Water-Insoluble Cyclodextrin-Epichlorohydrin Polymers

Abstract

Proposed and studied in the mid-1960s, water-insoluble cyclodextrin-epichlorohydrin polymers are of continued interest to the scientific community, particularly for their environmental applications. The most characteristic feature of these materials is their ability to form inclusion complexes with various contaminants through host-guest interactions. This leads to many environmental applications, including water and wastewater treatment, soil remediation, air purification, and the concentration or elimination of target substances such as cholesterol.

In the early 1990s, our group began working on the synthesis of water-insoluble cyclodextrin-based materials, their structural characterization, and their application in the removal of pollutants present in wastewater. One of the first results published in 1995 concerned the fact that this material was not a true polymer but a copolymer with a particular structure with two different molecular mobilities. In 1997, this was demonstrated for the first time by solid-state NMR spectroscopy. These materials were composed of a relatively dense, rigid, and hydrophobic cross-linked core and a more hydrophilic surface, less cross-linked containing long and highly mobile hydroxyalkylated polymer chains through the homopolymerization of the cross-linking agent. In 1998, cyclodextrin-based materials were used as adsorbents to efficiently remove organic contaminants from contaminated water. One year later, a more surprising result showed that a high proportion of cyclodextrin was not necessary to have useful performance in terms of pollutant removal. In 2000, using cross-polarization magic angle spinning with dipolar decoupling and high-resolution magic angle spinning spectra, we concluded that the mechanism of adsorption can be explained by the presence of two main interactions: the formation of an inclusion complex due to the cyclodextrin molecules and the physical adsorption in the polymer network. In 2005, a patent was filed on a process for the synthesis of cross-linked polysaccharides with ionic functional groups for the simultaneous removal of metals and organic contaminants present at low trace levels in polycontaminated effluents. At the end of the 2000s, we carried out the first pilot studies demonstrating that a single cyclodextrin material with amphoteric and ion-exchange properties could replace two conventional adsorbents to effectively treat multi-contaminated effluent. In the early 2010s, our group proposed for the first time biomonitoring tests using plants as bioindicators to determine and compare the toxicity of industrial effluent from wood, pulp and paper, textile, and surface treatment industries before and after treatment with a cyclodextrin material. In the mid-2010s, we confirmed the feasibility of implementing materials for the treatment of discharge waters from surface treatment industries on an industrial scale.

The purpose of this chapter is to summarize the research conducted over the past 30 years by our research group on water-insoluble cyclodextrin-epichlorohydrin polymers used as complexing materials to remove contaminants present in aqueous solutions. It shows the progress of our work and our contribution to a better understanding of these materials. These years were devoted to the synthesis of a series of water-insoluble materials with different functionalities in the form of gels or beads, their characterization by innovative solid-state NMR techniques, the demonstration of their effectiveness as adsorbents in wastewater treatment, and the explanation of contaminant removal mechanisms according to the type of material used.