Klinkenberg, Nele
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Great Location : About Effects of Surface Bound Neighboring Groups for Passive and Active Fine-Tuning of CO2 Adsorption Properties in Model Carbon Capture Materials
Improved carbon capture materials are crucial for managing the CO2 level in the atmosphere. The past focus was on increasing adsorption capacities. It is widely known that controlling the heat of adsorption (ΔHads) is equally important. If it is too low, CO2 uptake takes place at unfavorable conditions and with insufficient selectivity. If it is too high, chemisorption occurs, and the materials can hardly be regenerated. The conventional approach for influencing ΔHads is the modification of the adsorbing center. This paper proposes an alternative strategy. The hypothesis is that fine‐tuning of the molecular environment around the adsorbing center is a powerful tool for the adjustment of CO2‐binding properties. Via click chemistry, any desired neighboring group (NG) can be incorporated on the surfaces of the nanoporous organosilica model materials. Passive NGs induce a change in the polarity of the surface, whereas active NGs are capable of direct interaction with the active center/CO2 pair. The effects on ΔHads and on the selectivity are studied. A situation can be realized which resembles frustrated Lewis acid–base pairs, and the investigation of the binding‐species by solid‐state NMR indicates that the push–pull effects could play an essential role not only in CO2 adsorption but also in its activation.
Versatile surface modification of aerogels by click chemistry as an approach to generate model systems for CO2 adsorption features in amine-containing organosilica
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.
Microalgae lipids as a feedstock for the production of benzene
A two-step one-pot synthesis of benzene from the five-fold unsaturated fatty acid eicosapentaenoic acid (EPA), a component of microalgae oils, is presented. By a sequence of olefin metathesis and the catalytic dehydrogenation of the resulting 1,4-cyclohexadiene, two equivalents of benzene are effectively formed per EPA substrate molecule. As the only major by-products, 5-octenoic acid and 5-decenedioic acid are formed. Performing the dehydrogenation step under hydrogen pressure results in the formation of their saturated analogues, sebacic acid and octanoic acid, both desirable products, while the simultaneous dehydrogenation step to benzene is not hampered.
Creating Directionality in Nanoporous Carbon Materials : Adjustable Combinations of Structural and Chemical Gradients
The properties of porous materials benefit from hierarchical porosity. A less noted element of hierarchy is the occurrence of directionality in functional gradient materials. A sharp boundary is replaced by a transition from one feature to the next. The number of cases known for porous materials with either structural or chemical gradients is small. A method capable of generating combinations of structural and chemical gradients in one material does not exist. Such a method is presented with a focus on silver and nitrogen containing carbon materials because of the potential of this system for electrocatalytic CO2 reduction. A structural gradient results from controlled separation using ultracentrifugation of a binary mixture of template particles in a resorcinol–formaldehyde (RF) sol as carbon precursor. A new level of complexity can be reached, if the surfaces of the template particles are chemically modified. Although the template is removed during carbonization, the modification (Ag, N) becomes integrated into the material. Understanding how modified and unmodified large and small particles sediment in the RF sol enables almost infinite variability of combinations: chemically graded but structurally homogeneous materials and vice versa. Ultimately, a material containing one structural gradient and two chemical gradients with opposing directions is introduced.
Sunlight-Triggered Nanoparticle Synergy: Teamwork of Reactive Oxygen Species and Nitric Oxide Released from Mesoporous Organosilica with Advanced Antibacterial Activity
Colonization of surfaces by microorganisms is an urging problem. In combination with the increasing antibiotic resistance of pathogenic bacteria, severe infections are reported more frequently in medical settings. Therefore, there is a large demand to explore innovative surface coatings that provide intrinsic and highly effective antibacterial activity. Materials containing silver nanoparticles have been developed in the past for this purpose, but this solution has come into criticism due to various disadvantages like notable toxicity against higher organisms, the high price, and low abundance of silver. Here, we introduce a new, sunlight-mediated organosilica nanoparticle (NP) system based on silver-free antibacterial activity. The simultaneous release of nitric oxide (NO) in combination with singlet oxygen and superoxide radicals (O2•-) as reactive oxygen species (ROS) leads to the emergence of highly reactive peroxynitrite molecules with significantly enhanced biocidal activity. This special cooperative effect can only be realized, if the ROS-producing moieties and the functional entities releasing NO are spatially separated from each other. In one type of particle, Rose Bengal as an efficient singlet oxygen (1O2) producer was covalently bound to SH functionalities applying thiol-ene click chemistry. "Charging" the second type of particles with NO was realized by quantitatively transferring the thiol groups into S-nitrosothiol functionalities. We probed the oxidation power of ROS-NP alone and in combination with NO-NP using sunlight as a trigger. The high antibacterial efficiency of dual-action nanoparticles was demonstrated using disinfection assays with the pathogenic bacterium Pseudomonas aeruginosa.
Stimuli-Responsive Particle-Based Amphiphiles as Active Colloids Prepared by Anisotropic Click Chemistry
Amphiphiles alter the energy of surfaces, but the extent of this feature is typically constant. Smart systems with amphiphilicity as a function of an external, physical trigger are desirable. As a trigger, the exposure to a magnetic field, in particular, is attractive because it is not shielded in water. Amphiphiles like surfactants are well known, but the magnetic response of molecules is typically weak. Vice‐versa, magnetic particles with strong response to magnetic triggers are fully established in nanoscience, but they are not amphiphilic. In this work colloids with Janus architecture and ultra‐small dimensions (25 nm) have been prepared by spatial control over the thiol‐yne click modification of organosilica‐magnetite core–shell nanoparticles. The amphiphilic properties of these anisotropically modified particles are proven. Finally, a pronounced and reversible change in interfacial stabilization results from the application of a weak (<1 T) magnetic field.
Single-Step Catalytic Upgrading of Microalgae Biomass
A direct catalytic upgrading on as-cultivated microalgae biomass is demonstrated. Via CO-free alkoxycarbonylation of the contained lipids with the use of formates, diesters were produced in high conversion and selectivity from monounsaturated fatty acids from Phaeodactylum tricornutum microalgae. Via this procedure, extraction and functionalization occur in one step, circumventing the need for separate workup procedures of the biomass. The products are valuable building blocks for renewable polyester materials.
PMMA/PMMA Core–Shell Particles with Ellipsoidal, Fluorescent Cores : Accessing Rotational Dynamics
For several decades, nonaqueous dispersions of PMMA particles have played an important role in colloid research. They have found application as colloidal model systems, which are used to probe glassy dynamics or to explore crystal nucleation. To date, most research has focused on spherical particles, in which only translational motion can be investigated. Recently, however, there has been a surge of interest in analyzing also rotational dynamics. In this contribution, we introduce a new class of core-shell particles, which can be used as rotational probes. The colloids described herein are composed of shape anisotropic, fluorescent cores covered with nonfluorescent PMMA shells. The core-shell particles are built up in four steps. In a first step, we produce fluorescent and photo-cross-linkable PMMA colloids. In the second step, these particles are thermomechanically elongated and fixed in defined ellipsoidal shapes by photo-cross-linking. Subsequently, we cover the cross-linked, fluorescent core with a nonfluorescent PMMA shell. The shape of the resulting core-shell colloids is tunable between the initial anisotropic and perfect spherical shape. For shaping, we apply a simple solvent swelling procedure. As one option, this method yields perfect PMMA spheres with ellipsoidal, fluorescent centers. We also report morphological particle characterization using various fluorescence microscopy techniques. Finally, we demonstrate that the rotational dynamics of individual colloids can be tracked and analyzed.