Templated synthesis of electroactive periodic mesoporous organosilica bridged with oligoaniline

The synthesis and characterization of novel electroactive periodic mesoporous organosilica (PMO) are reported. The silsesquioxane precursor, N,N'-bis(4'-(3-triethoxysilylpropylureido)phenyl)-1,4-quinonene-diimine (TSUPQD), was prepared from the emeraldine base of amino-capped aniline trimer (EBAT) using a one-step coupling reaction and was used as an organic silicon source in the co-condensation with tetraethyl orthosilicate (TEOS) in proper ratios. By means of a hydrothermal sol-gel approach with the cationic surfactant cetyltrimethyl-ammonium bromide (CTAB) as the structure-directing template and acetone as the co-solvent for the dissolution of TSUPQD, a series of novel MCM-41 type siliceous materials (TSU-PMOs) were successfully prepared under mild alkaline conditions. The resultant mesoporous organosilica were characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry, X-ray diffraction, nitrogen sorption, and transmission electron microscopy (TEM) and showed that this series of TSU-PMOs exhibited hexagonally patterned mesostructures with pore diameters of 2.1-2.8 nm. Although the structural regularity and pore parameters gradually deteriorated with increasing loading of organic bridges, the electrochemical behavior of TSU-PMOs monitored by cyclic voltammetry demonstrated greater electroactivities for samples with higher concentration of the incorporated TSU units.     

Facile fabrication of hollow mesoporous silica nanospheres for superhydrophilic and visible/near-IR antireflection coatings

A series of hierarchically mesostructured silica nanoparticles (MSNs) less than 100 nm in size were fabricated by means of a one-step synthesis using dodecanethiol (C(12)-SH) and cetyltrimethylammonium bromide (CTAB) as the dual template, and trimethylbenzene (TMB) as the swelling agent. Silica nanoparticles with varied morphologies and structures, including mesoporous silica nanoparticles with tunable pore size, mesoporous silica nanoparticles with a thin solid shell, hollow mesoporous silica nanoparticles with tunable cavity size, and hollow mesoporous silica nanoparticles with a thin solid shell, were obtained by regulating the TMB/CTAB molar ratio and the stirring rate with the assistance of C(12)-SH. Silica particulate coatings were successfully fabricated by using MSNs with varied morphologies and structures as building block through layer-by-layer dip-coating on glass substrates. The thickness and roughness of the silica particulate coatings could be tailored by regulating the deposition cycles of nanoparticles. The silica particulate coatings composed of hollow mesoporous silica nanoparticles with a thin shell (S2) increased the maximum transmittance of slide glass from 90 to 96%, whereas they reduced its minimum reflection from 8 to 2% at the optimized wavelength region that could be adjusted from visible to near-IR with a growing number of deposition cycles. The coatings also exhibited excellent superhydrophilic and antifogging properties. These mesostructured silica nanoparticles are also expected to serve as ideal scaffolds for biological, medical, and catalytic applications.     

Surface chemistry in the process of coating mesoporous SiO2 onto carbon nanotubes driven by the formation of Si-O-C bonds

The deposition of mesoporous silica (SiO(2)) on carbon nanotubes (CNTs) has opened up a wide range of assembling possibilities by exploiting the sidewall of CNTs and organosilane chemistry. The resulting systems may be suitable for applications in catalysis, energy conversion, environmental chemistry, and nanomedicine. However, to promote the condensation of silicon monomers on the nanotube without producing segregated particles, (OR)(4-x)SiO(x)(x-) units must undergo nucleophilic substitution by groups localized on the CNT sidewall during the transesterification reaction. In order to achieve this preferential attachment, we have deposited silica on oxidized carbon nanotubes (single-walled and multiwalled) in a sol-gel process that also involved the use of a soft template (cetyltrimethylammonium bromide, CTAB). In contrast to the simple approach normally used to describe the attachment of inorganic compounds on CNTs, SiO(2) nucleation on the tube is a result of nucleophilic attack mainly by hydroxyl radicals, localized in a very complex surface chemical environment, where various oxygenated groups are covalently bonded to the sidewall and carboxylated carbonaceous fragments (CCFs) are adsorbed on the tubes. Si-O-C covalent bond formation in the SiO(2)-CNT hybrids was observed even after removal of the CCFs with sodium hydroxide. By adding CTAB, and increasing the temperature, time, and initial amount of the catalyst (NH(4)OH) in the synthesis, the SiO(2) coating morphology could be changed from one of nanoparticles to mesoporous shells. Concomitantly, pore ordering was achieved by increasing the amount of CTAB. Furthermore, preferential attachment on the sidewall results mostly in CNTs with uncapped ends, having sites (carboxylic acids) that can be used for further localized reactions.     

