Xue Duan

A clean method for preparing layered double hydroxides (LDHs) has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reaction. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester. The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps (SNAS) method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.

Large continuous, transparent and oriented self-supporting films of layered double hydroxides with tunable chemical composition

Co-reporter:Lianying Wang, Cang Li, Miao Liu, David G. Evans and Xue Duan

Chemical Communications 2007 (Issue 2) pp:123-125

Publication Date(Web):06 Nov 2006

DOI:10.1039/B613687G

Highly ordered transparent self-supporting films of layered double hydroxides (LDHs) with a size of the order of cm2 have been obtained by a simple method; the chemical composition of both the layers and interlayers can be readily tuned, as demonstrated by the preparation of [ZnAl–NO3] LDH, [NiAl–NO3] LDH and [Tb(EDTA)]− intercalated-ZnAl LDH films.

In Situ Microstructure Control of Oriented Layered Double Hydroxide Monolayer Films with Curved Hexagonal Crystals as Superhydrophobic Materials

Co-reporter:H. Chen;S. Fu;F. Zhang;X. Duan

Advanced Materials 2006 Volume 18(Issue 23) pp:3089-3093

Publication Date(Web):10 NOV 2006

DOI:10.1002/adma.200600615

Oriented NiAl-layered double hydroxide (LDH) films with micro-/nanometer scale binary structures are prepared by in situ crystallization, without using any external aluminum source or shape-directing surfactant, on a porous anodic alumina/aluminum substrate. The NiAl-LDH film structures can be controlled by tuning crystallization temperature and time. Facile hydrophobic modification of the film surface leads to superhydrophobicity, as shown in the figure.

Study on the intercalation and interlayer oxidation transformation of L-cysteine in a confined region of layered double hydroxides

Co-reporter:Min Wei, Zhiyu Shi, David G. Evans and Xue Duan

Journal of Materials Chemistry A 2006 vol. 16(Issue 21) pp:2102-2109

Publication Date(Web):07 Apr 2006

DOI:10.1039/B517980G

Two kinds of amino acids (L-cysteine and L-cystine, represented as L-CySH and L-Cys respectively) have been intercalated into MgAl layered double hydroxides by coprecipitation. The structure and composition of the intercalated materials have been characterized by X-ray diffraction (XRD) and elemental analysis. Furthermore, the oxidation of L-CySH intercalated LDHs by, respectively, hydrogen peroxide and bromine has been studied. Based on the FT-Raman, FT-IR, and 13C MAS NMR spectra data, it has been found that H2O2 oxidized the interlayer L-CySH to cystine, while the oxidation product of intercalated L-CySH by Br2 was cysteic acid regardless of the bromine/cysteine ratio, which is different from the bulk reaction. Therefore, this layered material may have prospective application as the basis of a novel “molecular reactor” for confined chemical reactions.

Preparation of layered double hydroxides and their applications as additives in polymers, as precursors to magnetic materials and in biology and medicine

Co-reporter:David G. Evans and Xue Duan

Chemical Communications 2006 (Issue 5) pp:485-496

Publication Date(Web):07 Nov 2005

DOI:10.1039/B510313B

In recent years layered double hydroxides (LDHs), also known as hydrotalcite-like materials, have attracted considerable interest from both industry and academia. In this article, we discuss methods of preparing LDHs with an emphasis on the way in which particle size and morphology can be controlled with regard to specific target applications; scale-up of one such preparation procedure is also described. In addition, we review selected applications of LDHs developed by our own and other laboratories.

Inhibiting the leaching of lipase from mesoporous supports by polymerization of grafted vinyl groups

Co-reporter:Jing He, Yan Xu, Hui Ma, David G. Evans, Zhiqiang Wang, Xue Duan

Microporous and Mesoporous Materials 2006 Volume 94(1–3) pp:29-33

Publication Date(Web):8 September 2006

DOI:10.1016/j.micromeso.2006.03.015

This communication reports a method to prevent leaching of porcine pancreatic lipase (PPL) from the pore channels of SBA-15, whereby the pore size is reduced by chemical modification after uptake of porcine pancreatic lipase (PPL). The concrete procedure involves silylation of the surface of SBA-15 entrapping PPL with 3-(trimethoxysilyl)-propylmethacrylate (H2CC(CH3)CO2(CH2)3Si(OCH3)3, PMA) followed by polymerization of the pendant vinyl groups and free PMA, initiated by 2,2′-azobisisobutyronitrile (AIBN).

