Space-confined Strategy Research Articles

Confined growth of ultrasmall monodisperse gold nanoparticles in amino functionalized cellulose beads as effective catalysts for 4-nitrophenol reduction.

This study aims to prepare a monodisperse catalyst with a space-confined strategy, employing cellulose beads (CBs) as a carrier. Amino functionalized cellulose beads (ACBs) were prepared by grafting polyethyleneimine into the space of CBs via glutaraldehyde cross-linking. The in-situ reduction method was successfully employed to confine monodisperse ultrasmall gold nanoparticles (AuNPs) within the amino functionalized cellulose beads (AuNPs@ACBs) matrix. The AuCl4- ions were first immobilized on the amino substance (such as -NH3+/-NH2+, CN and CN) by chelation and electrostatic interaction. Then the Au(III) was reduced to Au(0) by electron transfer. The presence of amino groups in ACBs controls the size and dispersion of AuNPs. AuNPs@ACBs was used as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), it reveals excellent catalytic activity, which can be ascribed to the smaller particle size of AuNPs (TOF = 7.86 min-1). The spherical structure of AuNPs@ACBs permits straightforward recovery from the aqueous solution after the reaction is completed, thus improving the reusability and catalytic stability. The catalytic efficiency of AuNPs@ACBs can still reach 64.7 % after 10 cycles. After more than 3000 min, the column continues to run without detecting 4-NP in the eluent, which is still working.

Single-Crystalline Nanowires of Molecular Ferroelectric Semiconductors for Optoelectronic Memory.

Though much progress has been achieved in the discovery of new molecular ferroelectrics in recent years, practical applications and related physics are still rarely explored due to the difficulty in high-quality film production and patterning issues. Single-crystalline films and patterns are in high demand for high device performance. Through a template-assisted space-confined strategy, herein, ordered single-crystalline nanowire patterns and optoelectronic devices of a semiconducting molecular ferroelectric (SMF), hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5), were successfully demonstrated. The coupling of semiconducting and ferroelectric polarization of the SMF devices enables a broadband self-powered photodetection from ultraviolet to visible light, as well as polarization-tunable photoresponsivity. These may open an avenue for high-performance SMF optoelectronic memory devices with low cost and flexibility.

Space-Confined Vertical Growth of Large-Size Organic Semiconductor Single Crystals.

Organic semiconductor single crystals (OSSCs) have garnered considerable attention because of their high charge mobility and atomic-scale smooth surface. However, their large-size high-quality preparation remains challenging due to the inevitable defects and limited growth speed brought by traditional epitaxial growth. Here, we demonstrate a space-confined strategy, named out-of-plane microspacing in-air sublimation (OPMAS), for growing vertically millimeter-sized OSSCs in several minutes by revolutionizing the heterogeneous epitaxial growth mode severely depending on substrates into a spontaneous homogeneous growth mode free from substrates. The intrinsic driven force of this transformation is proved to be the change of surface energy, and the maximum size of crystals is thermodynamically dependent on the distance of the microspace. OPMAS has been proven to be suitable for preparing single crystals of various typical organic semiconductors. Numerous characterizations have been conducted to prove the high quality and uniformity of the thus-produced OSSCs. In addition, the photoresponse of the prepared OSSCs is highly dependent on the illumination intensities, making it suitable for high-contrast Morse coding process, demonstrating a stable switch ratio of about 3.3. This work provides a universal platform for preparing large-sized OSSCs, advancing both fundamental (opto)electronic studies and a wide range of practical applications.

An Ultrasmall Ordered High-Entropy Intermetallic with Multiple Active Sites for the Oxygen Reduction Reaction.

