X-photoelectron Spectroscopy Research Articles

Copper Selenides as High-Efficiency Electrocatalysts for Oxygen Evolution Reaction

Designing high-efficiency water oxidation catalysts from earth-abundant resources has attracted significant attention in the last couple of years owing to the potential application of this technology in several energy conversion devices. Among the transition metals, copper is one of the cheapest earth-abundant nonprecious element which can enhance electrocatalytic activity due to heavily occupied d-orbitals. In this article we have shown electrocatalytic activity of copper selenide for the first time for water oxidation reaction. The copper selenide phases were synthesized by direct electrodeposition on electrodes, as well as by hydrothermal and chemical vapor deposition (CVD) techniques. Structure and morphology characterization through powder X-ray diffraction, Raman, X-photoelectron spectroscopy, and electron microscopy revealed that all the synthesized phases were pure crystalline copper selenide of composition Cu2Se and comprising nanostructured granular morphology. Electrocatalytic performance for w...

The Evaluation of the Perturbations Induced By Ionic Bombardment on Surfaces: A Challenge for Interfacial Electrochemistry

The electrochemical response of a material used as electrode is a very efficient and quantitative tool to provide information about its properties particularly its surface characteristic. When any surface is submitted to perturbation as plasma treatment, ionic bombardment, thermal annealing, etc., analysis of electrochemical response is very relevant to discuss the current level of disturbance induced by the treatments. Electrode materials are metals (M) or Semiconductors (SC) and the analysis of modifications of the electrochemical responses are very rich and sensitive due to the high number of parameters that govern the interfacial electrochemistry of the SC or M//electrolyte interface and for which well established data are available. Indeed, accurate analysis of electrochemical responses before and after the treatments gives rise to quantitative information about the electrical, chemical and structure evolutions of the modified surface and consequently on the amplitude of the perturbations. It is also a very efficient tool for estimation of the initial property recovery when additional treatments performed ex situ but also in situ, are carried on the treated surfaces. Comparing the degrees of modification can be used to evaluate the deepness of the perturbation inside de the material. When the electrochemical approach is linked to chemical surface analysis using X-Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) characterizations or to crystallographic analysis using Electron Back Scattering Diffraction (EBSD) the description of the modified surface becomes quantitative and complete at each stage of the treatment processes. In this contribution, attention will be focused on the evaluation of the perturbation induced on SC by different ionic bombardment conditions. The SC are mono-crystalline InP (n & p type) wafers with (001) or (111) orientations. Ionic bombardment is performed using an Argon MAGCIS dual ion source which provides accelerated Ar+ monoatomic ions or clusters (Arn)+. Controlling the nature, the acceleration, the exposure time, for the beam/SC interaction it is possible to study the consequences of the ion/InP interaction toward a large set of electrochemical parameters. We will present how open circuit rest potential measured in the dark or under illumination are progressively modified. A second important feature concerns the current-potential J(V) responses in the dark or under illumination which a obviously transformed (without current domains, water molecules or protons reduction over-potentials, photo-current anodic (or cathodic) threshold potential, photocurrent saturation domains, etc). Moreover reactivity toward redox species (Ce4+, Fe(CN)6 3-, etc ) can be also impacted depending on the strength of the imposed ionic interaction. The key question of the interface energy diagram through the flat band potential position determination, using for example capacitance measurements is also a main interfacial parameter which is very interesting to follow in term of surface modification. A very important characteristic of SC interfacial electrochemistry is its availability to generate in situ anodic dissolution with nano-metric control of the material releasing or transformation. Using this possibility it is possible to recover partially or totally the initial properties of the SC/solution interface. So the deepness of the perturbed region can be quantitatively determined. Considered alone the electrochemical characterization can be auto-sufficient for an evaluation of the induced perturbation. Coupled to the XPS analysis the electrochemical responses are now associated directly to surface chemical information as: loss of stoichiometry, Ar+ implantation, surface modification of the Fermi Energy level position, etc. As example of our experimental methodology, the evolution of the XPS core level modification (here P2p) and the associated modification of the Mott Schottky response are reported in figure 1. Both present correlated modifications that can be eliminated using anodic dissolution of the perturbed amount of material in surface. This experimental sequence illustrated the power of the electrochemical tool for a quantitative evaluation of ionic beam induced perturbation of InP surfaces in this study. Figure 1Variation of the Mott-Shottky Plots induced by ionic bombardment on n-InP_H2SO4 (0.5M) electrolyte. Insert: variations of the XPS response on P2p of n-InP induced by ionic bombardment. Figure 1

