Nanoconfinement Effect Research Articles

Water Self-Dissociation is Insensitive to Nanoscale Environments.

Nanoconfinement effects on water dissociation and reactivity remain controversial, despite their importance to understand the aqueous chemistry at interfaces, pores, or aerosols. The pKw in confined environments has been assessed from experiments and simulations in a few specific cases, leading to dissimilar conclusions. Here, with the use of carefully designed ab initio simulations, we demonstrate that the energetics of bulk water dissociation is conserved intact to unexpectedly small length-scales, down to aggregates of only a dozen molecules or pores of widths below 2 nm. The reason is that most of the free-energy involved in water autoionization comes from breaking the O-H covalent bond, which has a comparable barrier in the bulk liquid, in a small droplet of nanometer size, or in a nanopore in the absence of strong interfacial interactions. Thus, dissociation free-energy profiles in nanoscopic aggregates or in 2D slabs of 1 nm width reproduce the behavior corresponding to the bulk liquid, regardless of whether the corresponding nanophase is delimited by a solid or a gas interface. The present work provides a definite and fundamental description of the mechanism and thermodynamics of water dissociation at different scales with broader implications on reactivity and self-ionization at the air-liquid interface.

Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling

Piezoelectric biomaterials have attracted great attention owing to the recent recognition of the impact of piezoelectricity on biological systems and their potential applications in implantable sensors, actuators, and energy harvesters. However, their practical use is hindered by the weak piezoelectric effect caused by the random polarization of biomaterials and the challenges of large-scale alignment of domains. Here, we present an active self-assembly strategy to tailor piezoelectric biomaterial thin films. The nanoconfinement-induced homogeneous nucleation overcomes the interfacial dependency and allows the electric field applied in-situ to align crystal grains across the entire film. The β-glycine films exhibit an enhanced piezoelectric strain coefficient of 11.2 pm V−1 and an exceptional piezoelectric voltage coefficient of 252 × 10−3 Vm N−1. Of particular significance is that the nanoconfinement effect greatly improves the thermostability before melting (192 °C). This finding offers a generally applicable strategy for constructing high-performance large-sized piezoelectric bio-organic materials for biological and medical microdevices.

Nanoconfinement enabled non-covalently decorated MXene membranes for ion-sieving

Covalent modification is commonly used to tune the channel size and functionality of 2D membranes. However, common synthesis strategies used to produce such modifications are known to disrupt the structure of the membranes. Herein, we report less intrusive yet equally effective non-covalent modifications on Ti3C2Tx MXene membranes by a solvent treatment, where the channels are robustly decorated by protic solvents via hydrogen bond network. The densely functionalized (-O, -F, -OH) Ti3C2Tx channel allows multiple hydrogen bond establishment and its sub-1-nm size induces a nanoconfinement effect to greatly strengthen these interactions by maintaining solvent-MXene distance and solvent orientation. In sub-1-nm ion sieving and separation, as-decorated membranes exhibit stable ion rejection, and proton-cation (H+/Mn+) selectivity that is up to 50 times and 30 times, respectively, higher than that of pristine membranes. It demonstrates the feasibility of non-covalent methods as a broad modification alternative for nanochannels integrated in energy-, resource- and environment-related applications.

Molecular interaction-based reaction-diffusion coupling within catalytic nanochannels

The nanoconfinement effect on the inner reaction–diffusion coupling is significant, while the underlying common principle remains ambiguous, which is mainly attributed to the lack of a feasible model. Herein, the dynamic reaction density functional theory (DRxDFT) is extended, by involving the position-dependent local diffusion coefficient, to investigate the reaction–diffusion coupling of an irreversible unimolecular isothermal reaction within catalytic nanochannels. The local diffusion coefficient is jointly determined by the pore size and local density. For demonstration, the reaction–diffusion in a rectangle nanochannel is studied by means of DRxDFT, and the predicted steady-state productivities are in excellent agreement with reactive molecular dynamics simulations. The DRxDFT is further applied to analyze the RD coupling within generic catalytic nanochannels. Towards this end, a microscopic effectiveness factor is introduced to identify the dominant role in the competition between reaction and diffusion, with which it is found that the effect of nanochannel size on productivity exhibits a generic opposite trend under reaction-dominated and diffusion-dominated conditions. This work provides a microscopic insight into the coupling of reaction and diffusion in nanoconfinement.