Controlling multimetallic ensembles at the atomic level is significantly challenging, particularly for high-entropy alloys with more than five elements. Herein, we report an innovative ultrasmall (∼2 nm) PtFeCoNiCuZn high-entropy intermetallic (PFCNCZ-HEI) with a well-ordered structure synthesized by using the space-confined strategy. By exploiting these combined metals, the PFCNCZ-HEI nanoparticles achieve an ultrahigh mass activity of 2.403 A mgPt-1 at 0.90 V vs reversible hydrogen electrode for the oxygen reduction reaction, which is up to 19-fold higher than that of state-of-the-art commercial Pt/C. A proton exchange membrane fuel cell assembled with PFCNCZ-HEI as the cathode (0.03 mgPt cm-2) exhibits a power density of 1.4 W cm-2 and a high mass-normalized rated power of 45 W mgPt-1. Furthermore, theoretical calculations reveal that the outer electrons of the non-noble-metal atoms on the surface of the PFCNCZ-HEI nanoparticle are modulated to show characteristics of multiple active centers. This work offers a promising catalyst design direction for developing highly ordered HEI nanoparticles for electrocatalysis.

Defect-induced electron rich nanodomains in CoSe0.5S1.5/GA realize fast ion migration kinetics as sodium-ion capacitor anode

Optimizing charge migration and alleviating volume expansion in anode materials are the key to improve the electrochemical performance for sodium-ion storage devices. Herein, a hierarchical porous conducting matrix confining defect-rich selenium doped cobalt dichalcogenide (CoSe0.5S1.5/GA) is constructed as a promising SICs anode based on the guidance of theoretical calculation analysis. The increased defect concentration significantly enhanced the disorder degree of the compound and presented electron aggregation around the S atoms, which effectively modulated the electronic structure, further enabling high rate and ultra-capacity sodium storage. Moreover, strong interfacial coupling could construct spatial constraint to alleviate volume expansion as well as maintain electrode integrity and stability. The CoSe0.5S1.5/GA electrode can deliver a high capacity of 310.1 mA h g−1 after 2000 cycles at 1 A g−1, and the CoSe0.5S1.5/GA//AC sodium ion capacitor can exhibit an outstanding energy density of 237.5 W h kg−1. A series of characterization and theoretical calculation convincingly reveal that the defect moieties can regulate the Na+ storage and diffusion kinetics, which prove that our defect manufacture coupling with space-confined strategy can provide deep insights into the development of high-performance Na+ storage devices.

Two-dimensional confinement engineering of SiO2 nanosheets supported nano-cobalt for high-efficiency microwave absorption

Advanced electromagnetic (EM) absorbers containing magnetic and dielectric components have garnered substantial attention due to rapid expansion of wireless communication equipment. However, the EM absorbing performance of magnetic materials is greatly hindered by the substantial decrease in permeability at gigahertz frequencies, commonly referred to the Snoek limit. Confinement engineering provides effective strategy for precisely modulating particle size in a confined region to enhance the surface anisotropy and thereby surpass the Snoek limit. Herein, a novel space-confined strategy is proposed to develop two-dimensional (2D) SiO2 nanosheets that involves manipulating the topological exfoliation of CaSi2 with CoCl2 and thereafter high-temperature reduction. The resulting SiO2 supported nano-Co (Co-2DSiO2) heterostructure exhibits uniform dispersion and nearly single domain size. Contributing to the magnetic-dielectric synergistic effect, fascinating EM properties can be achieved by regulating the size of nano-Co at varied temperatures, and the Co-2DSiO2 delivers the optimal reflection loss of –51.6 dB at 2.5 mm and the effective absorption bandwidth of 4.6 GHz. Electronic structures of Co-2DSiO2 were simulated by theoretical calculation, further verifying the potential mechanism of enhanced dielectric loss and analyzing the formation of heterostructure. The proposed confinement strategy lays the groundwork for the development of advanced absorbers and provides a universal approach for other metal-based SiO2 nanosheets with tunable structures.

