Ab-initio structure determination of LiSbWO6 by X-ray powder diffraction

Photochemical splitting of water into H2 and O2 using solar energy is a process of great economic and environmental interest. Since the discovery of the first water splitting system based on TiO2 and Pt in 1972 by Fujishima and Honda, over 130 inorganic materials have been discovered as catalysts for this reaction. This review discusses the known inorganic catalysts with a focus on structure–activity relationships.

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Inorganic Materials as Catalysts for Photochemical Splitting of Water

Structure and electrochemistry of Li1±yNiO2 and a new Li2NiO2 phase with the Ni (OH)2 structure

In recent years, many soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions. Simple ion-exchange and intercalation reactions replace or modify the interlayer cations of layered perovskites, and more complex metathesis reactions replace interlayer cations with cationic structural units. Topochemical condensation reactions that involve dehydration and reduction provide access to a variety of metastable structural features in three-dimensional perovskites, and similar reactions can be used to convert among higher order layered perovskite homologues. Other techniques, such as high pressure and anion intercalation/deintercalation, also yield interesting metastable phases. When combined, the individual reactions complement each other, and a powerful toolbox of solid-state reactions emerges. By using layered perovskites as templates, it is possible to retrosynthetically design new product perovskites that retain the structural features of the...

Perovskites by Design: A Toolbox of Solid-State Reactions

CONSPECTUS: Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from the precursor materials releases 2D structures. In this Account, in addition to graphene and TMO, we focused on MXenes as an example for the use of selective extraction synthesis to produce novel 2D materials. About 10 new carbides and carbonitrides of transition metals have been produced by this method in the past 3 years. They offer an unusual combination of metallic conductivity and hydrophilicity and show very attractive electrochemical properties. We hope that this Account will encourage researchers to extend the use of selective extraction to other layered material systems that in turn will result in expanding the world of nanomaterials in general and 2D materials in particular, generating new materials that cannot be produced by other means.

Synthesis of two-dimensional materials by selective extraction.

Several layered perovskites $A_2Ln_2Ti_3O_{10}$ (A = K or Rb; Ln = rare earth) and their monohydrates, crystg. in tetragonal structures related to ${Sr_4Ti_3O_10}$, were prepd. The alkali ions in $K_2Ln_2Ti_3O_{10}$ are topochem. exchanged by protons in aq. acid or by other alkali ions in molten salts. $H_2Ln_2Ti_3O_{10}$ also adopt a tetragonal structure similar to the parent oxides. Dehydrated $H_2La_2Ti_3O_{10}$ crystallizes at 1000 giving a new defect perovskite, $La_2/3TiO_3$, possessing a tetragonal structure.

Vasudeva Bhat

Papers

A2Ln2Ti3O10 (A = potassium or rubidium; Ln = lanthanum or rare earth): a new series of layered perovskites exhibiting ion exchange

AILaNb2O7: A new series of layered perovskites exhibiting ion exchange and intercalation behaviour

HNbWO6 and HTaWO6: Novel layered oxides related to the rutile structure. Synthesis and investigation of ion-exchange and intercalation behaviour

Oxidative extraction and ion-exchange of lithium in Li2MoO3: synthesis of Li2−xMoO3 (0 < x ≤ 2.0) and H2MoO3

NMR study of fast protonic conduction in layered HLa2NbTi2O10·1.5H2O