In this work, a set of experimental electrophoretic mobility (μe) data was used to show how inappropriate selection of the electrokinetic model used to calculate the zeta potential (ζ-potential) can compromise the interpretation of the results for nanoparticles (NPs). The main consequences of using ζ-potential values as criteria to indicate the colloidal stability of NP dispersions are discussed based on DLVO interaction energy predictions. For this, magnetite (Fe3O4) NPs were synthesized and characterized as a model system for performing electrokinetic experiments. The results showed that the Fe3O4 NPs formed mass fractal aggregates in solution, so the ζ-potential could not be determined under ideal conditions when μe depends on the NP radius. In addition, the Dukhin number (Du) estimated from potentiometric titration results indicated that stagnant layer conduction (SLC) could not be neglected for this system. The electrokinetic models that do not consider SLC grossly underestimated the ζ-potential values for the Fe3O4 NPs. The DLVO interaction energy predictions for the colloidal stability of the Fe3O4 NP dispersions also depended on the electrokinetic model used to calculate the ζ-potential. The results obtained for the Fe3O4 NP dispersions also suggested that, contrary to many reports in the literature, high ζ-potential values do not necessarily reflect high colloidal stability for charge-stabilized NP dispersions.

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In this work, structural and active corrosion inhibition effects induced by lithium ion addition in organic-inorganic coatings based on polymethyl methacrylate (PMMA)-silica solgel coatings have been investigated. The addition of increasing amounts of lithium carbonate (0, 500, 1000 and 2000 ppm), yielded homogeneous hybrid coatings with increased connectivity of nanometric silica cross-link nodes, covalently linked to the PMMA matrix, and improved adhesion to the aluminum substrate (AA7075). Electrochemical impedance spectroscopy (EIS), performed in 3.5% NaCl aqueous solution, showed that the improved structural properties of

In this work, we report the effects of incorporation of variable amounts (1-20 wt %) of sodium montmorillonite (MMT) into a siloxane-poly(ethylene oxide) hybrid hydrogel prepared by the sol-gel route. The aim was to control the nanostructural features of the nanocomposite, improve the release profile of the sodium diclofenac (SDCF) drug, and optimize the swelling behavior of the hydrophilic matrix. The nanoscopic characteristics of the siloxane-cross-linked poly(ethylene oxide) network, the semicrystallinity of the hybrid, and the intercalated or exfoliated structure of the clay were investigated by X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. The correlation between the nanoscopic features of nanocomposites containing different amounts of MMT and the swelling behavior revealed the key role of exfoliated silicate in controlling the water uptake by means of a flow barrier effect. The release of the drug from the nanocomposite displayed a stepped pattern kinetically controlled by the diffusion of SDCF molecules through the mass transport barrier created by the exfoliated silicate. The sustained SDCF release provided by the hybrid hydrogel nanocomposite could be useful for the prolonged treatment of painful conditions, such as arthritis, sprains and strains, gout, migraine, and pain after surgical procedures.

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A variety of organic-inorganic hybrids have been designed to act as anticorrosive coatings of metallic substrates. Among them, epoxy-silica and poly(methyl methacrylate) (PMMA)-silica hybrids, prepared by the sol-gel process and deposited onto steel or aluminum alloys, have demonstrated high anticorrosive efficiency combined with high thermal and mechanical resistance. Lignin, carbon nanotubes, and graphene oxide have been incorporated into PMMA-silica hybrids as reinforcement agents, and cerium (IV) as corrosion inhibitor. Both hybrids were characterized in terms of their structural and thermal characteristics using different pectroscopies, microscopies and thermogravimetric analysis. Both hybrids present homogeneous nanostructure composed of highly condensed silica nanodomains covalently bonded to the polymeric phase. The transparent coatings with a thickness of 2-7 μm have low surface roughness, high adhesion to metallic substrates, elevated thermal stability, and excellent barrier behavior. Electrochemical impedance spectroscopy showed for coated samples a high corrosion resistance of up to 50 GΩ cm2 and durability >18 months in saline solution. Further improvement of corrosion resistance, thermal and mechanical stability was achieved by incorporation of lignin, carbon nanotubes, and graphene oxide into PMMA-silica matrix, and a self-healing effect was observed after Ce(IV) addition. The results are compared and discussed with those recently reported for a variety of hybrid coatings.

This paper describes the activation and catalytic performance of a multifunctional catalyst consisting of mixed oxides of vanadium and molybdenum supported on an acidic ZSM-5 zeolite. The zeolite was wet-impregnated with an aqueous solution containing a mixture of NH 4 VO 3 and (NH 4 ) 6 Mo 7 O 24 precursors at a V/(Mo+V) molar ratio of 0.6. Evolution of the phases during activation (by calcination under 20% O 2 /He) was followed by synchrotron X-ray diffraction (XRD), but detection of mixed oxides of Mo x V y O z was difficult, due to the high degree of dispersion on the zeolite surface. On the other hand, X-ray absorption spectroscopy (XAS) performed simultaneously at the Mo and V K-edges enabled confirmation of formation of the MoV 2 O 8 phase on the acidic ZSM-5 zeolite. The combination of the MoV 2 O 8 phase and the zeolite acid sites produced a highly active catalyst for gas phase glycerol dehydration-oxidation coupled reactions in which acrylic acid was the main product. The multifunctional catalyst presented only 6% of deactivation during a period of 8 h under glycerol stream, while the activities of the bulk mixed oxide and the pure ZSM-5 zeolite decreased by almost 20 and 31%, respectively.

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