A space-confined strategy towards stable α/β-Bi2O3 heterojunction anode for high-energy aqueous battery

It is very necessary to design a high-capacity and stable Bi2O3 anode for nickel-bismuth (Ni//Bi) batteries. In this work, a stable α- and β- phase Bi2O3 heterojunction nanocomposite (α/β - Bi2O3) was successfully prepared via a simple “space-confined” strategy and it was used as a superior anode for nickel-bismuth (Ni//Bi) battery. The α/β-Bi2O3 obtained by using MCM-41 as a space-confined template possesses a stable structure and enhanced charge transfer capability. Such superior traits vest the designed α/β-Bi2O3 electrode with high specific capacity (235 mAh g−1 at 1 A g−1), extraordinary rate performance (137 mAh g−1 at 40 A g−1, and ∼58% capacity retention vs 1 A g−1), and excellent cyclic durability (75% capacity retention after 5000 cycles). Such performances are far superior to that of mono-phase α-Bi2O3 and β-Bi2O3 electrodes. Furthermore, an excellent Ni//Bi battery with outstanding energy density (∼155 Wh kg−1) and long cycle life was assembled using the obtained α/β-Bi2O3 electrode and a NiC2O4 electrode as anode and cathode, respectively (NiC2O4//α/β-Bi2O3). This work opens a new alternative strategy for the rational design of efficient electrodes for reliable aqueous rechargeable batteries.

Exciton dispersion in two-dimensional organic perylene crystal indicates substantial charge-transfer exciton coupling

Two-dimensional, high-quality perylene single crystals were grown with a space-confined strategy method. The grown films crystallize in the $\ensuremath{\alpha}$ form, as is confirmed by a combination of techniques. Polarization-dependent optical absorption measurements show a strong anisotropy in very good agreement with the literature data, and the anisotropic mobility data in field-effect transistors document the very high crystalline order. Momentum-dependent studies using electron energy-loss spectroscopy reveal a negative dispersion of the first exciton along the crystal $b$ direction with an exciton bandwidth of 72 meV. We argue that this behavior is a result of charge-transfer exciton coupling between the perylene dimers in the unit cell.

Pt Single Atom-Anchored CeOx/SAPO-11 for Highly Efficient Hydroisomerization of n-Heptane

Single atomic catalysts (SAC) isolated in zeolite have been reported for hydroisomerization of n-alkanes. However, it is widely found that metal species located outside zeolite crystals have beneficial effects on catalytic performance, rather than inside zeolite. Herein, we introduce cerium oxide as a binder to anchor Pt single atoms on the catalyst surface. Pt species were atomically dispersed on catalyst surface certified by AC HAADF-STEM and XAS. Pt1@CeOx/SAPO-11 not only shows significant activity but also effectively inhibits the selectivity of cracking or hydrogenolysis. The turnover frequency value of 0.05%Pt1@CeOx/SAPO-11 reaches 9511 h−1, 13 times higher than reported catalyst prepared with the space-confined strategy. Reaction mechanisms have been proposed to explain the different effects of platinum status and location on the reaction. Platinum single atoms located outside the catalyst crystal are speculated more favourable to this reaction. Conceptually, catalytic efficiency of this reaction can be improved by dispersing the active sites to reduce the local concentration of the product of a reversible step in an intermediate reaction. An appropriate loading of 0.05 wt% is needed to achieve the high efficiency of the metal and acid sites simultaneously.

3D graphene-like oxygen and sulfur-doped porous carbon nanosheets with multilevel ion channels for high-performance aqueous Zn-ion storage

Zinc-ion hybrid capacitors (ZIHC) demonstrate impressive charge-storage performance and intrinsic safety due to the inherited superiorities of aqueous rechargeable batteries and supercapacitors. However, the promotion of electrochemical performance is usually hindered by the cathode materials that fail to hold high energy density and rate capability of ZIHC. The optimization of porous carbon cathodes into a hierarchical structure is an efficient strategy to break the bottlenecks of ZIHC. Herein, a metal oxide space-confined strategy is proposed to build 3D graphene-like porous carbon nanosheets (3DPC) with doping of O and S heteroatoms by using low-cost aromatic hydrocarbons as precursors. It is found that the obtained 3DPC consists of micro-, mseo- and macropores and further delivers a high specific surface area of 2813 m2 g−1 with a total pore volume of 1.82 cm3 g−1. Specifically, such a well-defined hierarchical porosity of 3DPC coupled with rich O and S heteroatoms enables sufficient multilevel ion transport channels and large accessible surface sites to capture the Zn2+ ions. As a proof of concept demonstration, the assembled aqueous ZIHC by employing the 3DPC cathode exhibits a desirable capacity of 194 mAh g−1 at 0.5 A g−1 with a superior rate capability of 53% at 30 A g−1 and excellent cycling stability of over 88% after 15000 cycles. Moreover, the remarkable electrochemical performance of the 3DPC cathode can be well-preserved in the case of a quasi-solid-state ZIHC device under various harsh bent states, highlighting the promising application in flexible and wearable energy storage.

