Synthesis of Na–O Functionalized Silicon Quantum Dots from Waste Coconut Shells: Structural Characterization, Optical Properties, and Application for theAdsorption Remediation of Textile Wastewater

Abstract

Silicon quantum dots (Si QDs) were successfully synthesized from waste coconut shells via a green, sodium-assisted route and systematically characterized for structural, optical, surface, and adsorption properties, with emphasis on their application in textile wastewater remediation. UV–Visible spectroscopy revealed strong ultraviolet absorption with pronounced peaks at 238 and 248 nm, corresponding to optical bandgap values of 5.21 and 5.00 eV, respectively, confirming strong quantum confinement. FTIR analysis showed abundant surface functional groups, including Si–O–Si, Si–O–C, C=O, C–O, and O–H, while SEM–EDS confirmed a silicon-rich core (≈90.3 at.% Si) with oxygen, carbon, and sodium surface functionalization. XRD patterns exhibited distinct crystalline Si reflections at 2θ ≈ 28.4°, 47°, and 56°, with an average crystallite size of ~0.324 nm, microstrain of 0.542, dislocation density of ~9.52 nm⁻², and a mixed crystalline–amorphous composition (≈43.2% crystalline, 56.8% amorphous). BET analysis indicated a high surface area and mesoporous structure with excellent linearity (R² ≈ 0.998), while DLS confirmed nanoscale dispersion and colloidal stability. The Si QDs demonstrated outstanding adsorption performance toward textile wastewater, achieving absorbance-based color removal efficiencies of ~65% within 15 min and up to ~95–96%.