Towards enhanced performance of fertilizer-drawn forward osmosis process coupled with sludge thickening using a thin-film nanocomposite membrane interlayered with Mxene scaffolded alginate hydrogel

Forward osmosis (FO) offers the potential for sustainable wastewater reuse and enhance water resource sustainability and resiliency. However, low performance of FO membranes due to the high structural parameter and poor fouling resistance limits their widespread implementation. Structural parameter minimization of substrates and modulation of the surface structures of polyamide nanofilms are crucial to achieve enhanced FO performance. Herein, a novel thin-film nanocomposite (TFN) FO membrane supported with Mxene scaffolded alginate hydrogel interlayer is fabricated. It is found that the incorporation of the hydrophilic and high surface energy alginate hydrogel@Mxene interlayer sandwiched between polyamide nanofilms and microporous substrate minimizes the structural parameter by creating abundant tortuous paths leading to minimized internal concentration polarization. Meanwhile, the nanoconfinement effect induced by the interlayer enabled the formation of lumpy network of bubble wrap-like textured polyamide structures on the membranes. Subsequently, the resulting membranes exhibited enhanced water flux of up to 45.6 LMH in PRO mode using 1.0 M NaCl as the draw solution, while the lower surface roughness bestowed the membranes with the minimal fouling propensity which resulted in more than 80% of the water recovery. Additionally, the integration of the fertilizer-drawn forward osmosis process with sludge thickening successfully enabled the dilution of a 2 M KCl fertilizer solution by 2.4 times after 12 h operation, while simultaneously concentrating the sludge from the MLSS of 2000 mg L−1 to 5183 mg L−1. This work provides important insightful concepts to inspire the development of advanced TFN-FO membranes with good overall performance suitable for sustainable water reuse using osmotically driven membrane processes.

Confining manganese-based peroxymonosulfate activation in carbon nanotube membrane for phenol degradation: Combined effect of oxygen vacancy defects and nanoconfinement

In this study, an open ends carbon nanotube (OCNT) membrane, which confined fine-tuned oxygen vacancy defects (Odef) modified MnOx inside OCNT (MnOx-in-OCNT), was developed for enhancing peroxymonosulfate (PMS) activation towards phenol (PE) removal. The MnOx-in-OCNT membrane filtration coupled with PMS activation process (MFPA process) achieved outstanding removal (100%) of PE at a high permeate flux of 585.0 L m2 h−1 bar−1 (residence time of only 8.8 s). The unit degradation rate (2 min running time) and mass transfer rate of MnOx-in-OCNT were 2.0 and 8.4 times higher than that of CCNT (closed caps CNT) membrane with surface-loaded MnOx (MnOx-out-CCNT) MFPA process, and its catalytic performance was much superior to MnOx-in-OCNT powder reactions and MnOx-in-OCNT membrane batch reactions. The PMS activation mechanism experienced an obvious enhancement yield of reactive oxygen species (ROS) from MnOx-out-CCNT to MnOx-in-OCNT MFPA process. The enhanced PMS activation and boosted ROS yield of MnOx-in-OCNT was mainly attributed to the co-effect of the fine-tuned Odef and nanoconfinement. The contact frequency between PMS, pollutant and Odef was greatly enhanced via nanoconfinement effect, leading to the enhanced yield of SO4•− and •OH. Meanwhile, the O2 was enriched and reacts with enhanced Odef under nanoconfined-space to produce O2•− and 1O2. Then, the co-enhanced ROS (SO4•−, •OH, 1O2 and O2•−) displayed wide applicability for phenolic pollutants removal owing to their presence of –OH. Finally, the possible degradation pathway of PE was deduced by DFT calculations and HPLC analysis.

