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Journal of Science: Advanced Materials and Devices (2018) 323e330 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Surface-protective assistance of ultrasound in synthesis of superparamagnetic magnetite nanoparticles and in preparation of mono-core magnetite-silica nanocomposites Thanh Quang Bui*, Hoa Thi My Ngo, Hoa Thai Tran Department of Chemistry, College of Sciences, Hue University, Viet Nam a r t i c l e i n f o a b s t r a c t Article history: Received March 2018 Received in revised form 23 June 2018 Accepted July 2018 Available online 11 July 2018 Ultrasound was throughout employed to enhance the co-precipitation process for the synthesis of € ber approach for the preparation of magnetite-silica magnetite nanoparticles (Fe3O4) and the Sto nanocomposites (Fe3O4/SiO2) The synthesised magnetite nanoparticles exhibited single-domain nanocrystallites with a uniform spherical morphology, a narrow size distribution (ca 10 nm), and negligible coercive field (~5 Oe) The prepared magnetite-silica nanocomposites possessed a mono core-shell structure with spherical morphology, biologically coherent size (ca 100 nm), and discrete monodomain behaviour The crystalline structure-magnetic behaviour relationships of the nanomaterials were investigated to imply the presence of a surface protection at nanoscale The speculation indicated that shock waves took place as the surface-protective role rather than the original mechanical interaction of ultrasound with a larger scope of impact © 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Fe3O4 nanoparticles Fe3O4@SiO2 nanocomposites Shock-wave Ultrasonic assistance Co-precipitation €ber method Sto Crystalline structure-magnetic behaviour relationships Introduction Magnetite (Fe3O4), well-known as the most strongly magnetic mineral in nature, has been attracting diverse researches and applications [1,2] Magnetite nanoparticles possess numerous potential applications in magnetic recording technology, pigments, catalysis, photocatalysis, medical uses, and environmental processes because of their good biocompatibility, strong superparamagnetic property, low toxicity, and easy preparation [3] In biomedical applications, magnetite nanoparticles have been applied in targeted drug delivery, hyperthermal treatment, cell separation, magnetic resonance imaging, immunoassay, and separation of biomedical products [4e6] Hence, many preparation methods of magnetite nanoparticles have been developed, such as co-precipitation, hydrothermal synthesis, solvothermal synthesis, sonochemical synthesis, and micro-emulsion [7] Co- * Corresponding author Building D, 77 Nguyen Hue, Hue, 53000, Viet Nam E-mail addresses: thanh.qt.bui@gmail.com, thanh.qt.bui@husc.edu.vn (T.Q Bui) Peer review under responsibility of Vietnam National University, Hanoi precipitation is the simplest and most efficient synthesis route to obtain the magnetic particles, based on the following reaction: Fe2ỵ þ 2Fe3þ þ 8OHÀ / Fe3O4 þ 4H2O [8]; in which, a stoichiometric mixture of ferrous and ferric precursors in aqueous medium is used as an iron source, yielding magnetite nanoparticles after introducing an alkaline solution into it However, the size distribution of as-prepared nanoparticles by co-precipitation is relatively broad because of the presence of both nucleation and particle growth throughout the synthesis process [4] Whilst most of the mentioned biochemical applications require magnetite nanoparticles with chemical stability, biocompatibility, biologically coherent size, and superparamagnetic property [9] a very recent finding revealed a negative correlation between the superparamagnetism of iron oxide nanoparticles and their heating efficiency (specific absorption rate, SAR) [10], which is an imperative factor for magnetic hyperthermia applications In order to retain such properties, the prepared magnetite nanoparticles also need a further proper modification for better fluidity and chemical stability [11,12] € ber et al., in 1968, reported a simple method to synthesise Sto silica submicro-sized particles, based on the hydrolysis of tetraethoxysilane (TEOS) in aqueous alcohol solutions with the presence https://doi.org/10.1016/j.jsamd.2018.07.002 2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 324 T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 of ammonium hydroxide as a catalyst [13] The work afterwards initiated the preparation of silica-nanocomposite materials NPs@SiO2 (NPs for nanoparticles) by forming cross-linked silica shell to protect the core nanoparticles extendedly Beside the hydrophilic property derived from an enormous number of silanol groups (eSieOH) on the material surface, these groups also possess high potential to be further modified for acquiring specific compatibility of