Space-confined synthesis of a novel Ge@HCS-rGO yolk-shell nanostructure as anode materials for enhanced lithium storage

Germanium (Ge) is considered as a promising anode material due to its high lithium storage capability. However, the huge volume change during cycling cause serious structural degradation and poor cycling stability. Yolk-shell nanostructure design is an effective way to solve such problems for electrode materials such as Ge and Si. Herein, we proposed the design and synthesis of a novel Ge@hollow carbon sphere-reduced graphene oxide (Ge@HCS-rGO) yolk-shell nanostructure as anode via a space-confined strategy for the first time. Rational void space is engineered in the yolk-shell structure, offering a buffer zone for adapting the volume expansion of Ge core particles with protective carbon shells upon lithiation, while the 3D conductive network with hierarchical pores provides fast electron and Li-ion transport channels. Benefiting from the unique structural dual-protection of 3D conductive network and yolk-shell nanostructure, the as-synthesized Ge@HCS-rGO anode exhibits high discharge capacity (2117.3 mA h g−1 at 0.2 C), enhanced cycling stability (958.6 mA h g−1 up to 200 cycles at 0.2 C) and excellent rate capability (1010.0 mA h g−1 at 4 C). The electrochemical performance of Ge@HCS-rGO yolk-shell anode is greatly improved compared with bare Ge and Ge@HCS anode, suggesting its great potential to develop high performance electrode materials with large volume expansion.

Space-confined fabrication of hydrophobic magnetic carbon nanofibers for lightweight and enhanced microwave absorption

Advanced microwave absorbers (MAs) containing magnetic particles and carbon nanofibers (CNFs) have raised widespread attention in the rapid popularization of electronic communication equipment. However, it is quite challenging to control the growth of magnetic particles in CNFs to improve electromagnetic waves (EMWs) loss and attenuation. Herein, a novel space-confined strategy was adopted to develop Co/CoO/SiO2/CNFs, in which Co/CoO nanoparticles (NPs) with single domain size and dispersed distribution could achieve enhanced magnetic loss and dielectric loss. The introduction of nano-SiO2 in the system could enhance the dielectric confinement effect of the nanofibers (NFs), while an interfacial confinement network could also be constructed to realize the refinement of Co/CoO NPs, enhance the electromagnetic (EM) loss, and ultimately ameliorate the microwave absorption performance of as-obtained NFs. When the additive amount of nano-SiO2 in the spinning solution was 1.0 mg, the as-prepared Co/CoO/SiO2/CNFs reached the optimal reflection loss (RL) of −52.9 dB at 12.64 GHz with a thickness of 2.5 mm, and the effective bandwidth (EBW) reached 5.67 GHz (10.46–16.13 GHz). Furthermore, the excellent hydrophobic properties of the CNFs endow them with potential self-cleaning function. The confinement strategy proposed in this work lays a foundation for the design of low-filling ratio and high-performance CNFs-based microwave absorbers, and presents a general approach for the synthesis of one-dimensional composite materials with controllable structures.

Rapid synthesis of self-standing covalent organic frameworks membrane via polyethylene glycol-assisted space-confined strategy

Owing to their high specific surface area, tunable pore sizes, excellent chemical/thermal stability and ability to allow easy modification of the nature of the surface, covalent organic frameworks (COFs) have shown great promise in membrane separation. However, until now, rapid preparation of self-standing COFs membrane has still been a great challenge. In this work, a polyethylene glycol-assisted space-confined strategy for rapid and simple synthesis of imine-linked self-standing COF (TB-DA COF) membranes was developed for the first time. By using this strategy, the molecular organic building unit 1,3,5-tri-(4-aminophenyl)benzene (TB) is confined in a thin layer of polyethylene glycol in conjunction with molecular organic building unit 2,5-dimethoxyterephthalaldehyde (DA). Therefore, the condensation reaction between TB and DA can occur directly without slow diffusion process. In addition, the amorphous-to-crystalline interconversion process can be completed rapidly. Based on this, the imine-based TB-DA COF membrane with high crystallinity can be synthesized within 2 min, which has been the fastest strategy for preparation of COFs membrane to date. The synthesized TB-DA COF2 membrane showed an excellent rejection (>96%) for dye molecules. This work opens a new fabrication route for COF-based membranes.

