Continuous Preparation Magnetic Iron Tetroxide Nanoparticles In A Microtubule Reactor And Their Application

Iron tetroxide nanoparticles(Fe3O4 NPs)have been widely used in many fields.Among the preparation methods of Fe3O4 NPs,the coprecipitation method is favored by many researchers because of its simplicity and feasibility,but it also has some disadvantages such as particle agglomeration and wide particle size distribution.Microchannel reactors can enhance the heat and mass transfer of materials to make it possible to control the particle size,shape,size distribution and particle agglomeration.The development on the continuous synthesis of Fe3O4 NPs in the microchannel reactor can help solve the problems in the process of Fe3O4 preparation by co-precipitation,and lay the foundation for the realization of industrial continuity.In this paper,Fe3O4 NPs is synthesized continuously by co-precipitation synthesis using a microtubule-reactor device,and the effects of various reaction conditions and surfactants on particles size are investigated.And then the prepared particles are applied to the preparation of water-based magnetic fluids with good stability.The main research contents and results are as follows:Firstly,a simple micro-tube reactor is designed to synthesize Fe3O4 NPs by chemical co-precipitation using pH-adjusted iron sulfate[Fe2(SO4)3]and ferrous sulfate(FeSO4)as raw materials,water as solvent and sodium oxide(NaOH)as precipitant with the product being protected by nitrogen and the fluid flow being improved by nitrogen agitation.During the process,reactants are not blocked.The influence of.reaction conditions such as helical diameter of the reactor,reaction temperature,reactant concentration,flow ratio between Solution A and Solution B,reactant velocity and deposition time on the particle size of the synthesized particles are investigated.As the helical diameter of the reactor is increased,the size of NPs increases.When the reaction temperature is increased,the particle size of NPs decreases.As the flow rate ratio between Solution A and Solution B is increased,the particle size decreases firstly and then increases.The concentration and velocity of reactants have no significant effects on NPs particle size under experimental conditions.Fe3O4 NPs with a minimum particle size of 9.11 nm can be obtained.The results of morphology characterization and structure analysis confirm that the Fe3O4 NPs have the spherical structure,and the magnetic property analysis shows that Fe3O4 NPs present superparamagnetism with saturation magnetization of 53 emu/g.Then on the basis of the optimal conditions,surfactants are added in the reactants to explore further the preparation of Fe3O4 NPs and select potential surfactant type,feed way of them,reaction temperature,content of surfactant,and then the influence of deposition time on the size of Fe3O4 NPs is investigated.The experimental results show that the particle sizes of the samples with PVP and CTAB are smaller than that of the particles without surfactants(9.11 nm).The particle size of Fe3O4/PVP has a minimum value at temperature of 70?,which is about 8.45 nm.For Fe3O4/CTAB,the particle size does not change significantly with the increase of temperature.With the increase of surfactant content in the reactants,the particle size gradually decreases and then increases,so the optimal contents of PVP and CTAB are found as 40 wt%.The change of surfactant feeding method has no significant effect on the average particle size,which is basically stable between 8.4-9.0 nm.With the increase of deposition time,PVP has a significant inhibitory effect on particle agglomeration,while CTAB has no significant inhibitory effect.FR-IR diagrams of Fe3O4/PVP and Fe3O4/CTAB samples show that there is certain amount of adsorption of PVP and CTAB on the particle surfactant.And the saturation magnetization of PVP treated samples is about 55 emu/g,and that of CTAB treated samples is about 48 emu/g.Both particles are superparamagnetic.Finally,in order to explore the application direction of Fe3O4 NPs prepared in microtubule reactor,the further preparation of water-based magnetofluids is preliminarily studied.The effects of surfactant type,dosage,preparation temperature,stirring rate and other conditions on the stability of magnetic fluid are investigated,and the stability is verified by Zeta potential test.The results show that the magnetic fluid with OA,PEG 4000 and PVP has the best stability.The optimal dosage of surfactant is:40%OA,60%PEG 4000,40%PVP.OA coating temperature largely determines the stability of magnetic fluid.The optimal coating temperature of surfactant was:OA 80?,PEG 4000 50? PVP 30?.With the increase of mechanical agitation rate,the magnetohydrodynamic settlement firstly decreases and then increases.When the rate is 600 r/min,the sample has the best stability.Zeta potential of OA/PEG 4000/PVP coated magnetic fluid reaches-40 mV,proving that the coating of three surfactants plays a good role in dispersion and stability of themagnetic fluid.The magnetofluid stabilizes for more than 30 days.