Sustainable Production of KOH-Activated Microporous Carbon From Walnut Shell Biomass for the Adsorption of Cationic and Anionic Dye Pollutants.

This study aimed to develop activated carbon (K-AC) from walnut shells and evaluate its effectiveness for removing malachite green (MG) and Acid Red 14 (AR14) from aqueous solutions. The adsorbent was characterized using TGA/DTA, SEM-EDX, XRD, XPS, FTIR, pHPZC, and textural analyses. K-AC exhibited a BET surface area of 750 m2 g-1, an iodine number of 660.04 mg g-1, and a methylene blue index of 55.61 mg g-1. Batch adsorption experiments were performed to investigate the effects of contact time, adsorbent dose, and pH, and equilibrium and kinetic data were modeled using established adsorption models. The maximum adsorption capacities were 424.31 mg g-1 for MG and 72.10 mg g-1 for AR14. The Langmuir and Temkin models provided the best fits for MG and AR14, respectively, while the adsorption kinetics followed the pseudo-second-order model for both dyes. Thermodynamic analysis indicated that adsorption was spontaneous and endothermic. These results demonstrate the potential of walnut shell-derived K-AC as an effective and sustainable adsorbent for dye removal from wastewater.