Eiji Kanezaki

Thermal behavior of the hydrotalcite-like layered structure of Mg and Al-layered double hydroxides with interlayer carbonate by means of in situ powder HTXRD and DTA/TG

Abstract High temperature powder X-ray diffraction (HTXRD) patterns of Mg/Al-layered double hydroxides (LDH) with interlayer carbonate (Mg/Al/CO 3 -LDH) indicate that a solid phase having a hydrotalcite-like layered structure (Phase I) is not stable when the temperature of solid samples is elevated. Another phase (Phase II) grows eminently and simultaneously with the degradation of Phase I. Phase II has smaller basal spacing than that of Phase I and is not stable when the temperature is elevated above 380°C. Both MgO and a stable spinel phase (MgAl 2 O 4 ) finally appear in the temperature range of 400–1000°C. Two endotherms associated with weight loss are observed in differential thermal analysis/thermal gravimetry (DTA/TG). Phase II appears at the endotherm of lower temperature and disappears at that of higher temperature. The temperature at which Phase II appears depends on atomic ratio Mg/Al in Mg/Al/CO 3 -LDH whereas the temperature at which Phase II disappears does not. Phase II is metastable at room temperature and it transforms to an amorphous phase slowly after days of storage in dry conditions although it returns quickly to Phase I in a wet atmosphere. Solid state chemistry of the synthetic Mg/Al/CO 3 -LDH is discussed by means of HTXRD, DTA/TG and X-ray photoelectron spectroscopy (XPS).

Effect of Atomic Ratio Mg/Al in Layers of Mg and Al Layered Double Hydroxide on Thermal Stability of Hydrotalcite-Like Layered Structure BY Means of In Situ High Temperature Powder X-Ray Diffraction

Abstract A solid phase having hydrotalcite-like layered structure (Phase I) of Mg and Al layered double hydroxide with interlayer carbonate (Mg/Al/CO3-LDH) is not stable in in situ high temperature powder X-ray diffraction patterns when the temperature of solid samples is elevated. Another phase (Phase II) grows with the decomposition of Phase I. Phase II has smaller basal spacing than that of Phase I and is not stable when the temperature is elevated above 380°C. The temperatures at which Phase II appears and disappears agree with temperatures of two endotherms that are observed in differential thermal analysis/thermalgravimetry. The temperature at which Phase II appears decreases with the increase of atomic ratio Mg/Al in layers of Mg/Al/CO3-LDH, whereas the temperature at which Phase II disappears does not.

Conformation of intercalated aromatic molecular anions between layers of Mg/Al- and Zn/Al-hydrotalcites

Abstract Giving the guest-dependent and enhanced interlayer distance, the intercalation of 1,5-, 2,6- and 2,7-naphthalenedisulfonates(abbreviated as N15DS, N26DS and N27DS, respectively) between layers of synthetic hydrotalcite and a hydrotalcite-like compound is observed in X-ray powder diffraction (XRD) patterns. Intercalated compounds are also characterized by means of X-ray photoelectron spectroscopy (XPS), diffuse reflection spectroscopy (DRS) and by DTA/TG thermal analysis. Dimensions are compared between the distance and the guest anion size which is estimated in a semiempirical MO calculation. Results are elucidated by the existence of the guest dianion which bridges between two adjacent layers of double-hydroxides.

Preparation of Layered Double Hydroxides

This chapter discusses preparation of layered double hydroxides (LDH). LDH is a mimic of naturally occurring hydrotalcite (MgA1/CO 3 -LDH), has a similar layered structure, which is called hereafter the hydrotalcite-like layered structure, and also known as the hydrotalcite-like compound. LDH is usually prepared in ordinary conditions of temperature, pressure and so on as a precipitate from solutions by means of environmentally benign methods. Therefore, it is easy to synthesize the LDH that has the desired anion(s) at the interlayer region when one carefully selects the combination of the metals and the organic compound. Both the facility in the synthesis and the potential variety in the combination of the components promise the usefulness of LDHs for developing new-type of materials. The interlayer anion of LDH is organic, inorganic, or coordination compounds that could be introduced into, LDH by means of anion-exchange, coprecipitation, or rehydration the last of which is very characteristic of the intercalation of LDH that is also discusses in the chapter.

Intercalation in hydrotalcite-like layered Zn/Al-double hydroxides with naphthalenedisulphonates

Hydrotalcite-like layered Zn/Al-double hydroxides (Zn/Al-HTs) with one of three naphthalenedisulphonates (NijDSs) as an interlayer guest dianion, were obtained as precipitates from weak alkaline solutions of NijDS admixed with calcined host powder. Two values of interplanar spacing were observed in the powder X-ray diffraction patterns of NijDS-intercalated Zn/Al-HTs with two guest isomers. Intercalated materials have been characterized by means of UV-vis diffuse reflectance spectroscopy, differential thermal analysis/thermogravimetry and X-ray photoelectron spectroscopy. A model has been proposed in which the organic dianion at the interlayer gallery region bridges two Al3+ cations in neighbouring layers of double hydroxides. The guest molecules have an orientation perpendicular to the internal surface of the layers for all NijDS-intercalated materials. Another orientation has been suggested in which the molecules tilt from the perpendicular position for two isomers of NijDS.

