Hierarchical Macropores Research Articles

A novel surface-oxidized rigid carbon foam with hierarchical macro-nanoporous structure for efficient removal of malachite green and lead ion

This study developed a method to fabricate a surface-oxidized rigid carbon foam (ORCF) with hierarchical macro-nanoporous structure via KOH activation of the carbon foam with two kinds of macropores followed by HNO3 hydrothermal oxidation. The structures of the prepared ORCF were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy, and N2 adsorption-desorption analyzer. Results demonstrate that the ORCF possesses a fluffy and porous structure with rich oxygen-containing groups. There are numerous through-holes on its pore surfaces connected with two-level macropores forming hierarchical macroporous channels. Meanwhile, the ORCF remains a good bulk structure with a compression strength of 0.74 MPa at a bulk density of 0.09 g cm−3. Batch adsorption experiments for malachite green (MG) and Pb2+ were studied through the single variable method to investigate the effects of different initial conditions on its adsorption process. The ORCF has maximum adsorption capacities for MG and Pb2+ of 587.68 mg g−1 and 157.80 mg g−1 with high partition coefficients of 17.41 mg g−1 µM−1 and 14.86 mg g−1 µM−1, respectively. The experimental data are suitable for Langmuir isotherm and Pseudo-second-order kinetic models, which correspond to monolayer chemisorption. Thermodynamic analysis indicates that the adsorption process is spontaneous and endothermic. Moreover, the removal percentages of MG and Pb2+ by the ORCF could remain above 90% after five cycles, implying that the ORCF is an efficient adsorbent with good adsorption ability and cycling stability.

Effects of a hierarchical macroporous–mesoporous structure with a low porosity porous ceramic preform on mechanical properties and Si particle refinement of RBBC composites

In this study, a hierarchical macroporous–mesoporous structure B4C/C preform was prepared via gel-casting, using which the pore structure, as well as the B4C slurry stability, could be adjusted by using B4C powders with varying multimodal particle size distributions. The coarse, medium, and fine particle distributions of the B4C powders, and their effects on mechanical properties of the RBBC composites obtained by liquid Si infiltration were investigated. The results showed that the lowest B4C slurry viscosity and the densest B4C/C preform were obtained at a 6:1:3 ratio of coarse, medium, and fine particles. The Vickers hardness, fracture toughness, and flexural strength of the RBBC composites reached 21 ± 3 GPa, 4.09 ± 0.17 MPa m1/2, and 299 ± 17 MPa, respectively. Furthermore, the lowest residual Si content was 7.22 vol%, and fine residual Si phases had a toughening effect owing to their internal compressive stress.

Promoting opposite diffusion and efficient conversion of polysulfides in “Trap” FexC-Doped asymmetric porous membranes as integrated electrodes

The shuttling effect in soluble polysulfides results in a sluggish redox reaction and poor cycling performance of Li-S batteries. Herein, a flexible asymmetric porous carbon membrane doped with iron carbide (FexC) nanoparticles was designed by a facile phase-inversion method to serve as an integrated electrode for high-performance Li-S batteries, replacing the traditional Al foil current collector. The strong Li-N binding of the membranes and Fe-S chemical adsorption of FexC can trap polysulfides and promote their gradual diffusion into the porous carbon membrane on the opposite side of the electrolyte. The unique triple-layer-structured multifunctional membrane is ideal as a Li-S battery electrode. The upper spongy-like pores realize physical confinement of polysulfides and sulfur loading; the hierarchical macropores can accommodate volume strain and provide reservoirs for the opposite diffusion of polysulfides; and the dense conductive lower layer can replace Al foil as a current collector. Furthermore, the electrocatalytic effect of FexC on promoting polysulfide conversion and accelerating redox reaction kinetics ensures a smooth trapping-diffusion-conversion mechanism, which greatly suppresses the shuttle effect. The opposite diffusion and catalytic conversion of this flexible membrane is expected to have significant potential for large-scale production in practical applications.

