Development of copper—iron bimetallic nanoparticle impregnated activated carbon derived from coconut husk and its efficacy as a novel adsorbent toward the removal of chromium (VI) from aqueous solution

The present work demonstrates the preparation of biodegradable coconut husk derived activated carbon (CAC) impregnated with bimetallic nanoparticles consisting of zerovalent iron and copper to produce a new adsorbent (Fe⁰/Cu-CAC). The new adsorbent was further employed to determine the removal efficiency of Chromium (VI) from aqueous solutions. Chromium (VI) adsorption process by Fe⁰/Cu-CAC was found to be favorable at pH ~ 3, attaining 95.28% removal efficiency while its counterpart CAC attained only ~41%. Negative ΔG⁰ value suggests that the process was thermodynamically spontaneous and ΔH⁰ was observed to be 8.496 kJ/mol, further corroborating the endothermic nature of the process. Pseudo-second order model was best suited to explain the kinetics of the process with R² value of 0.99683 and an error of 6.73%. Equilibrium parameter (R_L) derived from Langmuir isotherm was calculated to be 0.1103, indicating favorable adsorption and thus Langmuir isotherm can be used to describe the process of adsorption of Cr (VI) by Fe⁰/Cu-CAC. Finally, a maximum monolayer adsorption capacity of 173.9 mg/g indicated the suitability of the prepared adsorbent in treating chromium contaminated wastewater streams. Practitioner points: Facile development of novel adsorbent from biodegradable coconut husk via cost effective route. Utilization of the adsorbent towards removal of toxic pollutant like Cr (VI) from its aqueous solution. Validation of the effective adsorption mechanism by Kinetic and Thermodynamic study.