Education

OVERVIEW

Nitrate (NO₃^-) and nitrite (NO₂^-) are water contaminants that can cause human diseases such as blue baby syndrome when consumed with drinking water or which can lead to eutrophication in natural waters. NO₃^- and NO₂^- can be catalytically converted to N₂ by heterogeneous metal catalysts consisting of e.g. palladium and a promotor metal such as tin, indium or copper.^[1] Up until now, activity, selectivity and stability are insufficient for a commercial process. Therefore, we would like to fundamentally understand interaction of the two different catalyst metals to be able to prepare catalysts by design rather than by trial and error.

Figure 1: Proposed reaction pathway for bimetallic NO₃^- and NO₂^- reduction.

Heterogeneous catalysts typically consist of inorganic supports such as Al₂O₃ or SiO₂ on which metal particles are deposited. Depending on the preparation method the microscopic metal structure and the metal-support interaction varies. In case of bimetallic catalysts, the two metals can form e.g. well mixed alloys, core-shell arrangements or separated particles.^[2] For the nitrate reduction reaction close proximity or at least electron shuttle possibilities^[3] are required for the regeneration of the Sn active sites (Figure 1). Therefore, it is of particular interest to prepare catalysts with close interaction of the metals. To do so, the chemical toolbox offers advanced catalyst preparation techniques such as co- or sequential strong electrostatic adsorption (co-/sq.-SEA),^[4] charge enhanced dry impregnation (CEDI),^[5] controlled surface deposition (CSD)^[6] which exceed the potential of commonly applies dry- or wet impregnation preparations.^[2]

LEARNING OBJECTIVE 

In your project, you will use advanced catalyst preparation techniques to prepare well controlled bimetallic catalyst with strong metal-metal interactions. Based on existing knowledge in our research group and your catalytic reaction results you will optimize the formulation of your catalysts and characterize them in depth. The catalytic tests will be conduced in batch and/or flow condition with subsequent ion chromatographic (IC) analysis. For the catalyst characterization XRF, XRD, CO-chemisorption, N₂ physisorption, TPR/TPD are readily available in our Labs and STEM, EDS and ICP can be arranged.

CONTACT INFORMATION

Daily Supervisor: Janek Betting (j.betting@utwente.nl)
Supervisor: Prof. Dr. Jimmy Faria Albanese (j.a.fariaalbanese@utwente.nl)

 LITERATURE

[1] I. Sanchis, E. Diaz, A. H. Pizarro, J. J. Rodriguez, A. F. Mohedano, Sep Purif Technol 2022, 290, 120750.
[2] B. A. T. Mehrabadi, S. Eskandari, U. Khan, R. D. White, J. R. Regalbuto, Adv. Catal. 2017,61, 1-35.
[3] K. M. Lodaya, B. Y. Tang, R. P. Bisbey, R. P. Bisbey, S. Weng, K. S. Westendorff, W. L. Toh, J. Ryu, Y. Roman-Leshkov, Y. Surendranath, An electrochemical approach for designing thermochemical bimetallic nitrate hydrogenation catalysts, Nat Catal 2024.
[4] A. Wong, Q. Liu, S. Griffin, A. Nicholls, J. R. Regalbuto, Science 2017, 358, 1427-1430.
[5] X. Zhu, H.-R. Cho, M. Pasupan, J. R. Regalbuto, ACS Catal. 2013, 3, 4, 625-630.
[6] A. Garron, K. Lázár, F. Epron, Appl Catal B 2005, 59, 57–69.

OVERVIEW

A lean methane oxidation catalyst is needed to overcome the main problem of LNG-fueled ships, methane slip. The use of LNG-fueled instead of the standard MDO-fueled ships brings a reduction in emissions of harmful gases, such as SO_x, NO_x, and CO₂, among others. [1] Nonetheless, the utilization of natural gas as a propellant leads to the release of unburnt methane, known as methane slip. Considering the substantially higher global warming potential of methane compared to CO_2, [2] it is environmentally prudent to oxidize the unburnt methane into CO₂. This necessitates the development of catalysts with high activity and stability in the presence of sulfur and water.

Pd-Pt/CeO₂ morphs into nanorods, nano-octahedrons, and nanocubes. Palladium (Pd) stands out as the most active metal in the context of lean methane oxidation oxidation. [3] Nevertheless, Pd is highly vulnerable to water and sulfur poisoning. To address this issue, studies suggest that the addition of platinum (Pt) may enhance resistance to water and sulfur poisoning. [4] Additionally, the inclusion of cerium dioxide (CeO₂) has the potential to boost the concentration of oxygen vacancies, a crucial factor in oxidation reactions. Furthermore, tailoring different morphologies of CeO₂ could further amplify its catalytic capabilities [5]

LEARNING OBJECTIVE

• Synthesizing novel Pd-Pt/CeO2 nanorods, nano-octahedrons, and nanocube catalysts, to derive state-of-the-art kinetics using the experimental setup equipped with online GC
• Learning and performing multiple types of catalyst characterizations
• Learning about advanced infrastructure to acquire experimental data and perform the characterizations

CONTACT INFORMATION

Daily Supervisor: Martim Policano Chiquetto (m.chiquettopolicano@utwente.nl)
Supervisor: Prof. dr. Jimmy Faria Albanese (j.a.fariaalbanese@utwente.nl)

LITERATURE

[1] Gélin & Primet, 2002; Hua et al., 2017
[2] Derwent, 2020
[3ab] a.Fujimoto et al., 1998; b.Gélin & Primet, 2002
[4] Nassiri et al., 2018; Sadokhina et al., 2018
[5] Sakpal & Lefferts, 2018

OVERVIEW

Direct semiconductor-based photocatalytic conversion of solar energy to chemical fuels is considered an ideal renewable energy resource for the future. Yet, the relatively low energy conversion efficiency of current materials and systems has been limiting practical applications up until now. According to the current paradigm, optimum performance is achieved by using faceted semiconductor nanoparticles and by functionalizing them in a facet-selective manner with suitable cocatalysts for the desired redox reactions, such as water splitting or CO₂ reduction. In literature, it is often shown that Ag, Au, and Pt occur preferentially on electron-accumulating facets ({010} for BiVO₄), whereas the oxidative deposition of MnOx and PbO₂ takes place on hole-accumulating facets ({110} for BiVO4) (Fig. 1a-b). Recently, researchers at PCF observed, using the specific example of BiOBr and BiVO₄ particles, photo-induced reductive or oxidative deposition of co-catalysts onto plate-like semiconductor particles is pH-dependent and strongly affected by the presence of alkali chloride salts (Fig. 1c-d).