Triple-Layered Carbon-SiO2 Composite Membrane for High Energy Density and Long Cycling Li–S Batteries

Here we report a highly scalable yet flexible triple-layer structured porous C/SiO2 membrane via a facile phase inversion method for advancing Li-sulfur battery technology. As a multifunctional current-collector-free cathode, the conductive dense layer of the C/SiO2 membrane offers hierarchical macropores as an ideal sulfur host to alleviate the volume expansion of sulfur species and facilitate ion/electrolyte transport for fast kinetics, as well as spongelike pores to enable high sulfur loading. The triple-layer structured membrane cathode enables the filling of most sulfur species in the macropores and additional loading of a thin sulfur slurry on the membrane surface, which facilitates ion/electrolyte transport with faster kinetics than the conventional S/C slurry-based cathode. Furthermore, density functional theory simulations and visual adsorption measurements confirm the critical role of the doped SiO2 nanoparticles (∼10 nm) in the asymmetric C membrane in suppressing the shuttle effect of polysulfides via chemisorption and electrocatalysis. The rationally designed C/SiO2 membrane cathodes demonstrate long-term cycling stability of 300 cycles at a high sulfur loading of 2.8 mg cm-2 with a sulfur content of ∼75%. This scalable yet flexible self-supporting cathode design presents a useful strategy for realizing practical applications of high-performance Li-S batteries.

Hierarchically Porous Composite Scaffold Composed of SBA-15 Microrods and Reduced Graphene Oxide Functionalized with Cyclodextrin for Water Purification.

Large-scale decontamination of bisphenol A (BPA) from wastewater under field conditions is an urgent need because of the harmful toxic effects of BPA on living organisms. In this study, we report the fabrication of a three-dimensional (3D) hierarchically porous composite scaffold composed of mesoporous SBA-15 silica microrods and reduced graphene oxide (rGO-CD) functionalized with β-cyclodextrin (CD) and its application for BPA separation from contaminated water. The macroporous structure was achieved by sacrificial salt leaching, and the mesoporous structure was derived from the interparticle pores between compressed SBA-15 particles and intrinsic mesopores in SBA-15. The 3D hierarchical macroporous and mesoporous architecture of the scaffold enhances mass transport without any external forces, and the rGO-CD component provides good capture sites for BPA in solution via inclusion complexation between CD and BPA. The inorganic SBA-15 component of the scaffold also allows long-term operation of filters by increasing the mechanical strength of the scaffold. The hierarchically porous SBA-15/rGO-CD composite scaffold could separate BPA from contaminated water significantly better than the scaffold without rGO-CD in both batch and filter systems. Our study indicates that the functional hierarchically porous composite scaffold can be a potential material in wastewater treatment technology.

Nanocomposites based on 3D macroporous biomass carbon with SnS2 nanosheets hierarchical structure for efficient removal of hexavalent chromium

In this study, a novel nanocomposite, carbon/SnS2 with 3D hierarchical macroporous (MCS), was successfully prepared for rapid photocatalytic treatment of hexavalent chromium (Cr(VI)). The 3D macroporous carbon (MC) can be obtained through a simple carbonization process of loofah. Since the MCS has a large specific surface area, it can provide numerous photocatalytic active sites and has excellent adsorption properties for the Cr(VI). In addition, the excellent electrical conductivity and unique hierarchical nanoarchitecture of macroporous biomass carbon could rapidly absorb the Cr(VI) from wastewater and provide electron transport tunnel for rapid charge separation/transport to suppress hole electron recombination. It is confirmed that such three dimensional photocatalytic material can quickly purify Cr(VI)-containing wastewater under mild visible light irradiation, with a efficiency of 63.2% Cr(VI) reduction within 120 mins. Besides the high visible light-driven photocatalytic activity, MCS also exhibits excellent cycling stability. In addition, the SEM images of MCS before and after photocatalytic removal of Cr(VI) indicate that the morphology of composite was perfectly maintained and no peeling-off of SnS2 was observed. More importantly, this study demonstrated that MCS can be used for practical applications due to its stability and economic availability.

