| During the rapid development of human civilization,energy crisis and environmental problems become inevitable with serious depletion of natural resources.Photocatalytic technology has unique advantages in solving this series of problems caused by industrial and social development owing to its green,environment-friendly and cost-efficient characteristics.For photocatalysis,high-efficient migration and separation of photo-generated carriers is the most important factor to enhance photocatalytic activity.The current research focuses on the doping of photocatalytic materials,the construction of heterojunction structures and the coupling with noble metals,etc.,to achieve the high-efficiency separation of photo-generated carriers.However,it is difficult to improve the separation efficiency owing to the random direction separation of carriers in photocatalytic materials,because the random separation will lead to the recombination of extensive photo-generated electrons and holes,thus reducing the catalytic performance of photocatalytic materials.Therefore,in order to further improve the photocatalytic performance and the effective utilization of photo-generated carriers,the spatially directed separation and distribution of charge carriers is a very important factor.Therefore,the photocatalytic activity and carrier separation still need to be further improved to deal with the environmental pollution problems,so as to accelerate the practical application of photocatalysis in the field of environment.In this work,we firstly fabricated the Asy-Au/Zn O nanorod array on the conductive FTO glass substrate by a hydrothermal method combining with selective reaction site exposure and photoreduction technologies.The photoelectrochemical and catalytic properties were studied,and the mechanism of the enhanced catalytic performance was studied.The main findings are as follows:Firstly,a vertically aligned and uniform Zn O nanorods array was prepared by traditional hydrothermal method.The Zn O nanorods had a diameter of～120 nm and a length of～2μm.Then the asymmetric Au/Zn O nanorod array（denoted as Asy-Au/Zn O）was successfully prepared by selective exposure and photochemical in-situ reduction technologies,and the Asy-Au/Zn O showed an asymmetrical distribution of Au nanoparticles（NPs）（～10 nm）only on the tip 500 nm of the Zn O nanorod.Secondly,compared with Zn O and symmetric Au/Zn O（denoted as Sy-Au/Zn O）nanorod arrays,Under the same conditions,Asy-Au/Zn O could produce more active oxygen species（such as·OH）,that is,Asy-Au/Zn O has higher catalytic activity.Meanwhile,after catalytic degradation of Rh B dyes for 75 min,Asy-Au/Zn O exhibited the highest piezocatalytic activity（62%）and photocatalytic activity（62%）,and the piezo-photocatalytic performance.The morphology of the Asy-Au/Zn O after three cycles of Rh B degradation remained good,and the Au NPs were still tightly tethered on the Zn O nanorods.At the same time,after the degradation of methylene blue（MB）dye for 75 min,Asy-Au/Zn O also showed the highest piezo-photocatalytic activity（97%）.In addition,Rh B and MB were almost not degraded by ultrasound or light alone.The catalytic experimental data indicate that this unique asymmetric nanostructure with the synergistic effect of piezoelectric and localized surface plasmon resonance（LSPR）is superior in the field of photocatalysisThirdly,based on catalytic experiments and the characterization data of optical and photoelectric properties,the tentative mechanism for the greatly enhanced catalytic activity for Asy-Au/Zn O has been proposed.Zn O could be excited by ultraviolet（UV）light during the all-spectrum irradiation to produce a quantity of electron-hole pairs.When Au NPs was deposited on Zn O nanorods,a Schottky barrier would be formed at the Au/Zn O interface,which could efficiently prohibit the recombination of electrons and holes generated from light or ultrasound.Under the light irradiation,a large number of hot electrons with an energy higher than Schottky barrier would be excited by LSPR effect of plasmonic Au NPs,which could cross the Schottky barrier and be injected into the conduction band(ECB)of Zn O,and leave a corresponding number of holes in Au NPs.The hot electrons and holes would subsequently transfer to the surface of Zn O and Au,respectively,and then react with donors and acceptors in the solution and produce high-active reactive species to degrade dye molecules.In addition,the piezopotential induced by the deformation of Zn O nanorods under ultrasound actuation could not only lower the Schottky barrier to enhance the injection efficiency of the hot electrons from Au NPs to Zn O,but also further promote the separation and migration of the charge carriers,resulting in an enhanced catalytic performance.More importantly,the unique asymmetric one dimension（1D）nanostructure could regulate the spatially directed separation and distribution of the electrons and holes along the 1D nanostructure,thus achieving a long-term separation states of the charge carriers.This study provides a new way for high-efficiency carrier separation.Meanwhile,it also paves a new pathway for designing unique asymmetric nanostructure with the synergy of photocatalysis and piezocatalysis. |
