Müller, Magdalena

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Additive-controlled synthesis of monodisperse single crystalline gold nanoparticles : interplay of shape and surface plasmon resonance

2020-08-13, Kirner, Felizitas, Potapov, Pavel, Schultz, Johannes, Geppert, Jessica, Müller, Magdalena, Gonzalez-Rubio, Guillermo, Sturm, Sebastian, Lubk, Axel, Sturm, Elena V.

We introduce a three-step seed-mediated synthesis for single crystalline gold nanoparticles (Au NPs) stabilized by hexadecylpyridinium chloride (CPC) in variable sizes with an independently adjustable ratio of the cubic and octahedral facets. The effect of KBr and ascorbic acid (AA) on shape and growth kinetics is systematically investigated. The kinetic data were evaluated using the minimalistic Finke–Watzky autocatalytic two-step mechanism, which allows to estimate the rate constants of the “pseudoelementary” reactions. The proposed surface-mediated mechanism of reduction of gold ions and Au NP growth allows to explain the effect of gradual increase of bromide ion concentration on switching the Au NP morphology from cubic to octahedral. The plasmonic properties of single particles of different facetings and their assemblies are investigated.

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Versatile surface modification of aerogels by click chemistry as an approach to generate model systems for CO2 adsorption features in amine-containing organosilica

2020-03, Klinkenberg, Nele, Klaiber, Alexander, Müller, Magdalena, Polarz, Sebastian

The conversion of waste into valuable products is most appealing in the case of CO2, a molecule which is produced in mass by our society and industries. Because its atmospheric concentration correlates to climate change and the green-house effect, major efforts are on the way to reduce the emission of CO2. One promising strategy is the separation of CO2 from the gas-phase (e.g. flue gases) by solid-adsorbents containing amine moieties. The synthesis of tailor-made adsorbents with changing surface properties remains a challenge. This work presents a click chemistry approach that enables the easy modification of organosilica materials with functional groups that can be used as model systems to study the influence of surface chemistry on CO2 adsorption. As an example, the modification of the materials with primary amines is discussed in detail but furthermore the approach offers the possibility to tailor the surface properties using any desired functional group. The increased affinity of the used copper catalyst introduced some difficulties but we were able to remove all remains of copper. With this approach, we were able to synthesize materials with different degrees of functionalization up to 80%. This approach for the development of new carbon capture model systems offers high functionalization combined with the flexibility of a post-functionalization approach. Thus, surface chemistry can be tailored to study the influence of surface chemistry on CO2 adsorption. As an example for the model character of our materials, we could show that the heat of adsorption can be tuned by systematically varying the degree of amine functionalization.