₂Ag NCs are chosen as the electrocatalyst to evaluate the performance of Pd‐Ag nanoalloy and a novel non‐enzymatic glucose biosensor is fabricated. The biosensor exhibits an acceptable reproducibility, a good stability and low interferences, which can be used to examine glucose in clinic blood serum samples. This work provides a simple multiphasic reaction system to synthesize binary alloy NCs with well‐controlled componential ratio and opens the avenue to utilize them in biosensing or other advanced technological fields.     

Silver nanoparticles synthesized by direct photoreduction of metal salts. Application in surface‐enhanced Raman spectroscopy

A simple synthesis method of silver nanoparticles and its application as an active surface‐enhanced Raman spectroscopy (SERS) colloid are presented in this work. The photoreduction of AgNO₃ in presence of sodium citrate (NaCit) was carried out by irradiation with different light sources (UV, white, blue, cyan, green, and orange) at room temperature. The evaluation of silver nanoparticles obtained as a function of irradiation time (1–24 h) and light source was followed by UV‐visible absorption spectroscopy. This light‐modification process results in a colloid with distinctive optical properties that can be related to the size and shape of the particles. The Ag colloids, as prepared, were employed as active colloids in SERS. Pyridine and caffeine were used as test molecules. Copyright © 2008 John Wiley & Sons, Ltd.     

Formation of three‐dimensional GaAs microstructures by combination of wet and metal‐assisted chemical etching

Previously, plasma‐enhanced dry etching has been used to generate three‐dimensional GaAs semiconductor structures, however, dry etching induces surface damages that degrade optical properties. Here, we demonstrate the fabrication method forming various types of GaAs microstructures through the combination etching process using the wet‐chemical solution. In this method, a gold (Au)‐pattern is employed as an etching mask to facilitate not only the typical wet etching but also the metal‐assisted chemical etching (MacEtch). High‐aspect‐ratio, tapered GaAs micropillars are produced by using [HF]:[H₂O₂]:[EtOH] as an etching solution, and their taper angle can be tuned by changing the molar ratio of the etching solution. In addition, GaAs microholes are formed when UV light is illuminated during the etching process. Since the wet etching process is free of the surface damage compared to the dry etching process, the GaAs microstructures demonstrated to be well formed here are promising for the applications of III–V optoelectronic devices such as solar cells, laser diodes, and photonic crystal devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Raman spectroscopic investigation of a new self‐assembly monolayer material 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid for organic light‐emitting devices

We have synthesized 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid (4‐[PBA]) and investigated its molecular vibrations by infrared and Raman spectroscopies as well as by calculations based on the density functional theory (DFT) approach. The Fourier transform (FT) Raman, dispersive Raman and FT‐IR spectra of 4‐[PBA] were recorded in the solid phase. We analyzed the optimized geometric structure and energies of 4‐[PBA] in the ground state. Stability of the molecule arising from hyperconjugative interactions and charge delocalization was studied using natural bond orbital analysis. The results show that change in electron density in the σ* and π* antibonding orbitals and E₂ energies confirm the occurrence of intramolecular charge transfer within the molecule. Theoretical calculations were performed at the DFT level using the Gaussian 09 program. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution. The good agreement between the experimental and theoretical spectra allowed positive assignment of the observed vibrational absorption bands. Finally, the calculation results were applied to simulate the Raman and IR spectra of the title compound, which show agreement with the observed spectra. Copyright © 2011 John Wiley & Sons, Ltd.