Deposition Of Pd Nanoparticles Research Articles

Efficient Thermal- and Photocatalyst of Pd Nanoparticles on TiO2 Achieved by an Oxygen Vacancies Promoted Synthesis Strategy

Pd nanoparticles supported on defective TiO2 with oxygen vacancies (TiO2-OV) have been prepared by an oxygen vacancies mediated reduction strategy. The resulting Pd-TiO2-OV catalyst with uniform Pd nanoparticles deposition demonstrates a remarkably thermocatalytic activity toward rapid, efficient reduction of nitroaromatics in water. The reaction proceeds efficiently using HCOONH4 as a hydrogen source under ambient conditions. The controlled experiments show that the (•)CO2(-) radicals produced by dehydrogenation of HCOONH4 are the main active species for the selective nitro reduction. Moreover, defective TiO2 nanostructures deposited with Pd nanoparticles, featuring excellent visible-light absorption via the creation of oxygen vacancies, can take advantage of the solar and thermal energy to drive catalytic reduction reactions more efficiently at room temperature. During this process, the oxygen vacancies and Pd nanoparticles play synergetic roles in the photoreduction of nitro compounds. Our work would be beneficial for implementation of a novel defect-mediated catalytic system in which solar light energy can be coupled with thermal energy to drive an energy efficient catalytic process.

A comparative study of CO catalytic oxidation on Pd-anchored graphene oxide and Pd-embedded vacancy graphene

The catalytic oxidation of CO on Pd-anchored graphene oxide (Pd-GO) and Pd-embedded vacancy graphene (Pd-VG) is investigated by density functional theory calculations. The results validate both Pd-GO and Pd-VG show good catalytic performance for CO oxidation. Meanwhile, the more positive charge for Pd adatom and the lower reaction energy barrier make Pd-VG system slightly superior than Pd-GO system in catalytic performance. The reaction proceeds via Langmuir–Hinshelwood mechanism with a two-step route (CO + O2 → OOCO → CO2 + O), followed by the Eley–Rideal mechanism (CO + O → CO2). However, the synthesis of Pd-VG is more difficult in experiments compared with the readily available Pd-GO. Hence, graphene oxide may serve as the alternative substrate to deposit Pd nanoparticles.

Effective hydrodechlorination of 4-chlorophenol catalysed by magnetic palladium/reduced graphene oxide under mild conditions

Magnetic palladium/reduced graphene oxide nanocomposites (Pd/rGO-Fe3O4) were prepared by depositing Pd nanoparticles on an rGO-Fe3O4 magnetic support.

Layer-by-layer construction of caterpillar-like reduced graphene oxide–poly(aniline-co-o-aminophenol)–Pd nanofiber on glassy carbon electrode and its application as a bromate sensor

An electrochemical reduced graphene oxide/poly(aniline-co-o-aminophenol)/palladium (ERGO–PANOA–Pd) nanocomposite modified glassy carbon (GC) electrode was fabricated by electrochemical reduction of GO, electrochemical polymerization of PANOA and electrochemical deposition of Pd nanoparticles, respectively. TEM and SEM display a well-defined nanofiber with diameters of 60–70nm of PANOA synthesized on ERGO. After deposition of Pd nanoparticles, the ERGO–PANOA–Pd shows a caterpillar-like nanofiber structure. The ERGO–PANOA–Pd modified GC electrode exhibits excellent electrochemical activity in a 0.2M H2SO4 compared to the ERGO and ERGO–PANOA modified GC electrode. CV results also show the as-prepared electrode has good electrocatalytic behavior to bromate in a pH 4.0 PBS. Under the optimal conditions, the ERGO–PANOA–Pd modified GC electrode can be used to determine bromate concentration in a wide linear range of 4 and 840μM with a detection limit of 1μM. The sensitivity of the electrode was 33.2nAμM−1. The proposed sensor has good anti-interference property.

