Size Confinement Research Articles

Combining nanocrystalline NiCo with MOFs-derived carbon fibers skeleton: A dual confinement strategy to efficient electrocatalysts for oxygen evolution reaction

A dual-confinement strategy was developed to design efficient electrocatalysts for oxygen evolution reaction (OER). NiCo alloy nanoparticles (NPs) were synthesized and embedded in N-doped carbon fibers (NCF) by electrospinning and carbonization techniques. Dual effects of size confinement by the metal–organic frameworks (MOFs) derived carbon skeleton companied with spatial confinement by polyacrylonitrile (PAN) derived carbon fibers (CFs) for the NiCo NPs were executed to improve the electrocatalytic activity. In an alkaline solution, the prepared NiCo-C@CF exhibits significant advantages over the commercial RuO2 catalyst i.e., a 61 mV lower overpotential of 363 mV under 50 mA cm−2, and excellent durability of 87.5 % current density retention after 60 h of continuous OER polarization.

Carborazine doped nanographene (CBNG) sheet as a promising NO2 gas sensor: A theoretician’s approach

Nanographenes (NGs) are a distinct section of graphene in which the dangling bonds are saturated with hydrogen atoms (C42H18). This confinement in size results in unique properties and potential applications. The density functional theory (DFT) is used to investigate the reactivity and electronic sensitivity of a model carborazine (B2C2N2) ring doped nanographene (CBNG) for detecting NO2 gas. In CBNG/NO2 complex, one oxygen atom of the NO2 molecule is positioned at a distance of 2.93Ả from the center of the B2C2N2 ring, with an adsorption energy −6.2 kcal/mol. The adsorption energy of NO2 on CBNG is apparently larger than those of other gas molecules, which fall between the suitable range of strong physical adsorption and weak chemical adsorption. Upon NO2 adsorption, the band gap of CBNG sheet reaches 62.4 %. The outcome of the present study may be exploited in the industry, particularly in the synthesis of effective NO2 gas sensors.

Strain-induced modulations in nonlinear optical rectification of core/shell quantum dots within an MEH-PPV polymer matrix under electric field: a 3D finite-element modeling study

This research aims to explore how the MEH-PPV polymer matrix and the strength of the applied field (EF) affect an electron confined within strained CdSe/ZnSe spherical core/shell quantum dots (CSQDs). By solving the Schrödinger equation using the element method (FEM) and effective mass approximation we calculated eigenenergy values and their corresponding wavefunctions. Through a compact density matrix approach, we examined how the MEH-PPV polymer matrix, QDs size and electric field intensity impact nonlinear rectification (NOR), in both unstrained systems. By considering factors such as the surrounding polymer matrix and size confinement we analysed computed coefficients related to EF intensity, peak locations and shifts. Our key findings suggest that understanding NOR in relation to parameters and surrounding materials can provide insights, for improving future optoelectronic and photonic devices.

Bandgap tuning for transition metal oxides via PEGylation

Abstract Bandgap engineering is controlled manipulation of the bandgap of materials/meta-materials to achieve desired properties. The electrical and optical properties of materials are significantly affected by bandgap tuning; therefore, bandgap engineering is a powerful technique for designing electronic and optoelectronic devices. Compositional engineering, strain engineering, and nanoscience and technology are the three major fields associated with bandgap engineering. Any unique combination of this engineering can provide novel strategies to produce novel band-structured devices. In this method article, we have demonstrated how solvation energy can alter the bandgap energy, a fact that is generally ignored due to misconceptions about quantum/size confinement. Here, we prepare nanostructured transition metal oxides (Co3O4, CuO, and ZnO) with polyethylene glycol (PEG), and the method is termed PEGylation. We investigate the influence of PEGylation on the structural, electrochemical, and electronic nature of these oxides. It is observed that the bandgap tunability (7.33%) is maximum for ZnO. Our study suggests that band alteration is significantly correlated with the change in lattice parameters; however, it is orientation dependent as the correlation coefficient reduces to 0.85 from 1 for the change in lattice parameter b along the y-axis compared to the other two lattice parameters. Similarly, band alteration is also known to have some correlation with the electrochemical potential, but is surprisingly almost independent of size confinement.

