Mechanism enhanced active biochar support magnetic nano zero-valent iron for efficient removal of Cr(VI) from simulated polluted water

Abstract

This work focused on the use of low-cost magnetic biochar adsorbent prepared from Litchi chinensis peel for the Cr(VI) amelioration through the reduction-adsorption process. This magnetic biochar was prepared by the pyrolysis process, where the nano zerovalent iron (nZVIO) was decorated on the surface of Litchi peel biochar (LPBC). The XRD and TEM studies indicated that the nano-scale zerovalent iron nanoparticles were crystalline having a particle size of 5 ± 0.1 nm. The BET analysis showed the mesoporous nature of the material with good surface area (124 m2/g) and also material has a magnetic saturation value of 0.176 emu/g, where as surface area of LPBC were 325 m2/g and Ms valie 1.1 emu/g respectively. Three factorial Box–Behnken experimental design was simulated for Cr(VI) removal by taking key parameters initial concentration, adsorbent dose, and initial pH as independent factors. The optimum values obtained from desirability function and given by the model were initial Cr(VI) concentration of 5.87 mg/L, 3.14 for pH, and 0.195 g/L for adsorbent dose, which resulted in approximately 95.38% removal of Cr(VI) in these optimum conditions. Langmuir isotherm and pseudo-second-order kinetics data were explained in the adsorption studies. The adsorbent has an adsorption capacity of 98.36 mg/g at the obtained optimized conditions. The thermodynamics study specified a spontaneous process for Cr(VI) removal. The adsorption mechanism was detailed by XPS analysis which indicated a reduction of Cr(VI) to Cr(III) then adsorption of Cr(III) on the adsorbent surface.