High quantum yield graphene quantum dots decorated TiO2 nanotubes for enhancing photocatalytic activity

[Display omitted] •High concentration yellow GQDs and TiO2 nanotubes were achieved by a simple and green method.•High quantum yield GQDs enhanced the photodegradation capacity of TiO2 nanotube.•The catalytic performance of GQDs/TiO2 depends on the GQDs loading.•The improved photocatalytic activity of GQDs/TiO2 was attributed to three aspects. Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320nm) and GQDs/TiO2 nanotubes (GQDs/TiO2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420nm and up-conversion photoluminescence in the range of 600–800nm. The photocatalytic activity of prepared GQDs/TiO2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO2 nanotubes (TiO2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20min irradiation under UV–vis light irradiation (λ=380–780nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO2 composite.