ABSTRACT
Polypyrrole adhesion to indium-tin oxide electrodes was improved by adding pre-hydrolyzed alkoxysilanes to the electrodeposition media. The pyrrole oxidation and film growth rates were studied by potentiostatic polymerization in acidic media. The morphology and thickness of the films were studied by contact profilometry and surface-scanning electron microscopy. The bulk and surface semiquantitative chemical composition was studied by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Finally, the adhesion was studied by scotch-tape adhesion test, where both alkoxysilanes showed a significant improvement in adhesion. We proposed a hypothesis for the improvement in adhesion, that involves the formation of siloxane material as well as in situ surface modification of the transparent metal oxide electrode.
ABSTRACT
Multimetallic systems, instead of monometallic systems, have been used to develop materials with diverse supported species to improve their catalytic, antimicrobial activity, etc., properties. The changes in the types of nanospecies obtained through the thermal reduction of ternary Ag+-Cu2+-Zn2+/mordenite systems in hydrogen, followed by their cooling in an air or hydrogen atmosphere, were studied. Such combinations of trimetallic systems with different metal content, variable ratios (between them), and alternating atmosphere types (during the cooling after reducing the samples in hydrogen at 350 °C) lead to diversity in the obtained copper and silver nanospecies. No reduction of Zn2+ was evidenced. A low silver content leads to the formation of reduced silver clusters, while the formation of nanoparticles of a bigger size takes place in the trimetallic samples with high silver content. The cooling of the reduced trimetallic samples in the air causes the oxidation of the obtained metallic clusters and silver and copper nanoparticles. In the case of copper, such conditions lead to the formation of mainly copper (II) oxide, while the silver nanospecies are converted mainly into clusters and nanoparticles. The zinc cations provoked changes in the mordenite matrix, which was associated with the formation of point oxygen defects in the mordenite structure and the formation of surface zinc oxide sub-nanoparticles in the samples cooled in the air.
ABSTRACT
Mono- (Au, Ag and Cu) and bi-metallic (Au-Ag and Au-Cu) nanoparticles were deposited on TiO2 and tested for the photocatalytic degradation of sulfamethoxazole using either UV-C or simulated sunlight. The optimal loading of metallic nanoparticles was determined as 1.5â wt% for Au and Ag, and 1.0â wt% for Cu. In the case of bi-metallic nanoparticles, only the ratio 1:0.5â wt% for both Au-Ag and Au-Cu was tested. In experiments using UV-C light, the highest degradation performance was found for Ag/TiO2, while bi-metallic nanoparticles supported on TiO2 also showed increased photocatalytic activity compared with unmodified TiO2. In simulated sunlight irradiation tests, Au/TiO2 showed to be the most efficient material. Complete mineralization of sulfamethoxazole was achieved when surface-modified materials were tested in both UV-C and simulated sunlight experiments. Photolysis was efficient to fully degrade sulfamethoxazole, although mineralization was lower than 10% for both luminic sources. The main by-products of sulfamethoxazole were determined in photolysis and photocatalysis tests using UV-C light, and degradation paths were proposed. By-products showed non-toxicity and low antibiotic activity. Reuse of the catalysts upon three reaction cycles did not result in the loss of activity.
Subject(s)
Metal Nanoparticles , Photolysis , Sulfamethoxazole/chemistry , Catalysis , TitaniumABSTRACT
Copper-silver bimetallic system supported on natural clinoptilolite from Tasajeras deposit (Cuba) was studied. Bimetallic samples were prepared by simultaneous ion exchange, and reduced in a wide temperature range in a hydrogen flow. The main goal of the work was analysis of the mutual influence of both metals on their reduction process and the properties of the resultant particles. Analysis was done by combined use of XRD and UV-Vis spectroscopy. The reduction of Cu2+ and Ag+ cations shows existence of notable inter-influence between both cations during this process. The Cu2+ reduction is favored by the presence of Ag+, which should be related with the synergetic influence of silver cations and/or clusters formed on the first stages of reduction on Cu(2+)-framework interaction, facilitating the Cu2+ reduction even at low temperature (25 and 50 degrees C). The aggregation of the reduced highly dispersed species both for copper and silver is limited in this bimetallic system. The introduction of Ag+ as the second cation in the copper-exchanged zeolites favors the copper reduction at lower temperatures (25 and 50 degrees C), and appears to be the efficient tool for the control of the size of the resultant reduced nanoparticles (it means their dispersion).