Decontamination Performance Of Mustard Gas Simulant In POMs/H₂O₂ Systems

Mustard gas（HD）is notorious for its use in war,and its persistent toxicity poses a great threat to human beings.Destroying large stockpiles of HD is important for the safety of people and the environment.For a long time,A large number of small molecular size polyoxometalates（POMs）are used as catalysts for the oxidative degradation of HD and its simulants.Although they show certain catalytic activity and selectivity in organic solvents,they are faced with the difficulties of insufficient exposure of active sites,high price of organic solvents and environmental pollution during the degradation process.Keplerate-type POMs have a large surface area and full exposure of active sites.Based on this,we synthesized a series of materials.These materials can efficiently and selectively oxidize the HD simulant 2-chloroethyl ethyl sulfide（CEES）to the non-toxic 2-chloroethyl ethyl sulfoxide（CEESO）instead of the more toxic 2-chloroethyl ethyl sulfone（CEESO₂）in an environmentally friendly and economical H₂O₂/H₂O solution.At the same time,a series of comparative experiments were designed to explore the key factors affecting the catalytic performance of POMs by taking advantage of the adjustable composition and structure of POMs.The main results obtained are as follows:1.Two Keplerate type POMs were compared:{Mo₁₃₂-L}（L=Ac-,）showed different catalytic performance in the catalytic degradation of CEES in H₂O₂aqueous solution due to different ligands.By controlling the mole ratio of{Mo₁₃₂-L}L=Ac-,)to H₂O₂,CEES are selectively oxidized to the non-toxic CEESO instead of the more toxic CEESO₂.The experimental results showed that{Mo₁₃₂-}with more negative charge showed stronger catalytic activity under other conditions.The catalytic degradation processes of CEES by{Mo₁₃₂-Ac^-}and{Mo₁₃₂-}are first-order reactions,and the kinetic constants of the reactions are 0.39 and 0.60 min^-1,respectively.After the addition of H₂O₂,the oxidation peaks in CV curves of both catalysts shift negatively,indicating the formation of active intermediates{Mo₁₃₂-L}*（L=Ac-,）,which are the driving force for CEES to choose oxidation as CEESO.The first conversion of{Mo₁₃₂-Ac^-}and{Mo₁₃₂-}were 98.59%and 99.69%,respectively.After 5 cycles,the conversion was 98.59%and90.02%,respectively.The selectivity was>99%.2.Using green and economical H₂O as solvent and H₂O₂as oxidant,the catalytic degradation of CEES by{Mo₇₂M₃₀}（M=V,Cr,Fe,Mo）nanoclusters was compared under different reaction conditions.The experimental results show that CEES can be selectively oxidized to non-toxic CEESO instead of more toxic CEESO₂by controlling the molar ratio of H₂O₂and CEES.Under the same degradation conditions,{Mo₇₂M₃₀}（M=V,Cr,Fe,Mo）catalyzed degradation of CEES is a first-order reaction,and the kinetic constants of the reaction are 0.58,0.54,0.49 and 0.44 min^-1,respectively.The results showed that the catalytic activity of the four compounds was affected by the nodal metals.The response sequence is V>Cr>Fe>Mo.The corresponding conversion rates of the four catalysts were 99.82%,99.74%,99.73%and98.45%after the first reaction for 10min.The conversion and selectivity of the four catalysts were all>98%and>99%after 5 cycles.3.Keplerate-type POMs represented by{Mo₇₂Fe₃₀}is soluble in H₂O₂aqueous solution.The catalyst