Arsenic vitrification by copper slag based glass: Mechanism and stability studies

In the present work, the (100−x)(58SiO2-20Fe2O3-10B2O3-12Na2O)−xAs (x=0, 2, 4, 6, 8wt%) glasses, which are main constituents of the copper slag based glasses, were produced by conventional melting method to study the arsenic vitrification mechanism and stability. X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and X-photoelectron spectroscopy (XPS) were used to investigate the mechanism of arsenic vitrification. The XRD analysis for the x≤wt 8% samples shows that all the samples form homogeneous glasses and the arsenic is compatible with the copper slag based glass. The FTIR spectrum of the glasses have revealed that the arsenic exists in the form of AsO4 tetrahedra and the Qn structure of the copper slag based glass has been strengthened with the increase addition of arsenic. The changes of the binding energies of Si2p, O1s, As3d and Fe2p directly indicate the formation of SiOAs and FeOSi/As bonds in the glass, which strengthens the chemical stability of the glass. Lastly, USEPA toxicity characteristics leaching procedure (TCLP) and differential scanning calorimetry (DSC) tests were used to study the chemical durability and thermal stability of the glasses containing arsenic. The leaching concentrations of As, B, Fe, Na, and Si are under safety thresholds and the increase addition of arsenic into the glasses can decrease the leaching concentrations, indicating that the arsenic can improve the chemical stability of the glass. The arsenic added into the glass can improve the ΔT, which strengthens the thermal stability of the glasses.

Variable range hopping crossover and magnetotransport in PLD grown Sb doped ZnO thin film

We report on the variable range hopping (VRH) crossover in the electrical transport of Sb doped ZnO (SZO) thin film. Structural, chemical, electrical and magnetotransport properties were carried out on SZO thin film grown by pulsed laser deposition. X-photoelectron spectroscopy study confirms the presence of both Sb3+(33%) and Sb5+(67%) states. Sb doped ZnO thin film shows n-type behavior which is attributed to the formation of SbZn and/or SbZn–VZn defect complex. Temperature dependent resistivity measurement showed that in a low temperature regime ( K) transport is governed by the 3D-VRH mechanism. A crossover from 3D-VRH to Efros–Shklovoski VRH was observed around 12 K. Negative magnetoresistance (MR) is observed in the entire temperature range (300–5 K), however, there is an upturn in the MR behavior at 5 K suggesting the existence of a positive component. The MR behavior of Sb doped ZnO thin films is explained by the Khosla and Fischer model.

Galvanic replacement synthesis of NiPt/graphene as highly efficient catalysts for hydrogen release from hydrazine and hydrazine borane

NiPt nanoparticles (NPs) supported on graphene nanosheets were successfully synthesized via a galvanic replacement approach at room temperature with precursor Ni NPs as a sacrificial template. The as-synthesized NiPt/graphene catalysts were characterized by inductively coupled plasma, X-ray diffraction, transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy, X-photoelectron spectroscopy, and BET surface area measurement, and used as catalysts for H2 production from hydrazine and hydrazine borane. The characterization data showed that NiPt NPs with a small size of around 3.5 nm were dispersed on the graphene nanosheets. The as-synthesized NiPt/graphene exhibited high activity and 100% hydrogen selectivity toward the conversion of hydrazine or hydrazine borane to hydrogen. The turnover frequency (TOF) values of Ni0.58Pt0.42/graphene reached 434 h−1 at 30 °C and 846 h−1 at 50 °C for the decomposition of hydrazine, respectively, which are higher than those of most of the reported catalysts. In particular, a high TOF value of 2303 h−1 at 50 °C was obtained for dehydrogenation of hydrazine borane, which is among the highest for all the catalysts reported to date. The as-synthesized Ni0.58Pt0.42/graphene exhibited satisfactory durability for hydrogen evolution from hydrazine and hydrazine borane. This excellent catalytic performance could be attributed to the strong interaction of NiPt NPs and graphene, the small size and high dispersion of NiPt NPs, and NaOH promotion. The development of high catalytic activity catalysts is a promising step towards the application of hydrazine and hydrazine borane as hydrogen storage material.

