Decontamination of crystal violet using nanocomposite adsorbent based on pine cone biochar modified with CoFe2O4/Mn-Fe LDH

This study investigates the use of pine cones as a novel and readily available precursor for producing biochar (BC), which is then modified with CoFe₂O₄ magnetic nanoparticles and Mn-Fe layered double hydroxide (LDH) to enhance its adsorption capacity for removing the cationic dye crystal violet (CV) from aqueous solutions. The physical and chemical properties of the resulting adsorbents-BC (BCPC), BC/CoFe₂O₄, and BC/CoFe₂O₄/Mn-Fe LDH-were characterized using FTIR, XRD, VSM, SEM, EDX mapping, and BET analyses. BET results revealed that the specific surface areas of BCPC, BCPC/CoFe₂O₄, and BCPC/CoFe₂O₄/Mn-Fe LDH were 43.41, 95.81, and 98.85 m²/g, respectively, indicating a significant enhancement in surface area due to modification. Additionally, the magnetic saturation of the BCPC/CoFe₂O₄/Mn-Fe LDH composite was 32.35 emu/g, confirming that the composite could be easily separated from the solution using an external magnetic field. The composite achieved a maximum CV dye removal efficiency of 98.54% under optimal conditions: pH = 9, temperature 25 °C, adsorbent dose of 1 g/L, contact time of 70 min, and initial dye concentration of 10 mg/L. Isotherm studies revealed that the Langmuir model provided the best fit for the experimental data, suggesting a monolayer adsorption process on homogeneous surfaces. Kinetic studies indicated that the pseudo-second-order model was the most appropriate, highlighting the importance of chemical interactions in the adsorption process. Thermodynamic analyses revealed that the adsorption process was exothermic and spontaneous, as confirmed by negative enthalpy (∆H°) and Gibbs free energy (∆G°) values. In contrast, the negative entropy (∆S°) indicated a reduction in randomness during adsorption. This study demonstrates that the BCPC/CoFe₂O₄/Mn-Fe LDH magnetic nanocomposite is an effective, sustainable, and easily separable adsorbent for removing cationic dyes from aqueous environments.