Mechanism of coupling polymer thickness and interfacial interactions on strength and toughness of non-covalent nacre-inspired graphene nanocomposites

Nanoconfinement resulting from interfacial attraction leads to the formation of polymer interphases with outstanding stiffness, which profoundly impacts the toughness and strength of non-covalent nacre-inspired nanocomposites with “brick-and-mortar” structures. Nonetheless, challenges arise due to discrepancies in interphase thickness characterization and ambiguity in nanoscopic foundations of interfacial stiffening, which hinders systematic understanding of strengthening and toughening mechanisms. To address these issues, we conduct coarse-grained molecular dynamics simulations to investigate the effect of polymer phase thickness and interfacial strength on the toughness and strength of graphene-polyethylene nanocomposites. Our results indicate that when the interfacial adhesion is equal to 0.12 J/m2, nanocomposites possessing a polyethylene phase thickness of 3 nm exhibit significantly greater yield strength (590.8 ± 3.3 MPa) than those of other thicknesses, while nanocomposites with polyethylene phase thickness of 13 nm exhibit the highest toughness (83.3 ± 1.7 MJ/m3). When the interfacial interaction adhesion increases from 0.12 to 1.75 J/m2, both the yield strength and toughness of nanocomposites with polymer thickness 3 nm experience a three-phase increase, reaching up to 1442.3 ± 107.7 MPa and 119.8 ± 8.4 MJ/m3, respectively. The aforementioned improvement in both strength and toughness can be attributed to the nanoconfinement originating from strong interfacial adhesion, which enhances the stiffness and strength of the polymer glues filling the gaps of graphene “bricks”. Furthermore, the deviation of the simulation results from the shear-lag model with mechanical properties of bulk polymer can be remedied with the nanoconfinement effect and polymer stretch taken into account. Our findings provide timely guidance for future design of non-covalent nacre-inspired graphene-based polymer nanocomposites with high toughness and strength.

Ion-Specific Nanoconfinement Effect in Multilayered Graphene Membranes: A Combined Nuclear Magnetic Resonance and Computational Study.

Ion adsorption within nanopores is involved in numerous applications. However, a comprehensive understanding of the fundamental relationship between in-pore ion concentration and pore size, particularly in the sub-2 nm range, is scarce. This study investigates the ion-species-dependent concentration in multilayered graphene membranes (MGMs) with tunable nanoslit sizes (0.5-1.6 nm) using nuclear magnetic resonance and computational simulations. For Na+-based electrolytes in MGMs, the concentration of anions in graphene nanoslits increases in correlation with their chaotropic properties. As the nanoslit size decreases, the concentration of chaotropic ion (BF4-) increases, whereas the concentration of kosmotropic ions (Cit3-, PO43-) and other ions (Ac-, F-) decreases or changes slightly. Notably, anions remain more concentrated than counter Na+ ions, leading to electroneutrality breakdown and unipolar anion packing in MGMs. A continuum modeling approach, integrating molecular dynamic simulation with the Poisson-Boltzmann model, elucidates these observations by considering water-mediated ion-graphene non-electrostatic interactions and charge screening from graphene walls.

High-Performance Poly(1-naphthylamine)/Mesoporous Carbon Cathode for Lithium-Ion Batteries with Ultralong Cycle Life of 45000 Cycles at -15°C.

Organic electrode materials for lithium-ion batteries have attracted significant attention in recent years. Polymer electrode materials, as compared to small-molecule electrode materials, have the advantage of poor solubility, which is beneficial for achieving high cycling stability. However, the severe entanglement of polymer chains often leads to difficulties in preparing nanostructured polymer electrodes, which is vital for achieving fast reaction kinetics and high utilization of active sites. This study demonstrates that these problems can be solved by the in situ electropolymerization of electrochemically active monomers in nanopores of ordered mesoporous carbon (CMK-3), combining the advantages of the nano-dispersion and nano-confinement effects of CMK-3 and the insolubility of the polymer materials. The as-prepared nanostructured poly(1-naphthylamine)/CMK-3 cathode exhibits a high active site utilization of 93.7%, ultrafast rate capability of 60Ag-1 (≈320C), and an ultralong cycle life of 10000 cycles at room temperature and 45000 cycles at -15°C. The study herein provides a facile and effective method that can simultaneously solve both the dissolution problem of small-molecule electrode materials and the inhomogeneous dispersion issue of polymer electrode materials.

