Hybrid nanoporous materials for the separation of fluid mixtures

Project Information

NanoSep

Grant agreement ID: 101065060

DOI

10.3030/101065060

Project closed

EC signature date 30 August 2022

Start date 1 February 2023

End date 31 January 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 176 276,16

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 1 - NanoSep (Hybrid nanoporous materials for the separation of fluid mixtures)

Reporting period: 2023-02-01 to 2025-01-31

Summary of the context and overall objectives of the project

Fluid separation accounts for 10-15% of the world's energy consumption. Therefore, developing better and more affordable filtration membranes as alternatives to distillation is a pressing issue. If new separation processes were applied to sectors such as petroleum, chemical, and paper manufacturing, hundreds of millions of tonnes of carbon dioxide emissions could be prevented annually. To reach that goal, a deeper understanding of the behavior of confined mixtures within multiscale porous materials is crucial for developing new and efficient fluid separation processes.

Nanoporous materials have a large specific surface area, typically greater than 1000 square meters per gram, allowing them to interact strongly with fluids. This makes them an excellent choice for fluid separation applications. However, currently, only a few fluid mixtures can be separated using nanoporous materials. As a result, most large-scale fluid separation operations rely on costly thermal processes such as distillation and cryogenization. Developing new fluid separation processes based on nanoporous materials could provide cost-effective solutions to environmental and industrial challenges, such as CO2 and CH₄ emissions and water contamination. The objective of the MSCA fellowship NanoSep is to deepen our understanding of confined fluid behaviors within heterogeneous nanoporous materials and to develop new fluid separation processes based on this knowledge.

Currently, the development of new separation processes is hindered by two major obstacles. First, fluid mixtures confined at the nanoscale exhibit surprising and poorly understood behaviors, such as spontaneous phase demixing or dewetting transitions, where a normally wet nanopore becomes effectively non-wettable for a specific mixture composition and geometry. Second, the porous materials that are most promising for fluid separation applications exhibit a broad variety of pore sizes and surface heterogeneities, making the analysis of confined fluid behaviors more challenging. In fact, fluids confined within heterogeneous porous materials often simultaneously display several scale-dependent properties (e.g. viscous, capillary, activated fluid transport) and phases (e.g. liquid, vapor, adsorbed), which hinder direct comparisons between experiments and theories. As a consequence, it is still unknown how the exotic behaviors of nanoconfined mixtures reflect on large-scale demixing properties, limiting the conception of new fluid separation processes that would benefit from the molecular separation phenomena exhibited by nanoconfined mixtures.

If new separation processes were applied to the petroleum, chemical, and paper manufacturing sectors, hundreds of millions of tonnes of carbon dioxide emissions could be prevented every year. Therefore, the development of energy-efficient fluid separation technologies aligns with global and EU strategies for reducing industrial carbon emissions, such as the European Green Deal and the UN Sustainable Development Goals. By aiming to decrease reliance on energy-intensive distillation, this project supports the transition to a more sustainable and resource-efficient industrial sector.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The research performed during the NanoSep project aimed to elucidate the behavior and properties of fluids confined in nanoporous and interfacial environments using advanced molecular dynamics simulations. The studies addressed fundamental questions related to molecular exchange dynamics, interfacial interactions, and their implications for macroscopic properties, such as NMR relaxation rates and interfacial ethanol enrichment.

The first phase of the research project (corresponding to WP1 in the original proposal) focused on understanding the behavior and properties of fluids confined within nanoporous and interfacial environments through advanced molecular dynamics simulations. The primary goal was to establish a molecular-level understanding of how fluid dynamics, molecular exchange, and interfacial interactions influence macroscopic properties such as NMR relaxation rates and ethanol enrichment at interfaces.