Figure 1. Sketch of selective photo-deposition of cocatalysts on BiVO₄. SEM image of dual components (Au/PbO2/BiVO₄) photo-deposited on the surface of BiVO₄. Anion effects on the reductive and oxidative photo deposition (c-d). Reductive photo deposition of Au in 10 mM NaCl (b), 10 mM NaClO₄ (d).

RESEARCH OBJECTIVE

The big question of this Bachelor assignment is to identify how fluid composition (pH and salt content) influence cocatalyst deposition (metal/metal oxide) on faceted nanoparticles. To this end, you will perform the photodeposition of cocatalyst nanoparticles on well-defined, faceted BiVO₄  (or SrTiO₃) and quantify the influence of fluid composition. The morphologies and microstructures of the as-prepared samples will be analyzed by high-resolution Scanning Electron Microscopy. From these measurements, you will extract the location (facets and defects) and size of the cocatalyst, their coverage, as well as the amount of deposited cocatalyst. Depending on your expertise and/or interest, you can quantify the photocatalytic activity of materials using gas chromatography technology or assessed by dye degradation from the PhotoCatalyticSystems group. Controlled deposition of cocatalysts (metal or metal oxide) on faceted nanoparticles via fluid composition is easier as compared to controlling particle synthesis protocols. This could potentially give rise to better photocatalytic performance and stability for the materials.

LEARNING OBJECTIVE

In addition to the standard learning objectives for a Bachelor’s/Master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

·        Obtain knowledge on photocatalysis; NPs colloidal interaction; ions adsorption
·        Learn about the physical chemistry of aqueous electrolyte and solid-electrolyte interfaces (which are both ubiquitous in nature and technology)
·        Have basic chemical-lab training (preparing solutions and surfaces, etc.)
·        Learn how to handle colloidal suspensions and carry out photo-deposition of cocatalyst
·        Depending on your interests, may analyze the samples activity using Gas Chromatography

Contact Information

Daily Supervision: Dr. Igor Siretanu  (i.siretanu@utwente.nl)
Daily Supervision: Dr. Michel Duits (m.h.g.duits@utwente.nl)
Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

OVERVIEW

Olivine is one of the prime candidate materials for CO₂ conversion and capture because it is very abundant in the earths crust and can be converted into environmentally benign and thermodynamically stable MgCO₃ [1]. However under natural weathering conditions (exposure to atmosphere or seawater) the conversion of olivine rock is very slow (hundreds of years). This process can be accelerated by using reactors at elevated temperature and pressure and/or by increasing the reactive surface area via  grinding into small olivine particles [2].

Experiments with cm-scale Olivine crystals in our lab confirmed the strong effect of pH and temperature on dissolution rate [3], but also some unresolved mysteries were revealed. Evidence was found for the formation of a (passivating) Surface Alteration Layer (SAL) and also strong increases in surface rough-ness were observed. The question is, to what extent these phenomena play a role if instead of cm-scale crystals, 10-100 μm-scale grains are used. Crystal planes will be less prominent, and dissolution-induced erosion could make the grains smoother instead of rougher. At this smaller scale also the diffusion of released ions will be faster, with possible consequences for the formation of a SAL.

Left: SEM image of small Olivine grains obtained after milling [1]. Right: Confo-cal Raman microscope, here used for examining a large olivine pebble. Grinding the latter into 10-100 μm-scale grains should strongly enhance the dis-solution rate while still allowing optical microscopy.

RESEARCH OBJECTIVES

The main question to be addressed is: How do olivine micro-grains dissolve in acid? In particular: How fast do they dissolve? How does the shrink-rate depend on grain size? What happens to the shape? These questions will be approached via optical microscopy in a micro-container. High magnification microscopy allows studying the size and shape of the grain while it is dissolving. The small dimensions of the surrounding liquid (e.g. a microfluidic container) will ensure rapid homogenization via diffusion. Mg²⁺ (and Fe³⁺) and H⁺ concentrations will evolve as the dissolution proceeds, and can be detected in certain ranges with fluorescence- or Raman-based microscopies. Ex-situ characterization of pristine or partially dissolved grains with e.g. SEM, AFM, profilometry can be provided as service measurements.

LEARNING OBJECTIVES

In addition to the standard learning objectives for a Bachelor’s project (research planning, academic writing, data presenting, etc.), you will learn how to:

·         explore some unchartered terrain in the context of in situ dissolution of micro grains
·         perform mineral dissolution and optical microscopy experiments in the lab
·         interpret the measured morphologies, ion concentrations in the context of dissolution and diffusion 

CONTACT INFORMATION

·         Daily Supervision: Dr. Michel Duits (m.h.g.duits@utwente.nl)
·         Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

REFERENCES

1.       Rigopoulos, I, et al. Carbon dioxide storage in olivine basalts: effect of ball milling process. Powder technology 273 (2015): 220-229.

2.       White, Arthur F., and Susan L. Brantley, eds. Chemical weathering rates of silicate minerals. Vol. 31. Walter de Gruyter GmbH & Co KG, 2018.

