Obtaining Silicon Oxide Nanoparticles Doped with Fluorine and Gold Particles by the Pulsed Plasma-Chemical Method

+is paper presents a study on pulsed plasma-chemical synthesis of fluorineand gold-doped silicon oxide nanopowder.+e goldand fluorine-containing precursors were gold chloride (AuCl3) and sulphur hexafluoride (SF6). Pulsed plasma-chemical synthesis is realized on the laboratory stand, including a plasma-chemical reactor and TEA-500 electron accelerator. +e parameters of the electron beam are as follows: 400–450 keV electron energy, 60 ns half-amplitude pulse duration, up to 200 J pulse energy, and 5 cm beam diameter. We confirmed the composite structure of SixOy@Au by using transmission electron microscopy and energydispersive spectroscopy. We determined the chemical composition and morphology of synthesized SixOy@Au and SixOy@F nanocomposites.+ematerial contained a SixOy@Au carrier with an average size of 50–150 nm and a shell of fine particles with an average size of 5–10 nm.


Introduction
Silicon dioxide (SiO 2 ) nanopowder is widely used in various industries.It is used as a filler for polymeric paint and lacquer materials, improving the abrasion and durability of paints [1,2].SiO 2 is often used as a food additive with the intention of avoiding the clumping and caking of food [3,4].It is also used in the manufacture of toothpastes and medicines [5,6].SiO 2 is one of the main components in the production of glass, abrasives, ceramics, and concrete [7,8].Silicon dioxide is used in radio electronics, in particular, the production of microcircuits and fibre optic cables [9,10].At present, the properties of nanocomposite structures, which are used to create materials with preassigned properties, are being actively studied in modern solid-state physics [11][12][13][14].Production of a composite based on SiO 2 with various chemical elements (C, Au, and F) enables the improvement of the physical and chemical properties of the synthesized composite and expands its scope of use.Among such composites, SiO 2 @Au and SiO 2 @F composites deserve special attention.Nanoparticles of noble metals attract much attention because of their unique properties and many applications: chemical analysis, medical diagnostics and treatments, sensors, bactericidal materials, surface-enhanced Raman spectroscopy (SERS), enhancement of the fluorescence of organic dyes, etc. [15][16][17][18][19].To obtain the nanoscale composites of SiO 2 @Au and SiO 2 @F, the liquid-phase method, sol-gel method, classical chlorine process, and flame synthesis are used, among other methods [20][21][22][23][24][25][26][27].
In [21], a mesoporous SiO 2 @Au composite with a specific surface area of 650 m 2 /g was obtained using the solgel method.
e following silicon-and gold-containing precursors were used for the synthesis: tetraethoxysilane (C 2 H 5 O)4Si of high purity (99%) and sodium tetrachloroaurate (AuCl 4 Na).e obtained composite was stabilized by annealing in air at 600 °C.e composite would be useful as a standard for studying the optical and catalytic properties of particles of noble metals.
e SiO 2 @Au composite was synthesized in [22] using a combination of the sol-gel method and calcination processes.In studies of the physical and chemical properties of composites, it was found that the calcination temperature has an obvious e ect on the morphology and structure of the sample.e catalytic activity of the SiO 2 @Au nanocomposite was studied, and it was found that the synthesized SiO 2 @Au composites possess high catalytic activity.In [23], the SiO 2 @Au composite was synthesized by the sol-gel method.
