Effect of pH on the microwave-assisted degradation of methyl orange using poly(1-naphthylamine) nanotubes in the absence of UV–visible radiation

Abstract

Microwave-assisted degradation of dyes is being extensively investigated for wastewater remediation. The present work reports, for the first time, degradation of methyl orange (MeO) in neutral, acidic, and basic media under microwave irradiation using semiconducting polymer [poly(1-naphthylamine) (PNA)] nanotubes as catalyst in the absence of any light source. Degradation of the dye was followed spectrophotometrically and by total organic content (TOC) analysis. In the presence of poly(1-naphthylamine), microwave irradiation in 15 min caused 70, 84, and 64 % degradation at 280 nm, while at 460 nm the degradation values were 80, 96 and 78 % of MO in neutral, acidic, and basic media, respectively. The degradation of the dye in the absence and presence of PNA catalyst and in acidic, basic, and neutral media followed first-order rate kinetics. Rate constant, k, values were found to be slightly dependent on the pH of the dye solutions. Liquid chromatography–mass spectroscopy analysis confirmed that dye degrades into smaller fragments of low molar masses.