Uniform hierarchical silica film with perpendicular macroporous channels and accessible ordered mesopores for biomolecule separation

Herein, we demonstrate that silica films with perpendicular macroporous channels and accessible ordered mesopores can be conveniently prepared. The hierarchical macroporous–mesoporous silica films are synthesized by using zinc oxide nanorod array as macroporous template and CTAB surfactant as mesoporous template. In basic surfactant-containing solution, ordered mesoporous silica shells homogeneously grow on the zinc oxide nanorod array. The growth of the mesostructures do not require any chemical modification for the zinc oxide nanorod, which opens a new way for preparing hierarchical silica films with perpendicular mesochannels. The prepared hierarchical macroporous–mesoporous silica films possess a uniform thickness of 2 μm, large perpendicular macropores with a length of 1.8 μm and a width of 80 nm, and accessible ordered mesopores. Separation experiment demonstrates that this macroporous–mesoporous film can effectively separate biomolecules with different sizes.

Selective separation and preconcentration of Th(iv) using organo-functionalized, hierarchically porous silica monoliths

Hierarchical macroporous–mesoporous diglycolamide-modified silica monolith used as a selective sorbent for continuous flow separation of Th(iv) from rare earth elements.

Glucose/Graphene-Based Aerogels for Gas Adsorption and Electric Double Layer Capacitors.

In this study, three-dimensional glucose/graphene-based aerogels (G/GAs) were synthesized using the hydrothermal reduction and CO2 activation method. Graphene oxide (GO) was used as a matrix, and glucose was used as a binder for the orientation of the GO morphology in an aqueous media. We determined that G/GAs exhibited narrow mesopore size distribution, a high surface area (763 m2 g−1), and hierarchical macroporous and mesoporous structures. These features contributed to G/GAs being promising adsorbents for the removal of CO2 (76.5 mg g−1 at 298 K), CH4 (16.8 mg g−1 at 298 K), and H2 (12.1 mg g−1 at 77 K). G/GAs presented excellent electrochemical performance, featuring a high specific capacitance of 305.5 F g−1 at 1 A g−1, and good cyclic stability of 98.5% retention after 10,000 consecutive charge-discharge cycles at 10 A g−1. This study provided an efficient approach for preparing graphene aerogels exhibiting hierarchical porosity for gas adsorption and supercapacitors.

Hierarchical Macro–Mesoporous Polymeric Carbon Nitride Microspheres with Narrow Bandgap for Enhanced Photocatalytic Hydrogen Production

AbstractPolymeric carbon nitride (PCN) is emerging as promising visible‐light photocatalyst but remains a challenge in greatly improving its photocatalytic activity. The superiority of multiscale porous nanostructures in mass transfer, active site exposure, solar energy harvesting, and rates of reactions are verified in achieving superior photocatalytic activity; however, hierarchical porous PCN microspheres with macropores and mesopores simultaneously are rarely reported in the literature to date. Herein hierarchical macroporous–mesoporous PCN microspheres (HM‐PCNs) are presented for highly enhanced photocatalytic hydrogen production via an in situ precursor transformation technique. Utilizing the solubility difference between cyanamide and dicyanadiamide in aqueous solution, the in situ transformation of PCN precursor from cyanamide to dicyandiamide along the wall surfaces of the hierarchical porous SiO2 microspheres can produce robust HM‐PCNs with both hierarchical macro–mesopores structure and narrow bandgap (1.88 eV). The obtained HM‐PCNs present enhanced light absorption, promoted charge separation and transfer, and thus demonstrate highly enhanced hydrogen evolution activity (4635.8 µmol h−1 g−1) by a factor of 31.7 over the pristine PCN. Ab initio calculations indicate that C atoms at the outmost positions of the pores greatly reduce the bandgap and facilitate the electron–hole separation.

