Mesoporous Arrays Research Articles

Direct synthesis of Ti-SBA-15 in the self-generated acidic environment and its photodegradation of Rhodamine B

A series of Ti-containing SBA-15 samples were firstly prepared in the self-generated acidic condition. The samples were characterized by powder X-ray diffraction, N2-adsorption, transmission electron microscopy, inductively coupled plasma, Fourier-transform infrared spectroscopy, UV–vis diffuse reflectance spectra (UV–vis) and X-ray photoelectron spectroscopy. All the samples possessed well-ordered hexagonal arrays of mesopores and Ti ions could be incorporated into the framework of SBA-15. Catalytic performances of the obtained materials were evaluated in the photodegradation of Rhodamine B (RhB). Catalytic tests indicated that Ti-SBA-15 showed much higher photodegradation ability towards RhB than pure TiO2.

In situ observation of sintering of nickel nanoparticles during nanocasting into mesoporous silica

Hierarchically porous metals are of interest in several application fields, including heterogeneous catalysis. Here, we report the nanocasting of nickel metal into hierarchically porous SBA-15 type monoliths containing ordered arrays of mesopores. Upon removal of the silica template, nickel replicas showed no evidence of an ordered mesopore structure. TEM images and XRD measurements of the nickel–silica composite show that nickel nanoparticles larger than the silica mesopores have formed. In situ heated stage TEM measurements indicate that sintering of nickel nanoparticles occurs, which leads to rapid disruption of the silica template in vacuum. This disruption appears to occur more rapidly in vacuum than under hydrogen atmosphere.

Aligned Mesopore Arrays in GaN by Anodic Etching and Photoelectrochemical Surface Etching

Aligned mesopore arrays have many potential applications in bulk heterojunction photovoltaics, sensors, and photocatalysts. In this study, vertically aligned mesopores in n-doped GaN thin films were fabricated using an anodic etch procedure in nitric acid. The resulting porous structure remains monocrystalline and is highly conductive. After etching, a low-porosity nucleation layer was observed on the surface, and was subsequently removed with a UV-assisted anodic etch to expose the pores. Removal of the surface layer allows diffusion from the pores, suitable for sensitized photovoltaics and chemical sensors. Extremely fast etching rates of over 2 μm/s were recorded, with indication that hole transport in the epilayer was limiting the reaction rate even in highly doped samples.

Hydrothermal-synthesized mesoporous nickel oxide nanowall arrays with enhanced electrochromic application

Mesoporous NiO nanowall arrays are prepared by a facile hydrothermal synthesis method in combination with a following annealing process. The as-prepared NiO nanowalls have average diameters of ∼10nm and composed of interconnected nanoparticles ranging from 5 to 30nm. The NiO nanowall arrays show a hierarchical porous structure from mesopores of 5–20nm to macropores of 30–200nm. The electrochromic performances of the NiO nanowall arrays are characterized by means of UV–vis spectroscopy and cyclic voltammetry (CV) measurements. The mesoporous NiO nanowall arrays exhibit much better electrochromic performance with faster switching speed and higher color contrast than the dense NiO film. The mesoporous NiO nanowall arrays show a transmittance variation with 77% at 550nm, and the coloration and bleaching times are 2s and 2.5s, respectively. The improved electrochromic performances are due to the porous morphological characteristics, which provide fast ion and electron transfer resulting in fast reaction kinetics and high color contrast.

