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Synthesis and Properties of Core/Shell Silica Magnetic NanoparticlesA. Chatzipavlidis 1, 2* , P. Bilalis 2 , N. Boukos 2 , G. Mitrikas 2 , C.A. Charitidis 1 and G. Kordas 2TUE-5POS591. National Technical University of Athens, School of Chemical Engineering, Greece2. Institute of Material Science, NSCR ‘Demokritos’, Athens, Greece*alexchat@ims.demokritos.grIn recent years, the interest in using core/shell silica magnetic nanoparticles (MNPs) for biomedical andbioengineering applications is increasing significantly. Modification of MNPs’ surface can help to maintainbiocompatibility, chemical stability, and sufficient magnetic response. Silica coatings have several advantagessuch as high resistance against biodegradation. Moreover, they provide additional steric repulsion, which isimportant for sufficient colloidal stability and can be functionalized with active groups like amine, carboxyl etc.In the present work, we present the synthesis of silica-coated MNPs with different coating thickness. TheMNPs were pre-synthesized by co-precipitation method. Their surface was functionalized using trisodiumcitrate. In order to accomplish the coating of MNPs, we followed Stöber method with some modification [1,2].The coating was carried out in ethanol/water mixture at room temperature by using MNPs as seeds.The crystal structure of samples was analyzed using X-ray diffraction analysis (XRD). XRD analysisconfirmed that the iron oxide particles are mainly composed of the inverse cubic spinel structure of magnetite,Fe 3 O 4 . Crystallite sizes of the MNPs were calculated from the X-ray peak broadening of the (311) diffractionpeak using Scherrer’s formula. MNPs and silica-coated MNPs were imaged using Scanning and TransmissionElectron Microscopy (SEM and TEM) an example of which is shown in Fig. 1.(a) (b) (c)Figure 1- TEM images of (a) uncoated MNPs, (b) silica-coated MNPS and SEM image of silica-coated magnetite particlesRaman spectroscopy was employed to study the core-shell structure and to identify the nature of the MNPs thatwere encapsulated in silica shell. In Fig. 2 the appearance of a broad band around 670 cm -1 in Fig. 2 reveals thepresence of magnetite in the sample. In addition, spectral features show the characteristic maghemite (γ-Fe 2 O 3 )and hematite (a-Fe 2 O 3 ) bands. The appearance of these bands suggests that the laser overheating convertsmagnetite into maghemite and maghemite to hematite [3,4,5].18000Raman Intensity (a.u.)1500012000900060001200 1000 800 600 400 200Wavelength (cm -1 )Figure 2 – Raman spectrum of silica-coated MNPsMagnetization measurements were performed at room temperature using vibrating sample magnetometry(VSM). The silica-coated MNPs exhibit characteristics of superparamagnetic behavior. The following figure244