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1.
Molecules ; 27(1)2022 Jan 04.
Artículo en Inglés | MEDLINE | ID: mdl-35011534

RESUMEN

A low-temperature spray deposition synthesis was developed to prepare locally hexagonally ordered mesoporous titania films with polycrystalline anatase pore walls in an evaporation-induced self-assembly process. The titania film preparation procedure is conducted completely at temperatures below 50 °C. The effects of spray time, film thickness, synthesis time prior to spray deposition, and aging time at high relative humidity after deposition on the atomic arrangement and the mesoorder of the mesoporous titania were studied. We find the crystallite size to depend on both the synthesis time and aging time of the films, where longer times result in larger crystallites. Using the photocatalytic activity of titania, the structure-directing agent is removed with UV radiation at 43-46 °C. The capability of the prepared films to remove the polymer template increased with longer synthesis and aging times due to the increased crystallinity, which increases the photocatalytic efficiency of the titania films. However, with increasingly longer times, the crystallites grow too large for the mesoorder of the pores to be maintained. This work shows that a scalable spray coating method can be used to prepare locally ordered mesoporous polycrystalline titania films by judiciously tuning the synthesis parameters.

2.
Inorg Chem ; 60(22): 16977-16985, 2021 Nov 15.
Artículo en Inglés | MEDLINE | ID: mdl-34730983

RESUMEN

Recently, there has been an increased interest in quaternary clathrate systems as promising thermoelectric materials. Because of their increased complexity, however, the chemical ordering in the host framework of quaternary clathrates has not yet been comprehensively analyzed. Here, we have synthesized a prototypical quaternary type-I clathrate Ba8AlxGa16-xGe30 by Czochralski and flux methods, and we employed a combination of X-ray and neutron diffraction along with atomic scale simulations to investigate chemical ordering in this material. We show that the site occupancy factors of trivalent elements at the 6c site differ, depending on the synthesis method, which can be attributed to the level of equilibration. The flux-grown samples are consistent with the simulated high-temperature disordered configuration, while the degree of ordering for the Czochralski sample lies between the ground state and the high-temperature state. Moreover, we demonstrate that the atomic displacement parameters of the Ba atoms in the larger tetrakaidecahedral cages are related to chemical ordering. Specifically, Ba atoms are either displaced toward the periphery or localized at the cage centers. Consequently, this study reveals key relationships between the chemical ordering in the quaternary clathrates Ba8AlxGa16-xGe30 and the structural properties, thereby offering new perspectives on designing these materials and optimizing their thermoelectric properties.

4.
Langmuir ; 36(9): 2357-2367, 2020 Mar 10.
Artículo en Inglés | MEDLINE | ID: mdl-32075376

RESUMEN

In this study, the emulsification performance of functionalized colloidal silica is explored with the aim to achieve phase inversion of particle-stabilized (Pickering) emulsion systems. An increased understanding of inversion conditions can facilitate surfactant-free emulsion fabrication and expand its use in industrial applications. Phase inversion was achieved by adjusting the temperature but without changing the composition of the emulsion formulation. Silica nanoparticles modified with hydrophobic propyl groups and hydrophilic methyl poly(ethylene)glycol (mPEG) groups are used as emulsifiers, enabling control of the wettability of the particles and exploration of phase inversion phenomena, the latter due to the thermoresponsiveness of the attached PEG chains. The phase inversion conditions as well as the reversibility of the emulsion systems were examined at varying electrolyte concentrations and pH values of the suspensions. Transitional phase inversions, from oil-in-water and water-in-oil and back, were observed in functionalized silica particle-stabilized butanol emulsions at distinct temperatures. The phase inversion temperature was affected by electrolyte concentration and pH conditions due to salting-out effects, PEG-silica interactions, and the effects of the particle surface charge. Investigations of phase inversion conditions, temperature, and hysteresis effects in Pickering emulsions can improve the theoretical understanding of these phenomena and facilitate the implementation of low-energy emulsion preparation.

