31-35In the present study, bi-functional hybrid nanomaterial has been synthesized and characterized via facile method and characterized. The synthesized nanomaterial shows both magnetic and luminescent properties which are confirmed by VSM (vibrating sample magnetometer), UV-Vis spectra and the photoluminescence emission spectra. For the magnetic phase, i.e., nanocrystalline magnetite, Fe3O4 is used as the core which is then functionalized using polyethylene glycol (PEG) and for the luminescent phase, polyethylenimine (PEI) functionalized CaF2 doped with Tb3+is used as the emitter. Wherein, both PEG and PEI serve the dual purpose of functionalization as well as stabilization by steric repulsion. The structure and morphology of the synthesized bifunctional hybrid nanomaterial are studied with the help of scanning electron microscopy (SEM) and X-ray powder diffraction

Kumar, Rakesh

Luwang, Meitram Niraj

Sharma, Jyotsna

Vats, Monika

English

NOPR

Indian Journal of Pure & Applied Physics Vol. 58, January 2020, pp. 31-35       Magnetic and luminescent multifunctional nanohybrid:  Fe3O4@CaF2:Tb3+: A facile synthesis and characterization Monika Vatsa*, Rakesh Kumara, Jyotsna Sharmaa & Meitram Niraj Luwangb aAmity School of Applied Sciences, Amity University, Gurugram 122 413, India bCSIR-National Chemical Laboratory, Pune 201 303, India Received 6 June 2019; accepted 2 December 2019 In the present study, bi-functional hybrid nanomaterial has been synthesized and characterized via facile method and characterized. The synthesized nanomaterial shows both magnetic and luminescent properties which are confirmed by VSM (vibrating sample magnetometer), UV-Vis spectra and the photoluminescence emission spectra. For the magnetic phase, i.e., nanocrystalline magnetite, Fe3O4 is used as the core which is then functionalized using polyethylene glycol (PEG) and for the luminescent phase, polyethylenimine (PEI) functionalized CaF2 doped with Tb3+is used as the emitter. Wherein, both PEG and PEI serve the dual purpose of functionalization as well as stabilization by steric repulsion. The structure and morphology of the synthesized bifunctional hybrid nanomaterial are studied with the help of scanning electron microscopy (SEM) and X-ray powder diffraction. Keywords: Magnetic nanoparticles, Luminescent nanoparticle, Nanohybrid, Fe3O4, CaF2, Tb3+ doping, Biocompatible,  Co-precipitation 1 Introduction Nanoparticles (NPs) are submicron moieties  (1 to 100 nm) made up of inorganic or organic materials, which depict several novel properties when compared with the bulk materials. Magnetic nanoparticles are the nanostructured materials of current interest, due to their use in advance technology, bio-compatibility and medical applications. The magnetic NPs show unique properties such as superparamagnetic property, high coercivity, low Curie temperature, high magnetic susceptibility, etc. Among the various magnetic nanomaterials, magnetite (Fe3O4) nanoparticles have been extensively studied1 due to their broad range of applications like magnetic fluids, data storage, catalysis and bio-applications2. The super paramagnetic magnetite (Fe3O4) nanoparticles have different striking features, including ease of synthesis, chemical stability, narrow size distribution, and high dispersibility in various solvents2-4. In addition, Fe3O4 NPs also exhibit high biocompatibility5,6. The magnetic NPs can be functionalized with luminescent nanoparticle phase giving a hybrid nanomaterial which has both the properties of a magnetic NPs and luminescent NPs. Furthermore, with an eye on possibly altering the structure and properties of the parent nanoparticles and creating multifunctional materials, doping of magnetite nanoparticles with other metal ions has been explored7-9. The inorganic luminescent materials based on rare earth ions have been generally utilized for preparation such nano-hybrids due to their higher optical properties, such as high quantum yield, long lived emission, narrow bandwidth, and large stokes shift. These characteristics of dual nano-hybrids make them fit for biological applications such as magnetic