聚乙二醇和二乙二醇对溶剂热法合成Fe3O4纳米粒子的尺寸及形貌调控.pdf

采用溶剂热法，通过改变反应体系中聚乙二醇（PEG）用量、PEG分子量、二乙二醇（DEG）体积分数，实现了对Fe3O4纳米粒子的尺寸和形貌调控。利用SEM、TEM、XRD和VSM对制备的Fe3O4纳米粒子进行了表征。结果表明：核桃状的Fe3O4纳米微球由细小的纳米晶粒组成，随着PEG-4000用量的增加，从0.1 g至1.5 g，有利于生成小的Fe3O4纳米晶粒。适当增加PEG链的长度，当分子量从200增加到4 000，有利于促进Fe3O4纳米晶粒的生长；但进一步增加PEG链的长度，PEG分子量为20 000时，Fe3O4纳米晶粒变小。改变溶剂中DEG的体积分数，Fe3O4纳米粒子的形貌实现了从表面粗糙的核桃状大微球到表面光滑的小微球，再到规则的长方体晶粒的转变。基于PEG、DEG的吸附、桥连和空间位阻等作用，提出了利用PEG、DEG调控Fe3O4纳米尺寸和形貌结构的可能机理。所制备的Fe3O4纳米粒子饱和磁化强度约为 80 emu/g，表现为超顺磁性。关键词：Fe3O4纳米粒子；聚乙二醇；二乙二醇；溶剂热法中图分类号：TQ658；TB383.1 文献标识码：A 文章编号：2097-2806（2023）08-0882-09884第 53 卷开发与应用日 用 化 学 工 业（中英文）molecular weight.The encapsulation effect of polyethylene glycol with different hydrocarbon chain lengths on the solid surface varies,resulting in different steric hindrances.This indicates that polyethylene glycol,can act as a structural directing agent,can be used to control the morphology of grown nanoparticles 24,25.Diethylene glycol（DEG）can act as both capping agent and reducing agent,and has high reaction temperature and the solubility with inorganic and organic reagents,which gives DEG an advantage in preparing nanoparticles with controllable morphology 26.Most importantly,due to the surface coating of polyol molecules,the synthesized nanoparticles are water-soluble and easier to use for biomedical applications 27.At present,the research on the reaction mechanism,kinetic control,and crystal orientation growth of Fe3O4 nanoparticles in EG solvothermal synthesis using PEG and DEG is still not comprehensive and systematic,and further research is needed.This article systematically studied the size control and morphology regulation of Fe3O4 nanoparticles by changing the relative molecular weight,the dosage of PEG and the volume fraction of DEG.Fe3O4 nanoparticles with superparamagnetism in small size,spherical or regular shape were prepared,and the possible formation mechanism was provided.It can provide useful reference for the controllable preparation of Fe3O4 nanoparticles and endow Fe3O4 with broad application potential.1 Experimental section1.1 MaterialsFerric chloride（FeCl3 6H2O,w=99%）,polyethylene glycol 200（PEG-200）,polyethylene glycol 2 000（PEG-2000）,polyethylene glycol 4 000（PEG-4000）,polyethylene glycol 20 000（PEG-20000）were purchased from Shanghai Chemical Reagents Company（Shanghai,China）;sodium acetate（NaAc,w=99%）were purchased from Acros Organics（New Jersey,USA）;Ethylene glycol（EG,w99%）,diethylene glycol（DEG,w99%）was provided by Sigma-Aldrich.X-ray diffraction（XRD,Rigaku Ultima IV,Japan）;Scanning electron microscopy（SEM,JSM-7500F,JEOL,Japan）;Transmission electron microscopy（TEM,JEOL 2100,Japan）;Vibrating sample magnetometer（VSM,LakeShore 7407,USA）.1.2 SynthesisThe Fe3O4 was synthesized via a facile polyol based solvothermal method using different PEG and DEG.Typically,FeCl36H2O（0.25 mol）was dissolved in ethylene glycol（EG,20 mL）in a sonication bath to form a yellow transparent solution.Then,anhydrous sodium acetate（NaAc,0.2 mol）was added,and the mixture was heated until the reactants were fully dissolved.Thereafter,PEG-4000（0.3 g）was added and dissolved with stirring.Finally,the mixture was transferred to a Teflon-lined stainless steel autoclave（50 mL,capacity）,which was heated to 200 and kept at that temperature for 12 h.The autoclave was allowed to cool naturally to room temperature.The products were separated using a magnet,rinsed several times with deionized water and then ethanol,and then dried at 60 for 24 h in a drying oven.Herein,1.5 g PEG with various molecular weights from 200 to 20 000 was used to prepare magnetic iron oxide nanoparticles,the as-obtained Fe3O4 nanoparticals were denoted as PEG-200,PEG-2000,PEG-4000,PEG-20000,respectively.The Fe3O4 nanoparticals synthesized by using different dosages of PEG-4000（0.1 g,0.3 g,0.9 g,and 1.5 g in 20 mL）are hereafter indicated as samples PEG-0.1,PEG-0.3,PEG-0.9,and PEG-1.5,respectively.The content of DEG was varied by changing the volume ratio of DEG/EG to（0 mL/20 mL）,（5 mL/15 mL）,（10 mL/10 mL）,（15 mL/5 mL）,and（20 mL/0 mL）,corresponding to the samples named DEG-0%,DEG-25%,DEG-50%,DEG-75%,and DEG-100%,respectively.1.3 CharacterizationThe crystal structure of the as-prepared Fe3O4 samples was analysed by XRD.The morphology and size of Fe3O4 samples were detected by SEM and TEM.The magnetic property of Fe3O4 samples was measured by VSM at room temperature.2 Results and discussion2.1 Effects of PEG-4000 dosages on Fe3O4 nanoparticlesThe dosage of PEG is an important factor in the preparation of nanomaterials by solvothermal method.Fig.1 shows SEM images of Fe3O4 nanostructures with 885第 8 期开发与应用ZhuliangWang,etal:ThesizeandmorphologycontrolofFe3O4nanoparticlessynthesizedbysolvothermalmethodusingpolyethyleneglycolanddiethyleneglycol different dosage of PEG-4000,and the range of dosage changes from 