Integration of transition metal onto alginate activated carbon (M-AAC) for enhancing molybdate electro-adsorption

Molybdenum (Mo) in industrial effluents emerges both an environmental concern and a valuable recyclable resource. In this study, metal oxide-alginate activated carbons (M-AAC, M = Mn, Fe, Co, Ni, Cu, and Zn) were synthesized for Mo recovery in a membrane capacitive deionization (MCDI) system. Pyrolysis of alginate precursors significantly enhanced the effective surface area and dispersion of metal oxides within mesoporous carbon textures. The pseudocapacitive transformation of metal oxides contributed to charge storage, which increased the adsorption capacity for molybdate oxyanions under anodic potentials. Among the electrodes, Co-AAC demonstrated the highest Mo adsorption capacity (72 mg-Mo g^-1). Raman spectroscopy and free energy calculations indicated that Co₃O₄ active sites promoted molybdate uptake via multi-dentate complexation. At + 1.0 V (vs. RHE) and neutral pH, the Co-AAC electrode achieved excellent cycling stability for molybdate electro-sorption/desorption, along with strong selectivity over commons anions present in real water samples.