Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption

Abstract

In this work, simple conditions were applied to modify bentonite for the removal of pesticides from aqueous solution. Bentonite was modified in a single step as BA0.5 (with HCl 0.5 M) and BC500 (calcined at 500 °C) and combined steps with different sequences (BA0.5C500 and BC500A0.5). These adsorbents were characterised by XRD, XRF, FT-IR, 27Al MAS NMR, BET, NH3-TPD, TGA, HPLC, particle size analysis and zeta potential. Single-component adsorption with atrazine, diuron, 2,4-D and paraquat was used in aqueous solution at various pesticide concentrations, contact times and pH levels. It was found that the sequence of the treatment significantly affected atrazine adsorption. BC500A0.5 exhibited the highest efficiency for atrazine adsorption in a broad pH range of 3.0–9.0. Its adsorption at pH 6.0 was about 12 times greater than that of other adsorbents with an initial atrazine concentration of 50 mg L−1, which indicates BC500A0.5 specifically for the adsorption of atrazine. In addition, for the simultaneous adsorption of all four pesticides, BC500A0.5 was found to remove the maximum total amount of the pesticides, indicating that it could be used as a good multifunctional adsorbent. All modified bentonites showed similar diuron adsorption better than that of unmodified bentonite. The greatest adsorption of 2,4-D prefers BA0.5C500, occurring at pH 2–4. In the case of paraquat adsorption, all adsorbents are good at absorbing paraquat, but bentonite had the highest rate of paraquat removal, whereas BA0.5C500 was found to have the lowest, and the adsorption increased with increasing pH. Furthermore, the adsorption process on the adsorbents fits well with the Langmuir isotherm and pseudo-second-order kinetics models, as the thermodynamic parameters showed a spontaneous and endothermic process.