Dermot O’Hare

Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets

Layered double hydroxides (LDHs) are a class of ionic lamellar compounds made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Delamination of LDHs is an interesting route for producing positively charged thin platelets with a thickness of a few atomic layers, which can be used as nanocomposites for polymers or as building units for making new designed organic-inorganic or inorganic-inorganic nanomaterials. The synthesis of nanosized LDH platelets can be generally classified into two approaches, bottom-up and top-down. It requires modification of the LDH interlamellar environment and then selection of an appropriate solvent system. In DDS intercalated LDHs, the aliphatic tails of the DDS- anions exhibit a high degree of interdigitation in order to maximize guest-guest dispersive interactions. Bellezza reported that the LDH colloids can also been obtained by employing a reverse microemulsion approach.

Intercalation chemistry of layered double hydroxides: recent developments and applicationsBasis of a presentation given at Materials Discussion No. 5, 22???25 September 2002, Madrid, Spain.

Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions. In this role they have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers. More recently, there have been a tremendous number of new developments using these materials to store and deliver biologically active materials in vivo. Significant advances have been made recently on the characterisation of these materials, including structural studies and on the mechanism of intercalation using in situ techniques.

Ultrafine NiO Nanosheets Stabilized by TiO2 from Monolayer NiTi-LDH Precursors: An Active Water Oxidation Electrocatalyst

Faceted NiO nanoparticles preferentially exposing high surface energy planes demand attention due to their excellent electrocatalytic properties. However, the activity of faceted NiO nanoparticles generally remains suboptimal due to their large lateral size and thickness, which severely limits the availability of coordinatively unsaturated active reactive edge and corner sites. Here, ultrafine NiO nanosheets with a platelet size of ∼4.0 nm and thickness (∼1.1 nm) stabilized by TiO2 were successfully prepared by calcination of a monolayer layered double hydroxide precursor. The ultrafine NiO nanosheets displayed outstanding performance in electrochemical water oxidation due to a high proportion of reactive NiO {110} facets, intrinsic Ni(3+) and Ti(3+) sites, and abundant interfaces, which act synergistically to promote H2O adsorption and facilitate charge-transfer.

An Apparatus for the study of the kinetics and mechanism of hydrothermal reactions by in situ energy dispersive x-ray diffraction

The design and implementation of a pressure cell for the study of hydrothermal reactions by in situ energy dispersive x‐ray diffraction is described. The cell permits the study of both the kinetics and mechanism of formation of a wide range of important solid‐state compounds such as zeolites and other microporous solids. Reactions can be studied over a wide range of temperature (5–230 °C) and autogenous pressure [0–400 psi (gauge)] conditions. The use of this apparatus is illustrated by a study on the synthesis of a microporous tin chalcogenide phase performed on Station 9.7 of the UK Synchrotron Radiation Source.

Ammonia-rich high-temperature superconducting intercalates of iron selenide revealed through time-resolved in situ X-ray and neutron diffraction.

The development of a technique for following in situ the reactions of solids with alkali metal/ammonia solutions, using time-resolved X-ray diffraction methods, reveals high-temperature superconducting ammonia-rich intercalates of iron selenide which reversibly absorb and desorb ammonia around ambient temperatures.

Delamination of layered double hydroxides in polar monomers: new LDH-acrylate nanocomposites

The layered double hydroxide Mg2Al(OH)6(C12H25SO4) was delaminated to give high levels of inclusion in acrylate monomers; subsequent polymerisation of the monomers containing the LDH dispersion gave polyacrylates with the inorganic component still in the delaminated form.

