Colloidal Deposition Method Research Articles

Pt nanoparticles modified by rare earth oxides: Electronic effect and influence to catalytic hydrogenation of 3-phenoxybenzaldehyde

The rare earth elements (La, Ce, Nd, Sm, Pr, and Gd) modified Pt/Al2O3 catalysts were prepared by the colloidal deposition and chemical reduction methods, respectively. Pt nanoparticles with average size 3±0.5nm were uniformly dispersed on the surface of Al2O3 for the samples prepared by the colloidal deposition method, which exhibited higher activities in the hydrogenation of 3-phenoxybenzadehyde than the corresponding samples prepared by chemical reduction method. Moreover, except Gd, the catalysts modified by rare earth elements showed better catalytic performance than unmodified Pt/Al2O3. For Pt–Ce/Al2O3 catalyst, when the weight percent of Pt and Ce was 0.5 and 0.25, respectively, the hydrogenation conversion of 3-phenoxybenzaldehyde was 97.3% after 6h reaction. This activity improvement is due to the electronic interaction between Pt and rare earth elements, which was investigated by X-ray photoelectron spectroscopy.

Morphologic effects of nano CeO2–TiO2 on the performance of Au/CeO2–TiO2 catalysts in low-temperature CO oxidation

CeO2–TiO2 composite nanorods and nanoparticles were synthesized by hydrothermal and co-precipitation methods, respectively; with the CeO2–TiO2 composite of different morphologies as supports, Au/CeO2–TiO2 catalysts were prepared by the colloidal deposition method and used in CO oxidation at ambient temperature. N2 sorption, XRD, HRTEM, H2-TPR, XPS and XAS characterizations were used to clarify the relationship between the morphologic properties of CeO2–TiO2 and the catalytic performance of Au/CeO2–TiO2. HRTEM results show that Au/CeO2–TiO2 nanorods are dominated by CeO2 nanocrystals with (110) and (100) facets, while the Au/CeO2–TiO2 nanoparticles mainly expose (111) planes. XPS and XAS results reveal that both Au/CeO2–TiO2 nanorods and Au/CeO2–TiO2 nanoparticles are similar in the state of gold species. H2-TPR results indicate that the presence of Au strongly promotes the reduction of CeO2 in the Au/CeO2–TiO2 nanorods. The catalytic activity of Au/CeO2–TiO2 in CO oxidation is strongly related to the morphology of CeO2–TiO2; the CeO2–TiO2 nanorods as support endow the Au/CeO2–TiO2 catalyst with much higher activity than the CeO2–TiO2 nanoparticles. The (110) and (100) facets of CeO2 dominated in the Au/CeO2–TiO2 nanorods are able to promote the oxygen migration and gold dispersion, which may then evidently enhance the redox capacity and catalytic activity of the Au/CeO2–TiO2 nanorods in CO oxidation at low temperature.

Preparation of the Gold Nanoparticles and its Activity for Single-Step Amination of Benzene to Aniline

Gold nanoparticles (AuNPs) were attached to the surface of alumina particles by an in-situ immobilizing method. SEM and XPS analysis showed that the coverage of alumina particles by AuNPs increased as the amount of alumina decreased; AuNPs onto alumina particles by the conventional colloidal deposition method were also prepared, whose TEM showed that the coverage of AuNPs was evidently smaller than that in the case of modified colloidal deposition method，although the AuNPs were spread almost uniformly over the surface of alumina particles. Au-immobilized alumina particles were subsequently utilized as the catalysts for direct amination of benzene with NH3H2O as an aminating agent and H2O2 as an oxidant under mild conditions. The reaction conditions were optimized: when catalyst amount was 2.0 g, reaction temperature was 50 °C, NH3H2O amount was 60 mL, H2O2 amount was 30 mL, and reaction time is 2 h, Au-immobilized alumina particles showed the highest aniline yield (1.96 mg) for 25 mL benzene.

