Controllable Preparation Of Magnesium Peroxide And Its Degradation Performance Towards Organic Pollutants

With the rapid developments of industry and economy in recent decades,organic pollution in water and soil has become increasingly worse,which seriously threatens human health and the balance of environmental ecosystem.Thus,it is urgent to develop efficient,inexpensive and environmentally friendly technologies to remove these organic pollutants in environmental media.The Fenton/Fenton-like reaction can produce active oxygen species with strong oxidizing properties,and has high efficiency,low cost,and easy operation which is widely used in the treatment of various organic pollutants.However,in the conventional Fe²⁺-H₂O₂ Fenton system,H₂O₂ has poor stability,is easy to decompose,and can only work under acidic conditions,which greatly limits the practical application of Fenton reaction.Magnesium peroxide（MgO₂）,as a solid oxidant,has the advantages of good stability,environmental friendliness and high active oxygen content,making it an ideal oxidant in Fenton-like reactions.In this paper,the morphology controllable preparation of MgO₂ was the breakingthrough point and two-step and one-step methods were used to synthesize MgO₂ with different morphologies.The influence of process parameters on the morphology and microstructure of MgO₂ was investigated,and the performance of its degradation of organic pollutants was also explored.The details are as follows:（1）Magnesium peroxide with different morphologies were prepared by a two-step method.MgO rods,cubes and flowers were synthesized firstly by precipitation and hydrothermal methods using different magnesium salts and precipitating agents,respectively.Then,the isomorphic transformation of MgO was used to synthesize the corresponding morphology of MgO₂ under the oxidation of hydrogen peroxide（H₂O₂）.The morphology and microstructure of the obtained products were determined by XRD,SEM and TEM techniques.The research results indicated that rod,cube and flower MgO₂ were successfully synthesized.The order of the specific surface area of the three morphologies of MgO₂ was flower MgO₂>rod MgO₂>cube MgO₂.The order of active oxygen content of the three morphological MgO₂ samples was rod MgO₂>flower MgO₂>cube MgO₂.By controlling the oxidation time,the formation mechanism of MgO₂ was explored.The results showed that MgO first interacted with H₂O to form a hydrated MgO intermediate（MgOH⁺）,which was then oxidized to MgO₂by H₂O₂.（2）Flower-like magnesium peroxide（MgO₂）was synthesized through a facile one-step precipitation method.The effects of magnesium salt,reaction temperature,precipitant and surfactant on the morphology and structure of MgO₂ were systematically investigated.The results displayed that flower-like MgO₂ with a specific surface area of up to 385 m²/g using MgSO₄ as magnesium salt and ammonia as precipitant were prepared.The results of potassium permanganate titration experiment indicated that the active oxygen content of the flower-like MgO₂ sample was 24.10%.The analysis suggested that the chelation and steric hindrance of SO₄^2-were the key factors for the formation of flower-like morphology,and the bidentate coordination between CH₃COO^-and metal ions leaded to the flaky assembly of particles.The ionization rate of the precipitant was too fast,which resulted in a fast nucleation rate,leading to the formation of small nano-particles.The addition of 5%disodium citrate could improve the dispersibility of flower-like MgO₂.The increase of temperature caused the acceleration of the nucleation rate,which in turn leaded to the destruction of the flower-like MgO₂ morphology.（3）Methylene blue（MB）and tetracycline（TC）were chosen as pollution models,respectively,to explore the oxidative degradation performance of the prepared MgO₂towards organic pollutants.It was found that 5 mg of rod MgO₂ can degrade 98.7%of MB within 25 minutes under the catalysis of Fe³⁺.Among the three morphologies of MgO₂,rod MgO₂ exhibited the most excellent degradation performance due to its higher active oxygen content and specific structure.10 mg of flower-like MgO₂prepared by the one-step method can effectively degrade 90%of tetracycline within 60minutes under the catalysis of Fe³⁺.ESR tests and radical quenching experiments suggested that hydroxyl radicals were the main reactive oxygen species.Moreover,the column filled with flower-like MgO₂ could quickly and efficiently eliminate TC,and the degradation efficiency could still be up to 90%even after twenty consecutive runs.Additionaly,it could solve the problem of metal ions（magnesium and iron）leacking.Besides,High performance liquid chromatography（HPLC-MS）was utilized to measure the intermediate products produced in the TC degradation process to indentify the path of TC degradation.