Preparation Of Fe₃O₄ Nanodispersions By High Gravity Technology For Catalytic Degradation Of PET

Magnetic nanomaterials have attracted wide attentions from researchers in recent years because of their unique magnetic property and tremendous application potentials.Among magnetic nanomaterials,Fe3O4 has become an important magnetic inorganic nanomaterial because of its simple synthesis process,excellent chemical properties,and wide application fields.However,traditional Fe3O4 nanopowders normally have severe aggregation problems due to the surface effect and magnetic properties,which greatly affect its properties and limits its applications.In contrast,Fe3O4 nanoparticles with good dispersibility usually show excellent physicochemical properties and have a range of advantages in terms of stability,bio-compatibility and magnetic responsiveness.Therefore,it is an important prerequisite for its wide applications to prepare Fe3O4 nanoparticles with controllable morphologies,sizes and good dispersion stability.In view of this,dispersions of monodispersed hydrophobic Fe3O4 nanoparticles and dispersions of hydrophilic Fe3O4 nanoparticles were prepared by high-gravity rotating packed bed(RPB)in this paper.The effects of different process parameters on the phase,morphology,size and dispersion of the final product were investigated.In addition,the application performance of Fe3O4 nanodispersions on catalytic degradation of PET was further explored.The main contents and results of the full text are as follows:1.The dispersions of monodispersed hydrophobic Fe3O4 nanoparticles were successfully prepared by high-gravity air oxidation-precipitation in a rotating packed bed reactor combined with a solvothermal method.In this method,FeCl2·4H2O was selected as the iron source and NaOH as the alkali source,and the effects of different process conditions on the final product were investigated.The research results showed that the addition amount of NaOH can affect the degree of oxidation of the reaction system and the formation path of the product in the oxidation-precipitation stage,thereby affecting the product phase.In addition,in the solvothermal stage,monodispersed Fe3O4 nanoparticles with uniform morphology and size can be prepared by using oleic acid as a modifier,but the proportion of excess alcohol or water in the reaction solution is not beneficial to the dispersion of nanoparticles.The optimal process conditions were finally obtained as follows:the addition amount of NaOH was 60 mmol,the molar ratio of Fe2+ and OH-was 1:2,the addition amount of oleic acid was 1.2 mL(m(oleic acid)/m(Fe3O4)=45%),a mixed solution of ethanol and water was used during solvothermal stage and the ratio of ethanol and water was 1:1,the rotating speed of RPB was 500 rpm.Under optimal conditions,the product obtained is pure Fe3O4 with a spherical shape and a uniform particle size of about 11 nm.It can be stably dispersed in low-polar solvents such as cyclohexane.It is superparamagnetic at room temperature with a saturation magnetization of 45 emu/g.Compared with stirring tank reactor(STR),RPB has a shorter reaction time and a higher efficiency.2.The dispersions of hydrophilic Fe3O4 nanoparticles were prepared with compound a as the dispersant by the high-gravity co-precipitation method.The effects of different reaction conditions on the final product were investigated.The optimal process conditions were finally obtained:the addition amount of FeCl2·4H2O was 15 mmol,the molar ratio of Fe2+and Fe3+was 1:2,the mass fraction of NH3·H2O solution was 10%,and the addition amount of A was 0.28 g,the temperature of water bath was 90?,the rotating speed of RPB was 500 rpm.The as-prepared hydrophilic Fe3O4 nanoparticles had a uniform particle size.The Fe3O4 nanoparticles with an average size of 10 nm were prepared by modification after nucleation,and the nanoparticles with an average size of 5 nm were prepared by in-situ modification.The modification time is 1 h.In addition,the hydrophilic Fe3O4 nanoparticles can be magnetically separated by destroying its electrostatic balance,and the separated Fe3O4 nanoparticles can still be redispersed in water after washing.Compared with STR,RPB has the product with a smaller size and higher production efficiency.3.The application property of Fe3O4 nanodispersions as a catalyst on the degradation of PET was investigated.The effects of different reaction conditions on the degradation of PET were explored.The results showed that the glycol glycolysis process of PET can be accelerated,and the conversion percentage of PET can be improved by using Fe3O4 nanodispersions as catalyst.The optimal reaction conditions were finally obtained:the mass ratio of Fe3O4 to PET was 2%and the mass ratio of EG to PET was 13.The conversion of PET can reach to 100%when the degradation condition was 210? for 30 min or 220? for 15 min.Furthermore,the investigation of recycling performance of Fe3O4 nanoparticles showed that the conversion percentage of PET is still 100%when it is recycled for 5 times under optimal reaction conditions.