Prussian blue nanoparticles potentiostatically electrodeposited on indium tin oxide/chitosan nanofibers electrode and their electrocatalysis towards hydrogen peroxide

Chitosan (CS) nanofibers were successfully used to modify indium tin oxide (ITO) electrode by electrospinning technique. Then, Prussian blue (PB) nanoparticles were electrodeposited on the CS nanofibers by potentiostatic technique in an acidic solution containing single ferricyanide. By this method, direct synthesis of PB nanoparticles on the nanofibers that were used for modifying electrode came true. Transmission electronic microscopy (TEM) showed that the average size of PB nanoparticles was about 50 nm. Selected-area electron diffraction (SAED) showed diffusive diffraction spots, indicating the mosaic structure of the PB nanoparticles on the CS nanofibers. X-ray powder diffraction (XRD) displayed the long-range disorder of CS nanofibers and demonstrated the formation of PB nanoparticles. Results of the scanning electron microscope (SEM) images indicated that the PB nanoparticles could be electrodeposited on the CS nanofibers. The amount of the PB nanoparticles on the CS nanofibers increased with increasing potential value of the electrodeposition. In addition, the cyclic voltammetric response displayed two characteristic redox couples of PB. The modified electrode exhibited electrocatalytic activity towards reduction of H₂O₂.     

Microwave-electrochemical formation of colloidal zinc oxide at fluorine doped tin oxide electrodes

Colloidal ZnO is obtained during microwave-enhanced electrochemical deposition experiments from an aqueous solution containing 0.1 M Zn(NO₃)₂ and 0.02 M H₂O₂ via repetitive negative going potential cycles from 0.3 to −0.8 V vs. SCE. The effects of temperature and temperature gradients on ZnO electro-formation at fluorine doped tin oxide (FTO) electrodes are investigated with both a conventional thermostated bath system (isothermal) and an in situ microwave electrochemistry system (non-isothermal). Mainly electrodeposition of ZnO is observed in uniformly heated stagnant solution and predominantly the electro-formation of ZnO colloid is observed in the presence of microwave-induced temperature gradients in a flowing solution. For the ZnO colloid prepared via microwave activation, SAXS data suggests an average particle radius of ca. 18 nm. The increase of ZnO nanoparticle concentration during repetitive potential scans is followed by photoluminescence spectroscopy. A possible mechanism for ZnO colloid formation during electrochemical reduction of H₂O₂ is suggested.     

Effects of linker molecules on the attachment and growth of gold nanoparticles on indium tin oxide surfaces

As a linker molecule to attach gold nanoparticles (AuNPs) on indium tin oxide (ITO) surfaces, cysteamine was examined together with well-known 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltrimethoxysilane (APTMS). Systematic comparisons of AuNPs’ nanostructures formed on ITO were carried out after the room temperature treatment in an ethanol solution of linker molecules followed by the attachment of AuNPs using (i) one-step immersion into the 20-nm Au colloidal solution or (ii) two-step immersion, i.e., a seed-mediated growth treatment. Consequently, in case (i), it was found that APTMS was most effective for denser and homogeneous attachment of AuNPs on ITO surfaces with keeping the dispersion. With the MPTMS or cysteamine linkers in case (i), AuNPs aggregated on the ITO surfaces, and the attached amount of AuNPs were larger with the MPTMS linker. In contrast, in case (ii), nanostructural growth of AuNPs was possible with MPTMS or cysteamine using the seed-mediated growth, while the growth of AuNPs was significantly suppressed with the APTMS linker. Because quite different results were obtained between APTMS and cysteamine, it was found that the attachment and nanostructural growth of AuNPs on the organic linker layers cannot be simply governed by the functional groups, -NH₂, on the outer surfaces.     

