Functional cyclodextrin nanosponges as benzidines absorbing substrates

Hydrophilic cyclodextrin (CD) nanosponges, that is, insoluble cross-linked polymers with CD moieties connected by short covalent bridges, were synthesized as pre-concentrating substrates of electroanalytical devices for the detection of emerging water pollutants present in traces, with the aim to enhance their sensitivity and selectivity. Organic pollutants are amenable to be selectively included in α-, β-, and γ-CD cavities according to their molecular dimensions. Therefore, differently functionalized α-, β-, and γ-CD resins were prepared in pH> 11 aqueous solutions by the 1,4-polyaddition of CDs with either bisacryloylpiperazine or 2,2-bisacrylamidoacetic acid, or polyamidoamines bearing acrylamide terminals. Different organic pollutants, namely benzidine, o-toluidine, o-tolidine and tetramethylbenzidine, all ubiquitous aromatic pollutants, were used as model analytes. Resins with 30-50% by weight CD content were obtained at moderate cost in water by an eco-friendly process. They moderately swelled in water (20-50%) and were thermally stable up to 280°C . They proved suitable for the removal of benzidines from aqueous solutions down to the sub-ppm levels. The absorption capacities were maintained also after regeneration with methanol. The absorption selectivity was tuned by varying CD size and the length and polarity of the interconnecting bridge.