Queensland nut tree ( Macadamia integrifolia ) activated carbon-based material for methylene blue dye removal: experimental design optimization with desirability function

The discharge of dye-containing wastewater, particularly methylene blue (MB) dye, poses significant environmental and health concerns due to its toxicity and persistence in aquatic systems. Herein, Queensland nut tree (Macadamia integrifolia) biomass waste was converted into mesoporous activated carbon (MAC-AC) for MB dye removal from aqueous environment. The MAC-AC was produced by using microwave-assisted H3PO4 activation at operating power (600 W) and residence time (15 min). Several characterization methods such as BET, XRD, FTIR, SEM-EDX, and pHpzc were applied to investigate the physicochemical properties of MAC-AC. Moreover, Box-Behnken design (BBD) and desirability functions were applied to optimize and validate the MB dye removal by MAC-AC. The best removal (98.8%) of MB was achieved at optimal desirability functions parameter of solution pH 8.6, MAC-AC dose = 0.09 g/100 mL, and contact time 119 min. The adsorption kinetic and isotherm analysis revealed that the adsorption process of MB dye onto MAC-AC surface followed the pseudo-second order (PSO) kinetic model and Langmuir isotherm model respectively. Moreover, the maximum adsorption capacity of MAC-AC for MB dye was found to be 459.9 mg/g. The adsorption of MB dye onto MAC-AC can be attributed to π–π interactions, pore filling, hydrogen bonding, and electrostatic forces. Furthermore, the production yield of MAC-AC was 25.2%, while the adsorbent retained 63.9% of its initial adsorption efficiency after five regeneration cycles, demonstrating acceptable regeneration capability and practical applicability. This research introduces a cost-effective, renewable, and reusable mesoporous activated carbon material as a promising adsorbent for wastewater remediation.