Space Confinement Effect Research Articles

In English

Interfacial phenomena at a surface of porous and highly disperse adsorbents in the systems containing strongly and weakly bound and unbound liquids depend strongly on the confined space effects. These effects as well as the temperature behavior of liquids located in pores or voids between nanoparticles depend on many factors. They are the pore size distributions, pore volume, specific surface area, surface chemistry of adsorbents, chemical structure and molecular sizes of adsorbates, accessibility of pores vs. probe molecule sizes, as well as textural instability of adsorbents. This instability can appear, e.g., as compaction of fumed oxides under action of liquid adsorbates, especially water, or due to mechanochemical activation. The aim of this study is to analyze features of the interfacial phenomena upon interactions of fumed oxides (silica, alumina, alumina/silica/titania) and porous silicas (silica gels and precipitated silica) with polar (water, dimethyl sulfoxide), weakly polar (chloroform), and nonpolar (n-decane, aromatic benzene and toluene) liquid adsorbates depending on the morphological and textural characteristics of the adsorbents, various adsorbate characteristics, and temperature. The observed effects as well as related phenomena are important because they can differently influence the efficiency of practical applications of adsorbents under various conditions (temperature, pressure, concentrations) depending on the characteristics of adsorbents and adsorbates (liquids, solvents and solutes).

Front Cover: Hybrid Organic‐Inorganic Heterogeneous Interfaces for Electrocatalysis: A Theoretical Study of CO2 Reduction to C2 (ChemCatChem 4/2022)

The Front Cover shows carbon dioxide reduction reaction (CO2RR) to C2 (e.g., ethylene, ethanol) driven by aminothiolate self-assembled monolayer (SAM)-modulated copper (Cu) catalysts. In their Communication, M. Wan et al. demonstrated that aminothiolate SAM-modulated Cu catalyst could improve the activity and selectivity of CO2RR-to-C2 using DFT calculations. The amine group of SAM provides an organic active site to facilitate CO2RR rate-limiting steps, i.e., CO2 initial activation and carbon-carbon coupling. The confined space effect induced by the high surface coverage of SAM tunes the binding energy of the key intermediate CO* on the inorganic Cu site, enlarges the binding energy difference between CO* and COH*, and consequently, further promotes carbon-carbon coupling. This theoretical work guides a novel catalyst design that provides hybrid organic-inorganic active sites, confinement effects and localized electric fields, and enables efficient CO2RR-to-C2. More information can be found in the Communication by M. Wan et al.

Highly stable lithium metal anode enabled by lithiophilic and spatial-confined spherical-covalent organic framework

Li metal anode (LMA) has been considered as the most gifted anode material endowed with unprecedented theoretical specific capacity and ultralow redox potential. Nevertheless, the inevitable Li dendrite growth and frangible solid electrolyte interphase (SEI) severely impede its commercial application. Herein, a facile strategy via constructing an artificial SEI configured with highly-crystalline spherical covalent organic framework (S-COF) was applied to regulate the interfacial stability of LMA. Benefiting from the well balance of precise geometric symmetry and methodical morphology within S-COF, the regular 3D-spherical spreading with ordered 1D channels can effectively promote homogeneous distribution of Li+ flux. Meanwhile, the functional lithiophilic coordination has been identified by solid-state nuclear magnetic resonance, Fourier-transform infrared spectra and density functional theory calculations. The energetical Li+ affinity towards S-COF skeleton is prone to facilitate ion-pair dissociation and Li+ uniform transfer. Furthermore, the rigid nanochannels with space-confinement effect can also retard the large-scale lithium nucleation and dendrite formation. Consequently, the derived LiF and Li2S2/Li2S-riched S-COF@Li layer exhibits extraordinary cycling stability in Li|Li symmetrical cell, Li|LiFePO4, and Li|S full cells operated at higher current densities. The aforementioned experimental and theoretical evidences provide a viable guidance for further design and implementation of 2D COF in high energy density batteries.

