Synthesis of phenoxyherbicides-intercalated layered double hydroxide nanohybrids and their controlled release property.

Synthesis of new generation of agrochemicals of phenoxyherbicides-type, namely 2-chloro- (2CPA) and 2,4,5- trichlorophenoxy acetates (TCPA) were accomplished by hybridization of the phenoxyherbicides into zinc-aluminium-layered double hydroxide interlamellae for the formation of new nanohybrids of 2CPA and TCPA, labeled as N2CPA and NTCPA, respectively. Basal spacing expansion from 8.9 Å in the layered double hydroxide (LDH) to 18.5 and 26.2 Å in the resulting N2CPA and NTCPA nanohybrid, respectively, together with FTIR, CHNS and TGA/DTG data support that the phenoxyherbicides were successfully intercalated into the layered double hydroxide inorganic interlayers. The release of the phenoxyherbicides from their nanohybrids at various pHs can be expressed by parabolic diffusion at the beginning of the process, but the release data for the whole process followed the pseudo-second order equation. The release process was found to be pH-dependent, in the order of pH 12 > 3 > 6.25. In addition, the release time for TCPA is longer than 2CPA, suggesting a stronger interaction of TCPA than 2CPA with the layered double hydroxide inorganic interlayer. This study indicates the potential application of zinc-aluminium-layered double hydroxide as the matrix of the controlled release formulation of agrochemicals such as 2-chlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid.

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