All-inorganic core-shell silica-titania mesoporous colloidal nanoparticles showing orthogonal functionality

Colloidal mesoporous silica (CMS) nanoparticles with a thin titania-enriched outer shell showing a spatially resolved functionality were synthesized by a delayed co-condensation approach. The titaniashell can serve as a selective nucleation site for the growth of nanocrystalline anatase clusters. These fully inorganic pure silica-core titania-enriched shell mesoporous nanoparticles show orthogonal functionality, demonstrated through the selective adsorption of a carboxylate-containing ruthenium N3-dye. UV-Vis and fluorescence spectroscopy indicate the strong interaction of the N3-dye with the titania-phase at the outer shell of the CMS nanoparticles. In particular, this interaction and thus the selective functionalization are greatly enhanced when anatase nanocrystallites are nucleated at the titania-enriched shell surface

Colloidal Porous Nanoparticles

Colloidal porous hosts in the form of microporous aluminosilicate (zeolite) or mesoporous silica nanoparticles are attractive materials for a wide range of potential applications, i.e. controlled release drug delivery systems. However, many fundamental challenges still remain in this relatively young research field. The following work focuses on overcoming some of the present limitations by developing new concepts for the synthesis and functionalization of porous nanoparticles. The number of zeolite structures available for the synthesis of stable colloidal suspensions is very limited when compared to the large number of known frameworks in bulk materials. A novel class of zeolite templates in the form of metal ammines was developed by taking advantage of the unique synthesis conditions typical in colloidal zeolite systems, i.e. low temperatures and low alkalinity. Square planar copper(II) tetraammine complexes were employed as co-templates in the synthesis of nanosized EDI-type molecular sieves. It was shown that the complexes are the key elements responsible for formation and growth of the zeolite nanoparticles, and their role in the crystallization process was thoroughly investigated. Substitution of the copper complexes by isostructural palladium and platinum species was demonstrated. By employing templates with similar shapes but different effects on the nucleation rate it was possible to drastically decrease the particle size by several factors in comparison to previously known colloidal zeolite systems and to generate stable suspensions of non-agglomerated EDI-type nanocrystals with diameters below 20 nm. The size and morphology of mesoporous silica nanoparticles was controlled by co-condensation with additives, i.e. phenyltriethoxysilane, and subsequent simultaneous removal of the functional groups and template molecules by oxidation with hydrogen peroxide in a simple one-pot reaction. Conversion of colloidal mesoporous silica systems with metalorganic reagents was demonstrated. The key step for avoiding particle agglomeration and coalescence processes involves the removal of water from the mesopores at temperatures below 90 °C either by hydrolysis of triethyl orthoformate or by vapour adsorption from the gas phase. In a joint project with Alexander Darga from our group, thin films of different phenyl-substituted mesoporous silica nanoparticles were deposited on quartz crystal microbalance chips in order to probe the intrapore surfaces by toluene sorption. It was shown that samples prepared by grafting and co-condensation approaches bearing similar surface densities of functional groups display considerably different toluene heats of adsorption. Furthermore, a novel concept for the selective functionalization of mesoporous silica nanoparticles was developed. By using a time-delayed co-condensation approach, functional groups can be completely dispersed inside the channels, concentrated in parts of the mesopores, or exclusively placed on the external surface depending on the time of addition. Aminopropyl was used as a representative functionality in order to determine the density of functional groups on the outer surface via zeta potential measurements. Staining with iridium cations and subsequent scanning transmission electron microscopy studies allowed the visualization of metal clusters with different radial distributions depending on the addition time of the organosilane component. In contrast to grafting approaches, it was possible to easily adjust the concentration of functional groups on the outer surface by variation of the organosilane to silane ratio

Marlen Haushofer: Recollections of Crime and Complicity

This essay wants to introduce readers to one of Austria\u27s most astute women writers of the immediate postwar period. Marlen Haushofer, in contrast to her contemporary Ingeborg Bachmann, has not (yet) gained international renown despite her literary craftsmanship. Looking at those works of her that most poignantly thematize the postwar reaction to the years of National Socialism and deal with the issues of guilt and responsibility, I focus on Haushofer\u27s gendered perspective on the roles of victim, perpetrator, and bystander as played out in the seemingly apolitical microcosm of the family. The essay consists of an introductory discussion of the relevant political-historical context, a brief commentary on two thematically related short stories, and an analysis of the novella Wir töten Stella. In her scathing portrait of femininity in the patriarchal order of the fifties, Haushofer condemns women as accomplices in the perpetuation of corrupt structures and strategies of domination. She points to women\u27s subordination and conspiracy of silence about evil-doing as powerful factors in the perpetuation of destruction. The metaphorical representation of Austrians\u27 collective effort to forget their participation in Nazi crimes may be regarded as a gendered writing strategy allowing Haushofer to appear harmless and thus acceptable to her contemporaries

