A sustainable production of lignin-based activated carbon from sawdust for efficient removal of Basic Blue 9 dye from water systems

This study introduces a novel thermochemical conversion process to synthesize lignin-derived activated carbons (LEGHs) from sawdust, utilizing ethylene glycol (EG) as a liquefaction agent and phosphoric acid as an activating agent. The process was conducted at a 1:1 impregnation ratio, with temperatures ranging from 300 °C to 500 °C. The obtained materials were characterized using Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM–EDX), Fourier Transform Infrared Spectroscopy (FTIR), and nitrogen adsorption at 77 K. Optimal activation at 350 °C produced an activated carbon with a high surface area of 1230 m²/g and a micropore volume of 0.348 cm³/g. Adsorption tests for the removal of Basic Blue azo dye (BB9) were conducted in batch experiments mode to assess the influence of various parameters including pH, adsorbent dose, contact time, initial dye concentration, and temperature. The highest adsorption efficiency was obtained at pH 4, dose of 1 g/L and a contact time of 5 h, resulting in an adsorption capacity of 668 mg/g. The Langmuir isotherm model best described the adsorption equilibrium data (R² = 0.99), indicating adsorption on a homogeneous surface. The adsorption kinetics study well fitted by the pseudo-second-order model (R² = 0.99). Thermodynamic studies showed a spontaneous (ΔG°: −45.73 to −50.34 kJ/mol) and endothermic (ΔH° = 196 kJ/mol) adsorption process These findings underscore the potential of LEGHs as an effective and sustainable adsorbent for industrial wastewater dye removal, leveraging lignin, a byproduct of the paper and pulp industry, to enhance sustainability.