Publications by authors named "Nicola Hüsing"

37 Publications

A Facile One-Pot Synthesis of Hierarchically Organized Carbon/TiO Monoliths with Ordered Mesopores.

Chempluschem 2021 Feb;86(2):275-283

Dept. of Chemistry and Physics of Materials, Paris-Lodron-University of Salzburg, Jakob-Haringer-Straße 2a, 5020, Salzburg, Austria.

Sol-gel processing combined with soft templating and gelation-induced phase separation is very sensitive to the precursor sol composition. In this work we present a straightforward synthesis towards hierarchically structured, macroporous carbon/titania monoliths with ordered mesopores derived from resorcinol/formaldehyde monoliths and a glycolated titanium precursor. We demonstrate the influence of various reaction solvents, where diol-based media and the proportion of the catalyst seem to be essential in controlling spinodal decomposition, obtaining similar monolithic structures under different synthesis conditions. Based on these observations, we further homogeneously incorporated TiO into the carbon structure by an in situ synthesis approach, obtaining structural features similar to pure carbon materials with surface areas of about 400 m  g , periodically arranged mesopores with a mean distance of 10-11 nm and cellular macroporosity.
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http://dx.doi.org/10.1002/cplu.202000740DOI Listing
February 2021

Tannin-Based Hybrid Materials and Their Applications: A Review.

Molecules 2020 Oct 23;25(21). Epub 2020 Oct 23.

Salzburg Center for Smart Materials, Jakob-Haringer-Straße 2a, 5020 Salzburg, Austria.

Tannins are eco-friendly, bio-sourced, natural, and highly reactive polyphenols. In the past decades, the understanding of their versatile properties has grown substantially alongside a continuously broadening of the tannins' application scope. In particular, recently, tannins have been increasingly investigated for their interaction with other species in order to obtain tannin-based hybrid systems that feature advanced and/or novel properties. Furthermore, in virtue of the tannins' chemistry and their high reactivity, they either physicochemically or physically interact with a wide variety of different compounds, including metals and ceramics, as well as a number of organic species. Such hybrid or hybrid-like systems allow the preparation of various advanced nanomaterials, featuring improved performances compared to the current ones. Consequently, these diverse-shaped materials have potential use in wastewater treatment or catalysis, as well as in some novel fields such as UV-shielding, functional food packaging, and biomedicine. Since these kinds of tannin-based hybrids represent an emerging field, thus far no comprehensive overview concerning their potential as functional chemical building blocks is available. Hence, this review aims to provide a structured summary of the current state of research regarding tannin-based hybrids, detailed findings on the chemical mechanisms as well as their fields of application.
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http://dx.doi.org/10.3390/molecules25214910DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660623PMC
October 2020

Monolithic Spiropyran-Based Porous Polysilsesquioxanes with Stimulus-Responsive Properties.

ACS Appl Mater Interfaces 2020 Oct 7;12(42):47754-47762. Epub 2020 Oct 7.

Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer Straße 2a, 5020 Salzburg, Austria.

Dynamic materials comprising spiropyrans have emerged as one of the most interesting and promising class of stimulus-responsive materials. Spiropyrans are often embedded in polymer matrices; their covalent attachment into porous monolithic silsesquioxane frameworks, however, is virtually unexplored. We demonstrate that a silylated spiropyran derivative can be covalently incorporated into ultralight silsesquioxane-based bulk materials by a two-step co-condensation sol-gel approach without restricting its conformational freedom and thus its stimulus-responsive properties. UV-vis measurements prove the conversion of the colorless closed-ring form of the spiropyran molecule into its highly colored purple isomer or the yellow colored protonated structure thereof. The transformation can be triggered simply by irradiation of the spiropyran-containing silsesquioxane monolith with UV or visible light or by the pH value of the chemical environment. A strong dependence of the surface polarity and water wettability on the prevalent isomer was observed. The contact angle of a water droplet on the monolithic surface can be altered from 146 to 100° by irradiation of the monolith with UV light for 3 min. Additionally, the prepared materials possess high specific surface areas, low bulk densities, and porosities of up to 84%.
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http://dx.doi.org/10.1021/acsami.0c14987DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7586299PMC
October 2020

Hierarchically organized materials with ordered mesopores: adsorption isotherm and adsorption-induced deformation from small-angle scattering.

Phys Chem Chem Phys 2020 Jun;22(22):12713-12723

Institute of Physics, Montanuniversität Leoben, Franz-Josef Strasse 18, 8700, Leoben, Austria.

In situ small angle scattering is used to study the pore filling mechanism and the adsorption induced deformation of a silica sample with hierarchical porosity upon water adsorption. The high structural order of the cylindrical mesopores on a 2D hexagonal lattice allows obtaining adsorption induced strains from the shift of the corresponding Bragg peaks measured by in situ small-angle X-ray scattering (SAXS). However, apparent strains due to scattering contrast induced changes of the Bragg peak shapes emerge in SAXS. In contrast, small-angle neutron scattering (SANS) allows determining the real adsorption induced strains by employing a H2O/D2O adsorbate with net coherent scattering length density of zero. This allows separating the apparent strains from the real strains experimentally and comparing them with strains obtained from model calculations of the SAXS intensity. It is shown that the apparent strains cannot be described at all by a simple mesopore model of film growth and capillary condensation. A hierarchical model taking the scattering of the micropores and the outer surface of the mesoporous struts in the hierarchically porous sample properly into account, together with a modified mesopore filling mechanism based on a corona model, leads to satisfactory description of both, the adsorption isotherm and the measured apparent strains as derived by SAXS.
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http://dx.doi.org/10.1039/d0cp01026jDOI Listing
June 2020

Hierarchically Organized and Anisotropic Porous Carbon Monoliths.

