Síntese do nanocompósito híbrido formado pelo herbicida 2,4-D encapsulado no Hidróxido Duplo Lamelar baseado em Zn e Al

Abstract

The deliberate use of agrochemicals has become an environmental and public health problem. This fact has driven researchers to develop studies for their controlled application and reducing the amount to minimize environmental impacts. Research indicates that the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is the second most widely used herbicide worldwide and in Brazil. 2,4-D is applied by spraying aqueous solutions containing the herbicide, which has generated waste, since half of the herbicide is carried by the wind and what falls on the plantation undergoes leaching, contaminating the groundwater. Through Controlled Release Formulations (CRFs), it is possible to reduce environmental and economic impacts and make the application of agrochemicals more efficient. CRFs are solids in the form of hybrid nanocomposites that contain 2,4-D within a host structure, thus allowing its slow and controlled release. FLCs can be synthesized using Layered Double Hydroxides (LDHs) as the host matrix for the herbicide. The aim of this work was to synthesize a 2,4-D/LDH nanocomposite using the direct coprecipitation method to study the influence of aging time, using much shorter times (1, 2 and 4 h), and of the herbicide content used during the synthesis (0.1, 0.2 and 0.4 mol L-1 ), on the physicochemical properties of the nanohybrid and on the herbicide release properties in sodium carbonate saline solution. The synthesized samples were characterized using XRD, FTIR, SEM and TEM techniques. The results demonstrated that 2,4-D/LDH hybrid nanocomposites can be synthesized using very short aging times of up to 1 hour, when compared to the 18-hour time used in studies reported in the literature. It was also found that with increasing 2,4-D content during the synthesis up to 0.4 mol L-1 , there was an increase in the insertion of 2,4-D into the LDH structure, producing a more crystalline material. In all samples where 2,4-D was inserted into the LDH structure, a structural change was found, identified by the pronounced increase in basal spacing. The morphology of the nanohybrid was very different from that of the LDH without herbicide, represented by the decrease in particle size. The release of the herbicide was defined by the ion exchange mechanism between the carbonate ions and the 2,4-D molecules of the nanostructure. The release kinetics found in all samples was pseudo-second order.