Polyoxometalate based ionic crystal: dual applications in selective colorimetric sensor for hydrated ZnCl2 and antimicrobial activity†
Abstract
One-pot synthesis of POM-salt ([Himi]4[SiMo12O40] (1)) was achieved by mixing silicomolybdic acid and imidazole in acidic conditions and characterized by FTIR, TGA, SEM, EDX, ICP-OES and XPS. The structure of 1 was confirmed by single crystal X-ray analysis. The matching of the simulated PXRD pattern with the experimental pattern indicates the phase purity of 1. Interestingly, 1 showed highly selective and sensitive colorimetric detection of hydrated zinc chloride (ZnCl2·2H2O). The addition of ZnCl2·2H2O into 1 in the DMSO–H2O mixture shows the formation of blue colour. Furthermore, metal ions including other anionic zinc salts did not produce any colour change. The limit of detection was calculated to be 0.15 μM. Similarly, solid mixing of ZnCl2·2H2O with 1 can also produce a visible blue colour change. On the other hand, anhydrous ZnCl2 did not form any color change under the same conditions. The mechanistic studies indicate that the reduction of Mo6+ to Mo5+ might be responsible for the selective colour change. The reversible colour change between colorless and blue colour upon addition of EDTA into 1-ZnCl2·2H2O demonstrates the reusability of 1. Furthermore, microbial activity of 1 was investigated towards a series of Gram-positive and Gram-negative bacterial and fungal strains. Effective bactericidal activity of 1 was analyzed against Staphylococcus aureus.
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