Synthesis and characterization of a UV absorbent-intercalated Zn–Al layered double hydroxide

Co-reporter:Yongjun Feng, Dianqing Li, Yuan Wang, David G. Evans, Xue Duan

Polymer Degradation and Stability 2006 Volume 91(Issue 4) pp:789-794

Publication Date(Web):April 2006

DOI:10.1016/j.polymdegradstab.2005.06.006

Zn–Al-layered double hydroxides (LDHs) containing the organic anion of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (HMBA), a highly efficient UV absorber, have been synthesized by reaction in air of HMBA with an LDH-carbonate precursor obtained by a process involving separate nucleation and aging steps. The structural properties, photo- and thermal stability of the resulting Zn–Al–HMBA-LDHs were characterized by PXRD, FT-IR and UV–visible spectroscopy and laser particle-size analysis. The results obtained indicated that Zn–Al–HMBA-LDHs synthesized by this method were relatively highly crystalline and had a narrow distribution of particle size. Intercalation of HMBA in the LDH interlayer galleries resulted in an enhanced photo- and thermal stability without affecting its UV absorption capacity; this shows that the hybrid HMBA-LDH phase has potential applications as a UV absorber.

Study of the In Situ Postintercalative Polymerization of Metanilic Anions Intercalated in NiAl-Layered Double Hydroxides under a Nitrogen Atmosphere

Co-reporter:Min Wei;Xiaofei Tian;Jing He;Min Pu;Guoying Rao;Heli Yang;Lan Yang;Tao Liu;David G. Evans

European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 17) pp:

Publication Date(Web):11 JUL 2006

DOI:10.1002/ejic.200600215

A new route has been developed for preparing polyaniline (PANI) layered double hydroxide (LDH) nanocomposites through in situ chemical oxidative polymerization of metanilic anions (m-NH₂C₆H₄SO₃^–) intercalated in NiAl LDHs under a nitrogen atmosphere by using pre-intercalated nitrate as an oxidizing agent. The interlayer space of NiAl LDHs has been used as an original nanoreactor for the in situ polymerization of the intercalated monomer. The whole process involves the synthesis of the precursor LDH [Ni₂Al (OH)₆(NO₃)·nH₂O], the intercalation of the monomer metanilic anions into the LDH and its in situ polymerization between the layers by thermal treatment under a nitrogen atmosphere. The interlayer polymerization reaction was monitored by thermogravimetric analysis (TG), differential thermal analysis (DTA), mass spectrometry (MS), UV/Vis absorption spectroscopy, in situ X-ray absorption near edge structure (XANES) spectroscopy, in situ high-temperature X-ray diffraction (HT-XRD) and in situ Fourier transform infrared (FTIR) spectroscopy. The UV/Vis spectra provide evidence for the polymerization of the intercalated metanilic anions, and an increase in the interlayer distance from 16.0 to 17.2 Å is observed by HT-XRD. It has been found by the in situ techniques that the pre-intercalated nitrate anions act as the oxidizing agent that induces the polymerization of the interlayer monomer under a nitrogen atmosphere upon heating at 300 °C. The orientation of the interlayer polymerization product has also been proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Layered Double Hydroxides Containing Intercalated Zinc Sulfide Nanoparticles: Synthesis and Characterization

Co-reporter:Guoqing Wu;Lianying Wang;David G. Evans

European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 16) pp:

