Removal of benzene by ZnO nanoparticles coated on porous adsorbents in presence of ozone and UV

Abstract

Benzene is an air toxic that is released from various emission sources including traffic and various industries. The aim of this study was to investigate the benzene removal performance of ZnO nanoparticles (nZnO) coated on 13X zeolite and activated carbon (AC) at a ratio of Zn to zeolite and Zn to AC of 0.5:1.0 by weight. The coated adsorbents were characterized by scanning electron microscope (SEM) and wavelength dispersive X-ray Spectrometer (WDX). The laboratory scale experiments were conducted at ambient temperatures (∼30°C) with UV, O3 and UV+O3 respectively introduced. The inlet benzene was 5ppm in all the experiments. The coated zeolite had the benzene removal efficiency (RE) of 97.9±0.9% compared to 94.2±2.4% of the virgin zeolite. The UV, O3 and UV+O3 treatments slightly increased the RE of the zeolite experiments, i.e. 98.4±0.4%, 98.2±1.0% and 98.9±0.2%, respectively. Meanwhile, the RE by the virgin AC was slightly higher than the coated AC, i.e. 99.5±0.2% compared to 98.3±0.1%. With UV, O3 and UV+O3 introduced the coated AC adsorbent similarly demonstrated a good RE, i.e. 99.0±0.1%, 99.0±0.2% and 98.2±0.3%, respectively. A combination of UV, O3 and UV+O3 could produce combined effects of adsorption, photodegradation and oxidation for benzene removal. The breakthrough test results revealed that the coating significantly reduced the service time (the period before the breakthrough occurs) for both adsorbents (zeolite and AC) in all experimental conditions. Various intermediate products: formaldehyde, acetaldehyde, ethanol, methanol and carbon monoxide (CO) found in the outlet stream confirmed a potential competing adsorption of these intermediate products and also the final products (CO2, water vapor) that reduced the adsorbent capacity in addition to a partial blockage of AC pores by nZnO.