La-mediated green rust for synergistic nitrogen-phosphorus removal and targeted N₂ formation regulated by built-in...

Fe-based catalysts have garnered considerable attention for NO₃⁻ removal and conversion. However, antagonistic NO₃⁻/PO₄³⁻ removal, low N₂ selectivity, and slow degradation kinetics limit the application of Fe-based hydroxide catalysts in green denitration. In this study, an innovative La-mediated green rust (La-GR) bimetallic hydroxide was designed and synthesized, achieving over 80 % synchronous and targeted removal of NO₃⁻ and PO₄³⁻. Combined transient reaction analyses and DFT calculations revealed that La-O-Fe coordination reconstructs the electronic structure at the catalytic interface, decoupling reduction and adsorption processes to replace competitive antagonism with synergistic promotion, thereby enabling simultaneous nitrogen and phosphorus removal. The in-situ formation of LaPO₄ enhanced the built-in electric field of La-GR, creating a microenvironment conducive to local NO₃⁻ reduction. The La/Fe exchange process synergistically modulated magnetic exchange interactions within GR by elevating the d-band center and reducing the spin state of the Fe sites. This optimized d-orbital electron configuration lowered the adsorption energy of nitrogen at the Fe sites and facilitated N₂ desorption, thereby achieving precise regulation of N₂ selectivity up to 88.83 %. Overall, this coupling of functional differentiation and spin regulation offers new paradigms for designing high-performance catalysts and elucidating catalytic mechanisms at the spin-electron scale.