Nanoconfinement Effect Research Articles

Properties of Salvia officinalis L. and Thymus serpyllum L. Extracts Free and Embedded into Mesopores of Silica and Titania Nanomaterials.

This study evidenced the nanoconfinement effect on polyphenolic extracts prepared from Salvia officinalis L. and Thymus serpyllum L. into the mesopores of silica and titania nanomaterials on their radical scavenging capacity and antimicrobial potential. The ethanolic and hydroalcoholic extracts obtained either by conventional or microwave-assisted extraction were characterized in terms of total polyphenols, total flavonoids, and chlorophyll content, as well as radical scavenging activity by consecrated spectrometric determinations. The phytochemical fingerprint of extracts was analyzed by high-performance liquid chromatography-photodiode array detector. Salvia officinalis extracts exhibited better radical scavenging capacity and antimicrobial potential than Thymus serpyllum extracts. The mesoporous MCM-41 silica and titania nanomaterials, prepared by the sol–gel method, were characterized by small- and wide-angle powder diffraction, FTIR spectroscopy, nitrogen adsorption–desorption isotherms, scanning electron microscopy and transmission electron microscopy, while the materials containing embedded extracts were analyzed through Fourier-transform infrared spectroscopy, N2 sorption measurements, and thermal analysis. All extracts free and embedded in mesoporous matrix exhibited high radical scavenger properties and good bactericidal activity against several reference strains. It was proved that by embedding the polyphenolic extracts into mesopores of silica or titania nanoparticles, the phytochemicals stability was enhanced as the materials containing extract exhibited higher radical scavenger activity after 3–6 months storage than that of the free extracts. Additionally, the extract-loaded material showed mild improved antimicrobial activity in comparison with the corresponding free extract.

Confinement effect and low-defect density-induced long lifetime Er silicate nanowire embedded in silicon oxide film

In this study, we have developed a reduced Er-Er interaction strategy for pursuing long lifetime and high efficiency luminescence in Er compounds with higher Er concentration. Annealing temperature and atmosphere dependence of the optical properties from Er silicate nanowires embedded in silicon oxide films have been investigated. The record long lifetime α-Er2Si2O7 of 844 µs is achieved through simultaneously reducing defect density and Er-Er interaction. The low-defect density in the α-Er2Si2O7 nanowires is mainly attributed to following aspects: no hydroxyl groups contamination, effective surface passivation and saturation of oxygen vacancies. The interaction of Er-Er ions is confined by the alteration of phonon density of states effects in the α-Er2Si2O7 nanowires. More significantly, the up-conversion emissions in the α-Er2Si2O7 nanowires also reduce effectively because of the nanoconfinement effect.

Enhanced Low-Temperature Hydrogen Storage in Nanoporous Ni-Based Alloy Supported LiBH4.

To reveal the synergistic effect of nanoconfinement and metallic catalysis on the hydrogen storage properties of LiBH4, the nanoporous Ni-based alloy (np-Ni) was prepared herein by dealloying of the Mn70Ni30 alloy in (NH4)2SO4 solution, and then LiBH4 was loaded into np-Ni to construct the LiBH4/np-Ni hydrogen storage system using wet impregnation. It was found that dehydrogenation of the LiBH4/np-Ni (1:5) system starts at around 70°C and ends before 400°C, with ~11.9 wt.% of hydrogen desorbed. The apparent dehydrogenation activation energy for the LiBH4/np-Ni (1:5) system was remarkable decreased to about 11.4 kJ/mol. After rehydrogenation at 450°C under 8 MPa hydrogen pressure, ~8.2 wt.% of hydrogen can be released from about 60°C upon second dehydrogenation. These obtained results would provide an efficient strategy for improving the hydrogen storage properties of other metal borohydrides.

Heterogeneous catalysts with programmable topologies generated by reticulation of organocatalysts into metal-organic frameworks: The case of squaramide

