Mark MacLachlan


Research Interests

Supramolecular Chemistry
Cellulose nanocrystals
Materials Chemistry
Inorganic Chemistry

Relevant Thesis-Based Degree Programs

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I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.
I am interested in working with undergraduate students on research projects.

Research Methodology

Electron Microscopy
Gas sorption
NMR spectroscopy


Postdoctoral Fellows
Any time / year round
I support experiential learning experiences, such as internships and work placements, for my graduate students and Postdocs.
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Investigating gel properties of amino acid-based multicomponent low molecular weight gelators (2023)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Salphen and hemi-salphen macrocycles for host-guest chemistry and other supramolecular applications (2022)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Self-assembled materials based on cellulose nanocrystals and graphene oxide (2022)

Cellulose nanocrystals (CNCs) and graphene oxide (GO) can self-assemble into chiral nematic and lamellar (or nematic) liquid crystals, respectively; this offers an opportunity to introduce large-scale ordered structures into different assembled systems. This thesis focused on the introduction of chiral nematic and lamellar structure into aerogels, films, hydrogel microbeads, and suspensions. The self-assembly behavior of GO in confined geometry and in the presence of additives was also studied. Chiral nematic aerogels were developed. Through a solvent-exchanged method and silica condensation reaction, the chiral nematic liquid crystalline structure of CNCs was captured to produce CNC and CNC-silica alcogels. Both the chiral nematic CNC and CNC-silica aerogels were obtained after supercritical drying of their alcohol gels, and subsequent calcination of CNC-silica aerogels afforded silica aerogels with chiral nematic structure.To improve the mechanical performance and optical stability of chiral nematic CNC materials in water, CNCs were combined with epoxy resins to make composites with hydrogen-bonded/covalent dual networks. These composites not only displayed tunable chiral photonic properties, but also the ability to adapt their stiffness and toughness upon exposure to water. The changeable mechanical properties are related to the on/off switch of inter-CNC interactions.The self-assembly behavior of GO in spherical space was investigated. The arrangement of GO nanosheets was captured by inverse emulsion photopolymerization to form hydrogel microspheres. GO nanosheets in spherical confined space can form a concentric or pseudo-concentric structure.The effect of additives on iridescent GO photonic liquids was investigated. Colloidal additives added to GO suspensions led to dramatic color changes. On the other hand, blending polymeric or molecular additives with GO suspensions either deteriorated or did not impact the photonic properties. The phenomenon from hybrid colloidal photonic suspensions was explained by the depletion interaction between particles.Stable GO hydrophobic photonic liquids were developed. GO were directed into different hydrophobic organic solvents using phase transfer additives. The obtained GO liquids exhibit tunable reflection colors with improved stability relative to aqueous GO photonic suspensions at elevated temperatures or under ambient conditions. Furthermore, simultaneous infrared and visible light reflection can be achieved, enabling infrared photonic GO liquids to display visible colors.

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Functional materials from cellulose nanocrystals (2021)

The synthesis, characterization, and application of several materials with long range hierarchical ordering derived from cellulose nanocrystals (CNCs) is reported. CNCs are an interesting nanomaterial to work with owing to their chiral nematic liquid crystalline behaviour that is observed above a critical concentration. This property makes CNCs attractive for materials development as they can be used to direct the organization of other materials introducing long range order into substrates that do not traditionally possess order. Importantly, CNCs are an inexpensive, renewable, and biodegradable resource that can be exploited in the development of new nanomaterials. Although CNCs have impressive mechanical properties, they form intrinsically brittle materials. To address this, composites of CNCs and hydroxypropyl cellulose (HPC) were prepared. The inclusion of HPC enabled the modulation of mechanical and optical properties with increasing polymer content and molecular weight. Surface functionalization of the materials increased their hydrophobicity, addressing a common problem that limits the application of such composite materials. This work serves to deepen our understanding of molecular additives on CNC self assembly as well as demonstrates how CNC films can be modified for more practical applications such as in coatings and packaging.Extending beyond this, chiral nematic mesoporous silica (CNMS) – formed from CNCs – was used to form a variety of CNMS metal composite materials (metal = CuO, Cu, ZnO, Au, Ag, Ag/Cu). Selective removal of the silica afforded materials with a variety of nanostructures. Focusing on the materials which retained long range order, I demonstrated they could be used as catalysts. This work highlights of promise for ordered metal materials for high surface area applications such as in catalysis or separation. The development of CNC based aerogel materials for energy storage applications was also explored. CNCs provide a suitable scaffold to direct the assembly of metal precursors, and when incorporated into aerogels provides a lightweight, high surface area substrate that is a promising candidate for inclusion in supercapacitors. Chiral nematic CNC/germania and carbon/germania composites were prepared and when used as the electrodes in both symmetric and solid state symmetric supercapacitors showed good capacitance and cycling stability. This exciting discovery further cements the benefit of using renewable materials in high value applications.