0.1 g to 1.5 g in 20 mL ethyl alcohol.As can be seen from the images,in each case,the morphology of Fe3O4 is walnut like microspherical.Moreover,the high resolution SEM images of PEG-0.1（Fig.1e）and PEG-0.9（Fig.1f）further support that Fe3O4 microsphere is composed of small grains.The size of walnut like microsphere is not uniform ranging from about 150 nm to 270 nm,while the size of small grains ranges from 30 nm to 60 nm.It can also be seen from the figure that when PEG-4000 content is 0.9 g,the damage of Fe3O4 microspheres is less and the spheres are relatively intact.The aggregation of small grain size particles may be due to high surface energy and Vander-Waals forces.In order to minimize the total surface energy,Fe3O4 particles self-assemble into large irregular spherical structures 28.As the dosage of PEG-4000 increases,the size of the small grain tends to decrease.This may be due to the fact that when the dosage of PEG-4000 in the reaction solution is high,the primary Fe3O4 crystals tend to be completely covered by a layer of PEG-4000 in a relatively short period of time,resulting in the inhibition of grain growth and the formation of smaller grains.The crystal structure and size of nanoparticles can be determined from XRD patterns.Fig.2a shows the XRD patterns of Fe3O4 microspheres synthesized with different PEG-4000 dosage ranging form 0.1 g to 1.5 g in the reaction solution.The position and relative intensities of all peaks in figures confirm well with the standard XRD pattern of Fe3O4（JCPDS No.65-3107）,indicating the generation of nanoparticles with a cubic spinel structure.The XRD patterns show six characteristic peaks（2=30.27,35.53,42.95,53.60,57.18,62.69,71.31,and 74.14）,which are related to the corresponding indices（110）,（220）,（311）,（400）,（331）,（422）,（511）,（440）,and（531）,respectively 29.It confirmed that a single cubic magnetite phase is formed in the products without impurity phases.The width of X-ray diffraction peaks,full width at half maximum（FWHM）,can be correlated with the size of nanoparticles,which have been used to evaluate the average crystallite size.The diffraction peaks for the magnetite microspheres broaden with smaller crystallite sizes 30.With the increase of PEG-4000,the XRD peak width of Fe3O4 gradually becomes wider and the peak intensity gradually decreases,which indicates that the size of Fe3O4 nanoparticles decreases and the crystallinity becomes worse.It is noticed that,for Fe3O4 nanoparticles,the saturation magnetization values depend on the size of the crystal 31.Fig.2b shows the magnetic hysteresis loops of magnetite microspheres synthesized with PEG-4000 dosages ranging from 0.1 g to 1.5 g in the reaction solution adbecf200nm200nm200nm100nm200nm100nm56.5nm47.1nm36.6nm191nm213nm33.9nm267nm221nm241nm46.4nm153nm197nm48.8nmFig.1 SE M images of Fe3O4 microspheres with different dosages of PEG-4000.a,e,PEG-0.1;b,PEG-0.3;c,f,PEG-0.9;d,PEG-1.5Fig.2 XRD patterns（a）and magnetic hysteresis loops（b）of Fe3O4 microspheres with different dosages of PEG-4000 ranging from 0.1 g to 1.5 g203040506070802/()-20 00020 000-15 00015 000-10 00010 000-5 0005 0000-100-80-60-40-20020406080100 H/OeM/(emu/g)PEG-0.1 PEG-0.3 PEG-0.9 PEG-1.5 PEG-1.5 PEG-0.9 PEG-0.3 PEG-0.1 886第 53 卷开发与应用日 用 化 学 工 业（中英文）measured by VSM at room temperature.It can be seen that the magnetic saturation value of PEG-0.1 is slightly greater than that of PEG-0.3,PEG-0.9 and PEG-1.5,which is irrespective of Fe3O4 microspheres diameter.It indicates that the magnetic properties of nanoparticles are mainly determined by the size of nanocrystal grain,but not that of microsphere.The change in crystal grain size characterized by VSM is consistent with the XRD characterization results.In addition,the value of saturation magnetization（Ms）of the Fe3O4 nanoparticles is about 80 emu/g,and the coercivity（Hc）could be ignored over the applied magnetic field,which can be considered superparamagnetism 29.Combined with SEM and XRD analysis,Fe3O4 sample prepared with PEG-4000 addition of 0.9 g has relatively intact spherical microspheres,superparamagnetic and high saturation magnetization.PEG-0.9 is of optimal sample in our results.2.2 Effects of molecular weight of PEG on Fe3O4 nanostructuresThe molecular weight of PEG is another important factor in the preparation of nanomaterials by solvothermal method.Fig.3 shows SEM images of Fe3O4 nanostructures with different molecular weight of PEG,and the molecular weight varies from 200 to 20 000.As shown in SEM images,the morphology of Fe3O4 is walnut like microspherical,and the size of microsphere is ranging from about 90 nm to 290 nm.As the molecular weight of PEG increases from 200 to 4 000,the size of the generated Fe3O4 microspheres also increases.After the molecular weight of PEG exceeds 4 000,the size of the microspher