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’

Understanding the relationship between geopolymer composition, microstructure and mechanical properties

Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete

Building innovation through geopolymer technology

This study presents the synthesis, characteristics and catalytic reactivity of sustainable bifunctional heterogeneous catalysts derived from coal fly ash-based geopolymer, particularly those with a high Ca content (C-class) fly ash. The developed catalysts were synthesized at room temperature and pressure in a simple ecologically-benign procedure and their reactivity was evaluated in the Friedel-Crafts acylation of various arenes. These catalysts can be produced with multilevel porous architecture, and a combination of acidic and redox active sites allowing their use as bifunctional catalysts. The acidic sites (Lewis and Bronsted acidic sites) were generated within the catalyst framework by ion-exchange followed by thermal treatment, and redox sites that originated from the catalytically reactive fly ash components. The developed catalysts demonstrated higher reactivity than other commonly used solid catalysts such as Metal-zeolite and Metal-mesoporous silicate, heteropolyacids and zeolite imidazole frameworks (ZIF).

https://www.mdpi.com/2073-4344/9/4/372/pdf

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

Calcium dialuminate (CaAl4O7) powders were synthesised from mechanochemically treated mixtures of aluminium hydroxide + calcium hydroxide and aluminium hydroxide + calcium carbonate. On grinding, both mixtures produce X-ray amorphous precursor phases which show 27Al MAS NMR resonances characteristic of Al in octahedral and tetrahedral sites, and a site identified by a resonance at 37–39 ppm (possibly pentahedral Al). Although grinding does not completely destroy the carbonate XRD reflections in the carbonate mixture, both precursors show a high degree of homogeneity and behave similarly on heating, forming monophase CaAl4O7 at <1050 °C. By contrast, the same unground compositions form mixtures of α-alumina and various calcium aluminates (but not CaAl4O7) on heating as high as 1250 °C. Calcium dialuminate synthesised from the carbonate-containing mechanochemical precursor had a smaller particle size which may be advantageous for subsequent fabrication and sintering.

Effect of mechanochemical treatment on the synthesis of calcium dialuminate

Evolution of crystalline aluminates from hybrid gel-derived precursors studied by XRD and multinuclear solid state MAS NMR. III. Lanthanum hexaluminate, LaAl11O18

Kenneth J. D. MacKenzie

Papers

Building innovation through geopolymer technology

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

Effect of mechanochemical treatment on the synthesis of calcium dialuminate

Evolution of crystalline aluminates from hybrid gel-derived precursors studied by XRD and multinuclear solid state MAS NMR. III. Lanthanum hexaluminate, LaAl11O18

27Al multiple-quantum MAS NMR of mechanically treated bayerite (alpha-Al(OH)3) and silica mixtures.