Combined SANS and SAXS study of the action of ultrasound on the structure of amorphous zirconia gels

Abstract In the present work, we have studied for the first time the combined effect of both sonication and precipitation pH on the structure of amorphous zirconia gels synthesized from zirconium(IV) propoxide. The techniques of small-angle neutron and X-ray scattering (SANS and SAXS) and low temperature nitrogen adsorption provided the integral data on the changes in the microstructure and mesostructure of these materials caused by ultrasonic (US) treatment. Amorphous ZrO2·xH2O synthesized under ultrasonic treatment was found to possess a very structured surface, characterized by the surface fractal dimension 2.9–3.0, compared to 2.3–2.5 for the non US-assisted synthesis, and it was also found to possess a higher specific surface area, while the sizes of the primary particles remain unchanged

Structure of zirconium dioxide based porous glasses

This study is devoted to investigation of the micro- and mesostructure (including fractal properties) of porous zirconia glasses synthesized by precipitation from zirconium n-propoxide solutions in the presence of different hydrolyzing-agent (H2O) quantities at different temperatures. Analysis of small-angle neutron, ultra-small-angle neutron and X-ray scattering, scanning electron microscopy allows concluding that the synthesized glasses are complex systems with a three-level hierarchical fractal structure. It is revealed that both the temperature of synthesis and the H2O concentration in the initial solution significantly affect the structural characteristics of the glasses

Mesostructure of yttrium and aluminum basic salts coprecipitated from aqueous solutions under ultrasonic treatment

The influence of ultrasonic treatment on the micro and mesostructures and fractal characteristics of amorphous powders of yttrium and aluminum basic salts (precursors for the synthesis of neodymiumacti vated yttrium–aluminum garnet, Nd:YAG, which were coprecipitated from aqueous solutions by different precipitants, namely, aqueous solutions of ammonia and ammonium bicarbonate) is studied. It is established that ultrasonication applied during the precipitation of the aforementioned powders does not significantly change the structure of the obtained materials but always leads to the formation of structures with a less homogeneous nuclear density, i.e., a more developed surface area. Moreover, the ultrasoundassisted precip itation of the hydroxocompounds by ammonium hydrocarbonate results in a certain increase in the surface fractal dimension and the degree of aggregation for massfractal aggregates of particles

Mesostructure of yttrium and aluminum basic salts coprecipitated from aqueous solutions under ultrasonic treatment

The influence of ultrasonic treatment on the micro and mesostructures and fractal characteristics of amorphous powders of yttrium and aluminum basic salts (precursors for the synthesis of neodymiumacti vated yttrium–aluminum garnet, Nd:YAG, which were coprecipitated from aqueous solutions by different precipitants, namely, aqueous solutions of ammonia and ammonium bicarbonate) is studied. It is established that ultrasonication applied during the precipitation of the aforementioned powders does not significantly change the structure of the obtained materials but always leads to the formation of structures with a less homogeneous nuclear density, i.e., a more developed surface area. Moreover, the ultrasoundassisted precip itation of the hydroxocompounds by ammonium hydrocarbonate results in a certain increase in the surface fractal dimension and the degree of aggregation for massfractal aggregates of particles

Rationalizing the Influence of the Mn(IV)/Mn(III) Red-Ox Transition on the Electrocatalytic Activity of Manganese Oxides in the Oxygen Reduction Reaction

International audienceKnowledge on the mechanisms of oxygen reduction reaction (ORR) and descriptors linking the catalytic activity to the structural and electronic properties of transition metal oxides enable rational design of more efficient catalysts. In this work ORR electrocatalysis was studied on a set of single and complex Mn(III) oxides with a rotating disc electrode method and cyclic voltammetry. We discovered an exponential increase of the specific electrocatalytic activity with the potential of the surface Mn(IV)/Mn(III) red-ox couple, suggesting the latter as a new descriptor for the ORR electrocatalysis. The observed dependence is rationalized using a simple mean-field kinetic model considering availability of the Mn(III) centers and adsorbate-adsorbate interactions. We demonstrate an unprecedented activity of Mn2O3, ca. 40 times exceeding that of MnOOH and correlate the catalytic activity of Mn oxides to their crystal structure

Crystal and Supramolecular Structure of Bacterial Cellulose Hydrolyzed by Cellobiohydrolase from Scytalidium Candidum 3C: A Basis for Development of Biodegradable Wound Dressings

The crystal and supramolecular structure of the bacterial cellulose (BC) has been studied at different stages of cellobiohydrolase hydrolysis using various physical and microscopic methods. Enzymatic hydrolysis significantly affected the crystal and supramolecular structure of native BC, in which the 3D polymer network consisted of nanoribbons with a thickness T ≈ 8 nm and a width W ≈ 50 nm, and with a developed specific surface SBET ≈ 260 m2·g−1. Biodegradation for 24 h led to a ten percent decrease in the mean crystal size Dhkl of BC, to two-fold increase in the sizes of nanoribbons, and in the specific surface area SBET up to ≈ 100 m2·g−1. Atomic force and scanning electron microscopy images showed BC microstructure “loosening“after enzymatic treatment, as well as the formation and accumulation of submicron particles in the cells of the 3D polymer network. Experiments in vitro and in vivo did not reveal cytotoxic effect by the enzyme addition to BC dressings and showed a generally positive influence on the treatment of extensive III-degree burns, significantly accelerating wound healing in rats. Thus, in our opinion, the results obtained can serve as a basis for further development of effective biodegradable dressings for wound healin