Methoxy-modified kaolinite as a novel carrier for high-capacity loading and controlled-release of the herbicide amitrole

Abstract

Methoxy-modified kaolinite was used as a novel carrier for loading and release of the herbicide 3-amino-1,2,4-triazole, known as amitrole (abbreviated here as AMT). The methoxy modification made the interlayer space of the kaolinite available for AMT intercalation. The AMT loading content in methoxy-modified kaolinite reached up to 20.8 mass% (twice the loading content by unmodified kaolinite). About 48% of this amount is located in the interlayer space. The release profiles of the AMT fit with the modified Korsmeyer-Peppas model. Due to the diffusional restriction of the intercalated AMT by the lamellar structure of the kaolinite and the strong electrostatic attraction between the intercalated AMT and the kaolinite, a slow release of AMT from the methoxy-modified kaolinite was achieved. These results show that the methoxy-modification is a facile method to make the interlayer space of kaolinite available for hosting other guest molecules. The methoxy-modified kaolinite is a promising candidate for high-capacity loading and controlled-release of other molecules such as drugs, agrochemicals, and biochemicals.

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

“…The intercalated AMT was present as amorphous state, and arranged as a horizontal monolayer of which the plane of the five-membered heterocyclic of AMT was parallel to the clay mineral layers, and part of the AMT molecule was keyed into the plane of the grafted methoxy groups. These results had already been revealed in a previous work (Tan et al, 2015). AMT-Kaol MeOH had a highly symmetrical (001) reflection with high intensity, but a low symmetry and low intensity (001) reflection for AMT-Hal MeOH .…”

“…In the case of AMTKaol MeOH , the amount of intercalated AMT was 9.9 mass%, and the amount of non-intercalated AMT was 10.9 mass%. The detailed calculation on the amount of intercalated and non-intercalated AMT has been previously reported (Tan et al, 2015). These results mean there was approximately 47.6% AMT loaded into the interlayer space of Kaol and 52.4% AMT loaded onto the external surface of Kaol.…”

“…This further intercalation is ascribed to that the methoxy-modification introduced a plane of methoxy groups into the interlayer space of Kaol weakening the original hydrogen bonding between adjacent layers. Therefore, the carrier-performance of Kaol was significantly promoted by methoxy-modification (Tan et al, 2014a(Tan et al, , 2015.…”

“…When Kaol was used as carrier, the guest molecules (e.g., salicylic acid, ibuprofen) only adsorbed on the external surface of Kaol (Bonina et al, 2007;Mallick et al, 2008), could not be directly intercalated into the hydrogen-bonded interlayer. The previous studies have proved that the development of the interlayer space of Kaol as additional loading space for guest molecules (e.g., 5-fluorouracil, AMT) could be achieved by methoxy-modification (Tan et al, 2014a(Tan et al, , 2015. This further intercalation is ascribed to that the methoxy-modification introduced a plane of methoxy groups into the interlayer space of Kaol weakening the original hydrogen bonding between adjacent layers.…”

Properties and applications of halloysite nanotubes: recent research advances and future prospects

“…The interlayer space of the methoxy-modified Kaol has been used as host for guest molecules, such as ε-caprolactam (Komori et al, 1999a), poly(vinylpyrrolidone) (Komori et al, 1999b), alkylamines (Komori et al, 1999c), p-nitroaniline (Kuroda et al, 1999;Takenawa et al, 2001), nylon 6 (Matsumura et al, 2001), some quaternary ammonium salts (Kuroda et al, 2011), 5-fluorouracil (Tan et al, 2014a), and amitrole (Tan et al, 2015). In addition, the interlayer space of the methoxy-modified Hal is also available for the loading of guest molecules, such as the anticancer drug 5-fluorouracil and the herbicide amitrole.…”