Deposition of Monodisperse Platinum Nanoparticles of Controlled Size on Different Supports

Monodisperse platinum nanoparticles with controlled size were synthesized by polyol synthesis and supported on γ-Al2O3, SiO2 and carbon nanotubes (CNT) by the colloid deposition method. The average size of Pt nanoparticles in colloidal solutions and on supports were determined by TEM images and from XRD patterns. The size of Pt nanoparticles supported on SiO2 and CNT determined from XRD patterns is in a good agreement with size obtained from the TEM analyses. There were shown that no agglomeration and size changing of Pt nanoparticles on these supports were observed. All these findings illustrate that the method of colloid deposition allows one to obtain catalyst with monodisperse platinum nanoparticles of controlled size deposited on different supports without changing the nanoparticle’s size and morphology.

Hydrogen transport properties of palladium film prepared by colloidal spray deposition

Palladium films were fabricated by a novel colloidal spray deposition method. Dense, crack-free Pd films with thickness of 5–11 μm were successfully fabricated on porous yttria-stabilized zirconia (YSZ) substrates having pore size of 3–7 μm. Scanning electron microscopy showed that the film has uniform thickness and is well bonded to the substrate. The surface of the Pd film is composed of well-crystallized plate-like grains with diameter of 2–4 μm and has a rough texture. The X-ray diffraction pattern of the as-sintered Pd film indicates (111) preferred crystal orientation. The hydrogen permeation properties of the films were investigated at temperatures of 330–530 °C using 90% H2/balance He and N2 as feed and sweep gases, respectively. The hydrogen permeation of the supported Pd films with thickness of 5–11 μm was limited by both the diffusion of hydrogen through the metal bulk and the gas-phase transport through the support. The resistance of the gas-phase transport through the substrate was lowered significantly by reducing the thickness of the substrate.

High-performance low-temperature solid oxide fuel cells using thin proton-conducting electrolyte with novel cathode

We have fabricated BaCe0.8Gd0.2O3−δ (BCGO) thin films with thickness in the range of 5–10 μm over substrates composed of Ce0.8Gd0.2O1.9 (CGO)-NiO using a colloidal spray deposition method. A perovskite-type BaZr0.2Co0.4Fe0.4O3−δ (BZCFO) was employed as a novel cathode material. The performances of solid oxide fuel cells were investigated from 450 °C to 600 °C. The fuel cell with the BCGO film of 9 μm in thickness showed maximum power outputs of 237, 192, 136 and 89 mW cm−2 at 600, 550, 500 and 450 °C, respectively. The impedance measurements at open circuit conditions showed the polarization resistances of the electrode were about 0.25 and 1.00 Ω cm2 at 600 and 500 °C, respectively. The low interfacial resistances indicated that the BZCFO was a promising cathode material for low-temperature proton-conducing solid oxide fuel cells.

Enhanced microwave absorbing properties of carbonyl iron-doped Ag/ordered mesoporous carbon nanocomposites

Microwave absorbing materials carbonyl iron (CI)-doped Ag/ordered mesoporous carbon (OMC) paraffin wax composites were prepared by colloidal deposition and impregnation methods, and their electromagnetic and microwave absorbing properties were investigated in the frequency ranging from 2 to 18 GHz. The microstructures and chemical compositions of the Ag/OMC and Ag/OMC-CI paraffin wax composites were characterized by TEM, XRD, XPS, SEM and EDS, respectively. The complex permittivity of the paraffin wax composites show dual resonance behavior, resulting from the multi-interfaces among Ag nanoparticles, OMC nanorods, CI and paraffin wax. The magnetic loss was mainly caused by natural resonance and eddy current loss, respectively. The minimum reflection loss (RL) value of Ag/OMC-CI was below −10 dB at 12 GHz, which were superior to those of OMC-CI and Ag/OMC. This phenomenon is attributed to the enhancement of dielectric polarization and magnetic loss.

