3D Porous Nanostructures Research Articles

Facile Fabrication of Ordered Multi-Tiered Hierarchical Porous Alumina Nanostructures with Multiple and Fractional Ratios of Pore Interval toward Multifunctional Nanomaterials

Conventional nanoporous anodic alumina films are composed of one-tiered pore arrays that can only render to one-dimensional (1D) nano-structures if they are used as nano-templates. Hence, three-dimensional (3D) nanoporous alumina films are desirable to dramatically increase the variety of nanostructures by template-fabrication for various potentially enhanced performances. Herein we report a facile approach to fabricate a variety of ordered multi-tiered 3D porous alumina nanostructures with multiple integer (m = 2, 3, 4, 5, 7, 9, and 10) and fractional ratios (n = 1/2 and 1/3) of the pore interval and pore diameter among different tiers on ITO/glass and Al sheets. The multi-tiered nanostructures and the pore interval ratios of the neighboring tiers can be accurately and independently controlled by a tailored multiple stepwise anodization, successively in appropriate acidic electrolytes of sulfuric, oxalic, and/or phosphoric solutions at designed voltages of 15–180 V, corresponding to the multiple or fractional ratios of pore interspacing. Moreover, the multi-tiered hierarchical nanoporous alumina films on ITO/glass substrates exhibited a lower transmittance compared with that of the single-tiered films with ordered cylindrical pores, which can be attributed to the diffusive reflection from the tier interface with different pore intervals.

Highly efficient nonprecious metal catalysts towards oxygen reduction reaction based on three-dimensional porous carbon nanostructures.

Developing a low cost, highly active, durable cathode towards an oxygen reduction reaction (ORR) is one of the high-priority research directions for commercialization of low-temperature polymer electrolyte membrane fuel cells (PEMFCs). However, the electrochemical performance of PEMFCs is still hindered by the high cost and insufficient durability of the traditional Pt-based cathode catalysts. Under these circumstances, the search for efficient alternatives to replace Pt for constructing highly efficient nonprecious metal catalysts (NPMCs) has been growing intensively and has received great interest. Combining with the compositional effects, the accurate design of NPMCs with 3D porous nanostructures plays a significant role in further enhancing ORR performance. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within the nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. In this Tutorial Review, we focus on the rational design and synthesis of different 3D porous carbon-based nanomaterials, such as heteroatom-doped carbon, metal-nitrogen-carbon nanostructures and a series of carbon/nonprecious metal-based hybrids. More importantly, their enhanced ORR performances are also demonstrated by virtue of their favorably porous morphologies and compositional effects. Finally, the future trends and perspectives for the highly efficient porous NPMCs regarding the material design are discussed, with an emphasis on substantial development of advanced carbon-based NPMCs for ORR in the near future.

Au@Pt Core–Shell Mesoporous Nanoballs and Nanoparticles as Efficient Electrocatalysts toward Formic Acid and Glucose Oxidation

By effectively bypassing the common problem of the loss of contact of platinum nanoparticles to carbon black support involved in the traditional methodology, supportless Pt, Au@Pt 3D-porous nanostructures (PtNBs and Au@PtNBs), and Aucore-Ptshell nanoparticles (Au50Pt50NPs) were synthesized. The radiolytic synthesis provides a high control on the size, morphology, and composition of the nanoparticles. Nanoballs, 85 ± 5 nm for PtNBs and 75 ± 5 nm for Au@PtNBs, are formed by 3D-interconnected nanowires leading to a giant mesoporous structure. A single Au@PtNB is formed by an ca. 30 nm Au-core, surrounded by a porous Pt-shell of 15 nm thickness made by 3D-connected nanowires of 2 nm diameter. The high catalytic activity of these nanostructures toward organic electrooxidation was highlighted in aqueous media and attributed to their particular core–shell structure. The Au@PtNBs mesoporous materials exhibit improved kinetics toward glucose electrooxidation compared to their counterpart PtNBs and are a promising ...

