Hydrodechlorination of CCl4 over carbon-supported palladium–gold catalysts prepared by the reverse “water-in-oil” microemulsion method

Two series of carbon-supported Pd–Au catalysts were prepared by the reverse “water-in-oil, W/O” method, characterized by various techniques and investigated in the reaction of tetrachloromethane with hydrogen at 423 K. The synthesized nanoparticles were reasonably monodispersed having an average diameter of 4–6 nm (Pd/C and Pd–Au/C) and 9 nm (Au/C). Monometallic palladium catalysts quickly deactivated during the hydrodehalogenation of CCl₄. Palladium–gold catalysts with molar ratio Pd:Au = 90:10 and 85:15 were stable and much more active than the monometallic palladium and Au-richer Pd–Au catalysts. The selectivity toward chlorine-free hydrocarbons (especially for C₂₊ hydrocarbons) was increased upon introducing small amounts of gold to palladium. Simultaneously, for the most active Pd–Au catalysts, the selectivity for undesired dimers C₂H_xCl_y, which are considered as coke precursors, was much lower than for monometallic Pd catalysts. Reasons for synergistic effects are discussed. During CCl₄ hydrodechlorination the Pd/C and Pd–Au/C catalysts were subjected to bulk carbiding.     

Electrochemical behavior of CO2 reduction on palladium nanoparticles: Dependence of adsorbed CO on electrode potential

The electrochemical reduction of CO₂ is strongly influenced by both the applied potential and the surface adsorption status of the catalyst. In this work a gas diffusion electrode (GDE) coated with Pd nanoparticles/carbon black (Pd/XC72) was used to study the electrochemical reduction of CO₂. Cyclic voltammetric (CV) analysis of Pd/XC72 between 1.5 V and − 0.6 V (vs. RHE) shows the formation of intermediates and the blocking of hydrogen absorption on the Pd nanoparticles (NPs) under a CO₂ atmosphere. The relationships between the Faradaic efficiency/current density and the applied potential reveal that the onset potential of CO formation is around − 0.4 V. Moreover, the presence of adsorbed CO was confirmed through CV analysis of Pd/XC72 under CO₂ and CO/He atmospheres. This demonstrates that H atoms and CO intermediates co-adsorb on the surface of the Pd NPs at an applied potential of around − 0.4 V. When the applied potential is more negative than − 0.6 V, adsorption of CO intermediates on the surface of the Pd NPs becomes dominant.     

A facile preparation of carbon-supported Pd nanoparticles for electrocatalytic oxidation of formic acid

A low temperature approach via the complexing of PdCl₂ with EDTA followed by NaBH₄ reduction has been used to prepare Vulcan XC-72 carbon-supported Pd nanoparticles (Pd/C). The mean particle size of the Pd/C catalysts is found to increase from 3.3 to 9.2 nm with heat-treated temperature. TEM images demonstrated that the Pd nanoparticles are well dispersed on the support with a relatively narrow particle size distribution. A correlation between the electrocatalytic activity of formic acid oxidation and particle size of the Pd/C catalysts indicates that the highest activity of formic acid oxidation is found with a Pd mean particle size of ca. 4.7 nm. The preparation method used here is cost-effective and should be easily scaled for industrial production.     

Graphene nanoplatelets supported metal nanoparticles for electrochemical oxidation of hydrazine

Graphene nanoplatelets have been applied as the support to electrodeposit monometallic Au and Pd nanoparticles as well as bimetallic Au–Pd nanoparticles. These nanoparticles have been characterized with scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical techniques. They are further utilized as the catalysts for electrochemical oxidation of hydrazine. The oxidation peak potential is − 0.35 and 0.53 V (vs. SCE) when monometallic Pd and Au nanoparticle are used as the catalysts. When bimetallic nanoparticles are applied as the catalyst, their composition affects the peak potential and peak current for the oxidation of hydrazine. Higher oxidation current is achieved when bimetallic Au–Pd nanoparticles with an atomic ratio of 3:1 are deposited on graphene nanoplatelets. Metal nanoparticle-loaded graphene nanoplatelets are thus novel platforms for electrocatalytic, electroanalytical, environmental, and related applications.     

