Hierarchical Porous Architecture Research Articles

In Situ Electrochemical Fabrication of Three Dimensional Hierarchical Nanoporous Copper Films and Their Electrocatalytic Performance

We reported a facile strategy to fabricate three dimensional (3D) hierarchical nanoporous Cu films via simple in-situ electrochemical alloying/dealloying approach in a choline chloride-ethylene glycol (ethaline) deep eutectic solvent (DES) containing zinc chloride. The fabrication process involved electrochemical formation of Cu-Zn surface alloys (alloying), and followed by in-situ selective etching of the active zinc element from the alloys (dealloying). Compared with those exerted from choline chloride-urea (reline) based DES, the resultant nanoporous Cu (NPC) films obtained in ethaline exhibited a hierarchical porous architecture with a tailorable channel/pore size distribution. The evolution of nanoporosity was found to be highly temperature and time dependent, suggesting a thermal activation process controlled by surface diffusion. For kinetics investigation, the surface diffusivities of self-assembled copper atoms at the hierarchical layers, and their corresponding activation energies have been evaluated. The as-prepared NPC showed a significant catalytic activity for reduction of nitrate with a linear detection range of 10–100 μM. A fairly high nitrate sensitivity of 3415 μA mM−1 cm−2 coupled with a low detection limit of 1.92 μM is achieved.

Perovskite-Type LaSrMnO Electrocatalyst with Uniform Porous Structure for an Efficient Li-O2 Battery Cathode.

Perovskite is an excellent candidate as low cost catalyst for Li-O2 cells. However, the limited porosity, which impedes molecular transport, and the inherent low electronic conductivity are the main barriers toward production of high-performance electrodes. Here, we designed a hierarchical porous flexible architecture by coating thin mesoporous yet crystalline LaSrMnO layers throughout a graphene foam to form graphene/meso-LaSrMnO sandwich-like nanosheets. In this well-designed system, the macropore between nanosheets facilitates O2 and Li(+) diffusion, the mesopore provides large surface area for electrolyte immersion and discharge products deposition, the perovskite phase catalyst decreases reactive overpotential, and the graphene serves as conductive network for electrons transport. When used as a freestanding electrode of Li-O2 cell, it shows high specific capacity, superior rate capability, and cyclic stability. Combination of mesoporous perovskites with conductive graphene networks represents an effective strategy for developing efficient electrodes in various energy storage systems.

Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect

Critical size bone defects raise great demands for efficient bone substitutes. Mimicking the hierarchical porous architecture and specific biological cues of natural bone has been considered as an effective strategy to facilitate bone regeneration. Herein, a trimodal macro/micro/nano-porous scaffold loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) was developed. With mesoporous bioactive glass (MBG) as matrix, a trimodal MBG scaffold (TMS) with enhanced compressive strength (4.28MPa, porosity of 80%) was prepared by a “viscosity controlling” and “homogeneous particle reinforcing” multi-template process. A 7.5nm, 3D cubic (Im3m) mesoporous structure was tailored for a “size-matched entrapment” of rhBMP-2 to achieve sustained release and preserved bioactivity. RhBMP-2-loaded TMS (TMS/rhBMP-2) induced excellent cell attachment, ingrowth and osteogenesis in vitro. Further in vivo ectopic bone formation and orthotopic rabbit radius critical size defect results indicated that compared to the rhBMP-2-loaded bimodal macro/micro- and macro/nano-porous scaffolds, TMS/rhBMP-2 exhibited appealing bone regeneration capacity. Particularly, in critical size defect, complete bone reconstruction with rapid medullary cavity reunion and sclerotin maturity was observed on TMS/rhBMP-2. On the basis of these results, TMS/rhBMP-2 developed here represents a promising bone substitute for clinical application and the concepts proposed in this study might provide new thoughts on development of future orthopedic biomaterials. Statement of SignificanceLimited self-regenerating capacity of human body makes the reconstruction of critical size bone defect a significant challenge. Current bone substitutes often exhibit undesirable therapeutic efficacy due to poor osteoconductivity or low osteoinductivity. Herein, TMS/rhBMP-2, an advanced mesoporous bioactive glass (MBG) scaffold with osteoconductive trimodal macro/micro/nano-porosity and osteoinductive rhBMP-2 delivery was developed. The preparative and mechanical problems of hierarchical MBG scaffold were solved without affecting its excellent biocompatibilities, and rhBMP-2 immobilization in sizematched mesopores was first explored. Combining structural and biological cues, TMS/rhBMP-2 achieved a complete regeneration with rapid medullary cavity reunion and sclerotin maturity in rabbit radius critical size defects. The design conceptions proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

