Hydrophilic Pore Surface Research Articles

Methane hydrate formation in slit-shaped pores: Impacts of surface hydrophilicity

Gas hydrate accumulation and hydrate-based gas storage and transportation technology are intimately linked to the formation process of hydrates in the pore space. However, the molecular mechanism underlying this process remains unclear. Here, we employ molecular simulations to investigate methane hydrate formation in surface-modified silica pores, with specific emphasis on the impact of pore surface characteristics. Our results show that under the same thermodynamic conditions, methane hydrate shows no preference towards either the hydrophobic or hydrophilic pore surface, and tends to nucleate in the central part of the hydrophilic slit. It means that whilst the surface properties can impact the dynamics and structure of the molecules on it, thus affecting methane concentration and, as a result, the probability of cage formation, the confinement effect ultimately controls the nucleation process. Furthermore, the pre-filling of the pores with methane can significantly accelerate hydrate formation. This is because methane bubbles adsorbed in the pores can noticeably elevate methane concentration in solution. Moreover, the hydrophobic surface can help with methane dissolution in water, which can both promote the transportation of molecules between methane bubbles and enhance methane hydrate nucleation. This study enhances understanding of the hydrate formation process in pores, which can aid in the design of gas hydrate promoters or inhibitors that meet the demands of hydrate technologies.

Modeling of multiphase flow in low permeability porous media: Effect of wettability and pore structure properties

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications. However, a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability. To address this issue, based on the digital rock of low permeability sandstone, a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process. In addition, a dual-porosity pore network model (PNM) is constructed to obtain the water-oil relative permeability of the sample. The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties. Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability. The injected water breaks through the outlet earlier with a large mass flow, while thick oil films exist in rough hydrophobic surfaces and poorly connected pores. The variation of water-oil relative permeability is significant, and residual oil saturation is high in the oil-wet system. The flooding is extensive, and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces; thus, water relative permeability is lower in the water-wet system. While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity. Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance, and a large microporosity corresponds to low residual oil saturation. This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

COF-based nanofiltration membrane for effective treatment of wastewater containing pharmaceutical residues

Nanofiltration has been identified as an effective method for removing emerging pharmaceuticals from wastewater with potential to mitigate environmental impacts and improve water quality. However, the low separation efficiency from the current nanofiltration membranes impeded their development. Here, using the vacuum-assisted self-assembly method, we prepared a thin film composite membrane by stacking covalent organic framework (COF) nanosheets on a predesigned ceramic hollow fibre. By adding methanol as the co-solvent for the assembly, a continuous and defect-free COF TpPa-SO3H layer was formed on top of the YSZ hollow fibre. The resultant COF composite membrane showed high rejection for five environmentally persistent pharmaceuticals (i.e., diclofenac, sulfamethoxazole, ketoprofen, naproxen, and ibuprofen). The hydrophilic pore surface and strong keto-amine linkages of the COF ensured high and stable permeation during operation with separation governed by electrostatic repulsion and steric exclusion. Due to our design using ceramic hollow fibres, these membranes have a small footprint and can be easily integrated into existing water treatment systems. These features make COF-based nanofiltration membranes a promising option for mitigating the environmental impacts of emerging pharmaceuticals in wastewater.

Residual oil retention and stripping mechanism of hydrophilic pore surfaces during CO2 and N2 combined gas flooding

The mixed gas of CO2 and N2 can replace the great mass of the remaining oil in the center of the porous media channel, but the surface of the pore channels still retain more residual oil. Most of the previous studies focused on how to displace the residual oil in the center of the pore passages, while ignoring how to enhance the recovery degree of the residual oil on the pore surfaces. Moreover, there are few research results on the mechanism of residual oil retention and stripping on pore surfaces during CO2–N2 combined gas flooding, which need to be improved and supplemented. In this paper, the microscopic interaction process among gas phase, oil phase and pore surfaces were explored by molecular dynamics, the changes in microstructural between n-decane molecules and the spatial distribution of gas molecules and n-decane molecules in the system was clarified. The interaction energy between gas, n-decane and pore surfaces were analyzed to reveal the mechanism of remaining oil retention and stripping. The results indicated that when only CO2 in the gas phase, the oil films were easily divided by CO2 molecules, and the adsorption layer formed by CO2 molecules on the quartz surface could well detach the oil phase from the quartz surfaces. With the increase of the proportion of N2 in the mixed gas, the interaction energy between the gas and n-decane phase and between the gas phase and pore surfaces decreased, and the capacity of the gas phase to peel off the oil films from the pore surfaces was weakened. When the proportion of N2 in the gas phase exceeded 25%, the gas phase has no ability to peel off the oil films from the quartz surfaces. The research results have guiding significance for the CO2-N2 combined gas flooding to further tap the remaining oil.