TPR Study of Core-Shell Fe@Fe<sub>3</sub>O<sub>4</sub> Nanoparticles Supported on Activated Carbon and Carbon Nanotubes

Core-shell nanoparticles Fe@Fe3O4 supported on activated carbon (AC) and carbon nanotubes (CNTs) have been studied by H2 temperature-programmed reduction (TPR). Nanoparticles with size of 6.5 nm were synthesized by iron(II) oleate thermal decomposition and were supported on activated carbon and carbon nanotubes by colloid deposition method. The nanoparticles Fe@Fe3O4 are characterized by TEM and IR. Reduction of nanoparticles on AC starts at 140?C, whereas reduction of nanoparticles on CNTs starts at 200?C. Moreover, gasification of CNTs with methane releasing starts at 450?C, whereas gasification of AC is negligible at temperatures up to 800?C. All these findings illustrate a strong difference in the interaction between nanoparticles and the support material for AC and CNTs.

Dye-Sensitized Solar Cells TiO<sub>2</sub> Thin Film Preparation and Conditions in Laboratory

The use of colloidal solution deposition method on the preparation of the nanostructured TiO2 thin film for dye-sensitized solar cells in basic laboratory conditions was introduced. The effects of reaction temperature, time, and solvents on the film properties have been investigated. The experiments show that the use of dilute acetic acid could get a stable sol; 450°C 30 minutes in oven without preheat could have ideal TiO2 thin film.

Physico-chemical characterization of bovine serum albumin in solution and as deposited on surfaces

The interactions between proteins and solid surfaces are important for the formation of biocompatible materials. In this study, the physicochemical properties of Bovin serum albumin (BSA) in solution and on a solid surface were studied. The zeta potential and number of uncompensated charges on BSA surfaces were determined from electrophoretic mobility measurements. The dynamic viscosity was also measured to determine BSA conformations in solution, and the data were converted to the effective length Lef of the BSA molecule. The length of a BSA molecule was measured to be 8.3nm in the compact state (N form at pH 4–9) and 26.7nm in the extended state (F-form). This study demonstrates that the relationship between the hydrodynamic radius, dynamic viscosity and electrophoretic mobility can provide information about the shape and conformation of biopolymer in solution.The contact angle measurements and deposition of fluorescent latex particles were used to characterise BSA monolayers on a mica surface, which were produced by controlled adsorption under diffusion transport. The results suggest that the distribution of charge across a BSA molecule is heterogeneous as evidenced by the presence of positive and negative patches. The maximum contact angle was observed under conditions in which both BSA and mica were oppositely charged. A higher positive zeta potential of BSA was observed to correlate with a higher contact angle. However, at a higher negative zeta potential, BSA exhibited a lower binding affinity. The charge distribution across BSA monolayers was also studied via the colloidal deposition method using negatively charged fluorescent latex particles. Unexpectedly, the fluorescent latex particles adsorbed onto BSA monolayers, even when the effective zeta potential of BSA was negative. This phenomenon may originate from the heterogeneous charge distribution across BSA molecules.

In situ immobilizing of gold nanoparticles onto the surface of alumina particles

In this work, gold nanoparticles (AuNPs) were attached to the surface of alumina particles by an in situ immobilizing method. This modified colloidal deposition method allowed the immobilization of AuNPs with a much greater loading amount compared to the conventional one.

Selective hydrogenation of nitrocyclohexane to cyclohexanone oxime by alumina-supported gold cluster catalysts

Metal oxides (Al 2O 3, SiO 2, MgO)-supported Au cluster catalysts prepared by colloid deposition method and well established Au/TiO 2 prepared by deposition–precipitation method were tested for the selective reduction of nitrocyclohexane into cyclohexanone oxime. The activity and selectivity depended strongly on the size of Au and support material. Au/Al 2O 3 with smaller Au particle size (2.5 nm) was the most effective catalyst, exhibiting a high cyclohexanone oxime yield (86%) under mild condition (0.6 MPa H 2, 100 °C). To study the origin of support and size effects, in situ FTIR experiments for OH/D 2 exchange reaction and nitrobenzene adsorption combined with poisoning experiments using pyridine and acetic acid were carried out. It is suggested that cooperation of coordinatively unsaturated Au atoms and the acid–base pair site (Al δ+–O δ− site) plays an important role in H 2 dissociation step. Al δ+–O δ− site also acts as the adsorption site of the nitro group.