3.       Oelkers, Eric H., et al. Olivine dissolution rates: A critical review. Chem Geology 500 (2018): 1-19.

OVERVIEW

The interfacial water structure and the associated short-range hydration forces have long been recognized as essential for many phenomena and processes in nature and technology, including the stability of colloidal systems, the assembly of soft biological and non-biological matter on molecular and supramolecular scales, wetting, water desalination, lubrication, and catalysis, including in particular electro-(phooto)catalytic water splitting. In recent years, advances in atomic force microscopy technology have enabled the imaging and probing of Derjaguin–Landau–Verwey–Overbeek (DLVO) and hydration forces at solid-liquid interfaces with unprecedented resolution (Fig. 1a.). The charge and polarizability of the interface and surrounding ions, ion valency, and concentration are all expected to play a role in determining the relative magnitude of hydration forces. Recently, researchers at PCF observed that hydration forces (oscillatory and a monotonically decaying part) between sharp silica AFM tips at mica-water interfaces are strongly affected by the presence of alkali chloride salts (Fig. 1b.). The monotonic hydration force gradually decreases in strength with decreasing bulk hydration energy, leading to a transition from an overall repulsive (Li⁺, Na⁺) to an attractive (Rb⁺, Cs⁺) force. The oscillatory part, in contrast, is hardly affected by the presence of strongly hydrated cations (Li⁺, Na⁺), but it becomes completely suppressed in the presence of weakly hydrated cations (Rb⁺, Cs⁺) (Fig. 1b.).

Figure 1. a) Schematic of water layers with highly ordered surface-bound layers of opposite polarity and gradually increasing positional and orientational order with increasing distance from the solid surface. Schematics for the AFM measurement on hydration layers on a negatively charged surface. b) Averaged force gradient (−dF/dz; thick green lines) and normalised force (F/R; thin black lines) versus apparent tip-sample separation measured in 50 mM NaCl and CsCl solutions..

RESEARCH OBJECTIVE

The big question of this Bachelor assignment is to identify how anions influence hydration forces on mica surfaces. To this end, you will perform Atomic Force Microscopy measurements in ambient aqueous electrolytes of variable composition (salt content, pH) to follow the evolution of hydration forces for a set of common anions (ClO₄⁻, NO₃⁻, and SO₄²⁻) with Na⁺ and Cs⁺ as the co-ions. It will also be explored how the hydration forces depend on the AFM tip type and surface charge.

LEARNING OBJECTIVE

In addition to the standard learning objectives for a Bachelor’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

·        Learn to perform and interpret high resolution in situ Atomic Force Microscopy experiments
·        Learn about the physical chemistry of aqueous electrolyte and solid-electrolyte interfaces (which are both ubiquitous in nature and technology)
·        Have basic chemical-lab training (preparing solutions and surfaces, etc.)

CONTACT INFORMATION

Daily Supervision: Dr. Igor Siretanu  (i.siretanu@utwente.nl)
Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

INTRODUCTION

Interactions between colloidal particles (e.g. silica, polystyrene or PMMA latex spheres) are key determinants of their self-assembly into composite particles, aggregates or crystals, and macroscopic behaviors like phase transitions or flow mechanics. However, both theoretical expressions for the forces and experimental methods for measuring them have shortcomings. One approach for measuring the interaction free energy ∆G(r) between two colloids makes use of the Boltzmann probability:

P(r)=Poexp(-∆G(r)/kT).

Using optical microscopy and image processing software, it can essentially be ‘counted’ how frequently each distance r is found. However demonstrations of this principle are relatively scarce.

Meanwhile, knowing the colloidal interactions between two dissimilar spheres is important for the design of e.g. photocatalysts or diagnostic tracers. For example, the coating of a large (+) sphere with small (-) spheres, can be achieved via electrostatic attraction (see Figure). However as the adsorption progresses, the central particle will become less attractive while the adsorbing spheres will increasingly repel each other. The final state will then depend on the strength of the electrostatic interactions.

Left: fluorescence microscopy snapshot of 1 μm size spheres adsorbed onto a 5 μm sphere. The non-adsorbed 1 μm spheres are diffusing freely. Right: Time-projection image from a 5 minute video of the same experiment.The dark outer ring could be indicative of the electrostatic repulsion between the diffusing 1 μm spheres.

RESEARCH OBJECTIVES

The main goal of the BSc assignment is to demonstrate the capabilities of measuring the ∆G(r) between two dissimilar charged colloidal spheres. Insights into the dependence of ∆G(r) on the aqueous ion composition are available from colloid science, while state-of-the-art microscopy for live particle imaging and some analysis software are present in the PCF group. A possible challenge is the occurrence of interactions much stronger than the kT-scale; this could be mitigated by changing pH, salinity or particles (size, surface chemistry).

 LEARNING OBJECTIVES

In addition to the standard learning objectives for a Bachelor’s project (research planning, academic writing, data presenting, etc.), you will:

·        Increase your practical and theoretical skills on working with colloids (if needed, a personal ‘mini course’ will be included)
·        Learn how to work with a Confocal Scanning Laser Microscope
·        Use and (co-) develop image analysis software

CONTACT INFORMATION

·        Daily Supervision: Dr. Michel Duits (m.h.g.duits@utwente.nl)
·       Supervision: Prof. Dr. Frieder Mugele (f.mugele@utwente.nl)

REFERENCES

1.      Royall, CP, Louis, A A., & Tanaka, H. Measuring colloidal interactions with confocal microscopy. The Journal of chemical physics, 127(4) (2007).
2.      Adamczyk, Z, & Warszyński, P. Role of electrostatic interactions in particle adsorption. Advances in Colloid and Interface Science, 63 (1996), 41-149.

