Abstract
Nowadays, great focus is given to the contamination of surface and groundwater because of the extensive usage of pesticides in agriculture. The improvements of commercial catalyst TiO2 activity using different Au nanoparticles were investigated for mesotrione photocatalytic degradation under simulated sunlight. The selected system was 2.43 × 10−3% Au–S–CH2–CH2–OH/TiO2 (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy. It was found that TiO2 particles size was ~20 nm and ~50 nm, respectively. The Au nanoparticles were below 10 nm and were well distributed within the framework of TiO2. For 2.43 × 10−3% Au–S–CH2–CH2–OH/TiO2 (0.5 g/L), band gap energy was 2.45 eV. In comparison to the pure TiO2, addition of Au nanoparticles generally enhanced photocatalytic removal of mesotrione. By examining the degree of mineralization, it was found that 2.43 × 10−3% Au–S–CH2–CH2–OH/TiO2 (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates. The effect of tert-butanol, NaF and ethylenediaminetetraacetic acid disodium salt on the transformation rate suggested that the relative contribution of various reactive species changed in following order: h+ > ●OHads > ●OHbulk. Finally, several intermediates that were formed during the photocatalytic treatment of mesotrione were identified.
Highlights
Mesotrione, or otherwise known as [2-(4-methylsulfonyl-2-nitrobenzoyl)-1,3-cyclohexanedione], is the common name for a herbicide, which controls annual broadleaf weeds in maize fields
The selected system was 2.43 × 10−3% Au–S–CH2–CH2–OH/TiO2 (0.5 g/L) that was studied by transmission electron microscopy and ultraviolet-visible (UV-Vis) spectroscopy
By examining the degree of mineralization, it was found that 2.43 × 10−3% Au–S–CH2–CH2–OH/TiO2 (0.5 g/L) system was the most efficient for the removal of the mesotrione and intermediates
Summary
Mesotrione, or otherwise known as [2-(4-methylsulfonyl-2-nitrobenzoyl)-1,3-cyclohexanedione], is the common name for a herbicide, which controls annual broadleaf weeds in maize fields. There are many metal-oxides that serve as powerful photocatalysts, but the most frequently used is TiO2 [9,12,13,14,15] This compound has good features like biological and chemical stability, availability, insolubility in water, acids and bases, resistance to photocorrosion, low cost, and nontoxicity [12,16,17]. Reported results [18,19,20] have confirmed that enhancement of TiO2 with Au nanoparticles in the visible part of the spectrum is due to surface plasmon resonance, i.e., collective oscillation of free conduction band electrons. With addition of the chemical agents, surface of nanoparticles can alter the particle size, morphology, mechanical stability, optical properties, toxicity, and photocatalytic activities [24]. Identification of intermediates was performed for indicated reaction mechanism and to confirm the role(s) of OH and/or direct charge transfer reactions during the transformation process
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