Complexity of confined water vitrification and its glass transition temperature

The ability of vitrification when crossing the glass transition temperature (Tg) of confined and bulk water is crucial for myriad phenomena in diverse fields, ranging from the cryopreservation of organs and food to the development of cryoenzymatic reactions, frost damage to buildings, and atmospheric water. However, determining water's Tg remains a major challenge. Here, we elucidate the glass transition of water by analyzing the calorimetric behavior of nano-confined water across various pore topologies (diameters: 0.3 to 2.5 nm). Our approach involves subjecting confined water to annealing protocols to identify the temperature and time evolution of nonequilibrium glass kinetics. Furthermore, we complement this calorimetric approach with the dynamics of confined water, as seen by broadband dielectric spectroscopy and linear calorimetric measurements, including the fast scanning technique. This study demonstrated that confined water undergoes a glass transition in the temperature range of 170 to 200 K, depending on the confinement size and the interaction with the confinement walls. Moreover, we also show that the thermal event observed at ~136 K must be interpreted as an annealing prepeak, also referred to as the "shadow glass transition." Calorimetric measurements also allow the detection of a specific heat step above 200 K, which is insensitive to annealing and, thereby, interpreted as a true thermodynamic transition. Finally, by connecting our results to bulk water behavior, we offer a comprehensive understanding of confined water vitrification with potential implications for numerous applications.

Scaling Laws for Protein Folding under Confinement.

Spatial confinement significantly affects protein folding. Without the confinement provided by chaperones, many proteins cannot fold correctly. However, the quantitative effect of confinement on protein folding remains elusive. In this study, we observed scaling laws between the variation in folding transition temperature and the size of confinement, (Tf - Tfbulk)/Tfbulk ∼ L-ν. The scaling exponent v is significantly influenced by both the protein's topology and folding cooperativity. Specifically, for a given protein, v can decrease as the folding cooperativity of the model increases, primarily due to the heightened sensitivity of the unfolded state energy to changes in cage size. For proteins with diverse topologies, variations in topological complexity influence scaling exponents in multiple ways. Notably, v exhibits a clear positive correlation with contact order and the proportion of nonlocal contacts, as this complexity significantly enhances the sensitivity of entropy loss in the unfolded state. Furthermore, we developed a novel scaling argument yielding 5/3 ≤ ν ≤ 10/3, consistent with the simulation results.

Interfacial and Defective Construction from Diverse CuxSy Quantum Dots toward Broadband Carbon-Based Microwave Absorber.

In this study, highly monodisperse copper sulfide (CuxSy) quantum dots (QDs) have been successfully obtained using a ligand-chemistry strategy, and then a variety of S-deficient CuxSy/nitrogen-doped carbon (NC) heterointerfaces are constructed by compositional fine-tuning (Cu9S5 → Cu1.96S → Cu). First-principles calculations show that the S-deficient domains of CuxSy QDs and N-doped domains of carbon synergistically enhance the electron transfer from CuxSy to NC. In addition, the finite element simulations demonstrate that the diverse CuxSy QDs exhibit their intrinsic size and dielectric confinement effects to precisely manipulate the electric field distortion and improve the relaxation polarization. Consequently, CuxSy@NC achieves excellent impedance matching and a strong loss mode dominated by dielectric polarization. Among them, CuxSy@NC-650 has a maximum effective absorption bandwidth of 7.7 GHz at 2.5 mm, while CuxSy@NC-700 features a minimum reflection loss of -66.7 dB at 13.7 GHz, respectively. Furthermore, the simulations of radar cross-sections have confirmed that the CuxSy@NC series is promising in the field of radar stealth.

