Electrochemical preparation and characterization of a cobalt oxide–platinum composite with promising capacitive and electrocatalytic features

In the present work, boron-doped diamond polycrystalline films were used as support for direct anodic deposition of the cobalt oxide, and continuous Co₃O₄ coatings with reasonably good conductivity were obtained by appropriately adjusting the deposition charge. Further electrochemical deposition of platinum particles on the oxide substrate enabled the formation of a stable composite with a specific capacitance of ca. 431 F?cm^?3 that compares well with that available with similar materials obtained by non-electrochemical methods. Additional advantages of electrochemically obtained composites are the lower content of noble metal, the uniform distribution of the charge over an extended potential range, and, importantly, the simplicity of the preparation method. It was also found that when deposited on a Co₃O₄ substrate, Pt particles show, besides an enhanced active surface area, an improved catalytic activity for methanol anodic oxidation. This behavior was tentatively ascribed to the presence of a high amount of platinum-oxidized species.     

Silica veils-conductive diamond powder composite as a new propitious substrate for platinum electrocatalysts

An innovative composite was obtained by a straightforward sol-gel procedure, involving boron-doped diamond powder (BDDP) incorporation into a SiO₂ veil (SiO₂V) matrix. Composite-coated glassy carbon plates were used as substrate for Pt electrochemical deposition, and the electrodes thus obtained (Pt/BDDP–SiO₂V) were compared on a relative basis with those prepared in the absence of the silica matrix (Pt/BDDP). SEM measurements have shown that a BDDP substrate promotes Pt cluster formation, whereas on BDDP–SiO₂V, particles are much smaller (ca. 45 nm to ca. 140 nm). The activity for CH₃OH oxidation was checked by cyclic voltammetry, and it was found that at Pt/BDDP–SiO₂V, the main anodic peak is shifted with ca. 0.35 V toward lower potentials, indicating a considerable improvement in the overall process kinetics. Stripping experiments together with long-term polarization measurements demonstrated that when deposited on the BDDP–SiO₂V support, Pt particles are less susceptible to CO poisoning and this behavior was tentatively ascribed to the presence of a higher relative surface concentration of more stable, oxidized platinum species, as evidenced by XPS.     

Effect of the manufacturing parameters on the structure of nitrogen-doped carbon nanotubes produced by catalytic laser-induced chemical vapor deposition

Series of self-assembled and mono-dispersed bovine serum albumin (BSA)-conjugated ZnS/CuS nano-composites with different Zn/Cu ratios had been successfully synthesized by a combination method of the biomimetic synthesis and ion-exchange strategy under the gentle conditions. High-resolution transmission electron microscopy observation, Fourier transform infrared spectra and zeta potential analysis demonstrated that BSA-conjugated ZnS/CuS nano-composites with well dispersity had the hierarchical structure and BSA was a key factor to control the morphology and surface electro-negativity of final products. The real-time monitoring by atomic absorption spectroscopy and powder X-ray diffraction revealed that the Zn/Cu ratio of nano-composites could be controlled by adjusting the ion-exchange time. In addition, the metabolic and morphological assays indicated that the metabolic proliferation and spread of rat pheochromocytoma (PC12) cells could be inhibited by nano-composites, with the high anti-cancer activity at a low concentration (4 ppm). What were more important, Zn and Cu in nano-composites exhibited a positive cooperativity at inhibiting cancer cell functions. The microscope observation and biochemical marker analysis clearly revealed that the nano-composites-included lipid peroxidation and disintegration of membrane led to the death of PC12 cells. Summarily, the present study substantiated the potential of BSA-conjugated ZnS/CuS nano-composites as anti-cancer drug.     