Photocatalytic properties of TiO2-loaded porous silica with hierarchical macroporous and mesoporous architectures in the degradation of gaseous organic molecules

As an advanced support of TiO2 photocatalyst, mesoporous silica (MS) with hierarchical macroporous architecture (MMS) was prepared by applying templating synthesis techniques. Colloidal crystal of spherical poly(methyl methacrylate) (PMMA) particles and organic surfactant was used for construction of two types of pores with different size scales. The porous structure and state of TiO2 was investigated by various characterization techniques. Mesoporous and macroporous structure of MMS with interconnecting networks was maintained even after loading of TiO2 particles. The unique properties of macroporous structure were observed in the adsorption of acetone gas and 2-propanol gas. In comparison of TiO2-loaded MMS and MS (denoted as TiO2/MMS and TiO2/MS), TiO2/MMS showed a high adsorption rate and a large adsorbed amount in the case of 2-propanol at low and high relative pressure, respectively. However, each profile in the case of acetone was almost same in both samples. Based on the advantageous porous structure, TiO2/MMS also exhibited a good photocatalytic performance in the degradation of 2-propanol in gas phase under UV light irradiation.

The flow-through silica as the matrix to immobilize gold nanoparticles for HPLC applications

ABSTRACTIn the present study, the flow-through silica, featured with hierarchical pores, i.e., tunable mesopores and penetrable macropores, was attempted as the chromatographic stationary phase matrix to immobilize gold nanoparticles (AuNPs). It was first modified by mercapto groups (named as SiO2-SH), and then by AuNPs (named as SiO2-S-Au). Thanks to the characteristic macropores, the column backpressure of SiO2-S-Au was comparable to SiO2-SH, which effectively overcame the difficulty of high column backpressure upon the nanoparticles were introduced to the chromatographic matrix. Both the reversed-phase and hydrophilic interaction liquid chromatographic performance were observed on these two columns but with different selectivities. Hydrophobic, hydrophilic, hydrogen bond and electrostatic interactions between the SiO2-S-Au stationary phase and analytes could contribute to the retention. The SiO2-S-Au column showed excellent aqueous compatibility by “Stop-flow” test with the relative standard deviations (RSD) of analyte’s k (capacity factor) values from 0.59% to 2.88%. The reproducibility of SiO2-S-Au was acceptable with RSDs of analyte’s k values in the range of 3.13%-5.03%. In addition, compared with the SiO2-SH column, the SiO2-S-Au column had better separation performance and selectivity. The results demonstrated that the flow-through silica was a promising matrix for nanoparticles with low backpressure and different selectivities.

Immune Cell Recruitment: Mechanically Enhanced Hierarchically Porous Scaffold Composed of Mesoporous Silica for Host Immune Cell Recruitment (Adv. Healthcare Mater. 8/2017)

Recruiting immune cells (green) to subcutaneously-implanted hierarchical macroporous and mesoporous silica scaffold is described by Jaeyun Kim and co-workers in article number 1601160. The magnification of scaffold indicates that the scaffold is composed of mesoporous silica microparticles, which is releasing pro-inflammatory signals (red dot) to recruit host immune cells.

Hierarchical macroporous–mesoporous γ-alumina monolithic green bodies with high strength

