© Mohammad Zendehbad

Improving Accessibility of Active Sites in Hierarchical MOFs through Selective Ligand Removal Strategy

MOFs have demonstrated significant potential as photocatalysts, particularly in hydrogen evolution and CO2 reduction. Their ability to combine light-harvesting and catalytic functions with outstanding reactant adsorption capability make them highly desirable. However, in dynamic processes, particularly in liquid-phase catalysis, the accessibility of active sites becomes a critical parameter due to limited reactant diffusion caused by the small micropores of MOFs. To address this challenge, one promising strategy involves synthesizing mixed-ligand MOFs, followed by selective ligand removal (e.g., via selective oxidation, thermal degradation, or dissolution). This approach produces novel hierarchical microporous-mesoporous MOFs that facilitate reactant diffusion while inducing uncoordinated centres as potential catalytic sites. These materials are truly novel, combining hierarchical porosity with the multifunctionality of the inorganic-organic hybrid system. Characterizing the surface area and pore characteristics, including width, shape, connectivity, and distribution, is critical to their study.

Project funding: Austrian Science Fund (FWF) I 5413-N and Nancy and Stephen Grand Technion Energy Program (GTEP, upon work from COST Action CA18234, supported by COST (European Cooperation in Science and Technology).
Project partners: University of Vienna, Normandie University, Israel Institute of Technology
Project start: January 2019

2D MOF structures for visible hydrogen evolution reaction

The research aims to address key challenges in the field of photocatalysis by customizing innovative metal-organic framework compounds (MOFs). The primary focus is on enhancing stability, expanding the absorption spectrum, and improving charge extraction and recombination kinetics. The ultimate objective is to achieve overall water splitting. To accomplish this, the researcher investigates cutting-edge and water-stable MOFs based on titanium (Ti), zirconium (Zr), and cerium (Ce), while incorporating functional ligands to enhance light absorption. In the pursuit of improved charge extraction, the dimensionality of the secondary building units (SBUs) is increased from zero-dimensional (0D) to one-dimensional (1D) and even two-dimensional (2D) structures. Additionally, the researcher explores the concept of earth-abundant single-metal-site stabilization on MOF scaffolds, which serves as co-catalysts, essential components in photocatalysis.

Project partners: University of Vienna, Israel Institute of Technology
Project start: January 2020

MOFs for Sustainable Nitrogen reduction to Ammonia

Nitrogen fixation is a critical process for sustaining life on our planet. Ammonia, the most commonly synthesized nitrogen product, is a key component in the production of fertilizers, contributing significantly to global food production. However, the traditional ammonia production process is energy-intensive and environmentally damaging, making it unsustainable in the long run. Therefore, finding new and sustainable methods for ammonia synthesis is of paramount importance. In this regard, metal-organic frameworks (MOFs) have emerged as promising candidates for photocatalytic nitrogen fixation. Our study aims to explore the potential of MOFs as

efficient photocatalysts for nitrogen conversion, with the ultimate goal of designing highly effective and sustainable materials for future ammonia synthesis. Our research delves into the remarkable potential of MOFs to act as efficient photocatalysts for the conversion of nitrogen to ammonia in aqueous environments. We will carefully select a set of promising MOFs based on their structural, optoelectronic, and stability characteristics. Through extensive evaluations under various reaction conditions - including pH, temperature, and MOF loading - we will examine the photocatalytic performance of these MOFs while also analysing the underlying reaction mechanisms using advanced characterization techniques and density functional theory calculations.

To further enhance the photocatalytic activity of MOFs, we will employ a selective ligand removal strategy to introduce defects that fine-tune the electronic and optical properties of the materials. Our goal is to design MOFs that demonstrate exceptionally high photocatalytic activity for nitrogen conversion, achieving maximum ammonia yields under optimized catalytic conditions.

The resulting findings of our research will highlight the impressive potential of MOFs as highly effective photocatalysts for nitrogen conversion, paving the way for the design and development of novel MOF-based materials with broad implications for sustainable energy and environmental applications.

Project funding: Austrian Science Fund (FWF) I 5413-N and Nancy and Stephen Grand Technion Energy Program (GTEP, upon work from COST Action CA18234, supported by COST (European Cooperation in Science and Technology).
Project partners: University of Vienna, Israel Institute of Technology
Project start: November 2022

Single-Atom Modification of Ligands: Advancements in Tailoring MOFs for Enhanced Photocatalysis

The immobilzation of single-site co-catalysts on MOFs is of high interest to obtain well-defined active sites with maximum atom-utilization efficiency. Adrian is approaching this issue by using organometallic complexes as MOF linkers, either via direct synthesis or post-synthetic ligand exchange.

