Preparation and characterization of novel composites based on chitosan and clinoptilolite with enhanced adsorption properties for Cu2

Novel ionic composites based on chitosan (CS) and clinoptilolite (CPL), a widespread natural zeolite, were prepared in this work as microspheres by a "tandem" ionic/covalent cross-linking. The mass ratio between CPL and CS was varied in the range 1:10-1:2. The ionic gelation of CS was performed with sodium tripolyphosphate and epichlorohydrin was used as covalent cross-linker. An abrupt increase of the adsorption capacity for Cu(2+) with the increase of the CPL content loaded in the composite compared with cross-linked CS was observed, up to 20 wt.% of CPL. The external stimuli which control the adsorption of Cu(2+) were solution pH and temperature. The optimum adsorption pH was 5.0 and the adsorption process was well described by the pseudo-second-order kinetics. The maximum adsorption capacity of metal ions was observed after the 2nd cycle of adsorption, for all composites.