Investigation on acid functionalization of double-walled carbon nanotubes of different lengths on the development of amperometric sensors

Abstract

Double-walled carbon nanotubes (DWCNTs) of different length were submitted to acid functionalization and investigated as chemical modifiers on glassy-carbon electrode (GCE) for the sensing of dopamine and catechol. Acid functionalization introduced oxygenated groups and defects on the structure of DWCNTs, as detected by infrared, Raman and X-ray photoelectron spectroscopy. However, cyclic voltammetric experiments showed higher current responses on non-functionalized (NF) DWCNTs. The decrease in response was stronger for shorter length nanotubes (S-DWCNT) modified GCE, which was attributed to the reduction of electroactive area of functionalized nanotubes after acid treatment with HNO3/H2SO4. Brunauer-Emmett-Teller (BET) analyses confirmed the decrease in surface area of functionalized (F) DWCNTs, especially on FS-DWCNT. Amperometric measurements also showed decrease in sensitivity and higher detection limit values on the FS-DWCNT, which is also due to the decrease in electroactive area. As conclusion, DWCNT is a potential carbon-based material to the development of highly sensitive amperometric sensors and acid functionalization is not likely required due to the higher surface area provided by modification with the untreated material.