Size Confinement Strategy Effect Enables Advanced Aqueous Zinc–Iodine Batteries

AbstractAqueous Zn–I2 batteries have considerable potential owing to their environmental friendliness and high safety. However, the slow iodine conversion kinetics and shuttle effect prevent their practical applicability. In this study, a series of Zn‐MOF‐74 rods with controllable diameters of 40–500 nm are facilely prepared, denoted as P1–P5. A size confinement strategy effect of Zn‐MOF‐74 derived porous carbon as iodine hosts is proposed to suppress the formation of undesirable iodine species, such as I3− and I5−. Moreover, the graphitization degree of porous carbon samples, including P2‐900, P2‐1000, and P2‐1100, play a critical effect on the iodine conversion kinetics. The P2‐1000 sample possesses a high conductive skeleton and abundant mesopores, which improve the adsorption ability toward iodine species. The electrochemical tests and the in situ technology reveal the size confinement strategy effect and the conversion mechanism of iodine. As a result, the I2@P2‐1000 cathode exhibits a superior discharge capacity of 179.9 mA h g−1 at 100 mA g−1 and exceptional long‐term cycle ability after 5000 cycles. Furthermore, the soft batteries and the flexible quasi‐solid‐state batteries are capable of powering devices, promising to exhibit tremendous adaptability and realize flexible electronic devices in various scenarios.

Dynamics of confined water inside carbon nanotubes based on studying tetrahedral order parameters

Water dynamics inside hydrophobic confinement, such as carbon nanotubes (CNTs), has garnered significant attention, focusing on water diffusion. However, a crucial aspect remains unexplored - the influence of confinement size on water ordering and intrinsic hydrogen bond dynamics. To address this gap, we conducted extensive molecular dynamics simulations to investigate local ordering and intrinsic hydrogen bond dynamics of water molecules within CNTs of various sizes (length:20 nm, diameters: 1.0 nm to 5.0 nm) over a wide range of temperatures (260K, 280K, 300K, and 320K). A striking observation emerged: in smaller CNTs, water molecules adopt an icy structure near tube walls while maintaining liquid state towards the center. Notably, water behavior within a 2.0 nm CNT stands out as an anomaly, distinct from other CNT sizes considered in this study. This anomaly was explained through the formation of water layers inside CNTs. The hydrogen bond correlation function of water within CNTs decayed more slowly than bulk water, with an increasing rate as CNT diameter increased. In smaller CNTs, water molecules hold onto their hydrogen bond longer than larger ones. Interestingly, in larger CNTs, the innermost layer’s hydrogen bond lasts a shorter time compared to the other layers, and this changes with temperature.

High-capacity K+-pillared layered manganese dioxide as cathode material for high-rate aqueous zinc-ion battery

Sluggish kinetics and severe structural instability of manganese-based cathode materials for rechargeable aqueous zinc-ion batteries (ZIBs) lead to low-rate capacity and poor cyclability, which hinder their practical applications. Pillaring manganese dioxide (MnO2) by pre-intercalation is an effective strategy to solve the above problems. However, increasing the pre-intercalation content to realize stable cycling of high capacity at large current densities is still challenging. Here, high-rate aqueous Zn2+ storage is realized by a high-capacity K+-pillared multi-nanochannel MnO2 cathode with 1 K per 4 Mn (δ-K0.25MnO2). The high content of the K+ pillar, in conjunction with the three-dimensional confinement effect and size effect, promotes the stability and electron transport of multi-nanochannel layered MnO2 in the ion insertion/removal process during cycling, accelerating and accommodating more Zn2+ diffusion. Multi-perspective in/ex-situ characterizations conclude that the energy storage mechanism is the Zn2+/H+ ions co-intercalating and phase transformation process. More specifically, the δ-K0.25MnO2 nanospheres cathode delivers an ultrahigh reversible capacity of 297 mAh g−1 at 1 A g−1 for 500 cycles, showing over 96 % utilization of the theoretical capacity of δ-MnO2. Even at 3 A g−1, it also delivered a 63 % utilization and 64 % capacity retention after 1000 cycles. This study introduces a highly efficient cathode material based on manganese oxide and a comprehensive analysis of its structural dynamics. These findings have the potential to improve energy storage capabilities in ZIBs significantly.

