Team

Responsibilities

Biodegradable mineral plastics

Mineral plastics (MPs) are stable and multifunctional hydrogel phases, resulting from the physical crosslinking of poly(acrylic acid) (PAA) with amorphous calcium carbonate (ACC) particles, which exhibit interesting properties like stretchability, self-healability, non-flammability etc.. They have been well-established in our group. MPs are incorporated here as microphases in the matrix of polyethylene-like polymer (in collaboration with AG Mecking). By implementing these microphases as a reference model; the blended polymer materials’ persistence should be decreased by two pathways. First, the swelling pressure of the dried hydrogel particles should upon access to water during the materials’ breakdown induce cracks, and second, the hydrogels can provide nutrients for bacterial growth, promoting the colonization and degradation of the material (in collaboration with AG Schleheck). Currently, we aim to come up with biodegradable and environment-friendly alternatives which fulfill the conditions mentioned above. We have been exploring eco-friendly polyamines like poly(aspartic acid), poly(glutamic acid), chitosan which contain N in their backbone, and so on, crosslinking them with Ca(II) and Fe(III) ions. Poly(glutamic acid) has already shown promising results where it successfully forms a mineral plastic and also demonstrates ready biodegradability due to N and aforementioned ions, which serve as additional nutrients for the bacteria. We are now investigating the degradation behavior after blending this polymer into the polyethylene-like matrix. Simultaneously, we are examining the prospects of cost-effective and readily available chitosan as a biodegradable mineral plastic where the backbone possesses N and P, both of which are essential for promoting biodegradation.

Responsibilities

Writing Crystals with Light

Combining chemical and physical methods in synthesis is opening up a wide variety of new material preparation methods. In my project, I am synthesizing photolabile molecules with different protecting as well as different leaving groups which are split via the impact of light. Therefore, physical techniques such as nanosecond lasers are used. This will ensure a precise targeting of the irradiated area as well as high photon density resulting in a high conversion of the molecule into the individual constituent parts. The fundamental splitting mechanisms are investigated throughout my studies by for example NMR, UV/Vis, or titration studies. Additionally, suitable counter ions or counter molecules of the leaving groups are brought into the system and investigations are made on whether the leaving group and the counterpart are reacting with one another forming a solid material in the end. The nucleation process is analyzed and additionally, the resulting precipitate is characterized by solid-state techniques such as SEM, Raman, IR, and many more to ensure a full characterization. Combining chemical synthesis with physical irradiation techniques is ensuring the best control over the exact precipitate composition in a precise location and with a specified amount.

Responsibilities

Project title:

Binary Prussian Blue Analogue Mesocrystals

Project description:

My research focus is the preparation of binary Prussian Blue Analogue (PBA) mesocrystals, and the investigation of their formation mechanism and electrocatalytic performance.

PBAs are transition metal cyanide complexes that belong to the metal organic frameworks. A large variety of different transition metal ions with different oxidation states can be introduced and combined which allows for vast PBA compositions. The bridging of the transition metal centers via conductive cyanide ligands enables charge transfer within the framework. These properties make PBAs promising materials for electrochemistry and -catalysis.

In recent years, the controlled synthesis of PBA nanostructures has emerged which further enhances the unique properties due to the size-dependent properties of nanomaterials. The assembly of anisotropic PBA nanocrystals into crystallographically aligned superstructures, so-called mesocrystals, might enable the exploitation of the nanocrystals’ properties on macroscopic scale.

With this research project we intend to prepare novel functional materials for application in electrocatalysis, e.g., as catalysts for the hydrogen (HER) or oxygen evolution reaction (OER), which are crucial reactions for the future prospect of fuel cell-based energy supply. The preparation of binary PBA mesocrystals could allow the catalysis of two different reactions simultaneously with only one catalyst material.

Responsibilities

04/2021 – to present

M.Sc. & PhD thesis: “Chemical reactions in the analytical ultracentrifuge and global analysis”

Supervisor: Prof. Cölfen and Prof. Wittemann

The major goal is to gain new insights into the nucleation process through global analysis. Band-forming experiments in the analytical ultracentrifugation should be established as a method of choice for in-situ nucleation analysis. As part of this project, the analysis of such band-forming experiments should be integrated into the existing analysis software. By varying parameters of the reaction systems, the effect of multiple parameters in the nucleation process should be studied. This should lead to a better understanding and description of the nucleation and growth process of nanoparticles.