e synthesis process included four steps: (a) preparation of silicon dioxide; (b) grafting gold nanoparticles over a SiO 2 shell; (c) priming of the silica-coated gold nanoparticles with 2 to 10 nm gold colloids; and nally (d) formation of the complete shell.e average size of the synthesized particles was 170 nm with a standard deviation of 18 nm.e SiO 2 @Au composite was obtained in [27] via the Stöber chemical method.e composite consisted of two particles of SiO 2 and Au. e average particle size for SiO 2 was about 300 nm and 100 nm for Au. e SiO 2 @Au nanocomposites possessed enhanced electrical and mechanical properties compared with silicon dioxide nanoparticles.
At this stage of research in the eld of obtaining nanocomposites based on silicon dioxide doped with uorine or gold particles, the possibility of organizing a pulsed plasma-chemical process for producing such nanomaterials has not been studied.is work is devoted to experimental research in this direction.
e reaction chamber was pumped out to a pressure of ∼7.6 Pa before introducing the mixture of gases.Figure 1 shows the experimental setup.
To obtain Si x O y @Au nanocomposites, we used gold chloride (AuCl 3 ).e gold-containing precursor was obtained from jewellers' gold by dissolution followed by evaporation.
e composition of jewellers' gold contains 58.5% gold, copper 33.5%, and silver 8%.e plasma-chemical reactor was preevacuated to 5 Torr, while SiCl 4 , O 2 , H 2 , and AuCl 3 were simultaneously introduced; after that, the reactor was heated to 180 °C.As a result of heating, gold trichloride was decomposed into gold monochloride and molecular chlorine.
Next, a pulsed electron beam was injected into the reactor, initiating reactions to obtain a nanosized silica powder as described in [30].One of the by-products of plasmachemical synthesis is water vapour.e synthesis process had a chain character and proceeded with signi cant heat generation.Two factors, namely, elevated temperature and moisture, contributed to the decomposition of gold monochloride (AuCl) into Au and AuCl 3 .
As a result, Si x O y @Au nanopowder was produced (the mass of the obtained powder was about 1.2 g per one act of pulsed electron beam impact on the initial reagents).
To obtain the Si x O y @F composite, the following reagents were used: sulphur hexa uoride, silicon tetrachloride, hydrogen, and oxygen.e initial reagents were injected into the plasma-chemical reactor, followed by the injection of the electron beam.As a result of the action of a pulsed electron beam on a gas mixture (SF 6 + SiCl 4 + H 2 + O 2 ), several parallel chemical reactions were initiated.ese reactions stimulated the interaction of chlorine and hydrogen, the oxidation of hydrogen, and the oxidation of sulphur hexa uoride with the formation of oxo uorides (OF, OF 2 , etc.), which participated in the synthesis of the nal product of Si x O y @F.Synthesized Si x O y @F powders were white.During the action of the pulsed electron beam, the mass of the obtained powder was about 0.8 g.Pulsed plasma-chemical synthesis of the Si x O y @Au and Si x O y @F nanocomposites was implemented in one step; all reagents were mixed in advance, and the synthesis process was implemented in one pulse.Moreover, no additional technological operations were required such as hardening and drying.

