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

Abstract

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.