Synergistic adsorption of heavy metal ions and organic pollutants by supramolecular polysaccharide composite materials from cellulose, chitosan and crown ether

摘要

We have developed a simple one-step method to synthesize novel supramolecular polysaccharide composites from cellulose (CEL), chitosan (CS) and benzo-15-crown 5 (B15C5). Butylmethylimidazolium chloride [BMIm~+Cl~-], an ionic liquid (IL), was used as a sole solvent for dissolution and preparation of the composites. Since majority of [BMIm~+Cl~] used was recovered for reuse, the method is recyclable. The [CEL/CS + B15C5] composites obtained retain properties of their components, namely superior mechanical strength (from CEL), excellent adsorption capability for heavy metal ions and organic pollutants (from B15C5 and CS). More importantly, the [CEL/CS+ B15C5] composites exhibit truly supramolecular properties, By itself CS, CEL and B15C5 can effectively adsorb Cd~(2+), Zn~(2+) and 2,4,5-trichlorophenol. However, adsorption capability of the composite was substantially and synergistically enhanced by adding B15C5 to either CEL and/or CS. That is, the adsorption capacity (q_e values) for Cd~(2+) and Zn~(2+) by [CS + B15C5], [CEL+B15C5] and [CEL+CS + B15C5] composites are much higher than combined q_e values of individual CS, CEL and B15C5 composites. It seems that B15C5 synergistically interact with CS (or CEL) to form more stable complexes with Cd~(2+) (or Zn~(2+)), and as a consequence, the [CS + B15C5] (or the [CEL+ B15C5]) composite can adsorb relatively larger amount Cd~(2+) (or Zn~(2+)). Moreover, the pollutants adsorbed on the composites can be quantitatively desorbed to enable the [CS + CEL+ Bl5C5] composites to be reused with similar adsorption efficiency.