Amperometric sensor for the detection of hydrogen stable isotopes based on Pt nanoparticles confined within single-walled carbon nanotubes (SWNTs)

The development of hydrogen-based energy and nuclear energy requires new sensing material and high-performance gas sensor for hydrogen stable isotopes, hydrogen (H2) and deuterium (D2). Amperometric gas sensors based on SWNT-filled Pt composite material (Pt-SWNT-in) to combine the good electronic properties of SWNTs and space-confined effect of Pt catalyst have been investigated for detecting H2 and D2. The Pt-SWNT-in electrode shows an excellent linear response in a wide range of 160–8000 ppm hydrogen in N2 atmosphere with the correlation coefficient of 0.9993, and compared to the electrode with Pt nanoparticles supported outside of SWNTs, its sensitivity per Pt loading is 3 times, moreover, it gives larger response current for detection of H2 in air and D2 in N2 atmosphere. Additionally, the Pt-SWNT-in electrode provides a response current to deuterium 0.9 times that to hydrogen in N2. The results present the Pt-SWNT-in electrode with superior sensitivity, selectivity, stability and a response variation for detection of hydrogen and deuterium, which would take advantage of the space-confined effect of SWNTs on Pt catalysts to enhance the sensor performance for detecting hydrogen stable isotopes, and provide an approach to discriminate between hydrogen and deuterium.

TiCl4/MgCl2/MCM-41 Bi-Supported Ziegler–Natta Catalyst: Effects of Catalyst Composition on Ethylene/1-Hexene Copolymerization

TiCl4/MgCl2/MCM-41 type bi-supported Ziegler-Natta catalysts with different MgCl2/MCM-41 ratios were synthesized by adsorbing TiCl4 onto MgCl2 crystallites anchored in mesopores of MCM-41 (mesoporous silica with 3.4 nm pore size). Ethylene/1-hexene copolymerization with the catalysts was conducted at different 1-hexene concentrations and ethylene pressures. MgCl2/MCM-41 composite supports and the catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption analysis (BET), and elemental analysis. The copolymers were fractionated by extraction with boiling n-heptane, and comonomer contents of the fractions were determined. Under 4 bar ethylene pressure, the bi-supported catalysts showed higher activity and a stronger comonomer activation effect than the TiCl4/MgCl2 catalyst. In comparison with the TiCl4/MgCl2 catalyst, the bi-supported catalysts produced much less copolymer fraction of low molecular weight and high 1-hexene content, meaning that the active center distribution of the catalyst was significantly changed by introducing MCM-41 in the support. The copolymer produced by the bi-supported catalysts showed similar melting temperature to that produced by TiCl4/MgCl2 under the same polymerization conditions. The space confinement effect of the mesopores of MCM-41 on the size and structure of MgCl2 crystallites is proposed as the main reason for the special active center distribution of the bi-supported catalysts.

Self-supporting ZnP2@N, P co-doped carbon nanofibers as high-performance anode material for lithium-ion batteries

Searching for high specific capacity anode materials with an optimized structure to achieve high energy density, long cycling life-span, and high rate performance for lithium-ion batteries (LIBs) is a pressing assignment. Metal phosphides have aroused much attention, however, enormous volume variations, poor electrical conductivity, and aggregation of nanoparticles hamper their practical applications. Herein, ZnP2 nanoparticles grown on N, P co-doped carbon nanofibers (ZnP2 @NPCNFs) composite synthesized by electrospinning and heat treatment is reported to directly act as binder-free anode in LIBs. The 3D self-standing ZnP2 @NPCNFs featuring good flexibility can not only boost conductivity and alleviate the volumetric fluctuations in the cycling course, but also buffer the agglomeration and pulverization of nanoparticles. Lithium storage of ZnP2 @NPCNFs electrode obey the conversion reaction mechanism. Besides, the additional lithium intercalation active sites created by the doped-nitrogen and the existence of PC bond along with the space-confined effect of NPCNFs are conjointly beneficial to endow the ZnP2 @NPCNFs electrode with distinctive electrochemical properties. When assembled as the anode, the ZnP2 @NPCNFs electrode reached a high reversible capacity of 746 mA h g−1 after 100 cycles at 0.2 A g−1 and 406.49 mA h g−1 after 1000 cycles at 2 A g−1. Electrochemical tests manifest that most of the capacity contribution comes from capacitive process. Moreover, the similar superior electrochemical performances are obtained in the LiFePO4//ZnP2 @NPCNFs full cell. Generally, this study widens researchers’ horizons to conceive rational structure of metal phosphides anodes in LIBs with high capacity conservation.