Synthesis and Characterization of Cu and N Codoped RF-Sputtered TiO2 Films: Photoluminescence Dynamics of Charge Carriers Relevant for Water Splitting

Cu–N codoped TiO2 anatase thin films with a nanocolumnar architecture have been synthesized by RF-magnetron sputtering and characterized by Raman, scanning electron spectroscopy, and X-photoelectron spectroscopy. Absorption, photoluminescence, and photoluminescence lifetimes of the prepared samples have been investigated to understand the dynamics of the photogenerated carriers in connection to both introduced defects and the modified TiO2 band structure. At low concentrations Cu is mainly present as Cu+, while at higher concentrations the Cu2+ oxidation state prevails. Nitrogen, at low concentration and without the presence of copper dopant, substitutionally replaces oxygen to form a O–Ti–N linkage. With increasing concentration, interstitial nitrogen and Ti–O–N and Ti–O–N–O linkages are observed. In all codoped samples nitrogen is present as both interstitial and substitutional dopant. From photoluminescence spectra it is observed that nitrogen, in cooperation with Cu, more heavily affects the oxide str...

Influence of pH, layer charge location and crystal thickness distribution on U(VI) sorption onto heterogeneous dioctahedral smectite

The UO22+ adsorption on smectite (samples BA1, PS2 and PS3) with a heterogeneous structure was investigated at pH 4 (I=0.02M) and pH 6 (I=0.2M) in batch experiments, with the aim to evaluate the influence of pH, layer charge location and crystal thickness distribution. Mean crystal thickness distribution of smectite crystallite used in sorption experiments range from 4.8nm (sample PS2), to 5.1nm (sample PS3) and, to 7.4nm (sample BA1). Smaller crystallites have higher total surface area and sorption capacity. Octahedral charge location favor higher sorption capacity. The sorption isotherms of Freundlich, Langmuir and SIPS were used to model the sorption experiments. The surface complexation and cation exchange reactions were modeled using PHREEQC-code to describe the UO22+ sorption on smectite. The amount of UO22+ adsorbed on smectite samples decreased significantly at pH 6 and higher ionic strength, where the sorption mechanism was restricted to the edge sites of smectite. Two binding energy components at 380.8±0.3 and 382.2±0.3eV, assigned to hydrated UO22+ adsorbed by cation exchange and by inner-sphere complexation on the external sites at pH 4, were identified after the U4f7/2 peak deconvolution by X-photoelectron spectroscopy. Also, two new binding energy components at 380.3±0.3 and 381.8±0.3eV assigned to AlOUO2+ and SiOUO2+ surface species were observed at pH 6.

Reduced graphene oxide based a novel polymer inclusion membrane: Transport studies of Cr(VI)

In this study, the removal and recovery of hexavalent chromium using reduced graphene oxide based polymer inclusion membrane from chrome plating water was investigated. The prepared modified membrane improved the mechanical properties and permeability of polymer inclusion membrane. Important outcomes of this study are high permeability, seamless porous structure, high selectivity and development of the polymer inclusion membrane by minimized nano-reinforced against pollution in addition of the unique physical properties of graphene oxide. The effects of carrier concentration, plasticizer type and temperature on the transport, the membrane's stability and thickness were examined. The polymer inclusion membrane was characterized by using atomic force microscopy, X-photo electron spectroscopy and contact angle measurements. The transport efficiency of Cr(VI) from chrome plating bath water was found to be 100% under optimized conditions. The experimental results showed that reduced graphene oxide modified polymer inclusion membrane exhibits great stability and selectivity in the presence of other metal cations in chrome plating bath water for the removal of Cr(VI).

Cu (InGa) SeTe Nanocrystals Structural and Optical Properties

Cu (InGa) SeTe Nanocrystals Structural and Optical Properties Novel chalcogenide nanocrystals are the potential materials for the photovoltaic use. Predominantly, single phasic chalcogen materials are an area of the great attention. In this order it is important to demonstrate colloidal synthesis of Cu25(In16Ga9)Se40Te10 (CIGST-1) and Cu20(In14Ga9)Se45Te12 (CIGST-2) nanocrystals adopting the single step heating-up (170ºC) process. The synthesized materials single/ multi-phases crystallographic structures are verified from the X-ray diffractometer. The average size agglomerated nanocrystals/ particles is evaluated less than 10 nm from the Transmission Electron Microscopy and VU-Visible spectrum Lorentzian fit analysis. The UV-Visible optical absorption spectrum demonstrates a distinguishable blue shift. While the elemental presence and their particle distribution within the configuration is described with help of the energy dispersive X-ray mapping technique. The materials binding energy core level changes are verified from the X-photoelectron spectroscopy. The photoluminescence spectroscopic outcome is revealed a broad peak in wave length range 450 nm to 750 nm for these materials.

Multivalent Cu-Doped ZnO Nanoparticles with Full Solar Spectrum Absorbance and Enhanced Photoactivity

Full solar spectrum absorbers are widely pursued for applications related to photocatalysis and photovoltaics. Here we report multivalent Cu-doped ZnO nanoparticles which exhibit full solar spectrum absorbance and high photoactivity. Metathesis-based, green-chemical approaches with synthesis yield of ∼100% are used. Cu incorporation in ZnO results in an increase of average solar spectrum absorbance from a mere 0.4% to 34%. On the other hand, (Zn, Cu)O composites result in materials with up to 64% average solar spectrum absorbance. Doped systems operate well under both visible and UV illumination. The nanomaterials prepared are characterized by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS). Photocatalysts explored have particle sizes ≥50 nm. This is deliberately done in order to avoid the nanotoxic size regime of ZnO. Despite the large particle size and low specific surface area (<20 m2·g–1), the best catalyst reported here compare favorably with recent reports on ZnO based systems. Using X-photoelectron spectroscopy and synthesis–property correlations, we infer that the presence of multivalent Cu (most likely in the form of Cu1+δO) on ZnO surface is responsible for the observed photoactivity enhancement.

Wettability and osteoblastic cell adhesion on ultrapolished commercially pure titanium surfaces: the role of the oxidation and pollution states

The oxidation state of the surfaces of titanium-based biomaterials strongly depends on their previous history. This factor affects the titanium wettability and it probably conditions the success of the implanted biomaterials. However, the separate role of the pollution and oxidation states of metallic titanium surfaces remains still controversial. To elucidate this, it is required to standardize the initial surface state of titanium in terms of roughness and surface chemistry, and then, to monitor its wettability after the corresponding treatment. In this work, we studied finely polished surfaces of commercially pure titanium (cpTi) which were subjected to cleaning surface treatments. X-Photoelectron spectroscopy was used to characterize the surface chemistry and the oxide film thickness. The contact angle hysteresis in underwater conditions was measured with the growing/shrinking captive bubble method, which allowed for mimicking the real conditions of implantable devices. The water wettability of smooth cpTi surfaces was stabilized with weak thermal oxidation (230 °C, 30 min). The osteoblastic cell response of the stabilized and non-stabilized cpTi surfaces was analyzed. Although the oxidation and pollution states were also stabilized and normalized, no correlation was observed between the stable response in wettability of titanium and its cell adhesion.

Enhanced visible light activity and mechanism of TiO2 codoped with molybdenum and nitrogen

Abstract Mo-N-codoped TiO 2 was synthesized by using ammonium molybdate tetrahydrate and ammonia water as the sources of Mo and N, respectively. The resulting materials were characterized by X-ray diffraction (XRD), X-photoelectron spectroscopy (XPS) and UV–vis light diffuse reflection spectroscopy (DRS). Furthermore, the activity enhanced-mechanism was proposed. XRD results indicated that codoping favored the formation of anatase and improved the anatase crystallinity. XPS analysis revealed that N was incorporated into the lattice of TiO 2 through substituting lattice O and coexisted in the substitutional forms. Meanwhile, Mo was incorporated into the lattice of TiO 2 through substituting Ti and coexisted in the forms of Mo 6+ and Mo 5+ . DRS showed that the light absorption in visible region was improved by co-doping, leading to a narrower band gap and higher visible activity for the degradation of phenol than that of others. The enhanced activity was attributed to the high anatase crystallinity, large amount of surface oxygen vacancies, intense light absorption and narrow band gap.