Hierarchical macroporous–mesoporous alumina (HMMA) and hierarchical mesoporous alumina (HMA) monolithic green bodies were fabricated by cold isostatic pressing (CIP) of mesoporous alumina (MA) powder, which was prepared by a quick, facile and very pure synthesis route that involved exploitation of the naturally self-driven aluminum nitride powder hydrolysis. The hierarchically self-assembled, nanocrystalline, yet micron-sized MA powder exhibited a controlled porosity, a fine crystallite size, a relatively large surface area and large pore volumes. The textural characteristics of the MA powder were analyzed, while the effect of the consolidation pressure on the pore size evolution, mechanical and permeability properties of the consolidated HMMA and HMA monoliths were investigated. At the lowest CIP pressures, the HMMA monoliths possessed favorable permeability characteristics with Darcian permeability constants up to 2 × 10−15 m2, also exhibiting a low thermal conductivity (≥0.185 W/mK), sufficient flexural strength (≥6 MPa) with an accessible porosity of ≤65%, a pore volume of ≤0.69 cm3/g and a macropore opening diameter of ≤370 nm at a constant mesopore opening diameter of about 4.5 nm. Increasing the CIP pressure resulted in the shrinkage of the macropores and a consequent suppression of the permeability characteristics; however, the flexural strength of the HMA monolith CIPed at 800 MPa increased to 51 MPa, which is the highest reported strength for a dry-pressed, binderless ceramic green body with an accessible porosity of 42% and a theoretical density of 44.3%.

Mechanically Enhanced Hierarchically Porous Scaffold Composed of Mesoporous Silica for Host Immune Cell Recruitment.

Hierarchically porous materials have been of interest in many diverse fields, including catalysis, separations, and tissue engineering, because the hierarchical porosity of the materials contributes to improvements in mechanical properties, transport properties, and molecule selectivity. In this study, we, for the first time, introduce a new approach to fabricate hierarchical macroporous and mesoporous silica scaffolds based on a salt-leaching process using as-prepared mesoporous silica as a building block. The mechanical strength of the resulting inorganic 3D scaffold was significantly improved by controlling the interfaces of mesoporous silica particles, which allowed for high structural stability during in vivo implantation. Implantation of the scaffold loaded with pro-inflammatory cytokine in mesopores into mice successfully recruited a high number of host immune cells, including dendritic cells, into the macropores, which shows their potential use for immunomodulation.

Rational design of hierarchical macroporous–mesoporous magnesium silicate for highly efficient removal of organic dye and Pb2+

Magnesium silicate with a hierarchical macroporous–mesoporous nanostructure favours the mass transportation of pollutants and exhibits excellent removal performance for methylene blue and Pb2+.

Selective Adsorption of La3+ Using a Tough Alginate-Clay-Poly(n-isopropylacrylamide) Hydrogel with Hierarchical Pores and Reversible Re-Deswelling/Swelling Cycles

Rare earth elements are an important strategic resource, and it is urgent that the rare earth industry continue to explore and develop novel separation methods and technologies. Herein, we fabricated an efficient semi-IPN alginate-clay-poly(n-isopropylacrylamide) (NIPAm) hydrogel by a frozen polymerization method with the help of UV light irradiation, where alginate was employed as the main adsorption functional compound. The as-prepared hydrogel exhibits tough, sponge-like hierarchical macroporous and reversible temperature-responsive characteristics. The maximum adsorption capacity of La3+ is 182 mg/g for the hydrogel composition of 5.0% NIPAm, 4.0% clay, and 3.0% alginate. The Langmuir isotherm fits the data very well, and the adsorption follows the pseudo-second-kinetic equation. The trace of La3+ ions can be effectively separated from the coexisting metal ions. After six repeated adsorption–desorption cycles, no obvious deformation of the shape and or loss of adsorption capacity of the bulk hydrogel ...

Preparations and Characterizations of Hierarchical Macropore Activated Carbon Monolith Electrode from Rubber Wood for Supercapacitor Application

