Mordenite-Supported Ag+-Cu2+-Zn2+ Trimetallic System: A Variety of Nanospecies Obtained via Thermal Reduction in Hydrogen Followed by Cooling in an Air or Hydrogen Atmosphere

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.

Long-Lived Charge-Separated States in ZnS/Na-MOR Zeolite upon trans-Stilbene Adsorption

“…The bulk ZnS semiconductor exhibited a broad absorption band with a maximum of absorption (λ max ) around 326 nm, which is characteristic of the exciton (electron–hole) transition in the sphalerite phase of ZnS . On the other hand, the spectrum of the NH 4 -MOR exhibits a main absorption band centered around 275 nm which is ascribed to charge-transfer complexes between the metal cations and the oxygen/nitrogen atoms of the zeolite. , On the other hand, the spectrum of the ZnS/Na-MOR composite shows a blue-shift regarding its absorption band edge when compared to those of both bulk ZnS and NH 4 -MOR compounds. This feature is tentatively attributed to a quantum size effect and is ascribed to a decrease in the ZnS particle size, as observed for several semiconductors. − …”