Self-assembled NiFe2O4/carbon nanotubes sponge for enhanced glucose biosensing application

In this work, self-assembled NiFe2O4/carbon nanotubes (CNTs) sponge was prepared by ice-templating method. The device synergized the advantageous features of both the 3D porous nanostructure and the catalytic properties of CNTs with GOx and NiFe2O4 nanoparticles. The porous network construction of the NiFe2O4/CNTs sheets offered enlarged specific surface for GOx immobilization and opened channels for facilitating the electrons transport and reactants diffusion. With the help of the abnormal-valence elements Ni and Fe, double catalysis has happened and the enhanced glucose biosensing performance has been achieved. The fabricated glucose biosensor exhibited two large linear ranges (0–3.0 and 3.2–12.4mM) and distinct sensitivities (84.1 and 24.6μAmM−1cm−2).

In-Situ Growth of Few-Layered MoS2 Nanosheets on Highly Porous Carbon Aerogel as Advanced Electrocatalysts for Hydrogen Evolution Reaction

Molybdenum disulfide-based hybrids, acting as cost-effective and acid-stable electrocatalysts for hydrogen evolution reaction (HER), have been developed fast for providing sustainable hydrogen energy in recent years. Herein, few-layered molybdenum disulfide (MoS2) nanosheets/carbon aerogel (CA) hybrids were successfully obtained through the combination of sol–gel process, aging, freeze-drying, high temperature carbonization, and solvothermal reaction. CA with highly continuous porosity and high specific surface area is used as a matrix material for construction of hierarchical MoS2/CA hybrids where few-layered MoS2 nanosheets are uniformly covered on a CA surface. In this heterostructured system, CAs not only provide three-dimensional (3D) conductive pathway for fast transportation of electrons and ions, but also offer highly active regions for the growth of MoS2, greatly preventing the aggregation of MoS2 nanosheets. Due to the rationally designed hybrids with 3D porous nanostructures, the as-prepared Mo...

Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. 3D porous architectures featured by higher specific surface areas and larger pore volumes have received great interest, which not only maximize the availability of electron transfer within nanosized electrocatalyst surface area but also provide better mass transport of reactants to the electrocatalyst. Supercritical CO2 (scCO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials. Herein, we developed the scCO2 technique to synthesize boron-doped 3D graphene and low Pt group metal-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability for the ORR, holding great promise for the development of PEMFCs.

Porous hexapod CuO nanostructures: precursor-mediated fabrication, characterization, and visible-light induced photocatalytic degradation of phenol

A facile route was developed for the preparation of porous hexapod CuO nanostructures based on a solvothermal route with subsequent calcination. The CuO nanostructures are composed of numerous nanopaticles with high porosity resulting from the thermal decomposition of the Cu2O-CNTs precursors. The obtained CuO hexapod nanostructures were evaluated for their ability for the degradation of phenol under visible-light irradiation. Comparing with commercial CuO and P25, the as-prepared CuO hexapod nanostructures exhibit superior property on the photocatalytic decomposition of phenol. It is believed that the efficient photocatalytic property is originated from their unique 3D porous nanostructures which are highly beneficial to the reagent diffusion and mass transportation.

Nickel oxide grown on carbon nanotubes/carbon fiber paper by electrodeposition as flexible electrode for high-performance supercapacitors

Carbon nanotubes (CNTs) grown on the carbon fiber paper (CFP) via chemical vapor deposition system is used as flexible substrate. NiO nanoparticles are electrodeposited onto CNTs/CFP flexible substrate by electrochemical deposition technique, which is used as a flexible electrode for supercapacitors. The NiO@CNTs/CFP electrode displays specific capacitance as high as 1317 F g−1 at a current density of 1.2 A g−1, which can preserve a capacitance retention of 90.6 % with a high current density of 9.6 A g−1. After 3000 cycles, the composite electrode can retain 90 % of initial capacitance, showing good cyclability. Meanwhile, the 3D porous nanostructure of NiO@CNTs/CFP electrode can offer a great opportunity to fabricate a high-performance flexible binder-free supercapacitor electrode, in which all of the materials could take part in the charge-storage process with their surface in direct contact with the electrolyte.

Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. Although great progress has been made on ORR catalysts in recent decades, the further development of PEMFCs is severely restrained by high-priced Pt in the cathode catalysts and the slow kinetics of the ORR. Control of nanostructures at the atomic level can precisely and effectively tune catalytic properties of materials, optimizing the structural and compositional effect and further enabling enhancement in both activity and durability. Besides, most electrochemical systems consist of porous electrode materials. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. Fabricating interconnected mesoporous arrays/superstructures is critical to achieve both high surface area and fast mass transfer. Under the circumstances, constructing novel 3D porous nanostructures with non- and low Pt group metal (PGM) nanocatalysts have received significant attention to further enhance ORR electrocatalytic performance. Supercritical CO2 (sc-CO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials, consisting of active nanocarbon and nanocrystals. Herein, we developed the sc-CO2 technique to synthesize boron-doped 3D graphene and low PGM-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability toward the ORR, holding great promise for the development of PEMFCs.

Facile synthesis, photoluminescence properties and microwave absorption enhancement of porous and hollow ZnO spheres

Three-dimensional (3D) porous ZnO nanostructures were synthesized via one-pot solvothermal treatment. The structural, morphological and spectral properties were investigated using X-ray diffraction (XRD), N2 sorption measurement, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy. It was found that the minimum reflection loss value of ZnO calcined at 500°C reached −5.62dB at 16.24GHz with the thickness of 2.5mm, which had a superior performance of microwave absorption than those uncalcined and calcined at 600°C. The possible mechanism for the formation of porous ZnO hollow spheres was proposed. The relationship of the ZnO microstructure and the microwave absorption properties was revealed via studying the dielectric loss and interference multi-reflection absorption in this paper as well. In addition, the photoluminescence results show that the uncalcined ZnO and porous hollow ZnO calcined at 500°C and 600°C show a narrow and sharp UV emission at 355.8nm and a relatively broad visible spectra emission at around 423nm.

3D porous and ultralight carbon hybrid nanostructure fabricated from carbon foam covered by monolayer of nitrogen-doped carbon nanotubes for high performance supercapacitors

3D porous and self-supported carbon hybrids are promising electrode materials for supercapacitor application attributed to their prominent properties such as binder-free electrode fabrication process, excellent electric conductivity and high power density etc. We present here a facile chemical vapor deposition method to fabricate a novel 3D flexible carbon hybrid nanostructure by growing a monolayer of nitrogen-doped carbon nanotubes on the skeleton of carbon foam (N-CNTs/CF) with Fe nanoparticle as catalyst. With such 3D porous, flexible and ultralight carbon nanostructure as binder-free electrode material, large surface area is available and fast ionic transport is facilitated. Moreover, the carbon-based network can provide excellent electronic conductivity. The electrochemical studies demonstrate that the supercapacitor constructed from the N-CNTs/CF hybrid exhibit high power density of 69.3 kW kg−1 and good stability with capacitance retention ration above 95% after cycled at 50 A g−1 for 5000 cycles. Therefore, the prepared porous N-CNTs/CF nanostructure is expected to be a type of excellent electrode material for electrical double layer capacitors.

A strategy for fabricating porous PdNi@Pt core-shell nanostructures and their enhanced activity and durability for the methanol electrooxidation.

Three-dimensionally (3D) porous morphology of nanostructures can effectively improve their electrocatalytic activity and durability for various electrochemical reactions owing to big surface area and interconnected structure. Cyanogel, a jelly-like inorganic polymer, can be used to synthesize various three-dimensionally (3D) porous alloy nanomaterials owing to its double-metal property and particular 3D backbone. Here, 3D porous PdNi@Pt core-shell nanostructures (CSNSs) are facilely synthesized by first preparing the Pd-Ni alloy networks (Pd-Ni ANWs) core via cyanogel-reduction method followed by a galvanic displacement reaction to generate the Pt-rich shell. The as-synthesized PdNi@Pt CSNSs exhibit a much improved catalytic activity and durability for the methanol oxidation reaction (MOR) in the acidic media compared to the commercial used Pt black because of their specific structural characteristics. The facile and mild method described herein is highly attractive for the synthisis of 3D porous core-shell nanostructures.