the composites through facilitatory hydrolysis reactions [14] Also, by holding propagation transparency to light and magnetism, the silica-coated nanoparticles still retain their original optical and magnetic properties Finally, the most important feature is that the silica layer provides a chemically and physically inert surface for the core nanomaterials in biological systems [14] Besides, there are three other major methods that have been popularly utilised for preparation of silica-coated magnetic nanoparticles, i.e in situ formation of magnetic nanoparticles inside the pre-synthesised silica matrix [15], aerosol pyrolysis [16], and water/oil microemulsion method [16] However, by relying on un€ber complicated apparatuses and mild reacting conditions, Sto method is still considered as the most common approach However, fast hydrolysis of TEOS [17] and aggregate nature of magnetite nano-sized materials [18] could lead to formation of morphologically heterogeneous and considerably large microsizedcomposites Fe3O4/SiO2, which not only degrade mobility, but also deteriorate individual magnetite nanoparticle magnetism Ultrasound has been widely utilised in chemical synthesis and sol dispersion [19] With velocity in water around 1000 m sÀ1e1500 m sÀ1 and typical frequencies of laboratory ultrasonic irradiations from 20 KHz to 15 MHz, experimental ultrasonic wavelengths vary from 10 cm down to 100 mm [20], which are significantly larger than the molecular level or nano-scale Thus, there is apparently no direct interaction of ultrasonic waves with chemical species at the scale, but rather throughout the physical phenomenon called acoustic cavitation [21] This generates localised hot spots by the formation, growth, and implosive collapse of bubbles in liquid medium, creating a special reacting condition at near boundaries of liquidesolid interface, commonly used for utilisation and explanation in submicroscopic science [21e23] Otherwise, acoustic bubbles are also possibly considered as the storage of extremely high potential-energy, which could be released to be shock waves [20] after the compression of surrounding liquid inwardly to the spots These rebounding waves are considered as positive liquid pressure pulses with velocity and pressure being respectively up to km sÀ1 and 60 Kbar in water [20] Only these waves could directly interact with solid nanoscopic particles and accelerate them reaching to velocity of hundreds of metre per second, resulting in a phenomenon of micro-mass transport If maintaining the existence of these shock waves, the naturally high tension of magnetite nanoparticles would be overwhelmed by the stronger driving force, consequently, the nanoparticles would be discretely suspended in the liquid throughout further chemical processes Therefore, assisted techniques based on ultrasound represent a considerably high potential for microscopic sciences in general and magnetite nanoparticle chemical operations in particular Fig illustrates the development of acoustic cavitation and the formation of rebounding shock waves To the best of our knowledge, the powerful energy of shock waves, derived from extremely high velocity, temperature, and pressure, is mainly responsible for well-known treatments and processes such as cleaning, sonochemistry, and erosion [7,24e28] Otherwise, there are only vague explanations for the mechanism of ultrasonic assistance at the nano-scale [29,30] Besides, although magnetite nanoparticles sonochemically coated with silica has been widely reported, the strong agglomeration of the magnetite nanoparticles during the coating process still remains a challenging Fig Formation illustrations of acoustic cavitation throughout external ultrasonic propagation and of rebounding shock waves after implosive collapse task to obtain the nanocomposite with morphological and sized uniformity [31,32] In this study, coprecipitation-based experiments in synthesis of €ber approach in preparation of magnetite nanoparticles and Sto magnetite-silica nanocomposites have been proceeded to demonstrate the submicro-effect of shock waves in the reacting medium through the explanation for obtained characteristic results, rather than ultrasonic waves otherwise at much higher scale The introduction of basic solution into the iron precursor has also been examined A mild frequency ultrasonic source, 42 KHz and 100 W, was applied to limit high-energy interparticle collisions, which could change particle morphologies and surface compositions Experimental 2.1 Chemicals and reacting conditions Ferrous chloride tetrahydrate (FeCl2$4H2O), ferric chloride hexahydrate (FeCl3$6H2O), ammonia solution (NH3, 28% v/v), ethanol (C2H5OH), TEOS, trisodium citrate dihydrate (Na3C6H5O7$2H2O), and sodium silicate solution (Na2O(SiO2)x$xH2O, 8% of Na2O and 28% of SiO2) were