Preparation Of Zero-dimensional Quantum Dots/two-dimensional Nanosheet Composites And Study Of Photocatalysis And Gas Sensing Preformance

The environmental pollution generated in the process of human social development not only restricts the sustainable development of social economy,but also seriously threatens human health.Semiconductor photocatalysis technology and gas sensor have unique advantages in pollution control and monitoring.On the one hand,semiconductor photocatalysis technology can convert solar energy into chemical energy for deep degradation of pollutions;on the other hand,semiconductor gas sensor can detect and quantify toxic,harmful,flammable and explosive gases for environmental pollution detection and monitoring.In the aspect of improving the performance of semiconductor materials,using zero-dimensional quantum dots and two-dimensional nanosheets to form heteroj unctions or homoj unctions has been proved to be one of the most effective methods for building high-performacne semiconductor materials.Therefore,zero-dimensional quantum dots/two-dimensional nanosheet composites are synthesized to construct high-efficiency photocatalysts and gas sensors,and their mechanisms are discussed.The main research works include:1.The TiO2QDs/g-C3N4 nanosheet heterostructures are synthesized and the degradation efficiency toward RhB and photocatalytic mechanism are studied.The separation and transfer of photogenerated electron and holes are promoted by the construction of heterojunction between TiO2QDs and g-C3N4,thus the photocatalytic efficiency is improved significantly.The degradation rate of RhB on(3 wt%)TiO2QDs/g-C3N4 nanosheet heterostructure composites is 3.4 times higher than that of g-C3N4 nanosheets.2.The TiO2QDs/TiO2 nanosheet homostructures are synthesized and the photocatalytic performance and mechanism are studied.Through the construction of homojunction,the separation and transfer of photogenerated electrons and holes are promoted and the recombination of photogenerated carriers are inhibited,thereby their photocatalytic activity is improved significantly.Among them,RhB can be completely degraded within 30 min by TiO2QDs/TiO2-40 homostructure composites,which is about 5 times of the degradation rate of TiO2 nanosheets.3.The synthesized CQDS/TiO2 nanosheet heterostructures exhibit higher photocatalytic performance than TiO2 nanosheet under sunlight,and can degrade RhB even under visible light(λ≧420 nm).This is due to the fact that CQDs can be used not only as an electronic memory to separate photogenerated electrons and holes,but also as photosensitizer to convert long-wavelength light into short-wavelength that can be absorbed by TiO2,thus improving the photocatalytic activity of composites.4.The SnO2QDs/Co3O4 porous nanosheet heterostructures are synthesized and according to the founded that the strong interaction between SnO2QDs and Co3O4 promote the formation of Co2+ on the surface of composites and produce abundant vacancies which accelerate the transfer of interfacial electrons and increased the density of surface active sites.The gas sensing properties and electrocatalytic oxygen evolution properties of composites have been greatly improved compared with that of SnO2QDs and Co3O4 porous nanosheets.5.The SnO2QDs have a strong interaction with rGO and GO through Sn-O-C bond in the prepared SnO2QDs/rGO and SnO2QDs/GO heterostructures,which exhibit far superior gas sensing performance than SnO2QDs.It is found that the gas sensing performance of SnO2QDs/rGO heterostructures are much better than that of SO2QDs/GO heterostructures.Among the prepared SnO2QDs/rGO heterostructures,SnO2QDs/rGO(0.5 wt%)heterostructures show the best gas sensing performance,they can not only response to formaldehyde at room temperature with high sensitivity and also exhibit high sensitivity to ethanol at 220 ℃without interference from other gases.