The hybrid organic–inorganic perovskite (CH3NH3)PbI3 may find application in next generation solid-state sensitised solar cells. Although this material and related perovskites were discovered many decades ago, questions remain concerning their diverse structural chemistry and unusual properties. The article presents a review of previous work and provides a detailed description of the preparation, structural characterisation and physical characteristics of (CH3NH3)PbI3. The phase changes exhibited by (CH3NH3)PbI3 have been probed using variable temperature powder and single crystal X-ray diffraction, combined with differential scanning calorimetry, thermogravimetric analysis and phase contrast transmission electron microscopy. The optical band gap for (CH3NH3)PbI3 determined by UV-Visible spectroscopy was compared to values obtained from density-of-state simulation of the electronic band structure.

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Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3) PbI3 for solid-state sensitised solar cell applications

Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.

Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications

In the paragraph following eq 28, the average bond valence was incorrectly referred to as V/R. It has been corrected to V/N. The paper originally posted to the web on September 3, 2009, and was reposted on September 24, 2009.

http://pubs.acs.org/doi/pdf/10.1021/cr900053k

Recent developments in the methods and applications of the bond valence model.

Solar-driven reduction of dinitrogen (N2 ) to ammonia (NH3 ) is severely hampered by the kinetically complex and energetically challenging multielectron reaction. Oxygen vacancies (OVs) with abundant localized electrons on the surface of bismuth oxybromide-based semiconductors are demonstrated to have the ability to capture and activate N2 , providing an alternative pathway to overcome such limitations. However, bismuth oxybromide materials are susceptible to photocorrosion, and the surface OVs are easily oxidized and therefore lose their activities. For realistic photocatalytic N2 fixation, fabricating and enhancing the stability of sustainable OVs on semiconductors is indispensable. This study shows the first synthesis of self-assembled 5 nm diameter Bi5 O7 Br nanotubes with strong nanotube structure, suitable absorption edge, and many exposed surface sites, which are favorable for furnishing sufficient visible light-induced OVs to realize excellent and stable photoreduction of atmospheric N2 into NH3 in pure water. The NH3 generation rate is as high as 1.38 mmol h-1 g-1 , accompanied by an apparent quantum efficiency over 2.3% at 420 nm. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with light-switchable OVs toward efficient, stable, and sustainable visible light N2 fixation in mild conditions.

Light-Switchable Oxygen Vacancies in Ultrafine Bi 5 O 7 Br Nanotubes for Boosting Solar-Driven Nitrogen Fixation in Pure Water

Chemical etching preparation of BiOI/BiOBr heterostructures with enhanced photocatalytic properties for organic dye removal

The three quasi-binary phase systems BiOX-BiOY (X, Y = Cl, Br, I) have been investigated by X-ray powder methods. No quaternary phases were found in the three systems. BiOCl-BiOBr and BiOBr-BiOI form systems of unlimited mutual solubility. BiOCl-BiOI is a system of limited solubility at the iodine-rich side. In the BiOBr-BiOI system a strong deviation from Vegard's rule is observed with respect to one of the lattice parameters. A few methods to quantify such a deviation are briefly discussed and a possible explanation for the strong deviation in the BiOBr-BiOI system is proposed. Error calculations have been performed to estimate uncertainties in the concentration parameter x of the investigated mixtures. The crystal structure of BiOI has been re-determined by single crystal structure analysis.

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A Strong Deviation from Vegard’s Rule: X-Ray Powder Investigations of the Three Quasi-Binary Phase Systems BiOX–BiOY (X, Y = Cl, Br, I)

Structural characterization of the synthetic perites PbBiO2X, X I, Br, Cl

The crystal structures of Bi24O31X10 (X = Cl, Br; 24-bismuth 31-oxide decachloride/-bromide) have been redetermined. The structure models obtained resemble the model described in the literature about 60 years ago, but differ from it in some details of the O substructure and in the fact that the structure for X = Cl is a twofold superstructure of the literature model. A fictional mechanism is given by which the formerly described incorrect O substructure is transferred into the correct one.

Redetermination of the crystal structures of the 'Arppe compound' Bi24O31Cl10 and the isomorphous Bi24O31Br10

Preparation and structural characterization of the lead oxide iodide Pb3O2I2

Penta­bismuth heptoxide bromide, Bi5O7Br, crystallizes in the space group Cmca. Its structure is compared with the closely related Ibca structure of α-Bi5O7I. The change in the space group is assumedly the result of a compromise between the different spatial needs of Br and I and the rigidity of the {3∞}[Bi, O] frameworks into which they are embedded. A detailed procedure for the synthesis of Bi5O7Br is given.

Volker Krämer

Papers

A Strong Deviation from Vegard’s Rule: X-Ray Powder Investigations of the Three Quasi-Binary Phase Systems BiOX–BiOY (X, Y = Cl, Br, I)

Structural characterization of the synthetic perites PbBiO2X, X I, Br, Cl

Redetermination of the crystal structures of the 'Arppe compound' Bi24O31Cl10 and the isomorphous Bi24O31Br10

Preparation and structural characterization of the lead oxide iodide Pb3O2I2

Bi5O7Br and its structural relation to α-Bi5O7I