Hydrogels: Assembly of Viral Hydrogels for Three‐Dimensional Conducting Nanocomposites (Adv. Mater. 30/2014)

The cover image represents a bioengineered M13 virus (grey) that can be genetically programmed to bind pristine singlewalled nanotubes (SWNTs) (black) in a controlled fashion along the length of the virus homogeneously. These SWNTs–virus complexes are used as the basis for the formation of crosslinked hydrogel scaffolds for the design of 3D porous polyaniline nanostructures (green) which integrate SWNTs, as reported by P. T. Hammond, A. M. Belcher, and co-workers on page 5101. The templated assembly promises facile synthesis of 3D conducting nanocomposites for a myriad of applications, from sensing to energy conversion and energy storage.

Fabrication of three-dimensional graphene foam with high electrical conductivity and large adsorption capability

A three-dimensional (3D), free-standing graphene foam was prepared by plasma-enhanced chemical vapor deposition on nickel-foam. The prepared graphene foam was found to consist of few-layered vertically-aligned graphene sheets with highly graphite structure. Owing to the 3D interconnected porous nanostructures, the graphene foam exhibited a high electrical conductivity of 125 S/cm and a large surface area of 625.4 cm2/g. For practical application, we prepared the graphene foam/epoxy composites showing a maximum conductivity of 196 S/m at 2.5 vol.% filler loading, and a rather low percolation threshold of 0.18 vol.%. Furthermore, the derived graphene oxide foam exhibited an excellent absorption capability (177.6 mg/g for As(V), 399.3 mg/g for Pb(II)) and recyclability (above 90% removal efficiency after five cycles) for the removal of heavy metal ions. The present study reveals that the multifunctional graphene foam may broaden the graphene-based materials for the applications in electrically conductive composites and environmental cleanup.

Co@Co3O4 Core–Shell Three‐Dimensional Nano‐Network for High‐Performance Electrochemical Energy Storage

An alternative routine is presented by constructing a novel architecture, conductive metal/transition oxide (Co@Co3O4) core-shell three-dimensional nano-network (3DN) by surface oxidating Co 3DN in situ, for high-performance electrochemical capacitors. It is found that the Co@Co3O4 core-shell 3DN consists of petal-like nanosheets with thickness of <10 nm interconnected forming a 3D porous nanostructure, which preserves the original morphology of Co 3DN well. X-ray photoelectron spectroscopy by polishing the specimen layer by layer reveals that the Co@Co3O4 nano-network is core-shell-like structure. In the application of electrochemical capacitors, the electrodes exhibit a high specific capacitance of 1049 F g(-1) at scan rate of 2 mV/s with capacitance retention of ~52.05% (546 F g(-1) at scan rate of 100 mV) and relative high areal mass density of 850 F g(-1) at areal mass of 3.52 mg/cm(2). It is believed that the good electrochemical behaviors mainly originate from its extremely high specific surface area and underneath core-Co "conductive network". The high specific surface area enables more electroactive sites for efficient Faradaic redox reactions and thus enhances ion and electron diffusion. The underneath core-Co "conductive network" enables an ultrafast electron transport.

Electron diffusion in trap-contained 3D porous nanostructure: simulation and experimental investigation

Electron transport in the porous nano-structured media was investigated experimentally, and the results were examined by a random walk simulation. TiO2 nano-particles with an average diameter of about 150 nm ware prepared by sol–gel approach and spin coated on the glass substrate. Effects of porosity on the diffusion coefficient of the prepared nano-porous TiO2 were investigated by Hall measurement. Geometrically disordered nanoparticle was generated and utilized for simulations. Dependency of the diffusion coefficient on the network porosity was completely studied by assuming that the traps are placed mainly on the surface of the nanoparticles. It was shown in this study that the diffusion coefficient decreases by increasing the porosity. In this study, fabrication process was step by step simulated for the first time to compare the experimental achievements and the results of the simulation. Such comparison confirms the surface distribution of the traps in porous materials.

