Heteroatomic　doping　is　an　effective　way　to　optimize　the　electronic　structure　of　carbon　nitride　to　boost　photocatalytic　performance.　However,　the　extra　introduced　defects　could　result　in　the　decrease　of　its　crystallinity.　In　this　work,　crystalline　K–I　co-doped　carbon　nitride　(K–I–CCN)　was　simply　synthesized　from　molten　salt　ionthermal　post-calcination　in　nitrogen　atmosphere.　Structure　characterization　results　indicate　that　compared　to　K–CCN　synthesized　from　conventional　molten　salt　heat　treatment　in　air,　nitrogen　heating　atmosphere　is　more　conductive　for　the　formation　of　homogeneous　pore　structure　of　the　catalyst,　which　has　larger　surface　area　and　pore　volume,　while　could　repairing　some　defects　and　resulting　in　better　polymerization　crystallization.　In　addition,　except　the　implanting　of　K,　I　doping　is　still　retained　after　nitrogen　heat　treatment,　thus　forming　K–I　co-doping　structure.　Due　to　the　positive　charge　effect　of　K–I　co-doping,　K–I–CCN　has　a　narrower　band　gap,　higher　surface　charge　density　and　stronger　charge　transport,　so　it　performs　significantly　enhanced　photocatalytic　H2　evolution　activity　from　water　splitting.　©　2022　Hydrogen　Energy　Publications　LLC