10/2019 – 11/2021

Master studies Nanoscience at the University of Konstanz

08/2019 – 11/2019

Bachelor thesis: “Hard templating of porous materials using Ultracentrifugation”

Supervisor: Prof. Polarz, Dr. Jochen Bahner

This project evaluated the potential of the combination of precursors for carbon nitride and hard templates. Polystyrene and silica nanoparticles were used to create colloidal crystals in the force field of a preparative ultracentrifuge. By mixing different sizes of particles, templates with gradients in the particle sizes along the direction of the centrifugal force could be obtained. Those templates were then infiltrated by different techniques with various carbon nitride precursors to obtain a carbon nitride material with pores.

Responsibilities

Towards sustainable cements: Understanding the crystallization of cementitious hydrates in LC3 blends as eco-friendly binder--

Limestone calcined clay cements (LC³) are a very special and promising type of new cements. They take advantage of synergistic effects in the interaction of calcined clay and limestone as supplementary cementitious materials. With these cements it is already possible to reduce the clinker content to less than 50% and thus save more than 30% in CO₂ emissions. Additionally, LC³ blends are roughly 15-25% cheaper in production than ordinary Portland Cement (OPC). However, one of the few disadvantages still lies in the rheology of calcined clay-containing materials. Once water has been added, they are not as easy to handle as traditional Portland cement, making them somewhat more difficult to work with on the construction site. 

This is where my research comes in and tries to find a way to firstly investigate and secondly influence the crystallisation of the different hydrates in LC³, making it more applicable for construction. Hereby, the hydrates (C-S-H, C-A-S-H, ettringite, calcium carboaluminates, AFm and AFt phases,...) are synthesised via a precipitation reaction from an aqueous solute phase and subsequently analysed. The aim is to monitor the nucleation and control it through additive assistance. For that, analytical methods like FTIR, SEM, EDX, TEM, SAED, TGA, ITC, XRD, DLS, AUC, 1H-/ 13C-/ 27Al-/ 29Si-NMR, and more, are used.

Responsibilities

The design and synthesis of low-dimensional nanomaterials and hydroxides with intercalated anions

Qiqi's research mainly focuses on the design and synthesis of low-dimensional nanomaterials and hydroxides with intercalated anions. On the one hand, the performance of a material is strongly related to its size and dimensions. However, the complexity of the synthesis system caused by the multitude of hydroxide species and the lack of suitable research methods not only results in the current preparation of target hydroxides primarily relying on empirical "trial and error" methods, but also causes some technical deficiencies in existing preparation methods, such as high cost, cumbersome operation, and the use of toxic organic solvents in the synthesis process. In response to this problem, Qiqi plans to use a combination of “theoretical simulation, empirical knowledge analysis, and experimental verification” to explore how to establish a model that can guide the preparation of materials with specific dimensions/sizes. On the other hand, the intercalation of guest anions can affect the final size, composition, morphology, and performance of hydroxides. However, the ultra-small size of intercalated anions and the instantaneous nature of intercalation/deintercalation makes the feasible methods for studying the intercalation mechanism relatively scarce, leading to a bottleneck problem of the inability to deeply understand the mechanism of the effect of reaction parameters on the intercalation process of anions at the molecular/atomic level. To address this issue, Qiqi plans to explore and study the causal quantitative relationship between external reaction parameters (such as temperature, concentration, reaction pH, etc.) and the intercalation mechanism of anions with the help of NH₃ diffusion-induced hydroxide precipitation and in situ pH monitoring.

Responsibilities

Project Titel: Synthesis of Immiscible Noble Metal Alloy Nanocrystals by Pulsed Laser Irradiation

Research Interests:
The need for efficient catalysts in sustainable chemical industrial processes, as well as novel optic and medical applications have led to an increasing scientific interest in the synthesis of noble metal Nanocrystals with precisely tailored properties. In the field of catalyst development, the trend is going towards highly sophisticated Nanoparticles with novel compositions, morphologies and crystallographic properties, aiming to minimize the amount of rare and expensive metals needed.

In our work, we focus on developing advanced colloidal synthesis methods in non toxic solvents like water or ethylene glycol, that provide excellent control over particle size and shape. Transfering particles between different solvents enables us to connect classical Gold Nanoparticle syntheses in aqueous medium with polyol methods for elements like Iridium, Rhodium and Ruthenium, increasing the amount of opportunities for seed mediated growth syntheses.

