B. Sha
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Per- and polyfluoroalkyl substances (PFAS) are a large class of highly fluorinated chemicals that are environmentally persistent and difficult to remove from water. Activated carbon is widely used for PFAS removal because of its high surface area and porous structure. However, adsorption performance is not uniform and varies significantly across PFAS classes and operating conditions. The objective of this thesis is to investigate PFAS adsorption in activated-carbon-like nanopore environments using molecular simulation, with particular focus on how carbon pore width, surface functional-group type and density, and PFAS type together influence adsorption behavior. Rather than reproducing the full structural heterogeneity of real activated carbon, this work employs controlled slit-pore models to resolve fundamental adsorption mechanisms underlying experimentally observed trends.
Molecular dynamics (MD) simulations with explicit water are used to examine PFAS adsorption at the molecular scale within idealized carbon slit pores formed by two parallel carbon surfaces separated by a controlled distance that is varied to represent different pore widths. Surface functional groups are introduced to represent common oxygen- and nitrogen-containing functionalities, and surface chemistry is parameterized using surface functional-group density. Three PFAS are considered, one molecule per pore, to represent differences in perfluoroalkyl chain length and functional headgroup class.
Simulation trajectories are analyzed through number-density profiles normal to the pore walls, the time each PFAS spends in contact with the walls, PFAS–wall interaction energies, confined-water dynamics, and counter-ion distributions. The results show that adsorption is governed primarily by perfluoroalkyl chain length: the long-chain (C8) species adsorb strongly on every surface, whereas the short-chain (C1) species adsorbs less on every surface and much less on the anionic one. Surface chemistry acts as a secondary control that becomes decisive only for the short-chain species, for which the neutral polar surfaces give the highest adsorption and an anionic surface the lowest.
Wall chemistry and functional-group density instead set the confined-water dynamics and the counter-ion distribution, which are largely independent of the adsorbing PFAS. Confined water is slowest at the anionic carboxylate surface, where the sodium counter-ions also gather at the surface. This charged surface binds and slows the surrounding water most strongly and gathers the ions, yet captures PFAS least, because it electrostatically repels the anionic headgroup. Overall, long-chain PFAS are captured by almost any surface through their tail, while short-chain species such as trifluoroacetate remain the most difficult to retain and are captured best by the neutral polar surfaces.
...
Molecular dynamics (MD) simulations with explicit water are used to examine PFAS adsorption at the molecular scale within idealized carbon slit pores formed by two parallel carbon surfaces separated by a controlled distance that is varied to represent different pore widths. Surface functional groups are introduced to represent common oxygen- and nitrogen-containing functionalities, and surface chemistry is parameterized using surface functional-group density. Three PFAS are considered, one molecule per pore, to represent differences in perfluoroalkyl chain length and functional headgroup class.
Simulation trajectories are analyzed through number-density profiles normal to the pore walls, the time each PFAS spends in contact with the walls, PFAS–wall interaction energies, confined-water dynamics, and counter-ion distributions. The results show that adsorption is governed primarily by perfluoroalkyl chain length: the long-chain (C8) species adsorb strongly on every surface, whereas the short-chain (C1) species adsorbs less on every surface and much less on the anionic one. Surface chemistry acts as a secondary control that becomes decisive only for the short-chain species, for which the neutral polar surfaces give the highest adsorption and an anionic surface the lowest.
Wall chemistry and functional-group density instead set the confined-water dynamics and the counter-ion distribution, which are largely independent of the adsorbing PFAS. Confined water is slowest at the anionic carboxylate surface, where the sodium counter-ions also gather at the surface. This charged surface binds and slows the surrounding water most strongly and gathers the ions, yet captures PFAS least, because it electrostatically repels the anionic headgroup. Overall, long-chain PFAS are captured by almost any surface through their tail, while short-chain species such as trifluoroacetate remain the most difficult to retain and are captured best by the neutral polar surfaces.
...
Per- and polyfluoroalkyl substances (PFAS) are a large class of highly fluorinated chemicals that are environmentally persistent and difficult to remove from water. Activated carbon is widely used for PFAS removal because of its high surface area and porous structure. However, adsorption performance is not uniform and varies significantly across PFAS classes and operating conditions. The objective of this thesis is to investigate PFAS adsorption in activated-carbon-like nanopore environments using molecular simulation, with particular focus on how carbon pore width, surface functional-group type and density, and PFAS type together influence adsorption behavior. Rather than reproducing the full structural heterogeneity of real activated carbon, this work employs controlled slit-pore models to resolve fundamental adsorption mechanisms underlying experimentally observed trends.