BACKGROUND

Polar materials are a class of materials with a switchable electrical polarization that can affect surface stoichiometry, surface chemistry, the electronic structure of the surface and the bulk of the material. Furthermore, due to their persistent response to electric fields, ferroelectrics, a special class of polar materials, offer a unique opportunity to tune the properties of a surface via an external field. These properties make polar/ferroelectric materials very interesting for electrocatalysis as they potentially could be used to enable a new level of control over the surface of a catalyst during catalysis. [1]–[3]

Based on this idea various authors have reported different cases of experimental and theoretical work on enhancement of the OER in electrochemistry by using polar/ferroelectric catalysts. However, no clear mechanism for ferroelectric OER enhancement or design rules for polar/ferroelectric OER catalyst purposes have been found. Our challenge is  to find a clear correlation between activity and local polar/ferroelectric properties in OER catalysts such that a better understanding of the possible use of ferroelectric materials for OER catalysis can be obtained. We propose the use of epitaxial thin film oxides as model systems to experimentally investigate correlation. These pulsed laser deposition (PLD) grown well-defined epitaxial thin catalytic films allow us to carefully tune the polar properties of the material to try to differentiate magnetic induced effects from effects induced by its other properties. Moreover, as the surface chemistry, structure and charge are hypothesized to be the key parameters in understanding the correlation between polarity and OER activity [2,4,5,6] local probes of these parameters under OER conditions are identified as ideal candidates for studying polar/ferroelectric model systems. [7]

In this master thesis we will use a dual-scale Atomic Force Microscopy (ds-AFM) method that allows the determination of local surface potentials with a lateral resolution of ≤10nm in combination with atomic resolution imaging of surface structures, defects, and adsorbed ions in ambient electrolytes. In a previous thesis, it has been shown that the ds-AFM method with its unique resolution to operando conditions can be used to study polar/ferroelectric model electrocatalysts under operando conditions. Preliminary data and previous literature show indications for interesting effects when changing different parameters like, PH, salt concentration, local applied fields and applied potentials. [7, 8 ] However, additional research needs to be done to systematically study the effects of these external stimuli. Based on this enhanced understanding we will try to utilize these stimuli to tune our electrocatalysts while studying them in operando. Ds-AFM will be combined with x-ray photoemmision spectroscopy and kelvin force microscopy in respectively vacuum and air to compare surface charges in liquid, vacuum and air to further investigate the effect of the environment.

Figure 1: Summary of techniques which will be used in this master thesis

RESEARCH QUESTIONS

In this master thesis you will focus on answering the following questions:

• What is the local surface charge or potential of a polar/ferroelectric model system structure in different atmospheres (vacuum, air, water)? How does the history of the sample influence this? Can we use the atmosphere to tune the surface charge? F.e. change polarity with PH as shown in [8]
• How do the pH of the electrolyte, ions, and applied potential affect the local surface charge or potential of a polar/ferroelectric model system structure change under applied potential? And the morphology of the sample? And the local double layer environment?
• How do the morphology, surface charge and double layer affect OER activity measured of the polar model catalysts?
• Possibly: How do the measured surface charges couple to polarization?

These questions will be addressed by using a multidisciplinary approach wit different characterization techniques as summarized in figure 1. Using atomic force microscopy operated in ‘dual-scale’ mode, which combines colloidal scale AFM spectroscopy with somewhat larger tips (radius 5–50 nm) with atomic resolution imaging using ultra-sharp tips (radius 1-2 nm), you will measure local surface potentials with a lateral resolution of ≤10nm in combination with atomic resolution imaging of surface structures, defects, and adsorbed ions in of ambient electrolytes of a range of PHs containing different ions. Kelvin probe microscopy (KPFM) will be used to measure the surface charge of the polar catalyst in air. X-ray photoemission spectroscopy (XPS) will be used to determine the accumulation of charges at the surface in vacuum. X-ray diffraction will be used to verify crystallinity of model systems. Moreover, films will be grown using pulsed laser deposition. All these equipment is readily available at the labs of Mesa+ and PCF.

LEARNING OBJECTIVES

In addition to the standard learning objectives for a Master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

• Learn how to work with Atomic Force Microscopy in air/liquids and Electrochemical AFM (EC-AFM)
• Learn how to do pulsed laser deposition (PLD) and pre-characterize thin film catalysts using X-ray diffraction (XRD) and X-ray Photoemmision spectroscopy
• Learn how to work with kelvin probe AFM
• Acquire or increase your lab experience with thin film catalysts
• Learn fundamental concepts of electrocatalysis

CONTACT INFORMATION

Dr. Igor Siretanu (daily advisor)
MSc. Emma van der Minne (daily advisor)
Prof. Frieder Mugele and Dr. Chris Baeumer (thesis supervisors)

 REFERENCES 

[1] Y. Li, J. Li, W. Yang, and X. Wang, “Implementation of ferroelectric materials inphotocatalytic and photoelectrochemicalwater splitting,” Nanoscale Horiz, vol. 5, p. 1174, 2020, doi: 10.1039/d0nh00219d.

[2] A. Kakekhani and S. Ismail-Beigi, “Polarization-driven catalysis via ferroelectric oxide surfaces,” Phys. Chem. Chem. Phys, vol. 18, 1967, doi: 10.1039/c6cp03170f.

[3] A. Kakekhani, S. Ismail-Beigi, and E. I. Altman, “Ferroelectrics: A pathway to switchable surface chemistry and catalysis,” Surface Science, vol. 650, pp. 302–316, 2016, doi: 10.1016/j.susc.2015.10.055.

[4] A. Vijay, K. v. Ramanujachary, S. E. Lofland, and S. Vaidya, “Role of crystal structure and electrical polarization of an electrocatalyst in enhancing oxygen evolution performance: Bi-Fe-O system as a case study,” Electrochimica Acta, vol. 407, p. 139887, Mar. 2022, doi: 10.1016/J.ELECTACTA.2022.139887.

[5] I. Efe, N. A. Spaldin, and C. Gattinoni, “On the happiness of ferroelectric surfaces and its role in water dissociation: The example of bismuth ferrite,” Journal of Chemical Physics, vol. 154, no. 2, 2021, doi: 10.1063/5.0033897.

[6] A. Kakekhani and S. Ismail-Beigi, “Ferroelectric-Based Catalysis: Switchable Surface Chemistry,” ACS Catalysis, vol. 5, no. 8, pp. 4537–4545, 2015, doi: 10.1021/acscatal.5b00507.

