@phdthesis{Harmanli2020, author = {Harmanli, İpek}, title = {Towards catalytic activation of nitrogen in ionic liquid/nanoporous carbon interfaces for electrochemical ammonia synthesis}, doi = {10.25932/publishup-48359}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-483591}, school = {Universit{\"a}t Potsdam}, pages = {v, 126}, year = {2020}, abstract = {Ammonia is a chemical of fundamental importance for nature`s vital nitrogen cycle. It is crucial for the growth of living organisms as well as food and energy source. Traditionally, industrial ammonia production is predominated by Haber- Bosch process (HBP) which is based on direct conversion of N2 and H2 gas under high temperature and high pressure (~500oC, 150-300 bar). However, it is not the favorite route because of its thermodynamic and kinetic limitations, and the need for the energy intense production of hydrogen gas by reforming processes. All these disfavors of HBP open a target to search for an alternative technique to perform efficient ammonia synthesis via electrochemical catalytic processes, in particular via water electrolysis, using water as the hydrogen source to save the process from gas reforming. In this study, the investigation of the interface effects between imidazolium-based ionic liquids and the surface of porous carbon materials with a special interest in the nitrogen absorption capability. As the further step, the possibility to establish this interface as the catalytically active area for the electrochemical N2 reduction to NH3 has been evaluated. This particular combination has been chosen because the porous carbon materials and ionic liquids (IL) have a significant importance in many scientific fields including catalysis and electrocatalysis due to their special structural and physicochemical properties. Primarily, the effects of the confinement of ionic liquid (EmimOAc, 1-Ethyl-3-methylimidazolium acetate) into carbon pores have been investigated. The salt-templated porous carbons, which have different porosity (microporous and mesoporous) and nitrogen species, were used as model structures for the comparison of the IL confinement at different loadings. The nitrogen uptake of EmimOAc can be increased by about 10 times by the confinement in the pores of carbon materials compared to the bulk form. In addition, the most improved nitrogen absorption was observed by IL confinement in micropores and in nitrogen-doped carbon materials as a consequence of the maximized structural changes of IL. Furthermore, the possible use of such interfaces between EmimOAc and porous carbon for the catalytic activation of dinitrogen during the kinetically challenging NRR due to the limited gas absorption in the electrolyte, was examined. An electrocatalytic NRR system based on the conversion of water and nitrogen gas to ammonia at ambient operation conditions (1 bar, 25 °C) was performed in a setup under an applied electric potential with a single chamber electrochemical cell, which consists of the combination of EmimOAc electrolyte with the porous carbon-working electrode and without a traditional electrocatalyst. Under a potential of -3 V vs. SCE for 45 minutes, a NH3 production rate of 498.37 μg h-1 cm-2 and FE of 12.14\% were achieved. The experimental observations show that an electric double-layer, which serves the catalytically active area, occurs between a microporous carbon material and ions of the EmimOAc electrolyte in the presence of sufficiently high provided electric potential. Comparing with the typical NRR systems which have been reported in the literature, the presented electrochemical ammonia synthesis approach provides a significantly higher ammonia production rate with a chance to avoid the possible kinetic limitations of NRR. In terms of operating conditions, ammonia production rate and the faradic efficiency without the need for any synthetic electrocatalyst can be resulted of electrocatalytic activation of nitrogen in the double-layer formed between carbon and IL ions.}, language = {en} } @phdthesis{LopezdeGuerenu2020, author = {L{\´o}pez de Guere{\~n}u, Anna}, title = {Tm3+-doped NaYF4 nanoparticles}, doi = {10.25932/publishup-47559}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-475593}, school = {Universit{\"a}t Potsdam}, pages = {119}, year = {2020}, abstract = {Lately, the integration of upconverting nanoparticles (UCNP) in industrial, biomedical and scientific applications has been increasingly accelerating, owing to the exceptional photophysical properties that UCNP offer. Some of the most promising applications lie in the field of medicine and bioimaging due to such advantages as, among others, deeper tissue penetration, reduced optical background, possibility for multicolor imaging, and lower toxicity, compared to many known luminophores. However, some questions regarding not only the fundamental photophysical processes, but also the interaction of the UCNP with other luminescent reporters frequently used for bioimaging and the interaction with biological media remain unanswered. These issues were the primary motivation for the presented work. This PhD thesis investigated several aspects of various properties and possibilities for bioapplications of Yb3+,Tm3+-doped NaYF4 upconverting nanoparticles. First, the effect of Gd3+ doping on the structure and upconverting behaviour