Our goal is also to develope pulsed irradiation based methods to obtain Nanomaterials with new compositions, that cannot be obtained easily by classical syntheses. This involves investigating different pulse properties, like width, wavelength and energy as well as the parameters involved in colloidal stabilization of the particles during the irradiation. This may provide access to particles with highly strained crystal lattices and catalytically active surfaces, due to their unconventional compositions.

Responsibilities

Quantitative analysis of nanoparticle interactions and their distributions

The aim of the research is to develop a new methodology to determine size- and shape-dependent distributions of interaction constants, stoichiometry, and cooperativity of the aggregation process, even of polydisperse isotropic and anisotropic nanoparticles using combined sedimentation- and diffusion coefficient distributions from Analytical UltraCentrifugation (AUC).

Regarding anisotropic nanoparticles, face dependent interactions play a fundamental role, and this shall be investigated as well.

Once interactions between similar monodisperse, isotropic nanoparticles have been investigated, more complex systems, made up of polydisperse, isotropic nanoparticles shall be considered.

Despite the large volume of information on nanoparticles, regarding the systems per se, but also their applications in different fields, the determination of the strength of interaction and with it the thermodynamic driving force, as well as the stoichiometry of particle interactions and the cooperativity remains elusive. This is why this investigation is deemed necessary.

AUC is used to compare and implement the result normally obtained with Dynamic Light Scattering (DLS) and Isothermal Titration Calorimetry (ITC): the problem with the DLS, even though it has since been established as a solid analysis to evaluate the size of nanoparticles, is that it overestimates the larger sizes in the sample due to the ratio of scattering intensity to particle radius to the power of 6; on the other hand, ITC only gives average interactions values, and requires a substantial amount of sample.

Considering nanoparticles with broader size and/or shape distribution, a distribution in the interaction constant and stoichiometries is to be expected: AUC permits to physically separate nanoparticles of different size and shape and detects every particle. Thus, AUC is able to determine distributions rather than average values.

Still, the AUC analysis needs to be validated: for this, Field Flow Fractionation (FFF), separating the particles and determining their diffusion coefficient- and particle size distributions, and Transmission Electron Microscopy (TEM), for size and shape analysis, will come in hand to complement the results obtained from AUC.

Planned systems to be investigated are polystyrene and gold spherical nanoparticles, gold nanorods and cubic/cuboids nanoparticles based on oxides of manganese and iron.

Responsibilities

Project Title

Synthesis and Characterization of Multielemental Colloidal Nanocrystals

Research Interests

Plasmonic hybrid metal-semiconductor nanocrystals (NCs) have emerged as promising candidates to address energy and environmental challenges through solar-powered heterogeneous catalysis. By combining both plasmonic metal and quantum sized semiconductor (SC) materials, these nanocrystal heterostructures exhibit unique and enhanced synergistic properties which can be precisely tuned for the desired photocatalytic application via their composition, size, and shape.

However, the synthesis of metal-SC NCs prepared in an either aqueous or organic medium by colloidal chemistry methods using heterogeneous seeded nucleation and growth is still challenging. They either suffer from poor crystallinity of the SC shell when synthesized in water or are severely limited in the size of the metal NC core due to the lack of accessible surface ligands to stabilize large metal structures in organic solvents.

In the current project, we aim to bridge this gap by developing an advanced route for the synthesis of colloidal hybrid metal-SC NCs with tunable dimensions, morphologies, compositions and atomic distributions. The core of the proposed strategy consists of the use of a custom-designed polymer that enables the transfer of noble-metal nanoparticles of different dimensions and shapes from water to organic, apolar solvents. After stabilization in organic solvents, crystalline metal chalcogenides but also oxides, phosphides or nitrides can be successfully grown on the noble metal NCs.

The proposed strategy will open new pathways to exploit the full potential of previously inaccessible noble metal and semiconductor heterostructures by precisely fine-tuning dimension, morphology, and composition for potential photocatalytic applications.

