Fig. 8 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 b[r]
Trang 1Original Article
Surface-protective assistance of ultrasound in synthesis of
superparamagnetic magnetite nanoparticles and in preparation of
mono-core magnetite-silica nanocomposites
Department of Chemistry, College of Sciences, Hue University, Viet Nam
a r t i c l e i n f o
Article history:
Received 1 March 2018
Received in revised form
23 June 2018
Accepted 4 July 2018
Available online 11 July 2018
Keywords:
Fe 3 O 4 nanoparticles
Fe 3 O 4 @SiO 2 nanocomposites
Shock-wave
Ultrasonic assistance
Co-precipitation
St€ober method
Crystalline structure-magnetic behaviour
relationships
a b s t r a c t
Ultrasound was throughout employed to enhance the co-precipitation process for the synthesis of magnetite nanoparticles (Fe3O4) and the St€ober approach for the preparation of magnetite-silica nanocomposites (Fe3O4/SiO2) The synthesised magnetite nanoparticles exhibited single-domain nano-crystallites 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 mono-domain 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/)
1 Introduction
Magnetite (Fe3O4), well-known as the most strongly
mag-netic mineral in nature, has been attracting diverse
re-searches and applications[1,2] Magnetite nanoparticles possess
numerous potential applications in magnetic recording
technol-ogy, pigments, catalysis, photocatalysis, medical uses, and
envi-ronmental 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
prepara-tion methods of magnetite nanoparticles have been developed,
such as co-precipitation, hydrothermal synthesis, solvothermal
synthesis, sonochemical synthesis, and micro-emulsion[7]
Co-precipitation is the simplest and most efficient synthesis route
to obtain the magnetic particles, based on the following reaction:
Fe2þþ 2Fe3þþ 8OH/ Fe3O4þ 4H2O[8]; in which, a stoichio-metric mixture of ferrous and ferric precursors in aqueous me-dium 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, biologi-cally coherent size, and superparamagnetic property [9]a very
superparamagnetism of iron oxide nanoparticles and their heat-ing efficiency (specific absorption rate, SAR) [10], which is an imperative factor for magnetic hyperthermia applications In or-der to retain such properties, the prepared magnetite nano-particles also need a further proper modification for better fluidity and chemical stability[11,12]
St€ober et al., in 1968, reported a simple method to synthesise silica submicro-sized particles, based on the hydrolysis of tetrae-thoxysilane (TEOS) in aqueous alcohol solutions with the presence
* 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.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
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
Journal of Science: Advanced Materials and Devices 3 (2018) 323e330
Trang 2of 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
hy-drophilic 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
re-actions[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
nano-particles, 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-complicated apparatuses and mild reacting conditions, St€ober
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
microsized-composites Fe3O4/SiO2, which not only degrade mobility, but also
deteriorate individual magnetite nanoparticle magnetism
Ultrasound has been widely utilised in chemical synthesis and
1000 m s1e1500 m s1and typical frequencies of laboratory
ul-trasonic irradiations from 20 KHz to 15 MHz, experimental
ultra-sonic wavelengths vary from 10 cm down to 100mm[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
bub-bles 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 4 km s1and 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
sec-ond, resulting in a phenomenon of micro-mass transport If
main-taining 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 1illustrates 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
task to obtain the nanocomposite with morphological and sized uniformity[31,32]
In this study, coprecipitation-based experiments in synthesis of magnetite nanoparticles and St€ober approach in preparation of magnetite-silica nanocomposites have been proceeded to demon-strate 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 intro-duction 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
2 Experimental 2.1 Chemicals and reacting conditions Ferrous chloride tetrahydrate (FeCl2$4H2O), ferric chloride hexa-hydrate (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 puri fica-tion In all experiments, reacting solutions were deoxygenated by Nitrogen bubbling for 30 min 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 coprecipitation-based method following 3 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 40C, bubbling with N2 The assisted conditions were being kept in the further 30 min for ageing pur-pose.Table 1summarises the differences in synthesis procedure of M-01, M-02, and M-03 experiments, respectively
The black Fe3O4precipitates were isolated from the solutions by magnetic decantation and washed by deoxygenated distilled water several times; then dried in an oven at 50C for 4 h
Fig 1 Formation illustrations of acoustic cavitation throughout external ultrasonic propagation and of rebounding shock waves after implosive collapse.
