Preparation and application of L-cysteine-doped Keggin polyoxometalate microtubes

L-cysteine-doped tungstosilicate (Lcys-SiW12) microtubes are prepared, and the amount of L-cysteine doped in the microtubes can be tuned to some extent. The as-prepared Lcys-SiW12 microtubes are sensitive to ammonia gas exhibited through the distinct color change of the microtubes from light purple to dark blue after exposing to ammonia gas. A possible mechanism of the coloration is that the adsorbed ammonia molecules increase the basicity of the Lcys-SiW12 microtubes and promote the redox reaction between L-cysteine and polyoxometalate. This is a pH-dependent solid–solid redox reaction, which is triggered by proton capture agent. The Lcys-SiW12 microtubes show application in chemical sensors for alkaline gases. - Graphical abstract: The Lcys-SiW12 microtubes were formed during transformation of the monolacunary Keggin-type [α-SiW11O39]8− to the saturated Keggin-type [α-SiW12O40]4−, meanwhile L-cysteine molecules were doped during the growth of the microtubes. Highlights: ► L-cysteine-doped polyoxometalate microtubes are prepared. ► Amount of L-cysteine doped in the microtubes can be tuned to some extent. ► Lcys-SiW12 microtubes can be applied as a sensor for detecting alkaline gases. ► This is a proton capture agent-triggered solid–solid redox reaction.