In　this　study　a　new　photocatalytic　nanocomposite,　S-g-C3N4/MgAl-CLDH,　was　synthesized　and　implemented　into　cement　mortar　by　internal　mixing　or　coating.　The　photocatalytic　NOx　degradation　efficiency　of　the　S-g-C3N4/MgAl-CLDH　and　photocatalytic　mortar　was　investigated.　The　NOx　degradation　efficiency　and　photoluminescence　spectra　of　S-g-C3N4/MgAl-CLDH　after　being　immersed　in　the　simulated　concrete　pore　solution　were　evaluated　to　assess　its　chemical　stability.　The　results　show　that　compared　with　S-g-C3N4,　the　S-g-C3N4/MgAl-CLDH　exhibits　a　narrower　bandgap　(2.45　eV),　a　lower　photogenerated　electron-hole　pair　recombination　rate　and　a　higher　specific　surface　area　(36.86　m2　g−1).　After　21　min　of　visible　light　irradiation,　the　NOx　degradation　rate　of　S-g-C3N4/MgAl-CLDH　achieves　100%　as　compared　to　merely　81.5%　of　S-g-C3N4.　After　being　submerged　in　simulated　concrete　pore　solution,　the　S-g-C3N4/MgAl-CLDH　exhibits　only　a　slight　decrease　of　5%　in　degradation　rate　after　12　min　of　irradiation,　confirming　a　good　compatibility　and　stability　in　cement-based　materials.　The　NOx　degradation　ability　of　the　internally　mixed　mortar　is　enhanced　with　an　increase　in　the　dosage　of　S-g-C3N4/MgAl-CLDH.　For　coated　mortar,　in　contrast,　a　decline　in　NOx　degradation　rate　is　observed　after　5　layers　of　coating　owing　to　the　lower　porosity　of　mortar　after　excessive　coating.　©　2023　The　Royal　Society　of　Chemistry.