Síntese e caracterização do nanocompósito híbrido 2,4-D/HDL usado como Formulação de Liberação Controlada do herbicida 2,4-D

Abstract

Generally, the excessive use of pesticides has forced researchers to develop studies to apply these compounds in a controlled manner and smaller quantities in order to minimize the impacts caused on the environment. The 2,4-dichlorophenoxyacetic acid (2,4-D) is the second most used herbicide in the world and Brazil. Its disorderly use causes concern due to the possible environmental problems caused, such as the contamination of surface and groundwater. One of the most promising ways to improve the use of 2,4-D to reduce these problems is using Controlled Release Formulations (CRFs), which are solid hybrid nanocomposites that contain 2,4-D and allow its release slow and controlled. CRFs can be synthesized using Lamellar Double Hydroxides (LDH) as an herbicide host material. In the present work, nanocomposites of the 2,4-D/LDH type were synthesized by the direct coprecipitation method to verify the influence of the concentration of 2,4-D and the concentration of metallic salts on their physical-chemical characteristics and their release properties of 2,4-D. The samples were characterized by XRD, FTIR, SEM, and TGA. Release tests were performed using suspensions of the nanocomposite in sodium carbonate solution for 8 h. The results showed an increase in the basal spacing in the samples containing 2,4-D due to the intercalation of the organic molecule between the brucite-like layers. It was identified that, at low levels of 2,4-D, the pesticide molecule was intercalated in a monolamellar arrangement in a horizontal position. However, as the 2,4-D content increases during synthesis, a bilamellar arrangement is formed with the 2,4-D molecules in a vertical position between the brucite-like layers. This fact was inferred by the more significant increase in basal spacing (approx. 18 Å). The release of 2,4-D is higher in sodium carbonate solution compared to water. In the first minutes, there is a higher release rate, then this concentration of 2,4-D increases in the solution and finally remains constant when there is almost no more 2,4-D between the lamellar to be released. In water, the release of 2,4-D occurs in smaller amounts, at a lower rate, compared to the release in sodium carbonate, but also reaches an equilibrium. Therefore, it can be concluded that the CRFs are applicable to 2,4-D, both in an aqueous solution and a saline solution.