Effects of CH4/CO2 multi-component gas on components and properties of tight oil during CO2 utilization and storage: Physical experiment and composition numerical simulation

An essential technology of carbon capture, utilization and storage-enhanced oil recovery (CCUS-EOR) for tight oil reservoirs is CO2 huff-puff followed by associated produced gas reinjection. In this paper, the effects of multi-component gas on the properties and components of tight oil are studied. First, the core displacement experiments using the CH4/CO2 multi-component gas are conducted to determine the oil displacement efficiency under different CO2 and CH4 ratios. Then, a viscometer and a liquid density balance are used to investigate the change characteristics of oil viscosity and density after multi-component gas displacement with different CO2 and CH4 ratios. In addition, a laboratory scale numerical model is established to validate the experimental results. Finally, a composition model of multi-stage fractured horizontal well in tight oil reservoir considering nano-confinement effects is established to investigate the effects of multi-component gas on the components of produced dead oil and formation crude oil. The experimental results show that the oil displacement efficiency of multi-component gas displacement is greater than that of single-component gas displacement. The CH4 decreases the viscosity and density of light oil, while CO2 decreases the viscosity but increases the density. And the numerical simulation results show that CO2 extracts more heavy components from the liquid phase into the vapor phase, while CH4 extracts more light components from the liquid phase into the vapor phase during cyclic gas injection. The multi-component gas can extract both the light components and the heavy components from oil, and the balanced production of each component can be achieved by using multi-component gas huff-puff.

Magnetic nanoreactor Fe3O4@HNTs as heterogeneous Fenton-like catalyst for acid fuchsin degradation: Efficiency, kinetics and mechanism

Compared with traditional heterogeneous Fenton catalysis, iron-based catalysts with nano-confinement effect could significantly improve the effectiveness for organic pollutants degradation, due to the shorter migration distance and longer half-life of reactive oxygen species (ROS). Here, we encapsulated the Fe3O4 nanoparticles in the lumen of halloysite nanotubes (HNTs) by means of the electrostatic interactions to fabricate the Fe3O4@HNTs nanoreactor with an outstanding Fenton-like catalytic performance. The instrumental characterizations indicated that the Fe3O4 NPs successfully loaded on the inner wall of HNTs. An active dye acid fuchsin (AF) was chosen as the target pollution to evaluate the Fenton-like catalytic performance of Fe3O4@HNTs nanoreactor. The experimental results showed that the degradation efficiency of 50 mg L−1 AF could approach 100% in 120 min reaction time under almost neutral pHs. To have an insight into the Fenton-like mechanism of Fe3O4@HNTs nanoreactor, the comparisons of AF degradation in different systems, dominant free radicals, iron leaching concentration, H2O2 decomposition efficiency, and ·OH production efficiency were investigated in details. In addition, the degradation pathways of AF were also predicted based on the density functional theory, frontier orbit theory, and high performance liquid chromatography-quadrupole-time of flight mass spectrum (HPLC-QTOF-MS) technique.

Anchoring Mo single atoms on N-CNTs synchronizes hydrogenation/dehydrogenation property of Mg/MgH2