Acidic Electrocatalytic CO2 Reduction Using Space-Confined Nanoreactors.

Electrochemical CO2 reduction reaction (CO2RR) is an attractive strategy for sustainable production of chemicals and has mainly been implemented in alkaline or neutral electrolytes. However, part of input CO2 is consumed by the formation of carbonate under these conditions. Herein, a space-confined strategy is proposed for CO2RR in acidic media, and Ni nanoparticles are encapsulated inside N-doped carbon nanocages as yolk-shell nanoreactors. By confining CO2RR in the cavities of nanoreactors, a Faradaic efficiency (FE) of 93.2% for CO is achieved at pH 7.2 and 84.3% FE for CO at pH 2.5. The inhibited proton diffusion within the Nernst layer of a nanoreactor is responsible for suppression of competing hydrogen evolution in acid. Moreover, CO2RR in an acidic flow electrolysis system offers enhanced current density and sustainable operation, in comparison with the conventional neutral pH system. This work shows that steering of mass transport via a unique structure is a viable avenue toward selective CO2 conversion, and it provides a further understanding of the structure-performance relationship of electrocatalysts.

Thin MAPb0.5Sn0.5I3 Perovskite Single Crystals for Sensitive Infrared Light Detection.

Metal halide perovskite single-crystal detectors have attracted increasing attention due to the advantages of low noise, high sensitivity, and fast response. However, the narrow photoresponse range of widely investigated lead-based perovskite single crystals limit their application in near-infrared (NIR) detection. In this work, tin (Sn) is incorporated into methylammonium lead iodide (MAPbI3) single crystals to extend the absorption range to around 950 nm. Using a space-confined strategy, MAPb0.5Sn0.5I3 single-crystal thin films with a thickness of 15 μm is obtained, which is applied for sensitive NIR detection. The as-fabricated detectors show a responsivity of 0.514 A/W and a specific detectivity of 1.4974×1011 cmHz1/2/W under 905 nm light illumination and –1V. Moreover, the NIR detectors exhibit good operational stability (∼30000 s), which can be attributed to the low trap density and good stability of perovskite single crystals. This work demonstrates an effective way for sensitive NIR detection.

Confined growth of molybdenum disulfide in cellulose microspheres with highly porous structure for environmental applications

Molybdenum disulfide (MoS2) stands out as a promising candidate in environmental applications. However, the inherent stacking and nanosized features remain challenges in the high performance of such materials. In this work, we present a space-confined strategy to synthesize nanosized MoS2 within nanofibrous cellulose microspheres (NCMs). The NCMs matrix is well-designed and considered as an excellent scaffold with a hierarchical porous structure, mechanical stability and a considerable specific surface area of 212.06 m2/g, and the recyclability and dispersibility of nanosized MoS2 can be improved. The prepared MoS2/NCMs exhibit excellent performance in the removal of various contaminants, including Pb2+ (adsorption capacity of 327.68 mg/g, fast kinetics within 40 min), organic dyes (80% removal within 100 min for methylene blue and Congo red), doxycycline, p-nitrophenol, and the recyclability of MoS2/NCMs is also confirmed. Consequently, this study presents a well-designed confinement synthesis of MoS2, and provides a promising candidate for environmentally-sustainable treatment.

Polymer-Assisted Space-Confined Strategy for the Foot-Scale Synthesis of Flexible Metal-Organic Framework-Based Composite Films.