Shell with Striped, Helical, and Bipolar Lamellae Structures from Soft Confinement-Induced Self-Assembly of AB Diblock Copolymers on a Nanocylinder.

The soft confinement-induced self-assembly of AB diblock copolymers on a nanocylinder is studied via a simulated annealing method. The formation of multiple copolymer shells was predicted by varying the interfacial interaction, the size of confinement, and the height and diameter of the nanocylinder. The competition between solvent repulsion and nanocylinder attraction determined the degree of encapsulation of the copolymer shell. The formation of a helical copolymer shell was induced by the maximization of conformational entropy. The preferential distribution position of copolymers on anisotropic nanocylinder surfaces was induced by interfacial energy minimization. Our study contributes to the understanding of the formation mechanism of the helical structure in block copolymer aggregates and the fabrication of copolymer shells with predesigned morphologies.

Theoretical insights into size and dielectric confinement: Unraveling real and imaginary parts of the effective complex dielectric function in spherical multilayered quantum dots with oxide interfaces

A quantitative numerical exploration is conducted to scrutinize the combined effects of size and dielectric confinement consequences on the electronic and optical characteristics of spherical multilayered quantum dot CdSe/ZnS/CdSe/ZnS (SMLQD) and its inverted configuration ZnS/CdSe/ZnS/CdSe (ISMLQD) buried into two oxides: HfO2 and SiO2. By employing the effective mass approximation (EMA) and the density matrix approach (DMA), the derived quantized electron energy states and their associated wave functions were obtained by solving the Schrödinger equation in a spherical coordinates. The dipole transition element, both real and imaginary parts of the effective complex dielectric function (ECDF) as well as its linear, nonlinear and total counterparts are brought out for various values of inner core radii, number density of QDs and incident photon intensity. In addition, a specific analysis of electron probability distributions is provided to gain a clearer understanding of the underlying physical factors. Our findings point to a notable influence of these mentionned factors on the computed coefficients. The study unveils that the dielectric mismatch occurring at the system/oxide interfaces plays a crucial role in modifying the electronic structure and a substantial impact on both linear and third-order nonlinear components is witnessed.

Photocatalytic dye degradation, H2 evolution, electrical and mechanical performances of mechano-synthesized multifunctional Bi2Te3 nanoparticles: Effect of milling time and thermal treatment

Bi2Te3 nanoparticles are synthesized by mechanical alloying the Bi and Te powders under the Ar and pressed powdered samples are sintered at 573 K. Rietveld refined XRD patterns, FESEM images and EDX spectra reveal the microstructure, morphology and phase purity of the samples. Bandgaps are obtained from the FTIR spectra and a blue shift with size reduction indicates the size confinement effect. The non Debye type ac conductivity and dielectric constant variations with milling time and sintering are measured. The improved photocatalytic degradation efficiency of the sintered sample (83.59 %) using Rhodamine B dye under visible light elucidates reduced porosity effect. The photocatalytic hydrogen evolution efficiencies of these nanoparticles are measured and a probable mechanism is depicted. The highest H2 generation efficiency (1462.5 μmol g−1h−1) is observed with the sintered sample. Microhardness measurement reveals normal indentation size effect. Empirical correlations among electrical conductivity, microhardness and photodegradation are established for the first time.

Electrochemical Restructuring Driven Catalytic Cycle of Bi-Based Heterojunctions for High-Performance Lithium-Sulfur Batteries.