MgH2 has attracted substantial consideration mainly due to its sufficient content and high gravimetric density etc. However, its high thermodynamic stability and poor dynamics hinder its practical application. N-doping carbon nanotubes (N-CNTs) supported Mo single atoms (MoSA-N-CNTs) was constructed to facilitate the hydrogenation/dehydrogenation properties of the Mg/MgH2 system. According to the synergistic effect of N-CNTs nanoconfinement and MoSA catalysts, Mg@MoSA-N-CNTs can absorb 7.37 wt.% H2 during the milling within 15 h and the corresponding activation energy for hydrogenation can be reduced to 21.2 kJ·mol−1. MgH2 @MoSA-N-CNTs releases 7.23 wt.% H2 at 325 ℃ for 5 min, nearly 3 times pristine MgH2. Meanwhile, its initial dehydriding temperature decreases from 265.7°C to 204.6°C, and its apparent activation energy for dehydrogenation also greatly decreases from 108.6 kJ/mol to 68.4 kJ/mol. The above values are much lower than the pure MgH2. The synergistic effect mechanism of N-CNTs and MoSA on hydrogenation/dehydrogenation properties of Mg/MgH2 is proposed systemically. It is revealed that the MoSA and the N-CNTs not only accelerate H2 dissociation and diffusion but also effectively prevent the Mg/MgH2 nanoparticles agglomeration. The above results highlight the great promise of Mg/MgH2 @MoSA-N-CNTs composite for high-performance Mg-based hydrogen storage materials.

Molecular Recognition in Confined Space Elucidated with DNA Nanopores and Single-Molecule Force Microscopy.

The binding of ligands to receptors within a nanoscale small space is relevant in biology, biosensing, and affinity filtration. Binding in confinement can be studied with biological systems but under the limitation that essential parameters cannot be easily controlled including receptor type and position within the confinement and its dimensions. Here we study molecular recognition with a synthetic confined nanopore with controllable pore dimension and molecular DNA receptors at different depth positions within the channel. Binding of a complementary DNA strand is studied at the single-molecule level with atomic force microscopy. Following the analysis, kinetic association rates are lower for receptors positioned deeper inside the pore lumen while dissociation is faster and requires less force. The phenomena are explained by the steric constraints on molecular interactions in confinement. Our study is the first to explore recognition in DNA nanostructures with atomic force microscopy and lays out new tools to further quantify the effect of nanoconfinement on molecular interactions.

Reducing the Bulk Fragility and Suppressing the Fragility-Confinement Effect in Polystyrene with Very Low Levels of 2-Ethylhexyl Acrylate Comonomer

The effects of nanoconfinement on the glass-transition temperature (Tg) and fragility index (m) of thin polymer films, e.g., polystyrene (PS), can be substantial. We recently demonstrated the elimination of the Tg-confinement effect in supported PS films by including 2–6 mol % 2-ethylhexyl acrylate comonomer (Macromolecules 2022, 55, 9601). Here, we use spectroscopic ellipsometry and differential scanning calorimetry to characterize how m is affected by inclusion of low levels of 2-ethylhexyl acrylate (EHA), n-butyl acrylate (nBA), or n-octyl acrylate (nOA) in styrene (S)-based random copolymers. Relative to PS, the inclusion of 1 mol % EHA or 5 mol % nBA or nOA in S-based copolymers has no effect within uncertainty on bulk fragility, mbulk. In contrast, 98/2 mol % and 94/6 mol % S/EHA copolymers exhibit ∼21% and ∼30% reductions in mbulk relative to PS. In thin films supported on silicon, PS, 99/1 mol % S/EHA, 95/5 mol % S/nOA, and 95/5 mol % S/nBA exhibit similar, strong confinement effects on Tg and m. In contrast, 98/2 mol % S/EHA exhibits weak m-confinement effects in sub-100 nm thick films, and 94/6 mol % S/EHA shows no effect down to 22 nm. The strengths of the Tg-confinement effect for various systems are in accord with the m-confinement effects. Thus, the role of the EHA comonomer in suppressing or eliminating Tg- and m-confinement effects cannot be generalized to other acrylates. These results support previously reported correlations between the susceptibilities of Tg- and m-perturbations caused by nanoconfinement and provide a very simple route to suppress or eliminate confinement effects in linear polymers.

