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Dive into the research topics where Joel A. Kelly is active.

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Featured researches published by Joel A. Kelly.


Accounts of Chemical Research | 2014

The Development of Chiral Nematic Mesoporous Materials

Joel A. Kelly; Michael Giese; Kevin E. Shopsowitz; Wadood Y. Hamad; Mark J. MacLachlan

Cellulose nanocrystals (CNCs) are obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose. The nanocrystals have diameters of ~5-15 nm and lengths of ~100-300 nm (depending on the cellulose source and hydrolysis conditions). This lightweight material has mostly been investigated to reinforce composites and polymers because it has remarkable strength that rivals carbon nanotubes. But CNCs have an additional, less explored property: they organize into a chiral nematic (historically referred to as cholesteric) liquid crystal in water. When dried into a thin solid film, the CNCs retain the helicoidal chiral nematic order and assemble into a layered structure where the CNCs have aligned orientation within each layer, and their orientation rotates through the stack with a characteristic pitch (repeating distance). The cholesteric ordering can act as a 1-D photonic structure, selectively reflecting circularly polarized light that has a wavelength nearly matching the pitch. During CNC self-assembly, it is possible to add sol-gel precursors, such as Si(OMe)4, that undergo hydrolysis and condensation as the solvent evaporates, leading to a chiral nematic silica/CNC composite material. Calcination of the material in air destroys the cellulose template, leaving a high surface area mesoporous silica film that has pore diameters of ~3-10 nm. Importantly, the silica is brilliantly iridescent because the pores in its interior replicate the chiral nematic structure. These films may be useful as optical filters, reflectors, and membranes. In this Account, we describe our recent research into mesoporous films with chiral nematic order. Taking advantage of the chiral nematic order and nanoscale of the CNC templates, new functional materials can be prepared. For example, heating the silica/CNC composites under an inert atmosphere followed by removal of the silica leaves highly ordered, mesoporous carbon films that can be used as supercapacitor electrodes. The composition of the mesoporous films can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica films are obtained. These materials are flexible and offer the ability to tune the chemical and mechanical properties through variation of the organic spacer. Chiral nematic mesoporous silica and organosilica materials, obtainable as centimeter-scale freestanding films, are interesting hosts for nanomaterials. When noble metal nanoparticles are incorporated into the pores, they show strong circular dichroism signals associated with their surface plasmon resonances that arise from dipolar coupling of the particles within the chiral nematic host. Fluorescent conjugated polymers show induced circular dichroism spectra when encapsulated in the chiral nematic host. The porosity, film structure, and optical properties of these materials could enable their use in sensors. We describe the development of chiral nematic mesoporous silica and organosilica, demonstrate different avenues of host-guest chemistry, and identify future directions that exploit the unique combination of properties present in these materials. The examples covered in this Account demonstrate that there is a rich diversity of composite materials accessible using CNC templating.


ACS Nano | 2010

An investigation into near-UV hydrosilylation of freestanding silicon nanocrystals.

Joel A. Kelly; Jonathan G. C. Veinot

We present a study of the photochemical hydrosilylation of freestanding silicon nanocrystals (Si-NCs) using a near-UV source. The impact of reaction with alkenes and alkynes was studied using in situ photoluminescence (PL) spectroscopy, allowing measurement of both changes in intensity and PL maxima during the reaction. Understanding this behavior is important for the utilization of these materials in a number of applications where hydrosilylation is a leading method to functionalize Si-NCs. Changes in the PL were studied and shown arise from the influence of oxidation as well as the Si-C bond formation. Hydrosilylation with a range of conjugated alkynyl species was studied to understand how the introduction of these species to the NC surface can quench the PL from Si-NCs. These results were explained in context of the free-radical and exciton-mediated mechanisms for photochemical hydrosilylation proposed for Si-NCs. Materials in this study were characterized by Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), selected electron area diffraction (SAED), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA) and dynamic light scattering (DLS).


Journal of the American Chemical Society | 2011

Size-dependent reactivity in hydrosilylation of silicon nanocrystals.

