QUALITATIVE ANALYSIS OF HIGH GRADE NANOSILICON OBTAINED FROM COASTAL LANDFORM IN

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INTRODUCTION
Silicon is one of the best researched materials ever discovered by mankind and the semiconductor industry mostly uses silicon. The information technology revolution has been made possible by the discovery of silicon's properties. The developments in the vast area of nanotechnology have demonstrated that size reduction can be used to overcome the limits of bulk materials. When silicon is reduced to a size in the 1-100 nm range, quantum confinement has a significant impact on its properties and performance (Klaus, 2017). Research in electronics and photonics has revealed the peculiar properties of these materials, which have been used in biomedicine for tissue engineering, drug delivery, biosensing, radiotherapy, and sonodynamic therapy. This is possible because of the good biocompatibility and biodegradability of nanoscale silicon. Additionally, Si-based nanoparticles are being researched for application in optoelectronics (Sailor 2012), photovoltaics (Wu et al., 2001;Halbwax et al., 2008), and sensorics (Lin et al., 1997;Ahn et al., 2013). The nanoparticles differ from the bulk state of a similar material due to their larger surface area that is easily available (Obinson, 2013). In comparison to the bulk, the surface of nanoparticles typically exhibits softer vibration modes and thermal characteristics which work at lower temperatures. The synthesis of silicon by thermal reduction has employed a variety of materials such as Rice husks (Liu et al., 2013, Matsumoto et al., 2018, diatoms (Bao et al., 2007(Bao et al., ), land-based plants (batchelor et al., 2012 (rice grasses, sugarcanes), bamboo (batchelor et al., 2012(batchelor et al., , Kumar et al., 2016, silicon monoxide (Gao et al., 2017) and sand (Hai et al., 2009, Furquan et al., 2018. Sand is a naturally occurring, low-cost raw material. Magnesium is used as a reducing agent in the process of extracting silicon from sand. Recent interest has been focused to magnesiothermic reduction due its noticeably lower working temperatures (650 o C) (Favors, et al., 2014, Oluyamo, et al., 2023. The manufacture of silicon from sand by using magnesium as a reducing agent was primarily investigated as a potential anode material that might be used for rechargeable Lithium-ion batteries. (Hai et al., 2009, Favors et al., 2014Yoo et al., 2014 andArunmetha et al., 2018). Solar cell fabrication is another potential use of silicon (Arunmetha et al., 2018 andVenkateswaran et al., 2013). Similarly, luminous silicon nanoparticles were produced by reducing silica particles using a magnesiothermal (Matsumoto et al., 2018, Zhu et al., 2010and Chen et al., 2012. There are many ways of producing nanosilicon, including using sol gel, vapour phase, the thermal decomposition technique, thermal pyrolysis, chemical precipitation, electrospinning, lithography and biotransformation. Chemical treatment uses the acid and base solution method, but this procedure is costly, complex, and uses a lot of energy. Because of this, it is essential to use versatility and unique methods to produce silicon nanoparticles. The balling method has numerous advantages over other processes, including efficiency, high product purity, moderate reaction temperature, controllability, simplicity, and reproducibility. By reducing silicon to the nanoscale, it can adequately accept strain and avoid fracture (Chan et al., 2008, Liu et al., 2012. Several studies have been conducted on the extraction of elemental silicon using various starting materials, such as rice husk, sugarcane bagasse, corn cob, however there is little or no precise information on the isolation of nanosilicon from any of these materials. It is interesting to note that the landform in the studied areas have different colours and are merely utilized for agriculture. In addition to the possibility that the sand contain high grade silicon, the colour of the landforms is thought to have an influenced on silicon contents. In another way, it is believed that research on the qualitative analysis of nanosilicon will raise the landforms' industrial value. The study will provide a source of high grade silicon and nanosilicon for industrial uses and act as a data base for the creation of new strategies for transforming landforms into applications that are productive. The aims of the study is to investigate the qualitative analysis of high grade nanosilicon obtained from the coastal landform. Then the qualitative analysis was conducted using energy dispersive x-ray (EDX), scanning electron microscopy (SEM) and x-ray diffraction (XRD).

MATERIALS AND EXPERIMENTAL METHOD Materials
The sand used in this research work were from the coastal landform from Ese-Odo Local Government Area of Ondo State, Nigeria. Hydrochloric acid (HCl) (36%), sodium hydroxide (NaOH) and magnesium powder (Mg) were purchased from Pascal Scientific Ltd and used as analytical chemical reagents. Distilled water was used in the preparation of all solutions. Ball milling is a mechanical technique used to grind the materials into nanoparticles.

Collection of samples
The samples were collected into non-reacting polyethylene bags at a depth approximately about 30 cm below the surface. The locations of the areas where the samples were taken along with their sources are shown in Table 1.
Samples preparation 50 grams of each sand sample were successively washed for 3 hours in 250 ml of 1 M hydrochloric acid (HCl) at 75 o C and 1M sodium hydroxide (NaOH) at room temperature. After each process, distilled water was used to wash away any remaining acid or alkali traces. The washed sand sample was oven dried for a period of 2 hours at 105 o C. The sand samples were sieved into 63 µm using a mechanical test sieve shaker to ensure a homogenous size distribution and enhance purity of the materials.

