Pore Confinement Effect Research Articles

Interfacial Conductivity Enhancement and Pore Confinement Conductivity-Lowering Behavior inside the Nanopores of Solid Silica-gel Nanocomposite Electrolytes.

Solid nanocomposite electrolytes (nano-SCEs) that exhibit higher ionic conductivity than the individual confined electrolyte were investigated for high-performance solid-state batteries. Understanding the behavior of Li-ion conduction through the pores is important to design ideal nanoporous structures for nano-SCEs, which are composed of an ionic liquid electrolyte (ILE) in a highly porous (∼90%) silica matrix. To establish the relationship between the pore structure of the silica matrix and the ionic conductivity of the solid nanocomposite, the liquid electrolyte fraction was successfully extracted from the nano-SCE to reveal the fragile porous silica matrix. A careful drying using the CO2 supercritical drying method helps in sustaining the original structure, preventing its collapse due to surface tension. The pore size distribution, Brunauer-Emmett-Teller (BET) surface area, and porosity were characterized using scanning electron microscopy, transmission electron microscopy, and N2 adsorption/desorption techniques. Our results revealed a wide size distribution of macropores and mesopores in the silica matrix. The pore size increased and the effective surface area decreased with increasing ILE/SiO2 molar ratio. The interface conductivity enhancement was found to increase with the thickness of the adsorbed (ice-like) bound-water layer on the silica surface, confirming that the strong hydrogen bonding of the adsorbed ionic liquid molecules on the bound-water layer causes the conduction promotion effect in the nano-SCE. In addition, a large number of small pores lead to a severe pore confinement effect that results in a decreased conductivity due to the increasing viscosity of the ILE filling the pores. The conductivity can be improved by realizing a nano-SCE with an optimized pore size to minimize the pore confinement effect.

Dye encapsulation engineering in a tetraphenylethylene-based MOF for tunable white-light emission

The development of efficient and stable white-light emissive materials is highly desirable in displays and solid-state lighting. Here we present a high-quality white-light emitter based a dual-emitting MOF hybrid, which is achieved by dye encapsulation engineering within a robust Zr-MOF (PCN-128W) containing a highly luminescent tetraphenylethylene-based ligand. The pore confinement effect well isolates the incorporated dye molecules (trans-4-[4-(Dimethylamino)styryl]-1-methylpyridinium iodide (DSM)) and therefore suppress the aggregation caused luminescence quenching. The dye emission is mainly sensitized by PCN-128W host through Förster resonance energy transfer (FRET), and the FRET process is incomplete, thus enabling the hybrid to feature dual emissions upon a single excitation. The emission color of DSM@PCN-128W hybrid can be systematically tuned from blue to white, and to orange by regulating the dye encapsulation content. A broad white-light emission with a considerably high quantum yield (21.2%) is obtained in the case of dye contents of 0.15 wt%. The luminescence of DSM@PCN-128W hybrid is stable in ambient air for over 1 month, and show good resistance to continuous UV light irradiation, owing to the protective MOF Matrix that largely inhibits the UV exposure to dye molecules. What’s more, by combining DSM@PCN-128W with a commercial UV LED chip, we fabricate a white-light emitting prototype device showing CIE chromaticity coordinates of (0.34, 0.33), a CRI of 79.1, and a CCT of 5525 K.

Ultrasensitive all-solid-state electrochemiluminescence platform for kanamycin detection based on the pore confinement effect of 0D g-C3N4 quantum dots/3D graphene hydrogel

Quests for stable and highly efficient electrochemiluminescence (ECL) emitters and a full understanding of the relation between the ECL emitter structure and its properties are a continual and active theme in the fields of ECL. In this work, an intense and stable ECL platform was achieved by encapsulating 0D graphite carbon nitride quantum dots (g-C3N4 QDs) into 3D graphene hydrogel via a facile hydrothermal approach. The architectures of the as-fabricated 0D g-C3N4 QDs/3D graphene hydrogel nanocomposites showed 4.3-fold ECL intensity relative to that of pure g-C3N4. This phenomenon was caused by a pore confinement effect, which could increase the electrochemical reaction efficiency because the pore channels could promote electron transfer and mass transport. The confinement effect could also localise a very large luminophore near the electrode surface, resulting in enhanced ECL emission. Moreover, the as-fabricated architecture ensured the stability of the g-C3N4 QDs in the ECL field due to the increased dispersibility. On the basis of the excellent ECL performances, a novel ECL biosensor was fabricated for highly selective and sensitive detection of kanamycin (KAN) with the assistance of an aptamer. The proposed ECL sensor can quantify KAN from 1 pM to 50 nM with a limit of detection of 0.33 pM. Such work offers an efficient design idea for achieving a high-performance ECL platform and provides new insight into developing and applying a g-C3N4-based ECL system.

