Cyanide Sensing with Organic Dyes: Studies in Solution and on Nanostructured Al 2 O 3 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.