Anatase to rutile transition in titanium dioxide photocatalytic nanomaterials /

Abstract

Anatase and brookite are both considered metastable phases and transition irreversibly into the thermodynamically stable rutile phase at elevated temperatures (600-700°C in pure synthetic TiO2). Anatase TiO2 is widely accepted as the most photocatalytically active phase. However, TiO2 is only active under Ultraviolet (UV) light (~4% sunlight). A chemical precursor modifier, chemical additive or dopant can be used to alter the transition temperature and increase the photocatalytic activity of TiO2. These chemical additives/dopants/modifiers can result in a higher transition temperature and photocatalytic activity. However, some additives/dopants/modifiers have been known to reduce both. This work examined the effects benzoic acid, tungsten and boron nitride had on the transition temperature and the photodegradation of 1,4-dioxane. Benzoic acid and tungsten doping all increased the transition temperature compared to the control, with anatase still present at 800°C and 950°C respectively. All doped boron nitride samples were 100% rutile by 700°C, however the 0% BN-TiO2 was 100% rutile from 600°C. There were varying results when examining the percent removal of 1,4-dioxane. Benzoic acid, tungsten and boron nitride showed increased photocatalytic activity. Out of all of the samples examined, only 3 samples showed 100% removal of 1,4-dioxane, these were 2% W-TiO2, 4% W-TiO2 and 8% W-TiO2 at 800°C. When comparing the results for the transition temperature and photocatalytic activity of all dopants studied, 8% W-TiO2 is considered the optimim dopant and concentration. This is due to 26% anatase still being present at 950°C and it showed 100% and ~80% 1,4-dioxane removal when calcined at 800°C and 900°C respectively. The current investigation therefore showed that using the sol-gel method for doping with tungsten, benzoic acid and boron nitride successfully improved the anatase to rutile transition temperature and photocatalytic activity of TiO2.