Influence of anodization parameters on film thickness and volume expansion of thick- and large-sized anodic aluminum oxide film

Anodic aluminum oxide (AAO) film with a thickness ranging from 20 to 100 μm was prepared using a large-sized Al plate (4 cm × 10 cm) to investigate the anodization parameter effect on the film thickness and volume expansion factor. A corrosion treatment (voltage = 0 V) was performed to investigate the film dissolution caused by acid. The actual anode surface temperature was also measured to confirm the field-assisted nature of AAO dissolution. The film thickness increases exponentially with temperature, and increases approximately linearly with voltage, duration or concentration. The volume expansion factor gives a first rising and then falling trend with temperature or duration, while it has a nearly linear trend with voltage or concentration. The volume expansion factor increases with the intensified electric field, while its decrease is attributed to the Joule heat-enhanced dissolution. In the case of large film thickness (> 20 μm), the pore confinement effect may be one of the reasons for the change of volume expansion factor. In addition to the conventional parameters, the heat transfer-related parameters (for example, sample size) also greatly affect the AAO film growth.

Confinement-Driven “Flexible” Acidity Properties of Porous Zeolite Catalysts with Varied Probe-Assisted Solid-State NMR Spectroscopy

Although the acidity properties and pore confinement effect inside porous zeolite catalysts have been extensively explored to correlate with their catalytic performances, a comprehensive understand...

Contribution quantification of nanoscale gas transport in shale based on strongly inhomogeneous kinetic model

The small pore sizes and intense intermolecular interactions among gas-gas and gas-solid particles lead to complex gas transport in shale nanopores. The strong non-linear flow mechanics, e.g. viscous flow, slippage effect, surface diffusion, adsorption and desorption, may occur in such systems. In this study, a kinetic model for strongly inhomogeneous fluid systems is employed to quantify the contribution of different flow mechanisms to total mass flux in a nanoscale pore considering dense gas effect and pore confinement effect. It is shown that the overall mass flux is dominated by slip flow in bulk region and enhanced surface diffusion in adsorbed region in organic pores. But in inogranic pores, no slip is observed. Then, the contributions from the bulk flow and (enhanced) surface diffusion in organic and inorganic nanopores are quantified. The adsorption and desorption characteristics under different pressure and temperature conditions are consistent with previous studies, and the density and velocity profiles are validated by molecular dynamics simulations. Results show that the flow enhancement effect is significant in organic nanopores due to the large slip velocity and high adsorbed gas density. This study provides a quantitatively multi-scale approach to clarifying various gas transport mechanisms in shale gas reservoirs.

Stepwise or Concerted Mechanisms of Benzene Ethylation Catalyzed by Zeolites? Theoretical Analysis of Reaction Pathways

Benzene ethylation over zeolites has a long-standing controversy on two different possible reaction pathways, i.e., stepwise and concerted mechanisms. To solve this doubt and further find out the suitable zeolite to catalyze benzene ethylation with ethylene, we employed density functional theory (DFT) and molecular dynamic (MD) methods to insight the reaction mechanisms of benzene ethylation over five widely-applied zeolites, i.e., ZSM-5, ZSM-22, ZSM-12, Y and MOR. ZSM-5 is the optimal framework than the other zeolites in both stepwise and concerted mechanisms, and the host–guest interaction between the intersection pore and reacted species drives to the lower maximum free energy span (viz. 23.41 and 20.96 kcal/mol for stepwise and concerted mechanisms) thermodynamically, and stepwise mechanism was confirmed as the superior pathway to catalyze benzene ethylation kinetically. Moreover, the faster diffusion rate of ethylene (50 times) than that of benzene in ZSM-5 indicates that the ethylation is diffusion limited and ethylene could preferentially occupy the Bronsted acid site to form surface ethyoxyl. Furthermore, the quantitative Mulliken population analysis and qualitative reduced density gradient (RDG) analysis reveal that the pore confinement effect drives the priority of ZSM-5 to catalyze benzene ethylation.