Revival of the Cover Letter? Experimental Evidence on the Performance of AI-driven Personality Assessments

Organizations have long been trying to assess job applicants\u27 personality using self-reported psychometric tests, such as the Big Five personality test. However, these tests are not robust against incentives to pretend having certain desirable traits, for example, the disposition for being a good team player. We test whether machine learning classifiers trained on written self-descriptions, such as cover letters, predict people\u27s true cooperativeness better than psychometric tests. Based on data from a controlled online experiment with 400 participants, we find that - when people have incentives to fake their personality - linguistic classifiers based on self-descriptions significantly outperform psychometric classifiers based on the Big Five. Moreover, we find that a fine-tuned, pre-trained natural language model can detect incentives to fake in people\u27s self-descriptions. While further research is needed to achieve tamper-proof models, our findings illustrate the potential of automated personality tests based on job applicants\u27 cover letters

Marlen Haushofer: Recollections of Crime and Complicity

This essay wants to introduce readers to one of Austria's most astute women writers of the immediate postwar period. Marlen Haushofer, in contrast to her contemporary Ingeborg Bachmann, has not (yet) gained international renown despite her literary craftsmanship. Looking at those works of her that most poignantly thematize the postwar reaction to the years of National Socialism and deal with the issues of guilt and responsibility, I focus on Haushofer's gendered perspective on the roles of victim, perpetrator, and bystander as played out in the seemingly apolitical microcosm of the family. The essay consists of an introductory discussion of the relevant political-historical context, a brief commentary on two thematically related short stories, and an analysis of the novella Wir töten Stella . In her scathing portrait of femininity in the patriarchal order of the fifties, Haushofer condemns women as accomplices in the perpetuation of corrupt structures and strategies of domination. She points to women's subordination and conspiracy of silence about evil-doing as powerful factors in the perpetuation of destruction. The metaphorical representation of Austrians' collective effort to forget their participation in Nazi crimes may be regarded as a gendered writing strategy allowing Haushofer to appear harmless and thus acceptable to her contemporaries

Protocol optimization for the mild detemplation of mesoporous silica nanoparticles resulting in enhanced texture and colloidal stability

Porosity development of mesostructured colloidal silica nanoparticles is related to the removal of the organic templates and co-templates which is often carried out by calcination at high temperatures, 500-600 °C. In this study a mild detemplation method based on the oxidative Fenton chemistry has been investigated. The Fenton reaction involves the generation of OH radicals following a redox Fe3+/Fe2+ cycle that is used as catalyst and H2O2 as oxidant source. Improved material properties are anticipated since the Fenton chemistry comprises milder conditions than calcination. However, the general application of this methodology is not straightforward due to limitations in the hydrothermal stability of the particular system under study. The objective of this work is three-fold: 1) reducing the residual Fe in the resulting solid as this can be detrimental for the application of the material, 2) shortening the reaction time by optimizing the reaction temperature to minimize possible particle agglomeration, and finally 3) investigating the structural and textural properties of the resulting material in comparison to the calcined counterparts. It appears that the Fenton detemplation can be optimized by shortening the reaction time significantly at low Fe concentration. The milder conditions of detemplation give rise to enhanced properties in terms of surface area, pore volume, structural preservation, low Fe residue and high degree of surface hydroxylation; the colloidal particles are stable during storage. A relative particle size increase, expressed as 0.11%·h-1, has been determined

Imidazolium-based titanosilicate nanospheres as active catalysts in carbon dioxide conversion:Towards a cascade reaction from alkenes to cyclic carbonates

Porous silica-based nanospheres bearing titanium centres as single site were successfully synthesized employing a time- and energy-efficient procedure. The influence of the post-synthesis treatment on the insertion of Ti was investigated via DR UV-Vis and XPS spectroscopy and the titanium content was quantified through ICP-OES analysis. The textural and structural properties of the different solids were evaluated via XRD, TEM and N2 physisorption. The resulting materials were thereafter covalently functionalized with imidazolium chloride, followed by characterization via 29Si and 13C solid-state NMR, N2 physisorption and chemical combustion analysis. The bi-functional catalysts were tested in the challenging conversion of CO2 with cyclohexene oxide to the corresponding cyclic carbonate as well as with various other epoxides with excellent results. The insertion of Ti as single site played a key role substantially improving the activity of the solids. The most active bi-functional material was successfully recovered and reused through multiple cycle without loss of the catalytic activity. Moreover, the cyclohexene epoxidation reaction was tested as well employing the mono-functionalized Ti-based material. The catalytic mixture, composed by the mono-functional and bi-functional solids, was efficiently used to convert the cyclohexene into cyclohexene oxide and subsequently the cyclohexene oxide into the corresponding carbonate thus opening the prospect for a cascade reaction