Bayberry tannin-functionalized melamine foam: A recyclable scaffold for nZVI-catalyzed metronidazole reductive degradation.

The presence of metronidazole (MNZ) in medical wastewater poses a potential threat to environmental safety and people's health. Herein, we report an innovative strategy to fabricate a recyclable bayberry tannin (BT)-functionalized melamine foam (MF)-supported nanoscale zero-valent iron (MFBT-Fe0) catalyst for efficient MNZ degradation in medical wastewater. The through-pore structure of MF reduced mass transfer resistance in heterogeneous systems, while the amphiphilic BT stabilized nZVI via steric hindrance and chelating interactions and created a high-concentration MNZ microenvironment through hydrophobic combined with hydrogen bonding. The synergistic design overcame the long-standing challenges of mass transfer limitations in heterogeneous systems, nZVI aggregation- and shedding-mediated activity degradation, and the establishment of high-concentration microenvironments for MNZ reductive transformation. Consequently, the highly accessible nZVI catalyst, MFBT-Fe0, rapidly removed MNZ, achieving a 96.4 ± 0.82 % removal rate within 90 min, with a degradation capability 2.9-fold higher than the non-BT-functionalized MF-Fe0. MFBT-Fe0 exhibited exceptional cycle stability, maintaining an MNZ removal rate of up to 80 % after 6th cycles. Mechanistic studies revealed contributions from surface complexation, hydrogen bonding, and π-π stacking, with HPLC-MS confirming degradation pathways of nitro reduction, denitrification and hydroxyethyl cleavage. This work provides a sustainable, high-performance catalyst for practical MNZ removal, addressing both efficiency and recyclability challenges in medical wastewater treatment.