Tuning　the　bandgap　of　a　semiconductor　to　achieve　strong　band-to-band　visible　light　absorption　is　highly　desirable　but　challenging　for　photocatalysis.　This　work　presents　a　facile　molten-salt-assisted　route　to　prepare　red-colored　polymerized　carbon　nitride　(RPCN)　nanosheets　with　a　remarkable　redshifted　absorption　and　narrowed　bandgap　of　1.9　eV.　Both　experimental　findings　and　theoretical　calculations　reveal　that　alkali　heteroatoms　are　effective　to　tune　the　surface　and　electronic　structures　of　carbon　nitride,　resulting　in　significantly　reduced　bandgap　and　excellent　solubility.　The　RPCN-sensitized　TiO2　nanorod-based　photoanode　generates　an　impressive　photocurrent　density　of　approximate　to　2.33　mA　cm(-1)　at　1.23　V　versus　reversible　hydrogen　electrode　under　Air　Mass　1.5　G　illumination　without　any　cocatalyst,　which　is　2.6　folds　higher　than　that　of　the　bare　TiO2　photoanode.　The　new　findings　in　this　work　could　inspire　the　electronic　structure　engineering　of　semiconductor　photocatalysts　to　greatly　enhance　the　visible　light　absorption　and　provide　a　generic　strategy　to　enhance　the　photoelectrochemical　performance　of　wide-bandgap　semiconductor　photoelectrodes.