Characterization of sepiolite-gel-based formulations for controlled release of pesticides

Novel controlled release formulations (CRFs) were developed for reducing leaching of herbicides and contamination of groundwater. The herbicide metribuzin (MTB) was entrapped within a sepiolite-gel matrix using a novel and ultrasound-based technique. Different sepiolite/herbicide matrices (either as a gel or as a powder after freeze-drying) were prepared with pesticide loading between 28.6 and 9.1%. The release of MTB from the control released formulations into water was retarded when compared with commercial formulation (CF), except in the case of the sepiolite-gel-based formulations with lower amounts of sepiolite. The rheological properties and microstructure of these formulations were examined in detail. FTIR spectra showed that there was no evidence of herbicide inside the sepiolite tunnels. The SEM micrograph of the sepiolite-gel-based formulations showed the fibrous morphology typical of sepiolite and no separate particles of MTB were found. However, the chemical analysis by EDX confirmed the presence of S, N, and C, which were attributed to MTB, together with the fibers of sepiolite. Rheological characterization indicated that samples containing MTB develops a microstructure, which is irrespective of concentration above 1 mass % sepiolite. There was a good agreement between the microstructure characteristics and MTB release behavior.