Education

08/2022 – Present

University of Konstanz: Doctoral Candidate

Department of Chemistry

Topic: "Synthesis and Characterization of Multielemental Colloidal Nanocrystals"

Working Group: Prof. Dr. Helmut Cölfen in cooperation with Dr. Guillermo González-Rubio

(Physical Chemistry)

12/2022 Symposium NanoBW 2022

04/2019 – 06/2022

University of Konstanz: Master Studies in Nanoscience

Study Focus:

• Current Issues and Methods in Nanoscience
• Nano/Material Analytics
• Semiconductor Technology and Physics of Solar Cells (inorganic/hybrid/organic)
• Surface Science and Heterogeneous Catalysis

Thesis: "Preparation and Optical Gain Measurements of Homogeneous Nanocrystal Films for Lasing Applications"

Working Group: Prof. Dr. Klaus Boldt in cooperation with Prof. Dr. Helmut Cölfen

(Physical Chemistry)

01/2022 – 06/2022 Industrial Internship

Innovative Sensor Technology iST AG, Ebnat-Kappel, Sankt Gallen, Schweiz

Research and Development of Conductivity Sensors and Microheaters manufactured by Thick Film Technology

10/2015 – 03/2019

University of Konstanz: Bachelor Studies in Nanoscience

Thesis: "Two-dimensional Hybrid Perovskite Phases with a Photoswitchable Additive"

Working Group: Prof. Dr. Sebastian Polarz

(Material Science)

Responsibilities

Equipment Supervisor for Cary 60 UV/Vis in PAC

Responsibilities

From Biogenic to Advanced CaCO₃ Materials

Research Interests

Electric parts and circuits have become essential components of modern-day life. As we continue to rely on these technologies more and more, the search for materials that are both feasible and practical becomes increasingly important. Traditional materials like metals have drawbacks, such as being difficult to process, expensive, and not environmentally friendly. Finding alternative materials that can overcome these limitations is crucial to the ongoing advancement of electrical technology. This search for new materials leads us toward electrically conductive polymers.

Via chemical alterations of electrically conductive polymers and introducing other materials to the polymer we can enhance the material properties. This leads us towards waste seashells since its nanostructure can increase the conductivity of the polymer when this structure is transferred. Additionally, waste seashells are abundant (7 Mtons per year) and also a renewable resource.

Our goal is to create electrically conductive composite materials that are composed of seashell particles and electrically conductive polymers. To accomplish this, we utilize seashell waste and transform it into a CaCO₃ powder, which we then use as a template for polypyrrole (PPy) synthesis resulting in PPy/CaCO₃ composite particles. Depending on their further application (eg. antistatics, sensors), different composite particles are formed.

Responsibilities

Raman detection in Field-Flow-Fractionation

Asymmetric flow Field-Flow-Fractionation is a chromatographic technique that separates analyte particles, such as proteins, polymers, or inorganic nanoparticles, based on their size.
Commonly, light scattering, refractive index detection, and UVVis Absorption is used to detect the fractionated sample.

An on-line flow raman detection device is developed to extend this detection chain.

The raman effect is a scattering effect that induces a wavelength shift in the scattered light based on the bond structure of the sample.
Thus, information about the molecular structure of the sample can be obtained in a non-invasive way without the use of labels.

In the on-line flow raman detection device, these raman signals can be detected along the other detection signals from the detection chain.
This can be used to gain further insight into complex mixtures of different analytes using global analysis and reveal properties not otherwise accessible.

Responsibilities

Chemistry for cultural heritage preservation of porous stone materials

Andra-Lisa Hoyt's research focuses on the intersection of materials science with conservation and restoration of cultural heritage objects, specifically stone objects, which are subject to natural and human-accelerated degradation, e.g. through climate change. Her work involves the development and testing of treatment options for porous materials, which are particularly vulnerable to the ingress of pollutants. Her doctoral thesis includes the prediction of infiltration behavior of restoration-relevant material/liquid systems using a micro-model, characterization and testing of alternative restoration materials for porous carbonate stones, and the study of liquid mineral precursors as a binder for loose grains. The results of her research have the potential to shorten the time frame for object characterization and compatible treatment, as well as the development of new restoration materials.

In 2018 she was awarded a personal doctoral scholarship by the German Federal Environmental Foundation and now continues her research on a University scholarship. She has presented her work at multiple international conferences such as the American Chemical Society Meeting, assemblies of the young chemists’ society of Germany, and crystallization conferences (CRYSPOM).

