Preparation Of ZnO/TiO₂ Coupled Films And Its Photocatalytic Properties

Photocatalysis of semiconductors is a widely investigated subject during the past 30 years.Among them,titanium dioxide is the most latent material for its chemical stability,wearibility,low cost and innocuity.At the same time,some of the low-E thin films like AZO is photo-catalytic themselves.However,for their instability,they are not suitable to be photo-catalytic agent directly.Coupling these low-e films with TiO₂ thin films could prevent corrosion of the AZO and enhance photo-catalytic performance of the whole composite films.But simply coupled films doesn't make full use of the light-induced charges in the under-layer of the coupled films.This article determine to make the AZO under-layer partly exposed by different ways, and achieve an enhanced photo-catalytic performance.AZO films,TiO₂ films and their composite films are prepared by magnetron sputtering,and pretreated by PVA solution,or post-treated by annealing and plasma.Microstructure are investigated by XRD,SEM and optical microscopy;electrical performance are measured by FOUR-POINT PROBE METER;optical performance is investigated by UV-vis Spectrometer;and photo-catalytic performance is measured by the degradation of Rodanmine B under UV light in 2 hours.AZO films prepared by sputtering exhibit a relatively low resistance.After being treated by different plasma,the surface morphology behaves huge changes.Especially, N and Ar plasma treatment cause holes of different size and shape on the surface of the films.This phenomenon may be used to realize AZO under-layer exposure.AZO under-layer exposed composite films are obtained by pre-spraying of PVA solution.Such films turn out superior photo-catalytic performance to the simply composite films.Dip Such PVA treated composite films into AgNO₃ and Na₂S solution respectively,irradiate them with UV light for 45minutes',and then, precipitation of Ag and S appears on the exposed AZO part.That means,Magnetron sputtering AZO films are more active than TiO₂ films.But Ag and S has a different distribution.The amount of Ag precipitation has a ascendant grads toward the centre, but the amount of S precipitation has a ascendant grads outward the centre.As indicated by the following equations,Ag⁺+e^-→Ag↓and S^2-+2h⁺→S↓,Ag distribution exhibits e^- distribution and S distribution exhibits h⁺ distribution.That means light excitated h⁺ is drifted to the AZO side,and e^- to the TiO₂ side.Take the size of S precipitation enrichment into consideration,we anticipate the Optimum size of the exposed area is 10 micron.Ag⁺,S^2-are proved to be developer of the distribution of e^-,h⁺ respectively.Annealed AZO-TiO₂ composite films exhibit better photocatalysis even than the PVA treated ones.Higher crystallization of AZO under-layer is proved by XRD,and exposed AZO under-layer is also confirmed in such films.