Comparison of performances of bioanodes modified with graphene oxide and graphene–platinum hybrid nanoparticles

The performances of graphene oxide (GO) and graphene–platinum hybrid nanoparticles (Gr-Pt hybrid NPs) were compared for biofuel cell (BFC) systems. This is the first study that constitutes these nanomaterials in BFC systems. For this purpose, fabricated bioanodes were combined with laccase modified biocathode in a single cell membraneless BFC. Power and current densities of these systems were calculated as 2.40 μW cm^− 2 and 211.90 μA cm^− 2 for GO based BFC and 4.88 μW cm^− 2 and 246.82 μA cm^− 2, for Gr-Pt hybrid NPs based BFC. As a result, a pioneer study which demonstrates the effective performances of combination of graphene with Pt was conducted.     

Investigation of the electrocatalytic activity of boron-doped diamond electrodes modified with palladium or gold nanoparticles for oxygen reduction reaction in basic medium

The paper reports on the electrocatalytic activity of boron-doped diamond (BDD) electrodes electrochemically modified with palladium (Pd) or gold nanoparticles (Au NPs) towards oxygen reduction reaction (ORR) in alkaline medium. The BDD/Pd NP interface shows a well-defined diffusion-controlled voltammetric oxygen reduction peak at −0.25 V vs. Ag/AgCl. This is more positive than the ORR peak at −0.59 V vs. Ag/AgCl observed on BDD/Au-NP composite electrodes. The ORR proceeds via a four-electron process in both cases.     

Green synthesis of plant-stabilized Au nanoparticles for the treatment of gastric carcinoma

In this study, gold nanoparticles (AuNPs) were green synthesized using plant extract. The obtained nanoparticles (Au NPs) were characterized by advanced physical and chemical techniques like TEM, FTIR, UV–vis, SEM, XRD and EDX. SEM image displayed the quasi-spherical shaped nanoparticles of mean diameter 20–50 nm. All the particles were of uniform shape and texture. From the XRD pattern, four distinct diffraction peaks at 38.2°, 44.2°, 64.7° and 77.4° are indexed as (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of fcc metallic gold. The in vitro cytotoxic and anti-gastric carcinoma effects of biologically synthesized Au NPs against cancer cell lines were assessed. The IC₅₀ of the Au NPs were 192, 149, 76 and 85 µg/mL against NCI-N87, MKN45, GC1401 and GC1436 gastric cancer cell lines. The anti-gastric carcinoma properties of the Au NPs could significantly remove the cancer cell lines in a time and concentration-dependent manner. So, the findings of the recent research show that biologically synthesized Au NPs might be used to cure cancer.     

Physical and electrochemical characterizations of nanostructured Pd/C and PdNi/C catalysts for methanol oxidation

Pd and PdNi nanoparticles supported on Vulcan XC-72 carbon were prepared by a chemical reduction with formic acid process. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and chronoamperometry. The results showed that the Pd and PdNi nanoparticles, which were uniformly dispersed on carbon, were 2–10 nm in diameters. The PdNi/C catalyst has higher electrocatalytic activity for methanol oxidation in alkaline media than a comparative Pd/C catalyst and shows great potential as less expensive electrocatalyst for methanol electrooxidation in alkaline media in direct methanol fuel cells.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Graphene supported Sn–Sb@carbon core-shell particles as a superior anode for lithium ion batteries

This paper reports the preparation and Li-storage properties of graphene nanosheets(GNS), GNS supported Sn–Sb@carbon (50–150 nm) and Sn–Sb nanoparticles (5–10 nm). The best cycling performance and excellent high rate capabilities were observed for GNS-supported Sn–Sb@carbon core-shell particles, which exhibited initial capacities of 978, 850 and 668 mAh/g respectively at 0.1C, 2C and 5C (1C = 800 mA/g) with good cyclability. Besides the GNS support, the carbon skin around Sn–Sb particles is believed to be a key factor to improve electrochemical properties of Sn–Sb.     

