1-Bromopropane Capture with Hydrophobic Zeolites: Force Field Development and Molecular Simulations

1-Bromopropane is a solvent used in various industrial and commercial applications. United States Environmental Protection Agency recently concluded that 1-bromopropane posed unreasonable risks to human health in several conditions of use. In this work, the adsorption of 1-bromopropane vapors in zeolites was investigated using molecular simulations. First, a united-atom model of 1-bromopropane was developed and the model was validated to reproduce vapor-liquid equilibrium properties of 1-bromopropane by carrying out Gibbs ensemble Monte Carlo simulations. The new model was then used to investigate the capture of 1-bromopropane in hydrophobic zeolites with Monte Carlo simulations in the grand canonical ensemble. The results show that a filtering system that consists of MRE and STW zeolites can capture 1-bromopropane within its ambient concentration range that occurs as a result of 1-bromopropane release in various industrial and commercial applications as identified by the US EPA. While MRE zeolite has the optimal pore size that provides favorable host-guest interactions to capture 1-bromopropane at extremely low concentrations, rapid condensation of 1-bromopropane occurs at relatively higher concentrations in the intersections of narrow helical and straight pores in the STW zeolite

Biohybrid Membrane Formation by Directed Insertion of Aquaporin into a Solid-State Nanopore

Biohybrid nanopores combine the durability of solid-state nanopores with the precise structure and function of biological nanopores. Particular care must be taken to control how biological nanopores adapt to their surroundings once they come into contact with the solid-state nanopores. Two major challenges are to precisely control this adaptability under dynamic conditions and provide predesigned functionalities that can be manipulated for engineering applications. In this work, we report on the computational design of a distinctive class of biohybrid active membrane layers, built from the directed-insertion of an aquaporin-incorporated lipid nanodisc into a model alkyl-functionalized silica pore. We show that in an aqueous environment when a pressure difference exists between the two sides of the solid-state nanopore, the preferential interactions between the hydrocarbon tail of the lipid molecules that surround the aquaporin protein and the alkyl group functionalizing the interior surface of the silica nanopore enable the insertion of the aquaporin-incorporated lipid shell into the nanopore by forcing out the water molecules. The same preferential interactions are responsible for the structural stability of the inserted aquaporin-incorporated lipid shell as well as the water sealing properties of the lipid-alkyl interface. We further show that the aquaporin protein stabilized in the alkyl-functionalized silica nanopore preserves its biological structure and function in both pure and saline water, and, remarkably, its water permeability is equal to the one measured in the biological environment. The designed biohybrid membrane could pave the way for the development of durable transformative devices for water filtration

Biohybrid membrane formation by directed insertion of Aquaporin into a solid-state nanopore

Technical challenges in molecule sensing and chemical detection have created an increasing demand for transformative materials with high sensitivity and specificity. Biohybrid nanopores have attracted growing interest as they can ideally combine the durability of solid-state nanopores with the precise structure of biological nanopores. Particular care must be taken to control how biological nanopores adapt to their surroundings once in contact with the solid-state nanopore. Two major challenges are to precisely control this adaptability under dynamic conditions and provide predesigned functionalities that can be manipulated for engineering applications. Here, we report on the computational design of a distinctive class of biohybrid active membrane layer, built from the directed insertion of an aquaporin-incorporated lipid shell into a silica nanopore. First, we describe in detail the mechanisms at play in the insertion of the biological membrane into the solid-state nanopore. Then we analyze the structural stability of the system and demonstrate that its water permeability is comparable to the one measured in the biological environment. Finally, we discuss how the technology implemented could be applicable to environmental and biomedical applications, such as water desalination and drug discovery, where targeting and controlled permeation of small molecules must be efficiently addressed.Comment: 12 pages, 10 figures (including Supporting Information

Tuning the Transport Properties of Gases in Porous Graphene Membranes with Controlled Pore Size and Thickness

Porous graphene membranes emerged as promising alternatives for gas separation applications due to their atomic thickness enabling ultra-high permeance, but suffer from low gas selectivity. Whereas decreasing the pore size below 3 nm is expected to increase the gas selectivity due to molecular sieving, it is rather challenging to generate large number of uniform small pores on the graphene surface. Here, we introduce a pore narrowing approach via gold deposition onto porous graphene surface to tune the pore size and thickness of the membrane to achieve large number of small pores. Through our systematic approach, we determined the ideal combination as pore size below 3 nm obtained at the thickness of 100 nm to attain high selectivity and high permeance. The resulting membrane showed a H2 /CO2 separation factor of 31.3 at H2 permeance of 2.23 × 105 GPU (1 GPU = 3.35 × 10-10  mol s-1 m-2 Pa-1 ), which is the highest value reported to date in the 105 GPU permeance range. This result is explained by comparing the predicted binding energies of gas molecules with the Au surface, -5.3 versus -21 kJ mol-1 for H2 and CO2 , respectively, increased surface-gas interactions and molecular sieving effect with decreasing pore size. This article is protected by copyright. All rights reserved

Modelling of Gas Transport through Polymer/MOF Interfaces: A Microsecond-Scale Concentration Gradient-Driven Molecular Dynamics Study