In situ deposition of Pd nanoparticles with controllable diameters in hollow carbon spheres for hydrogen storage

A novel in situ synthesis of Pd nanoparticles supported in hollow carbon spheres (HCS) is reported. The size of the nanoparticles can be tuned via application of different Pd precursors. The hydrogen storage properties of Pd supported in HCS under room temperature were examined at partial pressures. We observed significant difference between the storage capacities of two samples containing Pd nanoparticles with different diameter distributions. The results showed that the sample with suitable diameters of Pd nanoparticles was more favorable for the H2 storage, even lower mass of Pd was used. The maximum hydrogen storage of 0.36 wt % exhibited the sample with Pd nanoparticles with the diameter of 11 nm (measured at 298 K and 24 bar) and it was enhanced by the factor of two in respect to the pristine HCS. The enhanced storage capacity is due to cumulative hydrogen adsorption by HCS and Pd nanoparticles. We also propose the mechanism of hydrogen storage in our material.

Electrocatalytic debromination of BDE-47 at palladized graphene electrode

Graphene electrodes (Ti/Gr) were prepared by depositing Gr sheets on Ti substrate, followed by an annealing process for enhancing the adhesion strength. Electrochemical impedance spectroscopies and X-ray diffraction patterns displayed that the electrochemical behavior of Ti/Gr electrodes can be improved due to the generation of TiO2 layer at Ti-Gr interface during the annealing process. The palladized Gr electrodes (Ti/Gr/Pd) were prepared by electrochemical depositing Pd nanoparticles on Gr sheets. The debromination ability of Ti/Gr/Pd electrodes was investigated using BDE-47 as a target pollutant with various bias potentials. The results indicated that the BDE-47 degradation rates on Ti/Gr/Pd electrodes increased with the negative bias potentials from 0 V to −0.5 V (vs. SCE). Almost all of the BDE-47 was removed in the debromination reaction on the Ti/Gr/Pd electrode at −0.5 V for 3 h, and the main product was diphenyl ethers, meaning it is promising to debrominate completely using the Ti/Gr/Pd electrode. Although the debromination rate was slightly slower at −0.3 V than that under −0.5 V, the current efficiency at −0.3 V was higher, because the electrical current acted mostly on BDE-47 rather than on water.

Electrocatalysis and detection of nitrite on a reduced graphene/Pd nanocomposite modified glassy carbon electrode

An electrochemical reduced graphene oxide/palladium (ERGO-Pd) nanocomposite modified glassy carbon (GC) electrode was fabricated by electrochemical reduction of GO and electrochemical deposition of Pd nanoparticles, respectively. Raman spectra indicate the GO can be successfully reduced to ERGO. SEM displays a high density of Pd nanoparticles loading on the surface of ERGO with a diameter of 50–100nm. The electrode exhibits enhanced electrocatalytic behavior to the oxidation of nitrite compared to the GO and ERGO modified GC electrode. The effects of solution pH and amount of Pd deposition onto the ERGO-Pd modified GC electrode were investigated and discussed. Under the optimal conditions, the ERGO-Pd modified GC electrode can be used to determine nitrite concentration in a wide linear range of 0.04 and 108μM and a limit of detection of 15.64nM. The sensitivity of the electrode was 7.672μAμM−1cm−2. It also shows good storage stability.

Synthesis of modified carbon nanotube-supported Pd and the catalytic performance for hydrodehalogenation of aryl halides

The effects of surface functionalization on the deposition of Pd nanoparticles on multi-walled carbon nanotubes (CNTs) have been studied. Two methods were used for the functionalization of CNTs: one employed a 1:1 (v/v) mixture of concentrated H2SO4/HNO3, sonicated at RT; the other employed a 3:1 (v/v) mixture of concentrated H2SO4/HNO3, sonicated at 60 °C. A large number of surface oxide groups were introduced on the surface of functionalized CNTs, especially in strong oxidation power (H2SO4/HNO3 = 3:1, 60 °C). The dispersion of Pd nanoparticles on CNTs was found to depend on the amount of surface oxide groups, with larger amounts of surface oxide groups resulting in higher dispersion of Pd nanoparticles. The effects of CNT surface functionalization on the performance of Pd/CNTs catalysts were studied, and the reaction conditions optimized, using the hydrodebromination of bromobenzene as model reaction. Under optimal conditions, the hydrodehalogenation of various aryl halides were tested over Pd/CNTs catalysts.