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Thermal behaviour of cellulose materials (2021)

Studying the high-temperature treatments of biomass-derived materials is essential to understand their thermal decomposition and characterize useful carbonized products in a frame of environmental sustainability. The goal of this thesis is the mechanistic understanding of thermal degradation (150-800 °C) in oxidizing and inert atmospheres of two types of cellulose materials, also identifying applications for the product.Cellulose filaments (CFs) are microfibril bundles and heterogeneous fibrillar mass extracted through mechanical refinement. Cellulose nanocrystals (CNCs) are produced through dissolution of amorphous regions and may contain sulfate (S-CNC) or carboxylate (C-CNC) surface groups, depending on the preparation conditions. Acid groups of as-prepared CNCs can be neutralized with alkali counterions. CNC suspensions can be freeze-dried or air-dried forming birefringent aerogels and iridescent chiral nematic films, respectively.The kinetics and thermochemistry of thermal degradation of cellulose materials, as well as their morphological and chiroptical modifications, were studied by several techniques, including thermogravimetric analysis, solid-state NMR spectroscopy, and scanning electron microscopy. From these and other techniques, it was deduced that CFs have a simple degradation mechanism, and the highest stability among the materials studied (325 °C), despite abundant amorphous regions and inhomogeneous fibrous mass. When fully gasified, CFs emit a large fraction of alcohol-based gases, including biofuels. CNC-H aerogels decompose in complex ways below 200 °C, with abundant char and sulfur evaporation at high temperatures. Sodium counterions in S-CNC-Na aerogels improve the stability up to 300 °C, where partial surface rehydration and formation of sodium hydroxide occur, while carbonization yields highly condensed structures. In their air-dried form, the thermal stability of S-CNC films can be improved with larger alkali counterions and the cholesteric structure is maintained even after prolonged thermal treatment, advantageous for potential applications as temperature sensors.In contrast to S-CNC, C-CNC aerogels are more thermally stable in acid form. Here, the presence of sodium often accelerates the degradation by decomposition into sodium carbonate. Higher carboxylate content and specific surface area were found to shift C-CNC degradation towards lower temperatures, as well as catalyzing decarboxylation in acid form. The results of this thesis will inform the development of novel cellulose materials with high thermal stability.

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Understanding the self-assembly process of cellulose nanocrystals: towards chiral photonic materials (2021)

Over millions of years, animals and plants have evolved complex molecules, macromolecules, and structures that endow them with vibrant colors. Among the sources of natural coloration, structural color arises from the interaction of light with nanoscale features rather than absorption from a pigment. Cellulose nanocrystals (CNCs) are materials derived from biorenewable resources that form a chiral nematic liquid crystal phase in water. Interestingly, the chiral nematic structures are maintained in solid films of CNCs obtained by drying the liquid crystalline phase. The self-assembly process of CNC building blocks is a complex topic that is not entirely understood; thus, further investigation of the self-assembly process will be crucial in developing tunable and colorful films. CNC films were prepared and the self-assembly process was investigated by varying the evaporation times for a drying CNC suspension. CNC films with reflected colors spanning the visible range were prepared by controlling the evaporation time, with the most blue-shifted reflection emerging from films formed with the slowest evaporation rates. An intermediate stage of self-assembly occurring before kinetic arrest helps explain the discrepancies in chiral nematic order of films prepared at different evaporation times. Local restriction of evaporation resulted in a patterned film with tunable optical properties. These thin film materials, although brittle, represent a system with localized control of the chiral nematic structures. The development of mechanically responsive photonic materials based on CNCs was made possible with the incorporation of elastomers. Elastomers containing a chiral nematic arrangement of CNCs inside were prepared and the resulting material showed reversible visible color upon mechanical stimulation. This material exhibits colors spanning the visible spectrum depending on the amount of stretching. CNCs are an exciting building block that can be applied to sustainable material development. To develop unique photonic materials for different applications, the intricacies of the self-assembly process must be further investigated. Specifically, the aim of this thesis is to study the chiral nematic organization of CNCs, starting from a suspension into a solid and colorful material. Photonic materials based on CNCs are attractive for applications in sensing and privacy but could also serve in decorations and coatings.

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Synthesis of nanostructured catalysts for low temperature methane combustion (2020)

The number of natural gas vehicles (NGVs) is increasing rapidly due to the growing concern for the environmental impact of gasoline and diesel-powered automobiles. However, the main component of natural gas, methane, is a potent greenhouse gas. Thus, removal of unburned methane from the exhaust of NGVs is important and this requires catalysts for methane oxidation at low temperature (less than 500-550 °C). In this thesis, different types of nanostructured catalysts were developed. Noble metal catalysts, like Pd-based catalysts, and non-precious metal catalysts, such as spinel catalysts, were synthesized, characterized and examined for catalytic methane combustion. To enhance the catalytic activity, NiCo₂O₄ catalysts with a unique bowtie-structure were synthesized. The morphology, growth mechanism, catalytic and kinetic performance were explored. These NiCo₂O₄ catalysts exhibited excellent activity for methane oxidation, but were unable to maintain their performance in the presence of water vapor.In addition, active site distribution plays an important role on catalytic activity. Taking this into account, MnO₂ aerogels supporting precious or non-precious metal oxide catalysts were explored. Both types of catalysts showed enhanced catalytic activity. The hydrothermal stability and sulfur tolerance were studied for PdO/MnO₂, and the deactivation mechanism was explored. Besides outstanding activity, commercial catalysts must be stable in practical usage. In order to improve the stability of Pd-based catalysts, nanostructured materials were prepared by embedding Pd into CeO₂ inside the channels of a mesoporous host, SBA-15. It was found that the materials showed excellent catalytic activity and improved activity after hydrothermal treatment. However, their performance in the presence of water vapor still needs to be enhanced.Furthermore, to solve the problem of poor water stability and sulfur tolerance, CoCr₂O₄ composites were selected as catalysts. Nanospheres of CoCr₂O₄ were prepared by a straightforward solvothermal method. These materials achieved 100% methane conversion below 500 °C and they also displayed excellent stability even in the presence of 10% water vapor and 5 ppm SO₂. Furthermore, the CoCr₂O₄ catalysts were scaled up and coated onto cordierite monoliths via a modified wash-coating method. The coated monolith showed excellent activity and stability, and these materials have potential to be applied for NGVs.