of the nanocrystals was assessed. The ageing process of the UCNP in cyclohexane was studied over 24 months on the samples with different Gd3+ doping concentrations. Structural information was gathered by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and discussed in relation to spectroscopic results, obtained through multiparameter upconversion luminescence studies at various temperatures (from 4 K to 295 K). Time-resolved and steady-state emission spectra recorded over this ample temperature range allowed for a deeper understanding of photophysical processes and their dependence on structural changes of UCNP. A new protocol using a commercially available high boiling solvent allowed for faster and more controlled production of very small and homogeneous UCNP with better photophysical properties, and the advantages of a passivating NaYF4 shell were shown. F{\"o}rster resonance energy transfer (FRET) between four different species of NaYF4: Yb3+, Tm3+ UCNP (synthesized using the improved protocol) and a small organic dye was studied. The influence of UCNP composition and the proximity of Tm3+ ions (donors in the process of FRET) to acceptor dye molecules have been assessed. The brightest upconversion luminescence was observed in the UCNP with a protective inert shell. UCNP with Tm3+ ions only in the shell were the least bright, but showed the most efficient energy transfer. In the final part, two surface modification strategies were applied to make UCNP soluble in water, which simultaneously allowed for linking them via a non-toxic copper-free click reaction to the liposomes, which served as models for further cell experiments. The results were assessed on a confocal microscope system, which was made possible by lesser known downshifting properties of Yb3+, Tm3+-doped UCNP. Preliminary antibody-staining tests using two primary and one dye-labelled secondary antibodies were performed on MDCK-II cells.}, language = {en} } @misc{WalkowiakLuGradzielskietal.2020, author = {Walkowiak, Jacek and Lu, Yan and Gradzielski, Michael and Zauscher, Stefan and Ballauff, Matthias}, title = {Thermodynamic analysis of the uptake of a protein in a spherical polyelectrolyte brush}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-51730}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-517307}, pages = {10}, year = {2020}, abstract = {A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding Delta Gb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.}, language = {en} } @misc{Koetz2020, author = {Koetz, Joachim}, title = {The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1022}, issn = {1866-8372}, doi = {10.25932/publishup-48517}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-485172}, pages = {15}, year = {2020}, abstract = {A surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface-enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI)-coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au³⁺ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the ultraviolet (UV)-absorption of the undulated Au@Ag nanoplatelets can be tuned depending on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4′-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by decoration with gold spikes.}, language = {en} } @phdthesis{Knauf2020, author = {Knauf, Jan}, title = {Synthesis of highly fluorinated precursors and their deposition conditions for self-assembled monolayers with defined small-scale surface structures as templates for the manipulation of wetting behavior}, doi = {10.25932/publishup-47380}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-473804}, school = {Universit{\"a}t Potsdam}, pages = {X, 204}, year = {2020}, abstract = {"How Wenzel and Cassie were wrong" - this was the eye-catching title of an article published by Lichao Gao and Thomas McCarthy in 2007, in which fundamental interpretations of wetting behavior were put into question. The authors initiated a discussion on a subject, which had been generally accepted a long time ago and they showed that wetting phenomena were not as fully understood as imagined. Similarly, this thesis tries to put a focus on certain aspects of liquid wetting, which so far have been widely neglected in terms of interpretation and experimental proof. While the effect of surface roughness on the macroscopically observed wetting behavior is commonly and reliably interpreted according to the well-known models of Wenzel and Cassie/Baxter, the size-scale of the structures responsible for the surface's rough texture has not been of further interest. Analogously, the limits of these models have not been described and exploited. Thus, the question arises, what will happen when the size of surface structures is reduced to the size of the contacting liquid molecules itself? Are common methods still valid or can deviations from macroscopic behavior be observed? This thesis wants to create a starting point regarding these questions. In order to investigate the effect of smallest-scale surface structures on liquid wetting, a suitable model system is developed by means of self-assembled monolayer (SAM) formation from (fluoro)organic thiols of differing lengths of the alkyl chain. Surface topographies are created which rely on size differences of several {\AA}ngstr{\"o}ms and exhibit surprising wetting behavior depending on the choice of the