Ultrasonic preparation of hierarchical graphene-oxide/TiO2 composite microspheres for efficient photocatalytic hydrogen production.

Hierarchical graphene oxide (GO)-TiO2 composite microspheres with different GO/TiO2 mass ratios were successfully prepared by mixing GO and TiO2 microspheres under ultrasonic conditions. Ultrasonication helped the GO and TiO2 microsphere to uniformly mix on the microscale. The results showed that the GO-TiO2 composites that were prepared by ultrasonic mixing exhibited significantly higher hydrogen-evolution rates than those that were synthesized by simple mechanical grinding, owing to synergetic effects, including enhanced light absorption and scattering, as well as improved interfacial charge transfer because of the excellent contact between the GO sheets and TiO2 microspheres. In addition, GO-TiO2-3 (3 wt.% GO) showed the highest hydrogen-generation rate (305.6 μmol h(-)), which was about 13 and 3.3-times higher than those of TiO2 microsphere and GO-P25 (with 3 wt.% GO), respectively. Finally, a tentative mechanism for hydrogen production is proposed and supported by photoluminescence and transient photocurrent measurements. This work highlights the potential applications of GO-TiO2 composite microspheres in the field of clean-energy production.