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Gelation of cellulose nanocrystals (2019)

Colloidal gels of cellulose nanocrystals (CNCs) were prepared using three different strategies by manipulating their colloidal stability. In the first approach, colloidal gels were prepared by hydrothermally treating CNC suspensions. Desulfation of the CNCs at high temperature appears to be responsible for the gelation of the CNCs, giving highly porous networks.In the second approach, a carbon dioxide-switchable (CO₂-switchable) hydrogel was prepared by adding imidazole to a suspension of CNCs. Sparging of CO₂ through the imidazole-containing CNC suspension led to gelation of the CNCs, which could be reversed by subsequent sparging with nitrogen gas (N₂) to form a low-viscosity CNC suspension. The gelation process and the properties of the hydrogels were investigated by rheology, zeta potential, pH, and conductivity measurements, and the gels were found to have tunable mechanical properties. This work describes a straightforward way to obtain switchable CNC hydrogels without the need to functionalize CNCs or add strong acids or bases. These CO₂-responsive CNC hydrogels have potential applications in stimuli-responsive adsorbents, filters, and flocculants.Lastly, physical colloidal gels were prepared by freeze-thaw (FT) cycling of CNC suspensions. The aggregation of CNCs was driven by the physical confinement of CNCs between growing ice crystal domains. FT cycling was employed to form larger aggregates of CNCs without changing the surface chemistry or ionic strength of the suspensions. Gelation of CNC suspensions by FT cycling was demonstrated in water and other polar solvents. The mechanical and structural properties of the gels were investigated using rheometry, electron microscopy, X-ray diffraction and dynamic light scattering. It was found that the rheology could be tuned by varying the freezing time, the number of FT cycles, and concentration of CNCs in suspension.Considering the wide natural abundance and biocompatibility of CNCs, these approaches to CNC-based hydrogels are attractive for producing materials that can be used in drug delivery, insulating materials, and as tissue scaffolds.

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Supramolecular chemistry of palladium and platinum-containing macrocycles: from ring-expansion to host-guest complexes (2019)

Two main projects are presented in this thesis. In the first project we used ligand exchange to influence the reactivity of an unstrained palladium-containing metallomacrocycle toward ring-opening metathesis polymerization (ROMP) reaction. The ligand-exchange rate on the palladium center between acetonitrile and six different ligands was investigated for an NNN pincer bis(amido)pyridine metallomacrocycle and compared with its corresponding open form. Kinetic studies showed that the small size of the macrocycle cavity impedes ligand exchange. We then used a bulky ligand (2,6-lutidine) to provide steric hindrance, blocking ring-closing and favouring ROMP of the NNN pincer bis(amido)pyridine metallomacrocycle. The second project involves the synthesis and characterization of several Pt²⁺, Pt³⁺, and Pt⁴⁺ phenylpyridine complexes. We first used a bidentate functionalized phenylpyridine ligand, then two flexible tetradentate ligands featuring an ethylene glycol chain, and finally two preorganized tetradentate ligands, one of which contained a full crown ether functionality. The presence of the crown ether functionality makes these compounds attractive for host-guest chemistry applications. The synthetic challenges related to obtaining biscyclometalated platinum monomeric complexes with phenylpyridine-containing ligands were addressed by using different approaches: high dilution, cation coordination, and ligand preorganization. Some of the complexes prepared appear to be promising for cation recognition and for the formation of supramolecular assemblies such as rotaxanes and pseudorotaxanes.

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Chiral nematic mesoporous organosilica materials templated with cellulose nanocrystals (2018)

The synthesis and characterization of new mesoporous organosilica materials with twisted porous networks and defined nanostructures was explored. Spindle-shaped cellulose nanocrystals (CNCs) with nanoscale dimensions can be isolated through the acid-catalyzed hydrolysis of wood pulp. These CNCs behave as chiral nematic lyotropic liquid crystals and are advantageous for the soft-templating of mesoporous materials as they can produce helically arranged pores. As such, CNCs show promise as inexpensive and renewable precursors for the development of nanomaterials.In this thesis, CNCs were used to template chiral nematic mesoporous organosilica (CNMO) materials through the co-condensation of bridged alkoxysilanes, R(Si(OR′)₃)₂, with aqueous CNC suspensions. Removal of the CNCs produced free-standing organosilica films that have interconnected pore structures and long-range chiral order imparted by the CNC template. Organic functionality was introduced as an integral component of the organosilica structure by varying the alkoxysilane precursors. The syntheses of alkylene-bridged (C₁-C₆), aromatic-bridged, ethenylene-bridged, and sulfur-containing CNMO films are reported. It was determined that phase separation between the alkoxysilanes and CNC suspension could be minimized by using mixed solvent systems of water and DMF during self-assembly. The new CNMO films display tunable photonic properties resulting from the repeating helical structure as well as thermal stabilities and pore connectivity that depend on the organic linker used. The combination of chirality and mesoporosity in these organosilica films suggests applications in hard templating, chiral catalysis, and sensing. CNMO films were investigated as support materials by functionalizing them with spiropyran molecules for sensing or manganese salphen complexes for catalysis. Spiropyran-bound CNMO films were used for photopatterning and behaved as reversible divalent metals sensors. Heterogeneous manganese salphen/CNMO films displayed similar catalytic conversion to the homogeneous catalyst, however, a small enantiomeric excess (5%) was observed suggesting that the chiral environment of the films may affect catalysis. Finally, metal ferrites [MFe₂O₄ (M = Ni, Cu, Zn, Co)] with chiral nematic nanostructures were prepared through hard templating with chiral nematic mesoporous silica. These materials beautifully replicated the three-dimensional structure of the CNCs liquid crystalline phase and their crystallinity and pore sizes were controlled by altering the calcination temperatures.

