Heterogeneous Activation Of Peroxymonosulfate Using Mn-Fe Layered Double Hydroxide:Performance And Mechanism For Organic Pollutant Degradation

Advanced oxidation processes?AOPs?,as a competitive alternative to industrial wastewater treatment,have attracted immense interests in recent decades,because of their high degradation efficiency for refractory organic pollutants.In the process,the oxidizing free radicals with high standard oxidation-reduction potential are the key to the degradation of organic pollutants,such as sulfate radicals and hydroxyl radicals.Peroxymonosulfate?PMS?,for its environmental friendliness,high safety and good stability,is frequently used to produce sulfate radicals and hydroxyl radicals,which need to be activated.It has great potential in the degradation of organic pollutants and is widely used.Among those activation agents,transition metal was widely used for its simple operation and low running cost as well as high efficiency.Previous studies were mainly focused on using Cobalt-based catalysts due to its high activation efficiency,such as Co₃O₄/GO and FeCo-LDH,whereas leading to a potential but serious risk to environment.To avoid this risk,the use of mixed metal catalysts of iron and manganese to activate PMS has been extensively investigated due to their cheapness,relatively non-toxic and environmental friendliness.Mn-Fe layered double hydroxide?MnFe-LDH?was primarily synthesized in this research by simple co-precipitation and subsequently utilized as an effective catalyst for peroxymonosulfate?PMS?to degrade organic pollutants.The common azo industrial dye,acid organic 7?AO7?was chosen as a targeted recalcitrant organic contaminant to evaluate the catalytic properties of the MnFe-LDH.?1?MnFe-LDH with different metal ratios was synthesized by coprecipitation method and analyzed by XRD,FT-IR,SEM and EDS.The catalytic performance was demonstrated by system degradation experiments,which showed that the structure of MnFe-LDH?1:1?and the catalytic performance of PMS were the best.?2?The experimental results testified that MnFe-LDH could act as an efficient PMS activator.The degradation efficiency of AO7 can reach 97.56%within 30 min when the concentrations of catalyst and PMS were both 0.20 g/L,the AO7concentration was 20 mg/L,the initial pH was 6.10 and the reaction temperature was25°C.The AO7 degradation process followed the pseudo-first-order kinetic well with an activation energy of 21.32 kJ/mol.?3?The prepared MnFe-LDH displayed high reusability and excellent stability,which can be recycled at least five times,further to confirm its actual application potentials.?4?The high-oxidative ability of resulting SO₄·^-and·OH was the crucial reason for the increase in AO7 degradation rate in MnFe-LDH/PMS system,which could be confirmed by ESR and quenching tests.?5?Based on the UV-vis spectrum and GC-MS analysis of intermediates,the probable pathways of AO7 degradation were presented,involving the cleavages of azo bonds,the generations of phenyl and naphthalene products,the openings of rings and the formations of small molecular compounds.