Restructuring is an important phenomenon in catalytic reactions. Conversion-type materials with suitable redox potential may undergo in situ electrochemically driven restructurings and induce highly active catalytic sites in a working lithium-sulfur battery. Herein, driven by the electrochemical conversion reaction of BiVO4, a reversible catalytic cycle of Bi/amorphous Li3VO4 (a-Li3VO4) and Bi2S3/a-Li3VO4 heterojunctions is constructed, which targets the oxidation of Li2S and the conversion of polysulfide, respectively. The heterostructures and electrochemically driven size confinement provide abundant sites for shuttle restraining and sulfur conversion. Especially, the p-block Bi and Bi2S3 could dramatically reduce the conversion energy barriers of Li2S and polysulfide by virtue of the p-p orbital hybridization, promoting bidirectional reactions of the sulfur cathode. As a result, the corresponding sulfur cathode possesses a high reversible capacity of 7.5 mAh cm-2 after 120 cycles under a high sulfur loading of 10.3 mg cm-2 with a current density of 0.38 mA cm-2. This study furnishes a feasible scheme to obtain highly effective catalysts for bidirectional sulfur redox by utilizing the electrochemically induced restructuring.

Optimal run-and-tumble in slit-like confinement

Run-and-tumble is a basic model of persistent motion and a motility strategy widespread in micro-organisms and individual cells. In many natural settings, movement occurs in the presence of confinement. While accumulation at the surface has been extensively studied, the transport parallel to the boundary has received less attention. We consider a run-and-tumble particle confined inside a slit, where motion in the bulk alternates with intermittent sojourns at the wall. We first propose a discrete-direction model that is fully tractable and obtain the exact diffusion coefficient characterizing the long-time exploration of the slit. We then use numerical simulations to show that with an adequate choice of parameters, our analytical prediction provides a useful approximation for the diffusion coefficient of run-and-tumble with continuous direction. Finally, we identify the conditions that maximize diffusion within the slit and discuss the optimal mean run time. For swimming bacteria, we find that the optimum is typically reached when the mean run length is comparable to the confinement size. Published by the American Physical Society 2024

Effect of aggregate sizes on dilation properties and stress−strain behavior of FRP-confined recycled aggregate concrete

Aggregate size plays a crucial role in determining the mesoscale uniformity and compactness of concrete, directly influencing its dilation characteristics. This dilation behavior, especially under axial load, has significant implications for the tri-axial stress conditions when the concrete undergoes passive confinement using Fiber-Reinforced Polymer (FRP). This study focuses on comprehensively investigating the stress−strain behavior and dilation properties of FRP-confined recycled aggregate concrete (RAC), with a specific emphasis on the effects of recycled aggregate (RA) sizes. A series of compression tests were conducted to examine the stress−strain response of FRP-confined RAC, shedding light on how the dilation properties are influenced by varying RA sizes. The results revealed notable differences in the physical properties (crushing index and water absorption ratio) of RA compared to natural aggregates, with these differences significantly impacting the unconfined concrete strength. Although, an increase in aggregate size demonstrated an improvement in FRP confinement efficiency, it did not bring about a change in the ultimate strength of FRP-confined concrete due to the interaction between the weakening of unconfined concrete strength and the increase in confinement efficiency. In addtion, the transition stress on the stress−strain curve proved highly dependent on both aggregate size and FRP confinement efficiency to RAC. Consequently, a new modified transition stress model, accounting for the effect of aggregate size and FRP confinement, was introduced. Incorporating this newly proposed transition stress model into the existing stress−strain expression yielded predicted stress−strain curves that closely matched the experimental results for FRP-confined RAC with varying RA sizes.

Spontaneous crystallization of strongly confined CsSnxPb1-xI3 perovskite colloidal quantum dots at room temperature.

