Titanium dioxide, TiO2, is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

https://link.springer.com/content/pdf/10.1007%2Fs10853-010-5113-0.pdf

Review of the anatase to rutile phase transformation

Pore size determination in modified micro- and mesoporous materials. Pitfalls and limitations in gas adsorption data analysis

The Role of Inorganic Polymer Technology in the Development of ‘Green Concrete’

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Chapter headings. Preface. Introduction. Physical background. Experimental approaches. 29Si NMR. 27Al NMR. 17O NMR. NMR of other commonly studied nuclei. NMR of low-gamma nuclides. NMR of other spin-1/2 nuclei. NMR of other quadrupolar nuclei. Solid state NMR of metals and alloys.

Multinuclear solid-state NMR of inorganic materials

Thermal behaviour of inorganic geopolymers and composites derived from sodium polysialate

Synthesis and thermal behaviour of potassium sialate geopolymers

Preparation and characterisation of fly ash based geopolymer mortars

The effect of SiO2 addition on the anatase-to-rutile phase transition was investigated by DTA, XRD, FTIR, and XPS. TiO2 xerogels containing SiO2 up to 20 mol% were prepared by mixing and hydrolyzing titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) with HNO3 as a catalyst. With increased amounts of SiO2 in the xerogels, the following results were obtained: (1) the crystallization temperature of anatase increased from 415°C in pure TiO2 to 609°C in 20-mol%-SiO2-containing xerogel in the DTA curves; (2) the formation temperature of rutile, according to quantitative XRD analysis, increased with increased SiO2 content up to 5 mol% SiO2 but became constant at higher SiO2 contents; (3) the crystallinity of anatase became lower; and (4) the lattice parameter a of the anatase decreased slightly, but the parameter c decreased greatly up to 20 mol% SiO2. Although the added silicon atoms were considered from these results to be incorporated into the amorphous TiO2 and anatase structures, the 29Si MAS NMR spectra of the xerogels containing 10 mol% SiO2 showed only tetrahedral silicon, with no indication of silicon in octahedral coordination. When calcined at higher temperatures, the xerogel showed polymerization of the SiO4 tetrahedra in the NMR spectra and the Si–O–Si vibration in the FTIR spectra. The chemical composition of the xerogel surfaces, measured using XPS, showed increased SiO2 content with increased calcining temperature, indicating the expulsion of silicon from inside the particles to form an amorphous SiO2 surface layer. The formation of this amorphous SiO2 surface layer was considered to be important in retarding the anatase-to-rutile phase transition by suppressing diffusion between anatase particles in direct contact and limiting their ability to act as surface nucleation sites for rutile. These effects of silicon additions were similar to those observed in the γ-Al2O3- to-α-Al2O3 transition.

Kenneth J. D. MacKenzie

Papers

Multinuclear solid-state NMR of inorganic materials

Thermal behaviour of inorganic geopolymers and composites derived from sodium polysialate

Synthesis and thermal behaviour of potassium sialate geopolymers

Preparation and characterisation of fly ash based geopolymer mortars

Effect of Silica Additive on the Anatase-to-Rutile Phase Transition