Mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides for the catalytic decontamination of sulfur mustard simulant

The Keggin-type mono-transition-metal-substituted [PW11M(H2O)O39]5- (PW11M, M = Ni, Co, Cu) were intercalated into Zn2Cr-based layered double hydroxide (Zn2Cr-LDH) by an exfoliation-reassembly method and the synthesized Zn2Cr-LDH-PW11M composites were thoroughly characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), solid state 31P nuclear magnetic resonance (31P NMR) spectroscopy, thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The three composites can be used as heterogeneous catalysts to promote the oxidative decontamination of the sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES). Interestingly, a cooperative effect between the PW11M cluster and Zn2Cr-LDH is evidenced by the fact that the composites have a higher catalytic performance than either of the individual constituents alone. The catalytic activity of Zn2Cr-LDH-PW11M is significantly influenced by the substituted transition metals, showing the order: Zn2Cr-LDH-PW11Ni > Zn2Cr-LDH-PW11Co > Zn2Cr-LDH-PW11Cu. Under ambient conditions, the Zn2Cr-LDH-PW11Ni composite can convert 98% of CEES in 3 h using nearly stoichiometric 3% aqueous H2O2 with the selectivity of 94% for the nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO). Moreover, the decontaminating material, Zn2Cr-LDH-PW11Ni, is stable to leaching and can be readily reused for up to ten cycles without obvious loss of its activity.