Characterization and controlled release studies of 4-(2,4 dichlorophenoxy) butyrate and 2-(3-chlorophenoxy) propionate nanohybrids

Controlled release formulations were developed by intercalation of organic anions, namely 4- (2,4-dichlorophenoxy)butyrate (DPBA) and/or 2-(3-chlorophenoxy)propionate (CPPA) into the inorganic Zn-Al layered double hydroxide (ZAL) and zinc layered single hydroxide (ZLH)interlayers. Both anions, DPBA and CPPA are herbicides, a group of herbicides which function by mimicking the action of auxins and plant growth hormones. In this study, the nanohybrid compounds were synthesized by direct co-precipitation and anion exchange method for ZAL nanohybrids while direct reaction of zinc oxide with both anions under aqueous solution was applied for the formation of ZLH nanohybrids. Simultaneous intercalation of the dual herbicides was confirmed by the expansion of the interlayer spacing from 8.9 Å in the ZAL to 25.1 Å and 26.9 Å for the nanohybrid prepared by direct and ion-exchange method while ZLH shows higher basal spacing up to 28.7 Å due to higher charge density which can accommodate more guest anions into the ZLH interlayers compared to ZAL. Generally, the loading percentage obtained from simultaneous equation derived from UV-Vis spectrophotometer data for DPBA was found to be higher than CPPA. Result shows, nanohybrid synthesized by co-precipitation method contain of 2.5 % CPPA + 41.4 % DPBA while the percentage loading of the nanohybrid synthesized by anion-exchange method is 8.6 % CPPA + 53.9 % DPBA. Dual intercalation of both herbicides anions into ZLH resulted in percentage loading of 25.3% CPPA + 78.4 % DPBA. The high content of DPBA indicates that it is the dominant species and preferentially intercalated into the host interlayers than CPPA. In addition, DPBA anion has two chlorine atoms attached to the benzene ring therefore interacts more strongly with the positive charged layers. The simultaneous release profiles of both anions from their respective nanohybrids into sodium carbonate aqueous solution were best described by the pseudo-second order kinetic. This demonstrates the potential application of layered materials as hosts especially for the preparation of a controlled release formulation of the two herbicides simultaneously. The bulky anionic size, orientation and interaction with the positively charged inorganic interlayer could affect the degree of intercalation as well as the release of these herbicides from the host interlamelae.

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