[7] Master thesis Nynke Wijnant, Characterization of BiFeO₃ as thin film polar model electrocatalyst, 2024, University of Twente

[8] Tian, Y., Wei, L., Zhang, Q. et al. Water printing of ferroelectric polarization. Nat Commun 9, 3809

OVERVIEW

Benefits that could arise from implementation of a lean methane oxidation reactor in LNG ships are a drastic reduction in the global warming potential. The use of LNG-fueled instead of the standard MDO-fueled ships brings a reduction in emissions of harmful gases, such as SO_x, NO_x, and CO₂, among others. [1] Nonetheless, the utilization of natural gas as a propellant leads to the release of unburnt methane, known as methane slip. Considering the substantially higher global warming potential of methane compared to CO₂, [2] it is environmentally prudent to oxidize the unburnt methane into CO₂. This necessitates the development of catalysts with high activity and stability, along with the design of reactors, regeneration systems, and other requisite processes for successful implementation.

LEARNING OBJECTIVE

In collaboration with your supervisors, the experimental kinetic data for both novel and commercial catalysts will be obtained using the experimental setup illustrated in Figure 1a. Additionally, existing data from the literature, for example, [3] will be utilized for comparing various catalysts. These data will play a crucial role in modeling the reactor and other processes within the lean methane oxidation gas treatment unit. Simulations will be conducted to compare the operation under different catalysts and conditions, including varying concentrations of poisons such as SO_x, [4] and water, [5] diverse temperatures, and different regeneration procedures.

CONTACT INFORMATION

Daily Supervisor: Martim Chiquetto Policano (m.chiquettopolicano@utwente.nl)
Supervisor: Prof. Dr. Jimmy Faria Albanese (j.a.fariaalbanese@utwente.nl)

LITERATURE

[1] Gélin, P., & Primet, M. (2002). Complete oxidation of methane at low temperature over noble metal based catalysts: a review. Applied Catalysis B: Environmental, 39(1), 1–37. https://doi.org/10.1016/S0926-3373(02)00076-0
[2] Derwent, R. G. (2020). Global Warming Potential (GWP) for Methane: Monte Carlo Analysis of the Uncertainties in Global Tropospheric Model Predictions. Atmosphere, 11(5), 486. https://doi.org/10.3390/atmos11050486
[3] Habibi, A. H., Semagina, N., & Hayes, R. E. (2018). Kinetics of Low-Temperature Methane Oxidation over SiO₂ -Encapsulated Bimetallic Pd–Pt Nanoparticles. Industrial & Engineering Chemistry Research, 57(24), 8160–8171. https://doi.org/10.1021/acs.iecr.8b01338
[4] Monai, M., Montini, T., Melchionna, M., Duchoň, T., Kúš, P., Chen, C., Tsud, N., Nasi, L., Prince, K. C., Veltruská, K., Matolín, V., Khader, M. M., Gorte, R. J., & Fornasiero, P. (2017). The effect of sulfur dioxide on the activity of hierarchical Pd-based catalysts in methane combustion. Applied Catalysis B: Environmental, 202, 72–83. https://doi.org/10.1016/j.apcatb.2016.09.016
[5] Mihai, O., Smedler, G., Nylén, U., Olofsson, M., & Olsson, L. (2017). The effect of water on methane oxidation over Pd/Al₂O₃ under lean, stoichiometric and rich conditions. Catalysis Science & Technology, 7(14), 3084–3096. https://doi.org/10.1039/C6CY02329K

OVERVIEW

Nitrate (NO₃^-) and nitrite (NO₂^-) are water contaminants that can cause human diseases such as blue baby syndrome when consumed with drinking water or which can lead to eutrophication in natural waters. NO₃^- and NO₂^- can be catalytically converted to N₂ by heterogeneous metal catalysts consisting of e.g. palladium and a promotor metal such as tin, indium or copper.^[1] Up until now, activity, selectivity and stability are insufficient for a commercial process. Therefore, we would like to fundamentally understand interaction of the two different catalyst metals to be able to prepare catalysts by design rather than by trial and error.

Figure 1: Proposed reaction pathway for bimetallic NO₃^- and NO₂^- reduction.

Heterogeneous catalysts typically consist of inorganic supports such as Al₂O₃ or SiO₂ on which metal particles are deposited. Depending on the preparation method the microscopic metal structure and the metal-support interaction varies. In case of bimetallic catalysts, the two metals can form e.g. well mixed alloys, core-shell arrangements or separated particles.^[2] For the nitrate reduction reaction close proximity or at least electron shuttle possibilities^[3] are required for the regeneration of the Sn active sites (Figure 1). Therefore, it is of particular interest to prepare catalysts with close interaction of the metals. To do so, the chemical toolbox offers advanced catalyst preparation techniques such as co- or sequential strong electrostatic adsorption (co-/sq.-SEA),^[4] charge enhanced dry impregnation (CEDI),^[5] controlled surface deposition (CSD)^[6] which exceed the potential of commonly applies dry- or wet impregnation preparations.^[2]

LEARNING OBJECTIVE 

In your project, you will use advanced catalyst preparation techniques to prepare well controlled bimetallic catalyst with strong metal-metal interactions. Based on existing knowledge in our research group and your catalytic reaction results you will optimize the formulation of your catalysts and characterize them in depth. The catalytic tests will be conduced in batch and/or flow condition with subsequent ion chromatographic (IC) analysis. For the catalyst characterization XRF, XRD, CO-chemisorption, N₂ physisorption, TPR/TPD are readily available in our Labs and STEM, EDS and ICP can be arranged.

CONTACT INFORMATION

Daily Supervisor: Janek Betting (j.betting@utwente.nl)
Supervisor: Prof. Dr. Jimmy Faria Albanese (j.a.fariaalbanese@utwente.nl)

 LITERATURE

[1] I. Sanchis, E. Diaz, A. H. Pizarro, J. J. Rodriguez, A. F. Mohedano, Sep Purif Technol 2022, 290, 120750.
[2] B. A. T. Mehrabadi, S. Eskandari, U. Khan, R. D. White, J. R. Regalbuto, Adv. Catal. 2017,61, 1-35.
[3] K. M. Lodaya, B. Y. Tang, R. P. Bisbey, R. P. Bisbey, S. Weng, K. S. Westendorff, W. L. Toh, J. Ryu, Y. Roman-Leshkov, Y. Surendranath, An electrochemical approach for designing thermochemical bimetallic nitrate hydrogenation catalysts, Nat Catal 2024.
[4] A. Wong, Q. Liu, S. Griffin, A. Nicholls, J. R. Regalbuto, Science 2017, 358, 1427-1430.
[5] X. Zhu, H.-R. Cho, M. Pasupan, J. R. Regalbuto, ACS Catal. 2013, 3, 4, 625-630.
[6] A. Garron, K. Lázár, F. Epron, Appl Catal B 2005, 59, 57–69.