Nanocrystal and surface alloy properties of bimetallic Gold-Platinum nanoparticles

We report on the correlation between the nanocrystal and surface alloy properties with the bimetallic composition of gold-platinum(AuPt) nanoparticles. The fundamental understanding of whether the AuPt nanocrystal core is alloyed or phase-segregated and how the surface binding properties are correlated with the nanoscale bimetallic properties is important not only for the exploitation of catalytic activity of the nanoscale bimetallic catalysts, but also to the general exploration of the surface or interfacial reactivities of bimetallic or multimetallic nanoparticles. The AuPt nanoparticles are shown to exhibit not only single-phase alloy character in the nanocrystal, but also bimetallic alloy property on the surface. The nanocrystal and surface alloy properties are directly correlated with the bimetallic composition. The FTIR probing of CO adsorption on the bimetallic nanoparticles supported on silica reveals that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core-surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition. Electronic Supplementary Material  Supplementary material is available to authorised users in the online version of this article at     

Electrochemical deposition of gold-platinum alloy nanoparticles on an indium tin oxide electrode and their electrocatalytic applications

Gold-platinum (Au-Pt) hybrid nanoparticles (Au-PtNPs) were successfully deposited on an indium tin oxide (ITO) surface using a direct electrochemical method. The resulting nanoparticles were characterized by scanning electron microscopy (SEM), UV-vis spectroscopy, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and electrochemical methods. It was found that the size of the Au-PtNPs depends on the number of electrodeposition cycles. Au-PtNPs obtained by 20 electrodeposition cycles had a cauliflower-shaped structure with an average diameter of about 60 nm. These Au-PtNPs exhibited alloy properties. Electrochemical measurements showed that the charge transfer resistivity was significantly decreased for the Au-PtNPs/ITO electrode. Additionally, the Au-PtNPs displayed an electrocatalytic activity for nitrite oxidation and oxygen reduction. The Au-PtNPs/ITO electrodes reported herein could possibly be used as electrocatalysts and sensors.     

Effect of stabilizer on synthesis of indium tin oxide nanoparticles

Indium tin oxide nanoparticles with shapes varying from sphere to cubic were synthesized by controlling the ratio of the concentrations of the protective polymer (PVP) to indium tin oxide precursor in their preparation by co-precipitation. Transmission electron microscopy was used to determine the size and shape. The XPS spectra of the particles revealed that the atomic ratios of In:Sn and (In + Sn):O are 10.0:1.0 and 1.0:1.5, respectively for both of the spheres and the cubes. X-ray diffraction study showed that these particles have the same crystalline structure. Thus, it is shown that the formation of the various shapes of the ITO particles could be achieved by using different ratios of protective polymer instead of varying the protective polymer or the sintering process.     

Tunable surface plasmon resonance frequencies of monodisperse indium tin oxide nanoparticles by controlling composition,size, and morphology

Monodisperse indium tin oxide nanoparticles (ITO NPs) with high crystallinity have been synthesized by the rapid thermal injection method and the seed-mediated growth method. We demonstrate that the surface plasmon resonance (SPR) frequencies of ITO NPs can be manipulated from 1,600 to 1,993 nm in near-infrared band by controlling the composition, size, and morphology. The doping Sn concentration in ITO NPs could be controlled via changing the %Sn in the initial feed from 0% to 30%. The shortest SPR wavelength at 1,600 nm with 10% Sn doping concentration indicates highest free electron carrier concentration in ITO NPs, which has direct relationship with doping Sn⁴⁺ ions. Furthermore, we demonstrate that the SPR peaks can also be tuned by the size of ITO NPs in the case of uniform doping. Besides, compared with the ITO NPs, single crystalline ITO with nanoflower morphology synthesized through the one-pot method exhibit SPR absorption peak features of red-shifting and broadening.     

Direct electrochemical detection of pyruvic acid by cobalt oxyhydroxide modified indium tin oxide electrodes

An enzyme-free electrode was fabricated by anodic electrodeposition of cobalt oxyhydroxide film on an ITO electrode (CoO_x(OH)_y/ITO) for direct electrochemical detection of pyruvic acid (PA) in solution. Scanning electron microscopy (SEM) and atom force microscopy (AFM) were employed to characterize the morphology of CoO_x(OH)_y film. Cyclic voltammetry (CV) was used to investigate the electrochemical properties of PA on CoO_x(OH)_y/ITO in order to select the optimal potential for the chronoamperometric detection of PA. It was found that the CoO_x(OH)_y/ITO electrode served as an excellent PA sensor with a linear detection range of 1.00 μM to 1.91 mM, a detection limit of 0.55 μM, and a high sensitivity of 417.1 μA mM⁻¹ cm⁻². Moreover, the response time of CoO_x(OH)_y/ITO to PA is less than 10 s, which is the shortest for PA detection reported in literature using electrochemical method. These properties and the high stability of CoO_x(OH)_y/ITO made it a good candidate for developing electrochemical enzyme-free PA sensing device.     