Bismuth as an additive modifying the selectivity of palladium catalysts

The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO₂ in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase activity and selectivity of PdBi/SiO₂ catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO₂, 3 wt.% Bi/SiO₂ and 5 wt.% Pd–5 wt.% Bi/SiO₂ show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of Pd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation.     

One-step synthesis of hollow structured Si/C composites based on expandable microspheres as anodes for lithium ion batteries

Si/C composites of carbon hollow structures loaded with Si nanoparticles (NPs) (Si/C-HSs) were prepared by one-step pyrolysis of a mixture of Si NPs and expandable microspheres (EMs). For the Si/C-HSs, hollow carbon shells with rough surfaces were formed by directly carbonizing the polymer shells of EMs, and the Si NPs fell into the void space or were loaded on the rough surfaces of the carbon shells. The EM-based carbon shells accommodated the volume expansion of the Si NPs and improved the electrical conductivity of the composites. As a result, the Si/C-HSs exhibited a high capacity (initial reversible capacity: 854.4 mAh g^− 1 at 300 mA g^− 1), stable cycling performance (capacity retention: 80% after 50 cycles), and excellent rate capability.     

Morphological and thermal behavior of porous biopolymeric nanoparticles

The aim of the present work is to design, develop and characterize biodegradable polymeric nanoparticles having well defined size and porous morphology. Poly(dl-lactide-co-glycolide) (PLGA) and poly(l-lactide) (PLLA) nanoparticles (NPs) were prepared by double emulsion method with subsequent solvent evaporation. NPs were characterized by electron microscopes, dynamic light scattering, XRD and thermal properties by differential scanning calorimetry and thermogravimetry. Finally, the in vitro degradation analysis was also performed. Biodegradable NPs display a spherical surface structure with a homogeneous size distribution, and an average diameter of 180 nm for PLLA and 218 nm for the PLGA. The NP nanoporous structure was analyzed by an innovative thermal method: thermoporosimetry, providing information about nanopore dimensions. In vitro degradation studies demonstrate the gradual surface aggregation and degradation of NPs and the effects on polymer properties. Biopolymeric porous nano-systems may offer promise properties for revolutionary improvements in tissue engineering, diagnosis and targeted drug delivery systems.     

Pd Nanostructures with High Tolerance to CO Poisoning in the Formic Acid Electrooxidation Reaction

Pd architectures such as nanobars and nanoparticles were synthetized by the polyol method using di-ethylene glycol as reaction media. The morphology, composition and electrocatalytic properties were investigated by transmission electronmicroscopy (TEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and electrochemical measurements. The electrocatalytic activity of Pd nanostructures was tested in terms of formic acid electrooxidation reaction (FAOR) in acid media (0.5 M H₂SO₄) and compared with commercial Pd/XC-72 (Pd/C). Results from the electrochemical studies showed that Pdnanobars (PdNB/C) presented higher tolerance to the CO and CO₂ poisoning effect compared with Pd nanoparticles (PdNP/C) and commercial Pd/C. Furthermore, the onset potential toward formic acid electrooxidation at high concentration (1 M) on PdNB/C exhibited a negative shift ca. 100 mV compared with commercial Pd/C. Finally, PdNB/C in the presence of 1 M FA showed a lower poisoning degree compared with commercial Pd/C and PdNP/C.     

Impact of palladium silicide formation on the catalytic properties of Pd/SiO2 catalysts in liquid-phase semihydrogenation of phenylacetylene

In this study, palladium silicide was formed on the sol–gel derived SiO₂ supported Pd catalysts when they were prepared by ion-exchange method using Pd(NH₃)₄Cl₂ as a palladium precursor. No other palladium phases (PdO or Pd⁰) were evident after calcinations at 450 °C for 3 h. The Pd/SiO₂ catalysts with Pd silicide formation were found to exhibit superior performance than commercial SiO₂ supported ones in liquid-phase semihydrogenation of phenylacetylene. From XPS results, the binding energy of Pd 3d of palladium silicide on the Pd/SiO₂ catalyst shifted toward larger binging energy, indicating that Pd is electron deficient. This could probably result in an inhibition of a product styrene on the Pd surface and hence high styrene selectivities were obtained at high phenylacetylene conversions. The formation of Pd silicide, however, did not have much impact on specific activity of the Pd catalysts since the TOFs were quite similar among the various catalysts with or without palladium silicides if their average particle sizes were large enough. The TOFs decreased by an order of magnitude when palladium dispersion was very high and their average particle sizes were smaller than 3–5 nm.     

