Metal-chelate sorbents based on carboxyalkylchitosans: Ciprofloxacin uptake by Cu(II) and Al(III)-chelated cryogels of N-(2-carboxyethyl)chitosan.

Here we propose a metal-chelate approach to removal of fluoroquinolones from aqueous solutions using their ability to bind strongly divalent and trivalent metal ions immobilized in a polymer matrix. Metal-affine sorbents for ciprofloxacin uptake have been fabricated via chelation of Cu(II), Al(III), and Fe(III) ions by supermacroporous cryogel of carboxyalkyl chitosan derivative (N-(2-carboxyethyl)chitosan, CEC) cross-linked with hexamethylene diisocyanate in aqeous medium. We have shown that virgin CEC cryogel adsorbed ciprofoxacin in a cationic form via electrostatic interactions at pH > pICEC, but the efficacy of recovery was below 50% and strongly pH-dependent. Modification of CEC cryogel with Cu(II) and Al(III) ions improved the ciprofloxacin (CIP) recovery by up to 98% in the pH range 7-10, the sorption capacity and affinity for CIP of metal-chelate sorbents increased with metal content and reached maximum values of 280 and 390 mg/g for Cu(II) and Al(III)-chelated cryogels, respectively. The metal-chelated CEC cryogels were efficient for ciprofloxacin removal from solutions with environmentally relevant concentration (50 µg/L) and were applicable as monolith sorbents under dynamic conditions.

Cryogels of carboxyalkylchitosans as a universal platform for the fabrication of composite materials.

Here we report a new simple method for fabrication of supermacroporous beads and monoliths via cross-linking of carboxyalkylated chitosan derivatives with hexamethylene diisocyanate in aqueous solution at subzero temperature. These materials provide high filtration rate and good mass-transfer that in combination with high binding capacity toward metal ions allows their application as a universal platform for fabrication of composite catalysts, sorbents, and metal-affine chromatography stationary phases. Using N-(2-carboxyethyl)chitosan (CEC), we have demonstrated that optimum chitosan carboxylation degree for cryogels synthesis is close to 1.0. Cu(II)-chelated CEC cryogels have shown high efficiency as metal-affinity sorbents for ciprofloxacin recovery. Co(II)-chelated CEC cryogels have been used for fabrication of Co(II) ferrocyanide-containing composite with the distribution coefficient for 137Cs of 140,000 ml/g and the adsorption capacity of ˜1 mmol/g. Composite Pd-catalysts supported on CEC cryogel provided tenfold higher reaction rate in 4-nitrophenol reduction in comparison with Pd-catalyst supported on chitosan beads.