Capture-to-catalyst hollow N-doped porous carbons for closed-loop gold recovery and nitrate-to-ammonia electrocatalysis

Materials that recover dilute metals and convert the recovered species into functional catalysts can link resource circularity with environmental remediation, yet their design is constrained by a trade-off between rapid transport and reactive binding. Here, we report a ZIF−8-derived hollow N-doped porous carbon (HNPC) as a capture-to-catalyst platform for closed-loop gold recovery and nitrate-to-ammonia electrocatalysis. The hollow mesoporous framework shortens diffusion pathways and improves access to internal surfaces, whereas graphitic-N-associated sites promote AuCl₄⁻ adsorption and Au(III)-to-Au(0) reduction. The optimized HNPC exhibits a Langmuir Au(III) capacity of 3245.1 mg·g^-1 and removes >99.9% of Au at trace concentrations under strong ionic competition, corresponding to a distribution coefficient of ~3×10⁹ mL·g⁻¹. Time‑resolved microscopy and spectroscopy reveal rapid Au nanoparticle nucleation and progressive conversion to Au(0), while finite−element simulations and density functional theory (DFT) identify the cooperative roles of hollow-structure-enabled transport and graphitic-N-regulated interfacial reactivity. The resulting Au/HNPC is directly reused as a gas-diffusion-electrode catalyst, delivering 96.6% Faradaic efficiency for nitrate-to-ammonia conversion and stable operation for 535 h at 200 mA·cm⁻²_. This work establishes a materials strategy for integrating selective recovery, in situ metal formation, and catalytic reuse in complex aqueous media.