A well-established strategy to synthesize heterogeneous, metal-organic framework (MOF) catalysts that exhibit nanoconfinement effects, and specific pores with highly-localized catalytic sites, is to use organic linkers containing organocatalytic centers. Here, we report that by combining this linker approach with reticular chemistry, and exploiting three-dimensioanl (3D) MOF-structural data from the Cambridge Structural Database, we have designed four heterogeneous MOF-based catalysts for standard organic transformations. These programmable MOFs are isoreticular versions of pcu IRMOF-16, fcu UiO-68 and pillared-pcu SNU-8X, the three most common topologies of MOFs built from the organic linker p,p’-terphenyldicarboxylic acid (tpdc). To synthesize the four squaramide-based MOFs, we designed and synthesized a linker, 4,4’-((3,4‐dioxocyclobut‐1‐ene‐1,2‐diyl)bis(azanedyil))dibenzoic acid (Sq_tpdc), which is identical in directionality and length to tpdc but which contains organocatalytic squaramide centers. Squaramides were chosen because their immobilization into a framework enhances its reactivity and stability while avoiding any self-quenching phenomena. Therefore, the four MOFs share the same organocatalytic squaramide moiety, but confine it within distinct pore environments. We then evaluated these MOFs as heterogeneous H-bonding catalysts in organic transformations: a Friedel-Crafts alkylation and an epoxide ring-opening. Some of them exhibited good performance in both reactions but all showed distinct catalytic profiles that reflect their structural differences.

Chemical reactivity under nanoconfinement.

Confining molecules can fundamentally change their chemical and physical properties. Confinement effects are considered instrumental at various stages of the origins of life, and life continues to rely on layers of compartmentalization to maintain an out-of-equilibrium state and efficiently synthesize complex biomolecules under mild conditions. As interest in synthetic confined systems grows, we are realizing that the principles governing reactivity under confinement are the same in abiological systems as they are in nature. In this Review, we categorize the ways in which nanoconfinement effects impact chemical reactivity in synthetic systems. Under nanoconfinement, chemical properties can be modulated to increase reaction rates, enhance selectivity and stabilize reactive species. Confinement effects also lead to changes in physical properties. The fluorescence of light emitters, the colours of dyes and electronic communication between electroactive species can all be tuned under confinement. Within each of these categories, we elucidate design principles and strategies that are widely applicable across a range of confined systems, specifically highlighting examples of different nanocompartments that influence reactivity in similar ways.

Nanoconfinement of salty water results in complex effects

Quantum mechanical simulations reveal the effects of ions and nanoconfinement on the structural and electronic properties of water.

Ultrafine SnO2 nanoparticles anchored on N, P-doped porous carbon as anodes for high performance lithium-ion and sodium-ion batteries

An ultrafine tin dioxide/N, P-doped porous carbon (SnO2/NPPC) nanocomposite is prepared through in-situ growth of tin dioxide (SnO2) nanoparticles in N, P-doped porous carbon (NPPC). Owing to the in-situ growth method, the size of SnO2 nanoparticles in SnO2/NPPC is quite small and uniform (generally less than 5.0 nm). NPPC provides a support and a conductive carbon skeleton for the SnO2 nanoparticles. The small SnO2 nanoparticles are less likely to aggregate during the discharge–charge process due to the presence of Sn–O–C bonding and nanoconfinement effect of SnO2 nanoparticles in carbon matrix. The N and P doping can provide abundant defects to facilitate the penetration of Li+ or Na+ into the interior of the electrode. In addition, the presence of Sn–N bonding can further improve the electrochemical properties of the electrodes. Thus, as an anode material for lithium-ion batteries, SnO2/NPPC possesses an enhanced rate performance, an excellent cycling stability, and a high initial Coulombic efficiency. The structure of the ultrafine SnO2 nanoparticles is well maintained in cycled SnO2/NPPC. Meanwhile, SnO2/NPPC also possesses good electrochemical performance as an anode for sodium-ion batteries. The good electrochemical properties for SnO2/NPPC materials can be ascribed to the synergetic effect between small SnO2 nanoparticles and NPPC.

A Scalable Nickel-Cellulose Hybrid Metamaterial with Broadband Light Absorption for Efficient Solar Distillation.

Sophisticated metastructures are usually required to broaden the inherently narrowband plasmonic absorption of light for applications such as solar desalination, photodetection, and thermoelectrics. Here, nonresonant nickel nanoparticles (diameters < 20 nm) are embedded into cellulose microfibers via a nanoconfinement effect, producing an intrinsically broadband metamaterial with 97.1% solar-weighted absorption. Interband transitions rather than plasmonic resonance dominate the optical absorption throughout the solar spectrum due to a high density of electronic states near the Fermi level of nickel. Field solar purification of sewage and seawater based on the metamaterial demonstrates high solar-to-water efficiencies of 47.9-65.8%. More importantly, the solution-processed metamaterial is mass-producible (1.8 × 0.3 m2 ), low-cost, flexible, and durable (even effective after 7 h boiling in water), which are critical to the commercialization of portable solar-desalination and domestic-water-purification devices. This work also broadens material choices beyond plasmonic metals for the light absorption in photothermal and photocatalytic applications.

