Simultaneous valorization of nitrate and formaldehyde waste streams to hexamethylenetetramine via photo-electro-thermo-catalysis.

To remediate nitrate (NO3-) pollution and recover resources from formaldehyde wastewater, this work presents a waste valorization strategy integrating photoelectrocatalytic nitrate reduction (PEC NO3RR) to ammonia (NH3) with downstream chemical upgrading. Herein, a hollow MoO2@CuFe2O4@MnFe2O4 Z-scheme-Schottky dual heterojunction nanoreactor array is developed to spatially separate proton and nitrate adsorption sites. The MoO2@CuFe2O4@MnFe2O4 improves photogenerated charge separation and retaining robust redox capability, while the oxygen vacancy-rich MoO2 layer exhibits favorable photothermal features to extend light harvesting, accelerate carrier migration and produce localized heating through localized surface plasmon resonance for reduced reaction energy barriers. Interfacial built-in electric field combined with spatial confinement jointly promote nitrate capture and enrichment. Fast hydrogen intercalation/deintercalation within MoO2 create a dynamically *H-enriched surface to boost NO3RR-to-NH3 conversion efficiency. This system resolves kinetic incompatibility between NO3- reduction and hydrogen supply, effectively suppressing NO2- accumulation and hydrogen evolution. It delivers an NH3 yield rate of 5.96 mM h-1 cm-2 at -0.6 V vs. RHE with high selectivity and stability over 24 h. The in-situ generated NH3 further transforms formaldehyde wastewater into high-value hexamethylenetetramine. This process enables simultaneous detoxification of two waste-streams and nitrogen/carbon feedstock upgradation, providing a closed-loop pathway for integrated pollution abatement and resource reclamation.