3D Hollow Research Articles

Excellent microwave response derived from the construction of dielectric-loss 1D nanostructure

Increasing efforts have recently been devoted to the artificial design and function of nanostructures for their application prospects in catalysis, drug delivery, energy storage, and microwave absorption. With the advantages of natural abundance, low cost, and environment friendliness, a one-dimensional (1D) MnO2 nanowire (MW) is the representative dielectric-loss absorber for its special morphology and crystalline structure. However, its low reflection loss (RL) value due to its thin thickness limits its wide development and application in the microwave absorption field. In this work, artificially designed MnO2@AIR@C (MCs), namely, 1D hollow carbon nanotubes filled with nano-MnO2, were designed and synthesized. It is found that the RL value of the MC is almost lower than −10 dB. Furthermore, the RL value was able to achieve −18.9 dB with an effective bandwidth (−10 dB) of 5.84 GHz at 2.25 mm. Simultaneously, the dielectric and interfacial polarization became stronger while the impedance matching was much better than in the single MWs. Hence, the rational design and fabrication of micro-architecture are essential and MC has great potential to be an outstanding microwave absorber.

Self-template synthesis of nickel silicate and nickel silicate/nickel composite nanotubes and their applications in wastewater treatment

Hierarchical one-dimensional (1D) hollow nanostructures have attracted intense research attention due to their unique structures that may be capable of many promising applications. Here, we report a facile and effective strategy to prepare nickel silicate nanotubes (NiSNTs). Using this approach, mesoporous SiO2 nanorods served as sacrificial templates for a simple hydrothermal process to prepare NiSNTs via a self-template route. The obtained NiSNTs preserve the tubular hierarchical morphology and hollow interior structures, which confer the NiSNTs with high surface areas and large pore volumes. These features point to NiSNTs as superior candidates for efficiently adsorbing heavy metal ions and organic dyes in wastewater. Moreover, NiSNTs can also serve as both supports and nickel sources, forming nickel silicate/nickel nanocomposite tubes (NiSNTs/Ni) via in situ reduction of NiSNTs under hydrothermal conditions. The addition of nickel precursors and surface pre-activation are therefore unnecessary. The NiSNTs/Ni exhibit efficient and recyclable catalytic properties when used for the reduction of 4-nitrophenol (4-NP). With a rational adaption, we believe this synthetic strategy can be extended to fabricate multifunctional one-dimensional hollow nanostructures with diverse compositions and morphologies, which may be useful for environmental protection, catalysis, energy and many other important domains.

A Living 3D In Vitro Neuronal Network Cultured inside Hollow Electrospun Microfibers.

Micro/nanofiber-based scaffolds are widely used as a physical graft for axon growth in vitro for nerve tissue engineering. In this study, the fabrication of hollow coaxial microfibers with a 3D structure for directional neuronal cell culture is reported. The coaxial microfibers with poly-ε-caprolactone (PCL) sheath and polyvinyl alcohol (PVA) mixed with PC 12 cells as core are prepared using a coaxial double cylinder based on the liquid-liquid coflowing electrospinning method. By optimizing the electrospinning conditions, uniform microfibers with an average diameter of 54.6 µm are obtained using a PCL concentration of 20% and a tip-to-collector distance of 6 cm with a voltage of 6 kV. After selectively dissolving the PVA core, pheochromocytoma 12 (PC12) cells are successfully cultured inside these fibers. It is experimentally confirmed that such 3D hollow fibers can support and guide PC12 cells to grow, proliferate, and differentiate inside the hollow fibers and form 3D-connected neuronal networks with axons extended along the hollow fibers. This implies that complex nerve connection could be constructed using the low cost and powerful liquid-liquid coflowing electrospinning method, which open the door to culture well-controlled nerve connections as in vitro models for neural tissue regeneration, brain disease models, and so on.

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.

Template-free hydrothermal synthesis of 3D hollow aggregate spherical structure WO3 nano-plates and photocatalytic properties

A new kind of 3D hollow aggregate spherical structure WO3 nano-plates was prepared via a simple hydrothermal synthesis without any template. In this paper, the effects of HNO3 addition on the preparation of WO3 powder were systematically investigated. With HNO3 concentration increasing, the product was converted from WO3(H2O)0.33 to monoclinic WO3·H2O until the reaction to complete. Meanwhile, the morphology and size of particles changed from mocro-scale spheres to nano-plates. In the WO3·H2O structure, H2O integrates the H2O molecules via hydrogen bond, while WO3 bonds with other WO3 molecules and finally form a hollow spherical structure. During subsequent drying, WO3·H2O is deprived of crystal water to become monoclinic WO3, remaining this porous spherical structure. Compared with the industry-use catalyst of Degussa P25 TiO2, the as-prepared WO3 exhibits the wonderful photocatalytic activity due to the plate-like morphology and porous structure.

Precise Molecular Sieving Architectures with Janus Pathways for Both Polar and Nonpolar Molecules.

Precise molecular sieving architectures with Janus superhighways are constructed via a molecularly engineered interfacial reaction between cyclodextrin (CD) and trimesoyl chloride (TMC). Interestingly, the CD/TMC nanofilms constructed with both hydrophobic inner cavities and hydrophilic channels exhibit exceptionally high permeances for both polar and nonpolar solvents. The precise molecular sieving functions are determined by the type of CD building blocks and the inner cavities of intrinsic 3D hollow bowls. Positron annihilation spectroscopy (PAS) confirms that a larger inner CD cavity tends to generate a larger free volume and higher microporosity. Based on the rejection ratio of various dyes, the estimated molecular weight cutoff of CD/TMC nanofilms follows the trend of α-CD/TMC (320 Da) <β-CD/TMC (400 Da) <γ-CD/TMC (550 Da), which is in strict accordance with the orders of their free volumes measured by PAS and inner cavity sizes of α-CD <β-CD <γ-CD. This kind of novel CD/TMC molecular sieving membrane with intrinsic microporosity containing tunable pore size and sharp pore-size distribution can effectively discriminate molecules with different 3D sizes.

Designing and synthesizing various nickel nitride (Ni3N) nanosheets dispersed carbon nanomaterials with different structures and porosities as the high-efficiency non-enzymatic sensors

Herein, we successfully dispersed nickel nitride nanosheets (Ni3N NSs) on various carbon matrices (i.e. graphene, macroporous carbon, carbon nanotube and hollow carbon fiber) through nitridation treatment of precursors. Characterization results demonstrated that Ni3N-PCF (hollow and porous carbon fiber) owned the 3D hollow and tubular architecture, abundant meso/macropores and large BET surface area compared with other control samples. Ni3N-PCF exhibit the best H2O2 and glucose detection abilities than another four samples because of the synergistic effect of metallic character of Ni3N, excellent electroconductibility of PCF and structural advantages of hierarchically meso/macroporous architectures. It afforded wide linear ranges (from 0.001 to 2.08 mM and 2.08–50.50 mM) and large sensitivity values (51.81 and 38.32 uA cm−2 mM−1) for H2O2 detection. Furthermore, it also displayed wide linear ranges (0.001–1.75 mM and 1.75–9.18 mM), large sensitivity values (1620.31 and 856.40 uA cm−2 mM−1) and a small response time (1.7 s) toward glucose detection. In addition, Ni3N-PCF can be used for detecting glucose concentrations in blood serums with satisfying results. Ni3N-PCF also revealed good reproducibility, good stability, and superior selectivity toward either H2O2 or glucose detection. This work opens new approach for boosting electroanalysis abilities of Ni based materials.

1D N-doped hierarchically porous hollow carbon tubes derived from a supramolecular template as metal-free electrocatalysts for a highly efficient oxygen reduction reaction

1D hollow nitrogen-doped carbon tubes (h-NCTs) were fabricated through a supramolecular template-derived approach and employed as the structure-guiding template, porogen and nitrogen source for in situ N-doping.

Hybrid NiO–CuO mesoporous nanowire array with abundant oxygen vacancies and a hollow structure as a high-performance asymmetric supercapacitor

This work presents an asymmetric supercapacitor based on advanced 3D hollow architectures of NiO–CuO mesoporous nanowires with high areal/specific capacitances and cycling stability.

Selective intracellular delivery and intracellular recordings combined in MEA biosensors.

Biological studies on in vitro cell cultures are of fundamental importance to investigate cell response to external stimuli, such as new drugs for the treatment of specific pathologies, or to study communication between electrogenic cells. Although three-dimensional (3D) nanostructures brought tremendous improvements on biosensors used for various biological in vitro studies, including drug delivery and electrical recording, there is still a lack of multifunctional capabilities that could help gain deeper insights in several bio-related research fields. In this work, the electrical recording of large cell ensembles and the intracellular delivery of few selected cells are combined on the same device by integrating microfluidic channels on the bottom of a multi-electrode array decorated with 3D hollow nanostructures. The novel platform allows the recording of intracellular-like action potentials from large ensembles of cardiomyocytes derived from human induced pluripotent stem cells (hiPSC) and from the HL-1 line, while different molecules are selectively delivered into single/few targeted cells. The proposed approach shows high potential for enabling new comprehensive studies that can relate drug effects to network level cell communication processes.

Controllable template-free hydrothermal synthesis of 3D porous CeO2 hollow nanospheres and their optical performances

The almost monodisperse three dimensional (3D) porous CeO2 hollow nanospheres with a diameter of about 200–500 nm and rough surface have been synthesized by a facile template-free hydrothermal route. It was found that each hollow spherical nanostructure is composed of numerous nubbly nano-particles with several decade nanometers in diameter as the building blocks, which are randomly assembled with lower density to form a 3D porous structure. Many characterization means have been employed to study the CeO2 hollow nanospheres, including X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman, and ultraviolet–visible spectrum. The 3D CeO2 hollow nanospheres own a cubic fluorite structure and many Ce3+ ions and oxygen vacancies exist in their surface. The morphology structure of samples, size of building blocks, and the oxygen vacancies may be the reason for the red-shifted in band gap of the 3D CeO2 hollow nanospheres.

Large-scale synthesis of lead telluride (PbTe) nanotube-based nanocomposites with tunable morphology, crystallinity and thermoelectric properties

A few millimeter-long lead telluride (PbTe) hollow nanofibers with thermoelectric properties was synthesized for the first time with high through manner via three-step sequential process of electrospinning, electrodeposition and cationic exchange reaction. As-synthesized electrospun Ag nanofibers with ultra-long aspect ratio of 10,000 were Te electrodeposited to obtain silver telluride nanotubes and underwent cationic exchange reaction in Pb(NO3)2 solution to obtain polycrystalline PbTe nanotubes with average diameter of 100 nm with 20 nm of wall thickness. Variation of the Ag-to-Pb ratio in the AgxTey-PbTe nanocomposites during the cationic exchange reaction enabled to control the thermoelectric properties of resulting 1D hollow nanofibers. The diameter of Ag nanofiber is the key factor to determine the final dimension of the PbTe nanotubes in the topotactic transformation and the content of Ag ion leads to the enhancement of thermoelectric properties in the AgxTey-PbTe nanocomposites. The synthesized 1D nanocomposite mats showed the highest value of Seebeck coefficient of 433 μV/K (at 300 K) when the remained Ag content was 30%, while the power factor reached highest to 0.567 μW/mK2 for the pure PbTe nanotubes. The enhancement of thermoelectric properties and the composite crystallinity are elucidated with relation to Ag contents in the resulting 1D nanocomposites.

Conjugated system in metal-free 1D polyaniline nanotubes/carbon nitride hollow composites with strong adsorption and enhanced visible-light photocatalytic activities

Metal-free 1D polyaniline nanotubes/carbon nitride (PNCN) hollow composites are fabricated by self-assembly chemisorption and solvent evaporation method for the first time. The results show that carbon nitride (g-C3N4) is successfully covered onto polyaniline (PANI) nanotubes. Due to similar electronic structures of nitrogen-rich materials of PANI and g-C3N4, the combination of two π-conjugated system not only benefits the separation of photogenerated charge carriers but also increases the light absorption range of g-C3N4. The compact contact of the PANI nanotubes and g-C3N4 nanosheets as well as their matched energy level is the determinant factor for interfacial heterojunction. Specially, the hollow 1D “Janus” heterojunction impels photogenerated charge pairs to separate and transfer to opposite directions in a short diffusion path, with the additional benefits of exposure of more active sites and transmission of reactants for catalytic surface reactions. As expected, PNCN composites are photoactive and exhibit enhanced photocatalytic performance under visible-light irradiation over pure g-C3N4 and PANI nanotubes. In addition, PNCN composites possess strong adsorption capacity. This versatile 1D PNCN hollow composites prepared from a cost-effective and green process have potential applications in catalysis, drug delivery system, sensors, and energy storage and conversion.

Cell Assembly in Self-foldable Multi-layered Soft Micro-rolls

Multi-layered thin films with heterogeneous mechanical properties can be spontaneously transformed to realise various three-dimensional (3D) geometries. Here, we describe micro-patterned all-polymer films called micro-rolls that we use for encapsulating, manipulating, and observing adherent cells in vitro. The micro-rolls are formed of twin-layered films consisting of two polymers with different levels of mechanical stiffness; therefore they can be fabricated by using the strain engineering and a self-folding rolling process. By controlling the strain of the films geometrically, we can achieve 3D tubular architectures with controllable diameters. Integration with a batch release of sacrificial hydrogel layers provides a high yield and the biocompatibility of the micro-rolls with any length in the release process without cytotoxicity. Thus, the multiple cells can be wrapped in individual micro-rolls and artificially reconstructed into hollow or fibre-shaped cellular 3D constructs that possess the intrinsic morphologies and functions of living tissues. This system can potentially provide 3D bio-interfaces such as those needed for reconstruction and assembly of functional tissues and implantable tissue grafts.

Hierarchical hollow MnO2 nanofibers with enhanced supercapacitor performance

One dimensional (1D) hollow nanostructures have been considered as one of the most fascinating materials for supercapacitors. Herein, the hollow MnO2 nanofibers are successfully synthesized through a two-step process, in which the electrospun carbon nanofibers acted as sacrificial template. The resulting hollow nanofibers are composed of ultrathin MnO2 nanosheets, which can offer rich electrochemical active sites for electrochemical reactions. Importantly, the open and free interspaces among these ultrathin MnO2 nanosheets can significantly enhance the utilization of the active material even at high current density. Such unique hollow nanostructure endow the hollow MnO2 nanofibers electrode better electrochemical performance with specific capacitance of 291 F/g at 1 A/g, superior rate capability of ∼73% (from 1 to 10 A/g), and excellent cycling stability of 90.9% retention after 5000 cycles, demonstrating the potential for practical application in energy storage devices.

Self-Assembled 3D Helical Hollow Superstructures with Enhanced Microwave Absorption Properties.

Helical structures at different scales endow functional materials with special optical, electrical, and magnetic properties. However, methods for constructing and regulating single-handed helicity, particularly complex 3D hierarchical structures, remain limited. In this study, co-self-assembly process combined with emulsion droplets is used to produce the various well-defined 3D hollow superstructures of conducting polyaniline (PANI) with single-handed helicity. The chirality of PANI is induced using enantiomeric r- or s-camphorsulfonic acid as a dopant; the chirality of the dopant is then transferred to the supramolecular chirality of PANI assemblies and consequently to the helicity of 3D superstructures by incorporating emulsion droplets to serve collectively as soft templates. The twisting and anisotropism of these superstructures vary with the enhancement of the supramolecular chirality and result in the transformation of their morphologies from seashell-like to spindle-like and their cavity becoming more slender than their original shape. Due to the supramolecular chirality and hierarchical characteristics of these superstructures, enhanced microwave absorption performance is observed under a filler content of as low as 20 wt%, suggesting their promising application as microwave absorbers.

3D MnO2 hollow microspheres ozone-catalysis coupled with flat-plate membrane filtration for continuous removal of organic pollutants: Efficient heterogeneous catalytic system and membrane fouling control

A heterogeneous catalytic ozonation/membrane filtration (HCOMF) system was fabricated by integrating a flat-plate polyvinylidene fluoride (PVDF) membrane module along with a slurry catalytic ozonation reactor. The performance and catalytic activity of HCOMF was evaluated for degradation of model wastewater containing bisphenol A (BPA) and humid acid (HA) under different permeation flux in long-term continuous experiments. The membrane fouling was investigated by trans-membranous pressure (TMP), membrane filtration resistance, scanning electronic microscopy (SEM), and fluorescence spectra. The results showed that HCOMF system exhibited an excellent and stable catalytic activity in long-term continuous experiments owning to integration of 3D MnO2 hollow microsphere ozone-catalysis with flat-plate membrane filtration. The TMP of HCOMF system didn’t increase significantly, and the membrane resistance Rp and Rc declined from 4% and 16% to 1% and 4%, respectively, thus, the membrane fouling of HCOMF system was mitigated compared to MF system. The mitigation of membrane fouling in HCOMF system was attributed to the increase of hydrophilicity of membrane surface and change of HA fractions.

In situ growth of ZnO nanodots on carbon hierarchical hollow spheres as high-performance electrodes for lithium-ion batteries

Metal-organic frameworks (MOFs) is an ideal class of precursors or templates to build up transition metal based composites with unique architectures and high electrochemical performance for energy storage applications. In this work, a hybrid hollow nanoarchitecture made of ultrasmall zinc oxide nanodots (less than 5 nm in diameter) and carbon with 3D ordered hollow structure have been synthesized through a simple surfactant-assisted hydrothermal method followed by thermal annealing treatment. This 3D ordered hollow structure not only offers good electronic transportation routes and ionic conductive channels, but also effectively relieves the stress and mitigates the volume variation during lithiation/delithiation process as reflected by the high cycle stability and excellent rate capability as anode materials for lithium ion batteries. Benefitting from the rational design of 3D hollow structure and the synergistic effect between the ultrasmall ZnO nanodots and carbon framework, the ZnO/C hollow structures exhibit decent electrochemical performance of lithium storage with excellent cycling stability (a reversible capacity of 919 mA h/g over 100 cycles at 100 mA/g) and enhanced rate capability (567 mA h/g at high current density of 2 A/g). In addition, it also can deliver a capacity of 741 mA h/g at 500 mA/g after 120 cycles. These results uncover a facile route for the material design for energy application.

Toward Aerogel Electrodes of Superior Rate Performance in Supercapacitors through Engineered Hollow Nanoparticles of NiCo2O4.

A biomass‐templated pathway is developed for scalable synthesis of NiCo2O4@carbon aerogel electrodes for supercapacitors, where NiCo2O4 hollow nanoparticles with an average outer diameter of 30–40 nm are conjoined by graphitic carbon forming a 3D aerogel structure. This kind of NiCo2O4 aerogel structure shows large specific surface area (167.8 m2 g−1), high specific capacitance (903.2 F g−1 at a current density of 1 A g−1), outstanding rate performance (96.2% capacity retention from 1 to 10 A g−1), and excellent cycling stability (nearly without capacitance loss after 3000 cycles at 10 A g−1). The unique structure of the 3D hollow aerogel synergistically contributes to the high performance. For instance, the 3D interconnected porous structure of the aerogel is beneficial for electrolyte ion diffusion and for shortening the electron transport pathways, and thus can improve the rate performance. The conductive carbon joint greatly enhances the specific capacity, and the hollow structure prohibits the volume changes during the charge–discharge process to significantly improve the cycling stability. This work represents a giant step toward the preparation of high‐performance commercial supercapacitors.

Study on the regulation of focal adesions and cortical actin by matrix nanotopography in 3D environment

Matrix nanotopography plays an important role in regulating cell behaviors by providing spatial as well as mechanical cues for cells to sense. It has been proposed that nanoscale topography is possible to modulate the tensions which direct the formation of cytoskeleton and the organization of the membrane receptor within the cell, which in turn regulate intracellular mechanical and biochemical signaling. With current studies on this topic being performed mainly in 2D platforms, the question on how nanotopography can influence cell bahaviors in 3D environments has yet to be addressed. In this paper, we explored this question by placing cells in 3D hollow spherical polydimethylsiloxane scaffolds. After culturing rat embryonic fibroblast cells in two kinds of scaffold, one with smooth surface and the other with numerous nano-spikes, we observed that cells in the smooth scaffold have more anchoring sites and more focal adhesions than in the etched scaffold. Moreover, we found the presence of correlation between cortical actin, the important component for supporting cell attachment, and local cell geometry.