Preparation of a novel magnetic composite based on rice straw derived biochar and chromium ferrite for enhanced absorption of organic dye

The modification of biochar (BC) with metal/metal oxides is expected to improve its adsorption capacity to pollutants, especially anions dyes. A green chromium ferrite-biochar composites (CF-BC) was synthesized to enhance the adsorption efficiency of Congo red (CR) via a simple co-precipitation method. The samples were characterized by different characterization techniques: XRD, FT-IR, SEM, XPS, etc, which showed that chromium ferrite was successfully loaded on the surface of biochar. The influencing factors of adsorption and recycling properties were discussed, and the adsorption mechanisms such as kinetics, isotherm, thermodynamics were explored. The results show that CF-BC2 achieves a removal rate of 92.29% for CR and maintains a removal rate of 90% even after three cycles. The addition of ferrite not only promoted the adsorption effect, but also increased the magnetic property, making the adsorbents easy to recycle. The equilibrium and kinetic studies suggested that the adsorption process followed Freundlich isotherm and pseudo-second order model, respectively. Furthermore, a study into the adsorption mechanism revealed that CF-BC2 primarily achieves CR adsorption through electrostatic attraction, hydrogen bonding, 2c-2c interactions, and pore filling.