Hydrothermally Prepared Sheep-Wool Biochar for Adsorptive Removal of Methylene Blue from Aqueous Solution

Abstract

Dye-contaminated effluents pose persistent environmental concerns, and low-cost biosource-derived adsorbents are attractive options for wastewater treatment. In this study, sheep wool was evaluated as a precursor for producing effective adsorbents for methylene blue (MB) removal from aqueous solution. Three materials were investigated: raw sheep wool, hydrothermally prepared wool biochar (180 °C, 5 h; 10 g wool in 100 mL distilled water), and solvothermally prepared wool biochar (180 °C, 5 h; 7 g wool in 100 mL ethanol). Batch adsorption experiments were conducted while varying contact time (5–40 min), initial MB concentration (10–50 ppm), adsorbent dose (0.04–0.20 g), temperature (25–55 °C), and solution pH (3–11), and residual dye concentration was quantified using UV–Vis spectrophotometry and percent removal calculations. Under representative conditions (20 ppm MB, 0.08 g adsorbent, pH 7), hydrothermal biochar achieved 81.17% removal, compared with 72.56% for raw wool and 36.54% for solvothermal biochar. Contact-time experiments at 20 ppm showed rapid uptake by hydrothermal biochar (79.93–84.49% from 5–40 min), whereas raw wool and solvothermal biochar exhibited lower performance over the same period. Overall, hydrothermal processing produced the most effective wool-based biochar for MB adsorption under the studied conditions.