Montmorillonite Functionalized with Zwitterionic Surfactant as a Highly Efficient Adsorbent for Herbicides

A novel adsorbent (DHAPS-Mt) was prepared with Na montmorillonite (Na-Mt) and a zwitterionic surfactant (3-(N,N-dimethylhexadecylammonio)propanesulfonate, DHAPS). Then DHAPS-Mt was characterized by a series of characterization techniques and applied in herbicide adsorption. Two representative herbicides in agriculture, paraquat (PQ, 1,1'-dimethyl-4,4'-dipyridinium dichloride) and amitrole (AMT, 3-amino-1,2,4-triazole), were removed by DHAPS-Mt varying with different experimental conditions. The adsorption mechanisms, obtained from a comparison of adsorption capacities of DHAPS-Mt and two other kinds of organomontmorillonite (CTAB-Mt and SDS-Mt), suggested that the surface electrostatic adsorption and electrostatic attraction between herbicide cations and negatively charged group of DHAPS were the main interaction in PQ and AMT removal. The results of anionic dye (methyl orange) removal onto these three kinds of clay indicated that DHAPS-Mt might be applied in the treatment of mixed-ion wastewater. The kinetic study indicated that the adsorption of herbicides onto DHAPS-Mt followed the pseudo-second-order model, and the Langmuir isotherm model agreed well with the experimental data. Furthermore, thermodynamic parameters illustrated that PQ removal by DHAPS-Mt was more spontaneous at higher temperature, and the process was endothermic and randomness increasing in nature, while the AMT removal presented an opposite tendency.