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 cheap source for the creation of activated carbon (AC) through the optimized ZnCl2-activation approach. 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 produced with a yield of 23.46% using a 1:1 ZnCl2:BAS impregnation ratio at 500 °C for 60 minutes. The ideal AC sample was identified by BET surface area (SABET), Boehm titration method, point of zero charges (pHPZC), FESEM, XRD, FTIR, and EDX. The identification consequences revealed that this 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 (AR) of methyl orange (MO) dye from its aqueous phase by this AC was accomplished at various solution pH (2–10), diverse mass of the AC (0.05-0.4 g), multiple initial concentrations (50–400 mg/L), variable temperature (30-50 °C) and diverse contact periods (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, 400 mg/L initial concentration of MO, 0.25 g AC dose, and 420 minutes contact period. 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 primarily involved electrostatic attractions and hydrogen bonding interaction. This work demonstrates that BAS is an excellent raw material for producing low-cost and effectual mesoporous AC carbon with substantive surface area.