Cyclodextrin as a complexation agent in the removal of chlordecone from water

Abstract

The pesticide chlordecone (CLD) has been used over decades to control the proliferation of various insects such as banana root borer especially in tropical countries. Although no longer employed, contamination of soils and rivers by this pollutant is persistent and causes deadly diseases, therefore its removal from water is a sanitary emergency. Common activated carbon (AC) filters have a limited efficiency. With the aim to enhance the adsorption efficiency of AC towards CLD by means of host-guest complexation, cyclodextrins (CDs) were investigated as hosts. Indeed, β- and γ-CD form stable complexes (CLD@CD) which are insoluble in most organic solvents (apart from DMF and DMSO) and therefore can be simply filtered to obtain pure water. Elemental analysis shows that a single CLD is included inside the inner rim of a single CD. ATR-FTIR analysis indicates interactions between the OH group of CD and the Cl atoms of CLD which likely contributes to the low solubility of the complex. Thermal analyses (DSC) show that the formation of the complex is thermodynamically favourable. Two techniques were developed to purify water. Firstly, the insoluble CLD@γ-CD complex was simply filtered from water with AC filters. Alternatively, γ-CD was further modified such it forms a bond/link to the surface of AC. By this route, a hybrid material (AC-γ-CD) was produced. This hybrid material was found to be an even better adsorbent for CLD from water. Both techniques lead to an enhancement of the absorbance and removal of CLD from water when compared to AC alone.