Developing giant grass biochar-Fe₃O₄-g-C₃N₄ composite for the adsorption of methylene blue from aqueous solutions

The presence of methylene blue (MB) in textile effluents poses significant environmental and public health risks. Therefore, this study aimed to develop a giant grass biochar magnetite graphitic carbon nitride (BC-Fe₃O₄-g-C₃N₄) composite adsorbent via a co-precipitation method for the effective removal of MB from aqueous solutions. The adsorbent was characterized through proximate analysis, BET, FTIR, SEM, and pHpzc measurements. The adsorption process was evaluated considering the effects of adsorbent dose, pH, initial MB concentration, and contact time using a Central Composite Design (CCD) within Response Surface Methodology (RSM). The material characterization results showed a high fixed carbon content of 55.06%, a low ash content of 4.02%, and a BET specific surface area of 690 m2/g. Similarly, the pHpzc was found to be 8.09, and SEM analysis confirmed a porous structure with notable surface cracks and diverse functional groups. Adsorption optimization revealed that the maximum MB removal of 93.3% occurred at an initial concentration of 100 mg/L, pH 7, an adsorbent dose of 1.25 g/100 mL, and a contact time of 72.5 min. Based on the adsorption isotherm and kinetic modeling, the experimental data closely fitted the Langmuir (R² = 0.99) and pseudo-second order (R² = 0.88) models, respectively. Regeneration studies showed the composite adsorbent was effective in the initial cycles, but performance gradually declined after three cycles. Overall, these findings suggest that the composite adsorbent has promising potential for the remediation of dye-contaminated wastewater. However, further improvements are needed to adapt the technology for use with real industrial wastewater.