An integrated model based on transient flow and the nanoconfinement effect of water transport through nanopores

The property of water confined in nanopores is significantly different from that of bulk water, resulting in a great influence on the rate of water development during the unsteady state. In this study, we focused on the unsteady behavior of water transport in nanopores. We established a transient equation and applied the Laplace transform and Bessel function of the imaginary argument according to the time-dependent momentum conservation equation of Poiseuille-flow. The apparent density, apparent viscosity, and slip of the confined water were modeled by considering the water-wall interactions and the pore size. Moreover, the transient transport equation was modified by these three models to obtain a transient analytical model, which considered the effect of the nanoconfinement effect. We verified the credibility of the proposed model compared with other models as well as through experiments and molecular dynamics simulations. The results indicated that the development rate of water confinement in the superhydrophobic nanopores was much greater than that in intermediate wettability and hydrophilic pores, and its velocity profile behaved as an approximately straight line throughout the unsteady state. Slip in the intermediate wettability pores was more likely to transmit its effects to the pore center than in hydrophilic pores. We found that small hydrophilic pores were dominated by the apparent density and apparent viscosity in the unsteady state, whereas large hydrophilic pores were dominated by slip in the initial state, which gradually changed to apparent density and apparent viscosity with time. For the superhydrophobic pores, regardless of pore size, slip was the main controlling factor in the unsteady state. Additionally, the sensitivity of confined water stabilization time to pore size was much greater in the superhydrophobic pores than in the hydrophilic pores.

Solid-State Nanopore/Nanochannel Sensing of Single Entities

Solid-state nanopores/nanochannels, with their high stability, tunable geometry, and controllable surface chemistry, have recently become an important tool for constructing biosensors. Compared with traditional biosensors, biosensors constructed with solid-state nanopores/nanochannels exhibit significant advantages of high sensitivity, high specificity, and high spatiotemporal resolution in the detection single entities (such as single molecules, single particles, and single cells) due to their unique nanoconfined space-induced target enrichment effect. Generally, the solid-state nanopore/nanochannel modification method is the inner wall modification, and the detection principles are the resistive pulse method and the steady-state ion current method. During the detection process, solid-state nanopore/nanochannel is easily blocked by single entities, and interfering substances easily enter the solid-state nanopore/nanochannel to generate interference signals, resulting in inaccurate measurement results. In addition, the problem of low flux in the detection process of solid-state nanopore/nanochannel, these defects limit the application of solid-state nanopore/nanochannel. In this review, we introduce the preparation and functionalization of solid-state nanopore/nanochannel, the research progress in the field of single entities sensing, and the novel sensing strategies on solving the above problems in solid-state nanopore/nanochannel single-entity sensing. At the same time, the challenges and prospects of solid-state nanopore/nanochannel for single-entity electrochemical sensing are also discussed.

Enzymatic Catalysis in Size and Volume Dual-Confined Space of Integrated Nanochannel-Electrodes Chip for Enhanced Impedance Detection of Salmonella.

Nanochannel-based confinement effect is a fascinating signal transduction strategy for high-performance sensing, but only size confinement is focused on while other confinement effects are unexplored. Here, a highly integrated nanochannel-electrodes chip (INEC) is created and a size/volume-dual-confinement enzyme catalysis model for rapid and sensitive bacteria detection is developed. The INEC, by directly sandwiching a nanochannel chip (60µm in thickness) in nanoporous gold layers, creates a micro-droplet-based confinement electrochemical cell (CEC). The size confinement of nanochannel promotes the urease catalysis efficiency to generate more ions, while the volume confinement of CEC significantly enriches ions by restricting diffusion. As a result, the INEC-based dual-confinement effects benefit a synergetic enhancement of the catalytic signal. A 11-times ion-strength-based impedance response is obtained within just 1min when compared to the relevant open system. Combining this novel nanoconfinement effects with nanofiltration of INEC, a separation/signal amplification-integrated sensing strategy is further developed for Salmonella typhimurium detection. The biosensor realizes facile, rapid (<20min), and specific signal readout with a detection limit of 9 CFU mL-1 in culturing solution, superior to most reports. This work may create a new paradigm for studying nanoconfined processes and contribute a new signal transduction technique for trace analysis application.

