Solution-Phase Synthesis,Structural Control And Photocatalytic Performances Of Semiconductor-Based Heterostructured Nanocrystals

The semiconductor-based nanohybrids exhibit improved and multifunctionalities properties compared to individual components due to the functional synergy between each component,and these hybrid nanocrystals show great potential in the field of photocatalysis.However,the design and performance optimization of semiconductor-based hybrid nanocrystals is not straightforward and has become a critical issue that needs to be solved.One of the main obstacles encountered is that there exists a large lattice mismatch between semiconductor and other components in hybrid nanosystems,which makes it rather difficult to integrate each component via firm heterostructures on nanometer-scale.In addition,the different condition of nucleation and growth of each component may lead to complicated synthesis of hybrid nanocrystals with uniform and controllable morphology.Thus it is an important research topic on the relationship between morphology,structure and their corresponding optical,electronic,magnetic and catalytic properties.Furthermore,considering the application of semiconductor-based nano-photocatalysts for the pratical applications in industry and daily life,it should completely avoid use or partially use precious noble metals,thus the selection of raw materials,the manufacturing processes and the performance optimization should be deeply investigated.In this dissertation,we have developed solution-phase strategies to prepare heterostructral semiconductor-based hybrid nanocrystals for the construction of hybrid nanosystems containing semiconductor components(ZnO,g-C3N4 and ZnIn2S4)and other components such as metal,metal phosphides and metal selenides.The morphology,structure and composition of hybrid nanocrystals can be controlled by employing a series of experiments,and the possible formation mechanisms of the hybrid systems with controllable morphology were discussed.Furthermore,the relationship between the morphology,structure and component of hybrid nanocrystals and their optical,magnetic and photocatalytic properties were further explored.The main results are as following:(1)We have developed a facile solution-phase route for the synthesis of three different structures of Ni-Au-ZnO hybrid nanocrystals including nanomultipods,matchstick-like nanorods and nanopyramids.In the synthesis,magnetic Ni component can be introduced to the preformed Au-ZnO nanocrystals by the injection of Ni precursor.These as-prepared Ni-Au-ZnO ternary nanocrystals inherited the original morphology of preformed Au-ZnO,and successfully integrated three different components into a hybrid nanosystem,especially Ni component can introduce the magnetic property for Ni-Au-ZnO hybrid nanocrystals.Furthermore,matchstick-like Ni-Au-ZnO nanorods exhibit higher photocatalytic performance in the degradation of RhB with respect to Ni-Au-ZnO nanomultipods and nanopyramids.(2)Flower-like Ni-ZnO hybrid nanocrystals were produced through a hot-injection solution-phase process by rapid injection of ZnO precusor.The average size of Ni core in Ni-ZnO hybrid systems is readily controlled from 25 to 50 nm.The as-obtained Ni-ZnO hybrid nanocrystals exhibit room temperature ferromagnetic properties and tunable magnetic properties.Furthermore,the as-prepared Ni-ZnO hybrid systems exhibit superior photocatalytic activity and stable ability in the degradation of RhB.(3)Cu-ZnO hybrid nanocrystals with well-controlled morphologies have been synthesized by using the preformed Cu seeds for the heterogeneous nucleation and growth of ZnO components with different experimental parameters.In addition,the novel Cu@CuNi-ZnO hybrid nanocrystals can be achieved by the incoproation of magnetic Ni component and exhibit room temperature superparamagnetic properties.Furthermore,unique optical properties and superior photocatalytic properties of the as-prepared hybrid nanocrystals can be observed.(4)OD Ni12P5 nanoparticles were successfully embedded into 2D porous g-C3N4 nanosheets,and enventually form a firm Ni12P5/g-C3N4 heterojunction through a self-assembled solution-phase route under sonication.The optimal phorocatalytic hydrogen evolution under visible light irradiation(?>420 nm)can be obtained by adjusting the weight perent of metal phosphides loaded on g-C3N4.The as-obtained g-C3N4-based photocatalysts with an optimum loading of 5 wt%of Ni12P5displayed an excellent H2 production rate of 535.7 ?mol g-1 h-1,with an apparent quantum yield(AQY)of 4.67%at 420 nm.(5)ZnIn2S4 hierarchical architectures assembled by ultrathin nanosheets were prepared by a facile one-pot route in TEG solution.Subsequently,ZnIn2S4/MoSe2 heterojunction hybrid systems were fabricated through a simple solution phase hybridization process combining ZnIn2S4 and layered MoSe2.It is note that the optimum loading of 2%MoSe2 of hybrid photocatalyst displayed an extremely high H2 production rate of 2228 ?mol g-1 h-1 under visible light irradiation(?>420 nm),and exhibited an impressive apparent quantum yield(AQY)of 21.39%at 420 nm.