Synthesis of one-dimensional nanocomposites based on alumina nanofibres and their catalytic applications

Materials with one-dimensional (1D) nanostructure are important for catalysis. They are the preferred building blocks for catalytic nanoarchitecture, and can be used to fabricate designer catalysts. In this thesis, one such material, alumina nanofibre, was used as a precursor to prepare a range of nanocomposite catalysts. Utilising the specific properties of alumina nanofibres, a novel approach was developed to prepare macro-mesoporous nanocomposites, which consist of a stacked, fibrous nanocomposite with a core-shell structure. Two kinds of fibrous ZrO2/Al2O3 and TiO2/Al2O3 nanocomposites were successfully synthesised using boehmite nanofibers as a hard temperate and followed by a simple calcination. The alumina nanofibres provide the resultant nanocomposites with good thermal stability and mechanical stability. A series of one-dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into a butanol solution, followed by calcination at 773 K. The materials were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and Fourier Transform Infrared spectroscopy (FT-IR). The results demonstrated that when the molar percentage, X, X=100*Zr/(Al+Zr), was > 30%, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals formed on their surface. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific drying techniques. The mechanism for the formation of these long ZrO2/Al2O3 composite nanorods is proposed in this work. A series of solid-superacid catalysts were synthesised from fibrous ZrO2/Al2O3 core and shell nanocomposites. In this series, the zirconium molar percentage was varied from 2 % to 50 %. The ZrO2/Al2O3 nanocomposites and their solid superacid counterparts were characterised by a variety of techniques including 27Al MAS-NMR, SEM, TEM, XPS, Nitrogen adsorption and Infrared Emission Spectroscopy. NMR results show that the interaction between zirconia species and alumina strongly correlates with pentacoordinated aluminium sites. This can also be detected by the change in binding energy of the 3d electrons of the zirconium. The acidity of the obtained superacids was tested by using them as catalysts for the benzolyation of toluene. It was found that a sample with a 50 % zirconium molar percentage possessed the highest surface acidity equalling that of pristine sulfated zirconia despite the reduced mass of zirconia. Preparation of hierarchically macro-mesoporous catalyst by loading nanocrystallites on the framework of alumina bundles can provide an alternative system to design advanced nanocomposite catalyst with enhanced performance. A series of macro-mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesised. The materials were calcined at 723 K and were characterised by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), and UV-visible spectroscopy (UV-visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100oC), which makes it possible to synthesize such materials on industrial scale. The performances of a series of resultant TiO2/Al2O3 nanocomposites with different morphologies were evaluated as a photocatalyst for the phenol degradation under UV irradiation. The photocatalyst (Ti/Al =2) with fibrous morphology exhibits higher activity than that of the photocatalyst with microspherical morphology which indeed has the highest Ti to Al molar ratio (Ti/Al =3) in the series of as-synthesised hierarchical TiO2/Al2O3 nanocomposites. Furthermore, the photocatalytic performances, for the fibrous nanocomposites with Ti/Al=2, were optimized by calcination at elevated temperatures. The nanocomposite prepared by calcination at 750oC exhibits the highest catalytic activity, and its performance per TiO2 unit is very close to that of the gold standard, Degussa P 25. This work also emphasizes two advantages of the nanocomposites with fibrous morphology: (1) the resistance to sintering, and (2) good catalyst recovery

Sulfated fibrous ZrO2/Al2O3 core and shell nanocomposites: A novel strong acid catalyst with hierarchically macro-mesoporous nanostructure

A series of solid strong acid catalysts were synthesised from fibrous ZrO2/Al2O3 core and shell nanocomposites. In this series, the zirconium molar percentage was varied from 2 % to 50 %. The ZrO2/Al2O3 nanocomposites and their solid strong acid counterparts were characterised by a variety of techniques including 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR), scanned electronic microscopy (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Nitrogen adsorption and infrared emission spectroscopy (IES). NMR results show that the interaction between zirconia species and alumina strongly correlates with pentacoordinated aluminium sites. This can also be detected by the change in binding energy of the 3d electrons of the zirconium. The acidity of the obtained solid acids was tested by using them as catalysts for the benzolyation of toluene. It was found that a sample with a 50 % zirconium molar percentage possessed the highest surface acidity equalling that of pristine sulfated zirconia despite the reduced mass of zirconia

