Fully quantitative X-ray characterisation of Evonik Aeroxide TiO2 P25®

doi:10.1016/j.matlet.2014.02.055

Materials Letters

Volume 122, 1 May 2014, Pages 345-347

https://doi.org/10.1016/j.matlet.2014.02.055 Get rights and content

Highlights

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First time fully quantitative X-ray characterisation of Evonik Aeroxide TiO₂ P25^®.
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P25^® composed of 76.3 wt% anatase, 10.6 wt% rutile, and 13.0 wt% amorphous phase.
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Anatase phase had an average crystalline domain size of 15.5 nm.
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Rutile phase had a larger average crystalline domain size of 19.3 nm.

Abstract

Photocatalysis with TiO₂ is one of the most promising methods for combatting environmental pollution. Of commercially available photocatalysts, Evonik Aeroxide (formerly Degussa) P25^® titania is probably the most extensively used. In this communication, we quantitatively characterise the full phase composition (both crystalline and amorphous content) of P25^®, as well as the microstructure of individual phases (crystalline domain size distribution and dislocation density). This was achieved with advanced X-ray diffraction (XRD) methods: Rietveld-RIR and whole powder pattern modelling (WPPM). Quantitative phase analysis (QPA) showed the precise composition of P25 to be 76.3 wt% anatase, 10.6 wt% rutile and 13.0 wt% amorphous, and microstructural details are given for the two crystalline phases.

Introduction

Titanium dioxide (TiO₂) is the most popular semiconductor material for photocatalytic applications [1], [2]. Amongst the wide number of commercially available photocatalytic titanias, Evonik Aeroxide TiO₂ P25^® (formerly known as Degussa P25^®, and hereafter referred to as P25), synthesised via flame pyrolysis of TiCl₄, is widely used because of its high photocatalytic activity in many reaction systems, thus becoming a standard for photocatalytic reactions.

From a mineralogical point of view, it is made of anatase and rutile phases, their ratio being typically reported as 70:30 or 80:20 [3], [4], [5], [6], [7], [8], [9], [10], [11]. Some authors have also reported that P25 contains some amorphous phase, from observations from TEM analysis [12], [13]. Recently, Ohtani et al. estimated that the crystalline composition of P25 is 78% anatase and 14% rutile, calculated from XRD calibrations with varying mixtures of rutile and anatase, and they assumed that the remaining 8% was an amorphous phase [14].

For many applications, especially photocatalysis where rutile and anatase phases have different band gap energies and therefore work under differing wavelengths of light, it is important to know the precise phase composition of this material. Therefore, here we report, for the first time, the fully quantitative determination of both crystalline and amorphous phase content in P25, and also a quantitative description of the microstructure of individual crystalline phases, both from advanced X-ray analyses. The phases were identified with the Rietveld-RIR (reference intensity ratio) method [15], [16], the microstructure characterised from whole powder pattern modelling (WPPM) [17], [18].

Section snippets

Experimental

P25 was supplied by Evonik (DE), and was used as received. X-ray powder diffraction (XRPD) data for the quantitative phase analysis (QPA) were collected using a laboratory θ/θ diffractometer (PANalytical X׳Pert Pro, NL), equipped with a fast RTMS detector, with Cu Kα radiation (40 kV and 40 mA, 20–80° 2θ range, a virtual step scan of 0.0167° 2θ and virtual time per step of 50 s). The incident beam pathway was as follows: 0.125° divergence slit, 0.125° anti-scattering slit, 0.04 rad soller slits,

Results and discussion

QPA data are reported in Table 1, while a graphic output of the Rietveld refinement is depicted in Fig. 1. Rietveld-RIR refinement showed P25 to be composed of 76.3 wt% anatase, 10.6 wt% rutile and 13.0 wt% amorphous phase. These findings are in contrast with many previously reported, e.g. by Datye et al. [26], who stated that P25 did not have any noticeable amount of amorphous phase. Rather, this is closer in agreement with the findings of Ohtani et al. [14], who estimated 8% amorphous phase. Our

Conclusions

The phase composition and microstructure of P25 was extensively studied via X-ray methods. From QPA data, we found P25 to be composed of 76.3 wt% anatase, 10.6 wt% rutile, and 13.0 wt% amorphous phase, although variations in this may arise between different production batches.

With WPPM microstructural analysis of P25, we found that the anatase phase had an average crystalline domain size of 15.5 nm with a narrow size distribution, its mode being 12.1 nm, and that it contained 9 times more screw

Acknowledgements

D.M. Tobaldi is grateful to the ECO-SEE project (European Union’s Seventh Framework Programme funding, grant agreement no 609234). Authors acknowledge PEstC/CTM/LA0011/2013; M.P. Seabra and R.C. Pullar wish to thank the FCT Ciência2008 programme for supporting this work.

References (28)

X Li et al.
J Photochem Photobiol, A
(2001)
G Colón et al.
J Photochem Photobiol, A
(2001)
J Kirchnerova et al.
Appl Catal, A
(2005)
N Bowering et al.
Appl Catal, B
(2006)
R Trejo-Tzab et al.
J Mol Catal A: Chem
(2008)
X Qin et al.
J Hazard Mater
(2009)
B Abramović et al.
Appl Catal, B
(2011)
R Quesada-Cabrera et al.
Appl Catal, B
(2014)
RI Bickley et al.
J Solid State Chem
(1991)
T Ohno et al.
J Catal
(2001)

B Ohtani et al.

J Photochem Photobiol, A

(2010)

G Caglioti et al.

Nucl Instrum Methods

(1960)

DM Tobaldi et al.

Appl Surf Sci

(2013)

AK Datye et al.

J Solid State Chem

(1995)

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View full text

Fully quantitative X-ray characterisation of Evonik Aeroxide TiO2 P25®

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

J Photochem Photobiol, A

J Photochem Photobiol, A

Appl Catal, A

Appl Catal, B

J Mol Catal A: Chem

J Hazard Mater

Appl Catal, B

Appl Catal, B

J Solid State Chem

J Catal

J Photochem Photobiol, A

Nucl Instrum Methods

Appl Surf Sci

J Solid State Chem

Fully quantitative X-ray characterisation of Evonik Aeroxide TiO₂ P25^®