Reversible Photochromic Coordination Polymer by Phototriggered Subtle Molecular Conformation Variations.

Photochromic materials are constructed with molecules accompanied by structural change after triggering by light, which are of great importance and necessity for various applications. However, because of space-confinement effects, molecule stacking of these photoresponsive chromophores within coordination polymers (CPs) always results in an efficiency decrement and a response delay, and this phenomenon will lead to a poor photochromic property. Herein, a CP (named CIT-E) with a 3-fold-interpenetrating network structure, which was prepared with (Z)-1,2-diphenyl-1,2-bis[4-(pyridin-3-ylmethoxy)phenyl]ethene (1Z) and a CuI cluster, showed fast reversible photochromic behavior. Under UV-light illumination, the color of CIT-Z changed from pale yellow to reddish brown. With the illumination of green light, the polymer could return to its initial color within 10 s. To reveal the mechanism of reversible photochromic behavior of CIT-Z, single-crystal structures of each color state were fully studied, and other scientific study methods were also used, such as time-dependent density functional theory calculation and control experiments. It was found that, with light illumination, this behavior of CIT-Z was the result of a ligand-to-metal charge-transfer process, and this process was triggered by subtle molecular conformation variation of tetraphenylethylene. It should be noted that CIT-Z has high thermal and chemical stability, which are excellent advantages as smart photoresponsive materials. As a proof of concept, a uniform thin film with such a fascinating photochromic property allows applications in invisible anticounterfeiting and dynamic optical data storage. Overall, the present study opens up a new avenue toward reversible photochromic materials.

Ultrahigh Rate and Ultralong Life Span Sodium Storage of FePS3 Enabled by the Space Confinement Effect of Layered Expanded Graphite.

Metal phosphorus trichalcogenides have been regarded as promising high-capacity anode materials for sodium-ion batteries (SIBs) owing to their high reversible capacity. Nevertheless, their practical application is plagued by poor diffusion kinetics and dramatic volume fluctuations during the charge-discharge process, resulting in no satisfactory rate and life span so far. Herein, we propose a space-confinement strategy to remarkably promote the cycling stability and rate capacity by embedding FePS3 particles in the interlayer of expanded graphite (EG), which are derived from in situ transformation of graphite intercalation compounds. The layered EG not only greatly alleviates the volume fluctuations of FePS3 by the space confinement effect so as to maintain the stability of the electrode microstructure, but it also ensures rapid Na+ and electron transfer during cycling. When acting as an anode for SIBs, the hybrid electrode delivers a highly reversible capacity of 312.5 mAh g-1 at an ultrahigh rate of 50 A g-1 while retaining an ultralong life span of 1300 cycles with a retention of 82.4% at 10 A g-1. Moreover, the excellent performance of the assembled full battery indicates the practical application potential of FPS/EG.

Bionic sunflower-like structure of polydopamine-confined NiFe-based quantum dots for electrocatalytic oxygen evolution reaction

NiFe-based nanostructures have been attracting attentions as a promising non-noble metal electrocatalysts for oxygen evolution reaction in alkaline. In this paper, a bionic sunflower-like NiFe-polydopamine film was prepared via self-polymerization of dopamine-Ni2+/Fe3+ followed by partial pyrolysis process. In the films, NiO quantum dots are embedded in Fe-coupled polydopamine due to the space-confined effect of PDA. The self-activation process effect led to in-situ reconstruction of the generation of NiOOH and the migration of Fe sites to NiOOH surface. Abundant Fe sites on the NiOOH surface facilitated formation of stable O* intermediate. Moreover, the coordination-confined effect of PDA for Fe ions in the PDA network gave the PDANF catalyst excellent durability. The NiFe-polydopamine film exhibited excellent intrinsic OER activity with a low overpotential of 254.1 mV for 10 mA cm−2 and an unprecedentedly low Tafel slope of 23.3 mV dec−1.