Enhanced fluorescence detection of metal ions using light-harvesting mesoporous organosilica

Enhanced fluorescence detection of metal ions was realized in a system consisting of a fluorescent 2,2′‐bipyridine (BPy) receptor and light‐harvesting periodic mesoporous organosilica (PMO). The fluorescent BPy receptor with two silyl groups was synthesized and covalently attached to the pore walls of biphenyl (Bp)‐bridged PMO powder. The fluorescence intensity from the BPy receptor was significantly enhanced by the light‐harvesting property of Bp‐PMO, that is, the energy funneling into the BPy receptor from a large number of Bp groups in the PMO framework which absorbed UV light effectively. The enhanced emission of the BPy receptor was quenched upon the addition of a low concentration of Cu²⁺ (0.15–1.2×10^?6 M ), resulting in the sensitive detection of Cu²⁺. Upon titration of Zn²⁺ (0.3–6.0×10^?6 M ), the fluorescence excitation spectrum was systematically changed with an isosbestic point at 375 nm through 1:1 complexation of BPy and Zn²⁺ similar to that observed in BPy‐based solutions, indicating almost complete preservation of the binding property of the BPy receptor despite covalent fixing on the solid surface. These results demonstrate that light‐harvesting PMOs have great potential as supporting materials for enhanced fluorescence chemosensors.     

Highly photoactive porous anatase films obtained by deformation of 3D mesostructures

A transparent film of three‐dimensional (3D) hexagonal (P6₃/mmc) mesostructured titania was fabricated according to a modified procedure using triblock copolymer Pluronic P123. The precursor solution was diluted with ethanol and spin‐coated to afford a transparent film with a thickness of less than 100 nm. The mesostructure was maintained (deteriorated) at 400 °C, converted to regularly arranged anatase nanopillars with sufficient porosity at 550 °C, and deformed at 700 °C to nanocrystals with intercrystalline mesospaces. The mesostructural variation was related to the degree of shrinkage of the film owing to condensation and crystallization of the titania frameworks. An anatase nanocrystal film having sufficient porosity and high crystallinity was most active in the photodegradation of methylene blue. Such intercrystalline mesospaces can be controlled by regular deformation of 3D mesostructures through anatase nanopillar structures. In addition to adequate crystallinity of the titania frameworks, smooth diffusion of target organic molecules and/or degraded organic compounds was important for effective photodegradation.     

Surfactant-free nonaqueous synthesis of metal oxide nanostructures

Surfactant-free nonaqueous (and/or nonhydrolytic) sol-gel routes constitute one of the most versatile and powerful synthesis methodologies for nanocrystalline metal oxides with high compositional homogeneity and purity. Although the synthesis protocols are particularly simple, involving only metal oxide precursors and common organic solvents, the obtained uniform nanocrystals exhibit an immense variety of sizes and shapes. The small number of reactants in these routes enables the study of the chemical mechanisms involved in metal oxide formation. Nonhydrolytic routes to inorganic nanomaterials that used surfactants as size- and shape-controlling agents have been discussed recently. This Minireview supplements this topic by discussing surfactant-free processes, which have become a valuable alternative to surfactant-assisted as well as to traditional aqueous sol-gel chemistry routes.     

Periodic Mesoporous Organosilica Materials: Self‐Assembly of Carbamothioic Acid‐Bridged Organosilane Precursors

A new series of carbamothioic acid‐containing periodic mesoporous organosilica (PMO) materials has been synthesized by a direct cocondensation method, in which an organosilica precursor N,S‐bis[3‐(triethoxysilyl)propyl]carbamothioic acid (MI) is treated with tetraethyl orthosilicate (TEOS), and the nonionic surfactant Pluronic 123 (P123) is used as a template under acidic conditions in the presence of inorganic additives. Moreover, the synthesis of the PMO material consisting of the MI precursor without TEOS has been realized. These novel PMO materials have large surface areas, well‐ordered mesoporous structures, hollow fiberlike morphologies, and thick walls. They are also structurally well‐ordered with a high organosilica precursor content, and the carbamothioic acid groups are thermally stable up to 250 °C. Furthermore, the organosilica materials exhibit hydrothermal stability in basic solution.     

Rational design of the pore system within the framework aluminium alkylenediphosphonate series