Publication Date(Web):29 JUN 2006

DOI:10.1002/ejic.200600203

Nanosized ZnS has been synthesized in the interlayer galleries of Mg–Al layered double hydroxides (LDHs) by a process involving ion exchange of a Mg₂Al-NO₃ LDH precursor with a zinc–citrate complex {Na₂[Zn(C₆H₄O₇)]·3 H₂O} followed by reaction between the intercalated [Zn(C₆H₄O₇)]^2– anions and H₂S. The materials have been characterized by elemental analysis, powder X-ray diffraction (XRD), transmission electron microscopy, FTIR spectroscopy, MAS ¹³C NMR spectroscopy, and UV/Vis diffuse reflectance spectroscopy, and structural models have been proposed. The XRD diffraction patterns indicate that the layered structure is maintained and that the basal spacing in the intercalated materials depends on the orientation of the citrate moiety. The results confirm that cubic ZnS (sphalerite) is formed in the interlamellar domain rather than on the external surfaces and is co-intercalated with citrate dianions. The growth of ZnS particles is constrained by the layers of the LDH resulting in a large blue shift in the bandgap compared with the bulk material. The thermal decomposition process of the hybrid material has been characterized by in situ high-temperature powder XRD and thermogravimetry-differential thermal analysis (TG/DTA) coupled with mass spectrometry. The thermal stability of the zinc–citrate complex anions intercalated in LDHs is lower than that in the sodium salt. Thermal treatment below 270 °C leads to a reorientation of the citrate anions in the interlayer galleries associated with a significant interlayer contraction. No obvious changes in the XRD peaks corresponding to ZnS are apparent below 400 °C, indicating that sintering to form larger particles is successfully inhibited by the layered host; at higher temperatures the ZnS is oxidized with evolution of SO₂. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Study on the Photochromism of Ni–Al Layered Double Hydroxides Containing Nitrate Anions

Co-reporter:Min Wei;Xiangyu Xu;Xinrui Wang;Feng Li;Hui Zhang;Yanluo Lu;Min Pu;David G. Evans

European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 14) pp:

Publication Date(Web):9 MAY 2006

DOI:10.1002/ejic.200600058

The photochromism of nitrate-containing nickel–aluminum layered double hydroxides (NiAl-NO₃-LDHs) has been studied. Powder X-ray diffraction (PXRD), FTIR, UV/Vis, XPS, ESR, EXAFS, and elemental analysis were used to investigate the structure, composition, and photochromic behavior of NiAl-NO₃-LDHs. A possible photochromic mechanism in NiAl-NO₃-LDHs has been proposed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Preparation of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonate anion-intercalated layered double hydroxide and its photostabilizing effect on polypropylene

Co-reporter:Dianqing Li, Zhenjun Tuo, David G. Evans, Xue Duan

Journal of Solid State Chemistry 2006 Volume 179(Issue 10) pp:3114-3120

Publication Date(Web):October 2006

DOI:10.1016/j.jssc.2006.06.006

An organic UV absorber has been intercalated into a layered double hydroxide (LDH) host by ion-exchange method using ZnAl–NO3–LDH as a precursor with an aqueous solution of the sodium salt of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonic acid (BZO). After intercalation of the UV absorber, the interlayer distance in the LDHs increases from 0.89 to 2.32 nm. Infrared spectra and thermogravimetry and differential thermal analysis (TG–DTA) curves reveal the presence of a complex system of supramolecular host–guest interactions. The thermostability of BZO is markedly enhanced by intercalation in the LDH host. ZnAl–BZO–LDHs/polypropylene composite materials exhibit excellent UV photostability.Intercalation of an organic UV absorber in a layered double hydroxide host leads to an enhancement of its photo- and thermal stability.

Nanostructural drug-inorganic clay composites: Structure, thermal property and in vitro release of captopril-intercalated Mg–Al-layered double hydroxides

Co-reporter:Hui Zhang, Kang Zou, Shaohuan Guo, Xue Duan

Journal of Solid State Chemistry 2006 Volume 179(Issue 6) pp:1792-1801

Publication Date(Web):June 2006

DOI:10.1016/j.jssc.2006.03.019

A nanostructural drug-inorganic clay composite involving a pharmaceutically active compound captopril (Cpl) intercalated Mg–Al-layered double hydroxides (Cpl-LDHs) with Mg/Al molar ratio of 2.06 has been assembled by coprecipitation method. Powder X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and Raman spectra analysis indicate a successful intercalation of Cpl between the layers with a vertical orientation of Cpl disulphide-containing S–S linkage. SEM photo indicates that as-synthesized Cpl-LDHs possess compact and non-porous structure with approximately and linked elliptical shape particles of ca. 50 nm. TG-DTA analyses suggest that the thermal stability of intercalated organic species is largely enhanced due to host–guest interaction involving the hydrogen bond compared to pure form before intercalation. The in vitro release studies show that both the release rate and release percentages markedly decrease with increasing pH from 4.60 to 7.45 due to possible change of release mechanism during the release process. The kinetic simulation for the release data, and XRD and FT-IR analyses for samples recovered from release media indicate that the dissolution mechanism is mainly responsible for the release behaviour of Cpl-LDHs at pH 4.60, while the ion-exchange one is responsible for that at pH 7.45.Based on XRD, FT-IR and Raman spectra analyses, it is suggested that captopril (Cpl) exists as its disulphide metabolites in the interlayer of Mg–Al-LDHs via hydrogen bonding between guest carboxylate function and hydroxyl group of the host layers. A schematic supramolecular structure of Cpl intercalates involving a vertical orientation of Cpl disulphide-containing S–S bond between the layers with carboxylate anions pointing to both hydroxide layers is presented.