Decontamination of chlorine gas by organic amine modified copper-exchanged zeolite

Removal of chlorine gas (Cl2) from air is of critical requirement in order to address point-source emissions possibly during a terrorist attack or an industrial accident resulting in Cl2 contamination of the atmosphere. In this work, copper (Cu) exchanged zeolite Y (CuY) was functionalised with triethylenediamine (TEDA) and the capacity to remove Cl2 was evaluated. The materials were characterised by nitrogen (N2) adsorption-desorption studies, Fourier Transform Infrared (FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The materials' ability to remove Cl2 was investigated via a dynamic breakthrough test. Copper exchanged zeolite displayed a low adsorption of Cl2 in spite of its large surface area. However, Cl2 removal greatly improved following functionalisation with TEDA. XPS analysis revealed that Cl2 was removed via a catalytic hydrolysis reaction where adsorbed water vapour transformed Cl2 into Cl- which could be further trapped in the zeolite structural framework. Moisture could increase the Cl2 removal capacity, but the competition for adsorption between water and chlorine molecules was also observed. The spent adsorbent after exposure to Cl2 could be easily recycled with an excessive water vapour treatment. The reusability was also investigated and the adsorbent could be used for more than five times. This material can potentially be used in air filters. It may provide an efficient way for decontaminating Cl2 during a terrorist attack or an industrial accident

Copper-complexed clay/poly-acrylic acid composites:Extremely efficient adsorbents of ammonia gas

Work reported in this manuscript takes into consideration the possible use of NH3 gas by terrorists and the potential for an effective and rapid removal of such toxic substance from air using a modified clay material. In this study, a series of clay/polymer composites were synthesised for ammonia gas (NH3) adsorption. The adsorbents were prepared by polymerisation of acrylic acid with N,N'-methylenebisacrylamide (MBA) as cross-linker in the presence of a large amount of highly dispersed clay nanoparticles, followed by interaction with copper ions (Cu2+). Two kinds of clays were used. One was an acid-treated bentonite that had a specific surface area (SSA) of 395 m2/g and the other was natural palygorskite with a SSA of 87 m2/g. The materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption and Fourier transform infrared spectroscopy (FTIR). The materials' ability to remove NH3 was investigated using NH3 breakthrough dynamic test while the strength of NH3 retention was characterised by Thermogravimetric Analysis (TGA) coupled with FTIR. The results indicate that clay/poly-acrylic acid composites are highly efficient adsorbents of NH3 after binding with Cu2+. Trapping NH3 on such adsorbents can lead to colour change and this makes it possible to predict the lifetime of the adsorption bed visually. In addition, the result of NH3 release from the material following adsorption showed that majority of the adsorbed NH3 desorbed at temperature above 180°C. The clay/polymer composites can potentially be used in air filters. They may provide an effective and cheap way for removing NH3 from contaminated air

Fabrication of macro-mesoporous titania/alumina core-shell materials in oil/water interface

A series of macro–mesoporous TiO2/Al2O3 nanocomposites with different morphologies were synthesized. The materials were calcined at 723 K and were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), N2 adsorption/desorption, Infrared Emission Spectroscopy (IES), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy (UV–visible). A modified approach was proposed for the synthesis of 1D (fibrous) nanocomposite with higher Ti/Al molar ratio (2:1) at lower temperature (<100 °C), which makes it possible to synthesize such materials on industrial scale. The performance–morphology relationship of as-synthesized TiO2/Al2O3 nanocomposites was investigated by the photocatalytic degradation of a model organic pollutant under UV irradiation. The samples with 1D (fibrous) morphology exhibited superior catalytic performance than the samples without, such as titania microspheres

Biomass derived palygorskite-carbon nanocomposites:Synthesis, characterisation and affinity to dye compounds

