## 1 Introduction
### Processes in the Synthesis of Silica Nano-Particles
It also uses potentially toxic reagents including SiCI\({}_{4}\), nickel tetracarbonyl (Ni (CO)\({}_{4}\)), and diborne (B\({}_{2}\)H\({}_{6}\)). Some of these reagents are explosive and caustic in nature [44]. Hydrothermal synthesis, in conjunction with CVD, is yet another method used to produce silica. Hydrothermal procedures are often carried out in a high-pressure confined compartment using subcritical or supercritical solvents [45]. Traditional hydrothermal methods have a number of limitations, including low yield, long process times, as well as heterogeneous structure. This problem can be fixed by using a regular microwave [46], which provides precise control of the shape of the resultant nanoparticles [47], as well as the production of materials that are unstable at the melting point and yet produce large, high-quality crystals [48]. It does, however, necessitate the use of a high-temperature furnace and substrate holder, as described by [PERSON] et al. [4]. Using similar chemicals, this approach may regulate the size, shape, and crystal structure of metallic nanoparticles, resulting in a sequence of seeds of varying shapes and sizes. Controlling reaction length, temperature, and reaction conditions will also provide a variety of geometries that might be useful in a variety of study domains [49]. Furthermore, this approach necessitates a substantial quantity of surfactant, and the stability of the microemulsion is impacted by the pH [48]. One of the earliest strategies for creating engineered nanomaterials was sonochemical synthesis [50]. Ultrasound irradiation is a straightforward method for producing a variety of nanomaterials from inorganic precursors, most often via primary, secondary, or combination methods (sonochemistry effects). Primary sonochemical synthesis refers to the intense transitory conditions such as high pressure and temperature from the collapse of the cavitation bubbles, whereas secondary sonochemical synthesis exploits the post-produced chemical repercussions in the liquid phase. As a result, this high-intensity ultrasonic method for nanoparticle synthesis eliminates the requirement for bulk high temperatures, high pressures, or long reaction times [47]. However, this approach yields a low number of materials [38]. Chemical precipitation is a popular approach for making SNPs since it is energy efficient and has a short processing time [51]. The co-precipitation approach, also known as the solid-state counterpart or a side-branch of the sol-gel process [52], is another successful soft chemical method of mixing oxide materials. Whenever deposition, development, coarsening, and/or agglomeration processes all occur simultaneously, it is termed a co-precipitation response. This process is straightforward, allows for precise size and depositing control, uses minimum heat, and hence is energy efficient [53]. It also has the advantage of immediately creating homogeneous nanomaterials with tiny sizes and dispersion into the solution via various chemical processes [54]. However, according to [PERSON] et al. [53], this method is not suitable for uncharged species, and the product produced may contain precipitated trace contaminants. It also has problems with batch-to-batch repeatability. Finally, the sol-gel approach has been widely used to create MSNPs because of its capacity to produce a pure and homogeneous product under moderate conditions [39]. It is a straightforward, cost-effective, and efficient production technique [38], however, the method utilizes expensive raw materials, as well as uses a high-temperature furnace [44]. This process involves the hydrolysis and condensation of metal alkoxides, such as tetraethyl orthosilicate, formally named tetraethoxysilane (TEOS) (Si (OEt)\({}_{4}\)), or inorganic salts such as sodium silicate (Na\({}_{2}\)SiO\({}_{3}\)) in the presence of an acid or base [4; 39].