Acid-activated natural zeolite and montmorillonite as adsorbents decomposing metsulfuron-methyl herbicide

Abstract

Modern technologies of intensive crop production demand a wide application of various types of pesticides. The adverse effect of cropping intensification is that toxic organic compounds, in particular herbicides of the sulfonylurea family, are accumulated in the soil. The herbicide metsulfuron-methyl is soluble in water and accumulates in soil moisture, causing a toxic effect on plant development. The work examines the issue of the chemical stability of metsulfuron-methyl in a model aqueous environment for the targeted selection of a mineral that adsorbs the herbicide and simultaneously catalyzes the process of herbicide hydrolysis. Degradation processes of sulfonylurea herbicide metsulfuron-methyl in aqueous media in the presence of natural zeolite, acid-activated natural zeolite, and montmorillonite К10 were investigated. Under conditions of static contact of the adsorbents with an herbicide aqueous solution, montmorillonite was more active in the sorption and degradation of metsulfuron-methyl. During the first 1–2 days the herbicide concentration decreased by a factor of 5. An almost complete degradation of metsulfuron-methyl in aqueous dispersions of the acid-activated zeolite and montmorillonite was attained within 20 days. Pore size distribution functions (Barrett-Joyner-Halenda and standard non-local density functional theory methods) were evaluated. The acid treatment of the natural zeolite changed its porous structure - its specific surface area grew by a factor of 5. Three fractions of mesopores 4–10, 10–20, 20–30 nm were revealed in the original zeolite, and one fraction of pores 2.0–3.5 nm was found in the acid-activated zeolite. In the montmorillonite, only one group of 3–15 nm pores was detected. Studies of structural changes in natural zeolite after acid modification were carried out using the methods of X-ray fluorescence and X-ray phase analysis, scanning electron microscopy and infrared spectroscopy. The acid-activated montmorillonite and natural zeolite show promise for land reclamation work on detoxification of soils contaminated by sulfonylurea herbicides.