Photo-Chlorine Production with Hydrothermally Grown and Vacuum-Annealed Nanocrystalline Rutile

Thom R Harris-Lee,S Andrew L Johnson,Yuanzhu Zhao,Christopher R Bowen,Jerome W F Innocent,Zhenyu Guo,Philip J Fletcher,Yan Zhang,Frank Marken

doi:10.1007/s12678-020-00630-x

Abstract

Photo-generated high-energy surface states can help to produce chlorine in aqueous environments. Here, aligned rutile (TiO2) nanocrystal arrays are grown onto fluorine-doped tin oxide (FTO) substrates and activated either by hydrothermal Sr/Ba surface doping and/or by vacuum-annealing. With vacuum-annealing, highly photoactive films are obtained with photocurrents of typically 8 mA cm−2 at 1.0 V vs. SCE in 1 M KCl (LED illumination with λ = 385 nm and approx. 100 mW cm−2). Photoelectrochemical chlorine production is demonstrated at proof-of-concept scale in 4 M NaCl and suggested to be linked mainly to the production of Ti(III) surface species by vacuum-annealing, as detected by post-catalysis XPS, rather than to Sr/Ba doping at the rutile surface. The vacuum-annealing treatment is proposed to beneficially affect (i) bulk semiconductor TiO2 nanocrystal properties and electron harvesting, (ii) surface TiO2 reactivity towards chloride adsorption and oxidation, and (iii) FTO substrate performance.Graphical abstractPhoto-chlorine production is possible in aqueous chloride media under neutral conditions with rutile nanocrystal arrays under illumination from band gap–matched LEDs.

Highlights

TiO2-based materials in doped or undoped forms are widely applied in photocatalysis, [1] but are generally found to be relatively inactive for photo-chlorine production [2]
We demonstrate vacuum-annealing of rutile nanocrystal arrays as a convenient method to “activate” the rutile surface for photochlorine production and to enhance charge carrier transport and collection
It has been shown that vacuum-annealing can be used to significantly enhance the efficiency of photo-chlorine production with rutile nanocrystal arrays on fluorine-doped tin oxide (FTO) substrates

Summary

Introduction

TiO2-based materials in doped or undoped forms are widely applied in photocatalysis, [1] but are generally found to be relatively inactive for photo-chlorine production [2] Harris-Lee and Yan Zhang are joint first authors

Results and Discussion

Vacuum-annealed TiO2 after use in photoelectrochemistry

Conclusions