Controllable synthesis of cobalt oxide nanoflakes on three-dimensional porous cobalt networks as high-performance cathode for alkaline hybrid batteries

Herein we report porous three-dimensional cobalt networks supported CoO nanoflakes by the combination of successive electro-deposition methods. The electrodeposited Co networks have average large pores of ∼5μm and all the branches are composed of interconnected nanoparticles. CoO nanoflakes with thickness of ∼15nm are uniformly coated on the Co networks forming self-supported Co/CoO composite films. The as-prepared Co/CoO composite films possess combined properties of porous structure and strong mechanical stability. As cathode for alkaline hybrid batteries, the Co/CoO composite films exhibit good electrochemical performances with high capacity of 83.5mAhg−1 at 1Ag−1 and stable high-rate cycling life (65mAhg−1 at 10Ag−1 after 15,000 cycles). The hierarchical porous architecture provides positive roles in the enhancement of electrochemical properties, including fast electronic transportation path, short diffusion of ions and high contact area between the active material and the electrolyte.

Porous Hybrid Composites of Few-Layer MoS2Nanosheets Embedded in a Carbon Matrix with an Excellent Supercapacitor Electrode Performance

Porous hierarchical architectures of few-layer MoS2 nanosheets dispersed in carbon matrix are prepared by a microwave-hydrothermal method followed by annealing treatment via using glucose as C source and structure-directing agent and (NH4 )2 MoS4 as both Mo and S sources. It is found that the morphology and size of the secondary building units (SBUs), the size and layer number of MoS2 nanosheets as well as the distribution of MoS2 nanosheets in carbon matrix, can be effectively controlled by simply adjusting the molar ratio of (NH4 )2 MoS4 to glucose, leading to the materials with a low charge-transfer resistance, many electrochemical active sites and a robust structure for an outstanding energy storage performance including a high specific capacitance (589 F g(-1) at 0.5 A g(-1) ), a good rate capability (364 F g(-1) at 20 A g(-1) ), and an excellent cycling stability (retention 104% after 2000 cycles) for application in supercapacitors. The exceptional rate capability endows the electrode with a high energy density of 72.7 Wh kg(-1) and a high power density of 12.0 kW kg(-1) simultaneously. This work presents a facile and scalable approach for synthesizing novel heterostructures of MoS2 -based electrode materials with an enhanced rate capability and cyclability for potential application in supercapacitor.

Crosslinking Graphene Oxide into Robust 3D Porous N-Doped Graphene.

3D N-doped graphene crosslinked by covalent bonds is fabricated through thermal treatment of graphene oxide with a nitrogen-contained resin. The material possesses a hierarchical porous architecture, robust mechanical stability, and abundant N-doped properties. As an electrode material for supercapacitors, this multifunctional material exhibits an unprecedented specific capacitance, high rate capability, and excellent long-term cycle stability.

Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework.

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 °C with record-high surface area (4073 m2 g–1), large pore volume (2.26 cm–3), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium–sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.