individual precursor system. Thus, contact angles are experimentally detected, which deviate considerably from theoretical calculations based on Wenzel and Cassie/Baxter models and confirm that sub-nm surface topographies affect wetting. Moreover, experimentally determined wetting properties are found to correlate well to an assumed scale-dependent surface tension of the contacting liquid. This behavior has already been described for scattering experiments taking into account capillary waves on the liquid surface induced by temperature and had been predicted earlier by theoretical calculations. However, the investigation of model surfaces requires the provision of suitable precursor molecules, which are not commercially available and opens up a door to the exotic chemistry of fluoro-organic materials. During the course of this work, the synthesis of long-chain precursors is examined with a particular focus put on oligomerically pure semi-fluorinated n-alkyl thiols and n-alkyl trichlorosilanes. For this, general protocols for the syntheses of the desired compounds are developed and product mixtures are assayed to be separated into fractions of individual chain lengths by fluorous-phase high-performance liquid chromatography (F-HPLC). The transition from model systems to technically more relevant surfaces and applications is initiated through the deposition of SAMs from long-chain fluorinated n-alkyl trichlorosilanes. Depositions are accomplished by a vapor-phase deposition process conducted on a pilot-scale set-up, which enables the exact control of relevant process parameters. Thus, the influence of varying deposition conditions on the properties of the final coating is examined and analyzed for the most important parameters. The strongest effect is observed for the partial pressure of reactive water vapor, which directly controls the extent of precursor hydrolysis during the deposition process. Experimental results propose that the formation of ordered monolayers rely on the amount of hydrolyzed silanol species present in the deposition system irrespective of the exact grade of hydrolysis. However, at increased amounts of species which are able to form cross-linked molecules due to condensation reactions, films deteriorate in quality. This effect is assumed to be caused by the introduction of defects within the film and the adsorption of cross linked agglomerates. Deposition conditions are also investigated for chain extended precursor species and reveal distinct differences caused by chain elongation.}, language = {en} } @misc{IlicTsoukaPerovicetal.2020, author = {Ilic, Ivan K. and Tsouka, Alexandra and Perovic, Milena and Hwang, Jinyeon and Heil, Tobias and L{\"o}ffler, Felix and Oschatz, Martin and Antonietti, Markus and Liedel, Clemens}, title = {Sustainable cathodes for Lithium-ion energy storage devices based on tannic acid-toward ecofriendly energy storage}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-57056}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-570560}, pages = {10}, year = {2020}, abstract = {The use of organic materials with reversible redox activity holds enormous potential for next-generation Li-ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox-active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g(-1) at 0.1 A g(-1) and low capacity fading, retaining approximately 80\% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone-catecholate redox mechanism responsible for the high capacity of tannic acid is confirmed by electrochemical characterization of a model compound similar to tannic acid but without catecholic groups.}, language = {en} } @misc{SchneiderFritzschePuciulMalinowskaetal.2020, author = {Schneider, Matthias and Fritzsche, Nora and Puciul-Malinowska, Agnieszka and Balis, Andrzej and Mostafa, Amr and Bald, Ilko and Zapotoczny, Szczepan and Taubert, Andreas}, title = {Surface etching of 3D printed poly(lactic acid) with NaOH: a systematic approach}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {8}, issn = {1866-8372}, doi = {10.25932/publishup-52508}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525088}, pages = {18}, year = {2020}, abstract = {The article describes a systematic investigation of the effects of an aqueous NaOH treatment of 3D printed poly(lactic acid) (PLA) scaffolds for surface activation. The PLA surface undergoes several morphology changes and after an initial surface roughening, the surface becomes smoother again before the material dissolves. Erosion rates and surface morphologies can be controlled by the treatment. At the same time, the bulk mechanical properties of the treated materials remain unaltered. This indicates that NaOH treatment of 3D printed PLA scaffolds is a simple, yet viable strategy for surface activation without compromising the mechanical stability of PLA scaffolds.