An effective method for the preparation of high temperature stable anatase TiO2 photocatalysts

Abstract

An efficient, rapid and straightforward method for the preparation of nitrogen and fluorine (N, F) codoped high temperature stable anatase using a microwave pre-treatment is reported. Using a single source, ammonium fluoride (NH4F) for both nitrogen and fluorine, effective doping of the precursor titanium isopropoxide (TTIP) was possible. These samples were characterised for their structural and optical properties using X-ray diffraction (XRD), Fourier transform IR (FTIR), Raman spectroscopy and UV-vis spectroscopy. In terms of the anatase to rutile transition enhancement using a novel microwave assisted technique, the sample prepared in a composition Fagan et al, Applied Surface Science 371, 2016, 447-452 of 1:8 TiO2: NH4F at 1200 °C was seen to be most effective, having stable anatase present at 57.1 % compared to undoped TiO2 being 100 % rutile from 900 °C. This method involves the production of ammonium oxofluorotitanates (NH4TiOF3) at low temperatures. The inclusion of these intermediates greatly reduces the particle size growth and delays the anatase to rutile transition. The photocatalytic activity of these materials was studied by analysing the degradation of an organic dye, rhodamine 6G as a model system and the rate constant was calculated by pseudo-first-order kinetics. These results showed that the doped sample (0.0225 min -1 ) was three times more active than the undoped sample (0.0076 min -1 ) and over seven times faster than the commercial TiO2 photocatalyst standard Degussa P-25 calcined at 1200 °C (0.0030 min -1 ). The formation of intermediate compounds, oxofluorotitanates, was identified as the major reason for a delay in the anatase to rutile transition.

Modification of TiO2 with hBN: high temperature anatase phase stabilisation and photocatalytic degradation of 1,4-dioxane

“…However, as noted by Byrne et al the use of metal dopants can result in the formation of impurities at elevated temperatures which can have a negative impact on the transition temperature and photocatalytic activity [14,20,35]. Consequently, the use of non-metal (anion) doping, which is the second type of chemical modifiers/dopants, has been studied [36,37], as for example carbon [35,[38][39][40][41], nitrogen [42][43][44][45], sulphur [11,22] and fluorine [46,47], or co-doping of these [37,[48][49][50][51][52][53][54].…”

Mo doped TiO2: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

“…The most commonly existing crystalline polymorphs of TiO 2 are anatase, rutile and brookite [10][11][12]. Anatase is accepted to be the more active phase of TiO 2 and is preferred by the ceramic industries to fabricate light active antimicrobial indoor building materials such as ceramics, glass, tiles and sanitary surfaces [13,14]. This requires thermal stability of the anatase phase under typical ceramic processing conditions.…”

“…ART of TiO 2 at high temperature could be controlled by the addition of metal ions, suitable chemical modifiers and an appropriate synthesis method [13]. Doping with metal ions is a one of the profitable ways to retard the ART [14,21,[23][24][25][26][27][28][29][30][31]. Metal ions could improve the thermal stability of TiO 2 through the reduction in contact points, and nucleation sites [32].Generally, doping of an element with higher oxidation state compared to Ti 4+ would improve charge carrier separation on the photocatalyst surface [33].…”

Synthesis of ascorbic acid enhanced TiO2 photocatalyst: its characterization and catalytic activity in CO2 photoreduction

“…The sharp absorption bands of bending bond of water Ti-OH can be observed in the range of 1623.63 cm -1 to 1630.76 cm -1 with 0.4AA signified the lowest intensity among the synthesized catalysts [24,25]. Meanwhile, the stretching vibration of hydroxyl groups (O-H) with broad peaks between 3367.36 cm -1 and 3434.31 cm -1 can be attributed to adsorbed water molecules with the highest intensity of 0.8AA [26].…”