Chem Mater 2020 May 20;32(9):3944-3951. Epub 2020 Apr 20.

Materials Chemistry, Paris Lodron University Salzburg, Jakob-Haringer Str. 2a, Salzburg 5020, Austria.

Anisotropy is a key factor regarding mechanical or transport properties and thus the functionality of porous materials. However, the ability to deliberately design the pore structure of hierarchically organized porous networks toward anisotropic features is limited. Here, we report two straightforward routes toward hierarchically structured porous carbon monoliths with an anisotropic alignment of the microstructure on the level of macro- and mesopores. One approach is based on nanocasting (NC) of carbon precursors into hierarchical and anisotropic silica hard templates. The second route, a direct synthesis approach based on soft templating (ST), makes use of the flexibility of hierarchically structured resorcinol-formaldehyde gels, which are compressed and simultaneously carbonized in the deformed state. We present structural data of both types of carbon monoliths obtained by electron microscopy, nitrogen adsorption analysis, and SAXS measurements. In addition, we demonstrate how the degree of anisotropy can easily be controlled via the ST route.
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http://dx.doi.org/10.1021/acs.chemmater.0c00302DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7222333PMC
May 2020

Synthesis of amorphous and graphitized porous nitrogen-doped carbon spheres as oxygen reduction reaction catalysts.

Beilstein J Nanotechnol 2020 2;11:1-15. Epub 2020 Jan 2.

Chemistry and Physics of Materials, Salzburg University, A-5020 Salzburg, Austria.

Amorphous and graphitized nitrogen-doped (N-doped) carbon spheres are investigated as structurally well-defined model systems to gain a deeper understanding of the relationship between synthesis, structure, and their activity in the oxygen reduction reaction (ORR). N-doped carbon spheres were synthesized by hydrothermal treatment of a glucose solution yielding carbon spheres with sizes of 330 ± 50 nm, followed by nitrogen doping via heat treatment in ammonia atmosphere. The influence of a) varying the nitrogen doping temperature (550-1000 °C) and b) of a catalytic graphitization prior to nitrogen doping on the carbon sphere morphology, structure, elemental composition, N bonding configuration as well as porosity is investigated in detail. For the N-doped carbon spheres, the maximum nitrogen content was found at a doping temperature of 700 °C, with a decrease of the N content for higher temperatures. The overall nitrogen content of the graphitized N-doped carbon spheres is lower than that of the amorphous carbon spheres, however, also the microporosity decreases strongly with graphitization. Comparison with the electrocatalytic behavior in the ORR shows that in addition to the N-doping, the microporosity of the materials is critical for an efficient ORR.
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http://dx.doi.org/10.3762/bjnano.11.1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6964652PMC
January 2020

Furfuryl Alcohol and Lactic Acid Blends: Homo- or Co-Polymerization?

Polymers (Basel) 2019 Sep 20;11(10). Epub 2019 Sep 20.

Forest Products Technology & Timber Constructions Department, Salzburg University of Applied Sciences, Marktstraße 136a, 5431 Kuchl, Austria.

Furfuryl alcohol (FA) and lactic acid (LA) are two of the most interesting biomolecules, easily obtainable from sugars and hence extremely attractive for green chemistry solutions. These substances undergo homopolymerization and they have been rarely considered for copolymerization. Typically, FA homopolymerizes exothermically in an acid environment producing inhomogeneous porous materials, but recent studies have shown that this reaction can be controlled and therefore we have implemented this process to trigger the copolymerization with LA. The mechanical tests have shown that the blend containing small amount of FA were rigid and the fracture showed patterns more similar to the one of neat polyfurfuryl alcohol (PFA). This LA-rich blend exhibited higher chloroform and water resistances, while thermal analyses (TG and DSC) also indicated a higher furanic character than expected. These observations suggested an intimate interconnection between precursors which was highlighted by the presence of a small band in the ester region of the solid state C-NMR, even if the FT-IR did not evidence any new signal. These studies show that these bioplastics are basically constituted of PLA and PFA homopolymers with some small portion of covalent bonds between the two moieties.
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http://dx.doi.org/10.3390/polym11101533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6835956PMC
September 2019

In Situ Small-Angle Neutron Scattering Investigation of Adsorption-Induced Deformation in Silica with Hierarchical Porosity.

Langmuir 2019 Sep 22;35(35):11590-11600. Epub 2019 Aug 22.

Institute of Physics , Montanuniversitaet Leoben , Franz-Josef-Str. 18 , 8700 Leoben , Austria.

Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A HO/DO adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the water-silica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption.
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http://dx.doi.org/10.1021/acs.langmuir.9b01375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6733155PMC
September 2019

Mechanically Strong Silica-Silk Fibroin Bioaerogel: A Hybrid Scaffold with Ordered Honeycomb Micromorphology and Multiscale Porosity for Bone Regeneration.

ACS Appl Mater Interfaces 2019 May 3;11(19):17256-17269. Epub 2019 May 3.

Department of Chemistry and Physics of Materials , Paris-Lodron University of Salzburg , Jakob-Haringerstr. 2A , 5020 Salzburg , Austria.

Due to the synergic feature of individual components in hybrid (nano)biomaterials, their application in regenerative medicine has drawn significant attention. Aiming to address all the current challenges of aerogel as a potent scaffold in bone tissue engineering application, we adopted a novel synthesis approach to synergistically improve the pore size regime and mechanical strength in the aerogel. The three-dimensional aerogel scaffold in this study has been synthesized through a versatile one-pot aqueous-based sol-gel hybridization/assembly of organosilane (tetraethyl orthosilicate) and silk fibroin (SF) biopolymer, followed by unidirectional freeze-casting of the as-prepared hybrid gel and supercritical drying. The developed ultralight silica-SF aerogel hybrids demonstrated a hierarchically organized porous structure with interesting honeycomb-shaped micromorphology and microstructural alignment (anisotropy) in varied length scales. The average macropore size of the hybrid aerogel lied in ∼0.5-18 μm and was systematically controlled with freeze-casting conditions. Together with high porosity (91-94%), high Young's modulus (∼4-7 MPa, >3 order of magnitude improvement compared to their pristine aerogel counterparts), and bone-type anisotropy in the mechanical compressive behavior, the silica-SF hybrid aerogel of this study acted as a very competent scaffold for bone tissue formation. The results of in vitro assessments revealed that the silica-SF aerogel is not only cytocompatible and nonhemolytic but also acted as an open porous microenvironment to trigger osteoblast cell attachment, growth, and proliferation on its surface within 14 days of incubation. Moreover, to support the in vitro results, in vivo bone formation within the aerogel implant in the bone defect site was studied. The X-ray radiology and microcomputed tomography analyses confirmed that a significant new bone tissue density formed in the defect site within 25 days of implantation. Also, in vivo toxicology studies showed a zero-toxic impact of the aerogel implant on the blood biochemical and hematological parameters. Finally, the study clearly shows the potential of aerogel as a bioactive and osteoconductive open porous cellular matrix for a successful osseointegration process.
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http://dx.doi.org/10.1021/acsami.9b04283DOI Listing
May 2019

Novel multifunctional polymethylsilsesquioxane-silk fibroin aerogel hybrids for environmental and thermal insulation applications.

J Mater Chem A Mater 2018 Jul 12;6(26):12598-12612. Epub 2018 Jun 12.

Chemistry and Physics of Materials , Paris-Lodron University Salzburg , Jakob-Haringer-Strasse 2a , 5020 , Salzburg , Austria . Email:

The development of aerogels with improved mechanical properties, to expand their utility in high-performance applications, is still a big challenge. Besides fossil-fuel based polymers that have been extensively utilized as platforms to enhance the mechanical strength of silsesquioxane and silica-based aerogels, using green biopolymers from various sustainable renewable resources are currently drawing significant attention. In this work, we process silk fibroin (SF) proteins, extracted from silkworm cocoons, with organically substituted alkoxysilanes in an entirely aqueous based solution a successive sol-gel approach, and show for the first time that it is possible to produce homogeneous interpenetrated (IPN) polymethylsilsesquioxane (PMSQ)-SF hybrid aerogel monoliths with significantly improved mechanical properties. Emphasis is given to an improvement of the molecular interaction of the two components (SF biopolymer and PMSQ) using a silane coupling agent and to the design of pore structure. We succeeded in developing a novel class of compressible, light-weight, and hierarchically organized meso-macroporous PMSQ-SF IPN hybrid aerogels by carefully controlling the sol-gel parameters at a molecular level. Typically, these aerogels have a compressive strength () of up to 14 MPa, together with high flexibility in both compression and bending, compressibility up to 80% strain with very low bulk density () of 0.08-0.23 g cm. By considering these promising properties, the superhydrophobic/oleophilic PMSQ-SF aerogel hybrids exhibited a high competency for selective absorption of a variety of organic pollutants (absorption capacities ∼500-2600 g g %) from water and acted as a high-performance filter for continuous water/oil separation. Moreover, they have demonstrated impressive thermal insulation performance ( = 0.032-0.044 W m K) with excellent fire retardancy and self-extinguishing capabilities. Therefore, the PMSQ-SF aerogel hybrids would be a new class of open porous material and are expected to further extend the practical applications of this class of porous compounds.
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http://dx.doi.org/10.1039/c8ta02821dDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6333272PMC
July 2018

Wet Imprinting of Channel-Type Superstructures in Nanostructured Titania Thin Films at Low Temperatures for Hybrid Solar Cells.

ChemSusChem 2018 04 15;11(7):1179-1186. Epub 2018 Mar 15.

Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748, Garching, Germany.