5.
Phys Chem Chem Phys ; 20(36): 23202-23213, 2018 Sep 19.
Artículo en Inglés | MEDLINE | ID: mdl-29947366

RESUMEN

Fluorescence spectroscopy of protein-bound molecular rotors Cy3 and Cy5 is used to monitor the effective viscosity inside the pores of two types of mesoporous silica (SBA-15 and MCF) with pore diameters between 8.9 and 33 nm. The ratio of the peak intensities is used to measure viscosity independently of solvent polarity, and the response of the lipase-bound dyes is calibrated using glycerol/water mixtures (no particles). The two dyes are either attached to the same protein or separate proteins in order to investigate potential effects of energy transfer (FRET) on the fluorescence properties, when using them as reporter dyes. The effective viscosity inside the pores at infinite protein dilution is one order of magnitude higher than in bulk water, and the effect of protein concentration on the measured viscosity indicates a stronger effect of protein-protein interactions in the pores than in similarly concentrated protein solutions without particles. In MCF-particles with octyl-groups covalently attached to the pore walls, a more efficient uptake of the lipase resulted in FRET between the protein-bound dyes even if the two dyes were attached to different proteins. In contrast to the unmodified particles the intensity-ratio method could therefore not be used to measure the viscosity, but the presence of FRET in itself indicates that octyl-protein interactions lead to a non-homogenous protein distribution in the pores. The dye labels also report a less polar pore environment as sensed by the proteins through a redshift in the dye emission. Both observations may help in understanding the higher efficiency of lipase immobilization in octyl-modified particles.


Asunto(s)
Colorantes Fluorescentes/química , Lipasa/química , Dióxido de Silicio/química , Transferencia Resonante de Energía de Fluorescencia , Glicerol/química , Lipasa/metabolismo , Estructura Molecular , Porosidad , Espectrometría de Fluorescencia , Viscosidad , Agua/química
6.
Phys Chem Chem Phys ; 19(35): 23878-23886, 2017 Sep 13.
Artículo en Inglés | MEDLINE | ID: mdl-28816320

RESUMEN

Core-shell microcapsules consisting of a titanium dioxide shell and a hydrophobic solvent core have been prepared with diameters of a few micrometers and a narrow size distribution using a simple and fast airbrush technique. These microcapsules were prepared at room temperature in a single-step process in which an oil with a dissolved titanium alkoxide precursor was forced together with an aqueous solution, containing a surface-active polymer, through a narrow spray nozzle using a nitrogen gas propellant. Several different parameters of chemical, physical, and processing origin were investigated to find an optimal recipe. Two different alkanes, one ketone, and four alcohols were tested and evaluated as core materials, alone or together with the antifungal biocide 2-n-octyl-4-isothiazolin-3-one (OIT). Long-chain alcohols were found suitable as core oil due to their low solubility in water and surface activity. The addition of the surface-active polymers in the water phase was important in aiding the formation and stabilization of the titanium dioxide shell. An impressive loading of 50 wt% of the semi-hydrophobic OIT was possible to encapsulate using this simple and applicable procedure.

7.
ACS Appl Mater Interfaces ; 14(18): 20349-20357, 2022 May 11.
Artículo en Inglés | MEDLINE | ID: mdl-34590838

RESUMEN

Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g-1 charging rate and fast discharge rate produces the best overall performance.

8.
Langmuir ; 26(3): 1983-90, 2010 Feb 02.
Artículo en Inglés | MEDLINE | ID: mdl-20041679

RESUMEN

The interaction between silica and poly(ethylene oxide) (PEO) in water may appear trivial and it is generally stated that hydrogen bonding is responsible for the attraction. However, a literature search shows that there is not a consensus with respect to the mechanism behind the attractive interaction. Several papers claim that only hydrogen bonding is not sufficient to explain the binding. The silica-PEO interaction is interesting from an academic perspective and it is also exploited in the preparation of mesoporous silica, a material of considerable current interest. This study concerns the very early stage of synthesis of mesoporous silica under mild acidic conditions, pH 2-5, and the aim is to shed light on the interaction between silica and the PEO-containing structure directing agent. The synthesis comprises two steps. An organic silica source, tetraethylorthosilicate (TEOS), is first hydrolyzed and Pluronic P123, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, is subsequently added at different time periods following the hydrolysis of TEOS. It is shown that the interaction between the silica and the Pluronic is dependent both on the temperature and on the time between onset of TEOS hydrolysis and addition of the copolymer. The results show that the interaction is mainly driven by entropy. The effect of the synthesis temperature and of the time between hydrolysis and addition of the copolymer on the final material is also studied. The material with the highest degree of mesoorder was obtained when the reaction was performed at 20 degrees C and the copolymer was added 40 h after the start of TEOS hydrolysis. It is claimed that the reason for the good ordering of the silica is that whereas particle formation under these conditions is fast, the rate of silica condensation is relatively low.

