Deformation behavior of nanograined platinum films

Anomalously low elastic moduli have been routinely reported in nanoindentation studies, but it was not clear if the behavior was real or an artifact of the measurement technique. Here, we report on similarly low elastic moduli of <111> textured, nanograined platinum films. In this work the presence of anomalous properties was verified by eliminating possible sources of experimental artifacts, namely the films' texture, piling-up of material around the indenter tip, substrate effects, microcracking, and delamination of the film from the substrate. Instead, the peculiar behavior of the nanograined, noble metal film was linked to time-dependent, elastic constitutive behavior (i.e., anelasticity).     

Electrochemical determination of cadmium(II) at platinum electrode modified with kaolin by square wave voltammetry

In this work, determination of cadmium(II) using square wave voltammetry (SWV) was described. The method is based on accumulation of these metal ions on kaolin platinum electrode (K/Pt). The K/Pt performance was optimized with respect to the surface modification and operating conditions. The optimized conditions were obtained in pH of 5.0 and accumulation time of 25 min. Under the optimal conditions, the relationship between the peak current versus concentration was linear over the range of 9 × 10⁻⁸ to 8.3 × 10⁻⁶ mol L⁻¹. The detection limit (DL, 3σ) was 5.4 × 10⁻⁹ mol L⁻¹. The analytical methodology was successfully applied to monitor the Cd(II) content in natural water. Interferences were also evaluated.     

Optical second harmonic generation at platinum phthalocyanine-modified platinum electrodes

Optical second harmonic generation (SHG) has been used to observe changes within electronically conducting platinum phthalocyanine (PtPc) films deposited on polycrystalline platinum electrodes as the film undergoes electrochemical modification. PtPc-modified electrodes produced enhanced SHG responses over bare platinum surfaces. This is proposed to be due to an electric quadrupole contribution from the PtPc molecule. Examination of the polarization dependence of the SHG response reveals that electroactive PtPc molecules exist in environments both parallel and perpendicular to the electrode surface. It has been possible to observe redox processes occurring within the films by monitoring the magnitude of the SHG response with variations in potential. The decrease in SHG signal has been shown empirically to be proportional to the charge removed from the film during oxidation of the phthalocyanine (Pc) ring.     

Characterization of electrode fouling and surface regeneration for a platinum electrode on an electrophoresis microchip

A method of electrochemically cleaning noble metal electrodes is presented and characterized for electrophoresis microchips with electrochemical detection. First, the loss of sensitivity due to electrode fouling by serotonin is characterized as a function of injection number and analyte concentration. Signal attenuation is observed to be greater at high concentrations (100 microM) and negligible at very low concentrations (approximately 1 microM). Next, an electrochemical treatment procedure is optimized to yield sensitive and reproducible amperometric detection of the highly adsorptive compounds, serotonin and histamine. Thus, the performance of the electrode is reproducibly regenerated following as much as a approximately 99% reduction in surface activity. Utilizing the optimized three-level waveform, derived from that used for pulsed amperometric detection, detection limits as low as 78 nM and 17 microM have been obtained for serotonin and histamine, respectively. In the case of serotonin, this represents the lowest detection limit for a neurotransmitter by microchip electrophoresis with amperometric detection and the first report of amperometric detection of histamine detection at an unmodified platinum electrode. Repeated use of the electrode and application of electrochemical treatment did not appear to measurably affect the noise, longevity, metal adhesion, or physical appearance of the electrode.     

Direct determination of oxalic acid by a bare platinum electrode contrasting a platinum nanoparticles-modified glassy carbon electrode

A bare platinum disk electrode without further decoration was directly used to determine oxalic acid (OA), showing good linear ranges of 0.57–104.01 μM and 104.01–228.75 μM with a low detection limit of 0.38 μM (S/N = 3). In contrast, platinum nanoparticles (PtNPs) dispersed on a glassy carbon electrode were successfully achieved by an one-step electrochemical deposition method, possessing relatively wider linear detection ranges of 1.14–342.80 μM and 342.80–548.92 μM for OA with a lower detection limit of 0.28 μM (S/N = 3). Both the proposed electrochemical sensors exhibit great reproducibility, stability and selectivity. In particular, they have been applied to the determination of OA in real spinach samples, showing excellent analytical performance.     

