Chrysophyllum albidum stem bark extract coated tillite adsorbent for the uptake of Cr(VI): thermodynamic, kinetic, isotherm, and reusability

In this research, a novel green tillite-based adsorbent (CMT) was synthesized by modifying the surface of natural/pristine tillite (PT) with Chrysophyllum albidum stem bark extract for the efficient removal of Cr(VI) from water. The physicochemical characteristics of PT and CMT were assessed by the use of the FTIR, XRD, BET, TGA, and SEM techniques. Cardinal adsorptive parameters such as solution pH, contact time, adsorbent dose, and initial concentration were used to optimize the efficiency of PT and CMT for Cr(VI) adsorption. The Elovich kinetic model was noticed to best describe the uptake of Cr(VI) onto PT and CMT. Hence, chemisorption was the rate-controlling step for Cr(VI) uptake onto both PT and CMT. Meanwhile, the Langmuir maximum adsorption capacity of PT and CMT was 51.06 and 291.8 mg g −1 respectively, which was higher than those obtained for most materials used for Cr(VI) uptake. The Langmuir and Freundlich models best describe the equilibrium adsorption data for PT and CMT respectively. The reusability assessment of PT and CMT showed over 90% of the initial Cr(VI) uptake even after the fifth cycle of reuse. Electrostatic interaction and reduction of Cr(VI) were responsible for the removal of Cr(VI) from water onto the green material. The uptake of Cr(VI) was thermodynamically feasible, entropy-driven, and endothermic on both PT and CMT. The outcome of this study revealed that the anchoring of Chrysophyllum albidum stem bark extract on tillite produced a green adsorbent, which was highly efficient for the removal of Cr(VI) from polluted water.