analytical grade, and were purchased from Xilong Chemical Co., Ltd All chemicals were used without further purification In all experiments, reacting solutions were deoxygenated by Nitrogen bubbling for 30 before use Ultrasonic condition was deployed with a cleaner-type bath (Cole-Parmer-8892, USA) with 42 KHz, 100 W 2.2 Preparation of magnetite nanoparticles Magnetite nanoparticles were synthesised by coprecipitationbased method following processes, notated by M-01, M-02, and M-03 In typical synthesis procedure, 1.5 mmol FeCl2$4H2O and 3.0 mmol FeCl3$6H2O were dissolved in 50 mL deoxygenated distilled water Under the assistance of mechanical stir or ultrasonic irradiation, 10 mL ammonia was differentially introduced to the iron precursor solutions at 40 C, bubbling with N2 The assisted conditions were being kept in the further 30 for ageing purpose Table summarises the differences in synthesis procedure of M-01, M-02, and M-03 experiments, respectively The black Fe3O4 precipitates were isolated from the solutions by magnetic decantation and washed by deoxygenated distilled water several times; then dried in an oven at 50 C for h T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 325 Table Procedural differences of experiment M-01, experiment M-02, and experiment M03 Experiment Ammonia introduction Assistance solution M-01 M-02 M-03 Droplet Pouring Pouring Mechanical stir Mechanical stir Ultrasonic irradiation 2.3 Preparation of magnetite-silica nanocomposites €ber Magnetite-silica nanocomposites were synthesised by Sto approach following processes, notated by MS-01, and MS-02 In typical preparation procedure, 35 mg M-03 magnetite nanoparticles powder and 200 mL sodium silicate solution was dispersed in 20 mL ethanol, mL distilled water, and mL ammonia solution With the assistance of mechanical shake or ultrasonic irradiation, 500 mL TEOS was added to the reactant solutions at room temperature The assisted conditions were being kept in the further h All the experiments were implemented at room temperature Table summarises the differences in the synthesis procedure of MS-01, and MS-02 experiments, respectively The Fe3O4/SiO2 colloids were isolated from the liquid by magnetic decantation and washed with distilled water and ethanol several times; then dried in an oven at 100 C for 12 h 2.4 Characterisation The crystal phase of products were characterised by X-ray diffraction (XRD, D8-BRUKER, Germany) equipped with Cu Ka radiation (l ¼ 1.5406 Å), and the mean crystallite size of nanoparticles were calculated by Scherrer's equation using XRD data [33,34] The morphology of the synthesised products was observed by transmission electron microscopy (TEM, JEOL-1010, Japan) The magnetic properties were investigated through collected magnetisation-hysteresis (M-H) curves using a vibrating sample magnetometer equipment (VSM, PPMS-6000, USA) at room temperature The molecular structure of silica-coated magnetite materials was examined by infrared spectrometer (IR spectrometer, SHIMADZU IR-PRESTIGE-21, Japan) Results and discussion 3.1 Magnetite nanoparticles XRD patterns shown in Fig are utilised to demonstrate the crystal structure of the synthesised nanoparticle samples, M-01 (Fig 2a), M-02 (Fig 2b), and M-03 (Fig 2c) The measured diffraction angles of all samples show a good consistency with those from standard XRD pattern of magnetite (Fe3O4, PDF card No 11-614) [35] with five pronounced peaks, appearing at 30.09 , 35.42 , 43.05 , 56.94 , and 62.51 correspondingly to (200), (311), (400), (511), and (440) lattices of magnetite crystalline structure The interplanar spacings, calculated by Bragg's Law [36] and referenced as shown in Table 3, indicate that all samples possess the inverse cubic spinel structure of magnetite with over 95% being consistent with the referenced date The average crystalline size of magnetite nanoparticles in M-01, M-02, and M-03 samples, estimated from Table Procedural differences of experiment MS-01, and experiment MS-02 Experiment Assistance solution MS-01 MS-02 Mechanical shake Ultrasonic irradiation Fig XRD patterns of (a) sample M-01, (b) sample M-02, and (c) sample M-03 Scherrer's equation with full-width at half-maximum values obtained from the corresponding strongest peaks (311), are 27 nm, nm, and nm, respectively In addition, XRD patterns of sample M-02 and sample M-03 appearing with lower intensities and broader reflections could be referred to the decrease of crystallite size of the nanoparticles, leading to the X-rays being more strongly and widely diffused than the one observed from sample M-01 [37] TEM images shown in Fig reveal the morphology and size distribution of as-prepared nanoparticles Sample M-01 (Fig 3a and b) appears with an unidentified morphology, widely distributing from tens to hundreds nanometres Whilst, sample M-02 (Fig 3c and d) and sample M-03 (Fig 3e and f) likely comprise homogenously spherical nanoparticles with the average diameter ca 10 nm, in form of tightly nanoparticle aggregates The upper bound on particle sizes, in comparing with the calculations from XRD analysis, could be explained by inhomogeneous strain and crystal lattice imperfections on the surface of the nanoparticles, leading to smaller calculated values in Scherrer's equation [38] (illustrated in Fig 5) Besides, in aqueous suspensions, a combination of Lifschitzvan der Waals and magnetic forces would result magnetite nanoparticles in tending to aggregate into considerably large nanoparticle clusters (>1 mm) [18], instead of discrete nanoparticles The aggregation not only reduces transport and delivery ability of magnetite inside biological medium, but also deteriorates the superparamagnetism due to the formation of grain-boundary crystallisation at closed contacts among these particles during ageing stage to form mesocrystal [39], a polycrystallite structure The inhomogeneous morphology of sample M-01 could be explained by simultaneous presences [40] of crystalline nucleation and growth throughout the synthesis process, induced from slowly dropping ammonia into the precursor solution This led to heterogeneous nucleation and condensational growth (Ostwald ripening process) [41], to form heterogeneous nano-sized particles as the product (illustrated in Fig 4a) In contrast, by pouring rapidly ammonia into reactant solution, the medium state promptly reached to solubility threshold and swiftly overcame the condensational growing process, leading to homogeneous mass nucleation [40] with uniformly sized monodispersed nanoparticles as the crystalline nuclei in M-02 and M-03 experiments As the result, the crystallites experienced a condensational clusterisation process by spontaneously clustering together to form larger clusters, which in order to reduce particle-solute concentration (illustrated in Fig 4b) However, these nanoparticles without a proper surface-protection could crystallisedly aggregate on neighbouring surface during the 326 T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 Table Comparison of the interplanar spacings of sample M-01, sample M-02 and sample M-03 to the standard data of magnetite (Fe3O4, JCPDS No 11-614) hkl Standard M-01 M-02 M-03 2q ( ) d (Å) 2q ( ) d (Å) Completeness (%) 2q ( ) d (Å) Completeness (%) 2q ( ) d (Å) Completeness (%) 200 311 400 511 440 30.09 2.967 32.22 2.776 95.36 30.08 2.968 99.95 30.32 2.945 99.28 35.42 2.532 35.64 2.517 99.41 35.60 2.519 99.52 35.60 2.519 99.52 43.05 2.099 43.34 2.086 99.38 43.44 2.081 99.17 43.10 2.097 99.91 56.94 1.616 57.26 1.608 99.48 57.26 1.608 99.48 57.58 1.599 98.98 62.51 1.484 62.86 1.477 99.54 63.00 1.474 99.34 62.80 1.478 99.63 synthesis processes, forming the secondary crystalline-aggregated structure that were composed of primary magnetite nanocrystallites, rather than terminating only at agglomeration Hence, responsiveness of the nanostructure to alternative external magnetic field, which applied to utilise superparamagnetic property [42], would be degenerated Unfortunately, the coalescence was unrecognisable by only TEM and XRD analyses Fig illustrates differences between coalescence and agglomeration, and imaginations for the unrecognisability Fig represents the room-temperature M-H curves of asprepared magnetite samples, measured by cycling the external magnetic field between À11,000 Oe and 11,000 Oe All samples, M01 (Fig 6a), M-02 (Fig 6b), and M-03 (Fig 6c) exhibit soft magnetic characteristic with large saturation magnetisation (Ms) values of 72.5 emu$gÀ1, 67.7 emu$gÀ1, and 57.7 emu$gÀ1, respectively, which equal to the sum of the magnetic moments in each cluster of magnetite nanoparticles [43] Whilst, the obtained coercive field (Hc) values are considerably distinguishable, with 75 Oe, 25 Oe, and Oe respectively according to coercivities of sample M-01, sample M-02, and sample M-03 The relatively high Hc value of sample M-01 is inferred from the over-threshold particle size of superparamagnetism, ca 20 nm, of magnetite material [44], explained by the formation of multi-domain magnetite nanoparticles [45] The weakest coercivity (5 Oe) of sample M-03 indicates the retained superparamagnetic property after completing the synthesis process This observation could be justified by the assumption that the as-prepared tiny and discrete magnetite nanoparticles, which freely alter following the applied external magnetic fields, and instantaneously respond to the magnetic alternatives Meanwhile, the modest coercivity of sample M-02 suggested the existence of polycrystallite clusters, which might embed many single-domain nanocrystallites by coalescence These domains might resist mutually from responding properly to the applied magnetic