Nitrate amperometric sensor in neutral pH based on Pd nanoparticles on epoxy-copper electrodes

Amperometric nitrate sensing at neutral pH using an epoxy-copper electrode modified with palladium nanoparticles is presented. After epoxy-copper is hardened and polished, electroless deposition is employed for the deposition of Pd nanoparticles. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal the morphology and composition of the Cu/Pd surface. The effect of Pd deposition time toward nitrate electroreduction is investigated, highlighting the importance of the bimetallic catalyst. The optimized electrode shows a linear response at pH=7 in the range from 2 to 35ppm of nitrate. The simplicity and cost effectiveness of the fabrication process makes this Cu/Pd electrode a good candidate for distributed nitrate monitoring and determination in the field.

Supercritical fluid chemical deposition of Pd nanoparticles on magnesium–scandium alloy for hydrogen storage

The deposition of Pd nanoparticles on the binary compound Mg0.65Sc0.35 using the Supercritical Fluid Chemical Deposition (SFCD) method was performed. There, the SFCD operating parameters (co-solvent, temperature, CO2 and hydrogen pressure, reaction time) have been optimized to obtain homogeneous deposition of Pd nanoparticles (around 10nm). The hydrogenation properties of the optimized Pd@Mg0.65Sc0.35 material were determined and compared to those of Mg0.65Sc0.35Pd0.024. The latter compound forms at 300°C and 1MPa of H2 a hydride that crystallizes in the fluorite structure, absorbs reversibly 1.5wt.% hydrogen and exhibits fast kinetics. In contrast, Pd@Mg0.65Sc0.35 compound decomposes into ScH2 and MgH2 during hydrogen absorption under the same conditions. However, reversible sorption reaches 3.3wt.% of hydrogen while keeping good kinetics. The possible roles of Pd on the hydrogen-induced alloy decomposition are discussed.

Preparation of yolk/shell Fe3O4@polypyrrole composites and their applications as catalyst supports

Yolk/shell composites with a movable Fe3O4 core inside the hollow polypyrrole (PPy) capsules were obtained through a template-assistant selectively etching method. The Fe3O4 nanoparticles were firstly synthesized according to the solvothermal method. Then, SiO2 shell was coated on the Fe3O4 nanoparticle surface by a sol–gel reaction. Subsequently, the PPy shell was covered on the surface of as-prepared Fe3O4@SiO2 composites and sandwiched Fe3O4@SiO2@PPy composites formed. After selectively etching the middle SiO2 layer, the yolk/shell Fe3O4@PPy composites were obtained. Both the PPy and SiO2 shell thicknesses could be readily turned during the preparation. The influence of poly(N-vinylpyrrolidone) on coverage of PPy shell onto Fe3O4@SiO2 composites surface was studied in detail. Yolk/shell Fe3O4@PPy composites were used as supports for deposition of Pd nanoparticles. Pd nanoparticles were densely and uniformly anchored on both outer and inner surface of PPy shell due to the coordination interaction between amino groups on PPy backbone and Pd2+ ions. Fe3O4@PPy/Pd catalysts showed excellent catalytic activity towards the reduction of methylene blue dye with sodium borohydride as reducing agent. In addition, such catalysts could be easily separated from reaction solution and reused due to the magnetic property originated from the Fe3O4 core.

Taking advantage of a terpyridine ligand for the deposition of Pd nanoparticles onto a magnetic material for selective hydrogenation reactions

A hybrid terpyridine ligand was designed to functionalize a magnetic support constituted of magnetite cores surrounded by a silica shell with the aim of improving the stabilization of supported-palladium nanoparticles for the later application of the obtained composite nanomaterial in hydrogenation catalysis. The preparation of the nanomaterial was performed by direct decomposition of the organometallic complex [Pd2(dba)3] on the terpyridine-modified magnetic support providing well-dispersed Pd NPs of 2.5 ± 0.6 nm mean size. This new nanomaterial is a highly active catalyst for the hydrogenation of cyclohexene under mild conditions reaching turnover frequencies up to ca. 58 000 h−1 or 129 000 h−1 when corrected for surface Pd atoms. Furthermore, in the hydrogenation of β-myrcene, this nanocatalyst is highly selective for the formation of monohydrogenated compounds. When compared to a similar nanocatalyst consisting of palladium nanoparticles supported on an amino-modified magnetic support or on Pd/C, the activity and selectivity of the nanocatalyst are largely increased. These results show how the design of an appropriate hybrid ligand used to functionalize the support can strongly influence the catalytic properties of supported metal nanoparticles.