Reducing dielectric loss by nanoconfined impurity ion transport in multilayer films under low electric fields

Despite higher dielectric constants than nonpolar polymers, polar polymers exhibit a high dielectric loss, which is detrimental for electric energy storage applications. To mitigate the ionic conduction loss, we have fabricated multilayer films (MLFs) with alternating layers of a high dielectric constant polar polymer and a high breakdown/low loss nonpolar polymer. In this study, we fabricated high temperature polycarbonate (HTPC)/poly (vinylidene fluoride) (PVDF) MLFs. The ionic transport behavior confined in the PVDF nanolayers under a low electric field was investigated using broadband dielectric spectroscopy (BDS). Direct analytical simulation was implemented to determine the concentration (n0) and diffusion coefficient (D0) for the confined impurity ions in PVDF at different temperatures and with and without the presence of lamellar crystals. It was found that both n0 and D0 increased upon increasing temperature. Using the simulated n0 and D0, nanoconfined transport of impurity ions was found for the PVDF layers with decreasing the layer thickness. Namely, a crossover PVDF layer thickness was predicted, below which the conduction loss from impurity ions substantially decreased. However, experimental BDS results systematically deviated from the theoretical predictions. One important reason for this deviation was attributed to the presence of edge-on lamellar crystals confined in the PVDF layers, which increased the tortuosity of the ion transport pathway. The knowledge gained in this study can be useful to understand the nanoconfinement and crystallinity effects on the ionic transport in MLFs, which is beneficial for the future development of MLFs for capacitor applications.

Nanoconfinement Effects on Redox Probe Transport in Lipid Assemblies on and in Mesoporous Silica Thin Films

AbstractRedox probe transport through supported lipid bilayers and nanopore‐confined lipid assemblies on silica thin films is examined using electrochemical impedance spectroscopy (EIS). These supported lipid systems are emerging biomimetic separation and sensor platforms. The ability to quantify the accessibility of the pore structure of the mesoporous silica thin films is demonstrated, which is essential for the incorporation of carriers into the lipids for selective solute transport. Redox probe molecules with varying hydrophilicity are used to compare ion transport in supported lipid pore‐spanning bilayers (enveloped bilayers) and novel lipid filled pores of mesoporous silica thin films. The films feature orthogonally oriented 8–10 nm cylindrical nanopores formed by deposition of P123‐templated silica sols onto chemically modified fluorine‐doped tin oxide. Nanopore accessibility is confirmed by EIS with hydrophilic probe 1,1′‐ferrocenedimethanol (FDM). Filling the pores with lipid 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine results in a superior barrier (with roughly 1/9 the permeability) to transport of FDM compared to fragile enveloped lipid bilayers deposited by vesicle fusion. The pore‐confined lipids not only provide a better barrier to FDM, but also a better pathway for the transport across the films of a hydrophobic redox probe 1,1′‐dioctadecyl‐4,4′‐bipyridinium dibromide, with an ideal transport selectivity of 11 compared to FDM.

Effect of vertical heterogeneity and nano-confinement on the recovery performance of oil-rich shale reservoir

Due to the effect of compaction, stress-dependent properties such as permeability, porosity, and pore size vary in the vertical direction of shale reservoir. The heterogeneity of physical properties influences the fluid flow in shale formation. Meanwhile, the confinement effects, including large oil-gas capillary pressure and critical property shifts, as a function of pore-throat radius could greatly alter phase behaviors in nano-pores. Thus, vertical heterogeneity affects the interpretation of production performance of an oil-rich shale reservoir. In this study, a compositional simulation model incorporated with confinement effects is applied to simulate primary depletion in an intensively fractured oil-rich shale formation. Stress-dependent properties are assigned to different depth of the pay zone. Two nano-confinement effects on phase behavior and recovery performance are examined, respectively. Simulation results show that nano-confinement effects affect the well productivity through altering the fluid properties and phase behaviors. Inclusion of capillary pressure effect increases oil production but suppresses gas production. Considering critical property shift enhances both oil and gas recoveries. In very tight shale formation, confinement effects are more comparable to gravity drainage on improving oil recovery. As pore size is reduced with depth, confinement effects become more apparent on increasing oil recovery. However, it still cannot exceed the benefits from drilling the well at high permeable formation. Drilling the horizontal well in relatively high-permeability layer that has high permeable adjacent layers could achieve the largest oil and gas recoveries.