Preparation and optical properties of Sn- and Ga-doped indium oxide semiconductor nanoparticles

Indium tin oxide (ITO) nanoparticles and gallium-doped indium tin oxide (GITO) nanoparticles with various molar ratios of dopants were prepared by a solution method in oleylamine. Characterization of crystal, morphology, and optical properties was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis), photoluminescent (PL), and Fourier transform infrared spectroscopy (FT-IR). XRD patterns show that with increasing of Sn, the crystal structure of ITO nanoparticles varies gradually from standard cubic bixbyite In₂O₃ to amorphous and to standard tetragonal SnO₂, whereas the GITO nanoparticles retain the crystal structure of ITO. The smallest particle size is around 10 nm, and the morphology of the particles is nearly spherical. The smallest particles, though coated with oleylamine, tend to aggregate forming larger flower-like particles. Defect level emission at the present of dopants was observed in the PL spectra of the ITO and GITO nanoparticles.     

Nucleation effects on structural and optical properties of electrodeposited zinc oxide on tin oxide

Zinc oxide was electrodeposited from oxygenated aqueous solutions of zinc chloride at 80 C on tin oxide covered glass substrates. A new activation treatment for the substrate is established. This consists in the initial formation, in the deposition solution, of a thin metallic zinc layer (5–50 nm) converted to ZnO by in situ reoxidation. Variable densities of nucleation centers (with values approaching 10¹⁰ cm^–2) are formed by this treatment. This allows control of the formation of a zinc oxide layer ranging from open deposits of isolated crystallites to compact and homogeneous layers. Compact layers have high specular transmission below the band gap value (3.5 eV), whereas open films exhibit extensive light scattering. The shapes of the current–time curves during deposition are discussed in terms of nucleation and structural effects. A possible influence of the semiconducting properties of the films is pointed out.     

Synthesis of antistatic hybrid nanocomposite coatings using surface modified indium tin oxide (ITO) nanoparticles

Several antistatic nanocomposite hybrid coatings based on epoxy-silane developed by sol–gel method are studied. The hybrid sols are prepared by hydrolysis and condensation of GPTMS and TMOS precursors in the presence of an acid, as catalyst, and EDA as curing agent. Considering their good electrical conductivity, indium tin oxide (ITO) nanoparticles are used as antistatic agents. To improve the distribution/dispersion of ITO nanoparticles in the polymer matrix, the surface of nanoparticles is modified with silane groups (m-ITO). The antistatic properties of the coatings, containing various amounts of m-ITO nanoparticles, are investigated through surface electrical resistivity measurements. FTIR is used to screen the reaction of epoxy groups and the effect of EDA on crosslinking in the hybrid coatings. Morphology, nanoparticle distribution and surface roughness of the coatings are studied through SEM and AFM microscopy techniques. Also, homogeneous distribution of ITO nanoparticles within the polymer matrix is confirmed by EDXA elemental mapping. The cubic shape and nanometric size of the nanoparticles in the hybrid coatings are monitored by transmission electron microscopy (TEM).     

Electrocatalytic oxidation of methanol on platinum nanoparticles electrodeposited onto porous carbon substrates

To achieve methanol fuel cell electrodes allowing a high catalyst use, thin layers of various carbon powders and recast Nafion® were electrochemically plated with platinum. The resulting Pt deposits were characterized by hydrogen and carbon monoxide electrosorption, as well as by transmission electron microscopy. Methanol oxidation was then carried out using cyclic voltammetry. The influence of the amount of carbon surface oxides and the effect of Pt specific surface area on the Pt catalytic activity were thus investigated.     

