2022, Sutter, Sebastian, Grings, Jonas, Boldt, Klaus

We present a highly chemoselective deposition of precious metals on semiconductor nanoheterostructures with a strong preference for cadmium and zinc telluride over the lighter chalcogenides. The selectivity is explained by p-type surface traps on the tellurides, compared to n-type defects of the homologous sulfides and selenides, and can be turned off by passivating the particle surface. The results give insight into the nature and role of surface defects for semiconductor nanocrystals. The fast formation of many, small metal seeds leads to aggregation of the particles into star-shaped or branched superstructures, leaving the rest of the semiconductor surface exposed. It provides a preparative route toward complex, yet well-defined semiconductor-metal hybrid structures with potential application in photocatalysis.

2019-10-28, Kunkel, Marius, Sutter, Sebastian, Polarz, Sebastian

Das natürliche Blatt ist ein Paradebeispiel für ein System, das kontinuierlich Wertschöpfung betreibt, indem es z. B. CO2 in Zucker umwandelt. Wichtigster Bestandteil sind die gekoppelten Photosysteme II und I, die in der Zellmembran eingebettet sind. Können ihre Schlüsselfunktionen auf ein Tensid übertragen werden? Wir stellen moderne Tenside vor, die sich zu zweischichtigen Vesikeln anordnen (ähnlich der Zellmembran), fähig sind, Photonen verschiedener Wellenlängen zu absorbieren und angeregte Ladungsträger auszutauschen (ähnlich zu Photosystem II und I), sowie CO2 umzuwandeln (analog zum Blatt). Die Tenside bestehen aus fünf Farbstoffeinheiten als hydrophobe Gruppe, allesamt auf einer Seite des polyhydroxylierten Fullerenols, das als Kopfgruppe dient (Janus‐artig). Wir berichten über tensidische, optische, elektronische und katalytische Eigenschaften, sowie davon, wie von den Farbstoffen absorbierte Photonen zur Fullerenol‐Kopfgruppe transportiert werden, wo sie z. B. mit CO2 reagieren und dieses zu Ameisensäure reduzieren können.

2019-05-01, Sutter, Sebastian, Trepka, Bastian, Siroky, Stephan, Hagedorn, Kay, Theiss, Sebastian, Baum, Peter, Polarz, Sebastian

The maximization of activity is a general aim in catalysis research. The possibility for light-triggered enhancement of a catalytic process, even if the process is not photochemical in nature, represents an intriguing concept. Here, we present a novel system for the exploration of the latter idea. A surfactant with a catalytically active head group, a protonated polyoxometalate (POM) cluster, is attached to the surface of a gold nanoparticle (Au NP) using thiol coupling chemistry. The distance of the catalytically active center to the gold surface could be adjusted precisely using surfactants containing hydrocarbon chains (C_n) of different lengths ( n = 4-10). Radiation with VIS-light has no effect on the catalytic activity of micellar aggregates of the surfactant. The situation changes, as soon as the surfactants have been attached to the Au NPs. The catalytic activity could almost be doubled. It was proven that the effect is caused by coupling the surface plasmon resonance of the Au NPs with the properties of the POM head group. The improvement of activity could only be observed if the excitation wavelength matches the absorption band of the used Au NPs. Furthermore, the shorter the distance between the POM group and the surface of the NP, the stronger is the effect. This phenomenon was explained by lowering the activation energy of the transition state relevant to the catalytic process by the strong electric fields in the vicinity of the surfaces of plasmonic nanoparticles. Because the catalytic enhancement is wavelength-selective, one can imagine the creation of complex systems in the future, a system of differently sized NPs, each responsible for a different catalytic step and activated by light of different colors.

2020, Sutter, Sebastian

This Ph.D. thesis mention the synthesis and physical properties of catalytic active surfactants. So, bolaamphiphiles showing a probable catalytic active polyoxometalate cluster (POM) and a highly coordinating thiol (SH) group were synthesized. After characterizing their molecular architecture, the physical properties of these compounds in aqueous solutions (i.e. self-assembly behaviour) were investigated. In a second step, these surfactants were coordinated by utilizing the thiol group on the surface of gold nanoparticles, realizing a nano-hybrid catalyst. The resulting catalytic system show a significant improvement of the performance by light irradiation. This improvement is based on a plasmonic enhancement, consisting of three separate effects. First, a nano-heating effect rise the catalytic conversion in accordance to the temperature dependence of the reaction. Additionally, a transfer of stimulated ‘hot electrons’ from the gold nanoparticle to the POM cluster can be strongly assumed. Thereby, the transfer depends on a distance and an electron-conductive parameter, resulting in a maximum of enhancement of 465%.

2019-08-27, Theiss, Sebastian, Voggel, Michael, Schlötter, Moritz, Sutter, Sebastian, Stöckl, Martin T., Polarz, Sebastian

Particle-based materials are expected to exhibit cooperative effects, if nanoparticles form periodic arrays. For particle shapes deviating from a spherical morphology, it is difficult to obtain monodisperse samples. Therefore, we investigated the influence of polydispersity of anisotropic nanoparticles in 2D colloidal crystallization. We work with hexagonal ZnO nanoplates with sizes below 50 nm, and tuned the directionality of the inter-particle interaction by choice of capping agents. Surprisingly, there was no glass to crystal transition for a critical polydispersity value, but a continuous transition.

2020, Enders, Florian, Sutter, Sebastian, Fischli, Danja, Köser, Rebecca, Monter, Samuel, Cardinal, Simon, Boldt, Klaus

Complex, anisotropic nanocrystals made from two or more components are extremely interesting functional materials that can drive directional, light-activated processes like charge separation and photocatalysis. However, while some synthetic protocols exist, little is known about the reaction mechanism for regioselective, heterogeneous nucleation of a second semiconductor material onto nanocrystal seeds. This paper presents the mechanism that leads to growth of a single tip at one end of CdS nanorods with yields between 50 and 80%. It is shown that the growth of only one tip is a result of tight control of the available, nucleating monomer in the reaction solution by working at a large chalcogenide excess. Conditions that facilitate this reaction pathway are characterized by a kinetic barrier to homogeneous growth. These match those for the formation of metastable magic-size clusters. Through this boundary condition, it can be understood why the formation of telluride tips is favored in comparison to selenides and sulfides, for which the regimes for cluster formation and nucleation on surfaces do not overlap.

2019-07-16, Kunkel, Marius, Sutter, Sebastian, Polarz, Sebastian

The leaf is paramount for a material converting waste (CO2) to value with maximum sustainability. As the most important constituent, it contains the coupled photosystems II and I imbedded in the cellular membrane of chloroplasts. Can key functions of the leaf be packed in soap? We present next generation surfactants, which self-assemble to bilayer vesicles (similar to the cellular membrane), are able to absorb photons of two different VIS-wavelengths and exchange excited charge carriers (similar to the photosystems), followed by conversion of CO2 (in analogy to the leaf). The amphiphiles contain five dye molecules as the hydrophobic entity attached exclusively to one hemisphere of a polyhydroxylated fullerene (Janus-type). The manuscript reports surfactant, optical, electronic and catalytic properties. Photons adsorbed by the dyes become transferred to the fullerenol head, where they are able react with different species like with CO2 to formic acid.