Kendu (Diospyros melanoxylon Roxb) fruit peel activated carbon-an efficient bioadsorbent for methylene blue dye: equilibrium, kinetic, and thermodynamic study.

In this work, activated carbon was synthesized by the carbonization of kendu fruit peel followed by chemical activation using ammonium carbonate as an activating agent to get modified kendu fruit peel (MKFP). The SEM and FESEM images of the biomaterial illustrated a highly porous honeycomb-like structure, further supported by the N2 sorption isotherm analysis. The FTIR spectra specified the presence of oxygen-containing functional groups such as carboxyl, carbonyl, and hydroxyl on the adsorbent surface. Batch experiments were performed for the optimization of methylene blue (MB) dye removal. The adsorption process followed pseudo-second-order kinetic model and Langmuir isotherm model with a maximum adsorption capacity of 144.9 mg g-1. No desorption was found because the adsorbent surface was bonded with the chromophoric group of the MB dye by means of strong chemical interaction evident from the high adsorption energy (E = 10.42 kJ mol-1) and enthalpy change (∆H = 42.7 kJ mol-1). Hence, the MKFP has the potential to act as an efficient bioadsorbent for MB dye removal. Graphical abstract.