Direct growth of mesoporous MnO2 nanosheet arrays on nickel foam current collectors for high-performance pseudocapacitors

Well-defined mesoporous MnO2 nanosheet arrays have been directly grown on Ni foam current collectors using one-step electrodeposition, followed by a low-temperature thermal annealing process. The as-deposited MnO2 nanosheets are 20–25 nm thick on average and are mesoporous with a pore size ranging from 2 to 8 nm. The potential for using these MnO2 nanosheet arrays as supercapacitor electrodes has been explored by cyclic voltammetry and galvanostatic charge/discharge tests within a potential window of 0–1.0 V versus saturated calomel electrode. The cyclic voltammograms of the MnO2 nanosheet electrode show a typical pseudocapacitive behavior. The nanosheets exhibit specific capacitance of 201, 150, 122, 105 and 96 F g−1 at current densities of 1, 5, 10, 15 and 20 A g−1, respectively. Furthermore, it is found that upon cycling at 5 A g−1, the specific capacitance loses 35% of its initial value in the beginning 1800 cycles and then remains constant up to 3000 cycles, showing reasonably good cycling performance. The electrochemical impedance spectroscopy demonstrates that the equivalent series resistance and charge transfer resistance of the electrode are very low, suggesting that the nickel foam supported MnO2 nanosheet array is a promising binder-free electrode for use in pseudocapacitors.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over trimethylbenzene-assisted ordered mesoporous nickel–alumina catalyst

A trimethylbenzene (TMB)-assisted ordered mesoporous nickel–alumina catalyst (denoted as TNA) was prepared by a single-step evaporation-induced self-assembly (EISA) method, and it was applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, an ordered mesoporous nickel–alumina catalyst (denoted as NA) was also prepared by a single-step EISA method in the absence of TMB. Pore volume and average pore diameter of TNA catalyst were larger than those of NA catalyst due to structural modification caused by TMB addition in the preparation of TNA catalyst. In addition, TNA catalyst showed less ordered mesoporous array than NA catalyst. Both NA and TNA catalysts exhibited diffraction patterns corresponding to nickel aluminate phase, and they retained surface nickel aluminate phase with high stability and reducibility. Crystallite size of metallic nickel in the reduced TNA catalyst was smaller than that in the reduced NA catalyst due to strong nickel–alumina interaction of surface nickel aluminate phase over TNA catalyst. In the hydrogen production by steam reforming of LNG, TNA catalyst with small crystallite size of metallic nickel showed a better catalytic performance than NA catalyst in terms of LNG conversion and hydrogen yield. Furthermore, steam reforming reaction rather than water–gas shift reaction favorably occurred over TNA catalyst.

In situ SAXS investigation of dibromomethane adsorption in ordered mesoporous silica

A SAXS/WAXS apparatus with the aid of a specially designed sample cell capable for performing both SAXS and WAXS experiments was used for adsorption studies in nanoporous materials. The applicability of the instrument for structural investigations and its ability for adsorption experiments because of the advanced sample environment were demonstrated by carrying out in situ SAXS measurements during gas physisorption. SAXS profiles of ordered mesoporous silica were measured at selected equilibrium points alongside a dibromomethane (CH2Br2) adsorption isotherm at 293 K. SBA-15 was the adsorbent of choice because it consists of a regular 2D hexagonal array of cylindrical mesopores that gives rise to Bragg reflections in the small-angle regime. CH2Br2 was selected as a contrast-matching fluid because it has almost the same electron density as silica. We obtained high-quality data comparable to those resulting from experiments performed in synchrotron light sources which produce intense beams of x-rays and support advanced instrumentation for high-resolution diffraction and SAXS studies. The Bragg peaks of the pore lattice are clearly visible for the evacuated sample and at the early stages of the adsorption process. The intensity decrease and the elimination of the Bragg peaks for the saturated sample suggest that an almost perfect contrast matching was achieved. A model has been used for monitoring the fluid condensation and evaporation regime in SBA-15 by taking into account both the Bragg scattering and the diffuse scattering for spatially random pore filling. The results show the absence of spatial correlations between filled pores suggesting random pore filling.

Nickel foam supported mesoporous MnO2 nanosheet arrays with superior lithium storage performance

Mesoporous MnO2 nanosheet arrays have been directly grown on nickel foam current collectors and exhibited a reversible capacity as high as 1690 mA h g(-1) even after one hundred cycles at 100 mA g(-1). They also reveal good rate capability and excellent cycling stability.

