Preparation and Characterization of Chlorpyrifos/Cyclodextrin Complex Intercalation into ZnAl-Layered Double Hydroxide

Chlorpyrifos (CPF) was firstly included in sulfonated hydroxyethyl-beta-cyclodextrin (SBECD) and carboxymethyl-beta-cyclodextrin (CMCD) in an ethanol or 1-methyl-2-pyrrolidinone (NMP) solvent. Inclusion complexes (CPF/SBECD and CPF/CMCD) were then intercalated into the galleries of ZnAl-layered double hydroxides (ZAL) to synthesize ZAL-SBECD-CPF and ZAL-CMCD-CPF intercalated materials. The structure and thermal stability of nanohybrids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermal gravimetric and differential thermal analysis (TG-DTA). The results showed that both CPF/SBECD and CPF/SBECD were successfully intercalated in the interlayer. The samples prepared in the NMP solvent had a stronger diffraction peak intensity than those prepared with ethanol. The intercalated CPF molecules had a high thermal stability. Furthermore, the release behaviors of CPF from ZAL-SBECD-CPF and ZAL-CMCD-CPF nanohybrids were investigated and analyzed at pH 5.0 and 6.8. ZAL-SBECD-CPF had almost no slow-release behavior, while ZAL-CMCD-CPF showed distinct slow-release, which was caused by the different arrangements of cyclodextrin (CD) in the interlayer. BC release from nanohybrids was faster and the amount released higher at pH 6.8 than at pH 5.0. This was closely correlated with the structural type of CD and the release media. The CPF release kinetic process can be fitted well by pseudo-second-order and parabolic diffusion models. ZAL-CMCD-CPF remarkably exhibited controlled release behavior, suggesting that it can be potentially applied as a controlled release pesticide formulation.