Synergistic Indigo Carmine Removal via Adsorption and Oxidation Using Iron-Loaded Coconut Biochars

High Resolution Image Download MS PowerPoint Slide Magnetic biochars (MBCs) integrate adsorption and heterogeneous Fenton-like oxidation and offer a sustainable strategy for removing recalcitrant dyes from water. Here, two iron-loaded coconut biochars, MBC1 and MBC2, were synthesized and evaluated for the removal of indigo carmine (IC). MBC2, which was prepared by impregnating prepyrolyzed biochar with FeCl 3, showed a higher adsorption capacity (112.1 mg/g) than MBC1 (51.2 mg/g). IC removal was investigated using two approaches: a stepwise process, in which adsorption equilibrium was reached prior to H 2 O 2 addition, and a simultaneous adsorption oxidation process. In the stepwise approach, catalytic oxidation increased IC removal, achieving up to 82% decolorization for MBC2 (15 mg; IC:H 2 O 2 = 1:150) within 3 h after adsorption. The simultaneous process was more efficient, enabling complete IC removal with MBC2 in 8 h, while also promoting the adsorption of oxidation byproducts. Radical-scavenging assays indicated that singlet oxygen ( 1 O 2 ), rather than hydroxyl radicals, is the main reactive species. Both MBCs demonstrated reusability, although a gradual decrease in activity was observed due to iron leaching. Overall, these results highlight coconut-derived MBCs as multifunctional materials capable of coupling adsorption and catalytic oxidation, offering an effective and sustainable platform for integrated water treatment.