Preparation and Characterization of High Surface Area Nanosilica from Iraqi Sand via Sol-Gel Technique

The present study revealed a low-cost process for utilizing desert sand for preparing nanosilica by sol-gel technique. This work required sodium hydroxide, concentrated hydrochloric acid, distillate water as raw materials, and Iraqi sand. Nanosilica sample was characterized by X-Ray Diffraction (XRD), scanning electron microscopy analysis (SEM), atomic


Introduction
In the last half-century, manufacturing processes, in general, have undergone a material application transformation as a result of a change from traditional bulk materials to nanoscale materials. The increase in possibilities for the manipulation of matter at the nanometer-scale has primarily led to this growth with nanomaterials at the leading edge of this fast-developing field [1]. Any substance with nanoscales in its structure is considered a nanomaterial, with dimensions ranging from one to one hundred nanometers [2].
Recent advancements in the field of nanotechnology have prompted several studies aimed at the synthesis and application of nanomaterials [3]. Because of their excellent physical and chemical properties, nanostructured materials have a broad range of applications, including electronics, textiles, agriculture, food, medicine, and cosmetics [1] [4].
In comparison to conventional methods, nanotechnology has been used as a very effective technique for improving the flow characteristics of heavy crude oil across pipelines via reduction the viscosity [5]. The nanomaterials may have unique benefits for the solvent deasphalting process because of their high surface area to volume ratio and hence a large number of available active sites, enabling them to selectively adsorb asphaltenes onto their surfaces and thus improve asphaltene removal [6].
Silica (SiO 2 ) has been the focus of extensive study because of the advantages it provides for a wide variety of applications. Silica can be present in nature as a major component of sand or in species such as rice husk, coffee husk, wheat husk, sugar cane bagasse, corn cob ash, and fly ash [7].Silica is widely available in the world, accounting for 59 percent of the Earth's crust [8].
The Western Desert of Iraq has enormous amounts of silica sand deposits [9]. These deposits are found in the Ga'ara, Hussainiyat, Najmah, Nahr Umr, and Rutbah. The Rutbah area was selected for the mine's location. Ardhuma is the name of the mine, which is situated about ten kilometers west of Rutbah Town. Silica sand deposits vary in particle size from extremely fine to coarse, although the most frequent are fine to medium grain sizes. The grains are sub-angular to sub-rounded in form, and the Fe₂O₃ content varies from 0.01 to 1.5% [10]. Nanosilica (NS) has the same structure as silica but with a particle size of less than 100 nm.
Nanosilica also gained popularity due to its highly reactive surface area [11], physical and chemical stability, and low toxicity [12]. In addition, silica nanoparticles (SNPs) have a large surface area and a small diameter, making them suitable for a wide range of applications, such as electronics and photonics, and energy harvesting and storage. In addition, they improve the solvent deasphalting process using nanosilica, which significantly impacts deasphalted oil and pitch yields. Finally, they have been shown to be effective at reducing the viscosity of heavy oil [5][6][13] [14].
NS was made using various procedures such as chemical precipitation process, sol-gel technique, vaporization with high temperature, and speed of the vertical rotating mill and planetary and ball mill are the most common methods for synthesis SNPs from Sand [14][15] [16].the raw materials used and the conditions of the process, such as temperature, time of precipitation, pH, addition of coagulants, and washing and drying methods. These Variables affect particle size, aggregation, and surface area [14].

.Chemical Materials
The chemicals used for Nanosilica preparation are listed in Table (2).

Procedure
A typical preparation of nanosilica using a chemical sol-gel technique that was modified from a previous study by Shakir [19], should be followed : The soild soduim silicate was cooled to room temperature and transferred to an 800 ml beaker. Next, 500 ml of distillate water was added to the beaker with vigorous stirring using a magnetic stirrer; the homogenous solution is produced when the reaction occurred. Finally, concentrated hydrochloric acid (36%) is added intermittently until pH reaches 1 to obtain a white gel, as shown in equation 2.
Continuous stirring at 400 rpm for one hour.

X-Ray Diffraction Analysis (XRD)
When X-rays scatter in many directions, forming a big hill-like bump, with a peak in the range 2Θ = 15°-30°, indicating the presence of amorphous structure and a highly disordered form of silica, amorphous phase would predominate [20]. Figure (2  clearly showed the amorphous nanosilica components are uniformly dispersed. However, it is essential to notice that agglomeration occurs and has an amorphous nature. Comparing the SEM micrograph analysis findings and the XRD pattern analysis reveals that the silica is amorphous nanosilica [22]. And the particles have a spherical shape with an average size of 26.75-28.93 nm and a porous appearance .this finding is in agreement with [13][17] [23].

Atomic force microscopy and Average particle size
AFM was used to detect the average diameter of SNPs, a high resolution of (444 * 452) pixels and a scanned area (1622*1651) nm² were used to obtain a sharp topography of NS. As a result, the average diameter of nanosilica prepared was 76.35 nm with a dimension range of 40-110 nm, as shown by the granularity cumulation distribution chart and particle size distribution as shown in Figure (4-a) and Table (3). The topography of the nanosilica surface can be seen very clearly in this research in two-dimensional and three-dimensional images, which displayed an aspherical shape and agglomerated tiny grains of nanosilica particles, as shown in Figure (

BET surface area analysis
The surface area was calculated using the BET procedure of physical nitrogen adsorption at liquid nitrogen temperature. The study found that silica nanoparticles prepared had surface areas of 510.96 m²/g. The BET surface area obtained by this study is higher than the surface area obtained by [14][17].

Conclusion
With the availability of high-quality sand in the western region of Iraq with a silica content of up to 98 %, the synthesis of silica nanoparticles from local raw sand is regarded as an ecofriendly and cost-effective process. Silica sand is a good alternative precursor that may be used as a silica source and chemically treated to produce silica nanoparticles. The surface area of chemically formed silica nanoparticles was quite high as compared to other methods of producing nanoparticles. The tests of the atomic force microscopy AFM prepared sample revealed that the production of silica nanoparticles in the average diameter of particles less than 100 nm, confirming the validity of the orientation in the selection of methods of preparation of nanosilica from the silica peak that resulted in the XRD experiments revealed that the silica nanoparticles was amorphous in shape. SEM scan identifies the spherical shaped morphology of produced nanosilica with a size ranging from 26.57 to 28.93 nm. The FTIR also show the NS spectrum at 1087.85 cm⁻¹. When the SNPs spectrum is compared and matched with the scientific literature, it is discovered to be entirely applicable with SNPs under study to ensure the validity of prepared nanomaterials; the FTIR spectra confirmed amorphous silica nanoparticles produced coinciding with the standard.