Acknowledgements On publication of my thesis, I am grateful for the contributions of several individuals, without which this would have been impossible to achieve. I am extremely indebted to my supervisor A/P Zeng Hua Chun for his invaluable direction, advice and encouragement throughout the duration of this research. His endless patience and understanding has allowed me to carry out this work to the best of my ability. I would sincerely like to thank Dr Xu Zhiping and Dr Gowry Sampanthar for many useful discussions and their assistance in carrying out research work in many aspects. For technical support, I am especially grateful to Dr Li Sheng and Mdm Sam Fam Hwee Koong for XPS, Mr Chia Phai Ann and Mr Mao Ning for TEM. Many thanks go to Ms Lee Chai Keng, Mdm Khoh Leng Khim and Ms Tay Choon Yen for their support manytimes in running other instruments. Special thanks must go to my husband, my parents and Ms Zhang Yingsu and her daughter Mao Bangyuan for their unfailing support, encouragement and understanding during the last three years. i Table of Content Acknowledgements i Summary vi Nomenclature viii List of Figures xi List of Tables xvi Publications Related to Thesis xviii Chapter Scope of the Thesis Chapter Literature Review 2.1 Overview 2.2 Layered Hydroxide Compounds 2.2.1 Introduction 2.2.2 Structural properties II III 2.2.2.1 2.2.2.2 2.2.2.3 2.2.2.4 The nature of M and M The values of x Nature of anions The values of m 11 13 14 16 2.2.3 Synthesis methods 17 2.2.3.1 2.2.3.2 2.2.3.3 2.2.3.4 2.2.3.5 2.2.3.6 2.2.3.7 Coprecipitation method Anion exchange method Rehydration method Hydrothermal synthesis Sol-gel method Oxidation method Microwave assisted method 18 19 22 22 23 24 24 2.2.4 Applications 25 2.2.4.1 2.2.4.2 2.2.4.3 2.2.4.4 2.2.4.5 2.2.4.6 2.2.4.7 2.2.4.8 2.2.4.9 N2O decomposition Catalytic partial oxidation (CPO) of methane Steam reforming Polymerization reactions Aldol condensation Hydrogenation of nitriles Oxidation Catalyst supports Anion adsorbents 26 27 27 28 28 29 30 31 32 2.3 Cobalt-Layered Hydroxides 33 ii 2.3.1 Introduction 33 2.3.2 Cobalt hydroxides 33 2.3.3 Cobalt-containing HTlcs 34 2.3.4 Cobalt-containing hydroxide salts 35 2.4 Nanostructured Materials 35 2.4.1 Introduction 35 2.4.2 Types of nanostructured materials 36 2.4.3 Synthesis of nanostructured materials 37 2.4.4 Chemical synthesis of Co-layered hydroxides and the related nanostructured materials 41 Chapter Experimental Methods 46 3.1 Materials Preparation 46 3.2 Characterization Methods 46 3.2.1 Powder X-ray diffraction (XRD) 46 3.2.2 Fourier transform infrared spectroscopy (FTIR) 47 3.2.3 Thermogravimetry analysis (TGA) 48 3.2.4 Thermogravimetry analysis-Fourier transform infrared spectroscopy (TGA-FTIR) 48 3.2.5 X-ray photoelectron spectroscopy (XPS) 49 3.2.6 Transmission electron microscopy (TEM) 50 3.2.7 Selected area electron diffraction (SAED) 50 3.2.8 Inductive coupled plasma –Atomic emission spectroscopy (ICP-AES) 51 3.2.9 Determination of carbon and nitrogen 51 Chapter A Comparative X-ray Photoelectron Spectroscopic 52 Investigation on Cobalt-Containing Layered Hydroxides 4.1 Introduction 52 4.2 Material Synthesis and Characterization 53 4.3 Results and Discussion 55 4.3.1 Overall bulk and surface compositional analyses 55 4.3.2 Surface adsorbed species and intercalated anions 57 4.3.3 Hydroxyl and other oxygen species 61 4.3.4 Trivalent metal cations in brucite-like layers 67 4.3.5 Divalent metal cations in brucite-like layers 70 4.4 Conclusions 78 iii Chapter Mechanistic Investigation of Self-Redox Decomposition of Cobalt-Hydroxide-Nitrate Compounds with 80 Different Nitrate Anion Configurations in Interlayer Space 5.1 Introduction 80 5.2 Material Synthesis and Characterization 81 5.3 Results and Discussion 83 5.3.1 Structural and chemical analysis 83 5.3.2 Configurations of nitrate anions in interlayer space 86 5.3.3 Self-redox decomposition of intercalated nitrate anions 93 5.3.4 Surface analysis