bio-separation, detection of biological entities (cell, protein, nucleic acids, enzyme, bacteria, virus, etc.), magnetic resonance imaging (MRI), magnetic fluid hyperthermia (MFH) and targeted drug delivery10-12. The luminescent phase NPs (organic compounds, polymers, quantum dots and rare earth-based) binds with microorganisms, antibodies, antigens, polypeptides or tumor tissue13,14, resulting in a bio-complex which can be easily detected on irradiation with UV or NIR radiations. These nano-materials have been reported to enhance drug delivery15. For non-radiative relaxation in the luminescence, Ln3+ ions have been utilized due to their appropriate lattice16. The fluorides, has low phonon energy, high transparency and thus, serve as perfect host materials among the inorganic matrices. Moreover, CaF2 has been reported as an ideal host matrix as it shows optically isotropic structure, high stability, non-hygroscopic behavior, non-toxicity and biocompatibility of among all the other fluorides make it17. Nanohybrid structures with ————— *Corresponding author (E-mail: mona2k42000@gmail.com)  INDIAN J PURE APPL PHYS, VOL. 58, JANUARY 2020   32 suitable dual or multifunctional properties have potential to display various applications in biology, biochemistry, pharmacy, industry, medicine and opto-electronics and lightening18.  Both the magnetic core and the luminescent phase must be biocompatible to yield a nanohybrid is also bio-compatible product. The magnetic phase Fe3O4 has been reported as biocompatible19 and as well as the luminescent phase Tb3+ doped CaF2 has been  said to have non-hygroscopic, non-toxicity and biocompatibility properties17. These modern biochemical and physicochemical approaches based on nanotechnology could be utilized to enhance the vital properties of these nanomaterials. However, it is important to select the materials for the fabrication of nanostructure and devices with controllable physical and chemical properties.  As mentioned above the biocompatibility aspect must be considered in choosing the luminescent phase as well magnetic phase. Hence, a properly functionalized magnetic core is made to form a core shell with the luminescent phase, which can be designed by functionalizing Fe3O4 with PEG and adding this magnetic core during the synthesis of Tb3+ doped CaF2 via co-precipitation method. The method opted here gives biocompatible multifunctional nanohybrid that shows both magnetic property and luminescent property owing to its magnetic core and the luminescent phase, respectively. Here we discuss the synthesis of a multi-functional nanohybrid wherein the magnetic phase is synthesized, i.e., nano-crystalline magnetite, Fe3O4 and is used as the core which was then functionalized using polyethylenelgycol (PEG). The luminescent phase is polyethylenimine (PEI) functionalized CaF2 doped with Tb3+ as the emitter. Wherein, both PEG and PEI serve the dual purpose of functionalization as well as stabilization by steric repulsion. The Tb3+doped hybrid of polyethylene glycol (PEG) functionalized Fe3O4 and polyethylenimine (PEI) functionalized CaF2 [Fe3O4@ CaF2:Tb3+] NPs have been synthesized, characterized and studied in this work.  2 Experimental Details  2.1 Chemicals and solvents used Ferrous sulphate exsiccated (dried) extra pure, (FeSO4.ca.1.5H2O), iron (III) chloride (anhydrous purified) and ammonia solution (25 %) are purchased from Merck. The chemicals, calcium chloride (anhydrous, granular), poly (ethylene glycol), ammonium fluoride (ASC reagent), polyethylenimine (branched), terbium (III) nitrate penta hydrate are purchased from Sigma-Aldrich, whereas, ethanol  (AR 99.9 %) is purchased from Changshu Hongsheng Fine Chemicals Co Ltd. All chemicals are used without any further purification(s).  2.2 Method of preparation The facile synthesis of the Fe3O4 NPs and CaF2 NPs are adopted and the biocompatibility of the final hybrid product opens up to a wide range of applications.   