The scalable and low-cost room temperature (RT) synthesis for pure-iodine all-inorganic perovskite colloidal quantum dots (QDs) is a challenge due to the phase transition induced by thermal unequilibrium. Here, we introduce a direct RT strongly confined spontaneous crystallization strategy in a Cs-deficient reaction system without polar solvents for synthesizing stable pure-iodine all-inorganic tin-lead (Sn-Pb) alloyed perovskite colloidal QDs, which exhibit bright yellow luminescence. By tuning the ratio of Cs/Pb precursors, the size confinement effect and optical band gap of the resultant CsSnxPb1-xI3 perovskite QDs can be well controlled. This strongly confined RT approach is universal for wider bandgap bromine- and chlorine-based all-inorganic and iodine-based hybrid perovskite QDs. The alloyed CsSn0.09Pb0.91I3 QDs show superior yellow emission properties with prolonged carrier lifetime and significantly increased colloidal stability compared to the pristine CsPbI3 QDs, which is enabled by strong size confinement, Sn2+ passivation and enhanced formation energy. These findings provide a RT size-stabilized synthesis pathway to achieve high-performance pure-iodine all-inorganic Sn-Pb mixed perovskite colloidal QDs for optoelectronic applications.

Kinetics of nanoconfined benzyl methacrylate radical polymerization

AbstractThe effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures.

Influences of molecular tail architectures of rejuvenators on their efficacies in restoring microstructures of reclaimed asphalt

The chemical structure of rejuvenators determines their rejuvenation performance. This work studied the influence of molecular tail architectures on efficacies of rejuvenators, through the combined use of molecular dynamics (MD) simulation and laboratory experiments. The solubility parameter was used to characterize rejuvenators changing in molecular tail structures. Then, microstructure changes of corresponding recycled asphalt were monitored with the confinement size of asphalt molecular diffusion. Accordingly, experiments were conducted for examining essential characteristics of rejuvenators with changing molecular tail structures and their efficacies in restoring mechanical properties of aged asphalt. The results show that the stronger interaction among molecular tails enhances cooperation effects of rejuvenator molecules, thus promoting higher efficacies and stabilities in separating asphaltene aggregates. This finally leads to greater reductions of elastic proportions within mechanical properties of aged asphalt. Moreover, the complex molecular tail structure of rejuvenators lowers down the molecular interaction. Thus, the surface tension of rejuvenators could be an indicator for predicting their efficacies.

Impact of Confinement within a Hydrogel Mesh on Protein Thermodynamic Stability and Aggregation Kinetics.

Though protein stability and aggregation have been well characterized in dilute solutions, the influence of a confining environment that exists (e.g., in intercellular and tissue spaces and therapeutic formulations) on the protein structure is largely unknown. Herein, the effects of confinement on stability and aggregation were explored for proteins of different sizes, stability, and hydrophobicity when encapsulated in hydrophilic poly(ethylene glycol) hydrogels. Denaturation curves show linear correlations between confinement size (mesh size) and thermodynamic stability, i.e., unfolding free energy and surface area accessible for solvation (represented by m-value). Two clusters of protein types are identifiable from these correlations; the clusters are defined by differences in protein stability, surface area, and aggregation propensity. Proteins with higher stability, larger surface area, and lower aggregation propensity (e.g., lysozyme and myoglobin) are less affected by the confinement imposed by mesh size than proteins with lower stability, smaller surface area, and higher aggregation propensity (e.g., growth hormone and aldehyde dehydrogenase). According to aggregation kinetics measured by thioflavin T fluorescence, confinement in smaller mesh sizes resulted in slower aggregation rates than that in larger mesh sizes. Compared to that in buffer solution, the confinement of a hydrophobic protein (e.g., human insulin) in the hydrogels accelerates protein aggregation. Conversely, the confinement of a hydrophilic protein (e.g., human amylin) in the hydrogels decelerates or prevents aggregation, with the rates of aggregation inversely proportional to mesh size. These findings provide new insights into protein conformational stability in confined microenvironments relevant to various cellular, tissue, and therapeutics scenarios.