of decomposed products 99 5.4 Conclusions 106 Chapter Investigation on the Effect of Molecular Symmetry on Decomposition Processes of PA/TA-Intercalated Layered 108 Hydroxides 6.1 Introduction 108 6.2 Material Synthesis and Characterization 109 6.3 Results and Discussion 111 6.3.1 Structure and composition of Co(Mg)Al-TA(PA)-HTlcs 111 6.3.2 Thermal decomposition 117 6.3.3 Formation of metal-oxide/carbon nanocomposites 126 6.4 Conclusions 137 Chapter Mechanistic Investigation on Salt-Mediated Formation of Free-Standing Co3O4 Nanocubes at 95 °C from 138 Cobalt-Layered Hydroxide Precursors 7.1 Introduction 138 7.2 Material Snthesis and Caracterization 139 7.3 Results and Discussion 140 7.3.1 Composition and structural phases 140 7.3.2 Thermal decomposition 148 7.3.3 Cystallite morphologies 152 7.4 Conclusions 162 Chapter Preparation of Nanorods of Cobalt Hydroxide Carbonate and the Derived Co3O4 One-Dimensional Nanostructures 163 8.1 163 Introduction iv 8.2 Material Synthesis and Characterization 165 8.3 Results and Discussion 166 8.3.1 Composition and structural phases 166 8.3.2 Crystallite microstructures 176 8.4 Conclusions 188 Chapter Concluding Remarks and Suggestions 189 9.1 Concluding remarks 189 9.2 Suggestions for future work 191 References 193 v Summary The research work carried out in this thesis is related to cobalt-containing layered hydroxide compounds and their derived nanostructured materials, due to the growing interest in new applications of such materials as catalysts, organic-inorganic hybrid nanocomposites and nanostructured materials. The element cobalt was chosen as it is an important transition metal having common oxidation states of +2 and +3, which gives interesting properties to the derived compounds, in the form of hydroxide and oxide. The layered materials studied in this thesis include hydrotalcite-like compounds and hydroxide salts. The basic structure of such compounds consists of metal hydroxide layers and anions intercalated or pillared into the layer structures. Chapter gives a literature review about such materials regarding their physicochemical properties, synthesis methods and applications. In addition, some introduction specifically on cobalt-containing layered hydroxide materials is provided. In this chapter, the nanostructured materials are also briefly introduced and the synthesis of cobalt-layered hydroxides and the related nanostructured materials is summarized. Chapter is an introduction to the experimental methods involved in this work. It presents the methods for materials preparation and characterization techniques. Chapter is concerned with surface chemical states of cobalt-containing layered hydroxides, as such information is rare in open literature despite that the bulk information of these materials have been well documented. The spectra obtained with XPS for various elements indicate the composition and bonding environment in the surface region. The effects of metals, population and valency of interlayer anions are observed and discussed. vi In Chapters and 6, investigation is carried out on decomposition processes of cobalt-layered compounds intercalated with anions. Chapter studies in detail about the mechanism of the self-redox decomposition of two nitrate-containing cobalt layered hydroxide compounds, with variable redox reagent contents and different configurations of nitrate anions in the interlayer space. It has been elucidated that divalent cations in resulting oxides, rather than in hydroxyl octahedral, are the active reductant for the redox reactions. Chapter presents the effect of molecular symmetry of the intercalated organic bi-carboxylate anions on the decomposition process. In this study, terephthalate (TA2-) and 1,2-phenylenediacetic (PA2-) anions have been intercalated into CoAl- and MgAl-hydrotalcite-like compounds. It has been found that within the same confined space and chemical environment provided by the hydroxide