HIGHLY CATALYTICALLY ACTIVE PALLADIUM NANOPARTICLES INCORPORATED INSIDE METAL-ORGANIC FRAMEWORK PORES BY DOUBLE SOLVENTS METHOD

Highly monodispersed palladium (Pd) nanoparticles have been successfully incorporated inside the mesopores of a metal–organic framework (MOF), MIL-101, without deposition of Pd nanoparticles on the external surfaces of framework by using the "double solvents" method, in which cyclohexane is used as a hydrophobic solvent to disperse the mesoporous MOF and an aqueous solution of Pd precursor is used as a hydrophilic solvent to fill the mesopores. The resulting Pd @MIL-101 composite is highly catalytically active for the reduction of 4-nitrophenol (4-NPh) by sodium borohydride ( NaBH4 ). The observed excellent catalytic performances are attributed to the small Pd nanoparticles within the pores of MIL-101.

Plasma-assisted Pt and Pt–Pd nano-particles deposition on carbon carriers for application in PEM electrochemical cells

Plasma-assisted deposition of platinum and platinum-palladium nano-particles at the surface of carbonaceous electronic carriers for application in proton-exchange membrane (PEM) electrochemical cells has been carried out using a conventional DC magnetron sputtering system. Different types of carrier have been used for that purpose: carbon powder (Vulcan XC-72), carbon nanotubes and carbon nano-fibers. The interest of initial chemical pretreatment or metallization of the electronic carrier to improve surface adhesion of catalyst nano-particles has been analyzed. Nanostructured catalytic powders thus obtained have been analyzed and characterized using TGA, SEM, TEM, XRD, XRF and cyclic voltammetry. The electrochemical performances of Pt/C and Pt–Pd/C electrodes have been measured in single-cell PEM fuel cell (PEMFC), water electrolyzer (PEMWE) and unitized regenerative fuel cell (URFC). Results show a high active surface area (up to 44 m2 g−1) and high electrochemical activity for a number of synthesized samples. A qualitative correlation has been established between sputtering parameters, type of carbon carrier and performances as electrocatalyst.

Preparation of Pd nanoparticles deposited on a polyaniline/multiwall carbon nanotubes nanocomposite and their application in the Heck reaction

In this work, we described the synthesis of a nanocatalyst, which consists of polyaniline (PANI)/multiwall carbon nanotubes (MWCNTs) and the deposited Pd nanoparticles. FT-IR, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis (TG) and transmission electron microscopy were used to characterize the nanocatalyst. The interaction between PANI and MWCNTs have been explained according to the results of the FT-IR and XRD analysis. This complex was an efficient catalyst for the Heck reactions of acrylic acid with aryl iodides in air at low temperature (60 °C) using 0.9 mol% Pd of the catalyst. Furthermore, it also exhibited catalytic properties for the bromide and activated chlorobenzene. The yield of cinnamic acid was 71 % for the Heck reaction of acrylic acid with iodobenzene even though the complex was used nine times.

The effect of operating temperature on gasochromic properties of amorphous and polycrystalline pulsed laser deposited WO3 films

In this study, tungsten oxide films were synthesized by pulsed laser deposition (PLD) method. The as-deposited films were annealed at a temperature of 250 and 350°C in air for 1h. The surface morphology, microstructure, crystalline phase and chemical composition of the as-prepared and annealed films were characterized by SEM, XRD and XPS techniques, respectively. Deposition of Pd nanoparticles onto the tungsten oxide surface was performed by hydrogen reduction of a drop-drying PdCl2 solution onto a WO3 surface at 60°C. The influence of the annealing temperature on microstructure and gasochromic performance as well as the effect of operating temperature is presented in this work. Results show that the gasochromic responses of the amorphous samples at temperatures below 100°C has attained approximately a constant value but these values for polycrystalline samples shows a significant increase with increasing temperature and the maximum gasochromic response was achieved at operating temperatures between 90 and 100°C. Because of the low surface to volume ratio and negligible diffusion length, the polycrystalline film shows intense decrease in ΔODm values compared to the amorphous film at operating temperatures above 100°C. Also the effect of water desorption at T∼100°C on gasochromic response was investigated.

