Use of natural and effective mandarin peel in elimination of malachite green from the aqueous media: adsorption properties, kinetics and thermodynamics

Dye residuals in wastewaters of many industries are among the most important sources of environmental pollution. Malachite green (MG), one of these wastes, was removed by adsorbent produced by carbonization of mandarin peels. The carbonized mandarin peel (CMP) was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and zero point of charge (pHzpc). The equilibration time in the adsorption process was 150 min. When the equilibrium data were analyzed in terms of different isotherms, the most suitable isotherm was obtained to be Freundlich isotherm (R-2 = 0.997) and the maximum adsorption coefficient was found to be 357.14 mg/g. Different kinetic models were applied to experimental data for adsorption kinetics of MG on CMP, and it was observed that it fitted to pseudo-second-order kinetic model according to the R-2, Chi-squared and residual root mean square error values. When the thermodynamic parameters were examined, it was found that Gibb's free energy change was negative (<=-6.94 kJ/mol) and enthalpy change was 55.64 kJ/mol. Therefore, it was possible to mention that the adsorption process was spontaneous, endothermic and physical. In addition, the irregularity in the interface of the dye and CMP increased because the entropy was positive. CMP could be considered as a good alternative to available adsorbents used in waste disposal due to its high adsorption capacity, low cost and being environmentally friendly.