Design Of TiO₂-based Hybrid Nanostructures And Their Performance In Photocatalytic Hydrogen Evolution

Conversion of solar energy into chemical energy in the form of H2 is considered as one of the most ideal strategies to solve the energy and environmental problems in the future.Photocatalysts that catalyze water splitting for H2 production by making use of solar energy have received a lot of attention.Being cheap,stable,nontoxic and environmentally friendly,TiO₂ has been widely investigated.However,the photocatalytic performance of TiO₂ is limited by the recombination of photogenerated charges and the lack of active sites.To enhance the photocatalytic activity of TiO₂,two kinds of TiO₂-based hybrid nanostructures are designed in this dissertation:1.Metal nanoclusters are used as cocatalysts on TiO₂.AuCu bimetallic nanoclusters are loaded on TiO₂ nanosheets for photocatalytic hydrogen generation.The results show that the photocatalytic hydrogen production rate of AuCu cluster/TiO₂ composites is 50-56 times that of bare TiO₂.AuCu nanoclusters mainly play two roles in the activity enhancement of TiO₂:i)promote the photo-excited charges separation and transport through the formation of Schottky junctions between AuCu nanoclusters and TiO₂;ii)serve as the catalytic sites for hydrogen evolution.The synthesis of nanoclusters is further modified for tunable structures.Consequently,Au12,Au14 and Aupph3 clusters are synthesized and loaded on TiO₂ nanosheets respectively for photocatalytic hydrogen production.Aupph3/TiO₂ presents the best photocatalytic performance among these composites.The photocatalytic hydrogen generation rate of Aupph3 cluster/TiO₂ composite could be further enhanced through heat treatment,reaching 50.8 mmol·g-1·h-1,which is 847 times of that of bare TiO₂.This work demonstrates that metal nanoclusters can function as effective cocatalysts on TiO₂ for photocatalytic hydrogen evolution.graphene2.TiO₂ nanosheets in different sizes are integrated with.The separation of the photogenerated charges in TiO₂/graphene composites is modulated by controlling the size of TiO₂ nanosheets,whose effect on the photocatalytic activity of TiO₂/graphene composites is investigated.The results show that the photocatalytic activity of TiO₂/rGO composites increases with the reduction in the thickness of TiO₂ nanosheets.As the thickness of TiO₂ nanosheets decreases,the migration distance of the photo-excited electrons is reduced so as to effectively suppress the recombination of the photo-excited charges.Meanwhile,the TiO₂/rGO interface is enlarged to promote the separation of the photogenerated charges in TiO₂.As a result,the utilization efficiency of the photogenerated charges has been substantially enhanced.This work demonstrates that modulating the separation of photogenerated charges in TiO₂/graphene composites by controlling the size of TiO₂ nanosheets is an effective strategy for improving the photocatalytic performance of Ti02.