Metal organic framework derived Ni/CeO2 catalyst with highly dispersed ultra-fine Ni nanoparticles: Impregnation synthesis and the application in CO2 methanation

CO2 methanation is a promising strategy to convert the greenhouse gas into synthetic natural gas, which is known as a clean fuel with higher energy density. Ni/CeO2 is one of the active catalysts for CO2 methanation reaction. However, Ni/CeO2 with conventional metal/support structure suffers from the problem of nanocrystal coarsening during high-temperature reaction and thus decreasing catalytic activity. In this work, a Ni/CeO2 catalyst with novel structure was designed and synthesized through impregnation of Ce-based metal organic framework (MOF) with Ni precursor followed by calcination process. Due to the confinement effect of ultra-small pores derived from the MOF, Ni/CeO2 catalysts with ultrafine Ni nanoparticles, high dispersion and good thermostability were resulted. Among all the samples, Ni/CeO2 calcined at 600 °C showed the best catalytic performance due to the highest amount of oxygen vacancies. This work demonstrates a facile way to synthesize a broad range of ultra-fine metal/metal oxide nanocomposite catalysts with high catalytic activity and good stability for various applications.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Covalent grafting of molecular photosensitizer and catalyst on MOF-808: effect of pore confinement toward visible light-driven CO2 reduction in water

We have fabricated Zr-MBA-Ru/Re-MOFvia post-synthetic modification of MOF-808. The integrated catalyst assembly was used to mimic natural photosynthesis for sunlight-driven CO2 reduction to produce CO in aqueous medium without external sacrificial electron donor.

Sustainable utilization of waste glycerol for 1,3-propanediol production over Pt/WOx/Al2O3 catalysts: Effects of catalyst pore sizes and optimization of synthesis conditions.

Recycling of waste glycerol derived from biodiesel production to high value-added chemicals is essential for sustainable development of Bio-Circular-Green Economy. This work studied the conversion of glycerol to 1,3-propanediol over Pt/WOx/Al2O3 catalysts, pointing out the impacts of catalyst pore sizes and operating conditions for maximizing the yield of 1,3-propanediol. The results suggested that both pore confinement effect and number of available reactive metals as well as operating conditions determined the glycerol conversion and 1,3-propanediol selectivity. The small-pore 5Pt/WOx/S-Al2O3 catalyst (6.1nm) gave a higher Pt dispersion (32.0%), a smaller Pt crystallite size (3.5nm) and a higher number of acidity (0.47mmol NH3 g-1) compared to those of the large-pore 5Pt/WOx/L-Al2O3 catalyst (40.3nm). However, glycerol conversion and 1,3-propanediol yield over the small-pore 5Pt/WOx/S-Al2O3 catalyst were significantly lower than those of the large-pore Pt/WOx/L-Al2O3 catalyst, suggesting that the diffusional restriction within the small-pore catalyst suppressed transportation of molecules to expose catalytic active sites, favoring the excessive hydrogenolysis of 1,3-propanediol, giving rise to undesirable products. The best 1,3-propanediol yield of 32.8% at 78% glycerol conversion were achieved over the 5Pt/WOx/L-Al2O3 under optimal reaction condition of 220°C, 6MPa, 5h reaction time and amount of catalyst to glycerol ratio of 0.25gmL-1. However, the 1,3-propanediol yield and glycerol conversion decreased to 19.6% and 51% after the 4th reaction-regeneration which were attributed to the carbonaceous deposition and the agglomeration of Pt particles.

Host-Guest Thin Films by Confining Ultrafine Pt/C QDs into Metal-Organic Frameworks for Highly Efficient Hydrogen Evolution.

Combining the features of host templates and guest species is an efficient strategy to optimize the photo/electrocatalytic performance. Herein, novel host-guest thin-film electrocatalysts are designed and developed with Pt doped carbon (Pt/C) confined into porphyrin-based metal-organic frameworks (MOFs). Porous MOF PCN-222 and PCN-221 thin films are used as the host templates and fabricated using vapor-assisted deposition method, and then the guest Pt/C quantum dots are encapsulated into the MOFs by loading the glucose mixed H2 PtCl6 and heating at 200 °C. Thanks to the confinement effect of MOF pores, the homogenous and ultrafine Pt/C nanowires (Pt/CNWs) and nanodots (Pt/CNDs) are confined in nanochannels of PCN-222 and nanocages of PCN-221 (Pt/CNW@PCN-222 and Pt/CND@PCN-221), respectively. The electrocatalytic study shows that the host-guest thin films have highly-efficient electrocatalytic hydrogen evolution performance under light irradiation. Furthermore, the time-resolved photoluminescent results reveal that Pt/CNW@PCN-222 has a faster charge transfer (441 ps) from PCN-222 to Pt/CNWs comparing to that (557 ps) of Pt/CND@PCN-221, indicating the guests with different shapes play an important role in the electrocatalytic performance. This work serves to present both the outstanding level of control in the precise synthesis and high potential for nanocomposite thin films in photo-electrocatalytic application.

