Atomic layer deposition of TiO2-nanomembrane-based photocatalysts with enhanced performance

Riyanto Edy,Jing Zhang,Jianjun Shi,Yuting Zhao,Gaoshan Huang,Yongfeng Mei

doi:10.1063/1.4967783

Abstract

In this study, TiO2 and TiO2-ZnO nanomembranes were fabricated by atomic layer deposition using the three-dimensionally porous template and their photocatalytic properties were investigated. The nanomembranes were firstly deposited onto the surface of polyurethane porous sponge templates (sacrificial templates), followed by a calcination at 500 or 800 °C. Three-dimensionally porous structures as a replica of the porous sponge templates were thus achieved. By a pulverizing process, the porous structures were broken into small pieces, which were then employed as photocatalyst. Experimental results show that the degree of crystallinity is raised by increasing of the nanomembrane thickness due to the increase of the grain size with minimizing the number of grain boundaries in the thicker nanomembrane, which is beneficial to enhance the photocatalysis efficiency. On the other hand, the photocatalytic activity can also be improved by TiO2-ZnO composite, due to lower electron-hole recombination possibility and better carrier conductivity.

Highlights

In our previous study,[32] it cannot be observed directly in X-ray diffraction (XRD), the asprepared TiO2 with fewer atomic layer deposition (ALD) cycles has a lower degree of local order, on the contrary more ALD cycles leading to an improvement of the degree of local order
TiO2 and TiO2-zinc oxide (ZnO) were well deposited onto the polyurethane porous sponge template by ALD at relatively low temperature
The three-dimensionally semiconductor porous structures which duplicate the structure of original sponge templates were obtained after calcination, which were broken into small pieces by a manual pulverizing process

Summary

INTRODUCTION

Semiconductor nanostructures are becoming an intensive research interest due to improved properties and promising technological applications.[1,2,3,4,5,6] Especially, oxides semiconductor such as titanium dioxide (TiO2), zinc oxide (ZnO) and related structures have attracted attention for applications in photocatalysis, gas sensing, and photovoltaic cells.[7,8,9,10,11,12] The enhancement of photocatalytic properties of the TiO2-ZnO composite structure, in comparison with TiO2 oxide has been reported.[8,9,13] It is believed that the coupling of anatase and rutile TiO2 with ZnO can achieve a more efficient electronhole pair separation under illumination and, a higher reaction rate.[14,15] the electronic properties modification of the composite materials is invoked to explain this behavior: the electron transfer from the conduction band of ZnO to the conduction band of TiO2 under illumination and, the hole transfer from the valence band of TiO2 to the valence band of ZnO give rise to a decrease of the pairs recombination rate, i.e., to an increase of their lifetime.[13,15] This phenomenon increases the availability of the pairs on the surface of the photocatalyst and an improvement of the occurence of redox processes can be expected.[15]. The experimental results indicate that the composite structure and the increased thickness have positive effects on the enhanced photocatalytic performance

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS