A　series　of　amorphous　nitrogen-doped　niobium　oxide　(X-N-Nb2O5,　X　=　2,　3,　4)　was　synthesized　via　high-temperature　annealing　under　an　ammonia　atmosphere.　Their　photocatalytic　performance　for　deep　NO　oxidation　under　visible　light　was　systematically　evaluated.　Nitrogen　doping　effectively　narrowed　the　band　gap　by　introducing　impurity　energy　levels,　enhanced　visible-light　absorption　responsiveness　and　improved　photogenerated　charge　separation　efficiency.　By　inducing　oxygen　vacancies　(OVs),　nitrogen　doping　improved　the　surface　reactivity　toward　NO　and　O2　adsorption　and　activation.　Among　the　as-prepared　samples,　3-N-Nb2O5　exhibited　the　highest　NO　removal　efficiency　and　excellent　cyclic　stability,　maintaining　80　%　conversion　after　five　cycles　under　50　%　relative　humidity,　with　markedly　suppressed　NO2　generation.　In-situ　DRIFTS　and　EPR　analyses　revealed　the　enhanced　production　of　reactive　oxygen　species　and　provided　insights　into　the　reaction　mechanism.　This　work　offers　a　promising　strategy　for　designing　visible-light-responsive　photocatalysts　for　air　purification.　©　2025　Elsevier　Inc.