Adsorption of platinum(IV) and palladium(II) from aqueous solution by thiourea-modified chitosan microspheres

The chitosan microparticles were prepared using the inverse phase emulsion dispersion method and modified with thiourea (TCS). TCS was characterized by scanning electron microscope (SEM), the Fourier transform infrared (FT-IR) spectra, sulfur elemental analysis, specific surface area and pore diameter. The effects of various parameters, such as pH, contact time, initial concentration and temperature, on the adsorption of Pt(IV) and Pd(II) by TCS were investigated. The results showed that the maximum adsorption capacity was found at pH 2.0 for both Pt(IV) and Pd(II). TCS can selectively adsorb Pt(IV) and Pd(II) from binary mixtures with Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). The adsorption reaction followed the pseudo-second-order kinetics, indicating the main adsorption mechanism of chemical adsorption. The isotherm adsorption equilibrium was well described by Langmuir isotherms with the maximum adsorption capacity of 129.9 mg/g for Pt(IV) and 112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and Pd(II) decreased with temperature increasing. The negative values of enthalpy (ΔH°) and Gibbs free energy (ΔG°) indicate that the adsorption process is exothermic and spontaneous in nature. The adsorbent was stable without loss of the adsorption capacity up to at least 5 cycles and the desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H₂SO₄ eluent was used. The results also showed that the preconcentration factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the recovery was found to be more than 97% for both precious metal ions.     

Effect of encapsulation with zeolite and coating with TiO2 on the thermal stability of caffeine during melt extrusion of a PET/TiO2@(zeolite/caffeine) nanocomposite

The practice of encapsulating a functional material in a thermally stable porous material displays great potential in preventing decomposition during high-temperature processing. In this study, caffeine encapsulated in zeolite was coated with TiO₂ to withstand high-temperature melt extrusion with poly(ethylene terephthalate) (PET). Two coating processes were trialed: in situ encapsulation and coating where TiO₂ precursor was added to zeolite/caffeine solution; and ex situ coating in which pre prepared zeolite/caffeine capsules were added to the TiO₂ precursor for coating. The TiO₂-coated nanocomposites were melt-extruded with PET at 285?°C. Residual amounts of caffeine confirmed the shielding effect of the TiO₂ coating during the high-temperature melt extrusion. The in situ TiO₂ coating process was more effective than the ex situ process.     

红景天苷在玻碳电极上的伏安行为研究

采用循环伏安法,线性扫描伏安法,微分脉冲伏安法等现代电化学技术研究红景天苷在玻碳电极(GCE)上的电化学行为。在p H=9.0的B–R缓冲液中,红景天苷在0.48V(vs.Ag/Agcl)电位处产生一灵敏的微分脉冲阳极氧化峰。峰电流与红景天苷的浓度在5×10-7mol/L~2×10-5mol/L范围内呈良好的线性关系,检测限为5.5×10-9mol/L。建立了一种简单、快速、灵敏的测定红景天苷的电化学分析方法,该法成功应用于鼠血清和人尿样中红景天苷的测定。     

XRF测定铂制品中Pt、Au、Pd、Ag、Cu、Ni等6种元素含量

本文利用XRF金标样的多元素回归方程,对Pt、Pd的荧光强度进行修正,修正后的荧光强度当作Au、Ag的荧光强度代入回归方程中,利用计算机编程计算铂制品中的Pt、Au、Pd、Ag、Cu、Ni等6种元素的含量。该法测定的准确度优于0.5％,适用于Pt的测定范围为85％～99.92％.具有无损、快速、准确、可靠等优点。     

Synthesis of platinum nanostructures in zeolite mordenite using a solid-state reduction method

Platinum nanoparticles and nanowires have been synthesized inside zeolite mordenite using a solid-state reduction method. Tetrammine platinum nitrate was introduced into the pores via incipient wetness impregnation and it was reduced using powder sodium borohydride. With this method it was possible to obtain single crystal nanowires along the edges of the zeolite particle. The molar ratio of the reducing agent to platinum atoms was a critical parameter for the formation of either uniform nanoparticles or nanowires. Using a regular aqueous sodium borohydride solution reduction it was not possible to obtain nanowires in this zeolite. To the best of the author's knowledge this is the first time sodium borohydride in its solid form is used as a reducing agent to form nanostructures and this is also the first time a solid-state method is used to form nanostructures in a zeolite.     

