# Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption
## Material and Methods
### Characterisation  
The chemical compositions of the major elements in bentonite and modified bentonite were determined by energy dispersive XRF (EDS, Oxford Instrument ED 2000, Abingdon, UK) using an Rh X-ray tube with a vacuum medium. The CEC was determined by a 9080 CEC standard method (US EPA, OSWER), in which all adsorbed cations in a bentonite sample were replaced by a common ion, such as NH\({}_{4}\)+, and then the amount of adsorbed common ion was determined. The interlayer spacing of the samples was determined by X-Ray diffraction patterns obtained from back-pressed powder samples recorded on a [PERSON], D5005, Germany, Cu K\(\alpha\) radiation, scanning from 3\({}^{\circ}\) to 50\({}^{\circ}\) at a rate of 0.05\({}^{\circ}\)/s at 35 mV and 35 mA. The framework and OH groups were confirmed by FT-IR spectroscopy (Spectrum GX, Perkin-Elmer, Waltham, MA, USA) as KBr pellets, over the range of 4000-400 cm\({}^{-1}\) and near-IR diffuse reflection (DRIFT) in the range of 8000-4000 cm\({}^{-1}\). The DRIFT technique was especially appropriate in this region because no sample dilution was required. Specific surface and pore size distributions were evaluated by nitrogen gas adsorption at \(-\)196 \({}^{\circ}\)C using a BEL JAPAN, BELSORP-mini II, Japan instrument, with the Brunauer-Emmertt-Teller (BET) method. All samples were characterised by solid-state \({}^{27}\)Al CP/MAS NMR (JEOL JNM-ECA600), with a static 11 T magnetic field at a spin rate of 11 kHz. The \({}^{27}\)Al CP/MAS NMR spectra were recorded at a frequency of 130 MHz. The NMR reference used was Al(NO\({}_{3}\))\({}_{3}\).9H\({}_{2}\)O with a chemical shift of 0.00 ppm. The particle size distributions (PDS) of all samples were analysed by a Horiba laser-scattering particle-size-distribution analyser (LA-950), Japan. The active site was determined using NH\({}_{3}\) temperature-program desorption (TPD) apparatus (BEL Japan, model BELCAT-B, Osaka, Japan). Samples were pre-treated at 300 \({}^{\circ}\)C for 2 h and then exposed to a flow of NH\({}_{3}\)/He at 100 \({}^{\circ}\)C for 30 min. Weakly adsorbed NH\({}_{3}\) was removed by flushing with He gas at 100 \({}^{\circ}\)C for 30 min. The NH\({}_{3}\) TPD profile was obtained over the range of 100 \({}^{\circ}\)C-600 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C/min. Desorbed NH\({}_{3}\) was detected using a thermal conductivity detector. TGA curves were obtained by heating the sample in an alumina70 cell from 30 to 800 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\) under air atmosphere using a thermogravimetric analyser (TGA-DSC, METTLER, Germany). Zeta potential measurements were performed using a Malvern, UK. Bentonite and modified bentonite slurries were homogenised using a Branson Sonifier, UK. Sonifier employs ultrasonic vibration to disperse the dry clay particle aggregates in suspensions. Before the sonication, the amount of clay powder and deionised (DI) water was kept constant at 10 wt.%. Dilution suspensions were prepared for the zeta potential measurement with a colloidal Dynamics Zeta Probe. The concentration employed was only 1 wt.% solids. The pH was increased to approximately 12 with 1 M NaOH before commencing the yield stress measurements. Concentrated HCl (1 M) was added dropwise to decrease the pH in a stepwise manner. Atrazine, diuron, 2,4-D, and paraquat concentration were determined using UV-visible spectrophotometry at 223, 247, 283 and 257 nm, respectively (T80 + UV-Vis spectrophotometer PG instruments, Alma Park, Leicestershire, UK). The mixture solution of atrazine, diuron, 2,4-D and paraquat concentration were determined using HPLC (Hewlett Packard series 1100, Palo Alto, CA, USA). All experimental measurements were made in duplicate.