Crystallographic orientation and morphology control of Sb2Se3 to sensitize TiO2 nanotube arrays for enhanced photoelectrochemical performances

Coupling the appropriate light-absorbing materials with titanium dioxide (TiO2) nanotube arrays (TNA) can significantly enhance the Performance of photoelectrochemical (PEC) devices. Anisotropic antimony selenide (Sb2Se3) is a promising photo-absorber, but optimizing its crystallographic orientation and morphology concurrently is challenging. Herein, we control the growth of Sb2Se3 utilizing the space-confined effect of TNA with varying electrodeposition strategies to regulate the nucleation position. The [211]-oriented rod-like Sb2Se3/TNA photoanode prepared by pulse electrodeposition generates a photocurrent of 3.02 mA cm−2 at 1.23 V (versus RHE) in an electrolyte of pH 7, which is ∼4.1- and ∼30.0-time as those of [230]-oriented octahedron-like Sb2Se3/TNA and bare TNA photoanodes, respectively. Photoelectron can travel easily along the vertical direction via the covalent bond of (Sb4Se6)n ribbons without the recombination loss along the van der Waals direction due to the optimized Sb2Se3 [211] orientation and 1D-1D array structure. In situ irradiation X-ray photoelectron spectroscopy is used to directly monitor photoelectron transfer from Sb2Se3 to TNA at the heterojunctions, which ensures the promoted photoelectron separation and extraction in the rod-like Sb2Se3/TNA photoanode at the positive bias. This work provides a new strategy for optimally orienting anisotropic semiconductors and a fundamental insight into their photoelectron separation for design of efficient photoanodes.

Electrocatalytic composite membrane with deep-permeation nano structure fabricated by flowing synthesis for enhanced catalysis

An electrocatalytic composite membrane with deep-permeation nano structure (DPNS) has been fabricated by flowing synthesis. The nano electrocatalyst MnO2 is in situ successfully assembled in membrane pores and uniformly immobilized in membrane pores along the direction of membrane thickness. The size of MnO2 nanoparticles immobilized in membrane pores is in the range of 33–35 nm, which is one-tenth of that immobilized on the membrane surface. The increased current density and the lower charge transfer resistance of the electrocatalytic composite membrane implied that a fast electron transfer can be achieved. As a concept-of-proof, the removal of phenol was applied to test the catalytic performance of the electrocatalytic composite membrane under the flow-through reaction mode, and the removal rate of phenol of being over 97% can be achieved under the condition of membrane flux of being 13.5 L m−2 h−1. The apparent reaction rate constant could be increased by 2–3 orders of magnitude, owing to the enhanced contact by uniform distribution of membrane pores, as well as the confined space effect of membrane pores and the flow-through synergism enhancing mass transfer. The species of free radical can be determined as ·OH via ESR measurements for phenol oxidation. This electrocatalytic composite membrane (ECCM) with DPNS has good reusability and can provide a promising prospect for industrial application.

Space and interface confinement effect of necklace-box structural FeS2/WS2 carbon nanofibers to enhance Na+ storage performance and electrochemical kinetics

Necklace-box structural FeS2/WS2 carbon nano-composite fibers (NB FeS2/WS2-CNFs) are fabricated by electrospinning-sulfuration-hydrothermal process. NB FeS2/WS2-CNFs exhibit the spatial confined structure, which is able to restrain volume expansion effectively in the process of Na+ intercalation/deintercalation and improve the cycling stability and rate performance. NB FeS2/WS2-CNFs exhibit remarkable initial coulombic efficiency (ICE = 87.0%) and stable long cycle (~422.6 mA h g−1 at 0.5 A g−1 after 500 cycles) for sodium storage capability. The heterojunction interface between FeS2 and WS2 can alleviate the damage of the micro-crystal plane and enhance electrochemical kinetic process. The structure evolution and mechanism of sodium storage are explored by ex-situ methods, which further confirm the spatial and interface confinement effect distinctly. In addition, the electrochemical kinetic properties of lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are compared, thereby revealing the energy storage mechanism and different ion migration modes of the three batteries. This work provides a guide for the synthesis of bimetallic compounds based on the spatial confinement and heterojunction interface confined strategy that efficiently improves energy storage performance of electrode material.