A nitrogen-doped ordered mesoporous carbon nanofiber array for supercapacitors

A nitrogen-doped ordered mesoporous carbon nanofiber array was prepared by a combination of a hard-templating and a soft-templating method. The obtained N-enriched carbon material has a high surface area (1030 m2 g−1) and a large pore volume (2.35 cm3 g−1), with uniform mesopores located at 15.0 nm. The material with a nitrogen content of 6.7 wt% shows a high capacitance of 264 F g−1 in 1.0 M H2SO4 electrolyte and a good rate capability with a capacitance retention of 86% at 10 A g−1vs. 0.5 A g−1. It also delivers an excellent cycling stability without capacitance fading over 10000 cycles.

Free-standing, well-aligned ordered mesoporous carbon nanofibers on current collectors for high-power micro-supercapacitors

The mesoporous carbon nanofiber arrays that stand on carbon-gold double-layer current collectors are synthesized by self-assembly of a PS-b-PEO copolymer and resol in AAO templates for a high-power micro-supercapacitor at high current densities.

Synthesis and characterization of mesoporous CeO2 nanotube arrays

Mesoporous CeO2 nanotube arrays were fabricated by the following procedure: ZnO nanorod arrays were prepared as templates, and then the templates were in turn submerged in the NaOH solution, deionized water and the Ce(NO3)3 solution at 60°C for 20 times. After annealed at 500°C for 30min, the mesoporous polycrystalline CeO2 nanoshells covered ZnO nanorod arrays were obtained. Through HNO3 treatments, ZnO nanorods were dissolved, as a result, the mesoporous CeO2 nanotube arrays were achieved. The XPS result demonstrates that the ratio of Ce3+ ions to Ce4+ ions is about 1:2. Nitrogen adsorption–desorption experiment results give that the specific surface area is 109m2/g. By using the mesoporous CeO2 nanotubes as the electrode in the H2O2 solution, the electrochemical experiment proves that these arrays have the reduction action. The formation mechanism of mesopores in the CeO2 nanotubes and the origin of the reduction action were discussed in detail.

Synthesis of the mesoporous TiO2 array for hydroxyapatite precipitation

In this study, the preparation of mesoporous TiO2 was based on an evaporation-induced self-assembly (EISA) method that used Pluronic P123 as the structure-directing agent and TBOT as the titanium source. We added TBOT to the P123 surfactant that was dissolved in ethanol and then added HCl to this mixed solution with stirring at 25°C. Then, the thin film of sol was prepared on the Ti substrate through spin-coating. The result was allowed to be sampled in an open Petri dish as it underwent solvent evaporation at 40 RH% and 35°C for 24h, and then the samples were calcined for 1h at various temperatures from 150 to 450°C. Finally, the mesoporous TiO2 array was formed on the Ti substrate. The mesostructures of the samples were characterized by a small angle X-ray diffraction on the 13A1 beam line at the National Synchrotron Radiation Research Center (NSRRC, Taiwan). The result demonstrates that the sample prepared with a P123/TBOT mole ratio of 0.6 clearly shows a main peak at 0.2° to 0.25°, thus revealing the presence of a hexagonal phase mesostructure. The mesoporous TiO2 film calcined at various temperatures between 150 and 450°C revealed that the calcination temperature of 250°C is the optimal temperature for the ordered mesoporous TiO2 that grew on the Ti substrate. The microstructures revealed that the tubular mesopores are arrayed on the Ti substrate. In vitro bioactivity appraisement results show that apatite was formed on the coating surface after immersion in simulated body fluid (SBF) for 3weeks, which indicates that the mesoporous film has the potential for chemical bonding with bone tissue after being implanted into an animal body.