9.
RSC Adv ; 10(34): 20279-20287, 2020 May 26.
Artículo en Inglés | MEDLINE | ID: mdl-35520456

RESUMEN

Ordered mesoporous titania, prepared via low-temperature spray deposition, was examined as an anode material for lithium ion batteries. The material exhibits an exceptionally high electrochemical capacity of 680 mA h g-1 during the first discharge, which rapidly decreases over the following cycles. The capacity stabilizes at around 170 mA h g-1 after 50 cycles and the material delivers 83 mA h g-1 at high charge/discharge rates (10C). A combination of electrochemical and structural characterization techniques were used to study the charge/discharge behavior of the material and the origin of the irreversible capacity. To determine the effect of cycling on the structure of the material, X-ray absorption spectroscopy (XAS) and energy filtered TEM were carried out on pristine and cycled samples in intercalated and deintercalated states. Titanium K-edge XAS measurements showed that intercalated lithium affects the NEXAFS region. By comparing peak intensity ratios, we propose a method to quantify the amount of lithium inserted into the titania structure and to differentiate between lithium bound in close proximity to titanium, and lithium bound further away from titanium. Additionally, we suggest that the irreversible loss in capacity is due to the formation of phases that are stable, and thereby electrochemically inactive, over the electrochemical cycling conditions applied.

10.
RSC Adv ; 10(60): 36459-36466, 2020 Oct 01.
Artículo en Inglés | MEDLINE | ID: mdl-35517959

RESUMEN

A novel template-free colloidal assembly method that combines colloidal zeolite (silicalite-1) suspensions in a water-in-oil emulsion with an evaporation-induced assembly process has been developed for preparing hierarchical micro-/mesoporous zeolite microspheres (MZMs). Such particles have an interconnected mesoporosity and large mesopore diameters (25-40 nm) combined with 5.5 Å diameter micropores of the zeolite nanoparticles. The method developed has the advantages of employing mild synthesis conditions, a short preparation time, and not requiring the use of a mesoporogen template or post-treatment methods. The method provides a new range of micro-/mesoporous zeolites with tunable mesoporosity dictated by the size of the zeolite nanoparticles. It also offers the possibility of combining several zeolite particle sizes or optionally adding amorphous silica nanoparticles to tune the mesopore size distribution further. It should be generally applicable to other types of colloidal zeolite suspensions (e.g. ZSM-5, zeolite A, beta) and represents a new route amenable for cost-effective scale-up.

11.
RSC Adv ; 9(23): 13297-13303, 2019 Apr 25.
Artículo en Inglés | MEDLINE | ID: mdl-35520810

RESUMEN

Temperature-dependent phase-separation, clouding, has been observed in suspensions of silica nanoparticles surface-functionalized with methyl-poly(ethylene glycol) silane. Interparticle interactions and conformational changes of the grafted poly(ethylene glycol) chains influence the observed cloud points, and can be controlled by electrolyte concentration and pH. These findings open new routes to tailoring properties of Pickering emulsions.

12.
Adv Mater ; 31(2): e1805392, 2019 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-30407664

RESUMEN

Designing alloys with an accurate temperature-independent electrical response over a wide temperature range, specifically a low temperature coefficient of resistance (TCR), remains a big challenge from a material design point of view. More than a century after their discovery, Constantan (Cu-Ni) and Manganin (Cu-Mn-Ni) alloys remain the top choice for strain gauge applications and high-quality resistors up to 473-573 K. Here, an average TCR is demonstrated that is up to ≈800 times smaller in the temperature range 5-300 K and >800 times smaller than for any of these standard materials over a wide temperature range (5 K < T < 1200 K). This is achieved for selected compositions of Alx CoCrFeNi high-entropy alloys (HEAs), for which a strong correlation of the ultralow TCR is established with the underlying microstructure and its local composition. The exceptionally low electron-phonon coupling expected in these HEAs is crucial for developing novel devices, e.g., hot-electron detectors, high-Q resonant antennas, and materials in gravitational wave detectors.