Uniform nanoparticles building Ce1?x Pr x O2?δ mesoarchitectures: structure, morphology, surface chemistry, and catalytic performance

The design of cell-based bioreactors for inorganic particles formation requires both a better understanding of the underlying processes and the identification of most suitable organisms. With this purpose, the process of Au³⁺ incorporation, intracellular reduction, and Au⁰ nanoparticle release in the culture medium was compared for four photosynthetic microorganisms, Klebsormidium flaccidum and Cosmarium impressulum green algae, Euglena gracilis euglenoid and Anabaena flos-aquae cyanobacteria. At low gold content, the two green algae show maintained photosynthetic activity and recovered particles (ca. 10?nm in size) are similar to internal colloids, indicating a full biological control over the whole process. In similar conditions, the euglenoid exhibits a rapid loss of biological activity, due to the absence of protective extracellular polysaccharide, but could grow again after an adaptation period. This results in a larger particle size dispersity but larger reduction yield. The cyanobacteria undergo rapid cell death, due to their prokaryotic nature, leading to high gold incorporation rate but poor control over released particle size. Similar observations can be made after addition of a larger gold salt concentration when all organisms rapidly die, suggesting that part of the process is not under biological control anymore but also involves extracellular chemical reactions. Overall, fruitful information on the whole biocrystallogenesis process is gained and most suitable species for further bioreactor design can be identified, i.e., green algae with external coating.     

Platinum–polytyramine composite material with improved performances for methanol oxidation

Polytyramine (PTy) is shown to be a possible alternative to other conducting polymers as a support material for fuel cell electrocatalysts such as platinum. In this work, a Pt–PTy composite was prepared via potentiodynamic deposition of polytyramine on graphite substrate, followed by the electrochemical deposition of Pt nanoparticles. The material obtained by this straightforward method exhibited, for platinum loadings as low as ca. 0.12 mg cm⁻², a specific electrochemically active surface area of the electrocatalyst of ca. 54 m² g⁻¹, together with a good electrocatalytic activity for methanol oxidation in acidic media, thus ensuring better efficiency of Pt utilization. The system Pt–PTy appears to be worthy of development for methanol fuel cell applications also because the results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to fouling during CH₃OH oxidation.     

Facile Polymer Functionalization of Hydrothermal‐Carbonization‐Derived Carbons

A simple and efficient polymer grafting onto hydrothermal carbonization (HTC)‐derived materials is described. The method pertains to the Diels–Alder cycloaddition reaction of furan moieties present on the surface of a HTC material with the maleimide groups stemming from a maleimide protected poly(ethylene glycol) (Me‐PEG‐MI) by a retro Diels‐Alder reaction. The precursor polymer, HTC material, and final product are characterized. Successful grafting is confirmed by elemental analysis, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and dispersion studies.

     

An XPS study on ion beam induced oxidation of titanium silicide

Titanium silicides (TiSi₂) films grown on Si(1 0 0) substrate were investigated by ex situ XPS depth profiling after athermal ion beam induced oxidation (IBO) at 12 keV O₂⁺ incident energy and normal incidence. The composition and stoichiometry of these films were quantitatively determined as chemical state relative concentrations versus sputter time. “In depth” silicon and titanium oxidation states have been obtained after spectra deconvolution, showing a mixture of silicon dioxide, titanium dioxide, titanium suboxides, elemental titanium and residual traces of titanium nitride. Thermochemical data based on the corresponding enthalpies of formation of the oxides cannot explain our experimental results as in the case of low energy IBO, an oxygen defective altered layer is formed, presenting features of a reduced TiO_x phase.     

Structure and surface chemistry in crystalline mesoporous (CeO(2-δ))-YSZ

Mesoporous metal oxides (CeO(2-δ))-YSZ have been synthesized by a versatile direct synthesis method using ionic cetyltrimethylammonium bromide (CTAB) and different nonionic (block copolymers) as surfactants and urea as hydrolyzing agent. The synthesis was realized at pH=9 using tetraethylammonium hydroxide (TEAOH) as pH mediator. Calcination at 550 °C led to the formation of crystalline metal oxides with uniform mesoporosity. The obtained materials have been characterized by thermogravimetric analysis (TG-DTG), wide and small-angle X-ray diffraction (XRD), Raman spectroscopy, Brunauer, Emmett and Teller (BET) surface area analysis, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). All the obtained materials exhibits mesoporous structure, crystalline structure indexed in a cubic symmetry, showing a high surface area, a uniform and narrow pore size distribution, spherical morphology typical for the mesoporous materials. The crystalline and mesoporous structures, surface chemistry and stoichiometry for the samples synthesized using ionic and nonionic surfactants have been discussed.