Research Projects – Institute of Inorganic Chemistry

Surface interaction and dynamics of molecular spin-probes as guests in tailor-made organosilica, porous hosts for applications in chromatography.

Mass transport in, trough and out of porous solids is a deciding factor in a number of applications in process engineering, e.g. chromatography. One has to consider a hierarchical process, spanning several orders of length- and time-scales. At the molecular scale, in the range of few nanometers and picoseconds, there is a complex interplay between guest-solvent and guest-surface interactions, and this determines directly the mobility of those guests inside the porous materials. A comprehensive and scale-spanning, experimentally underpinned understanding of the transport of dissolved molecular species inside (functionalized) porous matrices is pivotal for realizing porous solids designated for particular applications (e.g. chromatography) by design rather than by empiricism. However, it is very difficult to "spot" the confined guests with sufficient temporal and spatial resolution at technically relevant conditions (in the presence of solvents and at T >= r.t.). We have successfully established electron spin resonance (ESR) spectroscopy as an analytical "eye". Now, we will advance the ESR methodology, aiming at more precise and first and foremost scale-spanning insights into the diffusion of molecular spin probes in pores. Furthermore, we are going to establish a direct link between the synthesis of tailor-made, porous materials, which will enable to exert a much more controlled influence on the mass transport of dissolved species. We will dedicate ourselves to the exciting question of effects of spectator groups, which are present in addition to the active components (predominantly taking part in the guest-surface interaction). We expect that the mobility of guest molecules is mainly dependent on the surface density of the active components, but spectator groups may have a significant importance as well due to the local affect on solvent properties, for instance. The required, systematic variations of surface properties will be realized via bifunctional organosilica materials. Due to the high degree of novelty, we anticipate a substantial acquisition of new knowledge from the combination of materials with chemical gradients and imaging ESR spectroscopy. The imaging methodology allows recording the spectroscopic signature of the guests at every position of the porous material. From these data we can obtain information about the local dynamics and mobility, and at the same time one can analyse the mass transport through the porous medium at macroscopic dimensions. The direct correlation between molecular and macroscopic transport will finally enable to investigate the separation of a compound mixture, by means of spectroscopy using two different spin probes and also for the concrete application, a chromatographic measurement.

Led by: Professor Dr. Sebastian Polarz

Year: 2013

Funding: DFG

Duration: 5 Jahre

Materials World Network (MWN) for Particle-mediated Control Over Crystallization: From the Pre-nucleation Stage to the Final Crystal

A Materials World Network (MWN) will be formed to investigate mechanisms of particle-mediated crystallization through which mesocrystals — crystals structured on the mesoscale — are created. In biomineral systems, mes-ocrystal formation is a widespread phenomenon mediated by biomolecules and leading to the hierarchical organization commonly associated with these materials. Our ultimate goal is a mechanistic understanding of this process and a set of principles to guide biomimetic strat-egies to create hierarchically organized materials (e.g. bioceramics, photonic solids, energy harvesting materials). The value added by the international collaboration is that it facilitates this goal by combining expertise in chemistry and growth of mesocrystals with capabilities in high-resolution in situ imaging, measurement of interactions, determination of structure, and modeling and simulation from the atomic to mesoscale. Using the calcium carbonate, iron oxide and calcium-silicate hydrate (C-S-H) systems combined with polymers, the project will pursue three thrusts, structured around the key scientific questions: Thrust 1: The pre-nucleation stage, nucleation of primary nanoparticles and intermediate phases - The nature of pre-nucleation clusters will be determined using ion potential measurements, titration and ultracentrifugation. Their solution interaction dynamics will be probed through liquid cell TEM. Thrust 2: Interactions forces between nanocrystals and organic mediators of mesocrystal formation – The interactions responsible for particle co-orientation and reorientation will be determined through a combination of dynamic force spectroscopy (DFS) and modeling. DFS will provide a direct measure of the free energy of the orientation dependent crystal-crystal and -polymer interactions. Experimental measurements are supported by molecular model-ing, which allows us to determine molecular details of the effective interactions and provides parameters for the phase field calculations in Thrust 3. Thrust 3: Post-nucleation particle ag-gregation and co-orientation – The kinetics of particle aggregation, crystallographic orienta-tions of the aggregating particles as a function of time, and structural evolution of mesocrys-talline aggregates will be investigated by liquid cell TEM and ex situ HRTEM. Emphasis will be placed on distinguishing between oriented attachment and orientation following random aggregation either through whole-particle rotation or atomic-scale ripening. These data will be compared to phase-field models of mesocrystal assembly that utilize the interaction energies determined in Thrust 2.

