Rational design of a material for rapid colorimetric Fe2+ detection

We report on the rational design of a novel TiO2 based screen-printed material suitable for sensitive and selective detection of iron ions in water. This includes the synthesis and characterization of large mesoporous TiO2 nanostructures, screen-printing of thick titania films on glass surfaces and their functionalization with 2,2':6',2″-terpyridin-4'-ylphosphonic acid (terpy). The ultra-high affinity between iron ions and the TiO2-anchored terpy receptor makes this system potentially applicable to the analysis of iron in environmental, food, biological, and biomedical systems by a readily quantifiable colour change. Rapid (<30 s) colour change of the material from white to magenta permits easy detection of as low as 0.3 ppm of Fe2+ by the naked eye. The intensity of the colour change depends on the nature of the nanoparticles, the overall TiO2 film thickness, and the Fe2+ concentration. The material was characterized using profilometry, diffuse reflectance UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) before and after treatment with aqueous solutions of Fe2+. The designed material shows colour reversibility upon treatment with EDTA solutions, which allows for multiple reuses of the same film with no effect on sensitivity.