OVERVIEW

Calcium carbonate (CaCO3) is one of the most widespread minerals on earth. Thanks to its rather high solubility in water, it plays a very important role in the global carbon cycle in both inorganic geological as well as biological mineralization and CO2 fixation processes. Exposure to water can lead to dissolution as well as precipitation of various forms of amorphous as well as crystalline CaCO3 as well as transformations between different crystal structures (polymorphs). Recently, researchers at PCF observed that surfaces of calcite, the most stable polymorph of CaCO3 under ambient conditions, undergo a rather peculiar transformation upon exposure to salty water. As shown in the figure below, initially atomically smooth cleavage surfaces of calcite break up into an array of individual domains with characteristic dimensions of a few hundred nanometers. Each of these domains seems to be atomically smooth at its surface with its edges align with the crystallographic axes of the underlying calcite crystal (see figure).

RESEARCH OBJECTIVE

The big question of this Master assignment is to identify the physical mechanism that is responsible for the formation of these domains. To this end, you will perform Atomic Force Microscopy measurements in ambient aqueous electrolytes of variable composition (salt content, pH) to follow the evolution from an atomically flat cleavage surface to the pattern shown observed. How does this transition depend on the type of anions and cations and on their concentration in the fluid? Is this transformation accompanied by extensive dissolution and re-crystallization of CaCO3? Does it involve the incorporation of other ions into the lattice that generate elastic stresses? Does the transformation entail changes in the local surface charge that might affect the chemical reactivity?

LEARNING OBJECTIVE

In addition to the standard learning objectives for a master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

• Learn to perform and interpret high resolution in situ Atomic Force Microscopy experiments
• Learn about the physical chemistry of aqueous electrolyte and solid-electrolyte interfaces (which are both ubiquitous in nature and technology)
• Have basic chemical-lab training (preparing solutions and surfaces, etc.)

CONTACT INFORMATION

Daily Supervision: Dr. Igor Siretanu  (i.siretanu@utwente.nl)
Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

Overview

Direct semiconductor-based photocatalytic conversion of solar energy to chemical fuels is considered an ideal, renewable energy resource for the future. According to the current paradigm optimum performance is achieved by using faceted nanoparticles of semiconducting materials (SrTiO₃ and BiVO₄) and by functionalizing them in a facet-selective manner with cocatalysts (Pt, Au, PbO₂ and MnO_x) for the desired redox reactions, such as water splitting or CO₂ reduction. Cocatalysts can provide trapping sites for the photogenerated charge carriers (as sinks) and extend the lifetime of these carriers. Also, cocatalysts can provide the active sites for the surface oxidation/reduction reaction through lowering the activation energy in multiple electrons transfer-involved hydrogen evolution reaction and oxygen evolution reaction. Among various methods used to load cocatalysts, photodeposition (i.e., photochemical deposition) has been considered as one of the most promising means, with the advantages of intimate contact (promoted charge transfer), easy preparation under a mild condition and site-directed loading. After photodeposition, traditionally, various ex situ characterizations (e.g., scanning electron microscopes) are performed to confirm the loading of cocatalysts and check their sizes/locations. However, the growth kinetics of cocatalysts during photodeposition is largely a black box. This lack of information partially leads to a relatively empirical optimization of cocatalysts during photodeposition in the field of photocatalysis to date. Here, we aim to use Dynamic Atomic Force Microscopy to image the photodeposition process of single cocatalysts on semiconductor faceted particles in situ. The Bachelor project will provide both novelty and challenges as it has never been applied to faceted SrTiO₃/cocatalyst systems before.

RESEARCH OBJECTIVES

The goal is to directly study in situ the growth of individual cocatalyst nanoparticles on faceted particles of SrTiO₃ and the rates at which they appear over time. To do this, high resolution Atomic Force Microscopy imaging in liquids and ultra-sharp tips will be used. We are particularly interested in how light intensity, wavelength, and fluid composition (pH and concentration of precursor ions AuCl₄⁻ and Pb²⁺) can affect the spatial distribution and growth kinetics of cocatalysts nanoparticles. These experiments can be complemented with SEM measurements.

LEARNING OBJECTIVES

In addition to the standard learning objectives for a Bachelor’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

·         Learn how to work with  Atomic Force Microscope in air/liquids
·         Acquire or increase your lab experience with colloidal semiconductor nanoparticles
·         Learn fundamental concepts of photocatalysis and cocatalyst photo-deposition

CONTACT INFORMATION

Dr. Igor Siretanu (daily advisor) (i.siretanu@utwente.nl)
Prof. Frieder Mugele (thesis supervisor) (f.mugele@utwente.nl)

Overview

Due to a sustained progress in making and characterizing colloids over decades, many composite colloids are currently being developed. The potential application scope is broad, including the mimicking of individual molecules, controlling the collective optical and mechanical properties of suspensions, enhancing catalytic performance and more. The design principles vary per system, and same for the amount of complex colloids that can be obtained. One synthesis pathway that is currently under-explored is colloidal self-assembly via electrostatic heteroaggregation. Using oppositely charged ‘host’ and ‘guest’ particles, a variety of complex colloids can in principle be made. This principle has already been demonstrated in our group for spherical raspberries and faceted photocatalytists (see Fig) 

Examples of recent work where electrostatic interactions were used to assemble complex colloids. Left: all-silica raspberry colloids. Right: SrTiO₃ particles with a facet-selective coating of Au nanoparticles

RESEARCH OBJECTIVES

We will take self-assembly to the next level by using mixtures of guest particles. The latter will carry the same (positive/negative) type of charge but the size and/or magnitude of the (zeta) potential will be different. Key questions are: i) How will the two types of guests compete with each other for adsorbing onto the hosts? and ii) What are the roles of kinetics and thermodynamics in the self-assembly process?