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Liquid crystalline tactoids in microscopic ordered-disordered interfaces: emergence of self-assembly and topological defects (2018)

Liquid crystalline tactoids are discrete anisotropic microdroplets coexisting with continuous disordered phases. In this thesis, an in-situ photopolymerization method was designed to rapidly capture and solidify liquid crystalline tactoids in a crosslinked polymer matrix, which facilitated the direct observation of these fluid ordered microdroplets by scanning electron microscopy with the resolution of individual liquid crystal mesogens. Different stages of the evolution of tactoids were captured and examined, where the emergence of small-sized tactoids in initially disordered phases, the coalescence of multiple tactoids, the generation of topological defects in coalescence, and the sedimentation of tactoids were directly observed by electron microscopy.The in-situ photopolymerization method was then extended to inverse emulsions, where the structure and evolution of chiral nematic liquid crystalline tactoids in geometrical confinement of microspheres were investigated by both optical and electron microscopy. This study revealed the microstructures of topological defects of frustrated chiral nematic order in spherical confinement. Moreover, polymer and mesoporous silica microspheres with helical structures were obtained.The behavior of tactoids in the presence of colloidal doping nanoparticles was examined by electron microscopy at the resolution of individual particles, which showed that liquid crystalline tactoids have size-selective exclusion effects on foreign nanoparticles. This principle was applied to the separation of polymer nanospheres, gold nanoparticles, and paramagnetic nanoparticles by size. These results suggest an approach to size-selectively separate nanoparticles using lyotropic liquid crystals, where nanoparticles smaller than a threshold size will be selectively collected into the liquid crystalline tactoids and thus transferred from the disordered phase to the ordered phase during phase separation.The phase separation of liquid crystals in the presence of paramagnetic doping nanoparticles and gradient magnetic fields was studied. In this case, the disordered phases have higher volume magnetic susceptibility than liquid crystalline tactoids due to the exclusion effects of tactoids on paramagnetic nanoparticles. Thus, the movement and orientation of tactoids could be controlled by gradient magnetic fields as weak as several hundred Gauss/cm. This approach enables control of the phase separation rate and configuration, as well as the orientation of director fields in both discrete tactoids and continuous macroscopic ordered phases.

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Novel structures and unusual reactivity powered by tautomerism and electron delocalization in salicylimines (2017)

A family of tris(salicylaldimine) (TSAN) analogues was prepared by condensation of 2,4,6-triformylphloroglucinol (TFP) and various nitrogen-containing bases. Characterization of these compounds by ¹H NMR spectroscopy and single-crystal X-ray diffraction (SCXRD) revealed that some of them adopt the previously unknown enol-imine tautomeric form. Experimental data and ab initio modelling were used to establish which factors govern the keto-enamine/enol-imine tautomeric equilibrium, culminating in a simple structural model of TSAN behaviour. According to this model, π electron-withdrawing X groups in the NH₂X starting material stabilize the keto-enamine tautomeric form, whereas σ electron withdrawing X, e.g. electronegative heteroatoms, lead to the enol-imine form.The same tautomeric equilibrium has also been leveraged in a family of hydroxysalicylaldehyde Schiff bases to bring about facile exchange of specific aromatic CH hydrogen atoms when these compounds are dissolved in CD₃OD or D₂O under ambient conditions. The mechanism of this surprising isotopic exchange reaction has been investigated experimentally using ¹H NMR kinetic experiments on these Schiff bases and a number of control compounds as well as ab initio modelling. Both sources point to the involvement of the minor keto-enamine tautomeric form of the salicylimines, which facilitates electrophilic aromatic substitution of hydrogen with deuterium by stabilizing the sp³-hybridized Wheland intermediate formed in the course of the reaction.The impact of the keto-enamine tautomeric form on the electronic structure of TSANs has been studied in isolation by preparing a TSAN permanently “locked” in keto-enamine connectivity. This was achieved by replacing the labile proton present in regular TSANs with a non-labile methyl group. The resulting compound assumes the expected keto-enamine structure; however, a large degree of strain is introduced since coplanarity of the peripheral enamine arms with the central ring, required for electronic coupling between the two, results in steric repulsion between the methyl groups and the carbonyl oxygen atoms. The central ring of the product is consequently highly contorted.The unsatisfactory preparation of many of the salicylaldehyde precursors to the SANs above has been improved through a mild and efficient procedure using formamidine acetate and acetic anhydride. This method allows one to install up to three formyl group on various phenolic substrates without the harsh conditions encountered with common formylation techniques such as the Vilsmeier–Haack reaction.