On the Diffusion of Acetonitrile in Nanoscale Amorphous Silica Pores. Understanding Anisotropy and the Effects of Hydrogen Bonding

Molecular dynamics simulations are used to examine the diffusion of acetonitrile within ∼2.4 nm diameter amorphous silica pores with a focus on the mechanism. The role of the pore surface chemistry is examined by comparison of a hydrophilic, −OH terminated, silica pore with one that has hydrogen-bonding turned off and with an effectively hydrophobic pore obtained by setting all pore charges to zero. The anisotropy of diffusion, along and perpendicular to the pore axis, is examined through the mean-squared displacements. The origins of the anisotropy are investigated through the dependence on the acetonitrile position within the pore. The effect of hydrogen bonding of acetonitrile molecules to the hydrophilic pore surface is also probed. The simulations show that acetonitrile molecules do not diffuse axially next to the pore surface. Rather, axial diffusion is preceded by radial diffusion away from the pore surface. The same mechanism is observed for molecules independent of their hydrogen-bonding status t...

An unusual highly connected 3D net with hydrophilic pore surface

An unusual highly connected 3D framework, [K2Cd3(OBA)4(H2O)2(DMF)2](H2O)2 (1) that contains three windows along separate dimensions, has been constructed from a flexible V-shaped ligand 4,4′-oxydibenzoic acid (H2OBA) and a infinite linear {K2Cd3(COO)8}n cluster under solvothermal conditions. Owing to the existence of a polar Ccarboxyl–Ocore–Ccarboxyl moiety in the ligand and the coordinated hydrophilic DMF molecule, a hydrophilic environment is generated at the pore surface. Compound 1 shows high adsorption capacity for polar molecules, such as methanol (7.83%), ethanol (7.13%) and water (13.37%), but exhibits very low uptake capacity for non-polar molecules like methane (0.49%) and cyclohexane (0.68%). Furthermore, its luminescent properties including the quantum yield and lifetime value have also been investigated.

Terbium(III), Europium(III), and Mixed Terbium(III)–Europium(III) Mucicate Frameworks: Hydrophilicity and Stoichiometry-Dependent Color Tunability

Two 3D porous terbium(III) mucicate frameworks, {[Tb(2)(Mu(2-))(3)(H(2)O)(2)]·4H(2)O}(n) (1) and {[Tb(Mu(2-))(Ox(2-))(0.5)(H(2)O)]·H(2)O}(n) (2), have been synthesized under hydrothermal conditions by changing the pH of the reaction medium. Isostructural europium(III) and seven mixed terbium(III)-europium(III) mucicates were synthesized by doping different percentages of Eu(III) under similar reaction conditions and unveiling different emission colors ranging from green to red under the same wavelength. Both dehydrated Tb(III) metal-organic frameworks exhibit selective H(2)O vapor sorption over other solvent molecules (MeOH, MeCN, and EtOH) of less polarity and bigger size and have been correlated to the highly hydrophilic pore surfaces decorated with -OH groups and O atoms from the carboxyl groups of mucicate.

Condensation/Evaporation Transition of Water in Spherical Pores in Equilibrium with Saturated Bulk Water

Liquid−vapor phase transition of water in spherical pores with various strengths of water−surface interaction is studied under conditions of equilibrium with the saturated bulk water. The excess chemical potential of bulk liquid water along the liquid−vapor coexistence curve was determined by the overlapping distribution method. The adsorption and desorption of water in pores were studied by Monte Carlo simulations in the grand canonical ensemble in the temperature range T = 270−580 K with a step 10 K. The well depth U(0) of the water−surface potential was varied from ≈−0.6 kcal/mol (hydrophobic pore surface) to ≈−7.1 kcal/mol (hydrophilic pore surface). The diagram showing the areas of the stable, metastable, and unstable liquid and vapor phases of confined water in the T − U(0) plane has been constructed. Water vapor only exists in pores with U(0) > −1.2 kcal/mol, whereas liquid water only exists in pores with U(0) < −2.8 kcal/mol. The interval ΔU(0), where both stable and metastable states of confined water are possible, shrinks upon heating almost linearly and disappears at the hysteresis pore critical temperature T(p)(h). Above T(p)(h), there is a particular value U(0)(c) ≈ −1.35 kcal/mol that divides the regimes of capillary condensation and capillary evaporation up to the pore critical temperature T(p)(c). The obtained results can be used for the optimization of porous materials for applications that require controlled adsorption and desorption of water.

Construction of a trigonal bipyramidal cage-based metal–organic framework with hydrophilic pore surface via flexible tetrapodal ligands

A pcu network can be ordered through trigonal bipyramidal nanocages as secondary building blocks, which have the striking feature of hydrophilic affinity to the polar molecules and π-π interactions for aromatic molecules.