Led by: Prof. Dr. H. Cölfen, Prof. Dr. D. Gebauer, Prof. Dr. H. Emmerich

Year: 2013

Funding: Deutsche Forschungsgemeinschaft (DFG)

Duration: 2013-2017

From birth to growth of metastable metal oxides in ionic liquids

It is widely known from chemistry that the energy of transient states may be affected decisively by a surrounding solvent, so is the outcome of a chemical reaction. Also in materials science, one could interpret nanosized seeds as transient states for the generation of shaped particles or of phases with alternative crystal structure. In both cases, one is often interested in thermodynamically less favored (metastable) products, respectively unusual shapes or polymorphs. Besides crystal structure, also shape of a crystal is an important parameter determining its properties. This is, because a particular shape is characterized by a unique set and abundance of surfaces corresponding to different lattice planes. The accession of the mentioned, metastable materials products is linked to the possibility to generate the solid phase under kinetically controlled reaction pathways.The main task of the project is the investigation of the effects in highly polar, non-aqueous solvent environments (ionic liquids) with regards to the formation of metastable products. We will focus on the preparation of anisotropic particles deviating from the most stable shape (Wulff morphology). Furthermore, we are also interested in the role of the solvent concerning accession of metastable crystal structures.We will achieve such kinetically controlled conditions by interfacing molecular routes with materials synthesis, combined with refined in-situ investigations. Highly reactive, organometallic precursors will be used by us for the preparation of important metal oxide semiconductor materials like zinc oxide (ZnO) or manganese oxide (MnxOy). A particular challenge is the generation of novel precursors comprising reluctant groups (e.g. oxidizing and reducing) joined together in one molecule for the purpose of initiating particle growth either at very low temperatures near ambient or below, or initializing it by a non-conventional trigger such as light. A profound base of knowledge will be acquired by us, not only by a detailed analysis of the final materials, but also by comprehensive X-ray scattering investigations (small and wide angle) conducted in an in-situ mode. The advantage of the proposed transition metal oxides is that the contrast in electron density compared to the organic, ionic liquid environment is sufficient for performing scattering with a high tempospatial resolution. We will spot the very early stages of particle formation, raising the question at which point for instance formation of shape and crystal structure is determined.

Led by: Professor Dr. Sebastian Polarz, Professor Dr. Bernd Smarsly

Year: 2014

Funding: DFG

Duration: 4 years

Inorganic surfactants with multifunctional heads

Surfactants are molecules of enormous scientific and technological importance, which are widely used as detergents, emulsifiers or for the preparation of diverse nanostructures. Fascinating abilities regarding the formation of self-organized structures, like micelles or liquid crystals, originate from their amphiphilic architecture, which comprises a polar head group linked to a hydrophobic chain. While almost all known surfactants are organic, a new family of surfactants is now emerging, which combine amphiphilic properties with the advanced functionality of transition metal building blocks. The current project aims at the synthesis of unique inorganic surfactants (I-SURFs), which contain multinuclear, charged metal-oxo entities as heads, and their exploration with regard to additional redox, catalytic or magnetic functionalities. A particular challenge is the creation of smart surfactant systems that can be controlled via external stimuli. While thermotropic liquid crystals and their adjustment in electric fields (enabling LCDs) have been studied in depth, very limited research concerns the control of self-assembled amphiphilic structures by use of magnetic fields. It is obvious that exposure to a magnetic field has inherent advantages over electric fields for controlling structures in water. I-SURFs with single-molecule magnets as heads will be thus prepared and studied. Another groundbreaking task is the creation of I-SURFs with additional catalytic activities. Since catalytic heads can be positioned via self-organization, for instance on the surface of micellar aggregates, catalytic relay systems can be assembled with a second catalytic species in proximity to the first. Thus, cooperative effects in catalytic tandem reactions will ultimately be observed. These examples show that frontier research on I-SURFs is of outstanding relevance for supramolecular science and will certainly pave the way toward new technological applications with great benefits to society.

Led by: Professor Dr. Sebastian Polarz

Year: 2014

Funding: ERC

Duration: 5 Jahre

Advanced Hybrids of Calcium Carbonate and Nanocellulose

Led by: Prof. Dr. D. Gebauer

Team: Prof. Dr. L. Bergström

Year: 2014

Funding: Baden-Württemberg Stiftung (Stuttgart)

Duration: 2014-2017

Morphosynthesis of ceramic semiconductor and ferroelectric nanocrystals

For particle-based materials composed of defined nanocrystals, the ability to adjust the properties of the building blocks is vital. Such tuning can be achieved, when the shape gets correlated to the intrinsic anisotropy of the crystallographic system. For this purpose special additives with surfactant design will be synthesized and tailored for the interaction with inorganic surfaces. They will be used during the morphosynthesis of oxidic and non-oxidic semiconductor materials with ferroelectric characteristics. Furthermore, we aim at customizing the electronic properties of the particles via doping while preserving shape control.

