In this paper, the preparation of ascorbic acid (AA)-doped polyoxometalate (SiW(12)-AA) microtubes is described. The SiW(12)-AA microtubes convert to heteropoly blue microtubes upon exposure to ammonia gas, which is an ammonia-triggered solid-solid redox reaction between AA molecules and polyoxometalates, and can possibly be applied to a chemical sensor for detecting ammonia and volatile organic amines. Furthermore, the SiW(12)-AA microtubes have been applied to the in situ synthesis of Ag nanoparticles (NPs) through the redox reaction between the AA component and Ag(+) ions occurring on the surfaces of the SiW(12)-AA microtubes to give silver NPs immobilized on polyoxometalate microtubes (Ag@SiW(12)).
The synthesis and characterization of microtubes of SiMoW(11) Keggin polyoxometalates containing either an Mo(V) or Mo(VI) atom is reported. The introduction of a Mo atom into the Keggin-type tungstosilicate microtubes endows them with new properties. The Mo-substituted microtubes may exert both W and Mo functionalities in electrocatalytic reactions and in the immobilization of noble metal nanoparticles. The degree of reduction of the Mo component in the SiMoW(11) microtubes is controllable simply by tuning the amount of reductant present in the mother liquor. Mo-substituted Keggin tungstosilicate microtubes in their reduced state are more stable than the all-tungsten Keggin tungstosilicate heteropoly blue microtubes.
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