Preparation Of Two Dimensional Materials/Oxide Semiconductor Heterojunctions And Their Photoelectrochemical/Photocatalytic Properties

The solar energy can be converted into the electrical or chemical energy by the semiconductor photocatalytic technology environmentally friendly,which is one of the most effective means to solve the energy crisis and environmental problems.However,the development of photocatalytic materials is strictly limited by the low carrier separation efficiency and poor charge transport.Due to this,various methods has been improved,such as element doping,noble metal loading,nanostructures preparing,and semiconductor coupling.Recent studies show that the performance of photocatalytic materials can be greatly improved by enhancing the separation and transport efficiency of photo-induced carriers through rational construction of heterojunction photocatalyst for the good coupling between two semiconductors.In this paper,we prepared photo-response two-dimensional materials/oxide semiconductor heterojunction photocatalyst for the better photocatalyst activity by enhancing the separation efficiency and transport performance of the photocatalyst of the composite photocatalyst.There are four mainly chapters in this thesis:(1)In this chapter,MoS2/TiO2 nanohole arrays are prepared by combing colloidal lithography and dip-coating method.The decorating of MoS2 nanosheets can significantly improve the photoelectrochemical and photocatalytic activity of TiO2 nanohole arrays in the visible light region.On the basis of the experimental and theoretical results,such enhanced performances can be assigned to two reasons:one is the improved visible light harvesting owing to MoS2 nanosheets,and the other is the efficient separation of photogenerated carriers because of band alignment between MoS2 and TiO2.The related work has been published in Journal of Physical Chemistry C,2018,122(27),15055-15062.(2)The photoanode consisting of MoS2 nanosheet coating on the three-dimensional ordered BiVO4 inverse opal is fabricated by a facile combination of nanosphere lithography and hydrothermal methods.By taking advantage of the photonic crystal and two-dimensional material,the optimized MoS2/BiVO4 inverse opal photoanode exhibits a 560%improvement of the photocurrent density and threefold enhancement of the incident photon-to-current efficiency than that of the pristine BiVO4 film photoanode.Systematic studies reveal that the excellent PEC activity should be attributed to three advantages:the photonic crystal structure could enhance the light harvesting and reduce the diffusion length of photogenerated holes;MOS2 nanosheehs can enhance visible light harvesting and the heterojunction between BiVO4 and MoS2 could improved charge separation efficiency.The related work has been published in Applied Physics Letters,2018,112(17),173902.(3)The BiVO4 and g-C3N4 powders were prepared by and sol-gel and thermal polymerization methods,respectively,and then g-C3N4/BiVO4 composite heterojunction photocatalyst samples were prepared by stirring and grinding.Photocatalytic degradation rates for Rhodamine B(RhB)were studied by tuning the mass ratio of composite samples.The degradation rate for g-C3N4 was higher than the pure BiVO4,which could contribute more active sites due to the existence of the high specific surface area.The photocatalytic degradation rate could be further improved when g-C3N4 and BiVO4 were combined to form heterojunction.The heterojunction can promote efficient separation of carriers and result in the increased utilization of the carriers,which leads to improvement of photocatalytic degradation rate for RhB in composite system.(4)The BiFeO3 nanoparticles were prepared by sol-gel method,mixed with g-C3N4 according to a certain mass ratio,and then the g-C3N4/BiFeO3 composite heterojunction powder photoelectrode samples were prepared by scraping method.The photocurrent density increasement was detected,once the p-n junction between BiFeO3 and g-C3N4 was imported,which improved the separation efficiency of the carrier and enhanced the photoelectrochemical performance of the powder photoelectrode.Moreover,the PEC properties of the g-C3N4/BiFeO3 composites are dependent on ferroelectric polarization,which is mainly ascribed to the modulation of band structure at the BiFeO3/electrolyte interface by the polarization.