Results and Discussion
e chemical composition of the Si x O y @Au nanocomposite, obtained using the pulsed plasma-chemical method, was determined using an Oxford Instruments ED2000 energydispersive X-ray uorescence spectrometer.e X-ray uorescence spectrum of the synthesized composite is shown in Figure 2.  2

Journal of Nanotechnology
As can be seen from Figure 2, in addition to gold, the material contains a significant amount of impurities of copper, zinc, and nickel, which is likely because gold of gem quality was used to create the initial gold-containing precursor.Moreover, the iron content was noticeable, which can be explained by the participation of the metal parts of the reactor in the synthesis process during heating.
e Brunauer-Emmett-Teller (BET) method was used to study the specific surface area for all synthesized Si x O y @ Au samples.e specific surface area for the synthesized Si x O y @Au samples ranged from 140 to 220 m 2 /g.e morphology of the Si x O y @Au nanocomposites was determined using a JEOL-II-100 (Jeol Ltd., Japan) transmission electron microscope.e morphology of the Si x O y @ Au nanocomposites is shown in Figure 3.
e TEM images show that the synthesized particles had an irregular shape evenly covered with fine particles (Figures 3(a e phology of small particles was rounded (Figure 3(c)).Small particles of gold are evenly distributed on the surface of large particles (Figure 3(d)).e average size of the small particles (Au) ranged from 5 to 10 nm, and the diameter of the Si x O y particles ranged from 60 to 150 nm. Figure 4 presents the histogram of the particle size distribution.Histograms were constructed with a sample of over 1000 particles.
e silicon oxide in the obtained nanocomposites was amorphous.
e synthesized SiO 2 @Au composites were studied using an energy-dispersive X-ray spectroscopy (EDX method).e relative content of oxygen and silicon in the Si x O y @Au composite according to EDX-spectra was 26 wt.% and 57 wt.%, respectively.Mass content of gold in the composite was 17%.
Figure 5 shows micrographs of the synthesized Si x O y @F nanomaterial.
e nanomaterial had an amorphous structure, as evidenced by the absence of reflections on the microdiffractogram.e size of the Si x O y @F composite powders ranged from 20-45 nm (Figure 6).
Using the energy-dispersive X-ray spectroscopy (EDS) method, particles of the Si x O y @F nanocomposite were analysed to estimate the uorine content in the synthesized samples.e spectrum was taken at 20 points.Fluorine was rather evenly distributed throughout the nanomaterial particles.e average content reached 48 at.%, which indicates that uorine is mainly located on the surface.
Figure 7 shows the characteristic infrared absorption spectra of the Si x O y @F composite powders in the range from 400 to 4000 cm −1 (Nicolet 5700, ermo Fisher Scienti c, USA).
e studied powder was premixed with KBr and pressed into a tablet.e re ection spectrum of pure KBr was subtracted from the re ection spectrum of the mixture.
e IR absorption spectrum shows absorption bands typical for the Si x O y material.e 1090 and 815 sm −1 peaks responsible for Si-O-Si bond uctuation were typical for the samples under study.e 460 sm −1 peak is responsible for the bond oscillations in the Si-O-Si group.e band with a center of ∼940 cm -1 corresponds to the stretching vibrations of the internal OH-bond of SiOH.In addition, we recorded the bands at 1500-2000 cm −1 in the spectrum, which correspond to the H-O-H group.e stretching vibrations of hydroxyl groups and water molecules, ] oo , form an intense band in the region of 3200-3600 cm −1 [33,34]. is fact suggests that, in addition to physically adsorbed uorine, the surface of the nanoparticles probably contains largely silanol groups (SiOH), which adsorb water molecules [35].Comparing the re ection spectra of the composite Si x O y @F and the SiO 2 nanopowder obtained by the pulsed plasma-chemical method [36], an absolutely identical picture can be seen.Addition of sulphur hexa uoride to the initial mixture did not lead to the formation of chemical bonds that could be xed.

Conclusion
We have shown that it is possible to synthesize nanosized silicon dioxide doped with gold particles and uorine by using a pulsed plasma-chemical process.e Si x O y @Au and Si x O y @F composite powders, which consist of particles of irregular shape with a diameter of 20 to 100 nm, were synthesized.Silicon oxide in the obtained nanocomposites was amorphous.In the TEM images of Si x O y @Au nanocomposites, ne Au particles uniformly distributed on the surface of larger particles are visible.
Synthesized composites have a high potential for use as catalysts.e use of Si x O y @Au as a ller for conductive inks is also possible.e Si x O y @F-synthesized composites have a high potential as an additive for paints, as it is known from the literature that particles with a uorine-containing surface have hydrophobic properties.In addition, the synthesized composite can be of interest to additive technologies.Due to the uorine content in the surface layer of the nanoparticles, it is potentially possible to use the nanoparticles in order to reduce the temperature at which the 3D printing process takes place.
Data Availability e data used to support the ndings of this study are available from the corresponding author upon request.
Figure 2: e X-ray uorescence spectrum of the Si x O y @Au composite nanomaterials.
) and 3(b)).Powder morphology is represented by globules consisting of spherical-or oval-shaped fused nanoparticles.Two regions are noticeable in the images: dark (Au particles) and light (Si x O y particles), which indicates that the composite particles consisted of two components.e morphology of the composite was characterized by clusters of particles amalgamated into a single structure.

Figure 3 :
Figure 3: TEM images of the Si x O y @Au composite.

Figure 4 :Figure 5 :
Figure 4: Histogram of the distribution of sizes.

Figure 7 :Figure 6 :
Figure 7: IR absorption spectrum of the Si x O y @F-synthesized nanocomposites.