Synthesis, sorption and sensing capability of carbon nanotube based materials for gas-phase chlorinated phenols

Abstract

The adsorption equilibrium isotherms as well as gas sensing of three chlorinated phenolic compounds (CPCs) including phenol, 2-chlorophenol, and 2,4-dichlorophenol by acid-functionalized carbon nanotubes (CNT) were studied. CNTs were synthesized via floating catalyst chemical vapor deposition method at 800oC and then functionalized with a mixture of HNO3 and H2SO4. The functionalized CNTs were vacuum filtered to form CNT buckypaper. The adsorption isotherm followed the Langmuir adsorption model better than the Freundlich and Redlich-Peterson models. The maximum adsorption capacities were found to be 61.35, 93.46 and 104.17 mg/g for phenol, 2-chlorophenol and 2,4-dichlorophenol, respectively. The desorption activation energy determined via thermogravimetric analysis indicates that adsorption of all three CPCs onto the CNTs belonged to chemisorption type. For the gas sensing test, the CNT buckypaper showed fast response to the tested CPCs with good stability and repeatability. The sensitivity values obtained were 13.778 × 10-4, 8.835 × 10-4 and 7.122 × 10-4 for 2,4-dichlorophenol, 2-chlorophenol and phenol, respectively. It is noteworthy that the adsorption capacity and sensitivity of the CNT based materials to the target gases increased with the increase in the number of chlorine atoms in the phenolic compounds.