Membrane-based separation technologies offer a cost-effective alternative to many energy-intensive gas separation processes, such as distillation. Mixed matrix membranes (MMMs) composed of polymers and metal–organic frameworks (MOFs) have attracted a great deal of attention for being promising systems to manufacture durable and highly selective membranes with high gas fluxes and high selectivities. Therefore, understanding gas transport through these MMMs is of significant importance. There has been longstanding speculation that the gas diffusion behavior at the interface formed between the polymer matrix and MOF particles would strongly affect the global performance of the MMMs due to the potential presence of nonselective voids or other defects. To shed more light on this paradigm, we have performed microsecond long concentration gradient-driven molecular dynamics (CGD-MD) simulations that deliver an unprecedented microscopic picture of the transport of H2 and CH4 as single components and as a mixture in all regions of the PIM-1/ZIF-8 membrane, including the polymer/MOF interface. The fluxes of the permeating gases are computed and the impact of the polymer/MOF interface on the H2/CH4 permselectivity of the composite membrane is clearly revealed. Specifically, we show that the poor compatibility between PIM-1 and ZIF-8, which manifests itself by the presence of nonselective void spaces at their interface, results in a decrease of the H2/CH4 permselectivity for the corresponding composite membrane as compared to the performances simulated for PIM-1 and ZIF-8 individually. We demonstrate that CGD-MD simulations based on an accurate atomistic description of the polymer/MOF composite is a powerful tool for characterization and understanding of gas transport and separation mechanisms in MMMs

Supercritical carbon dioxide enhanced natural gas recovery from kerogen micropores

As the global energy demand increases, a sustainable and environmentally friendly methane (CH4) extraction technique must be developed to assist in the transition off of fossil fuels. In recent years, supercritical carbon dioxide (CO2) has been poised as a candidate for enhanced gas recovery (EGR) from CH4-rich source rocks, potentially with the reservoir serving as a carbon sink for CO2. However, the underlying molecular-scale mechanisms of CO2-EGR processes are still poorly understood. Using constant chemical potential molecular dynamics (CMD), this study investigates the CH4 recovery process via supercritical CO2 injection into immature (Type I-A) and overmature (Type II-D) kerogens in real-time and at reservoir conditions (365 K and 275 bar). A pseudo-second order (PSO) rate law was used to quantify the adsorption and desorption kinetics of CO2 and CH4. The kinetics of simultaneous adsorption/desorption are rapid in immature kerogen due to better connected pore volume facilitating fluid diffusion, whereas in overmature kerogen, the structural heterogeneity hinders fluid diffusion. Estimated second order kinetic rate coefficients reveal that CO2 adsorption and CH4 desorption in Type I-A are about two times and an order of magnitude faster, respectively, compared to those of in Type II-D. Furthermore, overmature Type II-D kerogen contains inaccessible micropores which prevent full recovery of CH4. For every CH4 molecule replaced, at least two and six CO2 molecules are adsorbed in Type-II-D and Type I-A kerogens, respectively. Overall, this study shows that CO2 injection can achieve 90 % and 65 % CH4 recovery in Type I-A and Type II-D kerogens, respectively

Fast light-switchable polymeric carbon nitride membranes for tunable gas separation

Switchable gas separation membranes are intriguing systems for regulating the transport properties of gases. However, existing stimuli-responsive gas separation membranes suffer from either very slow response times or require high energy input for switching to occur. Accordingly, herein, we introduced light-switchable polymeric carbon nitride (pCN) gas separation membranes with fast response times prepared from melamine precursor through in-situ formation and deposition of pCN onto a porous support using chemical vapor deposition. Our systematic analysis revealed that the gas transport behavior upon light irradiation is fully governed by the polarizability of the permeating gas and its interaction with the charged pCN surface, and can be easily tuned either by controlling the power of the light and/or the duration of irradiation. We also demonstrated that gases with higher polarizabilities such as CO2 can be separated from gases with lower polarizability like H2 and He effectively with more than 22% increase in the gas/CO2 selectivity upon light irradiation. The membranes also exhibited fast response times (<1 s) and can be turned “on” and “off” using a single light source at 550 nm

The role of surface thermodynamics and kinetics in the removal of PFOA from aqueous solutions

Perfluorooctanoic acid (PFOA) has been extensively used as surfactant in industrial applications. Human exposure to PFOA through contaminated water has been linked to serious adverse health effects. In this work, the removal of PFOA from water in all-silica zeolites, which are hydrophobic materials with diverse pore geometries and exceptional hydrothermal stability, is studied. Molecular scale structure, dynamics, kinetics, and free energy landscapes associated with PFOA adsorption are characterized. Interfacial adsorption constitutes the rate limiting step and the adsorption of PFOA is orientation competitive. The PFOA orientation where the hydrophobic perfluorinated methyl group is adsorbed first on the zeolite surface is thermodynamically favored; whereas the adsorption kinetics is faster when the hydrophilic carboxyl group is adsorbed first. Furthermore, the adsorption of PFOA in deprotonated state in hydrophobic pores is thermodynamically prohibitive. Based on computed permeabilities in the pores and kinetic rates associated with the adsorption of PFOA from water, three zeolites, MTW, VET and GON, are estimated to exhibit several orders of magnitude better PFOA removal performance compared to the benchmark material, zeolite Beta (BEA)

Fast light-switchable polymeric carbon nitride membranes for tunable gas separation

Switchable gas separation membranes are intriguing systems for regulating the transport properties of gases. However, existing stimuli-responsive gas separation membranes suffer from either very slow response times or require high energy input for switching to occur. Accordingly, herein, we introduced light-switchable polymeric carbon nitride (pCN) gas separation membranes with fast response times prepared from melamine precursor through in-situ formation and deposition of pCN onto a porous support using chemical vapor deposition. Our systematic analysis revealed that the gas transport behavior upon light irradiation is fully governed by the polarizability of the permeating gas and its interaction with the charged pCN surface, and can be easily tuned either by controlling the power of the light and/or the duration of irradiation. We also demonstrated that gases with higher polarizabilities such as CO2 can be separated from gases with lower polarizability like H2 and He effectively with more than 22% increase in the gas/CO2 selectivity upon light irradiation. The membranes also exhibited fast response times (<1 s) and can be turned “on” and “off” using a single light source at 550 nm