Use of Coffee Husk as an Adsorbent for Methylene Blue Dye

Abstract

This study evaluated the potential of raw coffee husk and activated carbon produced from this agroindustrial residue as adsorbents for the treatment of water contaminated with methylene blue. The moisture content of the biomass was determined, yielding a mean value of 12.97%. The biomass was subjected to calcination in a muffle furnace at temperatures ranging from 200 to 600°C, with 400°C identified as the most favorable condition, as it promoted adequate removal of volatile matter while maintaining a viable mass yield. Activated carbon samples and raw coffee husk were subjected to chemical treatments with HCl (0.1 mol·L⁻¹) and NaOH (0.1 mol·L⁻¹) at different contact times. Batch adsorption assays were conducted using an aqueous methylene blue solution (0.05 mg·mL⁻¹), monitored by visible-range spectrophotometry. Activated carbon demonstrated superior performance, achieving mean removal rates of 90.25% and 86.95% following NaOH and HCl treatments, respectively. Raw coffee husk reached removal rates of 44.09% (NaOH) and 67.45% (HCl). It is concluded that thermal activation combined with chemical treatment increases the porosity and active sites of the material, making coffee husk-derived activated carbon a promising adsorbent for the treatment of dye-containing effluents.