Mechanism And Efficiency Of Organic Pollutants Degradation By Activated Persulfate Using Fe/Mn Material

Advanced oxidation processes?AOPs?based on sulfate radicals?SO4-·?gradually become a popular new method to remove refractory organic pollutants.This method has broad prospects for application because of the high oxidation potential,stability of oxidants and limited effect of pH.The key of AOPs based on persulfate is the production of SO4-· by activating persulfate.Among various activating methods,homogeneous activation by transition metal has obvious advantages for its low power consumption and low technical difficulty.However,the introduction of the transition metal ions is easy to cause the secondary pollution,so the preparation of activator which is cheap,easy-to-get and no secondary pollution has become trend.Iron and manganese element are rich reserves in earth crust,the raw materials are easy to get,and the risk of secondary is low,thus,the development of heterogeneous activation of Fe and Mn is important for the removal of refractory organic pollutants in wastewater.Based on these facts,this study developed a series of Fe/Mn activation materials built the AOPs to remove aniline and phenol by Fe/Mn activation materials activating persulfate.Meanwhile,the mechanism and efficiency of these methods were studied systematically.The main contents include:?1?This study aimed to explore the optimum reaction concentrations of Fe2t and persulfate for efficient aniline degradation,and observe the influence of common groundwater ions on aniline degradation.Under the optimum operating conditions,86.33%aniline degradation?C0=11 mmol/L?was observed within 60 min.the optimum Fe²⁺ and PS concentrations were 3.3 and 4.4 mmol/L,respectively.An inhibitory effect was found with the addition of CO32-,PO43-,SO42-,HCO3-and NO3-.The order of the inhibition was PO43->CO32->>SO42->HCO3->>NO3-.Cations(Na+,K+,Mg²⁺ and Ca²⁺)common in water also had minimal and negligible effects on the degradation efficiency of aniline.Compared with the ions existed individually,the inhibition of ions existed in real aquatic environment has stacking effect.?2?Fe₃O₄ magnetic nanoparticles?MNPs?were prepared through liquid-phase co-precipitation method and characterized using transmission electron microscopy?TEM?and X-ray diffraction?XRD?for their shape and structure.The prepared Fe₃O₄ MNPs are quasi-spherical with diameters of 10-30nm.The target contaminant PNA can be effectively destroyed by Fe₃O₄ MNPs activating persulfate.Within 300 min of reaction time,the removal rate of PNA and the mineralization rate was almost 100%and 67%,respectively,at an initial PS dose of 8.0 mmol/L in the presence of 5.32 g/L Fe₃O₄ at pH = 7.0 ± 0.2 and T = 25?.Moreover,the Fe₃O₄ MNPs catalysts could be reused for four times.The results show that the degradation of PNA follows the pseudo-first-order kinetics.The apparent rate constant of PNA degradation was 0.0176min-1 at the above condition.?3?Fe⁰@Fe₃O₄ composites were prepared by gas-solid reaction method.The results showed that the Fe⁰@Fe₃O₄ composites could effectively activated persulfate to remove PNA in water.Compared with the system of Fe₃O₄/PS,the removal efficiency of PNA in Fe⁰@Fe₃O₄/PS system increased over 90%.At the initial condition of PS dose 30mmol/L,Fe⁰@Fe₃O₄ composites dose 0.05g/L and T=25?,the degradation efficiency of PNA was 100%after 180 min.The results show that the degradation of PNA follows the pseudo-first-order kinetics.The apparent rate constant of PNA degradation was 0.02898min-1 at the above condition.Quenching tests and electron paramagnetic resonance were conducted,and the results revealed that both hydroxyl radical and sulfate radical were responsible for the degradation of PNA in the Fe⁰@Fe₃O₄ composites activated PS system.The mechanism of Fe⁰@Fe₃O₄/PS system was elucidated.Introduction of Fe⁰@Fe₃O₄ composites as a activator in PS activation system achieve the rapid regeneration of Fe???on the surface of Fe₃O₄,and enhance the activating efficiency of Fe₃O₄.?4??-MnO₂ nanowires were synthesized in a hydrothermal process.These nanowires efficiently activated persulfate for 2,4-dichlorophenol oxidation.The maximum removal efficiency of 2,4-DCP and TOC were 90.2%and 62.37%at 20.0 mM PS,given 0.2 g/L a-MnO₂ nano wires,and under a temperature of 30.0.The half-time of 2,4-DCP was 18.1 min under the condition mentioned above.A novel?kinetic model was established to describe the deterioration of the contaminant.The ?-MnO₂ nanowires exhibited relatively stable catalytic activity after five instances of reuse,and the removal efficiency of 2,4-DCP was 81.2%.Quenching tests and electron paramagnetic resonance were conducted.and the results revealed that both hydroxyl radical and sulfate radical were responsible for the degradation of 2,4-DCP in thea-MnO₂ activated PS system,and the amount of radicals increased with time extend.?5?To reuse and recycle ?-MnO₂ in engineering,this study improved the traditional hydrothermal synthesis method,and prepared the Fe₃O₄/a-MnO₂ nano wires composites.The results revealed that Fe₃O₄/a-MnO₂ composites could efficiently activate persulfate for 2,4-dichlorophenol oxidation.The maximum removal efficiency of 2,4-DCP was 96.3%at 30.0 mM PS,given 0.4 g/L Fe₃O₄/a-MnO₂ composites,and under a temperature of 30.0?.The Fe₃O₄/a-MnO₂ composites exhibited relatively stable catalytic activity after four instances of reuse,and the removal efficiency of 2,4-DCP was as high as 94.5%.The half-time of 2,4-DCP was 26.1 min under the condition mentioned above.The results show that the degradation of 2,4-DCP follows the novel kinetics that Moreover,the mechanism of Fe₃O₄/?-MnO₂ coMposites/PS system was elucidated.