Research

 

Materials
 

    
 

Current Research
 

||| Heterogeneous catalysis

 

Activation of packing material for use in plasma-catalytic CO2 conversion
Bram Seynnaeve - bram.seynnaeveugent.be

The plasma-catalytic conversion of carbon dioxide to larger (oxygenated) carbon species is a relatively new approach for the capture and utilization of carbon. The use of plasma in this process allows for different reaction pathways as compared to thermal and electrochemical methods, even at low temperatures. The use of heterogeneous metal and metal-oxide catalysts can improve conversion and selectivity in these systems. The research aims at development of various nanosized metal catalysts and embedding these in the packing materials of the plasma reactor.

 

Metal-organic frameworks for photo(catalysis) and photoluminescence applications
Wafaa Ahmed - Wafaa.AhmedUGent.be

The major focus of my research includes; the synthesis, modification and characterization of MOFs and their applications in different domains e.g. photo(catalysis), luminescence, thermometry,... Designing highly crystalline MOFs based on bismuth as a metal node. Developing synthetic strategies to create structural defects within the lattice with a unique set of properties (larger surface areas and superior enhanced catalytic and luminescence activities). Also the study of defect-property relations of MOFs are one of my interest. Finally designing mixed metal MOFs for photocatalysis (e.g. fine chemical production, CO₂RR and overall water splitting) is also one of my interests.

 

||| Photocatalysis

Design of COFs with high selectivity for photocatalytic 2e- oxygen reduction (ORR)
Jiamin Sun - jiamin.sunugent.be

Hydrogen peroxide (H2O2), an environmentally friendly chemical with strong oxidative properties, is regarded as a vital component in various industrial processes. Compared to the current anthraquinone approach for H2O2production in industry, photochemical synthesis via a 2e- ORR pathway is a sustainable and promising alternative as a result of lower energy input and the possibility of on-site synthesis. COFs as emerging organic semiconductors serving as photocatalysts have attracted intensive attention. I mainly work on the design of COFs with high selectivity for photocatalytic 2e- oxygen reduction and study the relationship between linker/structure properties and catalytic behavior.

 

Covalent Organic Frameworks (COFs): design, synthesis and applications in photocatalytic organic transformations and hydroperoxide production
Linyang Wang - Linyang.WangUGent.be

 

Covalent organic frameworks (COFs) are considered a promising material due to their high stability and porosity, well-organized structure, manually designable topology and tunable bandgap properties. COFs have been employed in numerous photocatalytic applications such as hydrogen evolution, reduction of carbon dioxide, pollutants degradation, H2O2 production and organic transformations. Rational design of the COF structure, such as increasing the conjugation or donor-acceptor combination, can effectively increase the electron transport efficiency, reduce the photogenerated electron-hole recombination and improve the photocatalytic performance. I mainly work on the design covalent organic frameworks (COFs) materials for photocatlytic organic transformation and hyfrogen peroxide production.

 

Design of covalent organic frameworks (COFs) for photocatalytic carbon dioxide conversion
Zhongliang Wen - Zhongliang.WenUGent.be 

With rapidly increasing combustion of fossil fuels, an energy crisis and environmental pollution are becoming global challenges. Photocatalysis, achieving solar-to-chemical energy conversion, is recognized to be a very promising strategy to meeting these challenges. COFs are a new class of crystalline organic porous polymers, which are formed by the expansion of organic monomers in two-dimensional or three-dimensional space by covalent bonds. COFs materials have unique advantages in the field of photocatalysis: (1) Designability of structure. The absorption capacity and energy band structure of COFs can be finely adjusted by the change of monomer chemical structure. (2) Functionalization of skeleton. COFs skeleton can be functionalized by means of pre-modification and post-modification strategies, thus the catalytic sites can be easily introduced. (3) The catalytic sites can be effectively dispersed, completely exposed, and kept stable during catalytic process because of the large specific surface area and high stability of COFs. I mainly work on the design of stable and efficient COFs for photocatalytic carbon dioxide conversion.

 

Post-synthesis modification of MOFs, COFs for photocatalysis
Maojun Deng - Maojun.DengUGent.be

Metal- and covalent organic frameworks (MOFs, COFs) are an interesting class of porous materials with tunable structures, and large specific surface areas. In the past few years, MOFs and COFs have been rapidly developed towards multiple applications such as gas adsorption and separation, drug delivery, sensing and heterogeneous catalysis. More specially, MOFs and COFs show the tremendous possibilities for in photocatalytic hydrogen production, H2O2 production and organic transformation reactions. Whereas, pristine MOFs or COFs typically have weak light absorption and utilization capabilities, which greatly limitstheir application in photocatalysis. In this project, the focus is on the post-modification engineering of MOFs and COFs. Here, we present our results along with a post-sulfurization process, so the imine-linked COFs were converted into thiazole-linked COFs, to generate a highly conjugated and ultrastable photocatalyst for H2O2 production.

