Porous materials via nanocasting procedures: innovative materials and learning about soft-matter organization

Polarz, Sebastian; Antonietti, Markus

doi:10.1039/b205708p

Cited by 196 publications

(166 citation statements)

References 104 publications

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“…Mesoporous silica synthesis relies on the ability of organic molecules to build up 3D-nanostructured phases by self-assembly or cooperative aggregation with polysilicic acid molecules, thus acting as templates for the forming silica. In this way, nanopatterns with pore diameters in the range 2-50 nm can be produced, which correspond to the building block sizes of the nanostructured organic templates (27)(28)(29)(30). When natSil-2 and natSil-1A are mixed in the absence of silicic acid a silaffin phase distinct from the bulk aqueous phase is formed, as is evident from the fact that both natSil-1A and natSil-2 become almost quantitatively pelleted by centrifugation (Fig.…”

Section: Resultsmentioning

confidence: 81%

Biosilica formation in diatoms: Characterization of native silaffin-2 and its role in silica morphogenesis

Poulsen

Sumper

Kröger

2003

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

321

303

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The biological formation of inorganic materials with complex form (biominerals) is a widespread phenomenon in nature, yet the molecular mechanisms underlying biomineral morphogenesis are not well understood. Among the most fascinating examples of biomineral structures are the intricately patterned, silicified cell walls of diatoms, which contain tightly associated organic macromolecules. From diatom biosilica a highly polyanionic phosphoprotein, termed native silaffin-2 (natSil-2), was isolated that carries unconventional amino acid modifications. natSil-2 lacked intrinsic silica formation activity but was able to regulate the activities of the previously characterized silica-forming biomolecules natSil-1A and long-chain polyamines. Combining natSil-2 and natSil-1A (or long-chain polyamines) generated an organic matrix that mediated precipitation of porous silica within minutes after the addition of silicic acid. Remarkably, the precipitate displayed pore sizes in the range 100 -1000 nm, which is characteristic for diatom biosilica nanopatterns.T he biological formation of intracellular or extracellular skeletons made of amorphous hydrated SiO 2 (biosilica) is relatively frequent among the protists and also occurs in many higher plants (1, 2). To date the organic molecules involved in biosilica formation have mainly been studied in sponges and diatoms (3). From the silica spicules of the sponge Thetya aurantia, proteaselike proteins termed silicateins were characterized that catalyze silica formation from tetraethoxysilane in vitro (4, 5). Diatoms are unicellular algae that have the extraordinary capability to produce an enormous variety of biosilica structures (6). Each diatom species is characterized by a specific biosilica cell wall that contains regularly arranged slits or pores in the size range between 10 and 1,000 nm (nanopatterned biosilica). Biosilica morphogenesis takes place inside the diatom cell within a specialized membrane-bound compartment termed the silica deposition vesicle (SDV). It has been postulated that the SDV contains a matrix of organic macromolecules that not only regulate silica formation but also act as templates to mediate biosilica nanopatterning (7-9). Insight into the nature of this organic matrix has been gained through the characterization of diatom biosilica-associated peptides (silaffins) and long-chain polyamines (LCPA), both of which accelerate silica formation from a silicic acid solution in vitro (10-12). Although native silaffin-1A (natSil-1A) and LCPA, respectively, mediate the formation of unusual silica structures in vitro (networks of irregularly shaped silica bands and large spherical silica particles) (11, 12), none of these are akin to diatom biosilica nanopatterns.Recently, it was shown that phosphorylation of natSil-1A is essential for silica formation activity (12), leading to the speculation that phosphorylated components may be generally important for biosilica morphogenesis. Therefore, a search for additional silica-associated phosphoproteins, which are able...

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Section: Resultsmentioning

confidence: 81%

Biosilica formation in diatoms: Characterization of native silaffin-2 and its role in silica morphogenesis

Poulsen

Sumper

Kröger

2003

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

321

303

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“…The preparation of silica monoliths with tunable mesopore size via the true liquidcrystal templating route has been described elsewhere [16,25,26]. These materials have a bicontinuous pore system, with micropores connecting the mesopores.…”

Section: Methodsmentioning

confidence: 99%

Cu/ZnO aggregates in siliceous mesoporous matrices: Development of a new model methanol synthesis catalyst