Line defects in plasmatic hollow copper ball boost excellent photocatalytic reaction with pure water under ultra-low CO2 concentration

By using a low CO2 concentration as a C1 source, the design of a plasmonic catalyst that can effectively photocatalytic CO2 reduction is of great significance for sustainable and ecological development. Herein, the space confinement effect and liquid environment of the molten salt result in uniform hollow structure, while the strong aggressive force furnished via using molten salt enhances the formation of line defects. This special structure can not only provide a large number of active sites but also greatly accelerate the transport of photoinduced charge carriers. The hollow copper ball with line defects (CCu) shows excellent photocatalytic activity with pure water (1028.57 μmol g−1), and it also shows good catalytic activity even under ultra-low CO2 content, which far exceeds the catalytic activity of most semiconductor-based catalysts. This work is designed to simultaneously construct line defect and hollow structure in plasmatic metal nanoparticles for efficient photocatalytic CO2 reduction.

Synchronous reduction-oxidation of 2,4,6-tribromophenol using bifunctional AgPd@CDs in a three dimensional electrochemical reactor

Seeking bifunctional suspended catalyst for halogenated organics dehalogenation and mineralization is urgent. Herein, a novel suspended catalyst, AgPd nanoparticles supported on cyclodextrin polymers (AgPd@CDs), was designed for synchronous reduction-oxidation of 2,4,6-tribromophenol in a three-dimensional electrochemical reactor (3DER). In this 3DER, AgPd@CDs presented 100.0% 2,4,6-tribromophenol removal efficiency under the optimized condition. The superior catalytic activity of AgPd@CDs was due to monodispersion of AgPd nanoparticles on CDs matrix and electron density modulation for Pd hollow sites' activity via electron transfer from Ag to Pd. Scavenger experiments and EPR results revealed that •OH and H• were responsible for synchronous 2,4,6-tribromophenol abatement. Moreover, CDs matrix not only promoted interfacial affinity between 2,4,6-tribromophenol and catalyst, but also inhibited reduction of O2 by H2 due to hydrophilic surface property and confined space effect in cavity, thus facilitating 2,4,6-tribromophenol enrichment and synchronous oxidation-reduction on AgPd@CDs. These findings provide conceptual insights into catalyst design for advanced wastewater treatment.

Solid-State Synthesis of Layered MoS2 Nanosheets with Graphene for Sodium-Ion Batteries

Sodium-ion batteries have potential as energy-storage devices owing to an abundant source with low cost. However, most electrode materials still suffer from poor conductivity, sluggish kinetics, and huge volume variation. It is still challenging to explore apt electrode materials for sodium-ion battery applications to avoid the pulverization of electrodes induced by reversible intercalation of large sodium ions. Herein, we report a single-step facile, scalable, low-cost, and high-yield approach to prepare a hybrid material; i.e., MoS2 with graphene (MoS2-G). Due to the space-confined effect, thin-layered MoS2 nanosheets with a loose stacking feature are anchored with the graphene sheets. The semienclosed hybrid architecture of the electrode enhances the integrity and stability during the intercalation of Na+ ions. Particularly, during galvanostatic study the assembled Na-ion cell delivered a specific capacity of 420 mAhg−1 at 50 mAg−1, and 172 mAhg−1 at current density 200 mAg−1 after 200 cycles. The MoS2-G hybrid excels in performance due to residual oxygen groups in graphene, which improves the electronic conductivity and decreases the Na+ diffusion barrier during electrochemical reaction, in comparison with a pristine one.

Single-Photon Near-Infrared-Responsiveness from the Molecular to the Supramolecular Level via Platination of Pentacenes.