Reactive nanostructured membrane with high permeate flux under an ultralow pressure for excellent removal of refractory organic matter in actual water

Herein, we report a novel reactive nanostructured membrane (RNM) which integrated functionalities of effective peroxymonosulfate activation and advection-enhanced mass transfer rates, synthesized by anchoring nano-Co3O4 inside the nanochannel of Ti3C2 MXene as a co-catalyst, which was simultaneously embedded into a nickel foam support (denoted as Co/Ti3C2 RNM). The outstanding properties were mainly attributed to electron migration regulation through the nanoconfinement effect and the d-band center of the Co/Ti3C2 heterostructure close to the energy of the Fermi level. A 75.5 − 85.8% 1,4-dioxane (1,4-D) degradation in actual groundwater and bio-treated landfill leachate was achieved under a low pressure using a peristaltic pump and a high permeate flux of 237.8 L·m−2·h−1, corresponding to an ultrafast residence time of 3.7 s, in a single-pass flow-through mode. Singlet oxygen and Co(IV)-oxo species were mainly responsible for the 1,4-D removal. This study provides a strategy for the synthesis method of RNM combining the advantages of high catalytic activity and permeate flux.

Tellurium filled carbon nanotubes cathodes for Li-Te batteries with high capacity and long-term cyclability

Li-Te batteries, compared with traditional lithium-ion batteries and Li-other group VIA elements (including O, S, Se) batteries, have shown overwhelming features of high specific volumetric capacity and superior electrical conductivity. These features make the Li-Te batteries possess great importance in modern portable electronics and electric vehicles with limited battery package size. However, the Achilles' Heel in Li-Te batteries is the huge volume change and inevitable dissolution of polytellurides during cycling. Herein, we synthesize a cathode material based on polycrystalline Te encapsulated in N-doped multiwall carbon nanotubes (Te-filled CNTs) by physical vapor transport (PVT) method. With unique spatial restriction of the CNT hosts, the electrochemically active Te content can be well preserved, and the prepared Te-filled CNTs cathodes deliver a high specific capacity of 590 mAh g−1 based on Te content. More importantly, the reaction kinetics and electrochemical reversibility of the cathodes have been significantly improved by using nanoscale cavities (4–6 nm) which stabilize the polytellurides (Li2Ten). Meanwhile, a series of in situ characterizations are carried out to straightforwardly reveal a two-step discharge/charge mechanism for Te-filled CNTs. In addition, theoretical calculations prove that the encapsulated Te ensure a lower energy barrier for lithiation compared with bare CNT. This work sheds light on the nanoconfinement effect of CNT for improving the utilization and cycling stability of Te based cathodes in Li-Te batteries.

Restricted CO2/CH4 diffusion in nanopores: A quantitative framework to characterize nanoconfinement effect of shale organic pore

The utilization of carbon dioxide (CO2) to enhance depleted unconventional resources can reduce green-house gas emission and increase the recovery ratio. Self-diffusion coefficient of nanoconfined CO2/CH4 is a crucial factor in CO2-enhanced shale gas recovery and CO2 geological sequestration. A workflow was proposed which included the reconstruction of amorphous shale organic nanopores, detection of effective pore size, and integration of grand canonical Monte Carlo (GCMC) method with molecular dynamics (MD) simulations to calculate self-diffusion coefficient. Challenges such as complex pore surface and extreme reservoir condition were considered, and the self-diffusion coefficients of nanoconfined fluid were obtained. It was found that the self-diffusion coefficient of nanoconfined CO2/CH4 is much smaller than that of bulk CO2/CH4, as a concequence of nanoconfinement effect. The effects of temperature, pressure and pore size were considered, and a nondimensional self-diffusion coefficient was proposed to derive a concise relation with Knudsen number. Additionally, a two-segment correlation formula was proposed to describe the concise relation. Owing to the strong CO2-pore surface interaction, CO2 was adsorbed on the pore surface and CH4 was restricted in a smaller pore space. Therefore, this fluid-pore surface interaction reduced the self-diffusion coefficient of binary mixture CO2/CH4. The workflow, nondimensional self-diffusion coefficient, and correlation formula derived in this study can be used for extensive applications, such as catalyst, fuel cell and sewage treatment.