Controllable Synthesis and Structure-Performance Relationship of Silicalite-1 Nanosheets in Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime

Bulky silicalite-1 shows high catalytic activity for vapor phase Beckmann rearrangement of cyclohexanone oxime. However, it often deactivates rapidly and the structure-performance relationship is unclear. Here, a series of well-crystallized silicalite-1 catalysts from three-dimensional micron particles (n < 10) to two-dimensional nanosheets (10 ≤ n ≤ 18) were controllably synthesized using diquaternary ammoniums [CnH2n+1-N+(CH3)2-C6H12-N+(CH3)2-C6H13](Br−)2 (n = 6–18) as the structure directing agent. The influence of morphology of catalysts on active sites distribution and the pore confinement effect on caprolactam selectivity and the catalytic stability were studied by XRD, SEM, TEM, In situ vacuum IR, 29Si MAS NMR and N2 adsorption/desorption isotherms. The silicalite-1 nanosheets with relatively high crystallinity exhibited superior catalytic activity to almost 100% and remarkably high caprolactam selectivity (92%). The catalytic lifetime of silicalite-1 nanosheets could be increased by 28 times in comparison to bulky silicalite-1 zeolite. The external surface area and mesopore volume of the synthesized catalyst dramatically increase with increasing the tail length of surfactant from C6 to C18, leading to high active sites and coke tolerance capacity. It was found the lifetime of the catalysts is almost linearly related to the product of area of silanol nest and volume of mesopore (Asilanol·nest*Vmeso) with correlation coefficient of 0.97, which strongly supports the excellent performance of nanosheets results from the synergetic effect of its high active sites and high coke tolerance capacity. This provides a theoretic guide for designing new catalysts with high catalytic activity. Silicalite-1 nanosheets were controllable synthesized through adjusting alkyl tail length of diquaternary ammoniums, resulting in large mesoporous volume and external surface area, which effectively improve high coke tolerance capacity and active sites of catalysts and exhibit much longer catalytic lifetime and high selectivity.

Pore confinement and surface charge effects in protein-mesoporous silica nanoparticles formulation for oral drug delivery

Abstract The recent pharmaceutical interest toward confinement effects on the physical state, solubility and release of drugs has paved the way to new material designs for drug delivery. Deeper understanding on how the pore size or the additional functionalities of the nanocarriers can influence the bioavailability of the cargo is nonetheless needed to explore further the potential of nanocarriers in this area. Through the combination of pure or amino-functionalized MCM-48-type mesoporous silica nanoparticles (MSNs) and succinylated beta-lactoglobulin as a protein excipient, we developed versatile tablets for the oral delivery of resveratrol and omeprazole. pH-gating properties of the protein excipient refrained resveratrol from elution in simulated gastric fluid and, owing to effective nanopore confinement, an increased release in simulated intestinal conditions was successfully achieved. Specific effects of positively charged MCM-48-type nanoparticles on the stability of the protein tablets were encountered and appeared to be drug dependent.

Monomolecular Dehydration of Ethanol into Ethylene over H-MOR Studied by Density Functional Theory.

The framework effect of H-mordenite (H-MOR) zeolite on monomolecular dehydration of ethanol to ethylene has been simulated based on density functional theory. It is indicated that both the reaction mechanism and the activation energy barriers are significantly affected by the pore-confinement effect. In the 12-membered ring (12-MR), the energy barriers of the stepwise mechanism and the concerted mechanism are 35.0 and 42.4 kcal mol–1, respectively, suggesting that ethylene can be competitively formed through both pathways. While in the 8-membered ring (8-MR), the barrier of the concerted mechanism is 43.4 kcal mol–1, which is much lower than that of the stepwise mechanism with the ethoxy intermediate formation barrier of 53.7 kcal mol–1. Furthermore, the water molecule acts as the intermediate to stabilize the transition states (TSs) for both stepwise and concerted mechanisms and helps to transport protons during the reaction.

Evaluation of nanopore confinement during CO2 huff and puff process in liquid-rich shale formations

CO2 huff and puff (CO2 huff-n-puff) with multistage hydraulic fracture has been proven to be a feasible approach to enhance oil recovery in shale/tight formations. The present study investigates the effect of pore confinement on the incremental recovery of the CO2 huff-n-puff process in shale formation. The results demonstrate that neglecting nanopore confinement has a large impact on production forecasts from unconventional assets especially when the pore size is considerably less than 10 nm. Failure to correct the changes in fluid properties due to pore confinement might lead to errors in simulation results. Fine gridding plays an important role during simulation setup. Moreover, CO2 molecular diffusion is the most important mechanism by which the gas tends to move from fractures into the matrix. Although a short injection time cannot increase oil recovery significantly, a long injection time (more than 5 months) might not be economically or technically feasible.

