Diverse copper clusters confined in microporous nanocrystals

Abstract

A selective formation of copper clusters in zeolite nanoparticles with GIS type structure is demonstrated. The size and the shape of the metal clusters are depending on the amount of copper incorporated in the small pores of the GIS crystalline structure and on their aperture. Different kinetics of reduction of the metal cations to clusters is observed under controlled radiolytic treatment of suspensions with constrained nanosized GIS particles. The solvated electrons produced in the bulk water under gamma radiolysis migrate into the GIS nanocrystals and subsequently reduce Cu II to Cu I starting from the external surface layers and progressing towards the center of the particles; this results in the coexistence of both Cu II cations and Cu 0 atoms. In the samples with low copper content, the formation of Cu I species is not observed, which is associated with the confinement of copper into the small zeolite pores preventing the reaction between Cu 2+ and Cu n 0. The copper loading of the nanocrystals, the conditions of radiolytic treatment and the features of the framework type crystalline structure determine the development of the reduction process resulting in selective formation of Cu I or Cu 0 species in the GIS nanocrystals.