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The disparate symmetries in head-to-tail Schiff-base macrocycles (2017)

Two new Schiff-base macrocycles (called campestarenes) with 5-fold symmetry were prepared with bulky triphenylsilyl and triisopropylsilyl substituents. A single crystal structure of one campestarene showed an almost flat conformation of campestarenes are in their extreme enol-imine form. Tautomerization within the campestarene between the enol-imine and keto-enamine form was investigated by variable-temperature NMR and UV-vis spectroscopy. It was found that the molecule displays strong solvent- and temperature-dependent tautomerization that leads to large changes in color. These results were supported by computational investigations that showed the possibility of tautomerization between keto-enamine form and enol-imine form. The experimental studies showed the relative permittivity of solvents has a large influence on the relative stability of different campestarene tautomers in solution.Some methyl/phenyl substituted campestarene precursors were prepared for macrocyclization of methyl/phenyl substituted campestarenes. Different synthetic conditions were tested to facilitate the formation of campestarens. One phenyl substituted campestarene was synthesized under acid condition.Two new Pt₃ Schiff-base macrocycles with 3-fold symmetry were synthesized following a head-to-tail approach. Computational investigations showed an almost flat conformation of Pt₃ macrocycles. Aggregation of Pt₃ macrocycles in solid state was studied by MALDI-TOF, TEM and PXRD. It was found that Pt₃ macrocycles displays nanotubular structures due to aggregation. Aggregation of Pt₃ macrocycles in solution was investigated by variable-temperature 1D NMR and 2D NMR. The experimental results showed aggregation of Pt3 macrocycles at both high and low temperatures.

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Design and Synthesis of New Ceria-Based Materials for Low-Temperature Methane Oxidation (2016)

The main goal of this research is the development of new mesoporous materials for low-temperature methane oxidation that could be used in catalytic convertors of natural gas powered vehicles. Natural gas is a more environmentally friendly fuel than gasoline or diesel and is seen as a stepping-stone to renewable energy sources.The synthesis and characterization of novel ceria-based materials is reported. Modification of synthetic routes reported in the literature produced several new doped and undoped ceria samples, which were tested for catalytic activity for low-temperature methane oxidation. These tests showed that the presence of a second, redox active metal oxide results in materials with higher catalytic activity than those with only ceria. In addition, several new routes to ceria-based materials with various morphologies, including nanorods and hollow, mesoporous nanospheres, were developed. The nanospheres were successfully doped with lanthanum, giving rise to the first non-hydrothermal route to hollow, mesoporous nanospheres of both doped and undoped ceria.Further examination of materials containing two redox active metal oxides generated mesoporous cobalt oxide with doped and undoped ceria in the pores. Cobalt oxide was templated with KIT-6 silica to produce a material with highly ordered mesopores. The ceria/cobalt oxide materials have remarkably high activity for low-temperature methane oxidation given that they contain no noble metals. However, surprisingly, the mesoporous cobalt oxide on its own exhibited the highest catalytic activity with 50% complete methane conversion to carbon dioxide and water below 400 ˚C.Cerium-based precursors were also used as a starting material to synthesize Pd/ceria materials via a new method termed surface-assisted reduction. Surface-assisted reduction produces ceria with PdO highly dispersed on the surface. These materials showed exceptionally high activity for methane oxidation, with the best materials exhibiting 50% methane conversion below 300 ˚C. Exploration of the scope of surface-assisted reduction successfully produced ceria materials with gold or silver deposited on their surface.

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Synthesis of metal-organic frameworks from structure-directing iptycenyl ligands (2014)

Metal-organic frameworks (MOFs) are of great interest as hydrogen storage materials for use in vehicles. A series of triptycene-containing and pentiptycene-containing organic ligands was synthesized, characterized and used for MOF formation. A total of five unique triptycene-containing MOFs (TMOFs) and three pentiptycene-containing MOFs (PMOFs) were synthesized and examined using X-ray diffraction studies. Although the structure of each MOF was unique, structural adaptions to incorporate the rigid, bulky, structure-directing ligand into the framework were observed. For example, in some cases extended pseudo-[Zn₄O]⁶⁺ secondary building units (SBUs) were present in order to distort the framework to allow the ligand to coordinate. Reaction conditions also proved to be important in determining the dimensionality of MOF. It was shown that slight modifications of the reaction conditions using the same organic ligand could produce a 1-D, 2-D, and 3-D framework with different SBUs. The use of a ditopic bridging ligand, such as 4,4´-bipyridine, can also be used to increase the dimensionality of a structure. This protocol was used in converting 1-D chain structures and 2-D sheet structures into 2-D sheet structures and 3-D pillared structures, respectively. The overall functional groups in the ligand backbone can also have an adverse effect in the MOF structure. It was found that flexible linkages often led to collapse of the framework structure, whereas rigid linkages led to more robust structures. Extension along the carboxylate axis was also found to be important for iptycene incorporation. Unfortunately such extensions often led to close-packed or interpenetrated systems, which diminished porosity in the framework. Lastly, the long-range ordering of a MOF structure was predicted using modelling of powder X-ray diffraction (PXRD) peaks. When no single-crystal data were obtained, the PXRD data could suggest whether a material had a hexagonal structure or cubic structure. In all cases thermal stability studies were carried out and it was found that these TMOF and PMOF materials were thermally stable up to 400 °C. These iptycene-containing materials had been highlighted as potential hydrogen storage materials due to the potential for high aromatic surface areas and well-defined pore structure. As a result, nitrogen adsorption experiments were conducted on several of the robust frameworks to assess surface area. In each case, low surface areas were found.

