Abstract
Benzene, toluene, ethylbenzene and xylenes (BTEX) are some of the common environmental pollutants originating mainly from oil and gas industries, which are toxic to human as well as other living organisms in the ecosystem. Here we investigate photocatalytic degradation of BTEX under visible light irradiation using supported zinc oxide (ZnO) nanorods grown on glass substrates using a microwave assisted hydrothermal method. ZnO nanorods were characterized by electron microscopy, X-ray diffraction (XRD), specific surface area, UV/visible absorption and photoluminescence spectroscopy. Visible light photocatalytic degradation products of BTEX are studied for individual components using gas chromatograph/mass spectrometer (GC/MS). ZnO nanorods with significant amount of electronic defect states, due to the fast crystallization of the nanorods under microwave irradiation, exhibited efficient degradation of BTEX under visible light, degrading more than 80% of the individual BTEX components in 180 minutes. Effect of initial concentration of BTEX as individual components is also probed and the photocatalytic activity of the ZnO nanorods in different conditions is explored. Formation of intermediate byproducts such as phenol, benzyl alcohol, benzaldehyde and benzoic acid were confirmed by our HPLC analysis which could be due to the photocatalytic degradation of BTEX. Carbon dioxide was evaluated and showed an increasing pattern over time indicating the mineralization process confirming the conversion of toxic organic compounds into benign products.
Highlights
Petroleum industries are contributing largely in the global economy as well as in the development of oil-producing countries
Aromatic hydrocarbons in crude oil is composed of trace amounts of polycyclic aromatic hydrocarbons (PAHs) that are relatively less soluble in water and high concentrations of monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes (BTEX) that are grouped as volatile organic compounds (VOCs), some of which are relatively soluble in water
The annealing temperature was fixed based on our previous results where we have shown that the visible light photocatalytic (VLP) activity of the zinc oxide (ZnO) nanorods can be improved through temperature induced defect migration from the bulk to the surface of ZnO nanorods [41]
Summary
Petroleum industries are contributing largely in the global economy as well as in the development of oil-producing countries. Aromatic hydrocarbons in crude oil is composed of trace amounts of polycyclic aromatic hydrocarbons (PAHs) that are relatively less soluble in water and high concentrations of monoaromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes (BTEX) that are grouped as volatile organic compounds (VOCs), some of which are relatively soluble in water. Both groups contribute to environmental contamination when released into the environment finding their way to water, soil and air [5]. Benzene (5 ppb), toluene (1000 ppb), ethylbenzene (700 ppb) and xylene (10,000 ppb) are the permissible limits of drinking water maximum contaminant level (MCL) [11]
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