Ultrasound-Enhanced ‎Alkaline Modification ‎of Wheat Straw for ‎Efficient Removal of ‎Industrial Ionic Dyes

This study aims to support eco-friendly wastewater treatment by converting lignocellulosic waste into valuable biosorbents, thereby contributing to sustainable waste management technologies. Wheat straw and its ash were examined as low-cost adsorbents for the removal of industrial ionic dyes, including cationic methylene blue and anionic methyl orange. To enhance adsorption performance, several surface modification approaches, including alkaline, acidic, and ultrasound-assisted treatments, were evaluated. The structural and surface characteristics of the modified materials were analyzed using Brunauer&ndashEmmett&ndashTeller and Fourier transform infrared spectroscopy techniques. Among all prepared adsorbents, the sodium hydroxide&ndashultrasound-modified ash (WSA-U-NaOH) exhibited the highest adsorption efficiency under initial testing conditions (25 mg/L dye), achieving capacities of 12.38 mg/g for MB and 4.47 mg/g for MO, evidencing a synergistic enhancement attributable to the combined effects of alkaline activation and ultrasonic cavitation. Optimization using the Taguchi model revealed that the maximum adsorption capacity for MB (53.29 mg/g) occurred at pH=12 with 0.05 g of adsorbent and an initial MB concentration of 75 mg/L after 45 minutes. For MO, optimal conditions (pH=2, 0.05 g adsorbent, and 75 mg/L MO) produced a capacity of 22.36 mg/g after 60 minutes. The adsorbent exhibited a markedly higher affinity toward the cationic dye, consistent with electrostatic interactions governed by surface charge characteristics. Kinetic analyses showed that adsorption followed the pseudo-second-order model, suggesting chemisorption as the dominant rate-controlling step. Equilibrium data were best fitted by the Freundlich isotherm, indicating heterogeneous multilayer adsorption. Thermodynamic parameters confirmed that the biosorption of both dyes was spontaneous and endothermic.