Project start: January 2022

Hierarchically Porous MOFs for the Removal of Glyphosate from Water:

The process of selectively removing one ligand (SeLiRe) in mixed-ligand MOFs through thermolysis presents a potent approach for incorporating additional mesopores without compromising the MOF's overall structure. By manipulating the initial ligand ratio, we can synthesize MOFs from the MIL-125-Ti family that exhibit two distinct hierarchical pore architectures, with either large cavities or branching fractures. We evaluate the performance of these hierarchically porous MOFs for adsorbing organic contaminant (e.i., glyphosate) from water, examining the kinetics and mechanism of adsorption while also exploring the impact of type, connectivity, and size of the added mesopores. Furthermore, we investigate single-ligand MIL-125-Ti and

NH2-MIL-125-Ti as well as their corresponding mixed-ligand MOFs prior to SeLiRe to uncover the mechanism of glyphosate adsorption. Our results demonstrate that introducing large cavity-type mesopores enhances both the capacity and efficiency of glyphosate adsorption by improving accessibility to the interior surface and increasing the number of Ti sites created through the SeLiRe process. Thus, our study provides an intriguing illustration of how rationalized pore engineering can enhance the adsorptive properties of MOFs for larger molecules.

Project funding: Austrian Science Fund (FWF) I 5413-N, Natural Sciences and Engineering Research Council of Canada (NSERC) through the Discovery Grant (funding reference number RGPIN-2019-06304) and Nancy and Stephen Grand Technion Energy Program (GTEP, upon work from COST Action CA18234, supported by COST (European Cooperation in Science and Technology).
Project partners: University of Vienna, University of Northern British Columbia, University of Natural Resources and Life Sciences, Israel Institute of Technology
Project start: May 2021

Hierarchically Zeolite-imidazolate Frameworks (ZIFs) for removal of organic dyes from water

In this research, we employ a selective ligand removal strategy to construct mixed-ligand and ligand-removal zeolitic imidazolate frameworks (ZIFs). These frameworks are then subjected to in-situ transformations, such as thermolysis, acid etching, and ion-exchange, to engineer hierarchical pores within the ZIFs. The introduction of hierarchical pores significantly increases the spatial density of active sites, leading to enhanced efficiency in water purification and electrocatalysis applications utilizing ZIFs.

Project funding: CSC Funded
Project partners: Central China Normal University
Project start: May 2020

The effect of ligand removal in MOFs on the photocatalytic CO2 reduction performance (studied by operando DRIFTS)

This research involves the investigation of the effect of ligand removal in MOFs on the photocatalytic CO2 reduction performance (studied by operando DRIFTS). In his studies he is focusing on UiO-66, MIL-125 and other MOFs that have shown activity in CO2 absorption and photocatalytic CO2 reduction or hydrogen evolution. He is using diffuse reflection IR spectroscopy (DRIFTS) to study the processes and intermediate species on the catalyst surface during the reaction. He can study the catalyst under operando conditions by illuminating the MOF powder in the presence of gaseous CO2 and H2O and analyzing the products with an on-line GC. He will also study active sites by generating defects in the pristine MOF structure via selective ligand removal strategy. This strategy makes it possible to generate free binding sites on the SBUs while still keeping the parent MOF structure intact. By using in-situ PL he will additionally study the effect of ligand removal on the electronic properties of the MOFs.

Project funding: DOC Fellowship of the Austrian Academy of Sciences at the Institute of Materials Science (TU)
Project start: May 2022

This project called “Metal Organic Polyhedra as New Drug Delivery Systems (Acronym: MOP-as-DDS)” aims to demonstrate that Rh(II)-based Metal-Organic Polyhedra (MOPs) can become a novel multifunctional platform to develop new drug delivery systems (DDS).

MOPs are highly porous, can encapsulate drugs, and the size of their internal cavities can still be modulated by means of reticular chemistry. MOPs can also be seen as giant molecules or nanoparticles (NPs), so they also combine solubility in aqueous conditions with a large outer surface area that can be post-synthetically functionalized with stoichiometric control. As DDS, the smaller dimensions of MOPs (<10 nm) could be further advantageously used to tune their biodistribution and bioavailability, increasing their efficacy and decreasing toxic side effects.

In this MOP-as-DDS project, we will exploit all these properties to design the first proof-of-concept MOP-based delivery systems.

Project Funding: J-4637; FWF Erwin Schrödinger Fellowship

Project Partners: Catalan Institute of Nanoscience and Nanotechnology (ICN2), Supramolecular NanoChemistry and Materials, Bellaterra, Spain

Project Start: February 2022