Growth of anisotropic platinum nanostructures catalyzed by gold seed nanoparticles

This paper reports an effective method for the synthesis of platinum nanostructures with anisotropic morphologies by decomposition of platinum dichloride in oleylamine at intermediate temperatures catalyzed by gold seed nanoparticles. A small quantity of spherical gold nanoparticles formed in situ was used to trigger the nucleation and anisotropic growth of the Pt nanocrystals. By varying the amount of gold seed nanoparticles, porous flower-like, irregular polyhedron-shaped, multi-branched rod shaped, and caterpillar-like Pt nanostructures were produced in high yields at 190–240 °C in reaction times of a few minutes. Control of morphology under different conditions has been systematically studied and a kinetically controlled induced growth mechanism has been proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Synthesis of platinum nanoparticles by aerosol assisted deposition method

An atmospheric pressure aerosol assisted deposition method has been developed to grow highly oriented nanoparticles and thin continuous films of platinum on a variety of substrates for applications such as catalysts including their use in proton exchange membrane fuel cells. Pt nanoparticles with sizes ranging from 4 nm to 78 nm were synthesized on Si, silicon dioxide coated Si substrates and carbon nanotubes. The size and density of the nanoparticles was found to depend strongly on the precursor carrier gas flow rate and deposition time. The particles showed preferential orientation of (111) that was independent of substrate used. The resulting nanoparticles were characterized by Scanning Electron Microscopy, X-ray Diffraction Spectroscopy and X-ray Photoelectron Spectroscopy in order to obtain information about their morphology, crystallinity and composition. The method developed can deposit uniform coatings of highly oriented, pure Pt nanoparticles without the need of any substrate pretreatment such as surface functionalization, deposition of seed layer for electrodeposition on insulating or semiconducting substrates, and without the use of expensive vacuum equipment.     

Unipolar pulse electrodeposition of nickel hexacyanoferrate thin films with controllable structure on platinum substrates

Unipolar pulse electrodeposition was used to prepare nickel hexacyanoferrate (NiHCF) films on platinum substrates with controllable structure. The unipolar pulse waveforms consisted of an applied cathodic potential during the on-period and the open-circuit potential during the off-period. The effects of the pulse deposition parameters on the electrochemical properties of NiHCF films were investigated by potential cycling in K⁺-containing electrolytes. The morphology and composition of NiHCF films were characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. The charge transfer and the stability of the film electrodes were also examined by cyclic voltammetry (CV). Experimental results show that the cathodic pulse potential is the primary factor influencing the composition of the NiHCF films. The structure of NiHCF films prepared with a pulse potential of 0.7 V SCE appears close to that of the “insoluble” form with a single reversible CV peak at lower voltage and a unit cell with a stoichiometry close to KNi₄^II[Fe^III(CN)₆]₃. These films exhibit good stability and high dynamics for charge transport. The application of more negative cathodic potential pulses produces less dense and robust NiHCF films, with a structure closer to the “soluble” form and an approximate stoichiometry K₈Ni₄^II[Fe^II(CN)₆]₄.     

玻碳电极上核黄素的电化学行为研究

用循环伏安法和线性扫描伏安法探讨核黄素在玻碳电极上的电化学行为。在多种缓冲液中测试,发现HAe—NaAe作为缓冲液时电化学氧化还原峰形最好,峰电流较大,电化学过程表现出良好的可逆性,电子转移数n为2,扩散系数D0为2．3&#215;10^-5cm^2&#183;s^-1;改变缓冲液的pH值,峰电流随pH值增大而负移,说明其在电极表面有吸附作用;光照后核黄素在-0．35V和-0．45V附近出现两个还原峰;分析实验数据可得,在1．0&#215;10^-4mol/L数量级时还原峰峰电流与其浓度呈现良好的线性关系。     

Preparation of Pt-PtOx thin films as electrode for memory capacitors

Pt-PtO_x thin films were prepared on Si(100) substrates at temperatures from 30 to 700°C by reactive r.f. magnetron sputtering with platinum target. Deposition atmosphere was varied with O₂/Ar flow ratio. The deposited films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Resistively of the deposited films was measured by d.c. four probe method. The films mainly consisted of amorphous PtO and Pt₃O₄ (or Pt₂O₃) below 400°C, and amorphous Pt was increased in the film as a deposition temperature increased to 600°C. When deposition temperature was thoroughly increased, (111) oriented pure Pt films were formed at 700°C. Compounds included in the films strongly depended on substrate temperature rather than O₂/Ar flow ratio. Electrical resistivity of Pt-PtO_x films was measured to be from the order of 10⁻¹ Ω cm to 10⁻⁵ Ω cm, which was related to the amount of Pt phase included in the deposited films.     