13.
ACS Omega ; 4(18): 17662-17671, 2019 Oct 29.
Artículo en Inglés | MEDLINE | ID: mdl-31681872

RESUMEN

Doping carbon materials with transition metal ions can greatly expand their utility, given these metal ions' unique catalytic activity, for example, in oxygen reduction in proton exchange membrane fuel cells. Unlike main group dopants, a counter anion to the metal cation must be selected and this choice has hitherto received little attention for this synthesis method. Herein, we describe the profound effects that the anion has on the resultant iron/nitrogen-doped ordered mesoporous carbons (Fe-OMC). To increase the iron loading and the number of iron-centered catalytically active sites, we selected three iron salts Fe(OAc)2, Fe(OTf)2, and Fe(BF4)2·6H2O, which show greatly enhanced solubility in the liquid carbon precursor (furfurylamine) compared to FeCl3·6H2O. The increased solubility leads to a significantly higher iron loading in the Fe-OMC prepared with Fe(OTf)2, but the increase in performance as cathode catalysts in fuel cells is only marginal. The Fe-OMCs prepared with Fe(OAc)2 and Fe(BF4)2·6H2O exhibited similar or lower iron loadings compared to the Fe-OMC prepared with FeCl3·6H2O despite their much higher solubilities. Most importantly, the different iron salts affect not only the final iron loading, but also which type of iron species forms in the Fe-OMC with different types showing different catalytic activity.

14.
ACS Appl Mater Interfaces ; 11(43): 40424-40431, 2019 Oct 30.
Artículo en Inglés | MEDLINE | ID: mdl-31593430

RESUMEN

Microporous (<2 nm) crystalline aluminosilicates in the form of zeolites offer a great potential as efficient adsorbents for atmospheric CO2 in the eminent battle against global warming and climate change. The processability of conventional zeolite powders is, however, poor, which limits their implementation in many applications, such as in gas filtration industrial systems. In this work, we overcome this issue through the preparation of hybrid foams using mesoporous/macroporous supporting materials based on the strong network properties of gelatin/nanocellulose, which can support ultrahigh loadings of silicalite-1, used as a model sorbent nanomaterial. We achieved up to 90 wt % of zeolite content and a microporous/mesoporous/macroporous hybrid material. The application of hybrid foams for selective CO2 sorption exhibits a linear relationship between the zeolite content and CO2 adsorption capacity and high selectivity over N2, where the gelatin/nanocellulose foam efficiently supports the zeolite crystals without apparently blocking their pores.

15.
ACS Omega ; 4(3): 5750-5757, 2019 Mar 31.
Artículo en Inglés | MEDLINE | ID: mdl-31459727

RESUMEN

Evolution of the polymorph selectivity of titanium dioxide was studied under acidic and low-temperature synthesis conditions. Short synthesis times resulted in high relative amounts of the rutile phase, and long synthesis times resulted in high relative amounts of the brookite and anatase phases. The effect of titania precursor concentration was investigated and found to have a large impact on the polymorph selectivity. As the reaction proceeds with time, changes in the chemical environment, caused in particular by the gradually decreasing titania precursor concentration, are therefore likely the cause of the change in polymorph selectivity observed.

16.
Colloids Surf B Biointerfaces ; 163: 41-46, 2018 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-29274566

RESUMEN

Formaldehyde dehydrogenase (FaldDH) is used as a catalyst to reduce formate to formaldehyde in a cascade reaction to convert CO2 to methanol. This enzyme, however, has low activity and is sensitive to substrate/product concentration and pH. To improve the performance of FaldDH, it can be immobilized through physical adsorption in siliceous mesostructured cellular foams (MCF), which physical properties are suitable for the immobilization of large molecules as FaldDH (molecular size of 8.6 × 8.6 × 19 nm). In this work two MCF materials were synthesized: MCF1 with a pore size of 26.8 nm and window size of 10.5 nm; and MCF2 with a pore size of 32.9 nm and window size of 13.0 nm. The surfaces of the materials were functionalized with octyl, mercaptopropyl or chloromethyl groups. FaldDH was successfully immobilized inside all the materials, yielding enzyme loadings of about 300 mg g-1 in MCF1 and more than 750 mg g-1 in MCF2. However, the enzyme was inactive upon immobilization on MCF1, whereas on MCF2 the enzyme retained its catalytic activity presumably owing to the larger pores of this material and the need for the enzyme to undergo configurational changes during the reaction. Using MCF2 functionalized with mercaptopropyl groups the activity of FaldDH was enhanced beyond that of the free enzyme. Additionally, low leakage of the enzyme from the MCF2 was observed during the reactions. Thus, tailored MCF is a highly attractive material for employment of the FaldDH enzyme.


