Preparation and characterization of raw and carbon from banana peel by microwave activation: Application in citric acid adsorption

Microwave-assisted char (MBPC) was synthesized from raw banana peel (RBP) and the potential of these adsorbents to remove CA from aqueous solution is studied. The adsorbents were characterized by elemental analysis, BET surface area, point of zero charge, surface pH, surface charges, SEM, FTIR, and TGA/DTG. Following microwave treatment, the surface area of MBPC increased to 22.37 m2/g (from 0.65 m2/g) which is 34.41 times more. The adsorption properties of MBPC and RBP were compared using CA as the adsorbate. The FTIR result shows the interactions between the hydroxyl and amine groups during the adsorption process. The concentration of basic sites (4.9 and 5.2 mmol/g for RBP and MBPC, respectively) is found to be higher than acidic sites (0.75 and 0.85 mmol/g for RBP and MBPC, respectively). The surface of MBPC is rough and porous due to microwave treatment. Langmuir, Freundlich, and Temkin isotherms were applied to the system. The Langmuir adsorption capacity for CA removal on MBPC was 147.06 mg/g, which is two times higher than that achieved on RBP (76.13 mg/g) at pH 4.75, 50 °C. The equilibrium was achieved in about 240 and 330 min for adsorption of CA onto MBPC and RBP, respectively. For both adsorbents, the R2 values were close to 1, which indicates that the adsorption of CA follows the pseudo-second-order model.