Conjugated　carbon　nitride　nanosheets　modified　with　barbituric　acid　(BA)　were　synthesized　by　a　facile　one-pot　chemical　condensation　of　urea.　The　obtained　BA-modified　carbon　nitride　samples　were　termed　as　CNU-BAX　and　were　fully　characterized　by　XRD,　FTIR,　XPS,　NMR,　EPR,　FESEM,　TEM,　DRS,　PL,　BET　and　photocurrent　measurements.　The　performance　of　the　developed　carbon　nitride　based　semiconductors　was　investigated　by　applying　them　as　polymeric　photocatalysts　for　the　reduction　of　CO2　under　visible　light　illumination.　Results　revealed　that　the　copolymerization　of　urea　with　BA　co-monomer　strongly　alternated　the　physical　and　chemical　properties　of　carbon　nitride　polymer　by　improving　optical　absorption　and　creating　surface　molecular　heterojunction　that　promoted　charge　separation,　and　consequently　the　enhanced　photocatalytic　performance　was　achieved.　Various　reaction　parameters　were　investigated　and　optimized　for　the　reaction　system,　and　we　found　that　under　the　optimal　reaction　condition,　the　best　sample　(CNU-BA0.03)　could　effectively　photocatalyze　the　CO2-to-CO　conversion　reaction　with　15-fold-enhanced　catalytic　activity,　compared　to　the　non-modified　sample　derived　from　urea　(named　as　CNU).　Other　typical　comonomers　were　also　selected　to　polymerize　with　urea　to　study　the　beneficial　effect　of　copolymerization　on　the　development　of　efficient　carbon　nitride　based　nanostructures　for　CO2　photoreduction.　©　2015.