We report here on the solvothermal synthesis and crystal structure of the hybrid organic-inorganic framework material Al(2)[O(3)PC(3)H(6)PO(3)](H(2)O)(2)F(2).H(2)O (orthorhombic, Pmmn, a = 12.0591(2) A, b = 19.1647(5) A, c = 4.91142(7) A, Z = 4), the second member of the Al(2)[O(3)PC(n)H(2n)PO(3)](H(2)O)(2)F(2).H(2)O series. The structure consists of corrugated chains of corner-sharing AlO(4)F(2) octahedra in which alternating AlO(4)F(2) octahedra contain two fluorine atoms in a trans or a cis configuration. The diphosphonate groups link the chains together through Al-O-P-O-Al bridges and through the propylene groups to form a three-dimensional framework structure containing a one-dimensional channel system. The linkage of the corrugated inorganic Al-O-P layers within the structure results in the formation of two types of channel that differ in size, shape and composition. The smaller channel is unoccupied; the larger channel is more elongated and contains two extra-framework water molecules per unit cell. A computational investigation into the driving force that controls the stacking arrangement of the Al-O-P inorganic layers within this series of compounds reveals that the stacking is found to be controlled by thermodynamic factors, arising chiefly from the conformation of the organic linker molecule used to connect the inorganic sheets. It is found that the registration of the inorganic layers can be engineered by selecting an appropriate, simple organic spacer or linker alkyl chain, where an even number of carbon atoms in the alkyl chain directs formation of aligned, stacked, inorganic sheets (AAAAAA), and an odd number directs formation of unaligned, stacked sheets (ABABAB) and the formation of one or two channel types in the resultant structure, respectively. This combination of alkyl-chain linkers in conjunction with corrugated inorganic layers is an effective tool to rationally design the pore system of hybrid framework materials.     

Ultrahigh density arrays of toroidal ZnO nanostructures by one-step cooperative self-assembly processes: mechanism of structural evolution and hybridization with Au nanoparticles

A quick protocol for the fabrication of ultrahigh density arrays of toroidal ZnO nanostructures with tailored structures on a substrate surface is presented based on the one-step spin coating of a common solution composed of inverse micelles of polystyrene-block-poly(4-vinyl pyridine) copolymers (PS-b-P4VP) and sol-gel precursors without the need of conventional complex lithographic techniques. ZnO toroids decorated with gold nanoparticles are also obtained by subsequent loading and reduction of metallic precursors. It was elucidated that the diethanolamine moiety in the sol-gel precursors, which induces selective swelling and structural reorganization of the P4VP core blocks, plays a key role in the generation of toroidal nanostructures. Toroidal ZnO nanostructures embedded in a PS-b-P4VP matrix films or arrays of pure wurtzite ZnO nanorings are obtained by calcination under inert atmosphere. The structural parameters of the toroidal nanostructures such as the width, height, diameter of the rims as well as the spacing of their 2D arrays are controlled by employing PS-b-P4VP with different molecular weight and varying the mixing protocols.     

Control of Chiral Nanostructures by Self‐Assembly of Designed Amphiphilic Peptides and Silica Biomineralization

Peptides, the fundamental building units of biological systems, are chiral in molecular scale as well as in spatial conformation. Shells are exquisite examples of well‐defined chiral structures produced by natural biomineralization. However, the fundamental mechanism of chirality expressed in biological organisms remains unclear. Here, we present a system that mimics natural biomineralization and produces enantiopure chiral inorganic materials with controllable helicity. By tuning the hydrophilicity of the amphiphilic peptides, the chiral morphologies and mesostructures can be changed. With decreasing hydrophilicity of the amphiphilic peptides, we observed that the nanostructures changed from twisted nanofibers with a hexagonal mesostructure to twisted nanoribbons with a lamellar mesostructure, and the extent of the helicity decreased. Defining the mechanism of chiral inorganic materials formed from peptides by noncovalent interactions can improve strategies toward the bottom‐up synthesis of nanomaterials as well as in the field of bioengineering.     

Preparation and characterization of a novel organic-inorganic nanohybrid "cerasome" formed with a liposomal membrane and silicate surface

A novel class of organic-inorganic hybrids, the so-called cerasomes, which have a bilayer vesicular structure and a silicate surface, has been synthesized by combination of sol-gel reaction and self-assembly of organoalkoxysilanes with a molecular structure analogous to lipids. We have synthesized two cerasome-forming organoalkoxysilanes, N-[N-(3-triethoxysilyl)propylsuccinamoyl]dihexadecylamine (1) and N,N-dihexadecyl-N (alpha)-[6-[(3-triethoxysilyl)propyldimethylammonio]hexanoyl]glycinamide bromide (2), and investigated the synthetic conditions of the cerasomes and their structural characteristics. For the proamphiphilic 1, the cerasome was obtained under restricted pH conditions where acid-catalyzed hydrolysis of the triethoxysilyl moiety proceeded without disturbing the vesicle formation. In contrast, the amphiphilic 2, additionally having a hydrophilic quaternary ammonium group, formed stable dispersions of the cerasome in a wide pH range. The hydrolysis behavior of the triethoxysilyl groups was monitored by (1)H NMR spectroscopy. Morphology of the cerasomes having the liposomal vesicular structure was confirmed by TEM observations. Extent of the development of siloxane networks through condensation among the silanol groups on the cerasome surface was evaluated by using MALDI-TOF-MS spectrometry. Formation of oligomers of the cerasome-forming lipids in the vesicle was clearly confirmed. Due to the siloxane network formation, the cerasome showed remarkably high morphological stability compared with a reference liposome, as evaluated by surfactant dissolution measurements.