Sulfate Radical Mediated Degradation Of Organic Pollutants By Manganese Oxide Octahedral Molecular Sieve (OMS-2) Activation Of Peroxymonosulfate

In the 21st century,the fast expansion of industrialization has resulted in severe environmental problems,and human bodies and living conditions are being threatened by the increasingly produced refractory organics.Advanced oxidation processes（AOPs）has been applied in removing refractory organic pollutants owing to its effectiveness and the property of rapid degradation of pollutants.In fact,the main functioned groups are sulfate radical(SO₄^·-)and hydroxyl radical（HO^·）in AOPs.Activation of peroxymonosulfate（PMS）has been concentrated on degrading refractory organic pollutants owing to the generation ofSO₄^·-with high standard redox potential,which is being the substitute ofHO^·.In this study,manganese oxide octahedral molecular sieve（OMS-2）with cryptomelane type was synthesized by one-pot hydrothermal method and used to activate PMS for the degradation of phenol and methylene blue（MB）.Field emis sion scanning electron microscope（FESEM）,X-ray power diffraction（XRD）patterns,Fourier transform infrared（FT-IR）spectroscopy,X-ray photoelectron spectroscopy（XPS）,and N₂ adsorption/desorption isotherms were carried out to characterize the as-prepared composite.The effects of PMS concentration,OMS-2 dosage,initial pollutant concentration,initial pH,and chloride（Cl^-）on the degradation of phenol were elaborately investigated.As a result,the best concentration of PMS and dosage of OMS-2 was 0.6 g/L when 20 mg/L phenol was degraded.With the increase of phenol concentration,the required catalysts and oxidants also increased.When the initial pH varied from 3 to 9,phenol can be also completed degraded by PMS/OMS-2process.LowerCl^-（0.5 Mm）exerted adverse influence on the phenol degradation,however,the phenol degradation can be promoted when theCl^-increased from 2.0to 20 mM.In addition,the phenol degradation in PMS/OMS-2 system was fitted well by the pseudo-first-order kinetic model and the reaction rate constants were 0.129,0.160,0.196,0.202,0.225 min^-1,respectively.And the correlation coefficents are all more than 0.99.Moreover,the mineralization of phenol also was evaluated through the variations of total organic carbon（TOC）and three-dimensional excitation emission matrix（3D-EEM）spectroscopy.The TOC removal（20 mg/L phenol）was up to 85.2%within 30 min.The electron spin resonance（ESR）spectra confirmed the existence ofSO₄^-·andHO^·,and the comparative experiments using tertbutyl alcohol（TBA）and ethanol as radical scavengers suggested that bothSO₄^-·andHO^·took part in the degradation of phenol andSO₄^-·was more significant thanHO^·.In addition,the intermediates were detected by gas chromatography and mass spectrometry（GC-MS）.The main intermediates were acetic acid,crotonic acid,catechol and hydroquinone,and the proposed degradation pathway of phenol was identified.In the end,the degradation of phenol in real water（Xiangjiang river and sewage water）and the stability of OMS-2 were investigated.Compared with the original PMS/OMS-2 system,the degradation of phenol in real water was slower.But the phenol degradation could come up to 93.4 and 90.5%within 80 min.When OMS-2was reused for fourth time,the degradation of phenol（20 mg/L）induced by PMS/OMS-2 still reached to 88.2%within 30 min.The fine organics degradation efficiency and the nice stability after continuous use indicated the possible application of a novel AOPs PMS/OMS-2 in real organic wastewater treatment.