Highly efficient adsorptive removal of persistent organic pollutants using NPD-acid combined modified NaY zeolites

Abstract

Adsorption method is an effective way to remove persistent organic pollutants in air. In this study, nanosecond pulsed discharge plasma combined acid was employed to modify the NaY zeolites with the purpose of adsorbing persistent organic pollutants, comparing with the adsorption capacity of NaY zeolites modified by the solo acid and solo plasma treatment. The waveforms of pulse voltage and discharge current, and gas temperature of discharge were collected to investigate the plasma characteristics. The physical structure and chemical active sites of raw and modified zeolites were characterized by means of N2 adsorption–desorption analysis, Scanning Electron Microscopy, Fourier Transform Infrared Spectrum, Pyridine Infrared Spectrum, and X-ray Photoelectron Spectroscopy. It was found that the adsorption capacity of zeolites modified by NPD-acid combined system increased by 167%, 56%, and 40%, respectively, compared with the raw, solo 3 mol/L of acid and solo NPD modified zeolites, with the conditions of 3 mol/L of acid concentration, 1 mg/L of naphthalene initial concentration, 25 min of treatment time, and 30 kV of pulse peak voltage. This result can be ascribed to the increased acid sites (Brønsted and Lewis acid), O element content, specific surface area, and number of micropores and mesopores, which all played an important role in naphthalene adsorption. Additionally, the adsorption kinetics and mass transfer of raw and modified zeolites could be described by pseudo-second-order and intra-particle diffusion models.