layers, decomposition processes of PA2--containing HTlcs are distinctively different from those of TA2--containing HTlcs due to the variations in molecular structure and charge distribution. Chapters and are focused on synthesis of cobalt spinel oxide, Co3O4 nanocrystals. The generation of free-standing Co3O4 nanocubes of ca. 47 nm via increasing of the ionic strength in aqueous system at 95 oC and atmospheric pressure is described in Chapter 7. The formation of nanosized and faceted nanocubes is found to be attributed to the reduction of interfacial tension and the creation of salt-(solvent)n diffusion boundary in the solution with high ionic strength. In Chapter 8, the effort has been made to prepare Co3O4 nanocrystals assembled in rod-like shape via thermal transformation from rod-like cobalt hydroxide carbonate precursors. Finally, Chapter gives conclusions about the proceeding chapters and some suggestions for the future work. vii Nomenclature a unit cell in HTlc (inter-metal-distance in brucite-like layers) A′′2 symbol of IR vibrational symmetry AC adventitious carbon AES atomic emission spectroscopy BE binding energy (eV) BEs binding energies (eV) BET Brunauer-Emmett-Teller method c′ inter-brucite-like-sheet-distance c 3c′ or 2c′ (unit cell parameter in c-direction) C2v IR vibrational symmetry with only one double axis CHN elemental analysis of carbon, hydrogen and nitrogen CPO catalytic partial oxidation C x Hy unsaturated hydrocarbon compounds d distance between two planes δ bending vibration D diameter of ring in electron diffraction pattern D3h symmetry with one triple axis and three perpendicular double axes dhkl distance between reflection planes (hkl) Dia. diameter of γ-alumina pellets (mm) DNA deoxyribonucleic acid Dp average crystalline size (nm) DrTGA differential thermogravimetry analysis E′ ν vibrational mode of D3h viii ED electron diffraction Eq. equation Eqs. equations EXAFS extended X-ray absorption fine struture φ specimen tilted angle in transmission electron microscope analysis Fig. figure Figs. figures FTIR Fourier transform infrared spectroscopy FWHM full width at half maximum h hour(s) H height of γ-alumina pellets (mm) HC hydrocarbon HRTEM high resolution transmission electron microscope HT hydrotalcite HTlc hydrotalcite-like compound HTlcs hydrotalcite-like compounds ICP inductively coupled plasma λ wavelength of X-ray radiation (0.1506 nm for Cu Kα radiation) λe wavelength of electron beam m the amount of interlayer water in hydrotalcite-like compounds νn symbol of IR vibrational mode νas asymmetric stretching vibration νs symmetric stretching vibration N number of sites occupied by anions in interlayer space OC oxidized carbon ix PA 1,2-phenylenediacetic acid PA2- 1,2-phenylenediactate anion θ diffraction angle in the X-ray diffraction measurements (o) ss shake-up satellite SAED selected area electron diffraction T temperature TA terephthalic acid TA2- terephthalate anion TEM transmission electron microscope TGA thermogravimetry analysis vpm volume per million XPS X-ray photoelectron spectroscopy XRD X-ray diffraction x 312. 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Colloid Interface Sci., 254, 87-94. 2002. 249 [...]... hydroxide precursor compounds under oxidative conditions First of all, some effort was made in Chapter 2 to give an overall introduction on layered hydroxide materials regarding their general physicochemical properties, synthesis methods and applications, as well as nanostructured materials and in particular nanomaterials of cobalt layered hydroxides and their related compounds, mainly cobalt spinel oxide... involved: 1) Synthesis of cobalt layered hydroxide materials mainly by coprecipitation method; 2) Characterization of the above materials by XRD/FTIR/TGA/CHN/ICP/XPS, etc.; 3) Detailed investigation on their thermal decomposition behavior by in situ TGAFTIR experiment coupled with other characterization methods listed in 2); 1 4) Synthesis