Preparation and supercapacitive performance of clew-like porous nanocarbons derived from sucrose by catalytic graphitization

Highly graphitic clew-like porous nanocarbons (GCPNs) were prepared by using sucrose and nickel acetate as the carbon source and nickel catalyst precursor, respectively. The influences of the amount of nickel acetate on the microstructure, morphology, degree of graphitization, surface area and pore texture of GCPNs were investigated by scanning and transmission electron microscopy, power X-ray diffraction, Raman spectroscopy and Brunauer-Emmett-Teller measurement, respectively. Electrochemical performance of GCPNs was studied by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy measurements in 6molL−1 KOH aqueous electrolytes. GCPNs exhibit interestingly novel clew-like nanostructures, which are composed of interconnected and curled carbon nanowires with sizes ranging from 10 to 25nm. Especially, GCPN-2 (the mass ratio of nickel acetate to porous activated carbon was 0.22) shows the largest specific surface area of 691m2g−1, the highest degree of graphitization (0.81) and the lowest equivalent series resistance (ESR) of 0.53Ω, which ensures sufficient electro-active sites and rapid charge-discharge rates. In addition, GCPN-2 exhibits the hierarchical micro-meso porous architecture which favors the fast diffusion of electrolyte ions. Consequently, GCPN-2 delivers a high specific capacitance (248Fg−1 at 0.5Ag−1), a high rate performance (210Fg−1 at 5Ag−1) and an excellent cycling stability (94.3% retention after 5000 cycles at 0.5Ag−1), demonstrating that GCPN-2 would be a promising electrode for supercapacitors.

Template growth of porous graphene microspheres on layered double oxide catalysts and their applications in lithium–sulfur batteries

The wise integration of individual two-dimensional graphene nanosheets into three-dimensional (3D) macroscopic architectures is essential for full exploration of their potential applications in electrochemical energy storage. Graphene microspheres (GMSs) with hierarchical porous architectures and high 3D electrical conductivities are highly expected to be the host carbon to accommodate sulfur cathode for lithium–sulfur batteries. Herein we reported the direct synthesis of GMSs assembled by 3D interconnected graphene with hierarchical pores by template chemical vapor deposition (CVD) on layered double oxide (LDO) microspheres. The LDO templates were derived from conformally calcined layered double hydroxide microspheres produced by spray drying. After methane-CVD, graphene was catalytically grown on LDO templates. Subsequent routine chemical etching of the LDO templates enabled as-obtained GMSs with a large diameter of ca. 11μm and a high surface area of 1275m2g−1. The GMS was employed as carbon scaffold to accommodate sulfur for rechargeable lithium–sulfur batteries. An initial areal discharge capacity of 2.67mAhcm−2 was obtained at a current density of 0.83mAcm−2 on flexible GMS paper electrode with an areal sulfur loading of 2.5mgcm−2.

MIL-100 derived nitrogen-embodied carbon shells embedded with iron nanoparticles.

The use of metal-organic frameworks (MOFs) as templates and precursors to synthesize new carbon materials with controllable morphology and pre-selected heteroatom doping holds promise for applications as efficient non-precious metal catalysts. Here, we report a facile pyrolysis pathway to convert MIL-100 into nitrogen-doped carbon shells encapsulating Fe nanoparticles in a comparative study involving multiple selected nitrogen sources. The hierarchical porous architecture, embedded Fe nanoparticles, and nitrogen decoration endow this composite with a superior oxygen reduction activity. Furthermore, the excellent durability and high methanol tolerance even outperform the commercial Pt-C catalyst.

Effects of functional groups on the structure, physicochemical and biological properties of mesoporous bioactive glass scaffolds.

