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Effect of Chain Length and Functional Group of Organic Anions on the Retention Ability of MgAl- Layered Double Hydroxides for Chlorinated Organic Solvents

Nowadays, the contamination of groundwater and soils by chlorinated organic solvents is a severe and worldwide problem. Due to their swelling properties, Layered Double Hydroxides (LDHs) are potentially excellent compounds to retain chlorinated organic solvents from aquifers. By intercalating organic anions, the polarity of the interlayer space can be changed from hydrophilic to hydrophobic, enhancing the adsorption of chloro-organic molecules onto the alkyl chains of intercalated organic anions. In this study, organically modified LDHs were synthesized and their efficiency was tested in batch experiments with three different chlorinated organic solvents, namely trichloroethylene, 1,1,2-trichloroethane and trichloromethane (chloroform), to examine the influence of the chain length and the functional group of the intercalated organic anion upon the retention ability of a LDH due to different electronic interactions and different sizes of the interlayer space. All synthesized and used samples were characterized using powder X-ray diffraction, thermal analysis coupled with mass spectrometry and Fourier-transform infrared spectroscopy; freshly synthesized materials were additionally analyzed regarding their particle size distribution and specific surface area. Results of the batch experiments showed that only LDHs with intercalated long-chain organic anions could be efficient adsorbents for the removal of chlorinated organic solvents from contaminated water. A selective efficiency towards 1,1,2-trichloroethane and trichloromethane can be proposed for these reactants.