Catalytic oxidation of benzene, toluene and p-xylene over colloidal gold supported on zinc oxide catalyst

Abstract Au was loaded (1.5 wt.%) on the supports (ZnO, Al 2 O 3 and MgO) by a colloidal deposition method. For a range of low temperatures (50–300 °C), the catalytic activity of Au/ZnO was much greater than that of Au/Al 2 O 3 and Au/MgO. In particular, for the Au/ZnO, the benzene conversion exceeded 80% at 150 °C. The results of catalyst characterization suggested that the high catalytic activity of the Au/ZnO might be attributed to the effects of strong metal–oxide interaction which is possibly originated from the small lattice parameter difference between Au {111} and ZnO {101} lattice planes.

Deposition of colloid particles on protein layers: Fibrinogen on mica

Colloid particle deposition was applied to characterize fibrinogen (Fb) monolayers on mica, which were produced by controlled adsorption under diffusion transport. By adjusting the time of adsorption and the bulk Fb concentration, monolayers of desired surface concentration were obtained. The surface concentration of Fb was determined directly by AFM enumeration of single molecules adsorbed over the substrate surface. It was proven that Fb adsorbed irreversibly on mica both at pH 3.5 and at pH 7.4 with the rate governed by bulk transport. The electrokinetic properties of Fb monolayers produced in this way were studied using the streaming potential method. The dependence of the apparent zeta potential of Fb monolayers was determined as a function of the coverage. It was shown that for pH 3.5 the initial negative zeta potential of the mica substrate was converted to positive for Fb coverage exceeding 0.16. On the other hand, for pH 7.4, the zeta potential of a Fb-covered mica remained negative for the entire coverage range. The charge distribution in Fb monolayers was additionally studied using the colloid deposition method, in which negatively and positively charged polystyrene latex particles (ca. 800 nm in diameter) were used. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH 3.5 and 7.4, respectively. These results suggested that for pH 7.4, the distribution of charge on Fb molecules was heterogeneous, characterized by the presence of positive patches, whereas the average zeta potential was negative, equal to −19 mV. The utility of the colloid deposition method for studying Fb monolayers was further demonstrated in deposition experiments involving positive latex particles. It was shown that for a rather broad range of fibrinogen coverage, both the positive and the negative latex particles can adsorb on surfaces covered by Fb, which behaved, therefore, as superadsorbing surfaces. It was also concluded that the colloid deposition method can be used to determine the Fb bulk concentration for the range inaccessible for other methods.

Complete oxidation of formaldehyde at ambient temperature over supported Pt/Fe2O3 catalysts prepared by colloid-deposition method

The catalytic properties of iron oxide supported platinum catalysts (Pt/Fe2O3), prepared by a colloid deposition route, were investigated for the complete oxidation of formaldehyde. It is found that all the Pt/Fe2O3 catalysts calcined at different temperatures (200–500°C) were active for the oxidation of formaldehyde. Among them, the catalysts calcined at lower temperatures (i.e., 200 and 300°C) exhibited relatively high catalytic activity and stability, which could completely oxidize HCHO even at room temperature. Based on a variety of physical–chemical characterization results, it is proposed that the presence of suitable interaction between Pt particles and iron oxide supports, which is mainly in the form of Pt–O–Fe bonds, should play a positive role in determining the catalytic activity and stability of the supported Pt/Fe2O3 catalysts.

