Palm kernel shell based hydrothermal carbon for methylene blue removal in wastewater treatment: application of dual adsorption isothermal models

The application of hydrothermal carbonization (HTC) in biomass waste conversion has increased especially in preparation of adsorbent for waste water treatment.This study focuses on (i) the preparation of hydrothermal carbon (HC) from palm kernel shell (PKS), (ii) assessment of material quality by application of HC PKS on the removal of Methylene Blue (MB) and (iii) determination of maximum adsorption capacity (q m ) based on adsorption isotherm.Four isothermal adsorptions (Langmuir, Freundlich, Dubinin-Raduskevich (D-R) and Temkin) were used to analyze the results of adsorption experiment.The HC PKS tends to follow two isotherms simultaneously in MB adsorption.At low MB concentrations (10-50 ppm), HC PKS follows the Freundlich isothermal, while at high concentrations (75-130 ppm) HC PKS can also follow the Langmuir isothermal besides Freundlich.We introduce and discuss Dual Adsorption Isothermal Model for interaction between adsorbent -adsorbate at certain initial concentration.Isothermal D-R was used to determine the q m of HC PKS where it was found that HC PKS with chemical activation treatment after HTC (KCS-2) had the largest q m (54.01 mg/g).The surface area of KCS-2 is 32.21 m 3 /g which is the largest among HC PKS.The surface area supports the adsorption capacity value of KCS-2.The results of FTIR analysis show that the functional groups for all HC PKS are almost similar.