Fe-Gallic Acid Metal-Phenolic Network Redox Mediator Supports Concurrent Nitrate Reduction and Sulfamethoxazole Attenuation.

Nitrate-antibiotic co-contamination can suppress microbial respiration and compromise biological nitrate reduction. Here, an Fe-gallic acid metal-phenolic network redox mediator (FeGA-MPN RM) was prepared using a 1:1 Fe:GA feed ratio selected from comparative density functional theory models. Among the predefined simplified clusters, the 1:1 model showed the smallest calculated frontier-orbital gap and was selected as an electronically responsive candidate for experimental synthesis. At 50 mg L-1, FeGA-MPN RM increased the observed nitrate reduction rate 11.69-fold and maintained >98% nitrate removal over four short-term batch cycles. Material addition was associated with increased redox-active extracellular polymeric substances, higher cytochrome c levels, enhanced denitrification-related responses and enrichment of Pseudomonas (77.91% to 88.57%). X-ray photoelectron spectroscopy indicated substantial Fe(III)-to-Fe(II) transformation during nitrate reduction, supporting the participation of the Fe-GA network in redox exchange. Under batch conditions containing 1-20 mg L-1 sulfamethoxazole (SMX), nitrate removal remained near complete, while net aqueous-phase SMX removal ranged from approximately 80% to 96%. These results provide proof of concept that FeGA-MPN RM can support concurrent nitrate reduction and SMX attenuation, although the relative contributions of adsorption and transformation remain unresolved.