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Chiral nematic mesoporous materials templated by nanocrystalline cellulose (2012)

The synthesis, characterization, and application of the first examples of chiralnematic mesoporous materials are reported. Nanocrystalline cellulose (NCC) was used asa liquid crystal template to generate NCC/silica composite films through evaporationinduced self-assembly. The NCC was removed from the composite films by calcinationto generate mesoporous silica films with high specific surface areas and chiral nematicstructures. The chiral nematic ordering in these films gives rise to photonic properties thatcan be tuned depending on the synthetic conditions. Thus mesoporous silica films withcolours spanning the visible spectrum were synthesized. The combination ofmesoporosity and chiral nematic ordering in these materials causes them to change colourin response to liquids and show strong circular dichroism signals that depend on therefractive index within the mesopores. Chiral nematic mesoporous silica can also be usedas a hard template to generate nanocrystalline films of anatase titanium dioxide. Thetitanium dioxide replicas are mesoporous and show chiral nematic ordering and photonicproperties that mimic the original silica films.By exploring different methods to remove NCC from the composite films, theprocedure used to synthesize chiral nematic mesoporous silica films was expanded toorganosilica. The resulting chiral nematic mesoporous organosilica films show similarproperties to the mesoporous silica films but have superior flexibility in some cases.Methods to control the pore size of the mesoporous silica and organosilica materials weredeveloped.Nanocrystalline cellulose/silica composite films were also used as a starting pointto synthesize chiral nematic mesoporous carbon films. This was achieved by pyrolyzingNCC/silica composite films followed by dissolving the silica in strong base. The silica used in this procedure was shown to be necessary for both the retention of chiral nematicordering and the introduction of mesoporosity into the carbonaceous material. Finally,chiral nematic mesoporous carbon (CNMC) was shown to be a promising material as asupercapacitor electrode material both on its own and as a composite with polyaniline.

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Assembly of Prussian Blue Analogue Nanomaterials (2011)

Coordination polymers have many attractive properties but the development of applications has been hampered by the challenges associated with their processing and the preparation of nanosized analogues. In this thesis, the synthesis and characterization of new coordination polymer nanomaterials with previously inaccessible morphologies and compositions are reported. Prussian blue analogues (PBAs) were investigated as model compounds.Mesostructured PBAs were fabricated via a ligand-assisted liquid-crystal templating approach. Molecular surfactants having a charged iron cyanide complex as hydrophilic head group and metal-coordinated hydrophobic tails were synthesized. In formamide, the metal-containing template formed liquid-crystalline phases that were crosslinked into PBA mesostructures with the addition of transition metals. PBAs with well-ordered lamellar, hexagonal and cubic structures were obtained with a wide range of compositions. The materials made of iron(II) and iron(III) exhibited mixed-valency and ferromagnetic interactions in the PBA framework.A synthetic approach to attach a PBA precursor onto polymer-based structure-directing agents was developed. A preformed macromolecular backbone was functionalized with ionic pendent groups that can coordinate iron cyanide complexes. Metal-containing homopolymers and block copolymers were synthesized. In organic solvents, the ionic block copolymers behaved as a block ionomer and self-assembled into stable wormlike and toroidal reverse micelles whose cores were metallated with the iron cyanide complex or used as an ion confinement region for different cyanometallate compounds to be crosslinked into PBA-type frameworks. The soluble PBA nanomaterials are stable in solution, assemble into arrays on surfaces and were used as precursors for metal oxide nanostructures.Soluble hollow polymer capsules with PBA inner-shells were fabricated via emulsion-induced assembly of the iron cyanide block ionomer. The metal-containing amphiphilic macromolecules stabilized nanosized water droplets dispersed in organic solvent by assembling at the water-oil interface. The hydrophilic iron cyanide inner-shells were crosslinked into PBAs with zinc ions. The hollow capsules have selective permeability, are tunable in size, organize into hexagonal arrays in the solid state and were used as nanocontainers to encapsulate molecular compounds.A rigid structure-directing ligand was incorporated into the network of a PBA under solvothermal conditions to engineer the connectivity of a coordination polymer. A crystalline triptycene-scaffolded copper PBA was obtained.

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Construction of nanofibers from supramolecular self-assembly of Schiff-base macrocycles and metal salphen complexes (2010)

The work described in this thesis mainly covers the investigations of a series of conjugated Schiff-base macrocycles and metal salphen complexes. These compounds self-assemble into supramolecular structures through electrostatic or metal-ligand interactions, and their morphologies were studied by electron microscopy and atomic force microscopy. The Schiff-base macrocycles can bind alkali metal and ammonium cations into their crown-ether interior, leading to the formation of one-dimensional columns that can further organize into nanofibers with hierarchical organization. However, when macrocycles appended with long alkoxy chains were treated with the same conditions, lyotropic liquid crystallinity in organic solvents was observed under a polarized optical microscope. Among the metallosalphen complexes prepared, zinc(II)-containing salphen complexes were found to assemble into helical fibrous structures and exhibit gelation behavior in various solvents. Furthermore, modification of the peripheral substituents of the zinc(II) salphen complexes with carbohydrates further enhanced the helicity in the nanofibers. In addition, the surface texture and diameter of the nanofibers can be altered by the presence of ditopic 4,4′-bipyridine and the increase in hydrophobic effects during sample preparation.

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Studies of supramolecular chemistry through Schiff-base chemistry (2010)

This thesis describes the synthesis, characterization, and host-guest studies of a series of Schiff-base macrocycles. New [2+2] Schiff-base macrocycles were prepared by Schiff-base condensation. These macrocycles were shown to be wide-mouthed supramolecular hosts that can include organic cations such as pyridinium, paraquat and ammonium derivatives. A new kind of donor-acceptor-donor 3-in-1 complex was obtained in solution by combining macrocycle, cyclobis(paraquat-p-phenylene) and tetrathiafulvalene. Variations of these [2+2] Schiff-base macrocycles were prepared by modifying the substituents of the diformyl diol unit. In this way naphthalene-based macrocycles that undergo keto-enamine tautomerization were synthesized. These macrocycles can also combine with organic cations to form host-guest complex. The naphthalene-based [2+2] macrocycles can form lyotropic liquid crystals in chloroform and 1,2-dichloroethane. From the polarizing optical microscopy, it is proposed that the mesophases are lyotropic nematic liquid crystals based on a bilayer structure. A further study of these macrocycles shows that the host-guest complex can also form a lyotropic liquid crystalline phase.Covalently-linked macrocycles with isosceles triangle shapes were prepared by Schiff-base condensation. The molecular isosceles triangles proved to also be supramolecular hosts for pyridinium and ammonium cations, based on ¹H NMR, 2D-ROESY NMR, and mass spectrometry studies. In addition to the Schiff-base macrocycles, conjugated Schiff-base containing oligomers were synthesized via Gilch polymerization methods. The oligomers were characterized by gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and UV-Vis spectroscopy. For further proof of the oligomeric structure, a model compound was prepared by the Wittig reaction.

