Abstract
In this paper, the photocatalytic degradation of glyphosate by zinc oxide (ZnO) photocatalysts doped with tungsten (W) was investigated under solar simulated light. The photocatalysts were successfully synthesized through a simple precipitation method and subsequently characterized by different techniques: Raman spectroscopy, UV–Vis, N2 adsorption at −196 °C, X-ray diffraction, and SEM analysis. In particular, all the prepared catalysts were characterized by a crystallite size of about 28 nm and a hexagonal wurtzite structure. After the W doping, the bandgap energy decreased from 3.22 of pure ZnO to 3.19 for doped ZnO. This allowed us to obtain good results in terms of glyphosate degradation and simultaneous mineralization under solar simulated lamps, making the process environmentally friendly and with almost zero energy costs. In particular, the best photocatalytic performance was obtained with 100 W-ZnO (prepared with 1.5 mol% of W). With this catalyst, after 180 min of exposure to solar simulated light, the glyphosate degradation and mineralization was equal to 74% and 30%, respectively. Furthermore, it has been shown that the best catalyst dosage was equal to 1.5 g/L. The study on the influence of pH evidenced that the best photocatalytic performances are obtained at spontaneous (neutral) pH conditions. Finally, to determine the main reactive species in the glyphosate oxidation, the effects of different radical scavengers were tested. The results evidenced that the glyphosate oxidation mechanism seems to be related mainly to the O2•− generated under simulated solar light irradiation, but also in minor part to h+.
Highlights
The protection of water from pollution is just one of the aspects involving the most important problem of our existence, which is the protection and conservation of the environment in which we live
In order to separate the electron-hole photoinduced pairs, it is necessary to identify the optimal concentration of W6+ ions that can correspond to the thickness of the charge layer and to the depth of light necessary for the separation of the charges, as reported in a similar study on the photocatalytic activity of La-zinc oxide (ZnO) [61] finding the optimal concentration of W6+ ions is necessary to effectively separate the electron-hole pairs, an excessive amount of W can create a greater number of recombination centers, which worsens the photocatalytic activity
The results of this study clearly demonstrate that ZnO doped with tungsten can be used for the efficient degradation and mineralization of glyphosate under solar simulated lamps by the photocatalytic process
Summary
The protection of water from pollution is just one of the aspects involving the most important problem of our existence, which is the protection and conservation of the environment in which we live. The indiscriminate use of pesticides to increase agricultural production has led to the contamination of water, generating serious environmental damage [1]. Pesticides are chemical contaminants used to kill different types of pests that cause damage to cultures. Due to their nature, these compounds are potentially toxic to other organisms, including humans [2]. Glyphosate is a systemic herbicide, post-emergent, non-selective and belonging to the chemical group of phosphonate amino acids. It acts as a potent inhibitor of the activity of the enzyme 5-enolpyruvylshikimate
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