Molecular dynamics (MD) simulations with explicit water are used to examine PFAS adsorption at the molecular scale within idealized carbon slit pores formed by two parallel carbon surfaces separated by a controlled distance that is varied to represent different pore widths. Surface functional groups are introduced to represent common oxygen- and nitrogen-containing functionalities, and surface chemistry is parameterized using surface functional-group density. Three PFAS are considered, one molecule per pore, to represent differences in perfluoroalkyl chain length and functional headgroup class.
Simulation trajectories are analyzed through number-density profiles normal to the pore walls, the time each PFAS spends in contact with the walls, PFAS–wall interaction energies, confined-water dynamics, and counter-ion distributions. The results show that adsorption is governed primarily by perfluoroalkyl chain length: the long-chain (C8) species adsorb strongly on every surface, whereas the short-chain (C1) species adsorbs less on every surface and much less on the anionic one. Surface chemistry acts as a secondary control that becomes decisive only for the short-chain species, for which the neutral polar surfaces give the highest adsorption and an anionic surface the lowest.
Wall chemistry and functional-group density instead set the confined-water dynamics and the counter-ion distribution, which are largely independent of the adsorbing PFAS. Confined water is slowest at the anionic carboxylate surface, where the sodium counter-ions also gather at the surface. This charged surface binds and slows the surrounding water most strongly and gathers the ions, yet captures PFAS least, because it electrostatically repels the anionic headgroup. Overall, long-chain PFAS are captured by almost any surface through their tail, while short-chain species such as trifluoroacetate remain the most difficult to retain and are captured best by the neutral polar surfaces.
Molecular dynamics (MD) simulations with explicit water are used to examine PFAS adsorption at the molecular scale within idealized carbon slit pores formed by two parallel carbon surfaces separated by a controlled distance that is varied to represent different pore widths. Surface functional groups are introduced to represent common oxygen- and nitrogen-containing functionalities, and surface chemistry is parameterized using surface functional-group density. Three PFAS are considered, one molecule per pore, to represent differences in perfluoroalkyl chain length and functional headgroup class.
Simulation trajectories are analyzed through number-density profiles normal to the pore walls, the time each PFAS spends in contact with the walls, PFAS–wall interaction energies, confined-water dynamics, and counter-ion distributions. The results show that adsorption is governed primarily by perfluoroalkyl chain length: the long-chain (C8) species adsorb strongly on every surface, whereas the short-chain (C1) species adsorbs less on every surface and much less on the anionic one. Surface chemistry acts as a secondary control that becomes decisive only for the short-chain species, for which the neutral polar surfaces give the highest adsorption and an anionic surface the lowest.
Wall chemistry and functional-group density instead set the confined-water dynamics and the counter-ion distribution, which are largely independent of the adsorbing PFAS. Confined water is slowest at the anionic carboxylate surface, where the sodium counter-ions also gather at the surface. This charged surface binds and slows the surrounding water most strongly and gathers the ions, yet captures PFAS least, because it electrostatically repels the anionic headgroup. Overall, long-chain PFAS are captured by almost any surface through their tail, while short-chain species such as trifluoroacetate remain the most difficult to retain and are captured best by the neutral polar surfaces.
Master thesis
(2026)
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G. Blasi, O. Moultos, T.J.H. Vlugt, B. Sha, O. Moultos, Luis Cutz , M.B. Tanis
Per- and polyfluoroalkyl substances (PFASs), a broad class of synthetic organic micropollutants, have emerged as a threat due to their chronic toxicity in humans, bioaccumulation potential, and resistance to degradation. Developing efficient and affordable removal processes is a complex but necessary engineering challenge, motivated by established scientific consensus and stricter global regulations. Recently, adsorption onto all-silica zeolite beta has shown promising results for PFAS filtration from water, their primary medium for accumulation. However, molecular-scale insights into sorption under industrially relevant conditions are lacking, leaving unanswered questions and limiting opportunities for process optimization. This work conducts molecular simulations to characterize the behaviour of PFASs in both the aqueous and adsorbed phases in the presence of solvated inorganic ions. Using a broad set of tools from computational statistical mechanics, their concerted interactions are studied across multiple domains: molecular dynamics simulations in bulk water, Monte Carlo sampling in the adsorbed phase, and adaptive biasing methods to characterize the water-zeolite interface.
