[Fe(CN)6]4− decorated mesoporous gelatin thin films for colorimetric detection and as sorbents of heavy metal ions

Abstract

[Fe(CN)₆]⁴⁻ decorated mesoporous gelatin films, acting as colorimetric sensors and sorbents for heavy metal ions, were prepared by incorporating [Fe(CN)₆]⁴⁻ ions into the mesoporous gelatin films through electrostatic interaction. Gelatin–Prussian blue (PB) and gelatin–PB analogue composite films were successfully synthesized by immersing the [Fe(CN)₆]⁴⁻ decorated gelatin films into aqueous solutions of metal ions, such as Fe³⁺, Cu²⁺, Co²⁺, Pb²⁺ and Cd²⁺ (all as nitrates). The in situ formation process of PB or its analogues in the films was investigated using quartz crystal microbalance (QCM) measurements. According to the different colors of the PB nanoparticles and its analogues, the [Fe(CN)₆]⁴⁻ decorated mesoporous gelatin films demonstrated colorimetric sensor abilities for detecting the corresponding metal ions by the naked eye with sufficient sensitivity at 1 ppm level and a quite short response time of 5 minutes. Moreover, due to the [Fe(CN)₆]⁴⁻ functionality and other functional groups of gelatin itself, this [Fe(CN)₆]⁴⁻ decorated mesoporous gelatin film shows a tens times higher adsorption ability for heavy metal ions in water than that of activated carbon. Due to both the efficient detection and high adsorption ability for heavy metal ions, this film has wide potential applications for the detection and purification of heavy metal ions from polluted water.