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

The Keggin-type mono-transition-metal-substituted [PW ₁₁ M(H ₂ O)O ₃₉ ] ⁵⁻ (PW ₁₁ M, M = Ni, Co, Cu) were intercalated into Zn ₂ Cr-based layered double hydroxide (Zn ₂ Cr-LDH) by an exfoliation-reassembly method and the synthesized Zn ₂ Cr-LDH-PW ₁₁ M composites were thoroughly characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), solid state ³¹ P nuclear magnetic resonance ( ³¹ P 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 PW ₁₁ M cluster and Zn ₂ Cr-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 Zn ₂ Cr-LDH-PW ₁₁ M is significantly influenced by the substituted transition metals, showing the order: Zn ₂ Cr-LDH-PW ₁₁ Ni > Zn ₂ Cr-LDH-PW ₁₁ Co > Zn ₂ Cr-LDH-PW ₁₁ Cu. Under ambient conditions, the Zn ₂ Cr-LDH-PW ₁₁ Ni composite can convert 98% of CEES in 3 h using nearly stoichiometric 3% aqueous H ₂ O ₂ with the selectivity of 94% for the nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO). Moreover, the decontaminating material, Zn ₂ Cr-LDH-PW ₁₁ Ni, is stable to leaching and can be readily reused for up to ten cycles without obvious loss of its activity.