Acid-Treated Cotton Linter-Derived Mesoporous Activated Carbon for Textile Dye Removal: Effect of Hydrothermal Temperature on Pore Structure and Adsorption Mechanism

Activated carbons were prepared from acid-treated cotton linter waste, an industrial by-product, by hydrothermal carbonization at 160 and 200 °C for 12 h, followed by phosphoric acid activation and pyrolysis at 500 °C under nitrogen. The two carbons were tested against three dyes of different molecular size: Reactive Black 5, Basic Red 2, and Methyl Violet. The sample carbonized at 160 °C had the higher surface area (about 1156 m2 g-1), yet the more mesoporous sample carbonized at 200 °C (about 93% mesopores) removed the bulky Reactive Black 5 far more effectively (99.8% against 85.5%). Pore accessibility therefore mattered more than surface area for the large dye. All three dyes were removed by at least 97.6% within 90 min. Basic Red 2 and Methyl Violet followed the Freundlich isotherm, while Reactive Black 5 was taken up completely at every concentration tested. A moderate rise in carbonization temperature is thus a simple way to build mesopore-rich carbons for polishing dilute textile effluents.