Functionalization of biomaterials with specific functional groups is one of the most straightforward strategies to induce specific cell responses to biomaterials. In this study, thiol (SH) and amino (NH2) functional groups have been successfully modified on the surfaces of mesoporous bioactive glass (MBG) scaffolds to form thiol-functionalized MBG (SH-MBG) and amino-functionalized MBG (NH2-MBG) scaffolds by a post-grafting technique. The effects of the functional groups on the structure, physicochemical and biological properties of MBG scaffolds were systematically investigated. The results showed that the functionalization of MBG scaffolds did not change their structures, and the SH-MBG and NH2-MBG scaffolds still had hierarchical pore architecture (macropores of 300-500 μm and mesopores of 3.5-4 nm) and high porosity (84-86%), similar to the MBG scaffolds. Furthermore, the SH-MBG and NH2-MBG scaffolds possessed similar apatite mineralization ability and biocompatibility compared to the MBG scaffolds. Importantly, the SH-MBG and NH2-MBG scaffolds significantly stimulated adhesion, proliferation and differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs). Therefore, functionalization of MBG scaffolds with SH and NH2 functional groups would be a viable way to tailor the surface characteristics for stimulating biological responses of hBMSCs, and the functionalized MBG scaffolds would be a promising bioactive material for bone tissue engineering applications.

Fabrication of graphene foam supported carbon nanotube/polyaniline hybrids for high-performance supercapacitor applications

A large-scale, high-powered energy storage system is crucial for addressing the energy problem. The development of high-performance materials is a key issue in realizing the grid-scale applications of energy-storage devices. In this work, we describe a simple and scalable method for fabricating hybrids (graphene-pyrrole/carbon nanotube-polyaniline (GPCP)) using graphene foam as the supporting template. Graphene-pyrrole (G-Py) aerogels are prepared via a green hydrothermal route from two-dimensional materials such as graphene sheets, while a carbon nanotube/polyaniline (CNT/PANI) composite dispersion is obtained via the in situ polymerization method. The functional nanohybrid materials of GPCP can be assembled by simply dipping the prepared G-py aerogels into the CNT/PANI dispersion. The morphology of the obtained GPCP is investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which revealed that the CNT/PANI was uniformly deposited onto the surfaces of the graphene. The as-synthesized GPCP maintains its original three-dimensional hierarchical porous architecture, which favors the diffusion of the electrolyte ions into the inner region of the active materials. Such hybrid materials exhibit significant specific capacitance of up to 350 F g−1, making them promising in large-scale energy-storage device applications.

Three-dimensional hierarchical porous flower-like nickel–cobalt oxide/multi-walled carbon nanotubes nanocomposite for high-capacity supercapacitors

Three-dimensional (3D) hierarchical porous flower-like nickel–cobalt oxide/multi-walled carbon nanotubes (Ni–Co oxide/MWCNTs) nanocomposites were fabricated by a facile and template-free hydrothermal method as electrodes for high-capacity supercapacitors. The samples were characterized by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption and thermal gravimetric analysis (TGA). The electrochemical performance was investigated by cyclic voltammetry (CV), galvanostatic charge–discharge, and cycle life. It was found that Ni–Co oxide/MWCNTs nanocomposites displayed a high specific capacitance (1703Fg−1 at a discharge current density of 1Ag−1) and, additionally, an excellent cycling performance, retaining 97% of the maximum capacitance after 2000cycles at 10Ag−1. Even at a high current density (20Ag−1), the specific capacitance was still up to 1309Fg−1. This outstanding capacitive performance may be attributed to the ideal composition of the material and to its unique 3D hierarchical porous flower-like architecture.

A case study on fibrous porous SnO2 anode for robust, high-capacity lithium-ion batteries

Transition metal oxides have attracted considerable interest as promising anode materials for lithium-ion batteries (LIBs) due to their high energy densities. It is necessary, however, to resolve the foremost issue for them in terms of practical applications, relating to the large volume changes during cell operation. Herein, we report a SnO2 anode with a hierarchical fibrous porous architecture which was fabricated by electrospinning the Sn-precursor with poly(vinylpyrrolidone) and subsequent temperature-dependent pyrolysis processes, resulting in the distinctive morphology, featuring hierarchical fibrous porous structures on the microscale with numerous primary constituent nanoparticles. The porous fibres are composed of uniform polycrystalline nanoparticles (approximately 10–50nm in size) and abundant voids in close proximity to the constituent nanoparticles. By comparing with an anode containing commercial SnO2 nanopowder (with a size of <100nm), we found that the porous fibrous SnO2 anode featured superior rate capability, long-term cycling stability, and dimensional stability, which was attributed to the distinctive structural characteristics, which offered enhanced kinetics towards electrochemical reactions with lithium ions and space for alleviating the huge volume expansion during charging/discharging. These findings would pave the way for practical applications in LIBs with high capacity and long cycle life of transition metal oxide anodes that suffer from significant volume changes during cycling.