Layered and intercalated hydrotalcite-like materials as thermal stabilizers in PVC resin

Co-reporter:Yanjun Lin, Jianrong Wang, David G. Evans, Dianqing Li

Journal of Physics and Chemistry of Solids 2006 Volume 67(5–6) pp:998-1001

Publication Date(Web):May–June 2006

DOI:10.1016/j.jpcs.2006.01.016

In the light of the accepted mechanism of thermal stabilization of PVC by layered double hydroxides (LDHs), the layer cations and interlayer counterions in LDHs were tailored to give MgZnAl-CO3-LDH and MgZnAl-maleate-LDH. These materials were characterized by XRD, FT-IR, and TG–DTA. The thermal stability of PVC composites containing different LDH additives was tested in sheets having a thickness of about 1 mm. The results showed that compared with MgAl-CO3-LDH, MgZnAl-CO3-LDH enhances the thermal stability of PVC in terms of both long-term stability and early coloring. After intercalation of maleate in the LDH by reaction of maleic acid with the MgZnAl-CO3-LDH precursor, the interlayer distance increases from 0.75 to 1.11 nm. Since Cl− promotes the autocatalytic dehydrochlorination of PVC, which is responsible for its degradation, an increased interlayer distance should facilitate entry of Cl− into the interlayer galleries and inhibit the decomposition of PVC. In addition, maleic acid has a conjugated C=C double bond which can react with double bond formed in the dehydrochlorination of PVC and thus further inhibit the autocatalytic degradation reaction. The results show that the early coloring of PVC is markedly improved and the long-term stability slightly reduced by addition of the MgZnAl-maleate-LDH.

Layered solids as a “molecular container” for pharmaceutical agents: L-tyrosine-intercalated layered double hydroxides

Co-reporter:Min Wei, Qi Yuan, David G. Evans, Zhiqiang Wang and Xue Duan

Journal of Materials Chemistry A 2005 vol. 15(Issue 11) pp:1197-1203

Publication Date(Web):25 Jan 2005

DOI:10.1039/B416068A

L-Tyrosine has been intercalated into NiAl, MgAl and ZnAl layered double hydroxides by coprecipitation. The structure and composition of the intercalated materials have been characterized by X-ray diffraction (XRD) and elemental analysis. It is found that intercalation can inhibit racemization of L-tyrosine under the influence of sunlight, high temperature or ultraviolet light. Therefore, this layered material may have potential application as a “molecular container” for storing or transporting unstable chiral biomolecules or pharmaceutical agents. In addition, the thermal decomposition of the L-tyrosine intercalated NiAl-LDH has been investigated in detail by means of in situ HT-XRD, in situ FT-IR and TG-DTA. Loss of interlayer water occurs between room temperature and 150 °C while decomposition of intercalated L-tyrosine and dehydroxylation of the host layers begin at about 250 °C and 300 °C respectively.

In situ FT-IR, in situ HT-XRD and TPDE study of thermal decomposition of sulfated β-cyclodextrin intercalated in layered double hydroxides