Hierarchically structured titania films, exhibiting interconnected foam-like nanostructures and large-scale channel-type superstructures, were achieved in an energy-saving way at low temperatures by a polymer template-assisted sol-gel synthesis in combination with a wet-imprinting process. The surface morphology was probed with scanning electron microscopy and atomic force microscopy, whereas the inner morphology was characterized with grazing incidence small-angle X-ray scattering measurements. Compared to the initial hybrid films, the titania films showed reduced structure sizes caused by removal of the polymer template. UV/Vis measurements showed an additional light-scattering effect at various angles of light incidence in the hierarchically structured titania films, which resulted in higher light absorption in the wet-imprinted active layer. To give proof of viability, the titania films were evaluated as photoanodes for dye-free hybrid solar cells. The dye-free layout allowed for low-cost fabrication, avoided problems related to dye bleaching, and was a more environmentally friendly alternative to using dyes. Under different angles of light incidence, the enhancement in the short-circuit current density was in good agreement with the improvement in light absorption in the superstructured active layer, demonstrating a positive impact of the superstructures on the photovoltaic performance of hybrid solar cells.
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http://dx.doi.org/10.1002/cssc.201800129DOI Listing
April 2018

Quantifying adsorption-induced deformation of nanoporous materials on different length scales.

J Appl Crystallogr 2017 Oct 14;50(Pt 5):1404-1410. Epub 2017 Sep 14.

Institute of Physics, Montanuniversität Leoben, Franz-Josef Strasse 18, Leoben, 8700, Austria.

A new setup combining small-angle neutron scattering (SANS) and dilatometry was used to measure water-adsorption-induced deformation of a monolithic silica sample with hierarchical porosity. The sample exhibits a disordered framework consisting of macropores and struts containing two-dimensional hexagonally ordered cylindrical mesopores. The use of an HO/DO water mixture with zero scattering length density as an adsorptive allows a quantitative determination of the pore lattice strain from the shift of the corresponding diffraction peak. This radial strut deformation is compared with the simultaneously measured macroscopic length change of the sample with dilatometry, and differences between the two quantities are discussed on the basis of the deformation mechanisms effective at the different length scales. It is demonstrated that the SANS data also provide a facile way to quantitatively determine the adsorption isotherm of the material by evaluating the incoherent scattering contribution of HO at large scattering vectors.
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http://dx.doi.org/10.1107/S1600576717012274DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627682PMC
October 2017

Setting Directions: Anisotropy in Hierarchically Organized Porous Silica.

Chem Mater 2017 Sep 31;29(18):7969-7975. Epub 2017 Aug 31.

Chemistry and Physics of Materials, Paris Lodron University Salzburg, 5020 Salzburg, Austria.

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of sol-gel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the material's macroporosity is also reflected in its mechanical properties; i.e., the Young's modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy.
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http://dx.doi.org/10.1021/acs.chemmater.7b03032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627989PMC
September 2017

Enzyme adsorption-induced activity changes: a quantitative study on TiO model agglomerates.

J Nanobiotechnology 2017 Jul 21;15(1):55. Epub 2017 Jul 21.

Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg, Jakob-Haringer-Strasse 2a, 5020, Salzburg, Austria.

Background: Activity retention upon enzyme adsorption on inorganic nanostructures depends on different system parameters such as structure and composition of the support, composition of the medium as well as enzyme loading. Qualitative and quantitative characterization work, which aims at an elucidation of the microscopic details governing enzymatic activity, requires well-defined model systems.

Results: Vapor phase-grown and thermally processed anatase TiO nanoparticle powders were transformed into aqueous particle dispersions and characterized by dynamic light scattering and laser Doppler electrophoresis. Addition of β-galactosidase (β-gal) to these dispersions leads to complete enzyme adsorption and the generation of β-gal/TiO heteroaggregates. For low enzyme loadings (~4% of the theoretical monolayer coverage) we observed a dramatic activity loss in enzymatic activity by a factor of 60-100 in comparison to that of the free enzyme in solution. Parallel ATR-IR-spectroscopic characterization of β-gal/TiO heteroaggregates reveals an adsorption-induced decrease of the β-sheet content and the formation of random structures leading to the deterioration of the active site.

Conclusions: The study underlines that robust qualitative and quantitative statements about enzyme adsorption and activity retention require the use of model systems such as anatase TiO nanoparticle agglomerates featuring well-defined structural and compositional properties.
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http://dx.doi.org/10.1186/s12951-017-0283-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5521066PMC
July 2017

In Situ Measurement of Electrosorption-Induced Deformation Reveals the Importance of Micropores in Hierarchical Carbons.

ACS Appl Mater Interfaces 2017 Jul 3;9(28):23319-23324. Epub 2017 Jul 3.

Institute of Physics, Montanuniversitaet Leoben , Franz-Josef Straße 18, 8700 Leoben, Austria.

