The　crystallization　of　amorphous　TiO2nanotubes,　which　were　prepared　by　anodic　oxidation,　was　carried　out　by　a　water-assisted　method　at　low　temperatures.　The　crystalline　phase　and　the　morphology　of　TiO2nanotubes　were　observed　by　X-ray　diffraction　(XRD)　and　field　emission　scanning　electron　microscopy　(FESEM),　respectively,　and　the　photocatalytic　activity　was　characterized　by　the　degradation　of　methylene　blue　(MB).　Results　show　that　TiO2nanotubes　crystallized　by　a　water-assisted　method　at　50　°C　for　4　h　exhibited　high　crystallinity,　a　preferable　nanotube　structure　and　therefore,　high　photocatalytic　activity.　Sucrose　was　added　to　the　aqueous　solution　as　a　carbon　source　for　preparing　C-doped　TiO2nanotubes.　X-ray　photoelectron　spectroscopy　(XPS)　and　ultraviolet-visible　diffuse　reflectance　spectroscopy　(UV-vis　DRS)　were　used　to　observe　the　chemical　state　of　C-doped　TiO2nanotubes.　After　C-doping,　the　crystalline　phase　and　morphology　of　TiO2nanotubes　hardly　changed　but　the　bandgap　of　TiO2was　narrowed,　which　endowed　TiO2nanotubes　with　wide-range　light　absorption,　significantly　enhancing　the　photocatalytic　activity.　This　one-step　method　at　a　low　temperature　of　50　°C　provides　a　new　pathway　for　preparing　C-doped　TiO2nanotube　photocatalysts　with　enhanced　photocatalytic　activity.　©　The　Royal　Society　of　Chemistry　2021.