Binary adsorption studies of Cr(VI) and Cu(II) ions from synthetic wastewater using carbon from Feoniculum vulgare (fennel seeds)

Abstract

This study aims to remove Copper (Cu(II)) and Chromium (Cr(VI)) from aqueous solution using activated carbon (AC) from fennel seeds and potassium permanganate (KMnO4) treated fennel seeds. The activated carbon adsorbents were prepared from fennel seeds at different temperatures (500, 600 and 700°C). These adsorbents were designated as FS-500, FS-600 and FS-700. Each adsorbent was then chemically treated with KMnO4 solution to develop activated adsorbents, KMFS-500, KMFS-600 and KMFS-700. These six adsorbents were used for the binary adsorption of Cu(II) and (Cr(VI)) from an aqueous solution. The adsorbents were characterized by FTIR, SEM, UV-Vis and XRD. FTIR confirmed the presence of oxygen functional groups such as hydroxyl (-OH), carboxyl (-COOH) and carbonyl (-C = O) on the surface of the adsorbents. XRD confirmed a decrease in crystallinity as the temperature increased. SEM images showed that the morphology of the adsorbents was porous. KMFS-700 and FS-700 adsorbed more Cu(II) and Cr(VI) ions than KMFS-600, KMFS-500, FS-600 and FS-500. The maximum adsorption capacities for Cu(II) and Cr(VI) by FS-700 were 19.886 and 8.510 mg/g; for FS-600, it was 15.423 and 1.202 mg/g, and for FS-500, it was 16.921 and 1.722 mg/g, respectively. The maximum adsorption capacities for Cu(II) and Cr(VI) by KMFS-700 were 19.786 and 10.572 mg/g; for KMFS-600 it was 15.735, 8.109 mg/g, and for KMFS-500, it was 17.648 and 3.479 mg/g, respectively. All the adsorbents showed a stronger affinity for Cu(II) than Cr(VI). Kinetic studies showed that Cu(II) and Cr(VI) adsorption followed a pseudo-second-order reaction confirming that a chemical process controlled adsorption.