Caprylate intercalated layered double hydroxide as adsorbent of the linuron, 2,4-DB and metamitron pesticides from aqueous solution

Abstract

This study was carried out to elucidate the synthesis of organo-layer double hydroxide (LDH) and its capacity to adsorbs the widely applied pesticides linuron, 2,4-DB and metamitron from waters. The adsorbent (LDH-Cap) was synthesized by incorporating organic anion caprylate into magnesium aluminum layered double hydroxide with chloride as interlayer anion (LDH-Cl) via ion exchange. Characterization of the LDH-Cap adsorbent was carried out using powder X-ray diffraction (PXRD), infrared spectroscopy (FT-IR) and thermal analyses (TG and DTA). PXRD patterns indicate that caprylate anion was successfully intercalated in LDH according to the basal spacing d003=19.2Å. Adsorption results indicated that these three pesticides were adsorbed on LDH-Cap. The high percentage of initial pesticide amounts removed within the first 30min (~90% of the total amount adsorbed) for linuron and 2,4-DB revealed a rapid adsorption process, while it was more gradual for metamitron. PXRD results suggest that adsorbed 2,4-DB and metamitron were intercalated in the LDH interlayers probably between caprylate chains and the brucite layers. Linuron was probably adsorbed on the external particle surface of LDH. Adsorption kinetic study revealed that the adsorption process followed pseudo-second-order equation. Adsorption data were well fitted to the Freundlich isotherm. The desorption of the pesticides from adsorption products were tested with three different solvents (distilled water, ethanol and acetone) and it was partial in all cases.