field The submicro-effect of shock waves could be applied to explain for the obtained differences in magnetic properties between sample M-02 and sample M-03 By continuously forming the rebounding waves derived from the formation and collapse of acoustic cavitations, the liquid medium accelerated M-03 crystallites to maintain their oscillating suspended motion microscopically during the stabilisation stage This eventually resulted in only physical agglomeration as the crystalline discretion was still Fig Schematic illustration of nucleations and subsequent condensations Fig TEM images of (a, b) sample M-01, (c, d) sample M-02, and (e, f) sample M-03 Fig Differences between coalescence and agglomeration, and the obtained size from XRD estimation and TEM observation T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 327 3.2 Magnetite-silica nanocomposites Fig MeH curves of (a) sample M-01, (b) sample M-02, and (c) sample M-03 preserved; hence, the superparamagnetic behaviour was expected (Fig 7c) Whilst, without an efficient surface-protection against the naturally strong surface tension of magnetite nanoparticles, M-02 crystallites spontaneously aggregated on the surface of the neighbouring crystallites during the stage of stabilisation by condensational clusterisation with high-energy collisions This led to not only physical agglomeration, but also crystalline coalescence at the interfaces (Fig 7b) Besides, by slowly nucleating and growing, M-01 co-precipitated nanoparticles were more likely to contain heterogeneous magnetic domains (Fig 7a) In summary, by analysing the observable characteristic results, ultrasonic irradiation seems to reduce the aggregation effects, thereby increasing the crystalline discreteness of the synthesised nanoparticles Fig Formation illustrations of (a) M-01 multi-domain nanoparticles, (b) M-02 multidomain polycrystallite nanoclusters, and (c) M-03 single-domain nanocrystallites The diffusive and surface-protective propose of nanoscopic effect of shock waves would be reinforced through explanation for experimental results of silica coating processes onto the surface of €ber-approach experiments magnetite nanoparticles by Sto Fig shows TEM images of as-prepared nanocomposites, which all show a core-shell structure according to the magnetite-silica composite materials The dark magnetite nanoparticles can be observed to be embedded in the light-grey silica layer However, the morphologies are different by varying the apparatuses Sample MS01 (Fig 8a and b) appears to have an unidentified morphology and a micro-scaled size The images also reveal clear structure of embedded magnetite clusters, dense agglomeration of numerous primary magnetite nanoparticles, inside the silica matrix Meanwhile, sample MS-02 (Fig 8c and d) comprises spherical nanocomposites, observed in form of quasi-mono and discrete core of magnetite nanoparticles inside the silica matrix This indicates a significant contribution of the technique since in nano-synthesis, monocore-shell structures constituted by hydrophobic cores and hydrophilic shells can be only efficiently achieved by utilising highly surface-protective agents, such as Brij-30, Triton X-100, Igepal CO520, or other high-molecular surfactants [46] In addition, the average diameter of MS-02 nanocomposites is ca 100 nm, coherent size for biological applications; e.g., size of cell: 10e100 mm, size of virus: 20e450 nm, size of gene: nm wide and 10e100 nm long [47] Magnetic properties of the as-prepared nanocomposites are derived from the room-temperature M-H curves as shown in Fig All the nanocomposite samples possessed a high coercivity, ca 70 Oe, in comparison with the value of Oe that obtained from M-03 magnetite nanoparticles The rises could be explained by the presence of the silica layer as the magnetically dead contribution to the total volume and mass of the magnetic nanocomposite The layer is not contributing to the total magnetic moment, and considered as a high temperature antiferromagnetic order covering the ferromagnetic nanoparticles [48] The interaction between the antiferromagnetic shell and the ferromagnetic core induces the increase in coercive force Besides, a significant difference of Ms values between the nanocomposites would demonstrate the morphologies of as-observed nanocomposite samples First, the negligible magnetic saturation of sample MS-02, ca 3.2 emu gÀ1 (Fig 9b), has been expected since the minimal number of magnetite nanoparticles in the core were observed from TEM images (Fig 8a and b) This led to a deficiency of total magnetic moment inside Fig TEM images of (a, b) sample MS-01, and (c, d) sample MS-02 328 T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 Fig M-H curves of (a) sample MS-01, and (b) sample MS-02 a single nanocomposite particle In contrast, the existence