CN/rGO@BPQDs high-low junctions with stretching spatial charge separation ability for photocatalytic degradation and H2O2 production

Reduced graphene oxide modified black phosphorus quantum dots (rGO@BPQDs) were obtained through surface modification of BPQDs with rGO via an ultrasound-assisted liquid phase method. The rGO@BPQDs could effectively enhance the chemical and structural stability of BPQDs. Zero-dimension rGO@BPQDs were firmly anchored on mesoporous g-C3N4 (CN) via a self-trapping pore confinement effect and π-π interactions to form CN/rGO@BPQDs, which remarkably improved the photoelectric properties of CN. The responsive wavelength of CN/rGO@BPQDs could be extended to 800 nm. The kinetic constant of Rhodamine B and tetracycline degradation reached 0.183 and 0.0194 min−1, respectively. The H2O2 production rate of CN/rGO@BPQDs was 2.6 times that of porous CN. The improved photocatalytic performance and remarkable increase in free radicals are attributed to the formation of n-n type high-low junctions as well as the internal electric field based on different Fermi levels between CN and BPQDs. These collectively promote spatial separation of photogenerated carriers.

The Confinement Effect of Angstrom-Sized Pores in Asymmetrical Membrane Constructed by Zeolitic Imidazolate Frameworks: Partially Dehydrated Ion Transport Performance.

The confinement effect in asymmetrical biological ion channels makes the state of molecules and ions differs from that in the external environment, and the mass transfer confined in the biological ion channels is in a single strand form. Herein, an asymmetrical membrane with angstrom-sized pores is constructed by growth of ZIF-90 membrane on the porous anodic aluminum oxide film. Due to the confinement effect of angstrom-sized pores of ZIF-90, ions transport through the pores of ZIF-90 suffer from multiple dehydration-hydration-dehydration process in the form of a single ionic chain. Molecular dynamics simulations imply that ions inside the pores of ZIF-90 are partially dehydrated. In alkaline condition, high rectification ratios of 237, 295, and 357 can be achieved in 10 × 10-3 m KCl, NaCl, and LiCl electrolyte, respectively. Besides, the strong electrostatic interaction between ions and the confined ZIF-90 pores makes the ions transport through the asymmetrical membrane suffer from an energy barrier, and the energy barrier is different with different ion species. This work helps to understand the ions transfer mechanism through angstrom-sized pores, which can provide guidance for the design of asymmetrical membrane and boost their applications.

Capillary Condensation of Single- and Multicomponent Fluids in Nanopores

The phase behavior of fluids in nanopores deviates significantly from that in bulk space. However, the effect of pore confinement on the capillary condensation in nanopores has not been fully under...

Effect of Pore Confinement of NaNH2 and KNH2 on Hydrogen Generation from Ammonia.

The development of efficient catalysts for hydrogen generation via ammonia decomposition is crucial for the use of ammonia as an energy carrier. Here, we report the effect of pore confinement of NaNH2 and KNH2 on ammonia decomposition catalysis. For the first time, Ni- or Ru-doped NaNH2 and KNH2 were confined in carbon nanopores using a combination method of solution impregnation and melt infiltration. Structure characterization indicates the nanoscale intimacy between transition metals and alkali metal amides inside the pores of the carbon support. As a result, 8 wt % Ni-doped NaNH2 and KNH2 nanocomposites give NH3 conversions of 79 and 60%, respectively at 425 °C, close to the performance of a 5 wt % Ru/C reference catalyst. 0.8 wt % Ru-doped nanocomposites exhibit even better catalytic performance, with about 95% NH3 conversion at a moderate temperature of 375 °C. The hydrogen production rates of these Ni- and Ru-doped nanocomposites in a pure NH3 flow are about 3–4 times higher than for the recently reported novel catalysts such as Ni–Li2NH and Ru–Li2NH/MgO. Interestingly, the apparent activation energies of the Ru- or Ni-based catalysts decrease 20–30 kJ mol–1 by co-confinement with alkali metal amides. The strategy of nanoconfinement of alkali metal amides in porous hosts may open a new avenue for effectively generating H2 from NH3 at low temperatures.