Led by: Prof. Dr. Sebastian Polarz

Year: 2016

Funding: DFG

Shape dependent properties of anisotropic magnetic particles

The goal of the project is an understanding of how far the properties of magnetic, nanoscaled particles relate to their crystal shape. We will explore ensembles of tailored nanoparticles of ferro-, ferri- and antiferromagnetic magnetic oxides. A joint effort will be used, combining the synthesis of particles with well-defined morphologies with state-of-the-art analytical methods and accompanying computer simulations to reveal the expected complex spin structures. We aim for the development of novel magnetic materials on the basis of the morphology of the underlying nanoparticles.

Year: 2016

Funding: DFG

PAC: Particle Analysis Center

In addition to the synthesis of shape-anisotropic nanoparticles, done in the individual projects, their precise characterization and, where appropriate, purification with regards to size or shape distribution is of pivotal importance for the CRC as a whole. The particle analysis center bundles the experience in particle characterization and fractionation. Different methods (including PXRD, SAXS, AUC, light scattering and prep. Ultracentrifugation) will be used and allocated to the scientists of the entire CRC.

Led by: Professor Dr. Sebastian Polarz

Year: 2016

Funding: DFG

The onset of anisotropy during calcium carbonate and phosphate mineralization

Calcium carbonate and phosphate behave very distinctly during the early stages of precipitation, especially regarding the earliest development of morphological anisotropy. In this project, time-resolved in situ analyses of precipitation are designed to elucidate the underlying key factors. The goal is to enable a better understanding of the control of polymorphism and morphology of crystals, so as to pave the way to the rational generation of colloidal building blocks.

Led by: Prof. Dr. D. Gebauer and Prof. Dr. K. Hauser

Year: 2016

Funding: DFG

A07: Bifunctional hybrid nanoparticles via calcium carbonate crystallization driven by engineered protein surfaces

This project aims at the defined generation of structurally and functionally anisotropic nanohybrid particles of calcium carbonate and tailor-made genetically engineered proteins via non-classical pathways of crystallization. Iterative cycles of protein design and thorough investigations of their effect on in vitro calcium carbonate precipitation will identify the essential factors underlying this complex process. Eventually, this will pave the way for the rational generation of particle superstructures via directed self-assembly.

Led by: Prof. Dr. D. Gebauer, Prof. Dr. A. Marx

Year: 2016

Funding: DFG

Control of crystallisation in minerals

This project aims to increase our knowledge of the processes of mineral formation and crystallisation. Minerals play a vital role in our environment, for example as reservoirs for carbon dioxide, while also substantially contributing to the Australian economy. Conversely, undesirable formation of minerals can be detrimental to industries from the oil/gas sector through to desalination. Despite the benefits that would come from controlling such crystal growth, progress has been limited by the lack of a complete understanding of how minerals form at the microscopic level. This project aims to combine computer simulation, using the latest petascale resources, with experimental data to yield knowledge that would allow us to manipulate minerals, such as calcium carbonate, with the same control found in nature.

Led by: Prof. Dr. J. D. Gale

Team: Dr. R. Demichelis, Prof. Dr. D. Gebauer, Prof. Dr. C. Putnis

Year: 2016

Funding: Australian Research Council

Duration: 2016-2019

Functional interfacial additives as energy valves in particle-based gradient structures made of organic-inorganic perovskite phases

Recently, so-called hybrid perovskites such as CH3NH3PbX3 (X = Hal) have moved into the focus of international research because of their extraordinary semiconductor properties. A special feature is, the band-gap can be adjusted precisely by substitution in the anion lattice. The band-gap also depends on the extension of perovskite layers. One then speaks of Ruddlesden-Popper phases (RPPs), in which an organic phase has become an integral part of the crystal, a phenomenon unlike to other semiconductors. This makes the design of the internal and external interfaces highly important for RPPs. RPPs are established and well-investigated for alkyl ammonium compounds as interfacial additives. However, because of the electrically insulating character one is interested to advance to functional interfacial additives (FIAs). This is, where we begin. The proposed research project comprises the organic synthesis of new FGAs and their utilization for the preparation of RPP microparticles. For the direct interaction with the perovskite surfaces the FGAs carry a cationic head-group, attached to a -conjugated side chain. In addition, we aim at implementing photo-switchable groups, and the corresponding FGAs should be established as energy valves. The systems should now be developed further in work package 1 based on our successful, preliminary work on single-source precursors for hybrid perovskites, as well as on thiophene- and azobenzene-based FGAs. In work package 2, the generation of the microparticles is done in combination with single-particle studies, which represent ideal models for understanding the ensemble situation. We will finally (work package 3) assemble microparticles possessing a different band-gap into multi-junction architectures with gradient character. This should lead to energy cascades in the resulting particle-based materials. The work packages are accompanied by extensive photophysical measurements for determining and quantification of the intra-particle and inter-particle energy transfer mechanisms.