Time-resolved, in situ X-ray diffraction studies of intercalation in lamellar hosts

Abstract Energy dispersive X-ray diffraction (EDXRD) has been used to perform in situ kinetic studies on the intercalation of a range of guest molecules in layered lattices. The kinetics of the intercalation of cations (K+, PyH+ (Py=C5H5N), NMe4+) and the long chain ammonium ions C12TMA, C16TMA, C18TMA (C12TMA=dodecyltrimethylammonium, C16TMA=hexadecyltrimethylammonium and C18TMA=octadecyltrimethylammonium) into crystals of MnPS3 have been determined. These reactions are very fast, and in some cases novel transient phases are observed. The rate of cobaltocene, Co(η-C5H5)2, intercalation in layered metal dichalcogenides ZrS2, 2H-SnS2, 2H-SnSe2, 2H-TaS2, 2H-NbS2, 1T-TaS2 and TiS2 has also been investigated. Integrated intensities of the Bragg reflections have been used to determine the extent of reaction (α) versus time for each of these reactions. A number of kinetic models have been considered, including the Avrami–Erofeyev (m=1.5) deceleratory nuclei-growth model and statistical simulation. The concentration and solvent dependence of the rate of Co(η-C5H5)2 intercalation into 2H-SnS2 has also been determined. Surprisingly, we find that the rate of intercalation is invariant to the initial Co(η-C5H5)2 concentration over a wide concentration range. The rate of intercalation of the lithium salts (LiX; X=Cl, Br, NO3 and OH) into Gibbsite (γ-Al(OH)3) giving the layered double hydroxides [LiAl2(OH)6]X·nH2O (X=Cl, Br, NO3 and OH) and [LiAl2(OH)6]2SO4·nH2O has been studied. The temperature dependence of the rate of intercalation of LiCl yields an activation energy of 27 kJ mol−1. The reaction was also found to be half order with respect to the initial concentration of LiCl. Time-resolved in situ energy dispersive X-ray powder diffraction (EDXRD) spectra have been recorded following the addition of an aqueous solution of hexadecyltrimethylammonium chloride (C16H33N+Me3Cl−=C16TMACl) to kanemite (NaHSi2O5·3H2O). The diffraction data suggest that initially a layered phase forms due to intercalation of the alkylammonium ions which then transforms into a silicate-organic mesophase which is the precursor to the hexagonal mesoporous silicate, FSM-16.

The Oxford-Diamond In Situ Cell for studying chemical reactions using time-resolved X-ray diffraction

A versatile, infrared-heated, chemical reaction cell has been assembled and commissioned for the in situ study of a range of chemical syntheses using time-resolved energy-dispersive X-ray diffraction (EDXRD) on Beamline I12 at the Diamond Light Source. Specialized reactor configurations have been constructed to enable in situ EDXRD investigation of samples under non-ambient conditions. Chemical reactions can be studied using a range of sample vessels such as alumina crucibles, steel hydrothermal autoclaves, and glassy carbon tubes, at temperatures up to 1200 °C.

Novel apparatus for the in situ study of hydrothermal crystallizations using time-resolved neutron diffraction

The design and use of a pressure cell for the in situ study of hydrothermal crystallizations using time-resolved neutron diffraction are described. This novel apparatus allows the kinetics and mechanism of the crystallization of complex inorganic solids, such as zeolites and other microporous materials, to be investigated under laboratory conditions. Reactions can be studied over a wide range of temperatures (25–250 °C) under conditions of autogenous pressure (1–22 bar). The use of the cell is demonstrated by a study of the hydrothermal crystallization of the zeolite sodium hydroxosodalite with time-of-flight neutron diffraction data collected using the Polaris diffractometer of the United Kingdom’s pulsed spallation neutron source, ISIS.

Determination of the kinetics of crystallisation of gibbsite using time resolved in situ energy dispersive powder X-ray diffraction

Time resolved in situ powder X-ray diffraction has been used to study the kinetics of crystallisation of gibbsite from supersaturated synthetic Bayer liquors as a function of temperature and hydroxide ion concentration. It was found that the crystallisation data was best described in terms of the Avrami–Erofe’ev kinetic model. This analysis indicated a two-dimensional growth mechanism with a deceleratory nucleation rate.