Structure of nanoscale mesoporous silica spheres?

Tendeloo, Gustaaf Van; Lebedev, Oleg I.; Collart, O.; Cool, Pegie; Vansant, Etienne F.

doi:10.1088/0953-8984/15/42/004

Cited by 35 publications

(35 citation statements)

References 24 publications

(36 reference statements)

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“…The material used in this investigation (namely, MCM-41) consists of roughly spherical silica particles prepared by sol-gel methods with an average diameter of 620 nm as verified by SEM that are templated by cetyltrimethylammonium bromide to produce (34,39,40) pores with a diameter of 1.5-2.0 nm. The highly ordered pores form a two-dimensional hexagonal structure with a lattice spacing of 3.6 nm as measured by x-ray diffraction.…”

Section: Resultsmentioning

confidence: 99%

A reversible molecular valve

Nguyen

Tseng

Celestre

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

456

262

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In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.controlled release ͉ nanomachine ͉ nanovalve P rogress in designing and synthesizing nanovalves that control access to and from the pores in inorganic materials is proceeding apace. Our previous work (1), involving the fabrication of pseudorotaxane-derivatized, nanostructured thin films, demonstrated a reusable but irreversible nanovalve that acts like a cork in a bottle, opening the orifices of a two-dimensional hexagonal array of cylindrical pores and allowing the contents to spill out. Other examples, using more traditional control mechanisms, have been described in the literature. Based on photodriven motions involving cis-trans isomerizations of NAN double bonds, azobenzenes tethered to the walls of the nanoporous membranes function (2) as a regulatory mechanism for mass transport through the channels of nanoporous materials. Using the intermolecular dimerization of tethered coumarins, dimers act (3, 4) as a net to control the access to and from the pores of derivatized MCM-41 upon photoactivation and subsequent dedimerization. Chemically linked CdS nanoparticles on derivatized mesoporous silica nanospheres function (5) as caps to control the release of chemicals from the pores. Although, in the latter two examples, covalent bonds are broken to control the release of the pore's contents, the first instance is one in which a change in a molecule's configuration, and hence shape, does the trick. Based on pH-sensitive intermolecular hydrogen bonds between poly-(ethyloxazoline) and poly(methacrylic acid), a polymer gel can be eroded electrically, leading to the release of a trapped insulin load (6). A heat-responsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), has also been used (7) as the source of hindrance at the pores' orifices to modulate the transport of solute, albeit in an irreversible fashion. By using monolithic copolymers to define pores with tunable sizes ranging from tens to thousands of nanometers, PNIPAAm has been shown (8) to behave as a reversible valve in microfluidic chips. The electrochemical corrosio...

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Section: Resultsmentioning

confidence: 99%

A reversible molecular valve

Nguyen

Tseng

Celestre

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

456

262

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“…[102][103][104] Increasing the ethanol concentration in the TEOS-C 16 TMABr-ammonia-water system at room temperature led to the formation of a succession of mesophases in the order, MCM-41 (hexagonal phase), MCM-48 (cubic phase), and MCM-50 (lamellar phase). Such phase succession is the result of the cosurfactant behavior of the ethanol.…”

Section: Alternative Methodsmentioning

confidence: 99%

Silica-Based Mesoporous Nanospheres

Bhattacharyya

Ducheyne

2011

Comprehensive Biomaterials

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“…General Preparation of the Pseudorotaxane-MCM-41: MCM-41 was prepared according to literature procedures [28][29][30]. The doping of uranyl nitrate into the MCM-41 framework was carried out during the MCM-41 synthesis.…”

Section: Methodsmentioning

confidence: 99%

“…The nanoscale mesoporous particles, serving as both the solid support for the movable components and the containers for the probe molecules, were prepared [28][29][30][31][32][33][34][35][36][37][38][39][40] by surfactant-directed self-assembly to yield ordered arrays of tubes in sol-gel derived silica. The nanostructured silica, MCM-41, consists of nearspherical silica particles with an average diameter of 600 nm, as verified ( Fig.…”

Section: Preparation Of Supramolecular Nanovalvesmentioning

confidence: 99%

Versatile Supramolecular Nanovalves Reconfigured for Light Activation

Nguyen

Leung

Liong

et al. 2007

Adv Funct Materials

206

142

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All autonomous machines share the same requirement—namely, they need some form of energy to perform their operations and nanovalves are no exception. Supramolecular nanovalves constructed from [2]pseudorotaxanes—behaving as dissociatable complexes attached to mesoporous silica which acts as a supporting platform and reservoir—rely on donor‐acceptor and hydrogen bonding interactions between the ring component and the linear component to control the ON and OFF states. The method of operation of these supramolecular nanovalves involves primarily the weakening of these interactions. The [2]pseudorotaxane [BHEEEN ⊂ CBPQT]4+ [BHEEEN ≡ 1,5‐bis[2‐(2‐(2‐hydroxyethoxy)ethoxy)ethoxy]naphthalene and CBPQT4+ ≡ cyclobis(paraquat‐p‐phenylene)], when this 1:1 complex is tethered on the surface of the mesoporous silica, constitutes the supramolecular nanovalves. The mesoporous silica is charged against a concentration gradient with luminescence probe molecules, e.g., tris(2,2′‐phenylpyridyl)iridium(III), Ir(ppy)3 (ppy = 2,2′‐phenylpyridyl), followed by addition of CBPQT·4Cl to form the tethered [2]pseudorotaxanes. This situation corresponds to the OFF state of the supramolecular nanovalves. Their ON state can be initiated by reducing the CBPQT4+ ring with NaCNBH3, thus weakening the complexation and causing dissociation of the CBPQT4+ ring away from the BHEEEN stalks on the mesoporous silica particles MCM‐41 to bring about ultimately the controlled release of the luminescence probe molecules from the mesoporous silica particles with an average diameter of 600 nm. This kind of functioning supramolecular system can be reconfigured further with built‐in photosensitizers, such as tethered 9‐anthracenecarboxylic acid and tethered [Ru(bpy)2(bpy(CH2OH)2)]2+ (bpy = 2,2′‐bipyridine). Upon irradiation with laser light of an appropriate wavelength, the excited photosensitizers transfer electrons to the near‐by CBPQT4+ rings, reducing them so that they dissociate away from the BHEEEN stalks on the surface of the mesoporous silica particles, leading subsequently to a controlled release of the luminescent probe molecules. This control can be expressed in both a regional and temporal manner by the use of light as the ON/OFF stimulus for the supramolecular nanovalves.

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Structure of nanoscale mesoporous silica spheres?

Cited by 35 publications

References 24 publications

A reversible molecular valve

A reversible molecular valve

Silica-Based Mesoporous Nanospheres

Versatile Supramolecular Nanovalves Reconfigured for Light Activation

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