T.Q Bui et al / Journal of Science: Advanced Materials and Devices 3 (2018) 323e330 324
Trang 32.3 Preparation of magnetite-silica nanocomposites
Magnetite-silica nanocomposites were synthesised by St€ober
approach following 2 processes, notated by MS-01, and MS-02 In
typical preparation procedure, 35 mg M-03 magnetite
nano-particles powder and 200mL sodium silicate solution was dispersed
in 20 mL ethanol, 8 mL distilled water, and 2 mL ammonia solution
With the assistance of mechanical shake or ultrasonic irradiation,
500mL TEOS was added to the reactant solutions at room
temper-ature The assisted conditions were being kept in the further 4 h All
the experiments were implemented at room temperature.Table 2
summarises the differences in the synthesis procedure of MS-01,
and MS-02 experiments, respectively
The Fe3O4/SiO2colloids were isolated from the liquid by
mag-netic decantation and washed with distilled water and ethanol
several times; then dried in an oven at 100C 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
ra-diation (l ¼ 1.5406 Å), and the mean crystallite size of
nano-particles 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)
3 Results and discussion
3.1 Magnetite nanoparticles
XRD patterns shown inFig 2are 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
diffrac-tion 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 62.51correspondingly 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 inTable 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
Scherrer's equation with full-width at half-maximum values ob-tained from the corresponding strongest peaks (311), are 27 nm,
9 nm, and 9 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 3reveal 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 homoge-nously 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 anal-ysis, could be explained by inhomogeneous strain and crystal lat-tice 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 Lifschitz-van der Waals and magnetic forces would result magnetite particles in tending to aggregate into considerably large nano-particle clusters (>1mm)[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 het-erogeneous nucleation and condensational growth (Ostwald ripening process)[41], to form heterogeneous nano-sized particles
as the product (illustrated inFig 4a) In contrast, by pouring rapidly ammonia into reactant solution, the medium state promptly reached to solubility threshold and swiftly overcame the conden-sational 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 inFig 4b) However, these nanoparticles without a proper surface-protection could crystallisedly aggregate on neighbouring surface during the
Table 1
Procedural differences of experiment 01, experiment 02, and experiment
M-03.
Experiment Ammonia introduction Assistance solution
Table 2
Procedural differences of experiment MS-01, and experiment MS-02.
Fig 2 XRD patterns of (a) sample M-01, (b) sample M-02, and (c) sample M-03 T.Q Bui et al / Journal of Science: Advanced Materials and Devices 3 (2018) 323e330 325
Trang 4synthesis processes, forming the secondary crystalline-aggregated
structure that were composed of primary magnetite
nano-crystallites, rather than terminating only at agglomeration Hence,
responsiveness of the nanostructure to alternative external
mag-netic field, which applied to utilise superparamagnetic property
[42], would be degenerated Unfortunately, the coalescence was
unrecognisable by only TEM and XRD analyses Fig 5illustrates
differences between coalescence and agglomeration, and
imagi-nations for the unrecognisability
Fig 6 represents the room-temperature M-H curves of
as-prepared magnetite samples, measured by cycling the external
magneticfield between 11,000 Oe and 11,000 Oe All samples,
M-01 (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$g1, 67.7 emu$g1, and 57.7 emu$g1, respectively, which
equal to the sum of the magnetic moments in each cluster of
magnetite nanoparticles [43] Whilst, the obtained coercivefield
(Hc) values are considerably distinguishable, with 75 Oe, 25 Oe,
and 5 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 nano-particles[45] The weakest coercivity (5 Oe) of sample M-03 in-dicates 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 magneticfields, and instantaneously respond to the magnetic al-ternatives 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 magneticfield
The submicro-effect of shock waves could be applied to explain for the obtained differences in magnetic properties between sam-ple M-02 and samsam-ple M-03 By continuously forming the rebounding waves derived from the formation and collapse of acoustic cavitations, the liquid medium accelerated M-03 crystal-lites to maintain their oscillating suspended motion microscopi-cally during the stabilisation stage This eventually resulted in only physical agglomeration as the crystalline discretion was still
Table 3
Comparison of the interplanar spacings of sample M-01, sample M-02 and sample
M-03 to the standard data of magnetite (Fe 3 O 4 , JCPDS No 11-614).