Nanoconfinement and Salt Synergistically Suppress Crystallization in Polyethylene Oxide

Suppressing the crystallization of polyether-based solid electrolytes is a widely sought-after strategy to improve ionic conductivity. We report the effects of nanoconfinement on polyethylene oxide...

Theoretical investigation of electroviscous flows in hydrophilic slit nanopores: Effects of ion concentration and pore size

Nanopores with various shapes are well developed in unconventional reservoirs, and the transport phenomena of solutions in these reservoir rocks are ubiquitous but have not yet been fully understood. This article investigates the flow characteristics of solutions in hydrophilic slit nanopores through the combination of a modified Poisson–Boltzmann (MPB) model and the modified Navier–Stokes (NS) equation. To account for the nanoconfinement effects on ion concentration and fluid viscosity, an electrochemical potential term is used in the MPB model and a varying viscosity model (VVM) is introduced in the NS equation. The model rationality is first confirmed, and then the influences of ion concentration and pore size on the transport capacities of solutions in nanopores are illuminated. In addition, the hydrodynamic features of liquids in nanopores and the limitations of this coupled model are discussed as well. The results show that the dimensionless apparent permeability of the slit increases with an increase in ion concentration and pore size. The relative contributions of the electroviscous effect (EVE) and VVM to the total flow resistance reveal different varying trends as ion concentration or pore size increases, which is greatly related to the surface charge density and the sign of the charged wall. Additionally, although the effects of EVE and VVM resulting from the nanoconfinement are considered, average velocities of fluids in nanopores exhibit a linear correlation with the pressure gradient, which cannot be used to explain the nonlinear flow mechanism occurring in tight reservoirs. Furthermore, we also compare the velocity difference between the classical PB and MPB models. We hope that the findings in this work can help improve our understanding of the characteristics of liquid flow in tight reservoirs and provide vital practical implications for diverse engineering applications.

Combined Effects of Anion Substitution and Nanoconfinement on the Ionic Conductivity of Li-Based Complex Hydrides.

Solid-state electrolytes are crucial for the realization of safe and high capacity all-solid-state batteries. Lithium-containing complex hydrides represent a promising class of solid-state electrolytes, but they exhibit low ionic conductivities at room temperature. Ion substitution and nanoconfinement are the main strategies to overcome this challenge. Here, we report on the synthesis of nanoconfined anion-substituted complex hydrides in which the two strategies are effectively combined to achieve a profound increase in the ionic conductivities at ambient temperature. We show that the nanoconfinement of anion substituted LiBH4 (LiBH4–LiI and LiBH4–LiNH2) leads to an enhancement of the room temperature conductivity by a factor of 4 to 10 compared to nanoconfined LiBH4 and nonconfined LiBH4–LiI and LiBH4-LiNH2, concomitant with a lowered activation energy of 0.44 eV for Li-ion transport. Our work demonstrates that a combination of partial ion substitution and nanoconfinement is an effective strategy to boost the ionic conductivity of complex hydrides. The strategy could be applicable to other classes of solid-state electrolytes.

Effect of surface functionalization of molybdenum disulfide nanosheets with polysulfone on cyanate ester nanocomposites

The aggregation of two-dimensional (2D) layered nanofillers restricts their use as reinforcements in polymers. Herein, the bisphenol E cyanate ester resin (CE) nanocomposites based on surface functionalization of molybdenum disulfide (MoS2) nanosheets with polysulfone (PSF) are prepared. In the structures, PSF segment were sandwiched between adjacent MoS2 nanoplatelets, which restrained the restacking of the MoS2 nanoplatelets. The compatibility between PSF modified MoS2 and CE is improved as compared with MoS2 and CE. The tensile strength and apparent shear strength of the nanocomposite show that modified MoS2 nanosheets are very effective at increasing the adhesive and mechanical properties of cyanate esters at very low quality fractions. Pulling out effects, crack bridging, crack deflection, and crack pinning are the main strengthening mechanisms of mechanical properties. The glass transition temperature increases from 245 °C for the unfilled cyanate ester to 265 °C at 0.15 % MoS2 loading. The results are consistent with the nanoconfinement effect including a nanoscale interfacial layer that can support the effective reinforcements of functionalized MoS2 nanoplatelets over pure MoS2. The excellent properties of MoS2/PSF/CE nanocomposites indicate that the approach in this study is effective to prepare high-performance molybdenum disulfide/cyanate ester polymer composites.

