Thermal Carbonization of Biomass Wood Dust and Algae Wastes <i>via</i> Microwave-Assisted H<sub>3</sub>PO<sub>4</sub>: Desirability Function and Statistical Optimization for Methylene Blue Dye Removal

This research utilized a carbonization procedure via microwave irradiation assisted by H3PO4 to generate a cost-effective adsorbent (CWDAG) from wood dust (WD) and algal (AG) biomass. The resulting CWDAG adsorbent was characterized for its methylene blue (MB) dye adsorption properties. The activation process employs 800 W microwave radiation for 15 min under a nitrogen gas (99.99%) atmosphere. Multiple techniques were employed to study the physicochemical properties of CWDAG, such as FTIR, XRD, FSEM-EDX, pHpzc, and BET. Box-Behnken design (BBD) was employed to optimize the three important parameters of adsorption, as follows: A: CWDAG dosage (0.02–0.12 g), B: pH (4–10), and C: contact time (30–420) min. BBD results show the highest removal of MB (98.6%) was met with a contact period of 225 min, a dosage of 0.12 g/100 mL of CWDAG at pH 10. Analysis of the kinetic profiles show that MB adsorption onto CWDAG occurred via a pseudo-second order (PSO) model. Adsorption isotherm analysis at equilibrium confirm that the Freundlich and Langmuir isotherm models fit the equilibrium data with similar goodness-of-fit results. Based on the Langmuir model, the maximum adsorption capacity (qmax) of CWDAG for MB is 32.3 mg/g. The possible mechanism of MB adsorption on the CWDAG surface include several contributions such as π–π stacking, H-bonding electrostatic forces, and pore filling.