Effects of microwave radiation on electrodeposition processes at tin-doped indium oxide (ITO) electrodes

In situ microwave activation is investigated for the electrodeposition of a metal (gold) and for a metal oxide (hydrous Ti(IV) oxide) onto tin-doped indium oxide (ITO) film electrodes. It is demonstrated that localized microwave heating of the ITO film can be exploited to affect electrodeposition processes.The electrochemically reversible and temperature sensitive one-electron redox system Fe(CN)₆^3−/4− was employed in aqueous solution in order to calibrate the average surface temperature at the ITO film electrode. In the presence of microwave radiation the average electrode surface temperature reached ca. 363 K whereas under the same conditions the bulk solution temperature reached ca. 313 K. Therefore localized heating of the ITO film appears to be important.The rate of electrodeposition of gold from an aqueous 1 mM tetrachloroaurate(III) solution in 0.1 M KCl (adjusted to pH 2) is enhanced by microwave activation. However, the morphology of deposits remains un-effected. Hydrous titanium (IV) oxide films were electrodeposited from an aqueous solution of 1 mM TiCl₃ in 0.1 M acetate buffer pH 4.7. Dense films with blocking character were obtained with conventional heating but a fibrous more open deposit forms in the presence of microwaves.     

XPS and reactivity study of bimetallic nanoparticles containing Ru and Pt supported on a gold disk

We report a new method of immobilization of catalytic metal/alloy nanoparticles on a gold disk for transfer from an electrochemical cell to UHV (without sample exposure to air) for XPS analyses. Using this immobilization approach, several samples were examined: a core-shell Pt-on-Ru catalyst prepared from Ru black onto which Pt was spontaneously deposited, commercial Pt/Ru 50:50 nanoparticle alloy, as well as single metal Ru and Pt nanoparticle samples. The catalysts were characterized for the Ru oxidation state and for the methanol electrooxidation activity (as Pt was always metallic). For all bimetallic samples, we found that the reduced nanoparticles were more active towards methanol oxidation than the fully or partially oxidized samples. Regardless the Ru oxidation state however, the activity was lower than that previously reported for Ru decorated Pt nanoparticle catalysts (Ru-on-Pt). Possible reasons for the reactivity differences are discussed.     

Seed-mediated electrochemical growth of gold nanostructures on indium tin oxide thin films

Two-dimensional gold nanostructures (Au NSs) were fabricated on amine-terminated indium tin oxide (ITO) thin films using constant potential electrolysis. By controlling the deposition time and by choosing the appropriate ITO surface, Au NSs with different shapes were generated. When Au NSs were formed directly on aminosilane-modified ITO, the surface roughness of the interface was largely enhanced. Modification of such Au NSs with n-tetradecanethiol resulted in a highly hydrophobic interface with a water contact angle of 144°. Aminosilane-modified ITO films further modified with colloidal Au seeds before electrochemical Au NSs formation demonstrated interesting optical properties. Depending on the deposition time, surface colors ranging from pale pink to beatgold-like were observed. The optical properties and the chemical stability of the interfaces were characterized using UV-vis absorption spectroscopy. Well-defined localized surface plasmon resonance signals were recorded on Au-seeded interfaces with λ_max = 675 ± 2 nm (deposition time 180 s). The prepared interfaces exhibited long-term stability in various solvents and responded linearly to changes in the corresponding refractive indices.     

Photocatalytic properties of visible-light enabling layered titanium oxide/tin indium oxide films

Visible-light enabling titanium oxide/tin indium oxide (TiO₂/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (2 1 1) and the Raman peak intensity at 640 cm⁻¹ dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2 h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p_3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231 h⁻¹. Hydrophilic conversion rate was estimated to be 8.14 × 10⁻³ deg⁻¹ min⁻¹ and long-term UV-induced hydrophilicity of 10° in the dark storage up to 72 h was observed. In addition to its inherent characteristics of the layered TiO₂/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.     