Led by: Professor Dr. Sebastian Polarz

Year: 2018

Funding: DFG

Point-Defect Design and Facet-Selective Optoelectronic Properties in Doped Perovskite Microcrystals

Type and density of defects significantly affect the properties and function of a semiconductor leading to enhanced or reduced performance. The application in photovoltaics or in optoelectronics requires in-depth knowledge of defect-property relationships. This aspect is more prevailing for hybrid lead-halide perovskites, in which a high defect density exists due to relatively low cohesion energy of these solution-processed solids. The resulting films exhibit a broad range of defects such as various point-defects (vacancies, interstitials or heteroatoms), but also interfaces between phases within the perovskite or with charge injection/extraction materials (2-D defects) are relevant. Metal-halide perovskites show surprising tolerance to defects, nevertheless, non-radiative recombination is still the major loss channel and needs to be minimized to optimize device operation. Systematic investigations are aggravated by the complexity of hybrid perovskites and the technological need for sustainable, solution-based fabrication. Model systems are needed to answer questions about the limits and placing of defects in the lattice, and how their interplay determine associated electrical and photophysical properties. The generation of a specific defect architecture has not been achieved to enable, for example, controlled doping. The project brings together expertise in chemical synthesis (Polarz), physics of semiconductor nanostructures (Schmidt-Mende) and spatially resolved electronic and optoelectronic measurements (Weber, Deschler) to tackle following tasks: (i) aerosol synthesis of MAPX (CH3NH3PbX3); (ii) role of crystal direction and facets on optical and electronic properties; (iii) role of controlled dopant concentration (stoichiometry), (iv) advanced functionalization of MAPX by inclusion of new dopants. We apply a gas-phase based method, which generates highly crystalline and differently faceted microcrystals from special liquid single-source precursors. The precursor acts also as solvent, which allows us to dissolve heteroelements in the aerosol droplets for the controlled introduction of point-defects. The advantage of micropartices deposited on any desired substrate is, one can probe individual crystals, orientation and facets. We will apply techniques like conductive atomic force microscopy (C-AFM) and time-resolved Kelvin probe spectroscopy for clarification how the stoichiometry, presence of dopants and defects influence the local electrical and ionic conductivity. The effect of ferroelastic domains will be investigated on a single-particle level as well using piezoresponse force microscopy (PFM). Our understanding of electronic properties of defect-property correlations will be complemented by spectroscopic measurements on the photophysics of the defect-doped systems, with high-resolution photoluminescence microscopy, which is a unique method to resolve dynamical processes and radiative recombination on the relevant ultrafast time-scales.

Led by: Professor Dr. Sebastian Polarz,Professor Dr. Lukas Schmidt-Mende, Ph.D., Professor Dr. Stefan Weber

Year: 2019

Funding: DFG

The influence of supramolecular directors bound to surfaces of porous hosts with chiral walls on the dynamic of enantiomers as guests