Efficient visible light photocatalytic oxidation of NO in air with band-gap tailored (BiO)2CO3–BiOI solid solutions

Abstract In order to develop efficient visible light photocatalysts for air purification, three dimensional (3D) (BiO)2CO3/BiOI (BOC/BOI) solid solutions were synthesized by a template free method at room temperature. This environment benign route could avoid high temperature and reduce the production cost. The results indicated that the as-prepared hierarchical nanocomposites samples assembled with 2D nanosheets were solid solutions. The aggregation of nanosheets led to the formation of 3D hierarchical porous architecture. For the (BiO)2(CO3)x(I2)1−x solid solution with x = 0.5, 0.75, 0.95, the samples have down-lowered valence band (VB) and up-lifted conduction band (CB) in contrast to (BiO)2CO3. Compared with (BiO)2CO3 (3.14 eV), the (BiO)2(CO3)x(I2)1−x solid solution showed narrowed band gaps from 1.89 to 2.68 eV which are suitable for visible light excitation. The 3D (BiO)2(CO3)x(I2)1−x solid solutions displayed efficient photocatalytic activity and high durability toward photo-oxidation of NO (600 ppb) in air. The large surface areas, hierarchical structure, and tailed band-gap structure contributed to the efficient photocatalytic oxidation ability of (BiO)2(CO3)x(I2)1−x solid solution. As NO has very low solubility and NO2 has a large solubility in water. A high NO to NO2 conversion ratio is beneficial for NOx removal by aqueous absorption. The photo-oxidation products can be readily and inexpensively removed by alkaline aqueous absorption. This work could provide new insights into the design, synthesis and environmental application of hierarchical nanocomposites photocatalysts.

Large-scale facile synthesis of Fe-doped SnO2porous hierarchical nanostructures and their enhanced lithium storage properties

Metal oxide porous hierarchical structures are of great significance because of their unique structure-dependent physico-chemical properties and wide applications. Herein, a flower-like Fe-doped SnO2 (Sn1−xFexO2) porous hierarchical architecture was successfully fabricated via a facile coordination polymer (CP) precursor approach. The precursor Snm[Fe(CN)6]n with a flower-like hierarchical structure composed of interconnected nanoplates was obtained by the reaction between Sn2+ and [Fe(CN)6]3− in aqueous solution at ambient temperature without using any surfactant or template. The calcination of the precursor produces a Sn1−xFexO2 hierarchical architecture without any obvious morphological deformation but with numerous mesopores in the nanoplates. The Brunauer–Emmett–Teller N2 adsorption–desorption analysis showed that the sample of Sn0.72Fe0.28O2 obtained under 350 °C calcination had a specific surface area as high as 108.57 m2 g−1 with a pore size of ca. 4 nm. When evaluated as negative electrode materials for lithium-ion batteries, the sample showed a high initial specific capacity of 1281.3 mA h g−1 at a current density of 200 mA g−1, and retained a specific capacity of 600.5 mA h g−1 at the 100th cycle. The significantly enhanced performance towards lithium storage could be attributed to the cooperation of the highly stable hierarchical architecture, porous nanoplate building blocks, and Fe-doping in the SnO2-based materials. It is believed that this facile CP precursor route can be extended to fabricate other doped metal oxide porous hierarchical structures with various functions.

