Rice Husk–Sugarcane Bagasse-Derived Silica for Methylene Blue Removal in a Fixed-Bed Column: Synthesis and Characterization

Abstract

Methylene blue is a persistent dye that can impair light penetration and aquatic photosynthesis, while its chemical stability complicates conventional wastewater treatment. This study developed silica from a 3:1 mixture of rice husk and sugarcane bagasse, enabling the simultaneous valorization of two abundant agricultural residues, and evaluated its performance in a fixed-bed column. We subjected the mixed ash to alkaline extraction and acid precipitation, then characterized it by FTIR, XRD, SEM, and EDX. The product contained characteristic silanol and siloxane groups, exhibited an amorphous structure with a broad XRD peak at 2θ = 22.6°, and showed a rough, agglomerated nanoscale morphology that may provide accessible adsorption sites. At an initial methylene blue concentration of 23.846 mg L⁻¹ and a flow rate of 60 mL min⁻¹, the residual concentration decreased to 0.192 mg L⁻¹ after 80 min, corresponding to 99.19% removal. Removal reached 99.52% after 200 min, indicating promising performance under the tested conditions.