of cobalt spinel oxide nanomaterials from cobalt layered hydroxide. .. hydroxide compounds as precursors for related nanostructured materials The synthesis methods involved are mainly precipitation at ambient conditions The literature review in this chapter covers three parts: i) a detailed review of layered hydroxide materials, mainly hydrotalcite-like compounds; ii) a particular discussion about cobalt- layered hydroxides; and iii) a brief introduction of nanostructured materials. .. is concerning the cobalt layered hydroxides and their derived nanostructured materials, mainly cobalt spinel oxides Cobalt layered hydroxide is used as a broad name for several types of compounds in this work Besides the relatively simple compound, Co(OH)2, the current work has been more focused on the other two types of cobalt layered hydroxides incorporated with anions, namely, hydrotalcite-like compounds. .. compounds with different nitrate anion configurations in interlayer space, Chem Mater., in press 5 Xu, R and Zeng, H C Investigation on the effect of molecular symmetry on decomposition processes of PA/TA-intercalated clays, in preparation 6 Xu, R and Zeng, H C Preparation of nanorods of cobalt hydroxide carbonate and the derived Co3O3 one-dimensional nanostructures, in preparation xviii Chapter 1 Scope of... two nitrate containing cobalt layered hydroxide compounds, CoII0.80CoIII0.20(OH)2.00(NO3)0.14(CO3)0.03⋅0.77H2O and CoII(OH)1.50(NO3)0.40(CO3)0.05 ⋅0.05H2O under inert atmosphere condition These two compounds were purposely prepared with variable redox reagent contents and different configurations of nitrate anions in the interlayer space Based on the detailed investigation using TGA-FTIR and XPS methods,... Xu, R and Zeng, H C Sulfate-functionalized carbon/metal-oxide nanocomposites from hydrotalcite-like compounds, Nano Lett., 1, 703-706 2001 3 Xu, R and Zeng, H C Mechanistic investigation on salt-mediated formation of free-standing Co3O4 nanocubes at 95 oC, J Phys Chem B, 107, 926-930 2003 4 Xu, R and Zeng, H C Mechanistic investigation on self-redox decompositions of cobalt- hydroxide- nitrate compounds. .. salt mediation was also conducted for comparison The effort to prepare Co3O4 nanoparticles assembled in rod-like shape was made and the results are reported in Chapter 8 The precursor materials, cobalt hydroxide carbonate compounds, were synthesized by precipitation methods, either in heterogeneous or homogeneous way The addition of the solution containing NaOH and Na2CO3 into the solution of cobalt salt... Nitrate anion configurations in interlayer space for a Coxi hydroxide- nitrate compound in which all cobalt cations are in divalent oxidation state Starting from a hydroxyl vacancy, on one hand, a nitrate anion can be incorporated into the brucitelike plane through one of its three oxygen atoms (C2v; model I), which leads to a modification of hydroxyl sublattice On the other hand, a nitrate anion could... hydrotalcite-like compounds and hydroxide salts or basic salts In general, layered hydroxide consists of two-dimensional hydroxide sheets stacking one on top of each other The sheet is formed by edge-sharing octahedra In each octahedra, metal cation is located in the center and surrounded by 6 OH- groups If a fraction of Co2+ ions is replaced by trivalent cations (Co3+, or other trivalent cations), a net positive . properties, synthesis methods and applications, as well as nanostructured materials and in particular nanomaterials of cobalt layered hydroxides and their related compounds, mainly cobalt spinel. about such materials regarding their physicochemical properties, synthesis methods and applications. In addition, some introduction specifically on cobalt- containing layered hydroxide materials. Determination of carbon and nitrogen 51 Chapter 4 A Comparative X-ray Photoelectron Spectroscopic Investigation on Cobalt- Containing Layered Hydroxides 52 4.1 Introduction 52 4.2 Material Synthesis