Joel A. Kelly; Amber M. Shukaliak; M. D. Fleischauer; Jonathan G. C. Veinot

We present an investigation into the influence of nanocrystal size on the reactivity of silicon nanocrystals (Si-NCs) in near-UV photochemical hydrosilylation. The size-dependent reactivity of Si-NCs with photoluminescence (PL) in the visible and near-infrared regions was evaluated using PL and Fourier-transform infrared (FTIR) spectroscopy, and small-angle X-ray scattering (SAXS). Under near-UV excitation, Si-NCs with PL in the visible spectral region react faster than Si-NCs with near-IR PL, allowing partial separation of a mixture of Si-NC sizes through hydrosilylation. This is attributed to quantum size effects in the exciton-mediated mechanisms proposed for this reaction.


Nanotoxicology | 2012

Inhibition of enzyme activity by nanomaterials: Potential mechanisms and implications for nanotoxicity testing

Tyson J. MacCormack; Rhett J. Clark; Michael K. M. Dang; Guibin Ma; Joel A. Kelly; Jonathan G. C. Veinot; Greg G. Goss

Abstract The objective of this study was to investigate whether nanoparticle-exposure affects enzyme function and to determine the mechanisms responsible. Silicon, Au, and CdSe nanoparticles were synthesized in house and their physicochemical properties were characterized. The activity of purified lactate dehydrogenase (LDH) was inhibited or abolished by all nanoparticles tested. Inhibition was dependent upon particle core and surface-functional group composition. Inhibition of LDH was absent in crude tissue homogenates, in the presence of albumin, and at the isoelectric point of the protein, indicating that nanoparticles bind non-specifically to abundant proteins via a charge interaction. Circular dichroism spectroscopy suggests that the structure of LDH may be altered by nanoparticles in a manner different from that of bulk controls. We present new data on the specific physicochemical properties of nanoparticles that may lead to bioactivity and highlight a number of potentially serious problems with common nanotoxicity testing methods.


Langmuir | 2012

Chiral Nematic Stained Glass: Controlling the Optical Properties of Nanocrystalline Cellulose-Templated Materials

Joel A. Kelly; Kevin E. Shopsowitz; Jun Myun Ahn; Wadood Y. Hamad; Mark J. MacLachlan

Chiral nematic mesoporous materials decorated with metal nanoparticles have been prepared using the templated self-assembly of nanocrystalline cellulose (NCC). By adding small quantities of ionic compounds to aqueous dispersions of NCC and tetramethoxysilane (TMOS), the helical pitch of the chiral nematic structure could be manipulated in a manner complementary to the ratio of NCC/TMOS previously demonstrated by our group. We have studied the transformation of these ion-loaded composites into high surface area mesoporous silica and carbon films decorated with metal nanoparticles through calcination and carbonization, respectively. This general and straightforward approach to prepare chiral nematic metal nanoparticle assemblies may be useful in a variety of applications, particularly for their chiral optical properties.


Journal of Physical Chemistry Letters | 2012

Photothermal Response of Photoluminescent Silicon Nanocrystals

Sarah Regli; Joel A. Kelly; Amber M. Shukaliak; Jonathan G. C. Veinot

We demonstrate that silicon nanocrystals (Si-NCs) exhibiting relatively high near-IR photoluminescent quantum yields also exhibit a notable photothermal (PT) response. The PT effect has been quantified as a function of NC size, defect concentration, and irradiating energy, suggesting that the origin of the PT response is a combination of carrier thermalization and defect-mediated heating. The PT effect observed under NIR irradiation suggests that Si-NCs could find use in combined in vivo PL imaging and PT therapy.


