Statistical Optimization and Desirability Function for Producing Nano Silica from Dune Sand by Sol–gel Method Towards Methylene Blue Dye Removal

This work aims to extract amorphous, high-purity silica nanoparticles (n-SiO 2 ) from natural sand using the sol–gel method, a simple, economic, and environmentally friendly chemical process. The parametric optimization by Box–Behnken design was carried out to optimize the synthesis parameters (reaction temperature, reaction time, and SiO 2 /NaOH ratio). The as-produced silica was characterized by several analytical techniques. A maximum silica yield of 87.62% was achieved when the T = 495.3 °C, t = 2 h and SiO 2 /NaOH = 7.88. The XRF and EDX results affirmed the high purity of the synthesized silica at 98.4% SiO 2 . The XRD spectrum shows an amorphous structure of the as-produced silica. Furthermore, the extracted silica exhibited a high specific surface area of 632.7m 2 /g, an average pore diameter of 2.82 nm, and an average particle size of 9.48 nm. The applicability of the BBD-optimized n-silica as a low-cost adsorbent toward removing Methylene blue (MB) dye from the aqueous environment was investigated. The adsorption kinetic was in excellent accordance with a pseudo-second-order kinetic models and the Temkin isotherm model, with a maximum adsorption capacity of 209.23 mg/g at 55 °C. These findings demonstrate that sand is a promising precursor for producing highly pure mesoporous silica for removing cationic dyes from wastewater and other possible applications.