Efficient recovery of Cr(vi) from electroplating wastewater by iron-modified sludge-based hollow-structured porous carbon: coexistence effects and competition for adsorption

In the present work, porous carbon was made from sewage sludge and hybrid liriodendron leaves, and modified with iron ions (Fe@LS-BC) carried out on Cr(vi) in aqueous solution from a single-component system and in competitive biosorption with methyl orange (MO) from a binary-component system. The iron ion-modified porous carbon (Fe@LS-BC) showed higher efficiency in the removal of Cr(vi) compared to porous carbon prepared by the co-pyrolysis of sludge and hybrid liriodendron leaves. The incorporation of the Fe element improved the ability of the material to redox Cr(vi), while imparting magnetic characteristics to the porous carbon and improving the reusability of the porous carbon. On the other hand, Fe@LS-BC exhibited a better pore volume, facilitating the contact of the material with Cr(vi) ions. The highest adsorption capacity was 0.33 mmol g^-1, and the adsorption experimental results for the single-component and binary-component systems of Cr(vi) matched well with the Langmuir-Freundlich models. When the concentration of MO was 0.2 and 0.8 mmol L^-1, respectively, the highest adsorption capacity of Cr(vi) was 0.35 and 0.46 mmol g^-1 in the binary system. The positively charged N-CH₃ ⁺ on the MO molecule promoted the electrostatic adsorption between HCrO₄ ^-, CrO₄ ^2-, and Fe@LS-BC, and increased the adsorption potential of Cr(vi).