Dimensional changes in carbon-based supercapacitor electrodes were investigated using a combination of electrochemical dilatometry and in situ small-angle X-ray scattering. A novel hierarchical carbon material with ordered mesoporosity was synthesized, providing the unique possibility to track electrode expansion and shrinkage on the nanometer scale and the macroscopic scale simultaneously. Two carbons with similar mesopore structure but different amounts of micropores were investigated, employing two different aqueous electrolytes. The strain of the electrodes was always positive, but asymmetric with respect to positive and negative applied voltages. The asymmetry strongly increased with increasing microporosity, giving hints to the possible physical origin of electrosorption induced pore swelling.
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http://dx.doi.org/10.1021/acsami.7b07058DOI Listing
July 2017

Adsorption-Induced Deformation of Hierarchically Structured Mesoporous Silica-Effect of Pore-Level Anisotropy.

Langmuir 2017 06 26;33(22):5592-5602. Epub 2017 May 26.

Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey , 98 Brett Road, Piscataway, New Jersey 08854, United States.

The goal of this work is to understand adsorption-induced deformation of hierarchically structured porous silica exhibiting well-defined cylindrical mesopores. For this purpose, we performed an in situ dilatometry measurement on a calcined and sintered monolithic silica sample during the adsorption of N at 77 K. To analyze the experimental data, we extended the adsorption stress model to account for the anisotropy of cylindrical mesopores, i.e., we explicitly derived the adsorption stress tensor components in the axial and radial direction of the pore. For quantitative predictions of stresses and strains, we applied the theoretical framework of Derjaguin, Broekhoff, and de Boer for adsorption in mesopores and two mechanical models of silica rods with axially aligned pore channels: an idealized cylindrical tube model, which can be described analytically, and an ordered hexagonal array of cylindrical mesopores, whose mechanical response to adsorption stress was evaluated by 3D finite element calculations. The adsorption-induced strains predicted by both mechanical models are in good quantitative agreement making the cylindrical tube the preferable model for adsorption-induced strains due to its simple analytical nature. The theoretical results are compared with the in situ dilatometry data on a hierarchically structured silica monolith composed by a network of mesoporous struts of MCM-41 type morphology. Analyzing the experimental adsorption and strain data with the proposed theoretical framework, we find the adsorption-induced deformation of the monolithic sample being reasonably described by a superposition of axial and radial strains calculated on the mesopore level. The structural and mechanical parameters obtained from the model are in good agreement with expectations from independent measurements and literature, respectively.
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http://dx.doi.org/10.1021/acs.langmuir.7b00468DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5484557PMC
June 2017

Bovine Serum Albumin Adsorption on TiO Colloids: The Effect of Particle Agglomeration and Surface Composition.

Langmuir 2017 03 28;33(10):2551-2558. Epub 2017 Feb 28.

Department of Chemistry and Physics of Materials, Paris Lodron University of Salzburg , Jakob-Haringer-Strasse 2a, A - 5020 Salzburg, Austria.

Protein adsorption at nanostructured oxides strongly depends on the synthesis conditions and sample history of the material investigated. We measured the adsorption of bovine serum albumin (BSA) to commercial Aeroxide TiO P25 nanoparticles in aqueous dispersions. Significant changes in the adsorption capacity were induced by mild sample washing procedures and attributed to the structural modification of adsorbed water and surface hydroxyls. Motivated by the lack of information about the sample history of commercial TiO nanoparticle samples, we used vapor-phase-grown TiO nanoparticles, a well-established model system for adsorption and photocatalysis studies, and performed on this material for the first time a systematic and quantitative BSA adsorption study. After alternating vacuum and oxygen treatment of the nanoparticle powders at elevated temperatures for surface purification, we determined size distributions covering both the size of the individualized nanoparticles and nanoparticle agglomerates using transmission electron microscopy (TEM), X-ray diffraction (XRD), and dynamic light scattering (DLS) in an aqueous dispersion. Quantitative BSA adsorption measurements at different pH values and thus variable combinations of surface-charged proteins and TiO nanoparticles revealed a consistent picture: BSA adsorbs only at the outer agglomerate surfaces without penetrating the interior of the agglomerates. This process levels at coverages of single monolayers, which resist consecutive simple washing procedures. A detailed analysis of the protein-specific IR amide bands reveals that the adsorption-induced protein conformational change is associated with a decrease in the helical content. This study underlines that robust qualitative and quantitative statements about protein adsorption and corona formation require well-documented and controllable surface properties of the nanomaterials involved.
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http://dx.doi.org/10.1021/acs.langmuir.6b03785DOI Listing
March 2017

Potential of nanoparticles for allergen-specific immunotherapy - use of silica nanoparticles as vaccination platform.

Expert Opin Drug Deliv 2016 Dec 6;13(12):1777-1788. Epub 2016 Jul 6.

a Department of Molecular Biology, Division of Allergy and Immunology , University of Salzburg , Salzburg , Austria.