Palladium Nanoparticles/Defective Graphene Composites as Oxygen Reduction Electrocatalysts: A First-Principles Study

The impact of graphene substrate–Pd nanoparticle interaction on the O, OH, and OOH adsorption that is directly related to the electrocatalytic performance of these composites in oxygen reduction reaction (ORR) has been investigated by first-principles-based calculations. The calculated binding energy of a Pd13 nanoparticle on a single vacancy graphene is as high as −6.10 eV, owing to the hybridization between the dsp states of the Pd particles with the sp2 dangling bonds at the defect sites. The strong interaction results in the averaged d-band center of the deposited Pd nanoparticles shifted away from the Fermi level from −1.02 to −1.45 eV. Doping the single vacancy graphene with B or N will further tune the average d-band center and also the activity of the composite toward O, OH, and OOH adsorption. The adsorption energies of O, OH, and OOH are reduced from −4.78, −4.38, and −1.56 eV on the freestanding Pd13 nanoparticle to −4.57, −2.66, and −1.39 eV on Pd13/single vacancy graphene composites, showing ...

Unique Pd/graphene nanocomposites constructed using supercritical fluid for superior electrochemical sensing performance

Supercritical CO2 fluid (scCO2) with gas-like diffusivity, low viscosity, and near-zero surface tension can help debundle graphene nanosheets and uniformly disperse Pd nanocrystals (approximately 3 nm) between them. The in situ synthesis protocol of Pd (from scCO2), which does not require pretreatment of the support, preserves the peculiar characteristics of graphene, such as the excellent electrical conductivity. The deposited Pd nanoparticles (NPs) can act as spacers to prevent restacking of the graphene nanosheets. Since the Pd catalyst particles are sandwiched between the highly conductive sheets, a superior electrochemical utilization can be achieved. The obtained Pd/graphene nanocomposite exhibited superior sensing performance (in terms of response current and potential resolution) toward ascorbic acid, dopamine, and uric acid, compared to that of Pd/graphene prepared using a conventional process. Promising detection sensitivity and selectivity of various scCO2-synthesized NPs/graphene heterostructures for various biological analytes can be expected.

Enhanced Electrocatalytic Activity of TiO2 Nanotubes Modified with Pt and Pd Nanoparticles: Electro-Oxidation of Dopamine, Uric Acid and Ascorbic Acid

TiO2 nanotubes electrode was fabricated by anodizing Ti sheets in Fcontained solution. The final modified electrode was then prepared by electrochemical pulse deposition of Pd and Pt nanoparticles onto the surface of tubes. The morphological characterization of the modified electrode suggested a uniform and regular tubular structure which was decorated by metal nanoparticles. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Pt-Pd-TiO2 NTs modified electrode represented a relatively high sensitivity towards detection of dopamine in 0.1 M phosphate buffer solution (pH 7.00) as base solution. Over a wide concentration range of 2.0×10−7 to 1.0×10−4 M dopamine, the electrooxidation peak currents of dopamine experienced two limits of linearity. However the sensitivity of the PdTiO2 NTs was not acceptable for detection of dopamine. Furthermore, the Pt-PdTiO2 NTs modified electrode was able to distinguish the oxidation response of dopamine, uric acid and ascorbic acid in mixture solution of different acidity.

Hydrogen as an optimum reducing agent for metallization of self-assembled monolayers

We demonstrate a very efficient route for electroless deposition of Pd nanoparticles on self-assembled monolayers (SAMs) of a pyridine-terminated thiol. This method involves reduction of the coordinated Pd2+ on SAMs by exposure to molecular hydrogen. A complete Pd adlayer surface coverage can be obtained. Moreover, this work is the first experimental demonstration of hydrogen adsorption on Pd adlayers.