Combined macro-/mesoporous microelectrode arrays for low-noise extracellular recording of neural networks

Microelectrode arrays (MEAs) are appealing tools to probe large neural ensembles and build neural prostheses. Microelectronics microfabrication technologies now allow building high-density MEAs containing several hundreds of microelectrodes. However, several major problems become limiting factors when the size of the microelectrodes decreases. In particular, regarding recording of neural activity, the intrinsic noise level of a microelectrode dramatically increases when the size becomes small (typically below 20-μm diameter). Here, we propose to overcome this limitation using a template-based, single-scale meso- or two-scale macro-/mesoporous modification of the microelectrodes, combining the advantages of an overall small geometric surface and an active surface increased by several orders of magnitude. For this purpose, standard platinum MEAs were covered with a highly porous platinum overlayer obtained by lyotropic liquid crystal templating possibly in combination with a microsphere templating approach. These porous coatings were mechanically more robust than Pt-black coating and avoid potential toxicity issues. They had a highly increased active surface, resulting in a noise level ∼3 times smaller than that of conventional flat electrodes. This approach can thus be used to build highly dense arrays of small-size microelectrodes for sensitive neural signal detection.

Facile growth of hexagonal NiO nanoplatelet arrays assembled by mesoporous nanosheets on Ni foam towards high-performance electrochemical capacitors

In the work, we develop a novel two-step strategy to synthesize self-supported hexagonal nickel oxide nanoplatelet arrays on Ni foam: precipitating hydroxides followed by calcinating process. These nanoplatelets are composed of a multilayer of ultrathin mesoporous NiO nanosheets. The unique Ni foam-supported mesoporous NiO nanoplatelet arrays electrode promises fast ion and electron transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with large specific capacitance in the range of 1124–864Fg−1 and excellent cycling stability up to 5000 cycles, suggesting their promising application for electrochemical capacitors.

Synthesis, Characterization, and CO2 Adsorptive Behavior of Mesoporous AlOOH‐Supported Layered Hydroxides

A novel CO(2) solid sorbent was prepared by synthesizing and modifying AlOOH-supported CaAl layered double hydroxides (CaAl LDHs), which were prepared by using mesoporous alumina (γ-Al(2)O(3)) and calcium chloride (CaCl(2)) in a hydrothermal urea reaction. The nanostructured CaAl LDHs with nanosized platelets (3-30 nm) formed and dispersed inside the crystalline framework of mesoporous AlOOH (boehmite). By calcination of AlOOH-supported LDHs at 700 °C, the mesoporous CaAl metal oxides exhibited ordered hexagonal mesoporous arrays or uniform nanotubes with a large surface area of 273 m(2) g(-1) , a narrow pore size distribution of 6.2 nm, and highly crystalline frameworks. The crystal structure of the calcined mesoporous CaAl metal oxides was multiphasic, consisting of CaO/Ca(OH)(2), Al(2)O(3), and CaAlO mixed oxides. The mesoporous metal oxides were used as a solid sorbent for CO(2) adsorption at high temperatures and displayed a maximum CO(2) capture capacity (≈45 wt %) of the sorbent at 650 °C. Furthermore, it was demonstrated that the mesoporous CaAl oxides showed a more rapid adsorption rate (for 1-2 min) and longer cycle life (weight change retention: 80 % for 30 cycles) of the sorbent because of the greater surface area and increased number of activated sites in the mesostructures. A simple model for the formation mechanism of mesoporous metal oxides is tentatively proposed to account for the synergetic effect of CaAl LDHs on the adsorption of CO(2) at high temperature.

