The synthesis of biochar-supported nano zero-valent iron composite and its adsorption performance in removal of malachite green

Abstract

The new composite material was synthesised bonding nano zero-valent iron (NZVI) with liquid-phase chemical reduction method on the support material obtained by carbonising the organic waste mandarin peel, and the surface characteristics of it were determined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and zero point of charge (pHzpc). The effectiveness of the composite as an adsorbent in the removal of malachite green (MG) was investigated with different parameters. Equilibrium data were employed to different adsorption isotherms used in aqueous solutions, and the most suitable isotherm was found as Freundlich isotherm with the highest R2 =0.999 and the lowest chi-square (χ2) and residual root-mean-square error (RMSE) values. The maximum adsorption capacity was 909.09 mg/g according to Langmuir isotherm. When the kinetic data were analysed, the most appropriate kinetic model was determined as pseudo-second-order with the lowest χ2 and RMSE and the highest R2 (≥0.987) values. The adsorption process was carried out as endothermic (∆H°=145.79 kJ/mol) and spontaneously (∆G°≤−2.89kJ/mol) according to thermodynamic parameters. Also, it was possible to say that the irregularity at the adsorbent-adsorbate interface increased due to positive entropy. NZVI/carbonised mandarin peel (CMP) with high adsorption capacity could be used effectively to remove many industrial wastes.