NOx　is　a　harmful　gas　that　causes　respiratory　diseases　and　acid　rain.　Commonly　used　photocatalysts　for　degrading　NOx　such　as　UV　responsive　TiO2　show　weak　photocatalytic　degradation　efficiency　under　visible　light.　Furthermore,　the　great　concern　is　that　the　degradation　product,　nitrates　(NO3),　from　NOx　could　be　washed　away　and　increase　the　nitrogen　deposition　and　eutrophication　in　the　surrounding　soil　and　aquatic　environments,　resulting　in　serious　secondary　pollution.　To　address　these　issues,　this　study　proposes　a　novel　solution　by　incorporating　S-g-C3N4/MgAl-CLDH　nanocomposites　into　a　cementitious　system　which　features　high　NOx　degradation　efficiency　under　visible　light　condition　and　the　efficient　capture　and　adsorption　of　NO3　in　situ.　The　NOx　degradation　was　comprehensively　studied,　encompassing　the　influencing　factors　and　stability.　The　mechanism　for　NO3　adsorption　process　was　expounded　using　the　isothermal　model.　The　results　show　that　the　amount　of　exposed　S-g-C3N4/MgAl-CLDH　and　the　contact　area　between　S-g-C3N4/MgAl-CLDH　and　NOx　are　the　essential　reasons　affecting　the　NOx　degradation.　The　NOx　degradation　ability　of　photocatalytic　mortar　exhibits　excellent　stability　with　the　NOx　removal　ratio　decreasing　by　only　4.8　%　and　14.5%　after　ten　consecutive　tests　and　120　min　of　ultrasonic　washing,　respectively.　Furthermore,　S-g-C3N4/MgAl-CLDH　increases　the　NO3　adsorption　capacity　of　photocatalytic　mortar　by　about　1.5　times,　and　the　adsorption　process　of　NO3　follows　the　Freundlich　isotherm.　The　study　offers　an　alternate　method　for　designing　innovative　nanocomposites　in　cement-based　materials　to　control　environmental　pollution.