Hierarchical architectures of monodisperse porous Cu microspheres: synthesis, growth mechanism, high-efficiency and recyclable catalytic performance

Novel hierarchical architectures of porous copper (Cu) microspheres assembled with nanoparticles have been successfully synthesized by ingeniously selecting the precursor and complexant through a facile wet chemical reduction method. The resultant porous Cu microspheres have a size distribution of 700 ± 50 nm and have excellent monodispersity. The synergistic effect between the precursor of slightly soluble copper hydroxide and the complexants of polyacrylic acid and ethanol amine exactly induces the generation of unique porous hierarchical architectures. The obtained porous Cu microspheres were applied to reduce and degrade different organic dyes with high concentrations (4-nitrophenol, methylene blue, and rhodamine B) in the presence of NaBH4. Compared with solid Cu particles that have the same size, these porous Cu microspheres exhibit more excellent catalytic activity due to their hierarchical structures. Moreover, the catalyst with universal applicability could be easily separated from the catalytic system and sustainedly possess high stability in recycled reactions.

Dual template synthesis and photoelectrochemical performance of 3-D hierarchical porous zinc oxide

In this work, a novel hierarchical porous ZnO is successfully synthesized through a sol–gel method, in which a kind of biological material is used as hard template, block copolymer Pluronic F127 as soft template. The phase and morphology of the products are characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results show that the as-prepared ZnO with a hierarchical porous architecture is assembled by multiple-layered porous nanosheets, of which the pore structure is highly ordered. The photocatalytic activity of the as-prepared ZnO is evaluated by photodegradation reaction of methylene blue. The photoelectrochemical (PEC) property of the hierarchical porous ZnO film is also investigated in this work.

Solvothermal-Induced 3D Macroscopic SnO2/Nitrogen-Doped Graphene Aerogels for High Capacity and Long-Life Lithium Storage

3D macroscopic tin oxide/nitrogen-doped graphene frameworks (SnO2/GN) were constructed by a novel solvothermal-induced self-assembly process, using SnO2 colloid as precursor (crystal size of 3-7 nm). Solvothermal treatment played a key role as N,N-dimethylmethanamide (DMF) acted both as reducing reagent and nitrogen source, requiring no additional nitrogen-containing precursors or post-treatment. The SnO2/GN exhibited a 3D hierarchical porous architecture with a large surface area (336 m(2)g(-1)), which not only effectively prevented the agglomeration of SnO2 but also facilitated fast ion and electron transport through 3D pathways. As a result, the optimized electrode with GN content of 44.23% exhibited superior rate capability (1126, 855, and 614 mAh g(-1) at 1000, 3000, and 6000 mA g(-1), respectively) and extraordinary prolonged cycling stability at high current densities (905 mAh g(-1) after 1000 cycles at 2000 mA g(-1)). Electrochemical impedance spectroscopy (EIS) and morphological study demonstrated the enhanced electrochemical reactivity and good structural stability of the electrode.

Mesoporous carbon nanomaterials as environmental adsorbents.

The transportation and diffusion of the guest objects or molecules in the porous carbon nanomaterials can be facilitated by reducing the pathway and resistance. The reduced pathway depends on the porous nature of carbon nanomaterials. Classification of porous carbon materials by the International Union of Pure and Applied Chemistry (IUPAC) has given a new opportunity to design the pores as per their applicability and to understand the mobility of ions, atoms, and molecules in the porous network of carbon materials and also advanced their countless applicability. However, synthesis of carbon nanomaterials with a desired porous network is still a great challenge. Although, remarkable developments have taken place in the recent years, control over the pores size and/or hierarchical porous architectures, especially in the synthesis of carbon nanospheres (CNSs) and ordered mesoporous carbon (OMCs) is still intriguing. The micro and mesoporous CNSs and OMCs have been prepared by a variety of procedures and over a wide range of compositions using various different surfactant templates and carbon precursors etc. The mechanisms of formation of micromesopore in the CNSs and OMCs are still evolving. On the other hand, the urge for adsorbents with very high adsorption capacities for removing contaminants from water is growing steadily. In this review, we address the state-of-the-art synthesis of micro and mesoporous CNSs and OMCs, giving examples of their applications for adsorptive removals of contaminants including our own research studies.