The　semiconductor　heterojunction　has　been　an　effective　architecture　to　enhance　photocatalytic　activity　by　promoting　photogenerated　charge　separation.　Here,　graphitic　carbon　nitride　(CN)　and　B-modified　graphitic　carbon　nitride　(CNB)　composite　semiconductors　were　fabricated　by　a　facile　calcination　process　using　cheap,　sustainable,　and　easily　available　sodium　tetraphenylboron　and　urea　as　precursors.　The　synthetic　CN-CNB-25　semiconductor　with　a　suitable　CNB　content　showed　the　highest　visible-light　activity.　Its　degradation　ratio　for　methyl　orange　and　phenol　was　more　than　twice　that　of　CN　and　CNB　and　its　H2　evolution　rate　was　∼3.4　and　∼1.8　times　higher　than　that　of　CN　and　CNB,　respectively.　It　also　displayed　excellent　stability　and　reusability.　The　enhanced　activity　of　CN-CNB-25　was　attributed　predominantly　to　the　efficient　separation　of　photoinduced　electrons　and　holes.　This　paper　describes　a　visible-light-responsive　CN　composite　semiconductor　with　great　potential　in　environmental　and　energy　applications.　Photo　finish:　Graphitic　carbon　nitride　(CN)　and　B-modified　graphitic　carbon　nitride　(CNB)　organic-organic　isotype　semiconductors　are　fabricated　by　a　facile　calcination　method.　The　recombination　of　photoinduced　electrons　and　holes　in　CN-CNB　is　reduced,　which　thus　enhances　the　photocatalytic　H2　evolution　activity　in　water　splitting　and　improves　the　photodegradation　efficiency　for　methyl　orange　and　phenol　under　visible-light　irradiation.　©　2015　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim.