Porous Nanocages Research Articles

Fabricating carbon nanocages as ORR catalysts in alkaline electrolyte from F127 self-assemble core-shell micelle

In order to reduce the cost of oxygen reduction reaction (ORR) catalyst in fuel cell, polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) three-block copolymer (F127) and Zn(OH)2 were used as carbon resource and morphology retaining agent to prepare porous nanocages for ORR catalyst in alkaline solution. Its composition and microstructure were characterized by X-ray diffraction Raman spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) method. Electrochemical properties were evaluated in O2 saturated alkaline solution. Results showed the sample obtained at 700 °C (C-700) was composed of porous carbon nanocages with diameter of 50 nm and shell thickness of 4 nm. C-700 had the maximum surface area (1011 m2 g−1) and the best ORR catalytic performance. The main reason is that polypropylene oxide (PPO) group at the lipophilic end begins to decompose at 500 °C, and the polyethylene oxide (PEO) group at the lipophilic end at 700 °C decomposes completely. In O2 saturated 0.1 M KOH solution, C-700's oneset potential, limit current density and half-wave potential, which were 0.89 V, 5.59 mA/cm2@0.45 V and 0.71 V, respectively, were close to that of commercial 20% Pt/C catalyst. It was noted that the oneset potential and half-wave potential of C-700 had barely change, and limit current density attenuated about 87.8% after 2000 CV cycle. The obtained catalyst behaved good catalytic activity and stability for ORR in alkaline solution and a potential application prospect in fuel cells.

Nickel-cobalt oxide nanocages derived from cobalt-organic frameworks as electrode materials for electrochemical energy storage with redox electrolyte

Nickel-cobalt (Ni-Co) oxide nanocages were synthesized by etching the cobalt-based metal-organic framework (Co-MOF) with nickel nitrate in an isopropyl alcohol solution. The dodecahedral Co-MOF (300 nm in size) was composed of micropores, while the Ni-Co oxide nanocages gained additional mesopores and macropores. Both Co-MOF and Ni-Co oxide electrodes in KOH behaved more like the nondiffusion-controlled pseudocapacitor through the surface adsorption/desorption with a concomitant faradaic charge-transfer reaction. In the presence of ferrocyanide/ferricyanide redox electrolyte, both nondiffusion- and diffusion-controlled currents contributed equally to the current response of Ni-Co oxide electrode at lower scan rates. Nondiffusion-limited processes governed the charge-storage behavior of Ni-Co oxide electrode at faster scan rates. The Ni-Co oxide electrode with redox electrolyte showed high specific capacities of 810 and 496 C g−1 at the charge/discharge current densities of 10 and 50 A g−1, respectively, much greater than that electrode without redox electrolyte (384 and 348 C g−1). Ni-Co oxide electrode with highly porous nanocages could provide large electrolyte/electrode interface to store more charges and short pathways to expedite the transport of electron and ion, showing a noticeable increase in its electrochemical performance compared with Co-MOF electrode.

Colorimetric detection of ascorbic acid and alkaline phosphatase activity based on the novel oxidase mimetic of Fe–Co bimetallic alloy encapsulated porous carbon nanocages

A novel catalyst of FeCo nanoparticles (FeCo NPs) incorporated porous nanocages (FeCo NPs@PNC) was first synthesized by encapsulating of FeCo alloy into ZIF-8 and further carbonation of the composite. The FeCo NPs@PNC displays enhanced intrinsic oxidase-like activity compared to the individual FeCo NPs and porous nanocages (PNC). The FeCo NPs@PNC can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB) without H2O2, producing a blue color with a maximum absorption peak at 652 nm. The catalytic mechanism was investigated and it found that the intermediate (O2·-) produced from the catalytic process in the system of TMB-O2-FeCo NPs@PNC can accelerate the oxidation of TMB to oxTMB. However, ascorbic acid (AA) can reduce the oxTMB and result in a conspicuous blue color fading. Therefore, a novel colorimetric platform was constructed to quantify AA with the linear range of 0.5–28 μM and detection limit of 0.38 μM (at 3σ/m). Owing to the alkaline phosphatase (ALP) can catalyze the hydrolysis of AA 2-phosphate (AAP) into AA, ALP can also be quantified by the above method. And the linear range for ALP is 0.6–10 U L−1 and the limit of detection is 0.49 U L−1. The FeCo NPs@PNC also shows excellent stability and reproducibility. This study provides a new alternative oxidase mimetic on the basis of easily obtained metal-organic frameworks derivatives to replace the expensive natural enzymes and noble metal based nanoenzymes, which will show great potential in biological assays.

Ag@Au Core⁻Shell Porous Nanocages with Outstanding SERS Activity for Highly Sensitive SERS Immunoassay.

A highly sensitive immunoassay of biomarkers has been achieved using 4-mercaptobenzoic acid-labeled Ag@Au core–shell porous nanocage tags and α-fetoprotein immuno-sensing chips. The Ag@Au porous nanocages were uniquely synthesized by using an Ag core as a self-sacrificial template and reducing agent, where the slow reaction process led to the formation of a porous Au layer. The size of the remaining Ag core and surface roughness of the Au shell were controlled by adjusting the chloroauric acid concentration. The porous cage exhibited excellent surface-enhanced Raman spectroscopy (SERS) activity, presumably due to a synergetic interaction between newly generated hot spots in the rough Au shell and the retained SERS activity of the Ag core. Using α-fetoprotein as a model analyte for immunoassay, the SERS signal had a wide linear range of 0.20 ng mL−1 to 500.0 ng mL−1 with a detection limit of 0.12 ng mL−1. Without the need of further signal amplification, the as-prepared Ag@Au bimetallic nanocages can be directly used for highly sensitive SERS assays of other biomarkers in biomedical research, diagnostics, etc.

Synergistic Effect of Co-Ni Hybrid Phosphide Nanocages for Ultrahigh Capacity Fast Energy Storage.

Rational design of metal compounds in terms of the structure/morphology and chemical composition is essential to achieve desirable electrochemical performances for fast energy storage because of the synergistic effect between different elements and the structure effect. Here, an approach is presented to facilely fabricate mixed‐metal compounds including hydroxides, phosphides, sulfides, oxides, and selenides with well‐defined hollow nanocage structure using metal–organic framework nanocrystals as sacrificial precursors. Among the as‐synthesized samples, the porous nanocage structure, synergistic effect of mixed metals, and unique phosphide composition endow nickel cobalt bimetallic phosphide (NiCo‐P) nanocages with outstanding performance as a battery‐type Faradaic electrode material for fast energy storage, with ultrahigh specific capacity of 894 C g−1 at 1 A g−1 and excellent rate capability, surpassing most of the reported metal compounds. Control experiments and theoretical calculations based on density functional theory reveal that the synergistic effect between Ni and Co in NiCo‐P can greatly increase the OH− adsorption energy, while the hollow porous structure facilitates the fast mass/electron transport. The presented work not only provides a promising electrode material for fast energy storage, but also opens a new route toward structural and compositional design of electrode materials for energy storage and conversion.

Nano-array assisted metal-organic polyhedra membranes for the pervaporation of aromatic/aliphatic mixtures

Metal-organic polyhedra (MOP), as a new type of molecule-based porous nanocage, is a promising material in membrane separation. However, it is a challenge to obtain pure MOP membrane to take full advantage of its nanocage. In this study, [Cu24(5-tBu-1,3-BDC)24(S)24] (MOP-tBu) membranes were prepared on the surface of ceramic tubular substrate with the assistance of Co(OH)2 nano-array. MOP-tBu molecules were dynamic pressure-driven assembled into the confinement space of vertically arranged Co(OH)2 nanosheets, which were previously formed on the substrate through hydrothermal synthesis. With this strategy, the MOP-tBu molecules can form an ultrathin defect-free separation layer on the surface of the substrate. Due to the open Cu2+ unsaturated sites (CUSs) and rich benzene rings in its structure, the MOP-tBu membrane has permselectivity towards the aromatic compounds. In addition, the MOP-tBu membrane is endowed with high permeability because of its large cavity and small apertures. Therefore, the membranes were used to separate aromatic/aliphatic mixtures through pervaporation. When separating 50 wt% toluene/n-heptane mixtures, the permeate flux of the MOP-tBu membrane was 800 g m−2 h−1 with the separation factor of 5.4. The high permeability of the membrane exhibited great potential in the separation of aromatic/aliphatic mixtures.

Double-shelled hollow LaNiO3 nanocage as nanoreactors with remarkable catalytic performance: Illustrating the special morphology and performance relationship

Perovskites with ABO3 structure are the potential catalysts to replace the noble metals used in environmental catalysis, e.g. CO oxidation, volatile organic compounds (VOCs) and soot combustion. Herein, a novel double-shelled porous perovskite-type LaNiO3 nanocage (assigned as LaNiO3-Cage, with dual cage or cage in cage structure) was successfully synthesized via a facile hydrothermal method for the first time. LaNiO3-Cage displayed superior activity and stability for CO oxidation. The morphology and structure properties of the samples were confirmed by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), High-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), Elemental mapping, Powder X-ray Diffraction (PXRD) and N2 adsorption/desorption techniques. The inherent morphology-activity relationship was investigated through Temperature-Programmed Reduction with Hydrogen (H2-TPR), Temperature-Programmed Desorption with Oxygen and Carbon monoxide (O2-TPD and CO-TPD), and X-ray Photoelectron Spectroscopy (XPS) methods. LaNiO3-Cage showed superior catalytic performance among all the comparison samples (with lowest Ea, highest reaction activity, rate and TOF value) which should be ascribed to its special double-shelled porous nanocage structure (main factors) as well as larger surface areas and more active surface oxygen species. It should be noted that the outstanding catalytic performance of LaNiO3-Cage is well correlated with its special morphology structure. The porous double-shelled LaNiO3 nanocage prepared in this work can be used to design other type of catalysts with the similar morphology as novel nanoreactors.

ZnO/Cu2MgO3 hollow porous nanocage: A new class of hybrid anode material for advanced lithium-ion batteries

The lithium storage properties of hollow ZnO/Cu2MgO3 nanocages with porous outer shell as an efficient anode material for next generation lithium-ion battery (LIB) are demonstrated for the first time. The ZnO/Cu2MgO3 nanocages as anode material are synthesized by one-step cost-effective ultrasonic spray pyrolysis method. The porous outer shell with hollow interior not only offer ease of electrolyte diffusion and fast Li-ion transport, but also buffer the huge volume change during repeated lithiation/de-lithiation process. As a result, this novel anode demonstrates a high discharge capacity (441 mA h g-1 at the current density of 500 mA g−1 even after 400 cycles), excellent cycle stability, and outstanding rate capability.

MOF-Templated Fabrication of Hollow Co4N@N-Doped Carbon Porous Nanocages with Superior Catalytic Activity.

Metallic Co4N catalysts have been considered as one of the most promising non-noble materials for heterogeneous catalysis because of their high electrical conductivity, great magnetic property, and high intrinsic activity. However, the metastable properties seriously limit their applications for heterogeneous water phase catalysis. In this work, a novel Co-metal-organic framework (MOF)-derived hollow porous nanocages (PNCs) composed of metallic Co4N and N-doped carbon (NC) were synthesized for the first time. This hollow three-dimensional (3D) PNC catalyst was synthesized by taking advantage of Co-MOF as a precursor for fabricating 3D hollow Co3O4@C PNCs, along with the NH3 treatment of Co-oxide frames to promote the in situ conversion of Co-MOF to Co4N@NC PNCs, benefiting from the high intrinsic activity and electron conductivity of the metallic Co4N phase and the good permeability of the hollow porous nanostructure as well as the efficient doping of N into the carbon layer. Besides, the covalent bridge between the active Co4N surface and PNC shells also provides facile pathways for electron and mass transport. The obtained Co4N@NC PNCs exhibit excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy (Ea = 23.53 kJ mol-1), high turnover frequency (52.01 × 1020 molecule g-1 min-1), and high apparent rate constant (kapp = 2.106 min-1). Furthermore, its magnetic property and stable configuration account for the excellent recyclability of the catalyst. It is hoped that our finding could pave the way for the construction of other hollow transition metal-based nitride@NC PNC catalysts for wide applications.

Heterometallic metal-organic framework-templated synthesis of porous Co3O4/ZnO nanocage catalysts for the carbonylation of glycerol

The efficient synthesis of glycerol carbonate (GLC) has recently received great attention due to its significance in reducing excess glycerol in biodiesel production as well as its promising applications in several industrial fields. However, the achievement of high conversion and high selectivity of GLC from glycerol in heterogeneous catalytic processes remains a challenge due to the absence of high-performance solid catalysts. Herein, highly porous nanocage catalysts composed of well-mixed Co3O4 and ZnO nanocrystals were successfully fabricated via a facile heterometallic metal-organic framework (MOF)-templated synthetic route. Benefiting from a high porosity and the synergistic effect between Co3O4 and ZnO, the as-prepared composite catalysts exhibited a significantly enhanced production efficiency of GLC in the carbonylation reaction of glycerol with urea compared to the single-component counterparts. The yield of GLC over the Co50Zn50-350 catalyst reached 85.2%, with 93.3% conversion and near 91% GLC selectivity, and this catalytic performance was superior to that over most heterogeneous catalysts. More importantly, the proposed templated synthetic strategy of heterometallic MOFs facilitates the regulation of catalyst composition and surface structure and can therefore be potentially extended in the tailoring of other metal oxide composite catalysts.

Fabrication of High-Performance All-Solid-State Asymmetric Supercapacitors Based on Stable α-MnO2@NiCo2O4 Core–Shell Heterostructure and 3D-Nanocage N-Doped Porous Carbon

A stable α-MnO2 nanowire@NiCo2O4 nanosheet core–shell heterostructure and a 3D-nanocage N-doped porous carbon nanosheet with high electrical conductivity are synthesized by a two-solution phase reaction and a facile one-step self-template technique, respectively. The unique α-MnO2@NiCo2O4 heterostructure is characterized by a stable nanostructure, fast electron transport, and numerous ion diffusion channels. The electrode exhibits a high specific capacitance of 1101 F g–1, and a cycling stability of 95.8% after 10 000 cycles. Moreover, by introducing N atoms which is favorable for rate performance, the 3D porous carbon offers a large surface area, a proper pore structure and especially high electron conductivity. The specific capacitance of the 3D N-doped porous nanocage carbon electrode reaches 100 F g–1 at a current densities as high as 100 A g–1. The all-solid-state symmetric supercapacitor with excellent electrochemical properties is fabricated using the α-MnO2@NiCo2O4 core–shell heterostructure as positive electrode, a 3D N-doped porous nanocage carbon as negative electrode, and a PAAK/KOH gel as solid-state electrolyte. The supercapacitor demonstrates an expanded working potential of 1.7 V, a maximum energy density of 46.2 Wh kg–1, a maximum power density of 15.3 kW kg–1, and good capacitance retention of 90% after 2000 cycles.

Synthesis of ultrafine titania nano-cages by pulsed laser ablation of Ti/Al alloy in ammonium hydroxide

A simple and versatile strategy is designed to successfully fabricate ultrafine TiO2 nano-cages based on the rapid decomposition reaction between amphoteric hydroxide and ammonia solution by pulsed laser ablation of Ti/Al alloy in liquid. With the ammonia concentration (Vammonia:Vwater, where V is volume) increasing from 1:10 to 1:4, the diameter and shell thickness of quasi-spherical TiO2 nano-cages substantially decrease from 300 and 60 nm to 9.2 and 2.8 nm, respectively. The obtained results have significant implications for obtaining insight into the properties of the TiO2 porous nano-cages, offering the basis for further fabrication of other nano-cages.

MxCo3−xO4 (M = Co, Mn, Fe) porous nanocages derived from metal–organic frameworks as efficient water oxidation catalysts

MxCo3−xO4 (M = Co, Mn, Fe) porous nanocages derived from metal–organic frameworks showed efficient photochemical, chemical-driven (cerium(iv)-driven) and electrochemical water oxidation activity.

Zinc oxide porous nano-cages fabricated by laser ablation of Zn in ammonium hydroxide.

We report the successful synthesis of ZnO porous nano-cages with controllable hollow spaces by simply using laser ablation of Zn target in liquid medium containing deionized water and ammonia (V(water):V(ammonia) = 7:1~5:1). In addition to the porous surface, the created interior space of the ZnO nano-cage substantially increases with the ammonia concentration. The related growth mechanism has been illustrated based on the ultra-rapid alkaline etching process. Moreover, numerous Zn(NH3)(4)(2+) clusters generated by the selective etching route readily penetrate into the ZnO porous structures and can be embedded in these unique nano-cages. It is envisaged that these composite ions/ ZnO porous nano-cages have significant implications for gas sensing and catalytic applications. The synthetic scheme used here should also be applicable to other semiconductors.

Metal-organic framework derived Fe2O3@NiCo2O4 porous nanocages as anode materials for Li-ion batteries.

Metal-organic frameworks (MOFs) with high surface areas and uniform microporous structures have shown potential application in many fields. Here we report a facial strategy to synthesize Fe2O3@NiCo2O4 porous nanocages by annealing core-shell Co3[Fe(CN)6]2@Ni3[Co(CN)6]2 nanocubes in air. The obtained samples have been systematically characterized by XRD, SEM, TEM and N2 adsorption-desorption analysis. The results show that the Fe2O3@NiCo2O4 porous nanocages have an average diameter of 213 nm and a shell thickness of about 30 nm. As anode materials for Li-ion batteries, the Fe2O3@NiCo2O4 porous nanocages exhibit a high initial discharge capacity of 1311.4 mA h g(-1) at a current density of 100 mA g(-1) (about 0.1 C). The capacity is retained at 1079.6 mA h g(-1) after 100 cycles. The synergistic effect of the different components and the porous hollow structure contributes to the outstanding performance of the composite electrode.

Hollow/porous nanostructures derived from nanoscale metal–organic frameworks towards high performance anodes for lithium-ion batteries

Lithium-ion batteries (LIBs), owing to their high energy density, light weight, and long cycle life, have shown considerable promise for storage devices. The successful utilization of LIBs depends strongly on the preparation of nanomaterials with outstanding lithium storage properties. Recent progress has demonstrated that hollow/porous nanostructured oxides are very attractive candidates for LIBs anodes due to their high storage capacities. Here, we aim to provide an overview of nanoscale metal-organic frameworks (NMOFs)-templated synthesis of hollow/porous nanostructured oxides and their LIBs applications. By choosing some typical NMOFs as examples, we present a comprehensive summary of synthetic procedures for nanostructured oxides, such as binary, ternary and composite oxides. Hollow/porous structures are readily obtained due to volume loss and release of internally generated gas molecules during the calcination of NMOFs in air. Interestingly, the NMOFs-derived hollow/porous structures possess several special features: pores generated from gas molecules release will connect to each other, which are distinct from "dead pores"; pore size often appears to be <10 nm; in terms of surface chemistry, the pore surface is hydrophobic. These structural features are believed to be the most critical factors that determine LIBs' performance. Indeed, it has been shown that these NMOFs-derived hollow/porous oxides exhibit excellent electrochemical performance as anode materials for LIBs, including high storage capacity, good cycle stability, and so on. For example, a high charge capacity of 1465 mA h g(-1) at a rate of 300 mA g(-1) was observed after 50 cycles for NMOFs-derived Co3O4 porous nanocages, which corresponds to 94.09% of the initial capacity (1557 mA h g(-1)), indicating excellent stability. The capacity of NMOFs-derived Co3O4 is higher than that of other Co3O4 nanostructures obtained by a conventional two-step route, including nanosheets (1450 mA h g(-1) at 50 mA g(-1)), nanobelts (1400 mA h g(-1) at 40 mA g(-1)) and nanoflowers (694 mA h g(-1) at 100 mA g(-1)). The capacity is also better than Co3O4 octahedra obtained by a one-step hydrothermal method (946 mA h g(-1) at 100 mA g(-1)). In this review, we will summarize the recent research advances on NMOFs-derived hollow/porous oxides as LIBs anodes. The enhanced lithium storage properties have been discussed in relation to their special structural parameters. Moreover, remarks on the current challenges and perspectives for future NMOFs applications are proposed. Through this systematic review, we aim to stress the importance of NMOFs templates for the fabrication of hollow/porous functional materials that would result in improved physicochemical properties and provide insights to guide future research for LIBs applications.

Plasmonic modes of nanobox, nanocage, and nanoframe

The scattering, absorption, and extinction cross sections of Ag nanobox, nanocage, and nanoframe illuminated by a polarized plane wave are studied using the finite element method. Our numerical results show that the plasmon modes (dipole and quadrupole modes) of a single Ag nanocage are red-shifted as the thickness of the wall decreases. In addition, the plasmon modes of porous nanocage and nanoframe are red-shifted relative to the nanobox as the surface porosity of nanocage increases. In particular, the wavelengths at the peaks of these modes almost linearly depend on the surface porosity. Moreover, the scattering efficiency of the dipole mode is much higher than the absorption one. The former is broadband, while the latter narrowband. These modes are confirmed by their far-field scattering patterns, and the corresponding surface electric field distributions are also investigated.

ChemInform Abstract: Fabrication Based on the Kirkendall Effect of Co3O4 Porous Nanocages with Extraordinarily High Capacity for Lithium Storage.

AbstractCo3O4 porous nanocages are prepared by thermal decomposition of Co3[Co(CN)6]2 truncated nanocubes at 400 °C for 1 h in air.

Fabrication Based on the Kirkendall Effect of Co3O4 Porous Nanocages with Extraordinarily High Capacity for Lithium Storage

Herein we report a novel facile strategy for the fabrication of Co(3)O(4) porous nanocages based on the Kirkendall effect, which involves the thermal decomposition of Prussian blue analogue (PBA) Co(3)[Co(CN)(6)](2) truncated nanocubes at 400 °C. Owing to the volume loss and release of internally generated CO(2) and N(x) O(y) in the process of interdiffusion, Co(3)O(4) nanocages with porous shells and containing nanoparticles were finally obtained. When evaluated as electrode materials for lithium-ion batteries, the as-prepared Co(3)O(4) porous nanocages displayed superior battery performance. Most importantly, capacities of up to 1465 mA h g(-1) are attained after 50 cycles at a current density of 300 mA g(-1). Moreover, this simple synthetic strategy is potentially competitive for scaling-up industrial production.

Controllable Pt/ZnO Porous Nanocages with Improved Photocatalytic Activity

Composite Pt/ZnO porous nanocages with ultrathin porous ZnO shell layers and ultrafine embedded Pt nanoparticles were facilely fabricated by ultrasonic irradiation-assisted two-step etching of Zn/ZnO core/shell nanoparticle colloids. The Pt cluster size can be well adjusted by the applied ultrasonic power. These Pt/ZnO nanocages exhibit excellent photocatalytic performance and can be further improved by the control of the embedded noble metal nanoparticles, which can be attributed to the abundant nanoscale Schottky contacts in the Pt−ZnO metal−semiconductor interfaces as well as to the large specific surface area due to the unique porous structure. The selective etching route used here could be of considerable universality for fabrication of a series of noble metal/oxide porous nanostructures as photocatalysts, such as the (Au, Ag, Pt, Pd)/(ZnO, TiO2) system.