Introduction: Allergen-specific immunotherapy is the only curative approach for the treatment of allergies. There is an urgent need for improved therapies, which increase both, efficacy and patient compliance. Novel routes of immunization and the use of more advanced vaccine platforms have gained heightened interest in this field. Areas covered: The current status of allergen-specific immunotherapy is summarized and novel routes of immunization and their challenges in the clinics are critically discussed. The use of nanoparticles as novel delivery system for allergy vaccines is comprehensively reviewed. Specifically, the advantages of silica nanoparticles as vaccine carriers and adjuvants are summarized. Expert opinion: Future allergen-specific immunotherapy will combine engineered hypoallergenic vaccines with novel routes of administration, such as the skin. Due to their biodegradability, and the easiness to introduce surface modifications, silica nanoparticles are promising candidates for tailor-made vaccines. By covalently linking allergens and polysaccharides to silica nanoparticles, a versatile vaccination platform can be designed to specifically target antigen-presenting cells, render the formulation hypoallergenic, and introduce immunomodulatory functions. Combining potent skin vaccination methods, such as fractional laser ablation, with nanoparticle-based vaccines addresses all the requirements for safe and efficient therapy of allergic diseases.
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http://dx.doi.org/10.1080/17425247.2016.1203898DOI Listing
December 2016

Hierarchically organized silica-titania monoliths prepared under purely aqueous conditions.

Chemistry 2014 Dec 3;20(52):17409-19. Epub 2014 Nov 3.

Materials Chemistry, Paris-Lodron University Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg (Austria), Fax: (+43) 662-8044-622.

Hierarchically organized silica-titania monoliths were synthesized under purely aqueous conditions by applying a new ethylene glycol-modified single-source precursor, such as 3-[3-{tris(2-hydroxyethoxy)silyl}propyl]acetylacetone coordinated to a titanium center. The influence of the silicon- and titanium-containing single-source precursor, the novel glycolated organofunctional silane, and the addition of tetrakis(2-hydroxyethyl)orthosilicate on the formation of the final porous network was investigated by SEM, TEM, nitrogen sorption, and SAXS/WAXS. In situ SAXS measurements were performed to obtain insight into the development of the mesoporous network during sol-gel transition. IR-ATR, UV/Vis, XPS, and XAFS measurements showed that up to a Si/Ti ratio of 35:1, well-dispersed titanium centers in a macro-/mesoporous SiO2 network with a specific surface area of up to 582 m(2)  g(-1) were obtained. An increase in Ti content resulted in a decrease in specific surface area and a loss of the cellular character of the macroporous network. With a 1:1 Si/Ti ratio, silica-titania powders with circa 100 m(2)  g(-1) and anatase domains within the SiO2 matrix were obtained.
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http://dx.doi.org/10.1002/chem.201402873DOI Listing
December 2014

Membrane fuel cell cathode catalysts based on titanium oxide supported platinum nanoparticles.

Chemphyschem 2014 Jul 21;15(10):2094-107. Epub 2014 May 21.

Institute of Surface Chemistry and Catalysis, Ulm University,D-89069 Ulm (Germany).

The potential of platinum catalysts supported on pure, nitrogen-, or carbon-doped titania for application in the oxygen reduction reaction (ORR), as a cathode catalyst in polymer electrolyte membrane fuel cells, is investigated. The oxide supports are synthesized by using a sol-gel route. Modification with nitrogen and carbon doping is achieved by thermal decomposition of urea and the structure-directing agent P123. Platinum nanoparticles are prepared by reduction of a Pt(IV) salt in ethylene glycol and subsequently immobilized on different support materials. Structural and electronic properties of the support materials and the resulting catalysts are characterized by various methods, including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. These results and electrochemical characterization of the support materials and platinum nanoparticle catalysts indicate distinct support effects in the catalysts. The electrocatalytic performance of these catalysts in the ORR, as determined in rotating ring disc electrode measurements, is promising. Also here, distinct support effects can be identified. Correlations with the structural/electronic and the electrochemical properties are discussed, as well as the role of metal-support interactions.
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http://dx.doi.org/10.1002/cphc.201402019DOI Listing
July 2014

In situ modification of the silica backbone leading to highly porous monolithic hybrid organic-inorganic materials via ambient pressure drying.

ACS Appl Mater Interfaces 2014 Jan 10;6(2):1025-9. Epub 2014 Jan 10.

Bavarian Center for Applied Energy Research (ZAE Bayern) , Am Galgenberg 87, 97074 Würzburg, Germany.

We report the synthesis of monolithic porous hybrid organic-inorganic materials based on tetraethoxysilane (TEOS) and a bifunctional precursor synthesized from 3-aminopropyltriethoxysilane (APTES) and 3-glycidoxypropyltrimethoxysilane (GLYMO) via base catalysis. To compensate for the slower hydrolysis and condensation rate of the organically modified silane in basic media, it was prehydrolysed prior to adding it to the silane solution. This process leads to a lower shrinkage and stable monoliths with densities as low as 200 kg/m(3). Analysis of the samples supports the assumption that the porous monolithic materials derived via ambient pressure drying of the gels consist of a network of homogeneous hybrid primary particles. These particles are larger than their inorganic counterparts in classical silica gels and therefore the capillary forces while drying the gels at ambient pressure are reduced. This leads to less shrinkage and thus lower densities of the materials derived via ambient pressure drying. An inorganic xerogel with the same low density can be achieved by a subsequent oxidation step that decomposes the organic moieties.
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http://dx.doi.org/10.1021/am404005gDOI Listing
January 2014

Chemical phase separation strategies towards silica monoliths with hierarchical porosity.

Chem Soc Rev 2013 May 21;42(9):3833-46. Epub 2013 Mar 21.

Materials Chemistry, Paris Lodron University Salzburg, Salzburg, Austria.