Co-reporter:Min Wei, Ji Wang, Jing He, David G. Evans, Xue Duan

Microporous and Mesoporous Materials 2005 Volume 78(Issue 1) pp:53-61

Publication Date(Web):4 February 2005

DOI:10.1016/j.micromeso.2004.09.016

The thermal decomposition behavior of an intercalate derived from magnesium–aluminum layered double hydroxide (Mg/Al LDH) and hexa-sulfated β-cyclodextrin [NaSO3-β-CD(6)] has been studied by in situ Fourier transform infrared (FT-IR) spectroscopy, in situ high temperature X-ray diffraction (HT-XRD), temperature-programmed decomposition (TPDE), thermogravimetry (TG), and differential thermal analysis (DTA). In situ FT-IR shows that the decomposition of glucose groups of β-CD is complete at 230, 170 and 270 °C in NaSO3-β-CD(6), HSO3-β-CD(6) and SO3-β-CD(6)/LDH, respectively, indicating that intercalation of the SO3-β-CD(6) anion into an LDH host can increase its thermal stability. In the hybrid compound SO3-β-CD(6)/LDH the -SO3- groups are gradually converted to SO42- which are grafted to the LDH layers. In situ XRD shows that there are two decreases in d0 0 3 basal spacing of SO3-β-CD(6)/LDH observed in the temperature range 20–150 °C and 200–350 °C. The first corresponds to the destruction of the interlayer hydrogen bonding area and the second is attributed to the decomposition of SO3-β-CD(6) and dehydroxylation of the LDH layers. TPDE combined with GC-MS is used for the first time to study the thermal decomposition of LDHs, and the results are in accordance with those from in situ FT-IR, in situ XRD and TG-DTA.

Modulating effect of Mg–Al–CO3 layered double hydroxides on the thermal stability of PVC resin

Co-reporter:Yan-Jun Lin, Dian-Qing Li, David G. Evans, Xue Duan

Polymer Degradation and Stability 2005 Volume 88(Issue 2) pp:286-293

Publication Date(Web):May 2005

DOI:10.1016/j.polymdegradstab.2004.11.007

Mg–Al–CO3 layered double hydroxides (hydrotalcite-like materials) with different Mg/Al molar ratios and having small particle size and narrow size distribution have been prepared by a method involving separate nucleation and aging steps and characterized by XRD, FT-IR and TG-DTA, which clearly demonstrated that the charge density of the layers decreased with increasing Mg/Al molar ratio. Therefore, the electrostatic force of attraction between layers and interlayer counter-ions as well as the driving force for anion exchange decreased. Varying amounts of Mg–Al–CO3 layered double hydroxides with different Mg/Al molar ratio were mixed with PVC resin. Thermal aging tests of the resulting PVC composites were carried out in a thermal aging test box at 180±1 °C by observing the colour change of the samples. The results showed that Mg–Al–CO3 layered double hydroxide with Mg/Al=2 has the best stabilizing effect on PVC because of its higher layer charge density and consequent stronger driving force for uptake of Cl− in the interlayer galleries. Uptake of Cl− inhibits the autocatalytic dehydrochlorination of PVC which is responsible for its degradation. The optimum loading of layered double hydroxides was determined.

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

Co-reporter:Feng Li, Xiaofeng Liu, Qiaozhen Yang, Junjie Liu, David G. Evans, Xue Duan

Materials Research Bulletin 2005 Volume 40(Issue 8) pp:1244-1255

Publication Date(Web):11 August 2005

DOI:10.1016/j.materresbull.2005.04.011

In this paper, a series of pure Ni1 − xZnxFe2O4 (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)1 − x − yFey2+Fex3+(OH)2]x+(SO42−)x/2·mH2O at 900 °C for 2 h, in which the molar ratio of (Ni2+ + Zn2+)/(Fe2+ + Fe3+) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni1 − xZnxFe2O4 (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.

A magnetic organic–inorganic composite: Synthesis and characterization of magnetic 5-aminosalicylic acid intercalated layered double hydroxides

Co-reporter:Hui Zhang, Kang Zou, Hui Sun, Xue Duan

Journal of Solid State Chemistry 2005 Volume 178(Issue 11) pp:3485-3493

Publication Date(Web):November 2005

DOI:10.1016/j.jssc.2005.09.008

A core–shell structured magnetic layered organic–inorganic material involving 5-aminosalicylic acid (5-ASA) intercalated Zn–Al layered double hydroxides (LDHs) and magnesium ferrite (MgFe2O4) is assembled by a coprecipitation method. The powder X-ray diffraction results show the coexistence of the clear but weak diffractions of MgFe2O4 and ordered relatively stronger reflections of 5-ASA intercalated LDHs. The TEM image of magnetic 5-ASA intercalated LDHs reveals that the LDHs layer covers the MgFe2O4 particles or their aggregates with particle size of 50–80 nm. The vibration sample magnetization (VSM) measurements exhibit the increase in saturation magnetization of magnetic 5-ASA intercalated LDHs samples with increasing amount of magnetic core. The XPS analyses account for a majority of Zn, Al and O atoms on the surface of magnetic particles. It is suggested that the magnetic core MgFe2O4 was coated with LDHs layer probably through Zn–O–Mg and Al–O–Mg linkages, and a core–shell structured model is tentatively proposed.A schematic structural model of nanosized magnetic organic–inorganic hybrid composite involving 5-aminosalicylic acid intercalated layered double hydroxides coated on a ferrite core.