At the gas-liquid interface, the confined synthesis of metal-organic framework (MOF) films has been extensively developed by spreading an ultrathin oil layer on the aqueous surface as a reactor. However, this interface is susceptible to various disturbances and incapable of synthesizing large-area crystalline MOF films. Herein, we developed a polymer-assisted space-confined strategy to synthesize large-area films by blending poly(methyl methacrylate) (PMMA) into the oil layer, which improved the stability of the gas-liquid interface and the self-shrinkage of the oil layer on the water surface. Meanwhile, the as-synthesized MOFs as a quasi-solid substrate immobilized the edge of the oil layer, which maintained a large spreading area. Thanks to this synergistic effect, we synthesized the freestanding MOF-based film with a foot-level (0.66 ft) lateral dimension, which is the largest size reported so far. Besides, due to the phase separation of the two components, the MOF-PMMA composite film combined the conductivity of MOFs (1.13 S/m) with the flexibility of PMMA and exhibited excellent mechanical properties. More importantly, this strategy could be extended to the preparation of other MOFs, coordination polymers (CPs), and even inorganic material composite films, bringing light to the design and large-scale synthesis of various composite films for practical applications.

Vanadium -mediated ultrafine Co/Co9S8 nanoparticles anchored on Co-N-doped porous carbon enable efficient hydrogen evolution and oxygen reduction reactions.

Developing cost-effective, highly-active and robust electrocatalysts is of vital importance to supersede noble-metal ones for both hydrogen evolution reactions (HERs) and oxygen reduction reactions (ORRs). Herein, a unique vanadium-mediated space confined strategy is reported to construct a composite structure involving Co/Co9S8 nanoparticles anchored on Co-N-doped porous carbon (VCS@NC) as bifunctional electrocatalysts toward HER and ORR. Benefitting from the ultrafine nanostructure, abundant Co-Nx active sites, large specific surface area and defect-rich carbon framework, the resultant VCS@NC exhibits unexceptionable HER catalytic activity, needing extremely low HER overpotentials in pH-universal media (alkaline: 117 mV, acid: 178 mV, neutral: 210 mV) at a current density of 10 mA cm-2, paralleling at least 100 h catalytic durability. Notably, the VCS@NC catalyst delivers high-efficiency ORR performance in alkaline solution, accompanied with a quite high half wave potential of 0.901 V, far overmatching the commercial Pt/C catalyst. Our research opens up novel insight into engineering highly-efficient multifunctional non-precious metal electrocatalysts by a metal-mediated space-confined strategy in energy storage and conversion system.

Space-confined construction of two-dimensional nitrogen-doped carbon with encapsulated bimetallic nanoparticles as oxygen electrocatalysts

A space-confined strategy has been used to control the pyrolysis of two-dimensional (2D) NiCo-MOF@ZIF-L(Zn).

Amorphous molybdenum sulfide monolayer nanosheets for highly efficient electrocatalytic hydrogen evolution

Monolayer amorphous molybdenum sulfide (ML-a-MoSx) nanosheets were synthesized via a space-confined strategy, and their electrocatalytic activity was evaluated towards the hydrogen evolution reaction. The so-obtained ML-a-MoSx, with a quite high monolayer ratio of ~ 93%, shows a polymeric chain or network structure consisting of trinuclear [Mo3] clusters, with abundant Mo defects. ML-a-MoSx exhibits much higher activity in comparison with bulk a-MoSx (B-a-MoSx), and is superior among the Mo-S electrocatalysts reported to date. In particular, ML-a-MoSx can deliver a high current density of 400 mA cm−2 at an overpotential of 230 mV vs. RHE, which is similar to the state-of-the-art catalyst commercial 20% Pt/C. The Tafel slope of ML-a-MoSx remains almost unchanged with an increase in overpotential, very conducive to practical applications. The higher electrocatalytic activity of ML-a-MoSx than B-a-MoSx results from its larger specific surface area, higher active site density, stronger conductivity, and faster turnover frequency. The active sites of ML-a-MoSx are identified as Mo defects. This is the first report on the fabrication and catalytic activity of ML-a-MoSx. This work provides an effective route for large-scale fabrication of ML-a-MoSx and contributes to the understanding of the origin of its excellent electrocatalytic activity.