is recovered by evaporation of the solvent.Washing the catalyst in cold water also results in its loss.In order to change the current situation that Keplerate type POMs catalyst is difficult to recover and purify,using H₃PW₁₂O₄₀and H₅PMo₁₀V₂O₄₀as templates,two new water-insoluble materials were synthesized:PW₁₂{Mo₇₂Fe₃₀}and PMo₁₀V₂{Mo₇₂Fe₃₀}.The catalytic type of the two catalysts for degradation of CEES in H₂O₂aqueous solution is heterogeneous,but they have similar catalytic activity to{Mo₇₂Fe₃₀}with homogeneous catalysis and are easier to recover and purify.The experimental results showed that CEES can be oxidized to CEESO selectively by PW₁₂{Mo₇₂Fe₃₀}and PMo₁₀V₂{Mo₇₂Fe₃₀}as catalysts and by controlling the amount of H₂O₂.The catalytic degradation processes were all first-order reactions with kinetic constants of 0.58 and 0.39min^-1,respectively.PW₁₂{Mo₇₂Fe₃₀}(or PMo₁₀V₂{Mo₇₂Fe₃₀})has stronger catalytic activity than the mixture of PW₁₂(or PMo₁₀V₂)and{Mo₇₂Fe₃₀}in equal quantities.The excellent catalytic performance of PW₁₂{Mo₇₂Fe₃₀}(or PMo₁₀V₂{Mo₇₂Fe₃₀})depends on the highly ordered structure between PW₁₂(or PMo₁₀V₂)and{Mo₇₂Fe₃₀}.The first conversion of PW₁₂{Mo₇₂Fe₃₀}and PMo₁₀V₂{Mo₇₂Fe₃₀}were 98.47%and 98.72%,respectively.The conversion and selectivity of the two materials were>96%and>99%after 5 cycles.4.The composite{Mo₇₂V₃₀}@MIL-100（Fe）was synthesized by in situ synthesis using Keplerate POMs:{Mo₇₂V₃₀}as template.Elemental analysis shows that{Mo₇₂V₃₀}has a loading capacity of 3%.Using water as solvent and H₂O₂as oxidant,the effects of MIL-100（Fe）and{Mo₇₂V₃₀}@MIL-100（Fe）dosage,H₂O₂dosage and reaction time on the catalytic degradation of CEES were systematically compared.The results showed that the degradation of MIL-100（Fe）,{Mo₇₂V₃₀}@MIL-100（Fe）to CEES was in line with first-order reaction.The kinetic constants of MIL-100（Fe）and{Mo₇₂V₃₀}@MIL-100（Fe）degradation reactions were 0.37 and 0.49min^-1,respectively.After loading{Mo₇₂V₃₀},MIL-100（Fe）showed stronger catalytic activity due to the synergistic effect of the two materials.Both catalysts are difficult to dissolve in water and can be reused after filtration and washing.The first conversion of MIL-100（Fe）and{Mo₇₂V₃₀}@MIL-100（Fe）were 99.45%and 98.59%,respectively.The conversion and selectivity of both catalysts are>96%and>99%after 5 cycles.5.In order to systematically compare the catalytic activity of POMs@MOFs materials containing different counteractive cations in the degradation of CEES,and considering the excellent catalytic performance of Ag⁺in the process of catalytic degradation of CESS,we replaced part of Na⁺in Na₅PMo₁₀V₂@HKUST-1 with Ag⁺to synthesize the new material:Ag_2.7Na_2.3PMo₁₀V₂@HKUST-1.The catalytic activity of the two materials for the degradation of CEES in H₂O₂aqueous solution was systematically compared.The experimental results show that the degradation of CEES by Na_2.3PMo₁₀V₂@HKUST-1 and Ag_2.7Na_2.3PMo₁₀V₂@HKUST-1 accord with the first order reaction,and the kinetic constants of the reaction are 0.11 and 0.21min^-1,respectively.It is proved that the addition of Ag⁺can show enhanced catalytic activity for CEES degradation.The first conversion of Na₅PMo₁₀V₂@HKUST-1 and Ag_2.7Na_2.3PMo₁₀V₂@HKUST-1 were 76.98%and 93.57%,respectively.After 5 cycles,the corresponding conversion was67.03%and 91.74%,respectively,and the selectivity was>99%.