The guest particles will repel each other if they carry similar charges. Even so, it is not clear to what extent kinetics or thermodynamic equilibrium will determine the final outcome. Small guest particles diffuse faster but may be less strongly attracted to the host particle. Reversible adsorption by both guest types should lead to an equilibrium occupancy of the host particle surface, but not necessarily under all ambient conditions. Even in case of irreversible adsorption, the adsorbed guest particles might have freedom to ‘roam’ the surface of the host, and thereby form a (quasi) 2D-equilibrium structure.

Experiments will be performed with confocal fluorescence microscopy and supported with other methods like SEM. Use of large host particles, and guest particles labeled with different fluorecent dyes, should allow distinguishing all three types of particles in  live assembly experiments. Initially the host particles will be attached to a glass slide. The competition between the small and large guests will be influenced via their concentrations and via the pH and salinity of the liquid. For self-assembly in the bulk liquid, the overall concentration of the guests has to be high enough to ensure colloidal stability of the assembly. When studying the dynamics in concentrated systems, adsorbed and non-adsorbed guest particles have to be distinguished via the magnitude of their Brownian motion. This could be achieved by tracking the motions of the particles.

LEARNING OBJECTIVES

In addition to the standard learning objectives for a Master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will learn how to:

·         prepare colloidal suspensions in a chemical lab (with or without sytnhesis)
·         perform CSLM experiments
·         extract quantitative information from the image-time series
·         use insights from colloid science to interpret your findings

Contact Information

·         Daily Supervision: Dr. Michel Duits (m.h.g.duits@utwente.nl)
·         Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

OVERVIEW

Capturing and sequestering CO₂ from the atmosphere to mitigate global warming is one of the biggest challenges for mankind in the decades to come. Mineralization of CO₂ using olivine, a magnesium iron silicate, is a promising candidate process be it through natural weathering or industrial conversion. However, the formation of a silica-rich surface alteration layer (SAL) is reported to drastically slow down the exchange of ions with the ambient medium. Both ‘leaching’ and ‘reprecipitation’ have been proposed as mechanistic explanations for SAL formation. At PCF, we work on elucidating the micro-scopic origins by using a combination of high resolution techniques including Fluorescence Lifetime Imaging (FLIM), Confocal Raman (CRM), Atomic Force (AFM) and Scanning Electron (SEM) microscopies

a)_Typical aggregate of an olivine grain. b)_Evolution of the Raman spectrum of an olivine pebble dissolved in H₂SO₄ at pH 2. Strong peaks emerge after 21 days

RESEARCH OBJECTIVE

The main goal of the MSc project is to study the effects of cation and anion ‘scavengers’ [1,3] on the olivine dissolution rate and the SAL formation. Scavengers can facilitate the detachment of ions from the dissolving mineral and/or hinder reprecipitation of a new solid. We will measure this via the released Mg²⁺ ions, using FLIM with a Mg-responsive dye. After finding the right additive, we want to optimize its concentration. The additives’ effect on surface morphology will be studied with AFM and SEM, while changes in the chemical composition of the Surface Alteration Layer are studied with CRM.

LEARNING OBJECTIVE

In addition to the standard learning objectives for a master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

·         Acquire knowledge on mineral carbonation techniques, including dissolution-reprecipitation reactions, and their practical applications in CO₂ capture.
·         Gain experience in Fluorescence Lifetime Imaging Microscopy (FLIM) and data analysis.
·         Learn about high resolution Raman spectroscopy and data analysis.
·         Use / develop experience in MATLAB and Python (data analysis)

 CONTACT INFORMATION

·         Daily Supervision: Dr. Shilpa Mohanakumar (s.mohanakumar@utwente.nl)
·         Supervision:  Prof. Dr. Frieder Mugele  (f.mugele@utwente.nl)

 References

[1] Oelkers et al.,  Olivine Dissolution Rates: A Critical Review. Chem. Geol.,  2018, 500, 1-19

[2] Daval et al., Influence of amorphous silica layer formation on the dissolution rate of olivine at 90 °C
     and elevated pCO2, Chem. Geol., 2011, 284, 193-209.

[3] Olsen et al, Oxalate-promoted forsterite dissolution at low pH, Geochim. Cosmochim. Acta, 2008,
    72, 1758-66

Overview

The hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are the foundation stones of the renewable hydrogen economy and are core to the transition towards a sustainable carbon-neutral economy. Electrocatalytic water splitting is arguably the most critical reaction for the up-coming H2 economy. A standing puzzle in the fundamental hydrogen evolution even on the model system electrocatalyst Pt (111) is the origin of the orders of magnitude decrease in reaction kinetics when moving from acid to alkaline, which has seriously retarded the further development of electrochemical energy technologies and therefore has attracted great recent research interest. So far, there are several theories to explain the kinetic sluggishness of HER/HOR in alkaline environments and/or in the presence of specific ions in the electrolyte, for example: i) the hydrogen binding energy (HBE) theory, which states that the variation in surface charge in the double layer attracts and traps (in the double layer) the adsorbed H as well as H⁺, increasing the hydrogen binding energy; ii) the proton donor theory; iii) the interfacial water reorganization theory, where the highly organized surface hydration layers and H-bond networks act as barriers for proton transport to/from the surface that severely inhibit the hydrogen electrocatalytic reactions; and so on^1-3. However, these theoretical models are still under extensive debate, and little attention has been paid to the critical role of the surface charge, structure of the electric double layer (EDL), and interfacial hydration layers in electrocatalysis. So far, progress in understanding these processes has largely been hampered by the absence of suitable experimental techniques to characterize the electrocatalyst-electrolyte interface in situ and under operando conditions, as well as the quantification of local surface properties such as potentials, charge densities, defect distributions, and hydration effects with the required sub-particle or nanometer resolution. Recent improvements in various fields now allow for a detailed scrutiny of electrocatalytically active solid electrolyte interfaces from different experimental perspectives. In particular, we developed a dual-scale Atomic Force Microscopy (ds-AFM) method that allows the determination of local surface potentials with a lateral resolution of ≤10nm in combination with atomic resolution imaging of surface structures, defects, and adsorbed ions in ambient electrolytes. While earlier applied to insulating mineral particles, we recently used this technique for the first time to study photocatalytically active faceted nanoparticles of SrTiO₃ and demonstrated that (i) different facets display opposite surface charges within a specific pH range of 4-6, (ii) hydration is very facet-dependent, and (iii) defect-rich regions along the boundaries of adjacent facets edges contribute significantly to the total charge of the NPs (Figure 1 c)⁴. In this master project, we want to extend the ds-AFM method with its unique resolution to operando conditions to faceted platinum electrocatalyst nanoparticles (Figure 1 b), such that we will be able to follow the response to changes in fluid composition and applied potential of the local (facets) surface properties mentioned above. We expect that the resulting physical insights will lead to optimized hydrogen evolution reactions at platinum electrocatalysts.