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Supramolecular schiff base coordination chemistry : blueprints for self-assembling metallocavitands and nanotubes (2010)

Heptametallic zinc(II) and cadmium(II) clusters have been isolated after reactingthe metal-acetate salts with large diameter [3+3] Schiff base macrocycles. Two tetrazinccomplexes have been characterized and identified as intermediates in the formation of theheptazinc complexes. The heptametallic complexes are, in fact, templated by the Schiffbase macrocycles, a process that has been investigated with ¹H NMR spectroscopy andsingle-crystal X-ray diffraction. In the solid-state the heptametallic complexes have abowl-shaped geometry, reminiscent of organic cavitands, leading to them being calledmetallocavitands. Solid-state investigation of the heptazinc and heptacadmiummetallocavitands showed they organize into capsules with a cavity volume of 150 and215 ų, respectively. Solution dimerization was also observed in aromatic solvents andN,N-dimethylformamide (DMF). The thermodynamics of dimerization have beenquantified by van’t Hoff analyses of association constants measured with variabletemperature,variable-concentration ¹H NMR spectroscopy. Both metallocavitandsexhibit entropy-driven dimerization in all solvents in which dimerization occurs. Unusualfor dimerization of cavitands, this entropy-driven process can be attributed to theexpulsion of solvent from the monomeric cavity upon dimerization.Inside the cavity of heptacadmium metallocavitands is a μ₃-OH ligand where theproton is located at the base of the cavity and is capable of hydrogen bonding with guestmolecules. The μ₃-OH proton resonance is observable in low temperature 1H NMRspectra and exhibits two-bond J-coupling with three cadmium ions. Within capsules ofthe heptacadmium metallocavitands there are eight Lewis-acidic sites accessible to guestmolecules, six unsaturated cadmium(II) centers and two μ₃-OH ligands. Solid-stateanalysis shows that two DMF molecules are encapsulated in the heptacadmium capsulewhere they each simultaneously exhibit a host-guest hydrogen-bond and a dative metalligandinteraction.New methodology has been developed that facilitates synthesis of polydentate[2+2] Schiff base macrocycles with unsymmetrical salphen pockets. Also a [3+3]macrocycle with triptycenyl substituents has been synthesized to prohibit alkali-metalinduced solution aggregation.The one-pot twelve component head-to-tail self-assembly of Pt₄ rings directed bychelating imine-pyridyl donors has been demonstrated. These supramolecules exhibitextensive columnar organization in both solution and the solid-state, a phenomenon thatimparts liquid crystalline properties on the macrocycles.

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Conjugated schiff base-type metal-containing polymers (2008)

The work in this thesis describes the synthesis and characterization of a series ofconjugated polymers containing Schiff base transition metal complexes. High molecular weight poly(salphenyleneethynylene)s (PSPEs) were synthesized using the Sonogashira-Hagihara protocol and they were characterized using nuclear magnetic resonance spectroscopy and gel permeation chromatography. Their optical properties were investigated by UV-vis andfluorescence spectroscopies. PSPEs containing Zn saiphen moieties were found to exhibit strong aggregation that is facilitated by the presence of Zn to O interactions, and it was discovered thatthe polymers interact with various Lewis bases to undergo aggregation and deaggregation. New ladder-type conjugated polymers, as well as a series of model compounds that are representativeof the repeating units of the polymers, were synthesized using Schiff base condensation methods. The electronic and magnetic properties of these ladder-polymers were studied using cyclic voltammetry, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Towards arylene-ethynylene based supramolecular hosts (2019)

Motivated by the pursuit of shape-persistent macrocycles that could act as hosts for metal ions or clusters, we set out to construct arylene-ethynylene macrocycles with functionalized interiors. A step-wise synthesis using Sonogashira cross-coupling and deprotection reactions was used to make a series of arylene-ethynylene molecules. These compounds included a macrocycle with interior methoxy functional groups and trimers with methoxy or amine functionalities. These molecules were characterized using NMR spectroscopy as well as ESI-TOF mass spectrometry. The synthesis of these molecules provides the groundwork for the development of new aryleneethynylene based receptors to be used in host-guest chemistry.