Nanosheet-assembled 3D nanoflowers of ruthenium oxide with superior rate performance for supercapacitor applications

Novel ruthenium oxide nanostructures are synthesized via a microwave-hydrothermal process. An electrode based on the 3D nanoflowers exhibits high specific capacitance and superior rate capability, resulting from the hierarchical 3D porous nanostructures.

Porous nitrogen-doped carbon vegetable-sponges with enhanced lithium storage performance

Porous nitrogen-doped carbon vegetable-sponges (N-DCSs) have been fabricated by chemical treatment of the Cu@C precursors using HNO3 for the first time. The obtained N-DCSs are porous three-dimensional (3D)-structure and similar to numerous agglomerated fluffy micro-vegetable-sponges. When the precursors are treated by H2SO4, carbon vegetable-sponges (CSs) without nitrogen doping are prepared. As anode materials in lithium ion batteries, the as-prepared N-DCSs show improved Li-storage capacity and cycling stability as compared with the pure CSs. They offer 870mAhg−1 at 0.5Ag−1 after 300 cycles and high reversible capacity with 910mAhg−1 at 0.2Ag−1 after cycled at different current densities, which are much higher than those of CSs. It is envisaged that the large surface area, unique 3D porous nanostructure and appropriate nitrogen doping are favorable for the superior electrochemical properties of N-DCSs.

Synthesis of reduced graphene oxide/ZnO nanorods composites on graphene coated PET flexible substrates

In this work, reduced graphene oxide (rGO)/ZnO nanorods composites were synthesized on graphene coated PET flexible substrates. Both chemical vapor deposition (CVD) graphene and reduced graphene oxide (rGO) films were prepared following by hydrothermal growth of vertical aligned ZnO nanorods. Reduced graphene sheets were then spun coated on the ZnO materials to form a three dimensional (3D) porous nanostructure. The morphologies of the ZnO/CVD graphene and ZnO/rGO were investigated by SEM, which shows that the ZnO nanorods grown on rGO are larger in diameters and have lower density compared with those grown on CVD graphene substrate. As a result of fact, the rough surface of nano-scale ZnO on rGO film allows rGO droplets to seep into the large voids of ZnO nanorods, then to form the rGO/ZnO hierarchical structure. By comparison of the different results, we conclude that rGO/ZnO 3D nanostructure is more desirable for the application of energy storage devices.

Highly Sensitive and Selective Nonenzymatic Detection of Glucose Using Three-Dimensional Porous Nickel Nanostructures

Highly sensitive and selective nonenzymatic detection of glucose has been achieved using a novel disposable electrochemical sensor based on three-dimensional (3D) porous nickel nanostructures. The enzyme-free sensor was fabricated through in situ growing porous nickel networks on a homemade screen-printed carbon electrode substrate via electrochemically reducing the Ni(2+) precursor, along with continuously liberating hydrogen bubbles. The resulting nickel-modified electrode was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), powder X-ray diffractometry (XRD), and electrochemical techniques. Cyclic voltammetric, alternating-current impedance, and amperometric methods were used to investigate the catalytic properties of the assembled sensor for glucose electro-oxidation in alkaline media. Under optimized conditions, the enzymeless sensor exhibited excellent performance for glucose analysis selectively, offering a much wider linear range (from 0.5 μM to 4 mM), an extremely low detection limit (0.07 μM, signal-to-noise ratio (S/N) of 3), and an ultrahigh sensitivity of 2.9 mA/(cm(2) mM). Importantly, favorable reproducibility and long-term performance stability were obtained thanks to the robust frameworks. Application of the proposed sensor in monitoring blood glucose was also demonstrated.