Simultaneous Measurements of Thermal Conductivity and Seebeck Coefficients of Roughened Nanowire Arrays

ABSTRACTWe report simultaneous measurements of thermal conductivity and Seebeck coefficient on array-scale silicon nanowires fabricated by metal assisted chemical etching. The measurements are conducted on the solid and the mesoporous nanowire arrays (NWAs) obtained from etching 1 ohm-cm and 0.002 ohm-cm Si substrates respectively. We demonstrate control on sidewall morphology and doping of the arrays that have an aspect ratio up to 20 and 30 % areal coverage. We employ differential frequency-domain measurements, separately on the array and the corresponding substrate to obtain the temperature drop and Seebeck voltage contribution of the nanowire array. The technique is validated by measurements on bulk silicon across the resistivity 0.002-1 ohm-cm. The Seebeck measurements reveal quenching of the phonon drag in the nanowires in comparison to the bulk in the measured temperature range of 300 K- 500 K. The Seebeck coefficient shows a ~18 % decrease in the solid NWAs and ~22 % increase in the mesoporous NWAs at room temperature. The thermal conductivity is close to Casimir limit for the solid wires while it drops to ~2.5 W/mK in the mesoporous nanowires.

Ordered mesoporous/microporous carbon sphere arrays derived from chlorination of mesoporous TiC/C composite and their application for supercapacitors

Three dimensional ordered mesoporous/microporous carbon microsphere arrays (MMCSA) were derived from chlorination of mesoporous titanium carbide/carbon composites which were prepared by a hard-templating method combined with a soft-templating self-assembly approach. The obtained carbon material has a high surface area (1464.4 m2 g−1) and a large pore volume (1.483 cm3 g−1), with mesopore size at about 8.5 nm, micropore size of 0.69 and 1.51 nm and an interconnected window size of about 60 nm. It exhibits a high capacitance of 134 F g−1 in nonaqueous electrolyte and good cycling stability with capacitance retention of 84% over 5000 cycles. The unique mesoporous structure and sphere array morphology provide a more favorable path for electrolyte penetration and transportation and lower electrode resistance to achieve promising rate capability performance, while the micropores in the mesopore walls greatly enhance the specific capacitance.

Growth of ultrathin mesoporous Co3O4 nanosheet arrays on Ni foam for high-performance electrochemical capacitors

An advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co3O4 nanosheet arrays on the Ni foam support. This unique 3D electrode manifests exceptional supercapacitive performance with ultrahigh specific capacitance at high current densities and excellent cycling stability.

Facile fabrication of CuO mesoporous nanosheet cluster array electrodes with super lithium-storage properties

A facile and low-cost approach has been developed to fabricate CuO mesoporous nanosheet cluster arrays (MNCAs) directly grown on a Cu substrate via an ammonia vapor-phase corrosion route. As integrated anodes for lithium-ion batteries without binders and conductivity agents, CuO MNCAs exhibit a high reversible capacity of 639.8 mA h g−1 after 100 cycles at 1C rate and a high-rate capability of 548.8 mA h g−1 at 10C rate. Excellent lithium-storage properties may be ascribed to the unique MNCA structure, which offers a large surface to volume ratio that favors lithium-storage, and provides a large free space to alleviate the large volume variation during the charge–discharge process. The strategy of vapor-phase corrosion is promising for use in the construction other nanoarchitectured materials for high power applications.

A hierarchically assembled mesoporous ZnO hemisphere array and hollow microspheres for photocatalytic membrane water filtration

A mesoporous ZnO hemisphere array has been prepared via a topotactic transition of Zn(4)(OH)(6)CO(3)·H(2)O (ZCHH) by chemical bath deposition. Each hemisphere is comprised of a radially oriented nanoflake shell grown on the hemispherical interior. Reaction time-dependent SEM analysis shows that the morphological formation of ZCHH involves a deposition-growth-secondary growth-redeposition procedure. Upon calcination, ZCHH readily decomposes to nanocrystalline wurtzite-phase ZnO without significant change in morphology, and the release of CO(2) and H(2)O from ZCHH creates an additional mesoporous structure in both hemispherical interior and nanoflake shell. A similar process but without using a substrate has been developed for synthesis of mesoporous ZnO hollow microspheres in powder form. Both the elaborated superstructured photocatalysts consisting of mesoporous nanoflakes have been demonstrated to exhibit excellent performances in the photocatalytic membrane filtration.