A comparative study of tubular halloysite and platy kaolinite as carriers for the loading and release of the herbicide amitrole

Abstract

Nanosized tubular halloysite (Hal) and platy kaolinite (Kaol) were used as carriers for the loading and release of the herbicide amitrole (AMT). The AMT loading content in Hal was 17.5 mass% (69.9% greater than in Kaol). This result is attributed to the significant loading of AMT in the lumen of Hal. The methoxy modification of Hal and Kaol made their interlayer spaces available for the intercalation of AMT, which substantially promoted the AMT loading. The AMT loading content in methoxy-modified Hal was 30.5 mass%, corresponding to 27.9% intercalated AMT and 72.1% non-intercalated AMT. The AMT loading content in methoxy-modified Kaol was 20.8 mass%, corresponding to 47.6% intercalated AMT and 52.4% non-intercalated AMT. The release profiles of the AMT fit with the modified Korsmeyer–Peppas model. The methoxy-modified Kaol exhibited a slow release of AMT, which resulted from two factors: (i) the high proportion of intercalated AMT, the diffusion of which was restricted by the lamellar structure of the methoxy-modified Kaol, and (ii) the long diffusion path of intercalated AMT because of the large size of Kaol particles in comparison with Hal particles.