Coaxially enhanced photocarrier transport of a highly oriented Cu2ZnSnS4/ZnO photodetector through the nanoconfinement effect

This work demonstrates a highly c-axis-oriented Cu2ZnSnS4/ZnO (CZTS/ZnO) photodetector with coaxially enhanced photocarrier transport.

Low temperature dehydrogenation properties of ammonia borane within carbon nanotube arrays: a synergistic effect of nanoconfinement and alane.

Ammonia borane (AB, NH3BH3) is considered as one of the most promising hydrogen storage materials for proton exchange membrane fuel cells due to its high theoretical hydrogen capacity under moderate temperatures. Unfortunately, its on-board application is hampered by the sluggish kinetics, volatile byproducts and harsh conditions for reversibility. In this work, AB and AlH3 were simultaneously infiltrated into a carbon nanotube array (CMK-5) to combine the synergistic effect of alane with nanoconfinement for improving the dehydrogenation properties of AB. Results showed that the transformation from AB to DADB started at room temperature, which promoted AB to release 9.4 wt% H2 within 10 min at a low temperature of 95 °C. Moreover, the entire suppression of all harmful byproducts was observed.

Sucrose-mediated heat-stiffening microemulsion-based gel for enzyme entrapment and catalysis.

Formation of a thermally stiffening microemulsion-based gel showing a nanoconfinement effect of carbohydrates in terms of microviscosity and hydrodynamic diameter of the reverse micelle (specifically with sucrose) is reported. The advantage of this gel as an efficient batch bioreactor for entrapped enzymes (horseradish peroxidase and thermophilic α-glucosidase) was shown, and illustrated its potential biocatalytic application at high temperatures.

Effect of nano-confinement on the structure and properties of water clusters: An ab initio study

An ab initio investigation on water clusters confined to armchair carbon nanotubes (CNT) with varying diameters has been performed using the density functional theory-based calculations. Different parameters have been investigated including structure, hydrogen bonding pattern and vibrational spectra of water-CNT complexes. Our results reveal that one-dimensional water chain parallel to CNT axis is formed in narrow nanotubes CNT(4,4) and CNT(5,5), whereas in CNT(6,6), zigzag structure is observed. An increase in the CNT diameter results in more symmetric structures similar to the gas phase. The vibrational analysis shows a redshift in stretching frequency of the hydrogen bond assisted O–H in CNT(6,6) due to the reduction in O—O separation whereas a significant blue shift in stretching frequency mode is observed in highly confined CNT(4,4) and CNT(5,5). It implies that the hydrogen bond strength between water molecules is strongest in CNT(6,6). It is also observed that water cluster tends to be near CNT wall due to H···π interaction between water molecule and the π-electron cloud of CNT. An inverse relation between the electronic charge transfer (from CNT to water) and the diameter is also established. This study demonstrates that the degree of confinement is extremely important in deciding the properties of confined water molecules. The structure and hydrogen bonding properties of the water clusters under nano-confined regime is investigated and the results reveal that the intramolecular charge separation for each water molecule increases under confinement and irrespective of the number of water molecules, the highest tube-water interaction energy is achieved in CNT(5,5) (diameter~7 A). The important finding is that the degree of confinement (diameter of carbon nanotube) is extremely important in deciding the properties of confined water molecules.

Mean Free Path of Gas Molecules in Organic Nanochannels Using Molecular Simulations

SummaryA computational method using molecular–simulation data is introduced to estimate the average mean–free–path length of multicomponent hydrocarbon molecules in an organic nanochannel. Grand–canonical Monte Carlo (MC) simulation is used first to construct the equilibrium distribution of the gas molecules in the channel. These results show that the smaller the channel is, the denser the gas mixture becomes because of nanoconfinement effects. Capillary condensation occurs in the smaller channels. The fluid composition inside a channel becomes progressively heavier when the bulk–fluid pressure outside the nanopore is reduced and the lighter hydrocarbons leave the channel. The mean–free–path lengths of the confined molecules are computed using the trajectories of the molecules displaced over time in the equilibrium molecular–dynamics (MD) simulation. The average length of the confined molecules is estimated to be an order of magnitude smaller than the theoretical value. Further, the length does not show a strong dependence on the channel width and the pressure. Consequently, the predicted Knudsen–number value does not vary significantly, as anticipated by the kinetic theory of gases and by the molecular simulations of pure fluids. This invariance indicates that compositional change caused by nanoconfinement eliminates transition into other transport regimes where continuum mechanics is no longer valid.