Adsorptive Elimination of Methyl Orange Dye over the Activated Carbon Derived from Bitter Almond Shells. An Isothermal, Thermodynamic, and Kinetic Study

Abstract: Bitter almond shells (BAS) were inspected as a low-cost precursor in producing activated carbon (AC) through the optimized ZnCl2 activation route. The raw BAS were impregnated with ZnCl2 at multiple ratios (1:1 - 3:1 ZnCl2:BAS), followed by carbonization at various temperatures (400 – 800 °C) for different durations (30 – 120 minutes) in a tubular reactor. The typical AC sample was prepared using a 1:1 ZnCl2:BAS impregnation ratio and activated at 500 °C for 60 minutes. The AC yield under those conditions was 23.46%. The BET surface area (SABET), Boehm titration method, point of zero charge (pHPZC), Field Emission-Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), Fourier Transform Infra-Red spectroscopy (FTIR), and Energy Dispersive X-ray (EDX) of the optimal AC sample were determined. The identification outcomes disclosed that this AC sample is mesoporous with SABET, iodine number, total pore volume, and average pore width of 1221.60 m2/g, 1444.23 mg/g,1.50 cm3/g, and 4.98 nm, respectively. The adsorptive removal of methyl orange (MO) dye from its aqueous phase by this AC was accomplished at various solution pH (2–10), different amounts of the AC (0.05-0.4 g), multiple initial concentrations (50–400 mg/L), variable temperature (10-50 °C) and varied contact time (0–420 min) in a batch- mode operation. The maximum monolayer adsorption capacity of 224.71 mg/g was obtained at 323 K, pH= 2.0, initial (MO) concentration of 400 mg/L, 0.25 g AC dose, and 420 minutes contact time. The kinetic outcomes best fitted to the pseudo-2nd -order kinetics model, while the MO equilibrium capacity obeyed the Langmuir model rather than other models. Thermodynamic studies of the MO adsorption by the BAS-derived AC disclosed that the adsorption was spontaneous and endothermic. The adsorption mechanism of MO by the declared AC mostly involved electrostatic attractions and hydrogen bonding interaction. This work demonstrates that BAS is an advantageous raw material for producing low-cost and effectual mesoporous AC carbon with substantive surface area.