Fabrication of engineered biochar-iron oxide from date palm frond for the effective removal of cationic dye from wastewater

Wastewater containing dye is harmful to the environment. Methylene blue (MB) dye can be removed from wastewater using low-cost, renewable adsorbents. In this study, modified biochar (Biochar-Fe_xO_y), pristine biochar and Fe_xO_y were fabricated, characterized, and investigated for their performance to remove MB dye from wastewater. The Biochar-Fe_xO_y (85.1 mg/g) showed increased adsorption capacity in comparison to biochar (60.1 mg/g) and Fe_xO_y (50 mg/g) at an optimum pH of 8 due to the increase in surface area, porosity, and deposition of metal ions on its surface for adsorption. The enhanced MB adsorption by the Biochar-Fe_xO_y can be attributed to electrostatic attraction, hydrogen bonding, π-π interactions, and possible cationic exchange as evidenced by the result of the FTIR, EDX, and XRD analysis. Moreover, the adsorption of MB dye by the Biochar-Fe_xO_y showed an antagonistic effect in the presence of NaHCO₃⁻ and NaCl salt but showed a synergistic effect in the presence of Cu (II) ions. The Langmuir and pseudo-second-order isotherm model best describe the adsorption process of MB dye over the Biochar-Fe_xO_y. The adsorption capacity was still high after 4 regeneration cycles for the Biochar-Fe_xO_y which concludes that modified biochar can be effectively utilized for dye wastewater treatment. Finally, the fixed-bed column adsorption performance demonstrated that Biochar-Fe_xO_y could be used to polish real secondary textile industry effluents prior to treatment.