Efficient adsorption of anionic dye (congo red) using copper-carbon dots doped magnetic biochar: kinetic, isothermal, and regeneration studies

Novel copper-carbon dots doped magnetic biochar (CDMBC) was synthesized and applied for the remediation of congo red (CR) dye from an aqueous system. Copper doped carbon dots (Cu@CDs) were prepared by hydrothermal carbonization at 180 °C for 8 h using Ascorbic acid, urea, and copper chloride as precursors, and biochar was synthesized through pyrolysis of rice husk at 600 °C. The synthesized biochar was doped with Cu@CDs using the hydrothermal route at 150 °C for 4 h. The surface functionality and morphology of the as-synthesized CDMBC were analyzed using FESEM, XRD, RAMAN, FTIR, BET, and EDS studies. The as-synthesized CDMBC showed good adsorptive ability for the removal of CR dye in the shortest time of 10 min. The adsorption experiments were performed at different catalyst dosages, pH, initial concentrations, temperature, and contact time to determine the effect of different parameters on the removal rate. The kinetic and isothermal studies were evaluated at 20 mg L⁻¹ of CR concentration, 10 min contact time, pH-6.0, and 27 °C of temperature with 100 mg of catalyst dosage. The reaction followed second-order kinetics with an R² value of 0.992. The maximum adsorption capacity was observed to be 437.4 mg g⁻¹ at 100 mg of catalytic dose for the removal of 20 mg L⁻¹ of CR dye. The CDMBC exhibited excellent regeneration ability up to 5 cycles when treated with 0.1 M NaOH, showing removal of 90.1% after 5 cycles. These findings indicated that the CDMBC can be used as a potential catalyst in the removal of dyes from contaminated water.