Selective response of pyrylium-functionalized nanozeolites in the visible spectrum towards volatile organic compounds

Abstract

An optical detection of volatile organic compounds (VOCs) using nanosized zeolites functionalized with pyrylium salts is presented. Nanosized zeolite crystals firstly are functionalized with pyrylium salt (para-dimethylamino-2,4,6-triphenylthiopyrylium tetrafluoroborate, PNS). Then the optical response of the pyrylium-functionalized nanozeolites towards volatile organic compounds is investigated. Two possible modes of zeolite functionalization are proposed based on: (1) ion exchange between the pyrylium and sodium cations (Na+) in the zeolite (Si-O−-Al active sites), and (2) adsorption via electrostatic interaction between the electron lone-pair of amine of the PNS and the orbital vacancy of Al on the zeolite surface (Lewis acid sites). The experimental results verify that the great number of Lewis acid sites of the nanozeolites led to a significant adsorption of the PNS (mode 2) causing the hypsochromic (band shift to lower wavelength) shift in the visible light absorbance. Pyrylium-functionalized nanozeolites demonstrate a good sensitivity and reversibility toward volatile organic compounds investigated in this work.