}, language = {en} } @misc{WessigJohnSperlichetal.2020, author = {Wessig, Pablo and John, Leonard and Sperlich, Eric and Kelling, Alexandra}, title = {Sulfur tuning of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {3}, issn = {1866-8372}, doi = {10.25932/publishup-56624}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-566241}, pages = {15}, year = {2020}, abstract = {The replacement of oxygen by sulfur atoms of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes is an efficient way to adjust the photophysical properties (sulfur tuning). While previously developed S-4-DBD dyes exhibit considerably red-shifted absorption and emission wavelength, the heavy atom effect of four sulfur atoms cause low fluorescence quantum yields and short fluorescence lifetimes. Herein, we demonstrate that the replacement of less than four sulfur atoms (S-1-DBD, 1,2-S-2-DBD, and 1,4-S-2-DBD dyes) permits a fine-tuning of the photophysical properties. In some cases, a similar influence on the wavelength without the detrimental effect on the quantum yields and lifetimes is observed. Furthermore, the synthetic accessibility of S-1- and S-2-DBD dyes is improved, compared with S-4-DBD dyes. For coupling with biomolecules a series of reactive derivatives of the new dyes were developed (azides, OSu esters, alkynes, maleimides).}, language = {en} } @misc{WangSperlingReifarthetal.2020, author = {Wang, Xuepu and Sperling, Marcel and Reifarth, Martin and B{\"o}ker, Alexander}, title = {Shaping metallic nanolattices}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {11}, issn = {1866-8372}, doi = {10.25932/publishup-51434}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-514341}, pages = {10}, year = {2020}, abstract = {A method for the fabrication of well-defined metallic nanostructures is presented here in a simple and straightforward fashion. As an alternative to lithographic techniques, this routine employs microcontact printing utilizing wrinkled stamps, which are prepared from polydimethylsiloxane (PDMS), and includes the formation of hydrophobic stripe patterns on a substrate via the transfer of oligomeric PDMS. Subsequent backfilling of the interspaces between these stripes with a hydroxyl-functional poly(2-vinyl pyridine) then provides the basic pattern for the deposition of citrate-stabilized gold nanoparticles promoted by electrostatic interaction. The resulting metallic nanostripes can be further customized by peeling off particles in a second microcontact printing step, which employs poly(ethylene imine) surface-decorated wrinkled stamps, to form nanolattices. Due to the independent adjustability of the period dimensions of the wrinkled stamps and stamp orientation with respect to the substrate, particle arrays on the (sub)micro-scale with various kinds of geometries are accessible in a straightforward fashion. This work provides an alternative, cost-effective, and scalable surface-patterning technique to fabricate nanolattice structures applicable to multiple types of functional nanoparticles. Being a top-down method, this process could be readily implemented into, e.g., the fabrication of optical and sensing devices on a large scale.}, language = {en} } @phdthesis{Schmidt2020, author = {Schmidt, Bernhard V. K. J.}, title = {Polymers, self-assembly and materials}, doi = {10.25932/publishup-48481}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-484819}, school = {Universit{\"a}t Potsdam}, pages = {VI, 350}, year = {2020}, abstract = {In der vorliegenden Arbeit wurden die Selbstorganisation von hydrophilen Polymeren, verst{\"a}rkte Hydrogele, sowie anorganische/Polymer Hybridmaterialien untersucht. Dabei beschreibt die Arbeit den Weg von Polymersynthese mittels verschiedener Methoden {\"u}ber Polymerselbstanordnung bis zur Herstellung von Polymermaterialien mit vielversprechenden Eigenschaften f{\"u}r zuk{\"u}nftige Anwendungen. Hydrophile Polymere wurden verwendet, um Mehrphasensysteme herzustellen, Wasser-in-Wasser Emulsionen zu bilden und selbstangeordneten Strukturen zu erzeugen, z. B. Partikel/Aggregate oder hohle Strukturen aus komplett wasserl{\"o}slichen Bausteinen. Die Strukturbildung in w{\"a}ssriger Umgebung wurde ferner f{\"u}r supramolekulare Hydrogele mit definierter Unterstruktur und reversiblem Gelierungsverhalten eingesetzt. Auf dem Gebiet der Hydrogele wurde das anorganische Material graphitisches Kohlenstoffnitrid (g-CN) als Photoinitiator f{\"u}r die Hydrogelsynthese und als Verst{\"a}rker der Gelstruktur beschrieben. Hierbei konnten Hydrogele mit herausragenden Eigenschaften generiert werden, z. B. hohe Kompressibilit{\"a}t, hohe Speichermodule oder Gleitf{\"a}higkeit. Die Kombinationen von g-CN mit verschiedenen Polymeren erlaubte es zudem neue Materialien f{\"u}r die Photokatalyse bereitzustellen. Als weiteres anorganisches Material wurden Metall-organische Ger{\"u}ste (MOFs) mit Polymeren kombiniert. Es konnte gezeigt werden, dass die Verwendung von MOFs in der Polymersynthese einen starken Einfluss auf die erzeugte Polymerstruktur hat und MOFs als Katalysator f{\"u}r Polymerisationen verwendet werden k{\"o}nnen. Zuletzt wurde die MOF Synthese an sich untersucht, wobei Polymeradditive oder L{\"o}sungsmittel eingesetzt wurden um die kristalline Struktur der MOFs zu modulieren. Insgesamt wurden hier verschiedene Errungenschaften f{\"u}r die Polymerchemie beschrieben, z.B. neuartige hydrophile Polymere und Hydrogele, die zur Zeit wichtige Materialien im Polymerbereich durch ihre vielversprechenden Anwendungen im biomedizinischen Sektor darstellen. Außerdem ergab die Kombination von Polymeren mit Materialien aus anderen Bereichen der Chemie, z. B. g-CN und MOFs, neue Materialien mit bemerkenswerten Eigenschaften, die ebenfalls von Interesse f{\"u}r zuk{\"u}nftige Anwendungen sind, z. B. Beschichtungen, Partikeltechnologie und Katalyse.}, language = {en} }