Sustainable Methylene Blue Removal using NaOH-Activated Rice Husk Charcoal

Abstract

Water pollution from synthetic dyes such as methylene blue (MB) remains a serious environmental issue, particularly from textile and paper industries. This study explores rice husks as a low-cost bioadsorbent through four treatments: raw husks (SM), NaOH-activated husks (SA), rice husk charcoal (A), and NaOH-activated charcoal (AA). For the activated materials, the rice husks were immersed in a 6 M NaOH solution for 4 hours with intermittent manual stirring, followed by washing until neutral pH was reached and drying. Adsorption efficiency was evaluated using UV-Vis spectroscopy, while FTIR identified functional groups. AA demonstrated the best performance, reaching 95.28% efficiency at 6 hours and 96.96% at 18 hours, with equilibrium achieved at 6 hours. This enhanced adsorption is attributed to π–π stacking between aromatic structures and MB molecules, as well as electrostatic interactions from negatively charged –OH groups introduced by alkaline activation. In addition to its excellent adsorption capability, the application of rice husks as a renewable bioresource offers clear environmental and economic benefits through waste conversion and reduced dependence on conventional activated carbon. These results confirm the potential of NaOH-activated rice husk charcoal as an efficient, sustainable, and environmentally friendly adsorbent for dye wastewater treatment.