Berg

Polarz

Ткаченко

et al. 2006

Journal of Catalysis

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Copper and zinc were introduced into mesoporous siliceous matrices with the goal of obtaining model methanol synthesis catalysts with intense interaction between copper and the ZnO promoter. The preparation methods included various aqueous routes starting from acetate solutions (into MCM-48) and a route involving an organometallic step-thermolysis of a liquid heterocubane of Zn 4 O 4 type ([CH 3 ZnOCH 2 CH 2 OCH 3 ] 4 ) in a wormhole-type silica of 5 nm average pore size-followed by aqueous Cu (nitrate) impregnation. The materials were characterized by XRD, nitrogen physisorption, N 2 O frontal chromatography, TPR, and EXAFS, and their methanol synthesis activity was measured at 493 K and normal pressure. In the aqueous preparations with acetate solutions, excessive formation of silicates (particularly zinc silicate) led to damage of the pore system. A significant delay in Cu reduction was assigned to the influence of micropores formed, together with some copper silicate formation. These samples exhibited poorly accessible Cu surface areas despite small Cu particle sizes indicated by EXAFS and disappointing methanol synthesis activity. In contrast to this, a highly active catalyst was obtained via the heterocubane route that meets industrial standards in terms of reaction rate per Cu surface area. Orientation studies (EXAFS at the CuK and ZnK edges) reflecting a redox behavior of the ZnO x component illustrate the potential of this catalyst type for use in basic studies of the Cu-ZnO x interaction in methanol synthesis catalysts.

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“…When the quantity of Brij in the composite was 45% by weight, it formed a hexagonal phase that comprises a template of cylinders arranged on a hexagonal lattice with a hydrophilic core. 26,27 After the electrodeposition step, the Brij template was removed by washing with water to produce M-PANI films. The structure and morphology of the polymer films were investigated with the aid of a scanning electron microscope(SEM) and a transmission electron microscope (TEM).…”

mentioning

confidence: 99%

Mesoporous Polyaniline Films for High Performance Supercapacitors

Khdary

Abdesalam

Enany

2014

J. Electrochem. Soc.

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High surface area mesoporous polyaniline (M-PANI) films can be produced on the surface of glassy carbon electrodes by the electrochemical polymerization from a composite made by mixing a Brij 98 surfactant with a water solution of aniline and sulfuric acid. The surfactant serves as a structure directing agent. When the quantity of Brij 98 in the composite was 45% by weight, it formed a hexagonal phase that comprises a template of cylinders arranged on a hexagonal lattice with a hydrophilic core. The aniline monomer infiltrated the core of the templates. When the potential of the glassy carbon electrode was cycled, the polymerization occurred inside the hollow core and cast it with the PANI film. Subsequently, the Brij 98 template was removed by a thorough washing with water to produce a well-ordered M-PANI film. The structure and the surface morphology of the M-PANI films were fully characterized by a scanning electron microscope and a transmission electron microscope. The electrochemical capacitance properties were investigated using electrochemical techniques, e.g., cyclic voltammetry, galvanostatic cycling and electrochemical impedance. The data showed a significant increase in the specific capacitance (as high as 532 F g −1 ) of the M-PANI films when compared with a non M-PANI electrode, which delivered a specific capacitance of 228 F g Supercapacitors, also known as electrochemical capacitors, have attracted immense attention as one type of efficient energy storage device because of their unique capability to store and release the charge at a very high rate.1,2 Supercapacitors store electrical charges at the interface between high surface area electrodes and liquid electrolytes. The energy stored in supercapacitors comes from the non-faradaic current due to charging of the electrical double layer as well as the pseudocapacitance produced by the faradaic current, which is caused by oxidation-reduction processes that take place at the surface of the electroactive materials.3-5 Therefore, supercapacitors could store capacitances several orders of magnitude higher than conventional capacitors while still maintaining the unique advantage of a high power density and exhibiting excellent reversibility with a long life cycle. 6,7 Many materials have been used to fabricate supercapacitor electrodes, such as carbon 8 and metal oxides, e.g., RuO 2 and NiO x . 9,10Also, conducting polymers of polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), and polythiophene are widely employed as electrode materials in supercapacitor applications. 11,12 Conducting polymers mainly store energy through a faradaic current resulting from the transfer of charge between electrode and electrolyte (pseudocapacitors). The charge-transfer process is usually accompanied by electrosorption, oxidation-reduction reactions, and intercalation processes.13 When oxidation occurs, ions are transferred to the polymer backbone and, in case of reduction, the ions are released back into the solution; therefore, the charge-discharge process in con...

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Porous materials via nanocasting procedures: innovative materials and learning about soft-matter organization

Cited by 196 publications

References 104 publications

Biosilica formation in diatoms: Characterization of native silaffin-2 and its role in silica morphogenesis

Biosilica formation in diatoms: Characterization of native silaffin-2 and its role in silica morphogenesis

Cu/ZnO aggregates in siliceous mesoporous matrices: Development of a new model methanol synthesis catalyst

Mesoporous Polyaniline Films for High Performance Supercapacitors

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