The synthesis and characterization of nanosized orthorhombic LiMnO2 by in situ oxidation–ion exchange

Co-reporter:Xiao-Dan Li, Wen-Sheng Yang, Shi-Chao Zhang, David G. Evans, Xue Duan

Solid State Ionics 2005 Volume 176(7–8) pp:803-811

Publication Date(Web):28 February 2005

DOI:10.1016/j.ssi.2004.10.020

Nanosized orthorhombic LiMnO2 (o-LiMnO2) with high purity and good crystallinity has been synthesized by a simple process under mild conditions (80 °C) involving controlled oxidation of Mn(OH)2 followed by in situ ion exchange of lithium ions with the resulting intermediate MnOOH (in situ oxidation–ion exchange). By studying the effects of varying the lithiating agent, the oxidant and washing conditions, a mechanism for the synthesis of nano o-LiMnO2 by this method has been proposed. Nano o-LiMnO2 obtained by in situ oxidation–ion exchange has a high capacity with an initial discharge capacity of 220 mAh g−1and a good cycling performance with a reversible capacity of 194 mAh g−1 after 30 cyclings, indicating that it is a potential synthetic method for the positive electrode material of lithium ion secondary batteries.

Structure and properties of layered manganese–vanadium oxide as a cathode material for lithium secondary batteries

Co-reporter:Yanluo Lu, Min Wei, Zhiqiang Wang, David G Evans, Xue Duan

Electrochemistry Communications 2004 Volume 6(Issue 7) pp:672-677

Publication Date(Web):July 2004

DOI:10.1016/j.elecom.2004.04.023

MnxV2O5 · nH2O containing double sheets of V2O5 layers has been synthesized by a new method – oxidation of VOSO4 with layered MnO2. The Mn/V molar ratio is 0.068, and XPS indicates that the oxidation state of vanadium is +5 and that of manganese is +4. MnxV2O5 · nH2O has relatively promising lithium insertion properties, with a specific capacity of 200 mA h g−1 between 2.0 and 4.0 V, with the discharge capacity at the 18th cycle remaining as high as 208.3 mA h g−1. MnxV2O5 · nH2O is therefore a potential practical candidate as the cathode material for rechargeable lithium batteries.

Characterization of structure and electrochemical properties of lithium manganese oxides for lithium secondary batteries hydrothermally synthesized from δ-KxMnO2

Co-reporter:Yanluo Lu, Min Wei, Zhiqiang Wang, D.G. Evans, Xue Duan

Electrochimica Acta 2004 Volume 49(Issue 14) pp:2361-2367

Publication Date(Web):15 June 2004

DOI:10.1016/j.electacta.2004.01.017

Lithium manganese oxides have attracted much attention as cathode materials for lithium secondary batteries in view of their high capacity and low toxicity. In this study, layered manganese oxide (δ-KxMnO2) has been synthesized by thermal decomposition of KMnO4, and four lithium manganese oxide phases have been synthesized for the first time by mild hydrothermal reactions of this material with different lithium compounds. The lithium manganese oxides were characterized by powder X-ray diffraction (XRD), inductively coupled plasma emission (ICPE) spectroscopy, and chemical redox titration. The four materials obtained are rock salt structure Li2MnO3, hollandite (BaMn8O16) structure α-MnO2, spinel structure LiMn2O4, and birnessite structure LixMnO2. Their electrochemical properties used as cathode material for secondary lithium batteries have been investigated. Of the four lithium manganese oxides, birnessite structure LixMnO2 demonstrated the most stable cycling behavior with high Coulombic efficiency. Its reversible capacity reaches 155 mAh g−1, indicating that it is a viable cathode material for lithium secondary batteries.

Structure and thermal decomposition of sulfated β-cyclodextrin intercalated in a layered double hydroxide

Co-reporter:Ji Wang, Min Wei, Guoying Rao, David G. Evans, Xue Duan

Journal of Solid State Chemistry 2004 Volume 177(Issue 1) pp:366-371

Publication Date(Web):January 2004

DOI:10.1016/j.jssc.2003.09.006

The sodium salt of hexasulfated β-cyclodextrin has been synthesized and intercalated into a magnesium–aluminum layered double hydroxide by ion exchange. The structure, composition and thermal decomposition behavior of the intercalated material have been studied by variable temperature X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma emission spectroscopy (ICP), and thermal analysis (TG-DTA) and a model for the structure has been proposed. The thermal stability of the intercalated sulfated β-cyclodextrin is significantly enhanced compared with the pure form before intercalation.

