Polyoxometalate hybrid catalyst for detection and photodecomposition of mustard gas surrogate vapors

Abstract

The polyoxometalate hybrid (POM-h) nanorods were synthesized and tested as reactive adsorbents of the vapors of mustard gas surrogates, and in particular against 2-chloroethyl ethyl sulfide (CEES) and ethylethyl sulfide (EES). They were found to promote the photo-oxidation of the surrogates’ vapors to sulfoxide under ambient conditions and in the absence of an additional oxidation agent. The structural and morphological analysis by SEM, TEM, XRD, and BET showed that the non-porous bright-yellow powder consists of nanorods with diameter of 50–100 nm and length of around 1 μm, stacked together by forming star-like nanostructured aggregates. The FTIR, XRD, thermal analysis, and EDX mapping revealed that the obtained material consists of the Keggin-type cobalt containing heteropolytungstate polyoxometalate phase (K5CoW12O40·20H2O) and potassium persulfate. The estimated indirect band gap was in the blue region of the visible light. The decomposition/detoxification of CEES and EES vapors by POM-h occurred through various and complex photo-catalytic and photo-oxidative pathways. The degradation of the surrogates’ toxic vapors to non-toxic molecules was linked to the elevated surface photo-reactivity and the ability of the nanorods to form hydroxyl radicals. The latter ones were responsible for the cleavage of SC bonds and further photo-oxidation of the formed fragments to ethanol, formaldehyde and acetic acid. A fast and gradual color change of the nanomaterial upon exposure to surrogate vapors or droplets could be used in sensing/detecting the presence of toxic species.