Study Of Synthesis And Formation Of WO₃-ZnO Heterojunction

In modern society,the problem of air pollution becomes increasingly worse.In order to monitor the poisonous gases,more and more scientists are aware of the importance of gas sensors.The resistance type metal oxide gas sensors have been widely concerned and studied,because of their advantages of low cost,simple structure and microelectronic compatibility.Nowadays heterostructure is mainly synthesized through chemical vapor deposition,which is based on VS or VLS mechanism.The high temperature of the process always cause crystal defects and high cost.There are few reports on the synthesis of metal oxide heterostructure by wet chemical synthesis.In addition,they have many steps and complicated process.In order to synthesize WO3-ZnO heterostructure,this research is as follow:(1)One-dimensional WO3 nanobelts were prepared by the hydrothermal method where Na2WO4·2H2O is used as the raw material.In order to optimize the synthesis,reaction time and temperature of hydrothermal reaction is modified through control various method.After that,consumption of K2SO4 and concentrated HCl is optimized as well.WO3 nanobelts with width of 500nm,thickness of 50nm and length of 40?m were prepared under the most suitable condition.The growth theory of WO3 nanobelts is developed after the microstructure and growth orientat is observed by TEM,SEM and XRD.(2)In order to observe the growth of one dimensional WO3 nanorods directly,we try to synthesize WO3 nanorods through in-situ heating the tungstic acid microemulsion.Without heating drying,WO3 nanorods are droped on the copper net and observed in-situ in ETEM.WO3 nanorods can be observed in the O2.Trough in-situ observation of it,we think that in this situation,the growth of W03 is satisfied to OA theory.(3)One dimensional WO3 nanobelts prepared in the first steps are dipcoated in Zn(Ac)2 solution in order to set seed crystal on the surface.After annealing in the air,they are mixed in the Zn(NO3)2 and C6H12N4 solution with low temperature hydrothermal reaction.In the process of WO3-ZnO heterostructure synthesis,concentration of dipcoating solution is optimized to prepare appropriate product.Through TEM,SEM and XRD,it is observed that the growth direction and lattice parameter of ZnO and WO3 has obvious relation.A theory is developed to describe the formation of the oxide heterojunction according to the orientation attachment theory as well as the lattice mismatch.It accords with to the Volmer-Weber growth model.In our research,one dimensional WO3 nanobelts were successfully synthesized as the substrate of heterojunction.Through the in-situ observation in ETEM,we find out the growth of WO3 under this conditions.On this basis,we synthesize WO3-ZnO heterostructure through hydrothermal method and analyze the mircrostructure.The growth theory of WO3-ZnO can provide a theoretical basis for the growth of heterostructure.