Studies on the intercalation of naproxen into layered double hydroxide and its thermal decomposition by in situ FT-IR and in situ HT-XRD

Co-reporter:Min Wei, Shuxian Shi, Ji Wang, Yong Li, Xue Duan

Journal of Solid State Chemistry 2004 Volume 177(Issue 7) pp:2534-2541

Publication Date(Web):July 2004

DOI:10.1016/j.jssc.2004.03.041

Layered double hydroxides, novel anionic clay, meet the first requirement as inorganic matrices for encapsulating functional drugs or biomolecules with negative charge in aqueous media. In this study, naproxen has been intercalated into Mg–Al layered double hydroxide by the methods of ion exchange. The structure and composition of the intercalated material have been studied by X-ray diffraction (XRD), UV–vis spectroscopy and inductively coupled plasma emission spectroscopy. A schematic model has been proposed. Furthermore, in situ Fourier transform infrared spectroscopy, in situ high-temperature XRD, and thermogravimetry (TG) have been used to characterize the thermal decomposition of the hybrid material. It has been found that the thermal stability of the intercalated naproxen is significantly enhanced compared with the pure form before intercalation, which suggests that this drug-inorganic layered material may have prospective application as the basis of a novel drug delivery system.

Structure and surface characteristics of Cu-based composite metal oxides derived from layered double hydroxides

Co-reporter:Lihong Zhang, Feng Li, David G. Evans, Xue Duan

Materials Chemistry and Physics 2004 Volume 87(2–3) pp:402-410

Publication Date(Web):15 October 2004

DOI:10.1016/j.matchemphys.2004.06.010

Layered double hydroxides (LDHs) with Cu2+/Zn2+/Al3+ atomic ratios from 1:1:1 to 3:1:1 have been synthesized by coprecipitation method. The physicochemical properties of both the as-synthesized LDHs and their calcined products obtained at 773 K for 3 h have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), chemical analysis, transmission electron microscopy (TEM), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), N2 adsorption–desorption experiments and thermogravimetric analysis (TGA). The chemical states of metal species on the surface of the calcined LDHs were also characterized by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The results indicate that Cu2+/Zn2+/Al3+ atomic ratio in the synthesis mixtures influences crystallinity, purity, and thermal stability of the LDHs, and hence, the composition of the resulting calcined LDHs. At room temperature and atmospheric pressure, oxidation of aqueous phenol solutions by hydrogen peroxide in the presence of the calcined LDHs was carried out. The results show that the calcined LDHs with the Cu2+/Zn2+/Al3+ atomic ratio of 1:1:1 has the highest catalytic activity for conversion of phenol, which may be related to the formation of a great amount of composite metal oxide containing Cu2+ ions and to good dispersion property of active Cu2+ centers present on the surface.

Preparation of magnetic material containing MgFe2O4 spinel ferrite from a Mg–Fe(III) layered double hydroxide intercalated by hexacyanoferrate(III) ions

Co-reporter:Weiqing Meng, Feng Li, David G Evans, Xue Duan

Materials Chemistry and Physics 2004 Volume 86(Issue 1) pp:1-4

Publication Date(Web):15 July 2004

DOI:10.1016/j.matchemphys.2004.03.011

In this research communication, a novel method for improving magnetic properties of material containing MgFe2O4 spinel ferrite is presented. The key feature of this method is using a single molecular precursor. Mg–Fe(III) layered double hydroxide intercalated by [Fe(CN)6]3− ions with the low Mg/Fe molar ratio can be prepared by coprecipitation method. Compared with conventional ceramic method, the saturation magnetization for MgFeO4 ferrite produced by calcination of the intercalated LDH precursor is improved obviously. The major advantage of the method is that it affords uniform distribution of all metal cations on an atomic level in the intercalated LDH precursor, and supplies additional Fe3+ ions from the interlayer [Fe(CN)6]3− ions; hence the formation of a great amount of spinel ferrite starting from the LDH rather than a mixture requires a much shorter time and lower temperature.