The intra-diffusion coefficients in water, ranging from 5.4(5) to 9.2(11) × 10⁻⁶ cm² s⁻¹ depending on PFAS moiety and salinity, agree with experimental findings within a constant systematic error. The mobility of PFASs is weakly affected by ionic content, with microviscous effects playing a central role for shorter molecules. Adsorption sites are identified inside the zeolite beta framework and at the zeolite-water interface. Computing host-guest interaction energies reveals that adsorption is driven by both enthalpic effects (favourable van der Waals interactions) and entropic effects (hydrophobic interactions between framework and adsorbate). Free energy profiles at the water-zeolite interface suggest that inorganic ions stabilize PFASs into the interfacial adsorption sites, increasing the barrier for desorption by 10.1 to 27.1 kJ mol⁻¹ for long- and short-chain PFASs at 0.1 M CaCl₂. However, the ultra-short chain trifluoroacetic acid is not affected by the presence of inorganic ions. Additionally, higher salinities hinder adsorption instead, likely due to increased attraction between PFAS anions and solvated inorganic cations. ...
The intra-diffusion coefficients in water, ranging from 5.4(5) to 9.2(11) × 10⁻⁶ cm² s⁻¹ depending on PFAS moiety and salinity, agree with experimental findings within a constant systematic error. The mobility of PFASs is weakly affected by ionic content, with microviscous effects playing a central role for shorter molecules. Adsorption sites are identified inside the zeolite beta framework and at the zeolite-water interface. Computing host-guest interaction energies reveals that adsorption is driven by both enthalpic effects (favourable van der Waals interactions) and entropic effects (hydrophobic interactions between framework and adsorbate). Free energy profiles at the water-zeolite interface suggest that inorganic ions stabilize PFASs into the interfacial adsorption sites, increasing the barrier for desorption by 10.1 to 27.1 kJ mol⁻¹ for long- and short-chain PFASs at 0.1 M CaCl₂. However, the ultra-short chain trifluoroacetic acid is not affected by the presence of inorganic ions. Additionally, higher salinities hinder adsorption instead, likely due to increased attraction between PFAS anions and solvated inorganic cations. ...
Per- and polyfluoroalkyl substances (PFASs), a broad class of synthetic organic micropollutants, have emerged as a threat due to their chronic toxicity in humans, bioaccumulation potential, and resistance to degradation. Developing efficient and affordable removal processes is a complex but necessary engineering challenge, motivated by established scientific consensus and stricter global regulations. Recently, adsorption onto all-silica zeolite beta has shown promising results for PFAS filtration from water, their primary medium for accumulation. However, molecular-scale insights into sorption under industrially relevant conditions are lacking, leaving unanswered questions and limiting opportunities for process optimization. This work conducts molecular simulations to characterize the behaviour of PFASs in both the aqueous and adsorbed phases in the presence of solvated inorganic ions. Using a broad set of tools from computational statistical mechanics, their concerted interactions are studied across multiple domains: molecular dynamics simulations in bulk water, Monte Carlo sampling in the adsorbed phase, and adaptive biasing methods to characterize the water-zeolite interface.
The intra-diffusion coefficients in water, ranging from 5.4(5) to 9.2(11) × 10⁻⁶ cm² s⁻¹ depending on PFAS moiety and salinity, agree with experimental findings within a constant systematic error. The mobility of PFASs is weakly affected by ionic content, with microviscous effects playing a central role for shorter molecules. Adsorption sites are identified inside the zeolite beta framework and at the zeolite-water interface. Computing host-guest interaction energies reveals that adsorption is driven by both enthalpic effects (favourable van der Waals interactions) and entropic effects (hydrophobic interactions between framework and adsorbate). Free energy profiles at the water-zeolite interface suggest that inorganic ions stabilize PFASs into the interfacial adsorption sites, increasing the barrier for desorption by 10.1 to 27.1 kJ mol⁻¹ for long- and short-chain PFASs at 0.1 M CaCl₂. However, the ultra-short chain trifluoroacetic acid is not affected by the presence of inorganic ions. Additionally, higher salinities hinder adsorption instead, likely due to increased attraction between PFAS anions and solvated inorganic cations.
The intra-diffusion coefficients in water, ranging from 5.4(5) to 9.2(11) × 10⁻⁶ cm² s⁻¹ depending on PFAS moiety and salinity, agree with experimental findings within a constant systematic error. The mobility of PFASs is weakly affected by ionic content, with microviscous effects playing a central role for shorter molecules. Adsorption sites are identified inside the zeolite beta framework and at the zeolite-water interface. Computing host-guest interaction energies reveals that adsorption is driven by both enthalpic effects (favourable van der Waals interactions) and entropic effects (hydrophobic interactions between framework and adsorbate). Free energy profiles at the water-zeolite interface suggest that inorganic ions stabilize PFASs into the interfacial adsorption sites, increasing the barrier for desorption by 10.1 to 27.1 kJ mol⁻¹ for long- and short-chain PFASs at 0.1 M CaCl₂. However, the ultra-short chain trifluoroacetic acid is not affected by the presence of inorganic ions. Additionally, higher salinities hinder adsorption instead, likely due to increased attraction between PFAS anions and solvated inorganic cations.