In a first study, published in collaboration with Benoit Coasne, the role of hydrophobic and hydrophilic interactions in water-ethanol mixtures near planar organosilica surfaces was explored using molecular simulations [Gravelle and Coasne, hal-04917234, Submitted to Open Research Europe]. Organosilica surfaces, with their tunable hydrophobicity achieved by varying the ratio of methyl and hydroxyl groups, were shown to promote ethanol enrichment at the interface. Molecular dynamics simulations revealed that surfaces decorated with methyl groups exhibit significant preferential adsorption of ethanol, consistent with prior observations on graphite. This study also examined how surface roughness and the spatial organization of functional groups impact interfacial ethanol enrichment. These findings are particularly relevant for designing cost-effective, organosilica-based membranes for water-ethanol separation, presenting a promising alternative to carbon-based materials.

In parallel, a study conducted with Benoit Coasne and collaborators from the Institute for Computational Physics (ICP) in Stuttgart employed atomistic molecular dynamics simulations to investigate water confined in slit nanopores. The study highlighted how molecular exchange dynamics between surface-adsorbed layers and the bulk fluid influence NMR relaxation rates. Using first return passage time calculations, the adsorption time, pore size, and diffusion coefficient were linked to the relaxation behavior. This approach provides a predictive framework for understanding molecular relaxation at interfaces using principles of statistical mechanics.

Additionally, the research carried out in this first work package proved exceptionally productive and unexpectedly insightful, leading to new collaborations that resulted in two additional publications.

- The first study [Asha, Jamal, Gravelle, Mayes, and Shen, The Journal of Physical Chemistry B] investigated the role of minor water content in solid-state polymer electrolytes (SPEs), revealing how slight hydration enhances ionic conductivity while preserving mechanical integrity in polymers such as poly(ethylene oxide) (PEO) and poly(lactic acid) (PLA) when combined with lithium perchlorate (LiClO₄). The molecular dynamics code developed for the NanoSep project was extended to describe the transport properties of ions within polymer matrices, which was of interest to Professor Shen’s group (University of Massachusetts Dartmouth).

- The second study [Hayatifar, Gravelle, Moreno, Schoepfer, and Lindsay, Geochemical Transactions] focused on interfacial processes in ferrihydrite-water systems, employing reactive molecular dynamics simulations and synchrotron X-ray spectroscopy to elucidate the dynamics of surface restructuring, charge equilibration, and hydrogen bond networks.

Both of these studies are directly connected to the core themes of this work package, further extending its scientific impact. To help the Researcher develop independent research activities, the Supervisor was not involved in these works.

Building on the molecular dynamics results obtained during WP1—particularly those from publication hal-04917234—two possible models for upscaling the results to the mesoscale (WP2) and macroscale (WP3) were investigated. While these results remain unpublished, they are promising and have formed the basis for securing a follow-up grant (ANR JCJC). This grant, awarded to the Researcher, will enable direct continuation of the work initiated during the MSCA NanoSep project over the next four years. This will be achieved, in part, through the hiring of a postdoctoral researcher and a PhD student.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our studies on water-ethanol mixtures [Gravelle and Coasne, Submitted to Open Research Europe] demonstrated that hydrophobic organosilica surfaces preferentially enrich ethanol, matching the performances of carbon-based materials in specific scenarios. These findings directly inform the design of cost-effective, high-performance membranes for water-alcohol separation, a key technological need for sustainable chemical processes. By understanding ethanol enrichment and the role of surface properties, this model provides a significant advantage in the design of porous materials for separation applications, offering better control over transport properties and material performance.

Beyond this, our research on NMR relaxation rates in confined fluids [collaboration with the Institute for Computational Physics, Stuttgart] introduced a predictive framework that links adsorption times, pore sizes, and diffusion coefficients to relaxation behavior. This development represents a conceptual advance in the interpretation of relaxation signals in nanoporous materials, with potential applications in advanced material characterization and non-invasive diagnostic techniques.

Further, our work on ferrihydrite-water interfaces [Hayatifar et al., Geochemical Transactions] provided an atomistic-level understanding of surface restructuring, charge equilibration, and hydrogen bond dynamics using reactive molecular dynamics simulations and synchrotron X-ray spectroscopy. These findings are directly relevant to environmental chemistry, particularly in the context of water purification, heavy metal adsorption, and geochemical processes.

Water molecules nanoconfined in a silica porous material.