A　small　amount　of　cocatalysts　often　play　a　crucial　role　in　polymerization　semiconductor　photocatalytic　reactions,　and　precious　metals,　like　Pt,　remain　irreplaceable　as　cocatalysts　in　most　applications　due　to　their　excellent　properties.　Meanwhile,　maximizing　the　atomic　utilization　of　cocatalysts　and　enhancing　the　host-guest　interactions　are　important　routes　to　enhance　photocatalytic　efficiency.　Single　Pt　atoms　anchored　thiophene　ring-doped　carbon　nitride　nanosheets　(Ptx-CNA)　by　a　facile　incipient　wetness　impregnation　were　successfully　synthesized　in　this　work.　Single-atom　Pt　are　uniformly　embedded　in　CNA　nanosheets　through　Pt–N　coordination　bonds.　Coordinated　electron-rich　thiophene　ring-doping　and　single-atom　Pt　modifications　promote　wider　visible　light　response,　enhanced　charge　response,　and　fast　transport　capability　in　Pt-CNA　materials.　Pt1.0-CNA　sample　displays　the　most　outstanding　photocatalytic　H2　evolution　rate　(360.0　μmol　h−1),　which　is　nearly　5　times　that　of　Pt1.0-CN　(70.5　μmol　h−1).　Excellent　photocatalytic　degradation　performance　of　ciprofloxacin　is　also　achieved　and　the　degradation　rate　constant　of　Pt1.0-CNA　is　1.8　times　that　of　CNA.　Molecular　modifications　and　single-atom　cocatalytic　together　significantly　improve　the　photocatalytic　efficiency　of　polymer　semiconductors.　©　2023　Hydrogen　Energy　Publications　LLC