Intercalação de dicamba em hidroxissal lamelar de zinco para obtenção de um herbicida de liberação lenta

Abstract

With the increase in food demand, new techniques were developed to decrease losses in crops. One of the solutions was the creation of herbicides, which eliminate pests that compete with crops. Dicamba is an auxin herbicide widely used to control broadleaf weed pests, but it is volatile and causes mass migration problems to other areas causing damage in sensitive crops, in addition it is solubilized in water and deposit in water reservoirs. The objective of the present work was intercalated Dicamba in layered zinc hydroxysalt to obtain a slow release. The compound was obtained by coprecipitation method. X-ray diffractometry (XRD) analyzes were performed, the calculated basal distance 20.48 Å ratifying the intercalation of the herbicide between the layers. Corroborating the XRD results, analyzes performed by Fourier transform infrared (FTIR) show Dicamba’s characteristic bands, like, C=C, CH2, C-O-C and COO-. Furthermore, from the FTIR it was verified the binding of Dicamba carboxylate ion with the metals of the layered compound, which was in bridge. By thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), it was verified an increase in Dicamba stability at 122.33°C when intercalated, in comparison with the pure material. The general formula of the compound as Zn5(OH)8(Dicamba)2.4.14H2O and its molar mass of 979.86g.mol-1 was also verified from the TGA. The release profile of layered zinc hydroxysalt intercalated with Dicamba was performed on a kinetic curve. It was observed the release of 89.57% of Dicamba intercalated in 21 days, which stabilized up to 40 days of beginning of the analysis, releasing 94.36% of the intercalated Dicamba. The best model to describe the Dicamba’s release is Bhaskar model, which sheds light to the release mechanism suggesting that the process is diffusion controlled via intra-particle diffusion, with r2 = 0.98553. Based on the analyzes performed, the intercalation of Dicamba in the layered zinc hydroxysalt resulted in a slow releaser. It can contribute to the elimination of weeds, as well as a decreasing the leaching of Dicamba by rainwater and increasing the degradation of the herbicide by the soil.