极紫外Mg/SiC、Mg/Co多层膜的稳定性

To research the stability of Mg-based multilayers,two groups of multilayers,20 and [Mg/SiC]20 were coated on a Si(100) substrate by magnetron sputtering method.The two samples were tested by a microscopy,a surface roughness experiment and an X-ray grazing incidence reflectivity test at room temperature and a relative humidity of 80%.The contract experiments on multilayer damage for Mg/Co和Mg/SiC were performed in the same condition.The results show that after being exposed in the atmospheric environment for 4 days,the damaged area and surface roughness of the Mg/SiC multilayer sample are up to 26.34% and 10 nm,respectively,while those of the Mg/Co multilayer sample are 2.78% and 5 nm,respectively.After 6 days,the 1st reflection peak of Mg/SiC sample is completely disappeared,and Mg/Co sample still has a peak of 47.63% reflectivity.The experimental results show that the Mg/Co multilayer sample has a better environmental stability as compared with the Mg/SiC multilayer.The X Photoelectron Spectroscopy(XPS) shows that the productions of the damaged Mg-based multilayers are mainly MgCO3,Mg(OH)2 and modest MgO.Moreover,the content ratio of Mg(OH)2 and MgCO3 in the inner layer is significantly higher than that in the surface layer.Experimental results suggest that the reason for Mg-based multilayer damage is the erosion of H2O(g),so the capping layer of Mg-based multilayer should prevent the H2O(g) penetrating into the mulilayer.

Study of Copper Electrodeposition Mechanism on Molybdenum Substrate

In this paper, the copper electrodeposition on molybdenum (600 nm PVD layer, on a 3 mm glass support) has been studied, and particularly the behavior of microelectronic-dedicated bath formulation. The aim is to provide copper thin films with controlled thickness (<0.5 μm), later used as inner precursor for CZTS photovoltaic absorber. The film growth was studied since its initial nucleation step until the total coverage of the surface. The nucleation has been observed at different electrodeposition times, by combination of chronoaperometry, Scanning Electron Microscopy (SEM), X-Photoelectron Spectroscopy (XPS), nano-Auger (nano-AES) imaging. A uniform, adherent, homogeneous and thin (∼100 nm) electrodeposited copper layer was obtained on molybdenum substrate demonstrating the possible extension of the microelectronic-dedicated chemistry. By SEM, the morphology and the size of nuclei and their evolution, from nucleation to total paving, have been observed and correlated with the three step variations of the current density curves. Using Graphite Furnace Atomic Absorption Spectroscopy (GF-AAS), the electrodeposited copper growth rates have been quantitatively determined. Combined with SEM micrographs, the possibility to use XPS analyses as probe for global evaluation of the coverage evolution has been demonstrated. In addition, chemical analyses of individual nuclei have been performed by nano-Auger Electron Spectroscopy.

Microstructure and deuterium permeation resistance of the oxide scale prepared by initial oxidation method on vacuum solar receiver

Deuterium permeation resistant scales on vacuum solar receiver were developed by initial oxidation method. The initial oxidation atmosphere was produced by the H2–H2O mixtures at 827°C, with a low oxygen partial pressure of about 10−19Pa. The phases and morphologies of the oxide scales were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), X photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The formation of an oxide scale was observed with an inner layer essentially composed of chromium oxide and an outer layer mainly consisting of Mn1.5Cr1.5O4 spinels. The deuterium permeation of 316L stainless steel coated with Cr2O3 scale was only 1/80 of that of uncoated 316L stainless steel under loading of 80KPa at 600°C. The chromium oxide developed on the surface of 316L stainless steel revealed a marked inhibiting effect on the permeability of the deuterium and the associated mechanisms were discussed.

