The Degradation Performance Of MgO₂-based Fenton-like Systems Towards Organic Contaminants

With the rapid development of the textile,paper,pharmaceutical and other industries,the discharge of a large amount of wastewater containing organic pollutants posed a huge threat to human health and the ecological environment.Therefore,it is urgent to develop the treatment technology of organic-containing wastewater.Fenton/Fenton-like reaction,as an advanced oxidation technology,can produce active oxygen species with strong oxidizing capacities,which has the advantages of high efficiency,economy,and easy handling,so it is considered as an effective treatment for the degradation of organic pollutants.For the traditional Fenton reaction,liquid hydrogen peroxide(H₂O₂)is usually used as an oxidant.However,H₂O₂ has poor stability and is easy to decompose and needs to work under acidic condition(pH=2-4),which makes the application of Fenton reaction extremely limited.In this thesis,solid magnesium peroxide(MgO₂)nanoparticles were prepared as a substitute for liquid H₂O₂ and used in Fenton-like reaction system to degrade organic pollutants.The degradation performance of MgO₂ nanoparticles as Fenton-like oxidant under the activation of Fe³⁺and MgNCN/MgO composites towards organics was systematically studied.The specific research contents are as follows:(1)MgO₂ nanoparticles were prepared through the direct peroxidation of magnesium oxide(MgO)nanoparticles and H₂O₂,and used as a Fenton-like oxidant to degrade organic pollutants.The structure and morphology of as-prepared MgO₂ were characterized by XRD,FTIR,SEM and HRTEM.The potassium permanganate titration result showed that the active oxygen content of MgO₂ was as high as 26.93 wt%,which was close to the theoretical active oxygen content(28.57 wt%),indicating a high purity of as-prepared MgO₂.The degradation performance of MgO₂-Fe³⁺Fenton-like system towards organic pollutants was systematically studied by changing the amounts of MgO₂,and Fe³⁺,initial solution pH and different organic pollutants.The result showed that MgO₂-Fe³⁺Fenton-like system could effectively degrade organic pollutants in water.10mg of MgO₂ nanoparticles could almost completely degrade200 m L of 20mg/L methylene blue(MB)within 30 minutes,and the total organic carbon(TOC)removal rate reached 70.2%.Electron paramagnetic resonance spectroscopy(EPR)test and free radical scanveger experiment confirmed that hydroxyl radicals(·OH)were the main active species for degradation of organic pollutants.(2)MgO₂ nanoparticles were prepared through one-pot precipitation method using magnesium nitrate as magnesium source,ammonia as precipitant,and H₂O₂ as oxidant.In addition,the mixture of basic magnesium carbonate and thiourea were calcined at 550°C to prepare MgNCN/MgO composites.XRD,FTIR,SEM and TEM were used to characterize the structure and morphology of the prepared MgO₂ and MgNCN/MgO composites.The degradation performance of the novel MgO₂-MgNCN/MgO Fenton-like system under different experimental conditions was investigated.The result showed that 20mg of MgO₂and 10mg of MgNCN/MgO composites could almost completely degrade 100 m L of 10mg/L MB solution within 8 hours.Moreover,the MgO₂-MgNCN/MgO Fenton-like system could effectively degrade MB in wide pH(4-12)and temperature(5–35°C)ranges.The results of electron paramagnetic resonance spectroscopy test and free radical quenching experiment disclosed that·OH were the main free radicals produced in MgO₂-MgNCN/MgO Fenton-like system for the degradation of organic pollutants.