KOH-activated carbon developed from biomass waste: adsorption equilibrium, kinetic and thermodynamic studies for Methylene blue uptake

In this paper, fallen coconut (Cocos nucifera) leaves were used as precursors to prepare activated carbon by thermal carbonization using KOH-activation method. The physical properties of the prepared coconut leaves-activated carbon (KAC) were calculated through the bulk density, ash content, moisture content, and iodine number. The surface characterization of KAC was undertaken using Scanning Electron Microscopy, Fourier Transform Infrared, and point of zero charge (pH(PZC)) method. Batch mode experiments were performed to assess the influence of the adsorbent dose (0.02-0.25g), initial pH (3-11), initial dye concentration (30-400mg/L), contact time (5-300min), and temperature (303-323K) on the adsorption of the methylene blue (MB). The kinetic uptake profiles are well described by the pseudo-second-order model, while the Langmuir model describes the adsorption behavior at equilibrium. The adsorption capacity (q(m)) of KAC increased with temperature where q(m) varied as follows; 147.1 (303K), 151.5 (313K), and 151.5mg/g (323K). Thermodynamic parameters such as standard enthalpy (H degrees), standard entropy (S degrees), and standard free energy (G degrees) showed that the adsorption of MB onto KAC was spontaneous and endothermic in nature under examined conditions. The results showed the potential use of activated carbon developed from waste coconut leaves for the removal of cationic dye (MB).