pH effect on electrocatalytic reduction of CO2 over Pd and Pt nanoparticles

Adsorbed hydrogen participates in electrocatalytic reduction of CO₂ and competitive hydrogen evolution reaction (HER) simultaneously, and its reaction pathway greatly affects the activity and selectivity of CO₂ reduction. In this work, we investigate pH effect on electrocatalytic reduction of CO₂ over Pd and Pt nanoparticles (NPs) with a similar size in a pH range from 1.5 to 4.2. Pt NPs completely contribute to HER in the pH range. Over Pd NPs, Faradaic efficiency for CO production at − 1.19 V (vs. reversible hydrogen electrode) varies from 3.2% at pH of 1.5 to 93.2% at pH of 4.2, and current density for CO production reaches maximum at pH of 2.2. The significant enhancement of Faradaic efficiency and current density for CO production over Pd NPs at high pH values is attributed to decreased kinetics of hydrogen evolution reaction by increasing hydrogen binding energy and lowered adsorption affinity of CO-like intermediate compared to Pt.     

Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O₂ molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.     

Multilayer graphene nanoribbons exhibit larger capacitance than their few-layer and single-layer graphene counterparts

This article demonstrates that it is not always beneficial to exfoliate graphitic structures to single-layer graphene to achieve maximum electrochemical performance. Using electrochemical impedance spectroscopy, we show that multilayer graphene nanoribbons with cross sections of 100 × 100 nm provide larger capacitance (15.6 F/g) than do few-layer graphene nanoribbons (14.9 F/g) and far larger capacitance than single-layer graphene nanoribbons (10.9 F/g) with the same cross section.     

Synthesis of mesoporous hollow carbon hemispheres as highly efficient Pd electrocatalyst support for ethanol oxidation

The synthesis procedure of the highly mesoporous hollow carbon hemispheres (HCHs) using glucose as carbon source and solid core mesoporous shell silica (SCMSS) as template and the formation mechanism of the HCHs have been presented. The HCHs show an ultrahigh surface area of 1095.59 m² g^?1 and an average mesopore size of 9.38 nm. The hemispherical structure with large mesopores also results in the improvement in the mass transfer and therefore more concentrated ethanol solution can be used to increase the energy density. The additional advantage of the HCHs compared to the hollow carbon spheres is that they can provide the similar surface area at reduced volume. The current densities of ethanol oxidation on Pd nanoparticles supported on HCH (Pd/HCH) electrocatalyst are three times as many as on Pd/C at the same Pd loadings.     

Controlled synthesis of MnSn(OH)6/graphene nanocomposites and their electrochemical properties as capacitive materials

We report the synthesis of novel MnSn(OH)₆/graphene nanocomposites produced by a co-precipitation method and their potential application for electrochemical energy storage. The hydroxide decorated graphene nanocomposites display better performance over pure MnSn(OH)₆ nanoparticles because the graphene sheets act as conductive bridges improving the ionic and electronic transport. The crystallinity of MnSn(OH)₆ nanoparticles deposited on the surface of graphene sheets also impacts the capacitive properties as electrodes. The maximum capacitance of 31.2 F/g (59.4 F/g based on the mass of MnSn(OH)₆ nanoparticles) was achieved for the sample with a low degree of crystallinity. No significant degradation of capacitance occurred after 500 cycles at a current density of 1.5 A/g in 1 M Na₂SO₄ aqueous solution, indicating an excellent electrochemical stability. The results serve as an example demonstrating the potential of integrating highly conductive graphene networks into binary metal hydroxide in improving the performance of active electrode materials for electrochemical energy storage applications.