Valorization of Tunisian Silica Sand for the Synthesis of Silica Gel and its Application as a Sustainable Adsorbent for Crystal Violet Dye Removal

Abstract An eco-friendly mesoporous silica gel (SG) was synthesized from raw Tunisian sand and evaluated for the adsorption of the toxic crystal violet (CV) dye from water. The SG characterized using XRD, FTIR, SEM-EDX, N ₂ physisorption, TGA, and ZP. Structural analysis confirmed an amorphous phase and identified surface silanol (Si–OH) groups. The material exhibited a highly porous morphology and a pure SiO ₂ composition. N ₂ physisorption revealed a high SSA of 103 m²/g and a mesoporous structure with an average pore diameter of 19 nm. ZP measurements confirmed a negative surface charge, thereby promoting the uptake of CV. Optimal adsorption conditions were identified as pH 10, an adsorbent dosage of 0.05 g, and a contact time of 30 min. Equilibrium isotherms were well-described by both Langmuir and Freundlich models, with a maximum uptake of 164 mg/g. were found to be pseudo-second-order. The SG demonstrated remarkable stability, retaining 84% over three consecutive cycles. These findings confirm the use of the derived SG is reliable and stable, highlighting the successful valorization of natural sand for environmental remediation.