 

Study of the photophysical properties of Donor-Acceptor COFs and their use in photocatalysis
Yoran De Smet - Yoran.DeSmetUGent.be

The biggest enemy for photocatalysis is the recombination of free charges prior to reaction. One way to enhance the lifetime of these free charges is the inclusion of donor-acceptor (D-A) motif, where electron-donating and electron-accepting moieties are included in an alternating fashion, enhancing the charge separation. The inclusion of these motifs also changes the band gap and band positions. My current project consists of two parts. The first part concerns the influence of D-A topology and crystallinity on charge lifetime. High crystallinity is known to have a positive effect on charge mobility, reducing charge trapping and recombination. We aim to elucidate how crystalline a COF needs to be exactly, and whether a donor-acceptor topology can help to compensate for poor crystallinity. The second part concerns the fine band gap engineering of imine D-A COFs. We will include donor and acceptor monomers with gradually increasing strength into the COFs, and determine whether the band gaps, band positions, and charge lifetime also follows this gradual trend. 

||| Electrocatalysis

Custom gas diffusion electrodes based on covalent organic frameworks for stable CO2 reduction 
Andreas Laemont - andreas.laemontugent.be

Electrochemical CO2 reduction is a green and scalable way of converting CO2 to base chemicals such as carbon monoxide or formic acid. Intense research efforts are spent to discover new electrocatalysts for his process. In comparison, far less attention is spent on the design of the gas diffusion electrode (GDE). Recent publications have shown that specialized GDEs are vital for stable performance of large-scale CO2 reduction. Up till now, the most common GDEs used in CO2 reduction are based on carbon cloth or carbon paper, coated with a hydrophobic PTFE layer. Under operation at industrially relevant current densities, these materials suffer from flooding: electrolyte perspires through the hydrophobic layer and prevents CO2 from reaching the catalyst. This research aims to create a new class of GDEs, based on covalent organic frameworks grown directly on a current collector. Owing to their chemical stability and high porosity (up to 3000 m2/g), these materials will increase the overall reaction rate by providing a high influx of reagents to the catalyst which does not decrease over time as a result of flooding. Furthermore, the chemical structure of the covalent organic frameworks will be tuned to incorporate groups which non-covalently bond with CO2, lowering the overpotential for CO2 reduction and increasing the selectivity towards one specific endproduct. 

Covalent Triazine Frameworks for metal-free electrocatalysis
dr. Karen Leus - karen.leusugent.be

Besides the use of metal-based electrocatalysts, several low-cost metal-free carbon-based materials have shown comparable and even superior performance in comparison to the noble metal-based electrocatalysts. Although N-doped carbons as such or in combination with other heteroatoms (e.g S, B, P) have shown great potential, they still have some inherent shortcomings, including: the need for harsh synthesis conditions, the overall low N-doping levels, and the possible presence of trace amounts of metals after synthesis. One of the subclasses of COFs are the so called covalent triazine frameworks (CTFs), which are thermally and chemically very stable materials. The presence of nitrogen implies that these materials can be regarded as a form of nitrogen-doped carbons – and might thus be suitable candidates for metal-free CO2 reduction electrocatalysis.  For the construction of these frameworks however, typically a harsh ionothermal synthesis method is employed. While CTFs made using this method generally possess high surface area, the high temperature used during synthesis also gives rise to a significant degree of carbonization, defects and side reactions. This ultimately results in a material with poor electrical conductivity and thus poor electrocatalytic performance. For this reason, most reports of CTFs in electrocatalysis describe metallated CTFs, in which the framework acts as a support for the catalytically active metal particles or atoms. Here our focus lies on a novel type of metal-free electrocatalysts by using CTFs as a promising platform for electrocatalysis. The CTFs will be synthesized in the absence of metals and under mild synthesis conditions which will avoid carbonization and will result in the production of CTFs that have well-defined and highly ordered N-rich active sites. To even further improve the conductivity, the CTFs will be grown onto a conductive support,e.g. functionalized carbon nanotubes. 

 

(Photo)(Electro)catalysis using Covalent Organic Frameworks: VOC abatement and total water splitting
dr. Amrita Chatterjee - amrita.chatterjeeugent.be

With the rising concerns for alternative energy requirement and abatement of greenhouse gases, it is imperative to focus on green and sustainable methods to tackle the above-mentioned problems. Photoelectrochemical method is one such attractive scheme that combines the advantages of both electrochemical and photocatalysis in a single unit to offer a wide range of solutions. The underlying principle in photoelectrochemical cells (PECs) mimics photosynthesis: it harvests solar energy to convert the reactant into energy-rich fuels and chemicals as end products at ambient conditions. The recently developed COFs are a novel class of metal-free, highly porous organic polymers, with abundant nitrogen active sites, tunable bandgap and light harvesting properties, and stability. However, COFs existing on nanoscale, have low electron transport pathway, that makes them poor electrical conductors. Hence, they have been rarely used in PECs. At COMOC, we propose to use an un-biased Z-scheme tandem PEC with photocathode and photoanode developed from tailor-made COFs. These strategically designed COFs will encompass both electrical conductivity and photocatalytic features. The targeted end-products will mostly focus on (i) hydrogen from water splitting, but can further be extended to (ii) CO2 reduction to produce methanol/formic acid, and (iii) VOC oxidation to hydrogen.

