Nitrogen regulation in polyester-based carbons and adsorption of gaseous benzene and ethyl acetate

Abstract

Nitrogen doping effectively improves the adsorption properties of activated carbons towards volatile organic compounds (VOCs); however, the role of nitrogen elements with various chemical valence states need further evaluation. In this work, waste polyester fabrics were used as a low-cost source to prepare activated carbon, and melamine, pyridine, dimethylamine, and pyrrole were selected as nitrogen sources to compare their nitrogen-doping ability. The adsorption of low-concentration benzene and ethyl acetate on the resultant carbons and the effects of nitrogen, including its valence states and contents, were investigated. Characterizations showed that the nitrogen contents of carbons after doping with melamine (C-M), pyridine (C-P), dimethylamine (C-D), and pyrrole (C-Y) increased, while their corresponding specific surface areas were about 32.6%, 72.2%, 142% and 14.3%, respectively, of the original carbon value of 188.7 cm² g⁻¹. Dynamic breakthrough experiments verified the increase in adsorbed amounts of both non-polar benzene and polar ethyl acetate molecules, with a more significant enhancing effect on benzene. The specific surface area and pore volume mainly contribute to the adsorbed amounts. Regarding the influence of nitrogen-containing functional groups, pyridinic nitrogen was more conducive to benzene adsorption under dry conditions because of the stronger π–π interaction and N–H hydrogen bond; however, its water resistance was inferior to that of pyrrolic nitrogen. Saturated C-P can be effectively regenerated and the adsorbed capacity of benzene remained about 75% after five adsorption cycles. The increased adsorbed amount and super regeneration property identify pyridine as a nitrogen source with priority consideration in the nitrogen modification of activated carbons for VOC adsorption.