Preparation and characterization of PEG/PVDF composite membranes and effects of solvents on its pervaporation performance in heptane desulfurization

Polyethylene glycol/polyvinylidene fluoride (PEG/PVDF) composite membranes were prepared using different water–organic solvent mixtures and the composite membranes obtained were characterized by Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy, wide-angle X-ray diffraction (WAXD), and X photoelectron spectroscopy (XPS). Pervaporation (PV) experiments were conducted to characterize the sulfur removal properties of the PEG/PVDF composite membranes using a feed mixture of heptane and ethyl thioether with a sulfur concentration of 300 ng/μL over the temperature range of 65–80°C. All membranes investigated in this work showed proper PV performance and the E-PEG exhibited the highest PV flux and the highest sulfur enrichment factor of 5.17 at 65°C. The correlation of membrane crystallinity and surface oxygen content with PV performance was established. A decrease in membrane crystallinity or an increase in surface oxygen content greatly improved the membrane desulfurization property which was due to a decrease in mass transport resistance and an increase in sorption at membrane surface respectively. Finally, suggestions on the establishment of mass transfer model in PV process were made based on the results of the WAXD, FTIR-ATR, XPS studies and PV experiments.

Characterization of novel silane coatings on titanium implant surfaces

This in vitro study describes and characterizes a developed novel method to produce coatings on Ti. Hydrophobic coatings on substrates are needed in prosthetic dentistry to promote durable adhesion between luting resin cements and coated Ti surfaces. In implant dentistry the hydrophobic coatings on a Ti implant might be beneficial for osseointegration, preventing bacteria adhesion and for enhancement of resin composite adhesion as well. A silica-coating system, Rocatec™, was used for planar Ti coupons as instructed. After careful rinsing and drying, four experimental silane primers were applied onto silica-coated Ti specimens. The primers were prepared of 3-acryloxypropyltrimethoxysilane + bis-1,2-(triethoxysilyl)ethane (in four concentrations), diluted in acidified ethanol-water. The contact angles, surface free energies, and critical surface tensions were assessed. The chemical compositions of surfaces were analyzed using X-photoelectron spectroscopy. Atomic force microscopy was used to investigate the surface topographies. Non-treated Ti specimens and silanized with a commercial silane primer were used as the controls. There were observable differences in the surface free energy (contact angle) and chemical composition on specimens. The silane primers reacted and fully covered Ti surfaces, which produced more hydrophobic coatings, larger contact angles, and lower surface free energy and critical surface tension than controls. At the concentration of 1.0 vol% 3-acryloxypropyltrimethoxysilane and 0.3 vol% bis-1,2-(triethoxysilyl)ethane, the silane blend showed the lowest surface free energy. The silanes would not affect the surface roughness (P > 0.05). Novel coatings were successfully developed and optimized. They may produce a hydrophobic surface onto Ti implants without compromising the surface roughness.

Adsorption of Phenol onto Activated Carbons

Coal-based Activated carbon was modified by thermal and nitric acid treatment to adsorb phenol from aqueous solution. Boehm titration, point of zero charge ( pHPZC ) and X-photoelectron spectroscopy (XPS) were used to characterize activated carbons. Acid treatment leads to the increase of the content of surface oxygen, whereas thermal treatment causes the decrease of the content of surface oxygen.The surface characteristics of activated carbons have significant effect on phenol adsorption. The adsorption isotherms of phenol adsorption are described by Langmuir isotherm. The kinetic studies indicate that the adsorption process is fitted well by the pseudo-second- order kinetics.

Hydrogen generation by hydrolysis of alkaline NaBH4 solution on Co–Mo–Pd–B amorphous catalyst with efficient catalytic properties

Mo-modified Co–Pd–B (Co–Mo–Pd–B) and Pd-modified Co–B (Co–Pd–B) catalyst powders are synthesized by chemical reduction of cobalt and molybdenum salt at ambient conditions. The resulting catalyst powders are characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-photoelectron spectroscopy (XPS) and BET surface area measurement. The study on the catalytic efficiency of amorphous Co–Mo–Pd–B catalyst powders is performed in hydrogen generation by hydrolysis of alkaline sodium borohydride (NaBH4). The Co–Mo–Pd–B powders show the highest hydrogen generation rate as compared to Co–B, Co–Mo–B, and Co–Pd–B catalyst powders. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–Mo–Pd–B catalyst reveal that the concentrations of both NaBH4 and NaOH have essentially no evident effects on hydrogen generation rate. The promoting effect of Mo in Co–Mo–Pd–B catalyst results in lower activation energy for hydrogen production, which is 36.36kJmol−1 compared to 64.87kJmol−1 obtained with pure Co–B powder.

Silica-Ceria Hybrid Nanostructures

ABSTRACTA new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ∼50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ∼2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.