2.2.1 Synthesis of PEG functionalized Fe3O4 Fe3O4 is prepared via a simple co-precipitation method7 at a moderate temperature of 50 °C. 0.3259 g of FeCl3 is dissolved in 10 mL distilled water and 0.1528 g of FeSO4 dissolved in 10 mL distilled water which is added to the previous solution (so that the amount of Fe3+ and Fe2+ are in the ratio of 2:1) in a round bottom flask and stirred for homogenization under N2 atmosphere, followed by addition of 0.7 g PEG (in 5 mL distilled water) and stirred for 1 h at a temperature of 50 °C. Then, 40 mL distilled water is added to the RB and immediately 20 mL of 25 % NH3 solution (black colored ppt of Fe3O4 is formed immediately after the addition of NH3 solution) is added and stirred for another 1 h at 50 °C. The precipitate obtained is centrifugated and washed several times with water and ethanol to remove excess surfactants and ammonia. The black colored precipitate is collected and dried at room temperature and powdered after drying for characterization.  2.2.2 Synthesis of CaF2 and Tb3+ doped CaF2 0.4217 g of CaCl2 is dissolved in 10 mL distilled water in a round bottom flask and added 0.0870 g of Tb(NO3)3.5H2O (dissolved in 5 mL distilled water) and is stirred for 1 h under N2 atmosphere for preparing 5 % doped material for preparation of CaF2.doping is not added The NH4F solution (0.2963 g dissolved in 10 mL distilled water) dropwise added to the above reaction mixture and stirred for 2 h to obtain an opaque white suspension. The reaction mixture is then centrifuged to obtain the white precipitate of CaF2:Tb3+which is then centrifuged, washed several times via with distilled water and ethanol, and finally dried at room temperature.   2.2.3 Synthesis of Fe3O4@PEG/CaF2:Tb3+ hybrid The magnetic and luminescent nanohybrid Fe3O4@PEG/CaF2:Tb3+ is synthesized by a modified facile co-precipitation method. Wherein, the calcium VATS et al.: MAGNETIC AND LUMINESCENT MULTIFUNCTIONAL NANOHYBRID   33 precursor (CaCl2 dissolved in distilled water) is mixed with a specific amount of the dopant, Tb(NO3)3.5H2O and stirred for 1 h under nitrogen atmosphere followed by reduction by adding a certain amount of NH4F dropwise and stirred for 2 h under nitrogen atmosphere, which gives the precipitate of CaF2 followed by dropwise addition of water dispersed Fe3O4 and is stirred for another 1 h under nitrogen atmosphere at room temperature.  Here the ratio of the amount (in grams, Table 1) of Fe3O4 and all other components in hybrid material is 1:5 and the luminescent phase CaF2 is functionalized with PEI (by adding 0.49 g of PEI after addition of Tb(NO3)3.5H2O).  3 Results and Discussion  3.1 Powder-XRD analysis The XRD patterns of Fe3O4 (functionalized with PEG), is shown in Fig. 1 and the diffraction peaks are in agreement with the standard values for cubic Fe3O4 (JCPDS Reference Code 00-001-1111) and Space group: Fd-3m (227). The XRD results indicate that the products obtained are Fe3O4 nanoparticles and Scherrer equation is used for calculating average size of the Fe3O4 NPs and is found to be ~14 nm. The XRD patterns of CaF2 nanoparticles are shown in  Fig. 2, and the diffraction peaks are in agreement with the standard values for cubic CaF2 (JCPDS Reference Code 01-070-2049) Space group: Fm-3m (225).  The XRD results indicate that the products obtained are CaF2 nanoparticles and Scherrer equation is  used for calculating average size of the CaF2 NPs  and is found to be ~29 nm. Figure 3 shows the  XRD patterns of Fe3O4@ CaF2:Tb3+ nanohybrid.  The peaks shown in Fig. 3 clearly indicate that the hybrid have peaks corresponding to both the Fe3O4 and CaF2.   3.2 Scanning electron microscope (SEM) The morphology of synthesized multifunctional nanohybrid (Fe3O4@PEG/CaF2:Tb3+) is studied by scanning electron microscope. From Fig. 4 it is evident that synthesized hybrid nanoparticles are nearly spherical in shape and size of particles are in the range from 10 to 50 nm with average particle size 30 nm, which supports the XRD results. 