Cyanide sensing with organic dyes: studies in solution and on nanostructured Al2O3 surfaces

The synthesis of two new azo phenyl thiourea compounds and their optical response to different anions is reported herein. Solution studies in methanol indicate that cyanide induces a colour change in these dyes (whereas no changes are observed in the presence of other anions, such as F(-), Cl(-), Br(-), CH(3)COO(-), H(2)PO(4) (-), HSO(4) (-)). Interestingly, in DMSO these dyes are responsive not only to cyanide, but also to fluoride, acetate and dihydrogen phosphate. Each of these anions induces a different colour change. In the second part of the paper, we report the attachment of one of these dyes onto nanostructured TiO(2) and Al(2)O(3) films. The stability of these sensitised films to pH was studied and we concluded that the sensitised Al(2)O(3) films are more robust, and hence, better than the TiO(2) for anion sensing. The dye-sensitised Al(2)O(3) films were immersed in solutions of different anions and their response studied. The films can detect cyanide down to 3 ppm in aqueous solution with relatively good selectivity over other anions.