Silicate-intercalated NiFe layered double hydroxide for multi-pathway antibiotic degradation via enhanced...

Current catalysts face limitations in both weak radical and non-radical pathways, often leading to the production of toxic intermediates. To effectively degrade the refractory benzene rings of tetracycline (TC), it is crucial to control strong peroxymonosulfate (PMS)-activated radicals. To tackle these issues, a NiFe-silicate layered double hydroxide (NiFe-SiO₃ LDH) was synthesized using industrial waste montmorillonite as a silicon source through hydrothermal etching and co-precipitation. This approach promotes both waste valorization and the advancement of catalyst development. Comprehensive analyses (TEM, XRD, FT-IR, BET, XPS) showed that silicate doping triggers a "structural optimization- structural destabilization" mechanism. Adding SiO₃^2- made the pores smaller, down to 4.79 nm, and increased the surface area to 158.0 m²·g^-1, which helped mass transfer. It also changed the electronic structure by raising Ni²⁺ oxidation states (Δ ≈ 0.12 eV). Together, these effects synergistically improved PMS activation. Consequently, the optimized catalyst achieved 85.3 % TC mineralization within 20 mins with a rate constant of 0.13 min^-1, surpassing CoFe-based oxides and FeS benchmarks. However, excessive SiO₃^2- caused pore blockage and charge inversion, leading to catalytic deactivation. In-situ characterization (UV-vis, EPR) and HPLC-MS revealed a multi-pathway mechanism: Hydroxyl radicals (·OH) facilitate benzene ring epoxidation, whereas superoxide radicals (·O₂^-) and singlet oxygen (¹O₂) can promote heteroatom oxidation. This work establishes a paradigm of "precision doping-structural engineering-performance enhancement" for NiFe-LDH-based catalysts, offering sustainable technical solutions for aqueous antibiotic remediation.