Asunto(s)
Aldehído Oxidorreductasas/química , Proteínas Bacterianas/química , Enzimas Inmovilizadas/química , Formaldehído/química , Formiatos/química , Adsorción , Aldehído Oxidorreductasas/aislamiento & purificación , Proteínas Bacterianas/aislamiento & purificación , Biocatálisis , Dióxido de Carbono/química , Pruebas de Enzimas , Enzimas Inmovilizadas/aislamiento & purificación , Concentración de Iones de Hidrógeno , Cinética , Metanol/química , Porosidad , Pseudomonas/química , Pseudomonas/enzimología , Dióxido de Silicio/química
17.
J Colloid Interface Sci ; 305(1): 204-8, 2007 Jan 01.
Artículo en Inglés | MEDLINE | ID: mdl-17069827

RESUMEN

Platinum nanoparticles were incorporated within the pore system of ordered mesoporous carbon (OMC) by impregnating the carbon with a water-in-oil (w/o) microemulsion containing dissolved platinum salt followed by reduction of the platinum ions in situ inside the carbon pore system. The procedure provides preparation of metallic nanoparticles from hydrophilic precursors inside the hydrophobic carbon support structure with simultaneous control of the maximum metal particle size. Electron tomography was used to verify the presence of platinum nanoparticles inside the carbon material.

18.
J Colloid Interface Sci ; 487: 250-257, 2017 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-27776283

RESUMEN

Colloidal silica particles, functionalized with hydrophilic and hydrophobic groups, have been studied for utilization in particle-stabilized emulsions, so called Pickering emulsions. The amounts of attached groups have been characterized using NMR spectroscopy and elemental analysis. A range of particles were prepared, with sizes from around 13 to 70nm in diameter. Hydrophilic functionalization of the silica sols was achieved by attaching methyl poly(ethylene glycol) (mPEG) silane to the silica particle surface. This provides a reduction of surface charge density, a pH dependent and controllable flocculation behavior and surface activity. The hydrophobic functionalization of the silica sols was accomplished by attaching organosilanes containing mainly propyl and methyl groups. The emulsification abilities were evaluated by preparing Pickering emulsions using particles, with varying degrees and combinations of surface functionalization, as stabilizers and comparing the obtained emulsion droplet size distributions. It was found that colloidal silica functionalized with hydrophobic groups produced emulsions with smaller droplets compared to using unmodified silica. The emulsification performance was further improved by the combination of both hydrophilic and hydrophobic groups. All particles having this heterogeneous modification were found to generate emulsions with high stability towards coalescence (from five weeks to 1.5 years).

19.
Bioresour Technol ; 239: 57-65, 2017 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-28501686

RESUMEN

The immobilisation of four feruloyl esterases (FAEs) (FaeA1, FaeA2, FaeB1, FaeB2) from the thermophilic fungus Myceliophthora thermophila C1 was studied and optimised via physical adsorption onto various mesoporous silica particles with pore diameters varying from 6.6nm to 10.9nm. Using crude enzyme preparations, enrichment of immobilised FAEs was observed, depending on pore diameter and protein size. The immobilised enzymes were successfully used for the synthesis of butyl ferulate through transesterification of methyl ferulate with 1-butanol. Although the highest butyl ferulate yields were obtained with free enzyme, the synthesis-to-hydrolysis ratio was higher when using immobilised enzymes. Over 90% of the initial activity was observed in a reusability experiment after nine reaction cycles, each lasting 24h. Rinsing with solvent to remove water from the immobilised enzymes further improved their activity. This study demonstrates the suitability of immobilised crude enzyme preparations in the development of biocatalysts for esterification reactions.


Asunto(s)
Hidrolasas de Éster Carboxílico , Sordariales , Enzimas Inmovilizadas , Dióxido de Silicio , Solventes
20.
J Phys Chem B ; 110(37): 18392-400, 2006 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-16970463

RESUMEN

This study focuses on the mechanism of lean NO(2) reduction by hydrocarbons (propane, propene, and isobutane) over HZSM-5. In-situ FTIR measurements indicate a close correlation between formation of isocyanate species, consumption of water (formed in the reaction), and formation of amine species. The results in this investigation confirm our previously suggested reaction mechanism, which involves reaction of NO(+) species and hydrocarbon-derived species over Brønsted acid sites, forming isocyanate species. These species are hydrolyzed by water, forming amine species and, finally, N(2). Experiments with (18)O(2) show an enhanced oxidation of propane by oxygen, in the presence of NO(2). This effect can possibly be explained by a type of reaction mechanism where gas-phase and/or loosely bound NO(2) react with the adsorbed hydrocarbon-derived species (i.e., carbenium ion adsorbates and/or alkenes), which then more easily react with oxygen.

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