RESEARCH QUESTIONS

·         What structural features of platinum nanoparticles ranging from the micrometer to the atomic scale change during the electrochemical operation? How are the defects distributed on an electrode surface? And investigate whether the surface is static or dynamic, i.e., undergoes surface reconstructions during electro-chemical reactions. How is the active platinum electrode surface structure affected by variations in electrolyte composition (pH and concentration of specific ions)?
·         What is the local surface charge or potential of platinum nanoparticle facets and molecular double-layer structure near a conducting Pt electrocatalyst electrode? How are the EDL and EDL forces evolving during reactions?
·         What are the water molecule structure and interfacial hydration forces next to the passive and electrochemically active electrocatalyst surface? How do the pH of the solution, ions, and applied potential affect the hydration structure at the Pt-electrolyte interface?
·         What is the optimal applied potential, the local double layer environment for effective hydrogen evolution reactions at platinum nanoparticles, and a sufficiently robust surface structure?

These questions will be addressed using atomic force microscopy operated in ‘dual-scale’ mode, which combines colloidal scale AFM spectroscopy with somewhat larger tips (radius 5–50 nm) with atomic resolution imaging using ultra-sharp tips (radius 1-2 nm). AFM measurements in fluid will be performed in a dynamic mode with small oscillation amplitudes (<1nm) to enable high lateral and temporal force resolution. Two AFM setups are available (Cypher ES from Asylum Research and ICON from Bruker). Both instruments are equipped with electrochemical liquid cells enabling fluid exchange and electrochemical potential control (bi-potentiostat). Samples will be prepared by controlled solid state dewetting^{5, 6} that is, the heat induced agglomeration of thin metal films into defined nanoparticles. Pt thin films (e.g., 5 nm-thick or so) will be deposited by magnetron sputtering onto electri⁵cally conductive (Nb-doped) SrTiO₃ single crystal substrates. The samples will then be heat treated to convert the Pt film into a “monolayer” of spaced, faceted Pt NPs, with an average size of, e.g., 100-200 nm. Controlled faceting will be achieved by tuning the orientation of the single crystal substrate and the heat treatment conditions, e.g., temperature, duration, and gas.

Figure 1. a) Experimental setup sketch for the measurements dynamic AFM in Electrochemical cell. b) SEM image of dewetted, faceted Pt NPs formed on a SrTiO₃ single crystal substrate (unpublished data from Harsha et al.⁷ c) SEM image on SrTiO₃ nanocrystal; 2D charge map across (100) and (110) facets (red: positive charge, blue:-negative charge); Oscillatory hydration forces show that water molecules are more ordered on (110) facet (higher amplitude) High-resolution phase image of corner between several facets displaying steps and domains of crystalline and disordered structure. Inset: atomic resolution topography images on (100) facet in liquid. It displays a vacancy defect and square lattice in agreement X-ray resolved structure. (data from Su et. al.⁴)

LEARNING OBJECTIVES

In addition to the standard learning objectives for a Master’s project (research planning, academic writing, data presenting, how to work in a lab environment, etc.), you will:

·         Learn how to work with Atomic Force Microscopy in air/liquids and Electrochemical AFM (EC-AFM)
·         Acquire or increase your lab experience with faceted nanoparticle electrocatalysts
·         Learn fundamental concepts of electrocatalysis

CONTACT INFORMATION

Dr. Igor Siretanu (daily advisor) (i.siretanu@utwente.nl)
Dr. Marco Altomare (daily advisor) (m.altomare@utwente.nl)
Prof. Frieder Mugele (thesis supervisor) (f.mugele@utwente.nl)

REFERENCES

(1) Li P; Jiang Y; Hu Y; Men Y; Liu Y; Cai W; Chen S. Hydrogen bond network connectivity in the electric double layer dominates the kinetic pH effect in hydrogen electrocatalysis on Pt. Nature Catalysis 2022, 5 (10), 900-11

(2) Wilson, J. C.; Caratzoulas, S.; Vlachos, D. G.; Yan, Y. Insights into solvent and surface charge effects on Volmer step kinetics on Pt (111). Nature Communications 2023, 14 (1), 2384.

(3) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. Interfacial water reorganization as a pH-dependent descriptor of the hydrogen evolution rate on platinum electrodes. Nature Energy 2017, 2 (4), 1-7.

(4) Su, S.; Siretanu, I.; van den Ende, D.; Mei, B.; Mul, G.; Mugele, F. Facet‐dependent surface charge and hydration of semiconducting nanoparticles at variable pH. Advanced materials 2021, 33 (52), 2106229.

(5) Thompson, C. V. Solid-state dewetting of thin films. Annual Review of Materials Research 2012, 42, 399-434.

(6) Altomare, M.; Nguyen, N. T.; Schmuki, P. Templated dewetting: designing entirely self-organized platforms for photocatalysis. Chemical science 2016, 7 (12), 6865-6886.

(7) Harsha, S., Sharma, R.K., Altomare, M., in preparation.