The Preparation Of Au And CdS Nanoparticles Modified ZnO Nanotube Array And Its Photoelectrochemical Performance

In recent years,photoelectrochemical water splitting of semiconductor micro/nanostructures to generate storable clean energy such as H2 has attracted great attention in the field of optoelectronics.However,the single semiconductor micro/nanostructure always exhibits poor photoelectrochemical performance and low photoelectric conversion efficiency due to its high photo-generated carrier recombination.It has been proven that constructing a suitable semiconductor heterojunction micro/nanostructure is one of the effective ways to improve the photoelectrochemical performance of semiconductor photoelectrode materials.In this thesis,ZnO nanotube arrays were successfully prepared by combining electrochemical deposition method with chemical etching in alkaline solution.Then ZnO/Au,ZnO/CdS,and ZnO/Au/CdS nanotube arrays were successfully constructed by modifying ZnO nanotube arrays with Au and CdS nanoparticles via hydrothermal reduction and chemical bath deposition methods,respectively.The composition,morphology,optical and photoelectrochemical properties of the ZnO-based nanotube arrays were characterized and analyzed by several techniques.And the photon-generated carriers transfer and separation process as well as the enhancement mechanism of photoelectrochemical properties of ZnO/Au/CdS nanotube arrays were analyzed and elucidated on the basis of experimental results.The main contents and results of the thesis include:(1)Using zinc nitrate(ZnNO3·6H2O)as the Zn source,ZnO nanotube arrays with hexagonal wurtzite phase structure were successfully prepared by combining electrochemical deposition method with chemical etching in alkaline solution.Then,ZnO/Au nanotube arrays were fabricated by growing Au nanoparticles on the surface of ZnO nanotube arrays via hydrothermal reduction method in solution of chloroauric acid(HAuCl4)and trisodium citrate(C6H5Na2O7·2H2O).The light harvesting ability and photoelectrochemical performance of the prepared nanotube arrays were investigated.The results demonstrate that the ZnO/Au nanotube arrays display improved light absorption ability in the visible light range and significantly enhanced photoelectrochemical activity.And under simulated sunlight,the photocurrent density is 2 times higher than that of the bare ZnO nanotube arrays.The mechanism for enhanced photoelectrochemical performance of the fabricated ZnO/Au nanotube arrays was discussed and elucidated on the basis of the experimental results of visible-light-driven photoelectrochemical activity and room temperature photoluminescence property.(2)Using cadmium nitrate(CdN2O6·4H2O)and thiourea(CH4N2S)as starting materials,type ? ZnO/CdS nanotube arrays were fabricated by using chemical bath deposition method to grow CdS nanoparticle shell on the surface of ZnO nano tube arrays.The light absorption measurements show that the ZnO/CdS nanotube arrays exhibit strong light absorption capacity within visible lightragen(<500 nm).And the fabricated ZnO/CdS nanotube arrays display significantly enhanced photoelectrochemical activity.ZnO/CdS nanotube arrays achieve a photocurrent density of up to 4.7 mA/cm2 and the solar to hydrogen conversion efficiency(STH)of up to 2.3%(0.8 V vs.RHE)under the simulated sunlight irradiation.According to type ? band alignment,the process of the photon-generated carrier separation and transfer as well as the mechanism of enhanced photoelectrochemical performance of ZnO/CdS nanotube arrays were discussed and elucidated.(3)ZnO/Au/CdS nanotube arrays were constructed by suing hydrothermal reduction to grow Au nanoparticles on the surface of ZnO nanotube arrays and then using chemical bath deposition to grow CdS nanoparticle shell on the surface of nanotube arrays.The light absorption measurements show that ZnO/Au/CdS nanotube arrays exhibit enhanced light absorption in visible light range.And the fabricated ZnO/CdS nanotube arrays display significantly enhanced photoelectrochemical activity.The photocurrent density of ZnO/Au/CdS nanotube arrays is 24 times than that of ZnO nanotube arrays and 14 times than that of ZnO/Au nanotube arrays.At 0.72 V potential relative to standard RHE,the STH efficiency of ZnO/Au/CdS nanotube arrays is up to 3.2%,which is 1.5 times,23 times and 80 times higher than that of ZnO/CdS,ZnO/Au and pure ZnO nanotube arrays,respectively.The study on photoluminescence emission shows that photogenerated electrons of CdS are effectively transferred its conduction band to conduction band of ZnO via Au nanoparticles,as an electron relay.And the synergistic effect of surface plasmon resonance and electron relay of Au nanoparticles enable ZnO/Au/CdS nanotube arrays to achieve significantly enhanced photoelectrochemical activity.