Keywords: infiltration, porous materials, micromodels, liquid mineral precursors, stone treatment, material characterization

Education: 

01/2018 - Present
University of Konstanz: DBU-Fellow and Doctoral Candidate with Prof. Dr. Cölfen, Department of Chemistry  07/2017 - 09/2017
BASF, Ludwigshafen: Internship in Research and Development  06/2014 - 04/2017
University of Konstanz: Master studies and Thesis with Prof. Dr. Cölfen, Department of Chemistry
"Calcium Carbonate Precursor Formulations for Consolidation and Restoration of Carbonate-based Artifacts" 09/2013 - 05/2014
University of Massachusetts Amherst: Graduate Studies Abroad in the Chemistry Department and Research Internship in the Polymer Science & Engineering Department with Prof. Dr. Briseno 10/2010 - 08/2013
University of Konstanz: Bachelor studies and Thesis with Prof. Dr. Winter, Department of Chemistry
"Divinylphenylenverbrückte heterobimetallische Ru/Os-Komplexe: Synthese neuer Verbindungen und Studium der elektronischen Struktur"

Research Interests: 

"Preservation of carbonate-based natural materials based on a better understanding of crystallization processes in pores"
Liquid Precursors, Calcium Carbonate, Stone Conservation

Responsibilities

Project title:

Towards Monodispersity in Biomimetic Silica-Carbonate Microstructures

Project description:

In my research, I focus on optimizing the synthesis of biomimetic silica-carbonate microstructures (so-called Silica-Biomorphs) towards a selective, monodisperse production of the individual morphologies.

Silica-Biomorphs are a completely inorganic alternative to form microstructures showing a variety of biomimetic morphologies from atmospheric carbon dioxide and an alkaline solution containing silicate and alkaline earth metal salts. Thus, differently sized and shaped structures that can reach lengths of several hundred micrometres to millimetres can be obtained. They consist of amorphous silicon dioxide and self-assembled alkaline earth metal carbonate nanocrystals.

So far, the exact mechanisms of the formation and the factors influencing the self-assembly of the nanocrystallites and thereby the resulting morphology are still largely unknown. This knowledge, though, is necessary for the selective production of defined structures that allow the investigation of shape-property relationships to lead to new applications.

Therefore, I developed a flow cell setup that allows knowledge and control over system parameters during the reaction. With this, experiments are carried out to screen those system parameters and gain new insights into the dependence of the synthetic parameters on the morphological outcome. This already enabled a new selective synthesis of coral-like structures and could also make deterministic syntheses of other desired morphologies accessible in the future.

Responsibilities

Design of Polymeric Surface Ligands for the Controlled Growth and Assembly of Colloidal Nanocrystals

Research Interests

In recent years, intense research efforts have been dedicated to understanding the co-assembly of different colloidal nanoparticles into complex superstructures with emerging and unique physicochemical properties. In this context, mesocrystals represent a distinctive class of structured material in which crystalline faceted nanoparticles organize themselves following a defined pattern that results in long-range atomic ordering in at least one dimension. Thereby, mesocrystals can display directional, enhanced, or emerging properties not observed in non-mesocrystalline assemblies.

Unfortunately, it is challenging to fabricate mesocrystals consisting of two or more components due to different attractive van der Waals interactions between nanoparticles with various compositions. To face this challenge, it is fundamental to control the effective screening of attractive forces. Notably, this can be achieved by covering the surface of nanocrystals with surface ligands capable of providing desired repulsive interactions via steric or electrostatic repulsion.

In this research project, we have developed a method for the synthesis of surface ligands bearing different surface linkers and polymer chains for the stabilization of metal nanoparticles in different apolar solvents. With this surface ligands, we aim to achieve the fabrication of binary mesostructures and more complex superstructures by controlling the material, size and morphology of the applied nanoparticles.

Responsibilities

Block copolymers for the dissolution of atherosclerotic plaques

In my PhD project I am synthesizing copolymeric nanoparticles. These are composed of bio-inspired poly(2-oxazolines). Various analytical methods and techniques are used to characterize the functional polymers. Their chemical composition is determined using gel permeation chromatography (GPC), infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. Applying dynamic light scattering (DLS), analytical ultracentrifugation (AUC) and particle tracking microscopy (PTM), their sizes are investigated on the nanometer scale. By means of “click reactions”, the polymer backbones are equipped with diverse functional groups to dissolve pathological, cholesterol and mineral calcium phosphate deposits. Potentiometric titrations, UV/VIS and inductively coupled plasma optical emission spectrometry (ICP-OES) are employed to evaluate the maximum dissolution capacity in vitro. Thus, this nanomedicine approach aims to prevent the formation/development of atherosclerotic plaques in blood vessel walls. Furthermore, multiple cytotoxicity studies on different cell lines will be used to evaluate the biocompatibility of the functional nanoparticles. The polymers will be tested in vivo in cooperation with the Albert-Ludwigs-University Freiburg. The aim is to investigate whether the fluorescence-labeled polymers are excreted by the test animals.