The present study examines an alternative method for extracting silica from natural waste such as bamboo leaves (BL) via thermal combustion, followed by acid treatment and alkaline extraction. The physico-chemical properties of extracted silica were studied by comprehensive characterization tools. FESEM revealed that extracted silica is highly porous and interconnected. EDX, XRD and FTIR study confirmed the purity, amorphous nature and functional groups of extracted silica. The major interest of this paper was to functionalize extracted silica with alginate and to optimize the parameters such as pH (at 5), and equilibrium time (60 min) for the removal of methylene blue (MB) from aqueous solutions. The kinetic data was fitted well in the pseudo-second order model and the maximum adsorption capacity was found to be 54.35 mg/g. The favorability of the Langmuir isotherm suggested that the adsorption system was dominated by the monolayer adsorption process with uniform adsorption sites present on the surface. The morphological changes due to MB adsorption on prepared composites were authenticated by FTIR and DFT calculations. Therefore, the present investigation emphasizes the suitability of silica extraction from bamboo leaves waste over chemical precursors to synthesize adsorption composites.