Activated carbon of Coriandrum sativum for adsorption of methylene blue: Equilibrium and kinetic modeling

Abstract

Different biomasses have been used as sustainable alternatives in the production of activated carbon for the treatment of effluents containing organic compounds. This study applies Coriandrum sativum L. (stem, roots, leaves) (CSL) as a precursor source for the production of activated carbon (AC-CSL), through chemical activation (H3PO4). The CSL and AC-CSL were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM). AC-CSL, on the other hand, was investigated using the technique of X-ray diffraction (XRD), Energy dispersive X-ray fluorescence (EDXRF), and N2 adsorption–desorption isotherms. The adsorption of Methylene Blue (MB) onto the AC-CSL was investigated under various experimental conditions. The FTIR results show a band around 2928 cm−1 in CSL that is related to the C–H bond of cellulose and hemicellulose. However, this band disappeared in AC-CSL. In fact, differential thermogravimetry (DTG) peaks in the TGA showed also an absence of these compounds in AC-CSL, while the XRD showed the presence of an amorphous structure in AC-CSL. In addition, EDXRF result revealed that AC-CSL contain a high percent of P2O5, while SEM images revealed the presence of porous structure on the AC-CSL. The AC-CSL showed a surface area of 193 m2g−1 and meso-microporous structure. The efficiency of removing the MB increases with the addition of contact time and dosage. The optimum conditions were found to be 90 min contact time, 8.0 g/L AC-CSL dosage and solution pH 10 at a temperature of 25 °C. The pseudo-second-order kinetic model and the Temkin isotherm were better adjusted to the experimental data, implying that the process was chemical and the adsorbate loses heat occurs linearly with the increase in the adsorbent coverage, respectively. The maximum adsorption capacity of MB onto AC-CSL was 94.9 mg g−1.