Unexchangeable interlayer anions; Synthesis and characterization of Zn/Al- and Mg/Al-layered double hydroxides with interlayer Alizarin red S

Zn/Al- and Mg/Al-layered double hydroxides with interlayer 9,10-anthraquinone-1,2-dihydroxy-3-sulfonate (Alizarin red S anion abbreviated as ARS) are synthesized (products are abbreviated as M/Al/ARS-LDH where M=Mg or Zn) and the solid-state properties are characterized. In powder X-ray diffraction measurements, basal spacings of the layered compounds are elucidated on the basis of the molecular size of ARS and its conformation at the interlayer gallery region. 27Al MAS NMR spectra reveal that the Al3+ ions in the layers of Zn/Al/ARS-LDH or Mg/Al/ARS-LDH locate in the octahedral hexa-coordination sphere whereas some of the metal cations in the calcined Zn/Al/CO3-LDH, the precursor in the synthesis of Zn/Al/ARS-LDH, locate in the penta- or the tetra-coordination sphere. FT-IR spectra and 13C CP/MAS NMR spectra illustrate that the interlayer ARS anions are stable in both layered compounds and the coordination bond is formed in Zn/Al/ARS-LDH between the sulfonate of ARS and Al3+ in the layer. The interlayer ARS anions are not eliminated from the interlayer region of Zn/Al/ARS-LDH when the solid is immersed in an aqueous solution containing carbonate; the unexchangeable nature of the interlayer ARS with carbonate results from the coordination bond observed in FT-IR and 13C CP/MAS spectra.

Intercalation of naphthalene-2,6-disulfonate between layers of Mg and Al double hydroxide: preparation, powder X-Ray diffraction, fourier transform infrared spectra and X-Ray photoelectron spectra

Abstract By means of the coprecipitation method, a Mg/Al-layered double hydroxide with interlayer naphthalene-2,6-disulfonates having a basal spacing of 1.68 nm was prepared for the first time. Results are compared here with those of other layered double hydroxides having interlayer naphthalene disulfonates. Fourier transform infrared spectra of the intercalated compounds reveal that the organic anions located at the interlayer gallery are stable. Coordination of oxygen in the–SO 3 − group of the interlayer molecule is observed. X-ray photoelectron spectra indicate that Al 3+ ions in the layers are octahedrally coordinated.

Complete desorption of interlayer hydrogen phosphate in Mg/Al-layered double hydroxides by means of anion exchange with 1-octanesulfonate

Hydrogen phosphate intercalated Mg/Al-layered double hydroxides (LDH-HPO4) were synthesized by a homogeneous precipitation method with urea and anion exchange. The intercalated hydrogen phosphate was removed by anion exchange with Na2CO3, NaOH–NaCl, and 1-octanesulfonate solutions. The phosphate removal behavior was characterized by X-ray diffraction (XRD), Fourier Transform-InfraRed (FT-IR) spectroscopy, and elemental analysis. Complete removal of interlayer hydrogen phosphate from LDH-HPO4 was realized using 1-octanesulfonate solution. Two reasons are proposed to explain complete hydrogen phosphate removal from the interlayer space of LDH-HPO4. Complete desorption and cyclability suggest this is a viable technique to use as an efficient adsorption/desorption system in industrial applications.

Dual interlayer distances in synthetic solids of intercalated hydrotalcites with 9,10-anthraquinone-2,6-disulfonate

Intercalation of 9,10-anthraquinone-2,6-disulfonate (AQ26) between layers of synthetic hydrotalcite is observed in powder X-ray diffraction (XRD) patterns, from which a pair of enhanced interlayer distances are obtained in separate solid samples of intercalated products. The dimensions of the interlayer distance and the guest anion size, which is estimated in a semi-empirical MO calculation, are compared. Being correlated with the AQ26 : Al ratio in the intercalated products this duality is elucidated as a result of distinct conformations of the interlayer guest dianion which bridges adjacent layers of Mg and Al layered double hydroxides (Mg/Al-LDH). An absorption due to intercalation of the anthraquinone moiety appears in the visible region of the diffuse reflectance (DR) spectra of the products. The solid-state chemistry of the intercalated products is described on the basis of elemental analysis and X-ray photoelectron spectroscopy (XPS).

THERMAL BEHAVIOR OF PHOSPHATE INTERCALATED Mg/Al-LAYERED DOUBLE HYDROXIDES

The thermal behavior of Mg and Al layered double hydroxide with interlayer hydrogen phosphate (abb. as Mg/Al-HPO4-LDH) is investigated below 1273 K by means of XRD, TG-DTA, SEM and FT-IR. The basal spacing of Mg/Al-HPO4-LDH decreases with increasing heating temperature stepwise in two stages; from 1.07 nm at 293 K to 0.85 nm at 333 K in the first stage and to 0.73 nm between 373 K and 443 K in the second one. The LDH becomes amorphous above 443 K until Mg3 (PO4)2, MgO and MgAl2O4 (spinel) appear at 1273 K. SEM images of the LDH show plate-like crystallites both before and after heating at 473 K.