Near-infrared (NIR) responsiveness is important for various applications. Currently, single-photon NIR-responsive systems are rare compared to systems that display two-photon absorption and triplet-triplet annihilation processes. Supramolecular stacking of photo-responsive chromophores results in decreased efficiency due to space-confinement effects. Herein we show that σ-platination of pentacenes is a feasible protocol to build single-photon NIR-responsive systems, with advantages including a low HOMO-LUMO energy gap, high photochemical efficiency, and pathway specificity. The pentacene-to-endoperoxidation transformation is accompanied by color and absorbance changes. The high photo-oxygenation efficiency of σ-platinated pentacenes facilitates NIR responsiveness in one-dimensional supramolecular polymers, resulting in the disappearance of supramolecular chirality signals and disruption of self-assembled nanofibers. Overall, the σ-platination strategy opens up new avenues toward NIR photo-responsive materials at the molecular and supramolecular levels.

Driving Force of Molecular/Ionic Superfluid Formation

Driving Force of Molecular/Ionic Superfluid Formation

Micromembrane absorber with deep‐permeation nanostructure assembled by flowing synthesis

AbstractA micromembrane adsorber with deep‐permeation nanostructure (DPNS) has been successfully fabricated by flowing synthesis. The nanoparticles are in‐situ assembled in membrane pores and immobilized in each membrane pore along the direction of membrane thickness. The nanoparticles with a lower size and thinner size distribution can be achieved owing to the confined space effect of the membrane pores. As a concept‐of‐proof, the nano ZIF‐8 and ZIF‐67 are fabricated in porous membrane pores for methyl orange (MO) and rhodamine B (RhB) adsorption. The adsorption rate is increased significantly owing to the enhanced contact and mass transfer in the confined space. The adsorption capacity for the RhB is also increased, since the size of the nanoparticles assembled in membrane pores is smaller with more active sites exposed. This micromembrane adsorber with DPNS has good reusability and can provide a promising prospect for industrial application.

Efficient oxygen reduction reaction by a highly porous, nitrogen-doped carbon sphere electrocatalyst through space confinement effect in nanopores

A highly porous nitrogen-doped carbon sphere (NPC) electrocatalyst was prepared through the carbonization of biomass carbon spheres mixed with urea and zinc chloride in N2 atmosphere. The sample carbonized at 1000 °C demonstrates a superior oxygen reduction reaction (ORR) performance over the Pt/C electrocatalyst, while its contents of pyridinic nitrogen and graphitic nitrogen are the lowest among samples synthesized at the same or lower carbonization temperatures. This unusual result is explained by a space confinement effect from the microporous and mesoporous structures in the microflakes, which induces the further reduction of peroxide ions or other oxygen species produced in the first step reduction to water to have the preferred overall four electron reduction ORR process. This work demonstrates that in addition to the amount or species of its active sites, the space confinement can be a new approach to enhance the ORR performance of precious-metal-free, nitrogen-doped carbon electrocatalysts.

Synergistic enhanced catalysis of micro-reactor with nano MnO2/ZIF-8 immobilized in membrane pores by flowing synthesis

A catalytic membrane micro-reactor (CMMR) with nano MnO2/ZIF-8 immobilized in membrane pores has been fabricated by flowing synthesis and formaldehyde degradation was used to test its catalytic performance. The CMMR with deep-permeation nano structure (DPNS) has good stability, uniform nano MnO2/ZIF-8 dispersion and higher loading capacity. The MnO2 coated on the surface of nano ZIF-8 with the size in the range of 100–150 nm was obtained. The contact between formaldehyde and MnO2 is enhanced by the effect of even disperse of membrane pores. The enhanced mass transfer can be achieved in the micro-scale pores of the membrane by the confined space effect. A higher amount of MnO2 loading and higher formaldehyde absorption rate can be achieved by the effect of ZIF-8 in membrane pores. The formaldehyde degradation rate was increased from 82.6% to 94.0%, if the MnO2 loading capacity was increased from 98 mg g−1 to 344 mg g−1.