Clay minerals can act as a uniform dispersion medium for nano-sized carbon particles. However, literature on the preparation and characteristics of palygorskite-carbon nanocomposites is scant. Using a hydrothermal carbonisation technique this study developed two nanocomposites on fibrous palygorskite from starch: the first without a post-synthesis treatment (Composite 1); and the second with an activation at 550°C for 3h (ramp at 10°Cmin-1) under CO2 environment (200mLmin-1) (Composite 2). A uniform dispersion of nano-scale carbon spheres was formed on partially destroyed palygorskite structures. Composite 2, which indicated the formation of graphitised carbon nanoparticles, generated a 17-fold greater specific surface area than Composite 1 and also created micro- and mesopores in its structure. The nanocomposites, especially in Composite 1, contained organic surface functional groups (CH, CC, CO) and indicated variable affinity to cationic and anionic dye compounds. While Composite 2 adsorbed a larger amount of anionic orange II dye (23mgg-1), Composite 1 adsorbed more cationic methylene blue (46.3mgg-1). Isothermal and kinetic modelling of the adsorption data indicated that in addition to electrostatic attraction for methylene blue adsorption on both nanocomposites, a pore diffusion mechanism was involved and the boundary resistance was greater for orange II than methylene blue adsorption. Being a material developed from green biomass (starch) and an abundant natural resource (palygorskite), these nanocomposites have immense potential for application in environmental remediation including in situ immobilisation of contaminants in soil

Nickel on a macro-mesoporous Al2O3@ZrO2 core/shell nanocomposite as a novel catalyst for CO methanation

A novel nickel catalyst supported on Al2O3@ZrO2 core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H-2 temperature-programmed reduction (H-2-TPR), nitrogen adsorption desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 degrees C to 500 degrees C. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al2O3@ZrO2 core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al2O3@ZrO2-15 exhibited the highest CO conversion and methane selectivity at 400 degrees C, but they decreased dramatically above or below 400 degrees C due to the temperature sensitivity of the catalyst. Ni/Al2O3@ZrO2-30 exhibited a high and constant rate of methane formation between 350 degrees C and 450 degrees C. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Alumina nanofibres grafted with functional groups: a new design in efficient sorbents for removal of toxic contaminants from water

A new design in efficient sorbents for the removal of trace pollutants from water was proposed: grafting the external surface of ?-alumina (?-Al2O3) nanofibers with functional groups that have a strong affinity to the contaminants. This new grafting strategy greatly improves the accessibility of these sorption sites to adsorbates and thus efficiency of the fibrous sorbents. The product sorbents could capture the pollutants selectively even when the concentration of the contaminants is extremely low. Two types of ?-Al2O3 nanofibers with different size were prepared via facile hydrothermal methods. Thiol groups were then grafted on the ?-Al2O3 fibers by refluxing the toluene solution of 3-mercaptopropyltrimethoxysilane (MPTMS). The thiol group modified fibers not only can efficiently remove heavy metal ions (Pb2+ and Cd2+) from water at a high flux, but also display high sorption capacity under sorption equilibrium conditions. Similar result was obtained from the nanofibers grafted with octyl groups which are employed to selectively adsorb highly diluted hydrophobic 4-nonylphenol molecules from water. This study demonstrates that grafting nanofibers is a new and effective strategy for developing efficient sorbents.Full Tex

Fabrication of macro-mesoporous zirconia-alumina materials with a one-dimensional hierarchical structure

A series of one dimensional (1D) zirconia/alumina nanocomposites were prepared by the deposition of zirconium species onto the 3D framework of boehmite nanofibres formed by dispersing boehmite nanofibres into butanol solution. The materials were calcined at 773K and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 adsorption/desorption, infrared emission spectroscopy (IES). The results demonstrated that when the molar percentage X=100*Zr/(Al+Zr) was > 30 %, extremely long ZrO2/Al2O3 composite nanorods with evenly distributed ZrO2 nanocrystals on the surface were formed. The stacking of such nanorods gave rise to a new kind of macroporous material without the use of any organic space filler\template or other specific technologies. The mechanism for the formation of long ZrO2/Al2O3 composite nanorods was proposed in this work