Removal of Methyl Tertiary-Butyl Ether via ZnO-AgCl Nanocomposite Photocatalyst

Abstract

IntroductionMethyl tertiary-butyl ether (MTBE) has received a very high attention over the last decade due to its widespread detection in indoor environments 1,2 . MTBE is used as an additive of oxygen added to gasoline in order to elevate the octane number, combustion improvement, and reduce CO 2 production. However, MTBE has been recognized as a prevalent and persistent groundwater and surface water pollutant. Acute toxicity levels of MTBE for rodent LD 50 and lethal air concentrations for rats (LC 50 ) were estimated to be 3.8-3.9 g/kg and 65-126 g/m 3 , respectively 3,4 . However, the presence of MTBE in water is mainly responsible for taste and odor related problems. Moreover, the International Agency of Research on Cancer (IARC) and the U.S. Environmental Protection Agency (EPA) classified MTBE as a health risk threat in 2000 5 . Therefore, removal of MTBE from water is an important issue.So far, many methods have been studied for removing MTBE. Such as adsorption 6 , air stripping , biodegradation 13 and electrochemical oxidation 14 . Among them, designing suitable photocatalyst for MTBE degradation received a considerable attention due to its green approach, free sun energy and easy to scale-up. ZnO is a well-known n-type semiconductor with band gap energy of 3.37 eV, hence is considered as one of the best photocatalysts to deal with organic pollutant [15][16][17][18][19][20][21] . However, the photocatalytic activity of ZnO is still restricted by fast recombination of the photogenerated electron-hole pairs [22][23][24] . Many efforts have been made for extending the absorption range of ZnO, such as elements doping and metal-semiconductor heterostructure formation. Silver halides are widely recognized as photosensitive materials [25][26][27][28][29][30][31][32][33][34][35] . Recently, research showed that the Ag-AgCl supported metal oxide semiconductor has enhanced photocatalytic activity under visible or simulated solar light 36,37 . Therefore, combining ZnO with silver halide is expected as an ideal photocatalyst for MTBE removal. Herein, we proposed a simple one-pot hydrothermal method for ZnO-AgCl nanocomposite formation. The photocatalytic activity of prepared ZnO-AgCl nanocomposite was tested. To the best of our knowledge, this is the first report of using ZnOAgCl nanocomposite for MTBE photodegradation. Experimental MaterialsZinc nitrate hexahydrate (Zn(NO 3 ) 2 •6H 2 O), ammonium hydroxide (28-30% NH 3 basis), silver nitrate (AgNO 3 ) and methyl tert-butyl ether (99%) were purchased from Sigma-Aldrich. All other chemicals used were analytical grade reagents without further purification. Milli-Q water (18.2 MΩ cm) was used throughout the experiments. Preparation of ZnO-AgCl nanocompositeCertain amount of zinc nitrate hexahydrate was dissolved in 50 mL of water. Then, 5 mL of ammonium hydroxide was added into the solution for 15 min stirring. Afterward, a certain amount of AgNO 3 solution (50 mM) was slowly added. After 30 min stirring, 5 mL of NaCl (0.5 M) was slowly added into the formed suspens...

Modified Sequencing Batch Airlift Reactor Capability in MTBE Removal

“…There are various physical, chemical, and biological methods for MTBE treatment. Ozone ultrasonic irradiation [8], hybrid oxidation [11], ozonation [20], UV/chlorine advanced oxidation process [14], electro-photocatalytic processes such as TiO2 [21,23,27], ZnO-AgCl nanocomposite photocatalyst [18] and oxidation with per-sulfate to produce activated carbon for the removal of MTBE [10] are some of the methods used to reduce and eliminate this product. The most common methods of removing MTBE from drinking water are aeration [13], application of natural and modified diatoms [2,3,33] optical dispersion with nano-zeolite combinations ZnO [34], adsorption by activated carbon [26], advanced oxidation processes (using a fluoride ion, O3, and H2O2), Fenton and pseudoFenton [5,12], UV-Fenton [17] and using H2O2in the presence of Fe-zeolite catalysts [24].…”