Catalytic hydrogenation of benzaldehydes over platinum nanoparticles immobilized on magnesium aluminate spinel under mild conditions

Platinum nanoparticles, synthesized via ethanol reduction of hexachloroplatinic acid in the presence of poly-(N-vinyl-2-pyrrolidone), were anchored on magnesium aluminate spinel using a colloidal deposition method. The samples were characterized using the following methods: transmission electron microscopy, powder X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The results revealed that platinum nanoparticles, with an average diameter of 2.8 nm, are homogenously dispersed on the surface of the carrier. Under very mild conditions, supported Pt/MgAl2O4 catalysts demonstrated excellent catalytic activity and high selectivity in the hydrogenation reaction of benzaldehydes to benzyl alcohols. The reaction kinetics for the catalytic hydrogenation of 3-phenoxybenzaldehyde to 3-phenoxybenzyl alcohol on a Pt/MgAl2O4 catalyst can be described by equation $$ r = k \times c^{1.44} \times p_{{{\text{H}}_{ 2} }} $$ , and the apparent activation energy is 35.6 kJ mol−1.

Preparation of highly dispersed platinum catalysts on various oxides by using polymer-protected nanoparticles

Supported Pt catalysts were prepared by a colloidal deposition method including the photochemical preparation of Pt nanoparticles protected by poly( N-vinyl-2-pyrrolidone) and their deposition by liquid-phase adsorption on the various kinds of supporting materials, TiO 2, CeO 2, SiO 2, Al 2O 3 and MgO. We investigated the effect of preparation condition on the properties of supported Pt catalysts. The amount of Pt adsorbed and Pt dispersion depended on the kinds of supporting materials. The highest Pt dispersion was obtained when they were deposited on TiO 2 (P25). The Pt dispersion did not depend on the pH value of mother liquor and the amount of Pt used in the liquid adsorption process. Pt/TiO 2 and Pt/CeO 2 showed higher activity for CO oxidation than Pt/Al 2O 3 and Pt/MgO.

Highly Active Iron Oxide Supported Gold Catalysts for CO Oxidation: How Small Must the Gold Nanoparticles Be?

The shape of gold: The title catalyst has been prepared through a colloidal deposition method. Scanning transmission electron microscopy studies confirmed that for the catalyst, gold clusters with a bilayer structure and a diameter of about 0.5 nm are not mandatory to achieve the high activity (see image).

Catalytic Properties of Platinum Supported on Titanium Dioxide by Liquid-Phase Adsorption of Colloidal Nanoparticles

Pt/TiO2 catalysts were prepared by a colloidal deposition method including the photochemical preparation of Pt nanoparticles protected by poly(N-vinyl-2-pyrrolidone) and their deposition by liquid-phase adsorption on TiO2. Pt/TiO2 catalysts prepared by the colloidal deposition method with oxidation and H2 reduction treatment showed higher CO oxidation activity than those obtained by impregnation and photodeposition techniques. FTIR studies revealed the reactivity of CO species adsorbed on Pt sites of these catalysts. The higher activity was ascribable to higher dispersion and higher reactivity of CO adsorbed on Pt particles.

The preparation of nano-gold catalyst supported on iron doped titanium oxide

We have prepared iron doped TiO 2 samples by the impregnation of TiO 2 (Degussa—P25) with Fe(III) nitrate as an iron precursor. Obtained materials were then characterized by structural x-ray diffraction (XRD) and optical (Uv-vis, Raman) techniques. Later, we deposited very small gold nanoparticles (AuNPs; <5 nm) onto as-prepared supports by a colloidal deposition method, in which lysine was used as a capping agent and a short sonication time was applied to facilitate the dispersion and deposition of AuNPs. The presence of Fe +3 in the TiO 2 structure was confirmed by an increase in the number of oxygen defect sites that react with O 2 to form reactive oxygen species. Transmission electron microscopy (TEM) was used to determine the size of the gold particles before and after deposition. The AuNPs deposited on the FeTiO2 exhibited good thermal stability against sintering, even at 500 °C for 4 h.