Redox active porous materials: fundamentals and applications
dr. Jeet Chakraborty - Jeet.ChakrabortyUGent.be

“I am developing porous materials with tunable redox properties for heterogeneous photo and electrocatalysis. Particularly, green and sustainable synthesis of value-added organic compounds, CO2 utilization, and green hydrogen and peroxide production from water are of great interest. I am trying to understand the fundamentals of charge and energy transport in the materials during these reactions. For more information, cf. https://jeet-chakraborty.owlstown.net” 

 

Synthesis of COF/MOF for electrocatalytic applications
Rundong Wang - Rundong.WangUGent.be

 

||| Gas Sorption & Separation

Alternative ways for hydrogen storage
Geert Watson - geert.watsonugent.be

Porous frameworks are attractive candidates for gas storage due to their large surface areas and pore volumes. Periodic Mesoporous Organosilicas (PMOs) are interesting materials for such applications as they can easily be formed from readily available chemicals. Modification of the porous frameworks through incorporation of functional monomers or through post-modification processes allows for facile tuning of the surface chemistry to suit the final application. 

        

||| Luminescence & Sensing

Development of luminescent PMOs for ion sensing
Chunhui Liu - chunhui.liuugent.be

Recent research in lanthanide materials has strongly contributed to the development of high-performance chemical sensors. However, the current reported high-responsive chemical sensors still have a limited detection range, restraining their further application. We developed lanthanide-based periodic mesoporous organosilica (LnPMO) hollow spheres with interior lanthanide-doped fluorides for luminescence turn-off sensing of Hg²⁺ with a low detection limit and wide detection range. This yolk-shell structure was built of Tb³⁺ grafted diureido-benzoicacid PMO (shell) and lanthanide-doped fluoride NaYF₄:Yb,Er (yolk), exhibiting both downshifting (DS) and upconversion (UC) luminescence. Visible photoluminescence properties of the developed hybrid material were studied using UV and near-infrared (NIR) excitation. In DS mode, benzoic acid-functionalized PMO acts as an organic co-sensitizer for Tb³⁺ β-diketonate complexes, which can significantly enhance the ion sensing and detection range. In UC mode, Hg²⁺-responsive Rhodamine B thiolactone (RBT) was used as an antenna species for the lanthanide-doped fluorides to sense Hg²⁺ with high sensitivity.

Design, synthesis and characterization of Metal-Organic Frameworks and Covalent Organic Frameworks for detecting and removing p-arsanalic acid
Tingting Yang - Tingting.YangUGent.be

p-arsanilic acid is often used in poultry diets to improve feed efficiency due to its broad antimicrobial properties. However, 90% of these compounds could not be adsorbed in tissues and then released into the environment, in which these soluble organoarsenic compounds would gradually transform into highly toxic inorganic arsenic through biological and abiotic degradation processes, further posing environmental pollution and human health risks. How to effectively detect and remove the p-arsanilic acid is urgent to be addressed to protect aqueous environments.Framework materials (like COFs and MOFs) as the promising materials have been widely used to detect and remove the p-arsanilic acid. However, there is some distance for these materials to be applied in the actual water environment due to the various bottlenecks, such as limited coordination affinity and the existence ofcompeting pollutants. So I hope to design and synthesize a series of novel framework materials to enhance the affinity for low-concentration p-arsanilic acid in wastewaterand further achieve the bifunctional goals of detection and adsorption. Moreover, based on the structural advantages of the porous materials, such as the highly ordered structures, inherent porosities, adjustable structure-activity sites and so on. I will also explore other application about the porous materials.

||| Development of Preparation Methods of COFs

Crystallisation of imine COFs: relating structure to activity
Laurens Bourda - laurens.bourdaugent.be

Porous solid materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are promising for a variety of applications as exemplified above. Yet, before developing applications, it is important to have the synthesis tools required to prepare materials with the desired properties such as pore size, crystallinity, catalytic sites, etc. A part of the research led at COMOC is devoted to the preparation of COFs with new structural motifs and the development of methods to control the crystallinity and porosity of known COFs. Current research projects are notably exploring the use of metal cations to form new 3D porous COFs in a similar way to the reported preparation of woven-COFs (Yaghi et al. Science 2016, 351, 365-369) and the use of a toolbox of techniques (e.g. modulators, in-situ linker generation and advanced catalysts) to precisely control and study COF crystallinity and porosity.