Integrated approach for heavy metal ion adsorption and heterogeneous fenton denitrification using functionalized...

Industrial solid waste valorization and the synergistic treatment of heavy metal wastewater and NO_x emissions remain critical environmental challenges. Herein, we establish a novel "waste-treats-waste" closed-loop paradigm by engineering salicylic acid-functionalized steel slag (SA-SS) as a dual-functional material for integrated heavy metal adsorption and heterogeneous Fenton denitrification. The SA-SS was synthesized via salicylic acid modification with comprehensive structural and chemical characterization. Its adsorption performance for Pb²⁺, Cu²⁺, Ni²⁺, and Zn²⁺ was investigated through batch experiments and kinetic/isotherm modeling. The functionalized material exhibited a hierarchically porous structure and abundant oxygen-containing groups, achieving exceptional maximum adsorption capacities of 303.21 mg/g for Pb²⁺ and 226.95 mg/g for Cu²⁺, governed predominantly by surface complexation. Innovatively, the spent metal-laden adsorbents were directly repurposed as in-situ heterogeneous Fenton catalysts, with SA-SS-Cu and SA-SS-Ni delivering superior NO removal efficiencies of 94.35% and 91.53%, significantly outperforming pristine SA-SS (86.53%). Mechanistic studies revealed that the adsorbed Cu and Ni species act as efficient electron mediators, accelerating the rate-limiting Fe(III)/Fe(II) redox cycle and thereby enhancing hydroxyl radical (•OH) generation. Density Functional Theory (DFT) further confirmed stronger H₂O₂ and NO adsorption and charge transfer on Cu/Ni-modified surfaces. This work presents a sustainable and circular pathway for simultaneous wastewater and flue gas purification, transforming steel slag into a high-value environmental material.