Silica reduction with magnesium and synthesis of nanosilicon
To ensure effective reaction, 16.0 g of silica sand and 15.0 g of magnesium powder (180 µm) were thoroughly mixed together. This was then put into a crucible and heated for 30 minutes at 800 o C (Onojah et al., 2012;Vazeed et al., 2015 andOluyamo et al., 2023). The samples were then allowed to gradually cool to room temperature. The reaction's equation is as follows: SiO2 (s) + 2Mg (s) 2MgO (s) + Si (s) (1) MgO and Si are formed when silica and magnesium powder are heated. One gram (1 g) of silicon (Si) sample is washed in 20 ml of 5 M HCl at 100 o C and stirred with a magnetic stirrer for 60 minute for effective leaching to occur, the unreacted Mg and its products are entirely removed. Distilled water was thoroughly used to wash the product that had been leached by hydrochloric acid. The washed silicon (Si) samples are then dried for 5 hours at 105 o C in an oven before being stored in a desiccator. High energy ball-mill was used to grind dried silicon particles into nanoparticles. With the aid of EDX, SEM (using JOEL-JSM 7600F NanoSEM equipment) and XRD (using GBC EMMA XRD equipment, Australia), the isolated nanosilicon was analysed.

λ = 2
(2) where n denotes order of reflection, λ denotes wavelength of the incident X-ray (m), d denotes interplanar spacing of the crystal, and θ denotes Bragg's angle ( o ). Using Scherrer's equation, the crystallite size (L) was determined. It is given as: L = λ θ (3) where K is a constant value given as 0.91, λ is the incident Xrays' wavelength, θ is the Bragg's angle, B is the intensity of the full width at half maximum (FWHM).

RESULTS AND DISCUSSION Energy Dispersive X-ray (EDX) Analysis
Energy dispersive x-ray (EDX) analysis was used for determining the elemental composition of the raw samples from the coastal landform as indicated in Table 2. In terms of the elements observed in the spectra, EDX indicates that silicon has the highest percentage. Na, K, Al, and Fe impurities in quartz sands are assumed to originate from mica and feldspar minerals (Dal-Martello et al., 2011). For significant industrial use, the range of silicon content (i.e. 53.60 -58.52) in the raw samples as collected from the relevant sources (i.e. Pekahan, Igbekebo, and Oju-ala landforms) is considered to be quite low. 234 Nevertheless, the energy dispersive x-ray (EDX) analyses after the process of isolation indicated that the nanosilicon obtained from the samples ranged between 68.85% to 73.03% as shown in Figures 1-3. Coastal landform obtained from igbekebo had the highest percentage while that obtained from Pekehan had the lowest percentage value of nanosilicon. This may be as a result of the samples' chemical composition as previously established by Victor and Alvaro (2015). The values are high enough to be beneficial in the manufacture of materials and industrial use. Although sulphur and potassium were not detected in the raw samples, their appearance in the obtained samples may have been introduced into the materials via the sample holder of the EDX equipment as well as the chemicals used in the preparation of the samples.

Scanning Electron Microscopy (SEM) Analysis
As presented in Figure 1-3, the morphology of nanosilicon from Pekehan revealed the presence of agglomeration of irregular shaped particles with average particles sizes of 50.27 nm while Igbekebo and Oju-ala coastal landforms showed the presence of agglomerated ovoid shape with average particle sizes of 54.25 nm and 53.52 nm respectively. The result obtained showed that the high energy balling milling is effective for reducing the silicon into nanosize. The existence of agglomerates is an unavoidable phenomenon that is occur when small particles interact with one another due to electrostatic attraction or van der Waals force (Ruksudjarit & Rujijanagul, 2008). The small sizes of the nanosilicon obtained reveals that they can be effectively utilized for suitable application. The percentage values of the nanosilicon are also indications of possible attraction of the landforms for the production of high grade silicon materials for industrial applications and utilization which affirms findings in recent research by Oluyamo et al., 2023.

X-ray Diffraction (XRD) Analysis of Nanosilicon
Well-oriented and sharp distinct crystalline peaks were obtained in the X-ray diffraction patterns as shown in Figures 4-6. It was noticed that the silica had pronounced peak in the sample. This could be probably due to contact of the silicon powder with air especially during storage. Darghouth et al., 2021 had also attributed the presence of oxygen to the excess of silica that was not removed via HCl leaching. The nanosilicon's band position (2θ), full width at half maximum (FWHM), crystallite size, and d-spacing are all presented in Table 3. Calculations using Scherrer's equation (3) showed that the crystallite sizes were 45.37 nm, 47.55 nm and 45.80 nm for Pekehan, Igbekebo and Oju-Ala coastal landforms, respectively. As shown in Table 3, X-ray diffraction patterns of the nanosilicon for the coastal landforms showed that the diffraction peak planes are in good agreement with the International Centre for Diffraction Data (ICDD).

CONCLUSION
The study examined the qualitative analysis of high grade nanosilicon obtained from Coastal Landform in Ese Odo Local Government Area of Ondo State, Nigeria. The result obtained from EDX and SEM revealed that quality nanosilicon were produced. The samples that were analysed revealed that silicon and oxygen were prominent. Consequently, the result of the research indicates that nanosilicon can be obtained from the silica sand found in the study area. In addition, the value of silicon are of high grade that makes it suitable for industrial applications and use in sectors including the lithium ion battery, biomedical devices, photovoltaic/solar cell and computer industries.