Due　to　a　growing　number　of　significant　vitality　and　environmental　issues,　the　standardized　variation　of　carbon　nitride　(CN)　for　visible-light　photocatalytic　water　splitting　is　an　encouraging　scientific　topic.　By　revealing　this,　the　functionalized　monomer　2,6-dibromobenzimidazole　(BI)　was　successfully　embedded　within　the　heptazine　units　of　CN　via　a　molecular　engineering　(Co-polymerization　process)　approach,　and　the　as-synthesized　product　was　named　CN/BIx.　Thereafter,　as-synthesized　materials　were　employed　in　the　photocatalytic　production　of　hydrogen　(H2)　via　water　splitting　and　CO2　reduction　into　CO　under　visible　light　irradiance　(λ　=　420　nm).　Surprisingly,　the　substituent　framework　of　CN,　which　was　intimidated　by　the　description　of　BI　monomer,　acted　as　a　substitution　reaction　material　and　lubricated　the　electronic　structure　of　CN　by　endorsing　charge　transition　dissociation,　which　in　turn　boosted　its　photocatalytic　performance　under　visible　irradiation.　The　CN/BI10.0　yields　62.8　mol　of　CO　and　18.1　mol　of　H2　for　4　h　of　the　catalyzed　reaction　upon　photooxidation　under　light　irradiation,　emphasizing　the　maximum　photocatalytic　performance　with　response　to　CO2+.　Correspondingly,　the　H2　evolution　rate　(HER)　for　bulk　CN　was　estimated　as　17.6　mol/h1,　whereas　it　was　approximated　as　203.7　mol/h1　for　CN/BI10.0,　which　is　10　times　higher　than　that　of　CN.　Such　a　phenomenon　also　predicts　a　substantial　encroachment　in　the　surface　area,　energy　gap,　and　chemical　properties,　along　with　promotes　the　effective　segregation　of　photoinduced　charge　separation　from　the　valence　band　(VB)　to　the　conduction　band　(CB)　of　CN,　thereby,　making　it　a　good　alternative　for　the　photocatalytic　water　and　CO2　reduction　reaction　process.　©　2022　Elsevier　B.V.