- Title
- Fabrication of functionalised biomimetic silica shell – magnetic core particles and their applications in heavy metal ion and fine mineral particle recovery
- Creator
- Hyde, Emily Dawn Elizabeth Rodd
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- In our energy conscious world, magnetic separation provides a facile, low energy technique offering low operating costs, high yield and ease of operation. For nonmagnetic materials, their specific adsorption onto magnetic carrier particles allows those materials to be separated via the application of magnetic fields. Magnetic core – silica shell particles are ideally posed as magnetic carrier particles combining the magnetism offered by the core with an easily functionalised silica shell which provides adsorption selectivity. However, the fabrication of magnetic core-shell carrier particles reported in the literature often involve high temperatures, long reaction times, harsh reaction conditions and/or complex, multi-step methodologies, and, therefore, prove difficult to effectively scale up. Biomimetic silication, utilising the branched, polyamine, polyethyleneimine (PEI), as a scaffolding/silication directing molecule, was identified as a promising avenue for silica shell fabrication. In addition, a novel facile method of silica particle synthesis (NaOH-silica synthesis), requiring only two reactants, trimethoxymethylsilane (TMOMS) and sodium hydroxide (NaOH), was developed and characterised in this work. Functionalisation of the silica shell material is vital to achieve selective adsorption. The PEI-directed silication method, focused on in this work, introduces intrinsic amine (for PEI-silica) and amine/thiol functionalisations (for PEI-thiol silica) with the silane reactants, TMOMS and 3-mercaptopropyltrimethoxysilane (3mPTMOS), respectively. Control of the surface charge of NaOH-silica particles was achieved via the rapid electrostatic adsorption and acidic desorption of the PEI. In addition, a technique for the more permanent, covalent surface modification of the PEI-thiol silica particles utilised the thiol surface groups to covalently attach various surface modifiers to the particle surface. Successful surface modification was confirmed by Fourier transfer infrared (FTIR) spectroscopy and zeta potential measurements. The results from these studies convey rapid, reliable techniques for reversible and irreversible silica surface functionalisation. PEI-silica particle synthesis was adapted for coating micron-sized magnetic carbonyl iron cores, to develop the magnetic core-shell carrier particles. The PEI-silica coated carbonyl iron particles were characterized via scanning electron microscopy (SEM), energy dispersive x-ray (EDX) spectroscopy and FTIR spectroscopy. Varying the fabrication method and silane concentration successfully tuned the shell characteristics. Methods using sonication produced smooth, more evenly distributed coatings with a tendency towards multicore particles. In contrast, raspberry-like coatings were produced via slow reactant addition, one- and two-pot methods. The PEI-silica coating methodology was scaled up by factors of 10 and 50 to investigate the effect of increased reaction size on the core-shell particles produced. The scaled reactions were found to retain similar morphological features and core coverage to the small reaction size. Moreover, thiol/amine functionalised raspberry-like and smooth coatings were produced by applying the coating methods for PEI-thiol silica shell synthesis. Utilising the PEI-silica shell - magnetic core particles as magnetic carrier particles, the adsorption at pH 6.0 and magnetic recovery of the heavy metal ion, Cu (II), was demonstrated using UV-visible spectroscopy and SEM/EDX. To determine the viability of recycling the core-shell magnetic carrier particles, acid desorption in 1 mM HCl and re-adsorption of Cu(II) was also demonstrated. The raspberry-like PEI-silica shell morphology exhibited superior performance overall, when compared with smooth shell morphology, achieving a maximum adsorption capacity of 160 ± 10 mg Cu(II) per g coreshell particles. For both PEI-silica coating morphologies, Cu(II) adsorption showed good agreement with both the Langmuir and Freundlich adsorption models. The use of the PEI-silica shell – magnetic core carrier particles for fine particle magnetic separation was demonstrated in this study using SEM/EDX for characterisation. A large range of different target materials were investigated including fine clays (talc, montmorillonite and kaolin) and metal/metalloid oxides (quartz and TiO2). Control over the incubation pH was observed as paramount to the successful adsorption and subsequent magnetic separation of the target fine particles. Desorption was achieved via vigorous mixing and incubation in 3.00 mM NaOH, demonstrating the potential for carrier particle reusability. PEI-thiol silica and PEI-silica coated carbonyl iron carrier particles were also used for the successful adsorption and magnetic separation of Au nanoparticles (diameter 10 ± 2 nm). The PEI-thiol silica coated particles proved slightly more effective than the PEI-silica coated particles, due to their dual amine/thiol surface functionalisation. In conclusion, this thesis project pioneered the development of a biomimetic silica shell fabrication method for the production of functionalised magnetic core-shell carrier particles with proven applicability in the removal of heavy metal ion and fine particle species from solution.
- Subject
- core-shell particles; magnetic separation; biomimetic silica synthesis; polyethylenimine; heavy metal ion removal; fine mineral particle separation; surface modification; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1386320
- Identifier
- uon:32393
- Rights
- Copyright 2018 Emily Dawn Elizabeth Rodd Hyde
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 197 KB | Adobe Acrobat PDF | View Details Download |