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Investigations of chitin- and cellulose-based materials (2018)

Chitin plastic was fabricated from Dungeness crab shells. Chitin was purified from the shells, deacetylated, and then formed a gel in weak acid. The gel was poured into molds and then dried to leave behind a plastic film, which was strengthened by treatment with sodium hydroxide. Scanning electron microscopy (SEM) images of the dried film indicated that it adopts a layered structure. One sample batch was deacetylated for eight hours, and the other for twelve hours. The batch deacetylated for eight hours had superior characteristics, with a tensile strength of 93 ± 35 N/mm² and maximum strain of (7.5 ± 3) % while dry; after soaking in water for an hour, the tensile strength decreased to 7 ± 7 N/mm² and the strain at fracture increased to (31 ± 9) %. Contact angle experiments showed that the material is hydrophobic. Infrared (IR) spectroscopy confirmed a high degree of deacetylation in the final material. Results from IR spectroscopy and X-ray diffraction suggest a low degree of crystallinity in the material. This strong and waterproof chitin bioplastic is promising for use as packaging and for medical technology. Additionally, a new type of polypyrrole-cellulose composite was developed. Polypyrrole was synthesized, mixed with an aqueous suspension of cellulose nanocrystals, and dried to a homogeneous black iridescent film. The film showed iridescence that is attributed to the chiral nematic structure characteristic of cellulose nanocrystal films. Surprisingly, the film was not found to have any conductive or capacitative electrical properties. When doped, these new composite materials could have interesting electrical properties owing to the chiral structure of the films.

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Towards the Borphyrin Head-to-Tail Macrocycles Based on Boronate Esters (2015)

Inspired by the versatility of boronic acid condensation with catechols, we set out to construct boronate-ester based macrocycles by the head-to-tail assembly of precursor that contains both a catechol and a boronic acid on the same molecule. A series of expanded “borphyrin” macrocycles was prepared in the pursuit of increasing the solubility. Further characterization of the new macrocycles by UV-Vis and IR spectroscopy confirmed that they have extended conjugation. However, incorporation of sterically hindered bulky groups might also disrupt the trigonal planar geometry around the boron centers and limit the extent of conjugation of the macrocycles.

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Photonic materials based on cellulose nanocrystals (2014)

The self-assembly of cellulose nanocrystals (CNCs) into a chiral nematic structure exhibiting photonic properties has garnered much interest in recent years. The development of free-standing chiral nematic films composed of mesoporous silica and organosilica using CNCs as a template has led to a number of studies on producing photonic films composed of inorganic compounds. These films can be tuned to reflect light within the visible spectrum, yielding an assortment of films that exhibit structural colour that is retained once formed, and can no longer be modified. The incorporation of a photonic structure into a flexible material, such as a hydrogel, would allow for colour changes to transpire after the film is formed. Here, the integration of a chiral nematic photonic structure into hydrogel films prepared from different monomers is reported. The swelling of the photonic hydrogels was explored through the use of UV-visible spectroscopy, and the strength of the gels was investigated. In addition to the formation of tunable photonic structures based on CNCs, also reported is the formation of hybrid photonic structures produced by combining two classes of photonic crystals. These films build onto the chiral nematic mesoporous silica films by introducing a secondary photonic structure, based on the close packed arrangement of nanospheres. These novel hybrid photonic structures were synthesized, and characterized using electron microscopy. The successful formation of composite photonic materials, such as CNC-hydrogels, and hybrid photonic films displays the potential for CNC to be used as a template to build photonic structures in a wide array of systems.

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Studies of Nitration of Cellulose - Application in New Membrane Materials (2014)

Since the discovery of the production of nanocrystalline cellulose (NCC) from acid hydrolysis of bulk cellulose, this material has been used as a template for imparting photonic properties on materials without innate structural ordering and as an additive in polymer composites to increase structural strength. However, the potential of NCC as a feedstock for highly nitrated cellulose has not been investigated. It is postulated that the smaller chain lengths in NCC may permit a higher degree of nitration in comparison with conventional nitrocellulose. In this thesis, various nitration methods have been investigated for their ability to produce highly nitrated NCC. Traditional nitration methods using HNO₃/H₂SO₄ and less common nitration methods using HNO₃/P₂O₅ and HNO₃/Ac₂O were used and the differences between methods were studied. There was an effect in using H₂SO₄ as the desiccant on the hindrance of the degree of nitration. Titration of the nitrated material with base shows the presence of more sulfate groups in samples nitrated in the presence of H₂SO₄ than in the absence of it, demonstrating that H₂SO₄ is a less ideal desiccant. In addition, pretreatment of NCC with a desulfation procedure improved the degree of nitration. The investigation of the other desiccants showed the importance of using a miscible, non-degrading desiccant to obtain a high degree of nitration. The synthesized nitrated nanocrystalline cellulose, hereby abbreviated as NNC, were analyzed by elemental analysis for the nitrogen content, powder X-ray diffraction for crystallinity, Fourier-transform infrared spectroscopy and thermal gravimetric analysis for the stability of the compound.

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Switching the reflection in chiral nematic mesoporous silica and organosilica films (2013)

Recently, a new class of free-standing chiral nematic mesoporous silica and organosilica films was developed using nanocrystalline cellulose as a template. Due to their unique structures these films are iridescent, and by varying synthetic conditions it has been shown that this iridescence can be tuned to selectively reflect incident light of different wavelengths across the entire visible spectrum. However, upon formation of the mesostructure, these optical properties are locked in and can no longer be altered. Herein I describe alternate techniques to modify the optical properties of these silica and organosilica films by infiltration with guest molecules after the films have been prepared.Liquid crystal mesogen 5CB and 8CB were loaded into the pores of unfunctionalized and octyl and phenyl functionalized silica films. Thermal cycling of these new composite materials elucidated a sharp and reversible optical change in the 8CB loaded octyl functionalized silica films. Additional studies including variable temperature POM and UV-Vis spectroscopy were conducted on this system prepared with organosilica films. This approach was then expanded on by doping an azobenzene derivative in 1, 5, and 10 % by weight into the 8CB liquid crystal before loading the mixtures into the films. A reversible optical change was then brought about in this system by irradiation at different wavelengths. Further development of these methods could lead to their implementation in the still emerging fields of sensing and display technologies involving colour information.

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