3.3 UV-visible absorption spectra UV visible absorption spectra for CaF2 and CaF2:Tb3+ dispersed in ethanol are recorded in alcohol dispersion. The peak (Fig. 5) at around 214 nm corresponds to (5 % Tb3+ doped) CaF2:Tb3+ which is not observed in the case of pure CaF2 indicating that this peak appears due to the dopant Tb3+ and thereby, Table 1 – The amounts of various components for the synthesis of the nanohybrid Sample name Amount of Fe3O4 Amount of CaCl2 Amount of NH4F Amount of Tb(NO3)3.5H2O Doping percentage Fe3O4@PEG/CaF2:Tb3+ 0.1]]61 g 0.4217 g 0.2963 g 0.0870 g 5 %   Fig 1 – X-ray diffraction pattern of Fe3O4 (functionalized with PEG) nanoparticles.    Fig. 2 – X-ray diffraction pattern of CaF2 nanoparticles.  INDIAN J PURE APPL PHYS, VOL. 58, JANUARY 2020   34 indicating the successful doping with the facile synthesis method mentioned above.  3.4 Photoluminescence spectra The ideal excitation for Tb3+ was 220 nm which results in several emissive transitions. The obtained spectrum correlates well to the emissions for 5D47F6 (488 nm), 5D47F5 (541 nm), 5D47F4 (581 nm) and 5D47F3 (620 nm). The bands at 490 nm, 586 nm and 621 nm exhibit comparable intensity (the latter two peaks are not clearly distinguishable due to the broad emission band of the host CaF2 around 575 nm to 625 nm) which are exceeded by the prominent transition at 544 nm (Fig. 6). The measured spectrum of the Tb3+ doped particles are in accordance to literature data20. It is also seen that the intensity of the broad peak at 575 nm to 625 nm of the host CaF2 decreases with the introduction of iron oxide NPs. Moreover, the introduction of iron oxide NPs in CaF2:Tb3+ lowers the intensity of the prominent peaks of Tb3+, with the most intense peak at 544 nm.  3.5 Magnetic behaviour of Fe3O4, Fe3O4@CaF2 and Fe3O4@CaF2:Tb3+ The magnetic properties of the synthesized iron oxide containing NPs are studied via vibrating sample magnetometer (VSM) (Fig. 7). However, the magnitude of magnetization of the synthesized nano-  Fig. 4 – SEM Image of Fe3O4@ CaF2:Tb3+nanohybrid.   Fig. 3 – X-ray diffraction pattern of the multifunctional nanohybrid (Fe3O4@PEG/CaF2:Tb3+), sample R1 plotted with the standard X-ray diffraction pattern of Fe3O4 (JCPDS 00-001-1111) and CaF2 (JCPDS 01-070-2049).   Fig. 5 – The UV-visible absorption spectra of (a) CaF2, (b) CaF2:Tb3+ (5 %) and (c) magnified UV-visible absorption spectra of CaF2 and CaF2:Tb3+(5 % doping), which shows a peak at 214 nm due to Tb3+. VATS et al.: MAGNETIC AND LUMINESCENT MULTIFUNCTIONAL NANOHYBRID   35 hybrid Fe3O4:CaF2:Tb3+ is low in comparison to that of the pure Fe3O4. This can be explained as there is the possibility of magnetic & luminescent quenching and this is due to the large amount of Fe3O4 in case of the pure iron oxide NPs as compared to Fe3O4:CaF2:Tb3+.  4 Conclusions A bifunctional, magnetic-luminescent, nanomaterial is synthesized using a simple, co-precipitation method. The synthesized nanomaterial is characterized via XRD and SEM. However, VSM (vibrating sample magnetometer) is used to analyze the magnetic properties of synthesized material. UV-vis and photoluminescence spectroscopy are used to analyze luminescent properties of the nanomaterial. The described hybrid nanomaterial is sensitive to external magnetic fields. The obtained product is attracted to magnets both in the solid state (as a dry powder) and in water dispersed state as a colloid. The nanohybrid shows intense emission peak at 544 nm and is expected to show an intense green luminescence under a UV lamp. Such a luminescence is also expected in an aqueous system. This nanohybrid product shows simultaneously magnetic and luminescent properties and can be used for various medical & industrial applications. However, the mechanism of this phenomena and the influence of the environment should be examined and discussed in further research.   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Fig. 6 – Photoluminescence emission spectra of CaF2, CaF2:Tb3+ (5 %) and Fe3O4:CaF2:Tb3+ (5 %) at λex=220 nm.    Fig. 7 – The magnetic behavior of the synthesized nanohybrid in comparison to the pure iron oxide NPs.  

Magnetic and luminescent multifunctional nanohybrid:  Fe3O4@CaF2:Tb3+: A facile synthesis and characterization

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Magnetic and luminescent multifunctional nanohybrid: Fe3O4@CaF2:Tb3+: A facile synthesis and characterization

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