## 2 Materials and Methods--Pre-Preparation of Agricultural Waste Material
### Synthesis of Amorphous Nano-Silica  
To prepare amorphous nano-silica, a somewhat similar procedure is applied to agricultural waste, such as barley and wheat grass. To remove dirt and other particles, the agricultural wastes are generally rinsed with distilled water and dried for -24 h at 100 \({}^{\circ}\)C. As with other processes, a ball miller is used to grind the material into finely powdered samples of barley and wheat grass. To extract pure SNPs, 50 g of barley and wheat grass powder are processed in a solution of \(\sim\)250 mL 10\(\%\)\(w/v\) HNO3, cooled, and then washed with distilled water. The processed samples are then heated in a furnace at \(\sim\)700 \({}^{\circ}\)C for about 5 h after being refluxed with 250 cc of 2 M HCl for 6 h. From 50 g of barley powder, a total of 46.4 g of NSP was recovered, yielding a 92.4% yield. Depending upon the nature of agricultural waste and desired nature of nanoparticles, some of the following steps are used during synthesis. Figure 2: Schematic diagram of the experimental procedure to produce magnetic nano-silica. Adapted, in part, with permission from Ref. [30]. 2020, [PERSON] et al. _Pretreatment_: Normally the agricultural waste is cut into small pieces, weighed, soaked for about 3 h, and dried at 110 \({}^{\circ}\)C overnight. The resultant material is then crushed to 60-80 mesh before being submerged in hydrochloric acid for acid leaching. The material is then washed, filtered, dried, and then stored. _Heat treatment_: Roughly 2 g of processed rice husk is weighed and set in a controlled-environment furnace on a flat-bottomed crucible. The processed material is generally heat-treated in an atmosphere of air in a furnace heated to 500-700 \({}^{\circ}\)C at a rate of 10 \({}^{\circ}\)C/min. Once the desired temperature is attained, the sample is kept in the furnace for 3 h to eliminate organic materials from the pre-treated samples. _Preparation of a Ni/SiO\({}_{2}\) catalyst_. The impregnation process is used to make a 10 wt.% Ni/SiO2 catalyst. After dissolving a specified amount of nickel nitrate in water, the heat-treated sample is added and the suspension is agitated for 2 h before being transferred to a water bath and then dried. The samples are then baked overnight and calcinated for two hours in a muffled furnace heated at about 600 \({}^{\circ}\)C.  
_Acid treatment_: Many studies have looked at using industrial waste, notably fly ash (FA), to make SiO\({}_{2}\) nanoparticles [56; 57]. Due to the ease of these techniques, chemical pathways are used in the majority of such methods. Acid leaching treatment, alkaline treatment, and silica recovery are the three basic processes involved in chemical treatments. Acid leaching [58] is a useful pre-treatment method for removing organic materials and metallic contaminants from the waste. The output and purity of silica rise greatly while using the acid leaching technique, producing a greater surface area for silica products [59]. This is due to the fact that acid leaching alters the chemical makeup of the waste [59]. Acid-treated waste has a low degree of silica crystallization during the combustion process, according to [PERSON] and [PERSON] [58]. The waste is less sensitive to the combustion temperature since the crystallization catalyst has been eliminated. In comparison to non-acid-treated waste, the combustion process at a regulated temperature yields acid-treated waste with high amorphous SiO\({}_{2}\) content, low alkali oxides, low unburned carbon, smaller particle size, and large specific surface area. _Alkaline Treatment_ is a crucial step for breaking up the waste's chemical composition in an alkaline media and hence increasing silica production [60]. Due to its mild acidic nature, silica does not react with water [61], however, strong basic reagents, such as KOH and NaOH, do react with silica.