■ Metal-organic frameworks: a novel stationary phase for chromatography

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Description of the PhD project

Metal-organic frameworks (MOFs) are highly ordered crystalline micro or mesoporous hybrid solids synthesized via an almost endless combination of organic ligands and metals. This leads to a very large structural (pore sizes/shapes…) and chemical diversity (functional acid or basic groups, tunable hydrophilic/hydrophobic balance) beyond the one of conventional inorganic (zeolites, clays, silica) or organic (polymers, carbons…) porous networks. These features are true assets for several applications such as catalysis, gas storage, separation (CO2, olefins…), catalysis, sensing, biomedicine...

In this project we propose to use MOFs in chromatography, subject very sparsely covered until now. Their high modularity and their physicochemical properties, coupled to their high specific surface area make MOFs natural candidates for chromatographic applications as stationary phases (SP).

The project will consist in preparing several known functional water stable metal polycarboxylate MOFs (M=Al, Fe, Zr or Ti) with different pore sizes and functionalities (polarity, metal sites…), already available at IMAP, under different forms depending of the kind of chromatography considered. For gas chromatography (GC), suspension of MOFs particles will be used to coat the inner wall of capillary columns. For liquid chromatography (LC), nanometric particles of MOFs will be prepared and grafted at the surface of micrometric silica particles for packed columns. Different types and sizes of silica particles will be investigated including the recent ones used for Ultra High Performance LC. In both cases one will pay a particular attention to (1) graft functional groups on the substrate or the outer surface of the MOF particles to ensure a stable coating and/or (2) optimize the particle size for each application. We also encounter to synthesize monolithic MOFs SPs with a controlled macro and mesoporosity, which remains almost unexplored so far.

Once the material and the column have been obtained, a detailed chromatographic characterization of the column capability will be carried out. It will concern both kinetic (efficiency) and thermodynamic parameters (interactions), aiming at assessing the compatibility of the MOF for the selected chromatographic applications. At this level, not only the chemical structure will be considered but the synergy between this structure and the physical aspect of the material: porous particles, superficially porous particles, solid coating inside a capillary or monolith. Preliminary tests have been carried out in 2017 by our teams during a 6 months master degree internship.

The investigations of the performances of the SPs will be carried out in different chromatographic modes, using gas, liquid and supercritical mobile phases. The supercritical phase could be of interest for chiral separations, especially if preparative applications can offer high selectivity using a SP having a moderate cost compared to the commercial ones.

Keywords

MOF, synthesis, chromatography, chirality, retention mechanisms, kinetic, thermodynamic behaviors

Research unit

UMR8231
Chemistry, Biology & Innovation

Description of the research Unit/subunit

CBI Institute is a mixed research unit between CNRS and ESPCI composed of 5 teams. Our team, LSABM, has a long time experience in chromatography, especially the characterization of stationary phases and in the elucidation of the interactions involved in the retention mechanisms. Gas, liquid and supercritical fluid chromatography are been studied together with the steps of sample treatment and associate detection systems. Our activity also focus on fast analysis using miniaturized devices, trace analysis and complex samples elucidation.
The project will be co-leaded by IMAP (http://www.ens.fr/laboratoire/institut-des-materiaux-poreux-de-paris-imap), a new laboratory at ESPCI and ENS that possesses a strong expertise in the design, synthesis optimization (down to the nanoscale), and shaping of Metal Organic Frameworks (MOFs) for applications ranging from separation, catalysis, energy, sensing and health. In the field of adsorption, IMAP has been involved for years for the capture of green-house gases, water sorption, separation of olefins, and extraction of phenols and more recently for the selective capture of Volatile Organic Compounds.

Name of the supervisor
Jérôme Vial

Name of the co supervisor
Christian Serre

3i Aspects of the proposal

The project, in its initial stage, involves two different partners specialized in two different disciplines, physics and chemistry of hybrid porous materials (IMAP), and analytical chemistry (LSABM). The success of the project is related to the synergistic combination of the skills the two partners have been developing during the past years: the synthesis, functionalization and characterization of MOFs, their synthesis optimization (nanoscale, scale-up) and potential applications by IMAP and the understanding of the retention mechanisms involved with MOFs in view of improvement and development of enhanced chromatography techniques by LSABM. Analytical chemistry is involved in all the fields of human activities such as health, medicine, biology, environment, energy etc. to monitor, identify, and specify the composition of all types of media (liquids, solids, natural or synthetic…). Any substantial advance in the capabilities of the techniques – such as chromatography - used in analytical chemistry has immediate benefits for the whole community to perform better and/or faster analysis, to obtain more details on a sample, produce compounds having higher purity etc. With a view to reducing the consumption of fluids used in chromatography or to reduce analysis time, miniaturization of techniques is of great concern. The preparation of new SPs using the skills of IMAP based on MOFs in a miniaturized format such as capillary columns or microchip – as recently demonstrated for GC in LSABM -would be a real asset. Hopefully, the more efficient SPs developed by the consortium could have real impact on chromatography capabilities. Applications in routine analysis for analytical or purification purposes would require a larger scale manufacturing process. In that case, either the creation of a startup or the development of a partnership with a local column manufacturer (such as Interchim or AIT in France) could be considered in order to extend the processing capabilities of the consortium. During the last ten years, research in LSABM has been devoted to recent and original chromatographic techniques to be implemented in various disciplines:
- Two dimensional techniques – a MOF could serve as a stationary phase in one of the dimensions – for the detailed separation of complex samples from different sources (wastes, edible oil degradation, petroleum samples, human odor…) for different purposes (process monitoring, safety, health, toxicology, criminalistics etc.)
- very fast separations in Gas Chromatography using capillary or chips columns and their dedicated monolithic stationary phases (patented) for process monitoring.
Last but not least, as mentioned before, analytical chemistry, especially chromatography, is used in all disciplines for routine analysis. Hopefully, it is expected the newly MOF SPs developed during the project will serve for routine application too. During the past decade, researchers from IMAP have produced series of functional MOFs or MOFs nanoparticles in a view of potential applications in various fields (adsorption, sensing, catalysis, health…), requiring a strong crossover of expertises (chemical engineers, materials scientists, biologists, pharmacists…).

This project represents a fascinating opportunity to assess the potential of MOFs in a new field, analytical chemistry. IMAP has developed during the past decade a very strong international network in the field of MOFs and their applications throughout Europe or Asia. One could therefore establish here a collaboration with a foreign research team expert in fundamental aspects of porous materials used in chromatographic separations ; a possibility would be to send the PhD candidate for a research journey in the team of Prof. Joeri Denayer (Free university of Brussels, Belgium) that has investigated the use of porous solids for chromatographic separation for the past few years ; this could allow to collect fundamentals (isotherms, heat of adsorption…) for the best materials identified through this project. At longer term, this could set the basis of a new EU H2020 project. C. Serre has already discussed this possibility with Prof. Denayer.

Expected Profile of the candidate

Ideally, the candidate shall either possess a first experience both in the synthesis and characterization of nanomaterials (porous or dense) or in chromatographic separation. A good sense of communication, a will to work in a multidisciplinary team, a high level in English are also expected.
No specific softs skills are required, except the common use of office tools. Anyway, learning of chromatographic software will be unavoidable with modern chromatographic systems.





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