In this tutorial review the preparation of monolithic silica materials with hierarchical porosity by the competing processes of sol-gel transition and chemical phase separation is summarized. Four principally different routes will be discussed in detail, including multiple micellar as well as high internal phase emulsion templating routes. Special emphasis is given to polymer-induced phase separation strategies either based on the deliberate choice of the polymer that is mixed into the gelling system or by the application of specifically designed hydrophilic silane precursors.
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http://dx.doi.org/10.1039/c3cs35345aDOI Listing
May 2013

Novel sol-gel precursors for thin mesoporous eu(3+)-doped silica coatings as efficient luminescent materials.

Chem Mater 2012 Oct 29;24(19):3674-83. Epub 2012 Aug 29.

Materials Chemistry, Paris-Lodron University Salzburg , Hellbrunner Str. 34, A-5020 Salzburg, Austria.

Europium(III) ions containing mesoporous silica coatings have been prepared via a solvent evaporation-induced self-assembly (EISA) approach of different single-source precursors (SSPs) in the presence of Pluronic P123 as a structure-directing agent, using the spin-coating process. A deliberate tailoring of the chemical composition of the porous coatings with various Si:Eu ratios was achieved by processing mixtures of tetraethylorthosilicate (TEOS) and Eu(3+)-coordinated SSPs. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that the thin metal oxide-doped silica coatings consist of a porous network with a short-range order of the pore structure, even at high europium(III) loadings. Furthermore, luminescence properties were investigated at different temperatures and different degrees of Eu(3+) contents. The photoluminescence spectra clearly show characteristic emission peaks corresponding to the (5)D0 → (7)FJ (J = 0-5) transitions resulting in a red luminescence visible by the eyes, although the films have a very low thickness (150-200 nm).
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http://dx.doi.org/10.1021/cm300996jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3597185PMC
October 2012

Low-temperature sol-gel synthesis of nanostructured polymer/titania hybrid films based on custom-made poly(3-alkoxy thiophene).

Chemphyschem 2013 Feb 10;14(3):597-602. Epub 2013 Jan 10.

Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany.

A low-temperature route to directly obtain polymer/titania hybrid films is presented. For this, a custom-made poly(3-alkoxy thiophene) was synthesized and used in a sol-gel process together with an ethylene-glycol-modified titanate (EGMT) as a suitable titania precursor. The poly(3-alkoxy thiophene) was designed to act as the structure-directing agent for titanium dioxide through selective incorporation of the titania precursor. The nanostructured titania network, embedded in the polymer matrix, is examined with atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. By means of the scattering technique grazing incidence wide-angle X-ray scattering (GIWAXS), a high degree of crystallinity of the polymer as well as successful transformation of the precursor into the rutile phase of titania is verified. UV/Vis measurements reveal an absorption behavior around 500 nm which is similar to poly(3-hexyl thiophene), a commonly used polymer for photoelectronic applications, and in addition, the typical UV absorption behavior of rutile titania is observed.
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http://dx.doi.org/10.1002/cphc.201200808DOI Listing
February 2013

Low-temperature route to crystalline titania network structures in thin films.

Chemphyschem 2012 Jun 21;13(9):2412-7. Epub 2012 May 21.

Lehrstuhl für Funktionelle Materialien, Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany.

A low temperature route to crystalline titania nanostructures in thin films is presented. The synthesis is performed by the combination of sol-gel processes, using a novel precursor for this kind of application, an ethylene glycol-modified titanate (EGMT), and the structure templating by micro-phase separation of a di-block copolymer. Different temperatures around 100 °C are investigated. The nanostructure morphology is examined with scanning electron microscopy, whereas the crystal structure and thin film compositions are examined by scattering methods. Optoelectronic measurements reveal the band-gap energies and sub-band states of the titania films. An optimum titania thin film is created at temperatures not higher than 90 °C, regarding sponge-like morphology with pore sizes of 25-30 nm, porosity of up to 71% near the sample surface, and crystallinity of titania in the rutile phase. The low temperature during synthesis is of high importance for photovoltaic applications and renders the resulting titania films interesting for future energy solutions.
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http://dx.doi.org/10.1002/cphc.201200056DOI Listing
June 2012

Nanostructured, mesoporous Au/TiO(2) model catalysts - structure, stability and catalytic properties.

Beilstein J Nanotechnol 2011 15;2:593-606. Epub 2011 Sep 15.

Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany.

Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO(2) thin-film model catalysts consisting of a thin mesoporous TiO(2) film of 200-400 nm thickness with Au nanoparticles, with a mean particle size of ~2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO(2) film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition-precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N(2) adsorption, inductively coupled plasma ionization spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO(2) supported catalysts in their characteristic structural and catalytic properties, and hence can be considered as suitable for catalytic model studies. The linear increase of the catalytic activity with film thickness indicates that transport limitations inside the Au/TiO(2) film catalyst are negligible, i.e., below the detection limit.
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http://dx.doi.org/10.3762/bjnano.2.63DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3190629PMC
August 2012

Inorganic-organic hybrid materials through post-synthesis modification: Impact of the treatment with azides on the mesopore structure.