of numerous magnetite nanoparticles in a composite particle of MS01, as-observed in Fig 8c and d TEM images, consisted with a higher magnetisation value, 50.2 emu gÀ1 in Fig 9a Fig 10 illustrates proposed mechanism model of the silica coating processes resulting in the considerably different observations in structures and morphologies between as-prepared magnetite-silica composite materials By applying mechanical shake as diffusion solution, the unbalance between strong surface tension and significantly weaker diffusive driving force led to agglomerations of magnetite nanoparticles throughout the rapid hydrolysis and condensation of TEOS Therefore, micro-scaled composite structure containing dense magnetite clusters embedded inside silica matrix has been obtained as the product of experiment MS-01 (Fig 10a) In contrast, micro-massive driving force of shock waves would contribute to oscillating discretion of the nanocrystalltes This would lead to localised hydrolysis condensation of TEOS and growth of silica layer on the surface of single magnetite nanoparticles, forming spherical quasi-monocore nanocomposites (Fig 10b) Both samples of magnetite nanoparticles (M-03) and magnetitesilica nanocomposites (MS-02) were further characterised by IR spectroscopy (Fig 11) to demonstrate the capping role of silica on the surface of magnetite to form as-prepared nanocomposites Two main absorption bands of FeeO bonds, at 565.14 cmÀ1 and 397.34 cmÀ1 in magnetite spectrum (Fig 11a), are observed consisting with intrinsic stretching vibrations of metal-oxygen at tetrahedral site (Fetetra-O) and at octahedral site (Feocta-O), respectively [49,50] While, the corresponding bands are shifted to 559.36 cmÀ1 with significantly lower intensity or completely overlapped by an original high-intense shaped peak at 472.56 cmÀ1, which could be assigned to SieOeSi or OeSieO bending modes, in the nanocomposite spectrum (Fig 11c) The shifting and lessening observations between the spectra suggest a partial cleavage of these metal-oxygen bonds on the surface of magnetite nanoparticles to form SieOeFe bonds Besides, the bands at 802.39 cmÀ1, 958.62 cmÀ1, and 1105.21 cmÀ1, appeared in Fig 11c, Fig 11 IR spectra of (a) sample M-03, (b) silica, and (c) sample MS-02 Fig 10 Formation illustrations of (a) MS-01 multi-core nanocomposites, and MS-02 mono-core nanocomposites Fig 12 XRD pattern of sample MS-02 T.Q Bui et al / Journal of Science: Advanced Materials and Devices (2018) 323e330 refer to symmetric stretching mode of SieOeSi, symmetric stretching mode of SieO, and asymmetric stretching mode of SieOeSi, respectively [51,52] Also, a medium-intense peak at 1627.97 cmÀ1 and a broadening peak at 3433.29 cmÀ1 in Fig 11c are assigned to OeH bending vibration of SieOeH and OeH stretching vibration, respectively, on the silica-surface of the nanocomposite All the silica-related assignments are further confirmed by the corresponding characteristic peaks appearing in the reference spectrum of silica (Fig 11b) at 470.63 cmÀ1, 790.81 cmÀ1, 968.27 cmÀ1, 1105.21 cmÀ1, 1643.35 cmÀ1, and 3396.64 cmÀ1, entire-respectively In addition, two weak peaks observed at 3429.43 cmÀ1 and 1627.92 cmÀ1 in Fig 11a correspond to OeH vibrations of absorbed moisture on the surface of magnetite nanoparticles [53e55] Fig 12 represents the XRD pattern of MS-02 magnetite-silica nanocomposites Five clear-observed peaks, appearing at characteristic 2-theta positions of magnetite inverse cubic spinel structure lattices i.e 30.09 (200), 35.42 (311), 43.05 (400), 56.94 (511), 62.51 (440), indicate the well structural maintenance of magnetite nanoparticle cores after the formation of the composite material Besides, the amorphous silica matrix, coated onto the surface of magnetite nanocores, is revealed due to a high-intense broad peak observed between 20 and 30 [56] Conclusion The report proposed a facile technique based on the utilisation of ultrasonic assistance, consequently creating shock waves as diffusion technique and surface protection, to enhance coprecipitation method in synthesis of magnetite nanoparticles €ber approach 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observed in form of quasi -mono and discrete core of magnetite nanoparticles inside the silica matrix This indicates a significant contribution of the technique since in nano -synthesis, monocore-shell... technique and surface protection, to enhance coprecipitation method in synthesis of magnetite nanoparticles €ber approach in preparation of magnetite- silica nanoand Sto composites The synthesised magnetite. .. demonstrate the capping role of silica on the surface of magnetite to form as-prepared nanocomposites Two main absorption bands of FeeO bonds, at 565.14 cmÀ1 and 397.34 cmÀ1 in magnetite spectrum
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