Fabrication of magnetic activated carbon from corn-cob biomass for the removal of acidic dyes from wastewater

Herein, iron oxide nanocomposites were prepared using corn cob waste biomass and Fe (NO3)3.9 H2O as iron source. The dried corn cob in grinded form were mixed with Fe (NO3)3.9 H2O solution heated for 60 min at 300 °C in nitrogen atmosphere to ensure complete carbonization. The exterior morphology, particle sizes, crystallinity, and elemental content etc. of the fabricated composite were SEM, XRD, and EDX analysis respectively. The XRD confirmed the presence of iron oxide on activated carbon framework and also validated the nano sized dimensions of resulting magnetic adsorbent. The nanocomposites were then employed as adsorbent for the removal of acid orange 8 and acid red 4 dyes from aqueous medium. To get maximum adsorption of selected dyes the experimental conditions like dosage of the adsorbent, temperature, and contact time were optimized. Langmuir and pseudo second order kinetics models best fitted experimental isotherm and kinetics data respectively. The optimum removal of selected dyes was achieved with 0.01 g of adsorbent dosage whereas equilibrium for both the dyes were achieved in 1 h. Additionally, the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) of the adsorption were enumerated using Vant’s Hof plot. The adsorption processes were found to be endothermic, as evident from positive values of ΔH° = 9.651 kJ/mol for AO 8 and 16.493 kJ/mol for AR 4. The processes in both the cases were found as spontaneous at higher temperature, evident from the positive to negative trending values of ΔG° (714.29, 104.28, and −505.733 J/mol for AO 8 and 271.93, −835.306, and −1942.54 J/mol for AR 4 at 20 °C, 40 °C, and 60 °C respectively. The positive entropy change (ΔS°) values of 30.5007 J/mol.K and 55.362 J/mol.K recorded, indicates the increasing disorder at the solid-solution interface for both the dyes. An attempt was made to recycle adsorbent using suitable solvents and up to 5 cycles the removing efficiency retained was still 76%.