Standard 2q( ) 30.09 35.42 43.05 56.94 62.51
M-01 2q( ) 32.22 35.64 43.34 57.26 62.86
Completeness (%) 95.36 99.41 99.38 99.48 99.54
M-02 2q() 30.08 35.60 43.44 57.26 63.00
Completeness (%) 99.95 99.52 99.17 99.48 99.34
M-03 2q( ) 30.32 35.60 43.10 57.58 62.80
Completeness (%) 99.28 99.52 99.91 98.98 99.63
Fig 4 Schematic illustration of nucleations and subsequent condensations.
Fig 5 Differences between coalescence and agglomeration, and the obtained size T.Q Bui et al / Journal of Science: Advanced Materials and Devices 3 (2018) 323e330
326
Trang 5preserved; 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
irradia-tion seems to reduce the aggregairradia-tion effects, thereby increasing the
crystalline discreteness of the synthesised nanoparticles
3.2 Magnetite-silica nanocomposites The diffusive and surface-protective propose of nanoscopic ef-fect of shock waves would be reinforced through explanation for experimental results of silica coating processes onto the surface of magnetite nanoparticles by St€ober-approach experiments
Fig 8shows 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
MS-01 (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 Mean-while, sample MS-02 (Fig 8c and d) comprises spherical nano-composites, 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
CO-520, 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: 10e100mm, size of virus: 20e450 nm, size of gene: 2 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 9 All the nanocomposite samples possessed a high coercivity,
ca 70 Oe, in comparison with the value of 5 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 mor-phologies of as-observed nanocomposite samples First, the negli-gible magnetic saturation of sample MS-02, ca 3.2 emu g1 (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 6 MeH curves of (a) sample M-01, (b) sample M-02, and (c) sample M-03.
Fig 7 Formation illustrations of (a) M-01 domain nanoparticles, (b) M-02
multi-T.Q Bui et al / Journal of Science: Advanced Materials and Devices 3 (2018) 323e330 327
Trang 6a single nanocomposite particle In contrast, the existence of
numerous magnetite nanoparticles in a composite particle of
MS-01, as-observed in Fig 8c and d TEM images, consisted with a
higher magnetisation value, 50.2 emu g1inFig 9a
Fig 10 illustrates proposed mechanism model of the silica
coating processes resulting in the considerably different
observa-tions 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 ag-glomerations of magnetite nanoparticles throughout the rapid hydrolysis and condensation of TEOS Therefore, micro-scaled
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 magnetite-silica 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
397.34 cm1in magnetite spectrum (Fig 11a), are observed con-sisting 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 cm1 with significantly lower intensity or completely overlapped by an original high-intense shaped peak at 472.56 cm1, 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
802.39 cm1, 958.62 cm1, and 1105.21 cm1, appeared inFig 11c,
Fig 10 Formation illustrations of (a) MS-01 multi-core nanocomposites, and MS-02
Fig 9 M-H curves of (a) sample MS-01, and (b) sample MS-02.
Fig 11 IR spectra of (a) sample M-03, (b) silica, and (c) sample MS-02 T.Q Bui et al / Journal of Science: Advanced Materials and Devices 3 (2018) 323e330
328
Trang 7refer 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 cm1and a broadening peak at 3433.29 cm1inFig 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 cm1, 790.81 cm1,
968.27 cm1, 1105.21 cm1, 1643.35 cm1, and 3396.64 cm1,
entire-respectively In addition, two weak peaks observed at
3429.43 cm1 and 1627.92 cm1 in Fig 11a correspond to OeH
vibrations of absorbed moisture on the surface of magnetite
nanoparticles[53e55]
Fig 12represents the XRD pattern of MS-02 magnetite-silica
nanocomposites Five clear-observed peaks, appearing at
charac-teristic 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 20and 30[56]
4 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
co-precipitation method in synthesis of magnetite nanoparticles
and St€ober approach in preparation of magnetite-silica
nano-composites The synthesised magnetite nanoparticles possess
uniform spherical morphology and narrow dispersed distribution
(ca 10 nm for average size), and exhibit as single-domain
nano-crystallites (5 Oe for coercivity) The as-prepared magnetite-silica
morphology (ca 100 nm for average size) and clearly observed
monocore-shell structure, and perform discrete mono-domain
surface-protective mechanisms at the nanoscopic scale of shock
waves, derived from the implosive collapse of acoustic cavitation
in liquid medium under ultrasonic irradiation, were supported
by investigating the crystalline structumagnetic behaviour
re-lationships of the nanomaterials
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