Electrochemistry behavior of endogenous thiols on fluorine doped tin oxide electrodes

In this work the electrochemical behavior of different thiols on fluorine doped tin oxide (FTO) electrodes is reported. To this end, the mechanism of electrochemical oxidation of glutathione (GSH), cysteine (Cys), homocysteine (HCys) and acetyl-cysteine (ACys) at different pH was investigated. FTO showed electroactivity for the oxidation of the first three thiols at pH between 2.0 and 4.0, but under these conditions no acetyl-cysteine oxidation was observed on FTO.Voltammetric studies of the electro-oxidation of GSH, Cys and HCys showed peaks at about 0.35, 0.29, and 0.28 V at optimum pH 2.4, 2.8 and 3.4, respectively. In addition, this study demonstrated that GSH, Cys and HCys oxidation occurs when the zwitterion is the electro-active species that interact by adsorption on FTO electrodes. The overall reaction involves 4e⁻/4H⁺ and 2e⁻/2H⁺, respectively, for HCys and for GSH and Cys and high heterogeneous electron transfer rate constants.Besides, the use of FTO for the determination of different thiols was evaluated. Experimental square wave voltammetry shows a linear current vs. concentrations response between 0.1 and 1.0 mM was found for HCys and GSH, indicating that these FTO electrodes are promising candidates for the efficient electrochemical determination of these endogenous thiols.     

Optimization of the dispersion of gold and platinum nanoparticles on indium tin oxide for the electrocatalytic oxidation of cysteine and arsenite

Gold and platinum nanoparticles (NPs) were prepared by chemical reduction of the corresponding metal complex bound by ion-exchange to generation-4 poly(amidoamine) dendrimers (PAMAM). Arrays of the NPs on indium tin oxide (ITO) electrodes were formed by adsorbing a monolayer comprising a controlled ratio of NP-PAMAM to PAMAM on ITO that was modified with 3-aminopropyl triethoxysilane; subsequently, the organic components were thermally destroyed. Varying the above-defined ratio resulted in a commensurate change of the density of the NPs on the surface. Using an electrode modified in a solution with a mole fraction of Au-PAMAM (relative to total of Au-PAMAM and PAMAM) of 0.06, which gave NPs separated by 200 nm, the current for the catalytic oxidation of cysteine reached a value that did not increase when more nanoparticles were present. The analogous experiment on the oxidation of As^III with PtNPs as the catalyst was optimized at a mole fraction of 0.2. Calculations assuming hemispherical diffusion suggested that the diffusion domains during cyclic voltammetry at 5 mV s⁻¹ were less than the distance between the NPs.     

The sorption of acid dye onto chitosan nanoparticles

The behavior of chitosan nanoparticles as an adsorbent to remove Acid Green 27 (AG27), an acid dye, from an aqueous solution has been investigated with nanochitosan (particle size = 180 nm; degree of deacetylation = 74%). The dye concentration at equilibrium (Q_e, mg/g) was calculated using the weight of the nanoparticles in the mixed solution (Q_es) and the weight of chitosan in the nanoparticles (Q_ep). The experimental isotherm data were analyzed using the Langmuir equation for each chitosan sample; the Langmuir monolayer adsorption capacity (Q₀) was calculated with Q_es and Q_ep and the results were 1051.8 mg/g and 2103.6 mg/g, respectively, which were significantly higher than that of the micron-sized chitosan.     

Synthesis of polypyrrole/indium tin oxide nanocomposites via miniemulsion polymerization

Polypyrrole/indium tin oxide nanocomposites were synthesized via in situ miniemulsion polymerization of pyrrole monomer in the presence of indium tin oxide nanoparticles. Different nanocomposites were synthesized by different loadings of nano indium tin oxide. The morphology and nanoparticles distribution of the nanocomposites were characterized by electron microscopy. The results of XRD and TEM analysis showed that indium tin oxide nanoparticles were well placed in the polymeric structure of latex. FTIR analysis was used for the characterization of synthesized polypyrrole and its nanocomposites. TGA analysis was performed to investigate the thermal behavior of pristine polypyrrole and its nanocomposites. Conductivities of nanocomposites were measured by 4-point probe method and compared to the neat polymer.