A new absorbent by modifying walnut shell for the removal of anionic dye: Kinetic and thermodynamic studies

• Walnut shell was modified as an innovative biosorbent for dye removal.
• The effects of pH and absorbent dosage on adsorption capacity were evaluated.
• Adsorption process fits Langmuir isotherm and pseudo-second-order kinetic model.
• The modified walnut shell was an excellent biosorbent for K-2BP removal.

A novel, low cost and easy regeneration biosorbent, chem-modified walnut shell (MWNS), was studied to investigate its potential for removal of an anionic dye, reactive brilliant red K-2BP. The MWNS was synthesized with epichlorohydrin and diethylenetriamine as etherifying agent and crosslinking agent, respectively, and its characteristics were performed with Fourier transform infrared spectroscopy, scanning electron microscope, electron dispersive spectroscopy and thermogravimetric analysis. The influences of pH (0.5–11) and adsorbent dosage (0.1–6 g/L) on adsorption capacity of MWNS were evaluated. The maximum K-2BP adsorption capacities (Qm) calculated by best fitting model (Langmuir) were 568.18 mg/g at 313 K, which was almost 10 times than that of raw material. The adsorption kinetic was well confirmed with pseudo-second-order equation. Thermodynamic studies demonstrated adsorption process by MWNS was spontaneous and endothermic. Furthermore, the regeneration capability of MWNS implied MWNS was a cheap, excellent and promising biosorbent for K-2BP removal in azo dye wastewater treatment.

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