An important application of porous solids is for separation of (similar) chemical compounds by chromatography. Enantiomers represent the case of ultimate similarity between molecules and, thus, purification is in general demanding. Chromatographic separation also relies on statistics, a high number of contacts of the dissolved guest species with the surfaces via diffusion ensures, some events occur in proper orientation to induce stereochemical differentiation in intermolecular interaction. Maximum mobility discrimination of the enantiomers to be separated with a minimum amount of a chiral selector necessary at the surfaces of the solid phase is desired. For the identification of new concepts in stereoselective chromatography, it is helpful referring to a different area, asymmetric catalysis. There, the sole presence of a chiral ligand is not enough for achieving best enantiomeric excess. A precise control over the orientation of the starting compounds towards the active center is pivotal. The transfer of the latter concept to host-guest chemistry in porous materials leads to our long-term vision: The design of surfaces to become capable of orienting chiral guests for maximizing the effect on their mobility and reaching optimum enantioselective separation. For the target-oriented synthesis of such a complex host material, one has to be able to watch separation with molecular precision and quantify the molecular dynamics and mobility of guests confined to the pores of the material close to chromatographic process conditions. Our group has shown in preliminary work, this is possible using electron spin resonance spectroscopy (ESR) techniques. The methodology is now developed sufficiently, it can be applied to gather detailed information about separation using chiral, amino-acid modified organosilica materials as model systems. Our first work-package is concerned with gaining control over confinement conditions. We present new templating approaches for the synthesis of organosilica materials with narrow size distribution of pores in the 50-150 nm range. A systematic variation of the interaction of chiral nitroxides as paramagnetic spin-probes with the surfaces is realized in the second work-package. A particularly interesting question is, how non-chiral neighboring groups on the surface can influence the separation process and ultimately act as supramolecular directors for orienting the nitroxide guests in a specific way. Our main observable is the enantiomer selectivity factor alphaT obtained from cw-ESR experiments, and also coefficients for nanoscopic and macroscopic transport will be determined, for instance from imaging ESR spectroscopy. Finally, we want to perform a HPLC separation experiment using a monolithic organosilica material, to learn how the fundamental host-guest study translate to application.

Led by: Professor Dr. Sebastian Polarz

Year: 2019

Funding: DFG

Exzellenzcluster PhoenixD - Photonics, Optics, Engineering, Innovation across Disciplines

PhoenixD ist eine breit angelegte, disziplinübergreifende Initiative, um Design und Herstellung von Präzisionsoptik neu zu definieren. Sie beruht auf der Verwebung von Optikdesign, Optiksimulation und modernen Produktionsmethoden zu einer einzigen integrierten Plattform, mit der individuelle und hochfunktionelle präzisionsoptische Systeme entworfen und hergestellt werden sollen.

Led by: Prof. Dr. Uwe Morgner, Prof. Dr.-Ing. Ludger Overmeyer, Prof. Dr.-Ing. Wolfgang Kowalsky

Year: 2019

Funding: DFG

Duration: 7 Jahre

Cooperative effects for carbon dioxide capture in nanoporous, bifunctional organosilica materials

Atmospheric carbon dioxide (CO2) is an example for a plentifully available waste product. The chemical conversion of waste products into valuable compounds is highly desirable, in particular when no significant amounts of energy or other resources are consumed. The first necessary conversion step is the fixation of CO2 from the gas-phase. Sustainability is hardly realized considering the currently applied wet process, the so-called amine washing. Thus, numerous scientists became interested in developing solid adsorbents for carbon capture applications. The interplay between CO2 capture and release, the latter being required for succeeding process steps and the regeneration of the material, makes fine-tuning of the adsorption enthalpy desirable. Nanoporous silica materials with surfaces containing primary amines have already been demonstrated to be promising. However, the literature discusses almost exclusively mono-functional materials comprising only one single (amine) moiety. Here starts the current project. We want to understand, how the CO2 adsorption properties of a nanoporous material change, when an additional moiety is present on its surface in direct vicinity to the amine group. Such neighboring group effects have been described in only few papers, but a systematic, experimental study is missing. Half of the project is focused on materials synthesis providing bifunctional organosilica aerogels with monolithic shape. Close collaboration takes place with the physical chemistry part of the project, which analyzes the adsorption behavior using (T-dependent) volumetric methods as well as spectroscopic methods, most importantly infrared (IR)-spectroscopy including spatially resolved techniques. We expect that uptake capacities, adsorption enthalpies and kinetic data enable us to identify which neighboring group leads to strong interaction effects and why. After identification of promising combinations among amine- and neighboring groups, another parameter space opens up, namely the relative abundance of both moieties to each other. We will examine this parameter space by exploiting new materials characterized by chemical gradients, in which the density of one constituent systematically varies along one spatial coordinate. The anisotropic modification of the monoliths using click chemistry (azide-alkyne; thiol-alkene) will be applied for synthesizing the gradient materials. The uptake of CO2 can then be studied at different positions of the gradient materials using IR microscopy. The existence of a gradient material shall open new research possibilities, for instance for studying anisotropic and directional transport in the material.

Led by: Professorin Dr. Karin Hauser and Professor Dr. Sebastian Polarz

Year: 2020

Funding: DFG

Hierarchical Nanomaterials with Biological Functions for Anti-Biofilm Applications and Localized Toxicity

Led by: Professor Dr. Sebastian Polarz

Year: 2020

Funding: Dr. K. H. Eberle Foundation

New functional materials with directional porosity structure.

Led by: Professor Dr. Sebastian Polarz

Year: 2020

Funding: Carl-Zeiss Foundation

Sustainable synthesis of thin films for energy technology