Carbon nanotubes modified with porphyrin units for gaseous phase chemical sensing

In the present work the single wall carbon nanotubes (SWCNTs) were modified with porphyrin units and applied as sensing materials in quartz microbalance (QMB) sensors with an integrated preconcentration unit. Two strategies have been adopted for CNT–porphyrin composites formulation. In the first approach the electropolymerization of pyrrole or pyrrole-substituted porphyrin monomers occurred via formation of conjugated positively charged polypyrrole (PPy) backbone, while negatively charged carbon nanotubes functionalized with carboxylic groups (SWCNT-COOH) acted as a polymer dopant. In the second case the SWCNT–porphyrin composites were chemically synthesized via the interaction between glycyl-substituted porphyrin and non-modified CNTs and then entrapped in PPy/SWCNT-COOH film. The application of CNT–porphyrin composite, both as the preconcentrator adsorbing phase and QMB coating, permitted a substantial sensitivity improvement as far as the possibility to measure volatile organic compounds, such as 1-butanol, in concentrations close to the odor threshold.