Insight in the interaction mechanisms between functionalized CNTs and BTX vapors in gas sensors: Are the functional peripheral groups the key for selectivity?

Abstract

Herein we focus on gas sensor responses of both organic macrocycles (MCs) and carbon nanotubes (CNTs) functionalized with MCs (CNTs/MCs) to understand the interaction mechanisms of these materials exposed to aromatics volatile organic compounds (VOCs) such as benzene, toluene and xylene (BTX). The MCs-functionalized CNTs are prepared by non-covalent functionalization using phthalocyanines and porphyrins derivatives. We focus our analysis on the peripheral groups of both the MCs (tert-butyl, phenyl, ethyl) and BTX (methyl) by means of the analyses of both the desorption kinetics and surface interactions. A cross-analysis between the physisorption phenomena and kinetics of the responses is found to be relevant for understanding the interactions. The analysis of the sensing performances at room temperature (25 °C) for the MCs-based QCM sensors revealed that the nature of the peripheral moieties (aryl or alkyl of the MCs alone) dictates the kinetics and the desorption profile whatever the VOC. The similar analysis conducted on the sensing performances of the CNTs/MCs-based QCM sensors shows that, methyl groups of the BTX are the dominant parameter that modulate the response profile whatever the hybrid materials. A focus on dispersion interactions and desorption kinetics allows to evidence that the interaction between the VOCs and MCs or CNTs/MCs is reinforced or weakened depending on the peripheral moieties from the MCs or BTX. From this study, it is clearer that substituents of the VOCs are more important for kinetics of desorption than the functional groups of the CNTs/MCs.