<p>Preparation of hierarchical macropore activated carbon monolith (HMACM) from rubber wood was investigated. The samples were prepared with small cutting of rubber wood in cross sectional method. The electrode preparation was started by pre-carbonization process followed by carbonization at 600 <sup>o</sup>C and physical activation process at 900<sup> o</sup>C in N<sub>2</sub> and CO<sub>2</sub> gas atmosphere, respectively. The samples then were followed by chemical activation process with combination of chemical activation agent of KOH and HNO3 solutions. The HMACMs were neutralized by immersing the samples in copious amount of water and dried the samples for 24 hours. Porosity properties were performed by N<sub>2</sub> adsorption-desorption data and morphology characterization was analyzed by scanning electron microscope (SEM) instrument. The electrochemical properties was studied by electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge at constan current methode. The SEM micrograph and adsorption-desorption data were also proved that the HMACM sample have a hierarchical macropore at the surface and crossectional section. The porosity data shown the HMACM sample have BET surface area of 331 m<sup>2</sup>/g with average pore diameter of 1.7 nm. Equivalent series resistance and optimum capacitance specific of the HMACM electrode of 0.77 Ohm and 154 F/g, respectively. In conclusion, this study showed that the preparation method would propose as a simple method of HMACM electrode preparation technique for supercapacitor applications.</p>

Preparations and Characterizations of Hierarchical Macropore Activated Carbon Monolith Electrode from Rubber Wood for Supercapacitor Application

<p>Preparation of hierarchical macropore activated carbon monolith (HMACM) from rubber wood was investigated. The samples were prepared with small cutting of rubber wood in cross sectional method. The electrode preparation was started by pre-carbonization process followed by carbonization at 600 <sup>o</sup>C and physical activation process at 900<sup> o</sup>C in N<sub>2</sub> and CO<sub>2</sub> gas atmosphere, respectively. The samples then were followed by chemical activation process with combination of chemical activation agent of KOH and HNO3 solutions. The HMACMs were neutralized by immersing the samples in copious amount of water and dried the samples for 24 hours. Porosity properties were performed by N<sub>2</sub> adsorption-desorption data and morphology characterization was analyzed by scanning electron microscope (SEM) instrument. The electrochemical properties was studied by electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge at constan current methode. The SEM micrograph and adsorption-desorption data were also proved that the HMACM sample have a hierarchical macropore at the surface and crossectional section. The porosity data shown the HMACM sample have BET surface area of 331 m<sup>2</sup>/g with average pore diameter of 1.7 nm. Equivalent series resistance and optimum capacitance specific of the HMACM electrode of 0.77 Ohm and 154 F/g, respectively. In conclusion, this study showed that the preparation method would propose as a simple method of HMACM electrode preparation technique for supercapacitor applications.</p>

A simple and effective approach to prepare injectable macroporous calcium phosphate cement for bone repair: Syringe-foaming using a viscous hydrophilic polymeric solution

In this study, we propose a simple and effective strategy to prepare injectable macroporous calcium phosphate cements (CPCs) by syringe-foaming via hydrophilic viscous polymeric solution, such as using silanized-hydroxypropyl methylcellulose (Si-HPMC) as a foaming agent. The Si-HPMC foamed CPCs demonstrate excellent handling properties such as injectability and cohesion. After hardening the foamed CPCs possess hierarchical macropores and their mechanical properties (Young’s modulus and compressive strength) are comparable to those of cancellous bone. Moreover, a preliminary in vivo study in the distal femoral sites of rabbits was conducted to evaluate the biofunctionality of this injectable macroporous CPC. The evidence of newly formed bone in the central zone of implantation site indicates the feasibility and effectiveness of this foaming strategy that will have to be optimized by further extensive animal experiments. Statement of significanceA major challenge in the design of biomaterial-based injectable bone substitutes is the development of cohesive, macroporous and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with adequate initial mechanical properties without the use of complex processing and additives. Thus, we propose a simple and effective strategy to prepare injectable macroporous CPCs through syringe-foaming using a hydrophilic viscous polymeric solution (silanized-hydroxypropyl methylcellulose, Si-HPMC) as a foaming agent, that simultaneously meets all the aforementioned aims. Evidence from our in vivo studies shows the existence of newly formed bone within the implantation site, indicating the feasibility and effectiveness of this foaming strategy, which could be used in various CPC systems using other hydrophilic viscous polymeric solutions.