Temperature- and Stoichiometry-Controlled Dimensionality in a Magnesium 4,5-Imidazoledicarboxylate System with Strong Hydrophilic Pore Surfaces

1D, 2D, and 3D three metal-organic hybrid frameworks of Mg (II) have been synthesized using 4,5-imidazoledicarboxylic acid (H 3idc) with control of the temperature and stoichiometry in a hydrothermal technique. All of the frameworks show high thermal stability, and frameworks 1D and 3D provide highly hydrophilic pore surfaces, correlated by the selective sorption of water molecules over the organic vapor and other gases like N 2 and CO 2.

Nanopore Formation and Phosphatidylserine Externalization in a Phospholipid Bilayer at High Transmembrane Potential

Atomic-resolution molecular dynamics simulations of lipid bilayers containing 7% phosphatidylserine (PS) on one leaflet are consistent with experimental observations of membrane poration and PS externalization in living cells exposed to nanosecond, megavolt-per-meter electric pulses. Nanometer-diameter aqueous pores develop within nanoseconds after application of an electric field of 450 mV/nm, and electrophoretic transport of the anionic PS headgroup along the newly constructed hydrophilic pore surface commences even while pore formation is still in progress.

Release evaluation of drugs from ordered three-dimensional silica structures

Cubic mesoporous structures with Ia3d symmetry, such as MCM-48 and large pore Ia3d material (LP- Ia3d), which present different pore size (3.6 and 5.7 nm, respectively), have been prepared, characterized and used as drug delivery systems. Ibuprofen and erythromycin have been chosen as drug models for delivery studies. The influence of the pore size at these structures has been studied and the results show that the delivery rate of drugs decreases with the pore size of the matrix. The influence of chemical nature of the pore surface on the delivery process has been also studied. In this case, the hydrophilic pore surface has been modified with hydrocarbon chains (C8 and C18 moieties) and the effect upon drug delivery of hydrophobic drugs like erythromycin has been studied. The results show a noticeable decrease of the delivery rate when the surface of the matrices is modified.

Control of pore hydrophilicity in ordered nanoporous polystyrene using an AB/AC block copolymer blending strategy

Ordered nanoporous plastics with hydrophilic pore surfaces were prepared by the degradative removal of polylactide from a self-organised, multi-component composite containing two block copolymers: polystyrene-polylactide and polystyrene-polyethylene oxide. The solid-state characterization of blends containing up to 12 wt.% polyethylene oxide was consistent with nanoscopic cylinders of mixed polyethylene oxide and polylactide hexagonally packed in a polystyrene matrix. Orientation of these materials through simple channel die processing resulted in good cylinder alignment. Subsequent methanolysis/hydrolysis of the polylactide component gave nanoporous polystyrene with polyethylene oxide coated pores. The resulting nanoporous materials were able to imbibe water, in contrast to nanoporous polystyrene with no polyethylene oxide component.

Nafion membrane electrophoresis with direct and simplified end-column pulse electrochemical detection of amino acids.

A novel electrophoresis technique, in which the separation column was replaced by a strip of Nafion membrane (5.0 cm x 0.20 mm x 0.25 mm), was developed for the separation of an amino acid mixture (glycine, asparic acid and lysine), followed by quadruple-pulse electrochemical detection. Nafion membrane contains hydrophilic pores (10-20 A and 50-60 A in size) acting as very narrow electrophoresis channels. The fixed-charge sites (-SO(3) (-)) on the hydrophilic pore surface provide a strong charged background. A platinum disk electrode (0.90 mm inner diameter) was employed as the detection electrode and the electrophoresis cathode was used as the quasi-reference and counter electrode for the end-column electrochemical detector, without decoupler. Under optimized conditions the mixture of amino acids could be separated at a voltage of only 90 V with a detection limit of 10(-7) M, indicating that Nafion membrane electrophoresis is a potentially attractive technique for the separation of small organic molecules or ions.

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

We present results of molecular dynamics simulations of water confined in a silica pore. A cylindrical cavity is created inside a vitreous silica cell with geometry and size similar to the pores of real Vycor glass. The simulations are performed at different hydration levels. At all hydration levels water adsorbs strongly on the Vycor surface; a double layer structure is evident at higher hydrations. At almost full hydration the modifications of the confinement-induced site-site pair distribution functions are in qualitative agreement with neutron diffraction experiment. A decrease in the number of hydrogen bonds between water molecules is observed along the pore radius, due to the tendency of the molecules close to the substrate to form hydrogen-bonds with the hydrophilic pore surface. As a consequence we observe a substrate induced distortion of the H-bond tetrahedral network of water molecules in the regions close to the surface.