## 2 Materials and Methods--Pre-Preparation of Agricultural Waste Material
### Synthesis of Amorphous Nano-Silica
The method of creating Na\({}_{2}\)SiO\({}_{3}\) solution from raw materials using a NaOH solution is well known as an alkaline treatment, where numerous factors must be managed, including the concentration, temperature, and duration of the process. The purity, crystallinity, and surface area of the silica product are all affected by such variables. The crystallinity and specific surface area of the particles are affected by the concentration of the alkaline solution, according to [PERSON] et al. [61]. The two Si-O amorphous silica bonds must split the linkages based on bond energy to form the intermediate monomer structure. Quartz, on the other hand, necessitates the dissolution of four Si-O bonds and a single Si-O bond, which is usually accomplished using a high-pressure hydrothermal process. [PERSON] et al. [62] also observed that the reaction temperature of the alkaline treatment impacted the rate of silica extraction. This is because amorphous silica has a high dissolving capacity. However, the process duration has an effect on silica solubility, which also impacts the purity of silica. Thus, the alkaline content is one critical factor that has a considerable impact on the silica product. The greater the concentration of the silicate solution, the smaller the crystallinity of the particles formed and the larger the specific surface area of the particles generated [61]. [PERSON] et al. [15] used a 2 M NaOH solution to perform an alkaline treatment on sugarcane bagasse ash. It effectively achieved high purity amorphous silica with a specific surface area of 240 m\({}^{2}\)/g and a purity of 98.92% with a range from 6 to 24 nm During the synthesis stage, the alkaline treatment caused particle agglomeration, which resulted in clusters. In comparison to the commercial silica used in this study, the surface area of the synthesized silica was also higher. [PERSON] et al. [62] also examined the silica extraction rate of five different concentrations of NaOH solution employed during the alkaline treatment (1, 2, 3, 4, and 5 M). The silica extraction rate rose from zero to 85.66% when the concentration of the NaOH solution was raised from 0 to 5 M. The amount of NaOH in the solution had a large influence on silica extraction. The silica recovered was mostly in the form of amorphous silica, which was obvious. Concurrently, [PERSON] et al. [63] produced Na\({}_{2}\)SiO\({}_{3}\) from bamboo leaf ash using a 1 M NaOH solution. Along with a few large-sized agglomerated nanoparticles, a high percentage of amorphous silica nanoparticles with an average particle size of 20 nm were produced. [PERSON] et al. [64] employed a 4 M NaOH solution in an alkaline treatment procedure to extract silica from bamboo leaf ash. Amorphous biogenic silica with a purity of 96.4% and a surface area of 98 m\({}^{2}\)/g was successfully produced, with no impurities found [65]. It is vital to think about how reaction temperature affects silica extraction, especially in terms of yield, purity, crystallinity, and surface area of the silica product. [PERSON] et al. [66] investigated the effectiveness of silica extraction at six different alkaline reaction temperatures (25, 60, 70, 80, 90, and 100 \({}^{\circ}\)C) and discovered that only a small quantity (1.4-14%) of silica leached from the rice husk into the NaOH solution at 25 \({}^{\circ}\)C. At 60 \({}^{\circ}\)C, the silica output increased to 68.4%. The silica production, however, did not improve after reaching 70 \({}^{\circ}\)C. The optimal reaction temperature for the alkaline solution of rice husk was found to be 70 \({}^{\circ}\)C. As a consequence, 98.5% pure amorphous silica with a surface area of 1.97 m\({}^{2}\)/g was effectively produced.