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Acc. Chem. Res.最新综述：手性向列介孔材料的发展
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The Development of Chiral Nematic Mesoporous Materials 共9页 引文59篇 Joel A. Kelly,‡ , † Michael Giese,‡ , † Kevin E. Shopsowitz,‡ Wadood Y. Hamad,§ and Mark J. MacLachlan * , ‡ ‡Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada §FPInnovations, 3800 Wesbrook Mall, Vancouver, Bristish Columbia V6S 2L9, Canada CONSPECTUS: 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 fi lm, 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 re fl ecting 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 fi lm 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 fi lms may be useful as optical fi lters, re fl ectors, and membranes. In this Account, we describe our recent research into mesoporous fi lms 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 fi lms that can be used as supercapacitor electrodes. The composition of the mesoporous fi lms can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica fi lms are obtained. These materials are fl exible and o ff er 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 fi lms, 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, fi lm 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 di ff erent 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. Biography Joel Kelly received his B.Sc. degree from King’s University College and his Ph.D. from the University of Alberta in 2011. In 2011, he joined the MacLachlan lab as an NSERC Postdoctoral fellow. Biography Michael Giese studied chemistry at the RWTH Aachen University where he received his Ph.D. in 2011. After graduation, he joined the group of Prof. Mark MacLachlan as a DAAD Postdoctoral Fellow working on new functional materials templated by cellulose nanocrystals. Biography Kevin Shopsowitz completed his B.Sc. degree in Biochemistry at McGill University and his Ph.D. degree at UBC under the guidance of Prof. MacLachlan. He received the Award for Graduate Research in Inorganic Chemistry from the Chemical Institute of Canada (2012) and is now an NSERC Postdoctoral Fellow in Chemical Engineering at MIT. Biography Wadood Hamad holds a Ph.D. in polymer physics and micromechanics from McGill. He is Principal Scientist at FPInnovations whose work over the past decade has focused on scaling up CNC production and exploring new advanced applications. Biography Mark MacLachlan has been at UBC since 2001, where he is now Professor. He is the 2012 recipient of the NSERC E.W.R. Steacie Memorial Fellowship and 2013 Rutherford Medal of the Royal Society of Canada.   |
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