Synthesis and characterization of a novel nano-scale magnetic solid base catalyst involving a layered double hydroxide supported on a ferrite core

Co-reporter:Hui Zhang, Rong Qi, David G Evans, Xue Duan

Journal of Solid State Chemistry 2004 Volume 177(Issue 3) pp:772-780

Publication Date(Web):March 2004

DOI:10.1016/j.jssc.2003.09.009

A nano-scale magnetic solid base catalyst MgAl-OH-LDH/MgFe2O4 (where LDH denotes layered double hydroxide) composed of MgAl-OH-LDH Brønsted base catalytic layers coated on MgFe2O4 spinel cores has been prepared. A magnetic precursor MgAl-CO3-LDH/MgFe2O4 was prepared by a method involving separate nucleation and aging steps, and subsequently calcined to give a mixed metal oxide composite MgAl(O)/MgFe2O4 which was rehydrated to give MgAl-OH-LDH/MgFe2O4. The structure and magnetic properties of the nano-scale magnetic solid base MgAl-OH-LDH/MgFe2O4, together with those of the magnetic precursor MgAl-CO3-LDH/MgFe2O4 and MgFe2O4 were characterized by XRD, XPS, low temperature N2 adsorption and vibrating sample magnetometry (VSM). The MgAl-OH-LDH/MgFe2O4 composite possesses a mesoporous structure with pore size ranging from 2 to 20 nm with particle size mainly in the range 35–130 nm. The catalytic properties of MgAl-OH-LDH/MgFe2O4 were evaluated using the self-condensation of acetone at 273 K as a probe reaction. The results showed that the conversion of acetone to diacetone alcohol reached the thermodynamic equilibrium value of 23% at 273 K. The catalyst was easily recovered through application of an external magnetic field, and when the reclaimed catalyst was used in a second run for the same reaction, the reactivity remained unchanged.

New molybdenum(VI) catalysts for the epoxidation of cyclohexene: synthesis, reactivity and crystal structures

Co-reporter:Ge Wang, Gang Chen, Rudy L. Luck, Zhiqiang Wang, Zhongcheng Mu, David G. Evans, Xue Duan

Inorganica Chimica Acta 2004 Volume 357(Issue 11) pp:3223-3229

Publication Date(Web):5 August 2004

DOI:10.1016/j.ica.2004.03.030

Compounds 1–6 of the type MoO2X2L2 (X=F, Cl, Br; L=OPMePh2, OPPh3) have been prepared in order to investigate the variation in catalytic activity with changes in electronic and steric properties. All six complexes catalyze the epoxidation of cyclohexene with tert-butylhydroperoxide, and the species with X=Cl and L=OPMePh2 (2) displays the best activity with 83% conversion and 90% selectivity in one hour at ambient atmosphere. These inexpensive and easily prepared dioxo catalysts are stable to air and water. Reactions of the dioxo compounds with H2O2 and t-BuOOH have also been carried out. The structures of MoO2F2(OPMePh2)2 (1) and the product of its reaction with H2O2, MoO(O2)2(OPMePh2)2 (7) have been solved by single crystal X-ray diffraction.Compounds the type MoO2X2L2 (X=F, Cl, Br; L=OPMePh2, OPPh3) catalyze the epoxidation of cyclohexene with tert-butylhydroperoxide. These inexpensive and easily prepared dioxo catalysts are stable to air and water, and therefore potentially more useful in practical terms than current catalysts.

Stoichiometric synthesis of a pure ferrite from a tailored layered double hydroxide (hydrotalcite-like) precursor

Co-reporter:Junjie Liu, Feng Li, David G. Evans and Xue Duan

Chemical Communications 2003 (Issue 4) pp:542-543

Publication Date(Web):27 Jan 2003

DOI:10.1039/B212233B

Calcination of a layered double hydroxide precursor containing MgII, FeII and FeIII cations with an Mg2+∶(FeII + FeIII) ratio of 0.5 affords a pure ferrite spinel, MgFe2O4, which has a higher saturation magnetization than samples of the same material produced by conventional ceramic routes.

Large continuous, transparent and oriented self-supporting films of layered double hydroxides with tunable chemical composition

Co-reporter:Lianying Wang, Cang Li, Miao Liu, David G. Evans and Xue Duan

Chemical Communications 2007(Issue 2) pp:NaN125-125

Publication Date(Web):2006/11/06

DOI:10.1039/B613687G