Journal of Materials Chemistry C | 2014

Evaluation of form birefringence in chiral nematic mesoporous materials

Joel A. Kelly; C. P. Kyle Manchee; Susan Cheng; Jun Myun Ahn; Kevin E. Shopsowitz; Wadood Y. Hamad; Mark J. MacLachlan

We present a detailed investigation into the form birefringence of chiral nematic mesoporous materials templated by the self-assembly of cellulose nanocrystals as the potential basis to detect changes in refractive index in an optical sensor using circular dichroism (CD) spectroscopy. The behavior is in excellent agreement with a model of form birefringence in a chiral nematic structure. We characterize the variability introduced by the self-assembly of the biologically-derived cellulose nanocrystals, which can partially be accounted for through normalization to address reproducibility in thickness and helical pitch within each sample. As one potential application, we show that the refractive index performance of these materials is maintained in strongly absorbing solutions due to the chiral nature of the form birefringence.


IOP Conference Series: Materials Science and Engineering | 2009

Galvanic displacement of metals on semiconductor nanocrystals

Melanie Johnson; Joel A. Kelly; Eric J. Henderson; Jonathan G. C. Veinot

We report the galvanic displacement (GD) of germanium from germanium nanocrystals (Ge-NCs) with silver. The Ge-NCs are synthesized by reductive thermal processing of germanium suboxide sol-gel prepolymers. Thermal processing yields size-controlled oxide-embedded Ge-NCs, which are liberated by dissolution of the germanium oxide matrix in water. Subsequent exposure of the freestanding Ge-NCs to aqueous solutions of AgNO3 leads to deposition of silver nanostructures by GD. The resulting metal structures were analyzed by XRD, XPS, TEM and EDX, confirming deposition of elemental silver in a variety of shapes and sizes.


Journal of Chemical Physics | 2016

Communication: Chemisorption of muonium on gold nanoparticles: A sensitive new probe of surface magnetism and reactivity

M H Dehn; Donald J. Arseneau; P Boni; Michael D. Bridges; T Buck; David L Cortie; Donald G. Fleming; Joel A. Kelly; W A MacFarlane; Mark J. MacLachlan; Ryan M. L. McFadden; Gerald D. Morris; P-X Wang; J Xiao; Vitor M. Zamarion; Robert F. Kiefl

Chemisorption of muonium onto the surface of gold nanoparticles has been observed. Muonium (μ+e-), a light hydrogen-like atom, reacts chemically with uncapped 7 nm gold nanoparticles embedded in mesoporous silica (SBA-15) with a strong temperature-dependent rate. The addition rate is fast enough to allow coherent spin transfer into a diamagnetic muon state on the nanoparticle surface. The muon is well established as a sensitive probe of static or slowly fluctuating magnetic fields in bulk matter. These results represent the first muon spin rotation signal on a nanoparticle surface or any metallic surface. Only weak magnetic effects are seen on the surface of these Au nanoparticles consistent with Pauli paramagnetism.


Journal of Physics: Conference Series | 2014

Interaction of the Mu-cyclohexadienyl radical with metallic (Au, Pt) nanoparticles in mesoporous silica

J Xiao; Donald J. Arseneau; M D Bridges; David L Cortie; S.P. Cottrell; M H Dehn; Donald G. Fleming; Joel A. Kelly; Robert F. Kiefl; W A MacFarlane; Mark J. MacLachlan; Iain McKenzie

μSR and ALCR techniques have been used to investigate the structure and dynamics of the Mu-cyclohexadienyl radical interacting with Au and Pt metal nanoparticles (MNPs) supported in mesoporous silica (SBA-15). Surprisingly, coherent precession signals are observed and the isotropic hyperfine coupling constants are almost the same in loaded and unloaded samples, implying that the electronic structure of MuC6H6 is only weakly perturbed by the presence of the MNPs. We propose the observed radicals are shielded from the metallic surfaces by a benzene coating on the MNPs. The Δ1 resonance is observable in MNP-loaded samples at higher temperatures than in the unloaded SBA-15. This is attributed to stronger binding of MuC6H6 to the benzene coated MNPs.

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Mark J. MacLachlan

University of British Columbia

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Kevin E. Shopsowitz

Massachusetts Institute of Technology

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David L Cortie

University of British Columbia

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Donald G. Fleming

University of British Columbia

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