Silver confined within zeolite EMT nanoparticles: preparation and antibacterial properties

Abstract

The preparation of pure zeolite nanocrystals (EMT-type framework) and their silver ion-exchanged (Ag⁺-EMT) and reduced silver (Ag⁰-EMT) forms is reported. The template-free zeolite nanocrystals are stabilized in water suspensions and used directly for silver ion-exchange and subsequent chemical reduction under microwave irradiation. The high porosity, low Si/Al ratio, high concentration of sodium and ultrasmall crystal size of the EMT-type zeolite permitted the introduction of a high amount of silver using short ion-exchange times in the range of 2–6 h. The killing efficacy of pure EMT, Ag⁺-EMT and Ag⁰-EMT against Escherichia coli was studied semi-quantitatively. The antibacterial activity increased with increasing Ag content for both types of samples (Ag⁺-EMT and Ag⁰-EMT). The Ag⁰-EMT samples show slightly enhanced antimicrobial efficacy compared to that of Ag⁺-EMT, however, the differences are not substantial and the preparation of Ag nanoparticles is not viable considering the complexity of preparation steps.