Catalytic Peroxide Oxidation Of Chlorophenol In Aqueous Solution In Presence Of Fe₃O₄ Nanoparticles Or Its Composites

Along with the development of the society and economy,the demand of the water resource becomes greater.On the other hands,the water pollution is still deteriorating,which is a critical threat for human health,leading to the aggravation of the water resource shortage.Therefore,development of the efficient water treatment technology is significant for relief of the water crisis and improvement of the water environment.Heterogeneous Fenton oxidation technology has high efficiency for the organic contamination removal.However,harsh reaction conditions and inefeciency of catalysts are the main drawback.In this paper,a serias of novel nanomaterials were synthesized as heterogeneous catalysts in order to solve the problems existed in the Fenton oxidation technology.The catalytic capacity of these catalysts was evaluated through the experiemnts carried out at near neutral condition?pH 5.0?.And then,the feasibility using sulfate radical oxidation technology as an alternative technology for Fenton technology was investigated.Some creative results were obtained.Using Fe₃O₄ nanoparticles as heterogeneous catalysts,its performence of H₂O₂decomposition for 4-chlorophenol removal was assessed at pH 5.0.The results showed that 4-chlorophenol can be oxidized completely in the Fe₃O₄/H₂O₂ system.The removal efficiency of 4-chlorophenol was up to 96.8%and the concentration of dissolved iron ion was only about 2 mg/L as the reaction finished.The addition of the radical scavenger lead to the decline of the 4-chlorophenol removal efficiency.In the successive repeated experiments,the removal efficiency of 4-chlorophenol was down to91.8%in 5^thexperiment when 96.8%in 1^stexperiment,while the removal efficiency of TOC was down to 42.7%when 48.7%in 1^stexperiment.Both of the results demonstrated the good stability and reusability of the Fe₃O₄ nanoparticles.To solve the low catalytic capacity of the Fe₃O₄ in Fenton system,Fe₃O₄-Au nanocomposites were designed and synthesized as Fenton catalysts.The catalytic capacity of the as-synthesized solids was higher than Fe₃O₄.Additionally,comprehensive consideration of the cost and catalytic performance,the optimal Au content in the nanocomposites was 1%in weight.The activation energy of Fe₃O₄-Au/H₂O₂ system was 23.18 kJ/mol,far lower than the Fe₃O₄/H₂O₂ system.Meanwhile,metal ions were in absence in the solution after the catalytic experiment.After 8successive reactions,the 4-chlorophenol removal efficiency during the 4 h was down to90.5%from the 94.6%in 1^stexperiment,which exhibited the high stability of the Fe₃O₄-Au nanocomposites.Fe₃O₄-Ag nanocomposites were prepeared by means of the method with some modification of the Fe₃O₄-Au synthesis method for H₂O₂ catalytic decomposition.The results showed that the catalytic property of Fe₃O₄-Ag is much higher than Fe₃O₄-Au.However,the results were induced by the dissolution of the Ag.On the other hands,as a disinfectant,Fe₃O₄-Ag can make the bacterials death rapidly and efficiently.Moreover,no dissolved Ag ion appeared in the solution.Its reusability eliminated the subsequent risk of Ag particles.Due to the high cost of the Fe₃O₄-Au nanocomposites,Fe₃O₄-MnO₂ core-shell nanocomposites were synthesized by means of the reaction between Fe?OH?₂ and KMnO₄ as Fenton catalysts.The as-synthesized nanocomposites can make the H₂O₂decomposed efficiently to oxidize the 4-chlorophenol.And then,the composites with Fe/Mn molar ratio of 6:1 had the highest catalytic capacity,which demonstrated the synergetic effect existed between Fe₃O₄ and MnO₂.The active energy of the Fe₃O₄-MnO₂/H₂O₂ was 30.42 kJ mol^-1,lower than the Fe₃O₄/H₂O₂ system.Next,the Fe₃O₄-MnO₂ were applied to activate the Potassium peroxymonosulfate for the 4-chloropehnol removal to overcome the drawbacks of Fenton reaction including low reation rate,high dosage of the oxidant and pH adjustment.According to the experimental results,4-chlorophenol can be degradated completely in the Fe₃O₄-MnO₂/Oxone system.The catalytic capacity of Fe₃O₄-MnO₂ towards potassium peroxymonosulfate was higher than MnO₂.At the same time,the nanocomposites with Fe/Mn molar ratio of 4:1 had the highest catalytic activity.The successive experiments revealed the chemical and catalytic stability of Fe₃O₄-MnO₂.In comparison with previous catalytic systems,Fe₃O₄-MnO₂/Oxone had the higher degradation efficiency and was close to the practical engineering.In addition,Fe₃O₄-MnO₂ core-shell nanocomposites were used as oxidants and adsorbents for the removal of As?III?in aqueous solution.The results showed the nanocomposites with Fe/Mn molar ratio of 3:1had the highest saturated adsorption capacity,up to 80.40 mg/g.The adsorption kinetic was fitted well with the pseudo-second-order kinetic model.According to the XPS analysis,the As?III?adsorbed on the surface of was oxidized to As?V?.Above of all,application of heterogeneous catalysis technology in presence of nanocomposites for the removal of typical organic contaminants such as chlorophenol has broad prospects and is an efficient way to solve the environmental pollution,which should be studied entensively in future.