Effects of electrochemical synthetic conditions on surface property and photocatalytic performance of copper and iron-mixed p-type oxide electrodes

Earth-abundant copper and iron-mixed oxide(CuO/CuFeO_2; CFO) film electrodes are synthesized using an electrochemical deposition(ED) technique at two different ED potentials(-0.36 and-0.66 V vs saturated calomel electrode(SCE); denoted as ED-1 and ED-2, respectively). Then, their surface morphologies are compared, and the photo(electro)catalytic activities for the reduction of Cr(VI) are examined in aqueous solutions at pH 7 under simulated sunlight(AM 1.5 G; 100 mW cm~(-2)). The degree of the electrical potential applied to the ED process significantly affects the thickness of the synthesized electrode film and the intensity ratio of the diffraction peaks of CuO(111) and CuFeO_2(012). A 200 μm thick ED-2 sample with a distinct stacking of CuO on CuFeO_2 exhibits a larger broadband absorption spectrum than the 50-μm thick ED-1 with less separate stacking. Furthermore, the ED-2 sample has a higher intensity ratio of the diffraction peaks of CuO(111) and CuFe02(012) than ED-1. As-synthesized ED-2 samples produce larger photocurrents, leading to faster Cr(VI) reduction on the surface under given potential bias(-0.5 V vs SCE)or bias-free conditions. The energy levels(i.e., flatband potential) for the two samples are almost the same(only 10 mV difference), presumably supposing that the enhanced photoactivity of the ED-2 sample for Cr(VI) reduction is due to the facilitated charge transfer. The time-resolved photoluminescence emission spectra analysis reveal that the lifetime(r) of the charge carriers in the ED-1 sample is 0.103 ns, which decreases to 0.0876 ns in the ED-2. The ED-2 sample synthesized at a high negative potential is expected to contribute greatly to the application of other solar-to-fuel energy conversion fields as a highly efficient electrode material.     

Interaction of caffeine with montmorillonite

In this study, caffeine was adsorbed onto montmorillonite and the surface of the montmorillonite was observed before and after the adsorption. Observations were performed by X-ray diffractometry (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning probe microscopy (SPM). Measurement of the interlayer distance by XRD revealed that it narrowed to 1.09?nm after caffeine adsorption. Adsorption of a small amount of caffeine causes a broadening of d₀₀₁ peaks. This suggested that caffeine molecules were adsorbed into the interlayer space in part, resulting in an irregular layer stacking. The results of SPM observations of caffeine-adsorbed montmorillonite showed the existence of protrusions that are different from minerals on the surface of montmorillonite and suggested a possibility that the protrusions were caffeine molecules adsorbed onto the surface of montmorillonite. DRIFTS demonstrated that the intensity of peaks assigned to Si–OH and siloxane decreased with the increase in the amount of caffeine adsorbed. These results suggested that caffeine molecules were adsorbed both into the interlayer space and onto the surface and interacted with Si–OH and siloxane, in particular. These findings will help us to select ions to be held in the interlayer space and organic compounds to improve the amount of adsorption when montmorillonite is used in the manufacture of caffeine-free drinks and foods.     

Fabrication of platinum microheater on alumina substrate by micro-pen and laser sintering

This paper investigates an alternative method for rapid prototyping and manufacturing of platinum microheaters, in which a micro-pen is used to deposit thick-film platinum paste and laser sintering is employed to pattern the micro-pen-deposited coating. This work aims to enhance the efficiency of microheater fabrication and to reduce platinum-paste waste. The effect of laser power on the microstructure of the platinum microheaters was investigated. Thermal characterization of the microheater was also performed. The microheater can be operated at about 400 °C with a power of 3.55 W. The temperature of the microheater can change from 27 °C to 350 °C in less than 35 s.