Beilstein J Nanotechnol 2011 26;2:486-98. Epub 2011 Aug 26.

Inorganic Chemistry I, Ulm University, Albert-Einstein Allee 11, D-89081 Ulm, Germany.

Hybrid, hierarchically organized, monolithic silica gels, comprising periodically arranged mesopores and a cellular macroscopic network, have been prepared through a co-condensation reaction of tetrakis(2-hydroxyethyl)orthosilicate with chloromethyl-trimethoxysilane or 3-(chloropropyl)-triethoxysilane. Subsequent conversion of the chloro groups into azido groups, by nucleophilic substitution with NaN(3) in N,N-dimethylformamide, was conducted upon preservation of the monolithic structure. However, treatment with NaN(3) had a strong influence on the structure in the mesoporous regime, with changes such as an increase of mesopore diameter, pore volume and lattice constants, as well as a concomitant decrease of the pore wall thickness, as confirmed by small angle X-ray scattering, transmission electron microscopy, and nitrogen sorption analysis. Similar effects were observed for unmodified silica gels by simple ageing in azide-containing media, whether a relatively small or a sterically demanding counter ion (Na(+) or (H(3)C)(4)N(+)) was used. The structural modification did not seem to depend greatly on whether an organic aprotic solvent (N,N-dimethylformamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone) or a protic solvent that can form hydrogen bonds, such as water, was used.
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http://dx.doi.org/10.3762/bjnano.2.52DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3190618PMC
August 2012

TiO2 anatase nanoparticle networks: synthesis, structure, and electrochemical performance.

Small 2011 Jun 3;7(12):1690-6. Epub 2011 May 3.

ZSW-Zentrum für Sonnenenergie und Wasserstoff Forschung, Helmhotzstraße 8, 89081 Ulm, Germany.

Nanocrystalline anatase TiO(2) materials with different specific surface areas and pore size distributions are prepared via sol-gel and miniemulsion routes in the presence of surfactants. The samples are characterized by X-ray diffraction, nitrogen sorption, transmission electron microscopy, and electrochemical measurements. The materials show a pure anatase phase with average crystallite size of about 10 nm. The nitrogen sorption analysis reveals specific surface areas ranging from 25 to 150 m(2) g(-1) . It is demonstrated that the electrochemical performance of this material strongly depends on morphology. The mesoporous TiO(2) samples exhibit excellent high rate capabilities and good cycling stability.
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http://dx.doi.org/10.1002/smll.201001943DOI Listing
June 2011

Molecular approaches towards mixed metal oxides and their behaviour in mixed oxide support Au catalysts for CO oxidation.

Dalton Trans 2011 Apr 23;40(13):3269-86. Epub 2011 Feb 23.

Institute of Inorganic Chemistry I, Ulm University, D-89069, Ulm, Germany.

We herein report a water-based sol-gel approach towards porous mixed Si/Ti oxides using co-precipitated glycol-modified precursors. By adjusting synthesis parameters such as the pH value and the Si/Ti ratio of the precursor, the morphology as well as the Si/Ti-composition of the resulting mixed oxide particles can be varied in a wide range. The behaviour of the mixed oxides as substrates for Au catalysts and the performance of the resulting catalysts in the CO oxidation reaction was investigated and compared to catalysts supported on mesoporous anatase and rutile synthesized analogously. For comparable Au particle sizes and Au loadings, the composition of the mixed oxide support was found to significantly affect the reactivity and reaction behaviour, with mixed oxide supported Au catalysts synthesized at pH=5 or 10 and with a Si/Ti-ratio of 1:19 and 1:34 exhibiting the maximum activity. In contrast to the enhanced activity, the mixed oxide supports do not lead to a significant improvement in deactivation behaviour and catalyst stability.
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http://dx.doi.org/10.1039/c0dt00911cDOI Listing
April 2011

Solid-solid interface formation in TiO2 nanoparticle networks.

Langmuir 2011 Mar 25;27(5):1946-53. Epub 2011 Jan 25.

Institute of Particle Technology, Friedrich-Alexander University Erlangen-Nuremberg, Cauerstrasse 4, 91058 Erlangen, Germany.

Aiming at a comparison of microstructure and paramagnetic properties of mesoporous TiO(2) nanoparticle networks, we subjected entirely different TiO(2-x) precursor structures to vacuum annealing. The transformation of an amorphous TiO(2-x) gel--obtained by sol-gel processing of an ethylene glycol-modified titanium precursor--into a network of interconnected anatase nanocrystals was explored by means of X-ray diffraction, nitrogen sorption, and electron microscopy. Crystalline junctions between the particles emerge from temperature treatment. This process of particle network formation is different from that related to the vapor phase grown anatase nanocrystals where particle-particle interface formation is induced by contact with water. It was found that, after annealing up to 873 K and controlled sample purification in oxygen atmosphere, both types of samples exhibit high concentrations of particle-particle interfaces and comparable properties in terms of surface area, porosity, and microstructure. With electron paramagnetic resonance (EPR) we observed on nonstoichiometric TiO(2-x) networks an identical type of subsurface defect which is related to the presence of solid-solid interfaces.
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http://dx.doi.org/10.1021/la104213dDOI Listing
March 2011