Adsorption and Controlled Release of Acetochlor by Organically Modified Bentonites

Bentonites modified with the organic cation cetyltrimethylammonium (CTMAB-Bents) were utilized as adsorbents and controlled release carriers of acetochlor.The experimental results indicated that CTMAB-Bents provided 3~5 times higher adsorptive capacities of acetochlor than the raw bentonite (Na-Bent),and their adsorptive capacities positively related to the amount of CTMAB used in modification.The adsorption isotherms were fit to the Freundlich equation with correlation coefficients R>0.99.The adsorptive capacity mainly resulted from the partition of acetochlor between water and organo-bentonites.Compared with Na-Bent,CTMAB-Bents could apparently retard the release of acetochlor.The time taken for 50% of the acetochlor to be released (t50) ranged from 6.57 h for the 20CTMAB-Bent formulation to 19.0 h for the 100CTMAB-Bent formulation.The prolonged t50 was consistent with the increased adsorptive capacity of the bentonites.The release dynamics were fit to the Ritger and Peppas equation with n values (0.429~0.618) close to that of Fickian diffusion model,which indicated a diffusion-dominated release mechanism of acetochlor from organo-bentonites.