Nanoparticles of γ-Sitoesterol and Ag on Clinoptilolite Zeolites

Abstract

This work reports, the obtainment and stabilization of organic nanoparticles (γ-sitosterol) and Ag cations on the external area of Ca-clinoptilolite zeolite (Z17) are presented. The novelty of the present study lies in the formation and stabilization of nanoparticle organic molecules (γ-sitosterol) and inorganic cations (Ag) on the external area of Ca-clinoptilolite zeolite. The γ-sitosterol nanoparticles were obtained using Tournefortia hirsutissima and were later stabilized on the external area of Ca-clinoptilolite. The Ca-clinoptilolite-rich mineral as well as silver zeolitic minerals was characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM); elementary composition of the zeolitic mineral was determined by microanalyses (EDS) and high-resolution adsorption (HRADS) using N2 adsorption as a probe molecule. The EDS results about the exchange with Ag indicate the following sequence: Z17Ag03 > Z17Ag-09 > Z17Ag-06 > Z17Ag-01. The XRD studies indicate that only in the sample Z17Ag-03 there is an average crystal size of nanoparticles formed of 45.387 nm as determined by Sherrer’s equation. SEM images of clinoptilolite showed the presence of crystals with irregular and poorly defined box shapes that are typical for this type of zeolites. The nanoporosity of natural zeolites was studied by N2 adsorption; external areas were estimated through the De Boer and BET equations. The specific surface area calculated by BET equation, $A_{\text{SB}}$ , presents the following sequence: γ-SZ17 > Z17 > Z17Ag09 > Z17Ag03 > Z17Ag01 > Z17Ag06, while for the values of the external area obtained by the $t$ method, the sequence is $A_{\text{ST}}$ : γ-Z17 > Z17 > Z17Ag03 > z17Ag09 > Z17Ag06 > Z17Ag01. For its part, the pore size distributions tell us that the sample Z17 exhibits a sharp multimodal distribution with pore size maxima happening at 1.262, 1.933, 3.824, and 4.282 nm. Z17Ag01 exhibits a bimodal distribution with pore size maxima occurring at 5.45 and 5.533 nm. The sample Z17Ag06 exhibits a sharp bimodal distribution with pore size maxima happening at 3.666 and 7.021 nm, and the sample Z17Ag09 exhibits a sharp trimodal distribution with pore size maxima happening at 1.853, 4.275 and 5.967 nm. Antibacterial activities of the exchanged samples with Ag on the external surface area were measured as a function of exchange level against Gram-positive bacteria (P. aureoginosa, K. pneumonie, and A. baumannii) and Gram-negative bacteria (E. coli, S. saprophyticcus, S. aureus, and E. feacalis); the selectivity sequence of the clinoptilolite and antibacterial activity results are presented. Z17Ag09 clinoptilolite seemed to be a promising antibacterial material.