Orientation Of Mesopores Research Articles

Tuning Internal Accessibility via Nanochannel Orientation of Mesoporous Carbon Spheres for High‐Rate Potassium‐Ion Storage in Hybrid Supercapacitors

AbstractEnhancing the accessibility and utilization of active sites through mesopores in carbon anode materials is crucial for developing high‐power potassium‐ion hybrid supercapacitors (PIHCs). Here, a multiscale phase separation method combining block copolymer (BCP) microphase‐ and homopolymer (HP) macrophase‐separation is utilized to produce two model carbon materials with controlled mesopore orientation: open‐end (oe‐MCS) and closed‐end mesoporous carbon sphere (ce‐MCS). BCPs form identical cylindrical micelles, and HPs encapsulate these cylindrical micelles within spheres and control their orientations relative to the interface. This approach manipulates only the degree of mesopore openings in the MCS materials while maintaining all other factors at similar levels. Opening mesopores in carbon anode materials primarily enhances K+ adsorption capacity, reduces K+ diffusion length, and improves ion transport. Thus, oe‐MCS anode exhibits a higher specific capacity with a significant capacitive‐controlled contribution. The resulting PIHC device displays maximum energy and power densities of 103 Wh kg−1 and 12 300 W kg−1, respectively, along with capacity retention of 86.1% after 20 000 cycles at 2.0 A g−1. This study significantly advances the understanding of mesopore design to improve capacitive K+ storage in hard carbon materials, paving the way for the development of high‐power PIHCs.

Continuous Mesoporous Aluminum Oxide Film with Perpendicularly Oriented Mesopore Channels.

Mesoporous aluminum oxide (MAO) films with perpendicularly oriented cylindrical mesopores (pore diameter: ca. 10 nm) were successfully deposited on a glass substrate by a surfactant-templating approach using aluminum nitrate as an aluminum source. The perpendicular orientation of mesopores was confirmed by grazing-incidence small-angle X-ray scattering and neutron reflection experiments. The thickness of the MAO film was around 100 nm, with a surface roughness of less than 6 nm. Since the inner surface of MAO pores was positively charged, negatively charged glucose oxidase molecules could be densely loaded into the cylindrical mesopores without significant loss of enzymatic activity. The present MAO film is potentially useful as an inorganic host material for an enzyme toward the development of a biocatalytic system.

Mediating Short-Term Plasticity in an Artificial Memristive Synapse by the Orientation of Silica Mesopores.

Memristive synapses based on resistive switching are promising electronic devices that emulate the synaptic plasticity in neural systems. Short-term plasticity (STP), reflecting a temporal strengthening of the synaptic connection, allows artificial synapses to perform critical computational functions, such as fast response and information filtering. To mediate this fundamental property in memristive electronic devices, the regulation of the dynamic resistive change is necessary for an artificial synapse. Here, it is demonstrated that the orientation of mesopores in the dielectric silica layer can be used to modulate the STP of an artificial memristive synapse. The dielectric silica layer with vertical mesopores can facilitate the formation of a conductive pathway, which underlies a lower set voltage (≈1.0 V) compared to these with parallel mesopores (≈1.2 V) and dense amorphous silica (≈2.0 V). Also, the artificial memristive synapses with vertical mesopores exhibit the fastest current increase by successive voltage pulses. Finally, oriented silica mesopores are designed for varying the relaxation time of memory, and thus the successful mediation of STP is achieved. The implementation of mesoporous orientation provides a new perspective for engineering artificial synapses with multilevel learning and forgetting capability, which is essential for neuromorphic computing.

In-Situ GISAXS Investigation of Pore Orientation Effects on the Thermal Transformation Mechanism in Mesoporous Titania Thin Films

This study addresses the effects of mesopore orientation on mesostructural stability and crystallization of titania thin films during calcination based on measurements with in-situ grazing incidence small angle X-ray scattering (GISAXS). Complementary supporting information is provided by ex-situ electron microscopy. Pluronic surfactant P123 (with average structure (EO)20(PO)70(EO)20 where EO is an ethylene oxide unit and PO is a propylene oxide unit) serves as the template to synthesize titania thin films on P123-modified glass slides with 2D hexagonally close-packed cylindrical mesopores. The orientation of the pores at the top surface is controlled by sandwiching another P123-modified glass slide on top of the titania thin film to completely orient the pores orthogonal to the films in some samples. This provides the opportunity to directly observe how pore orientation affects the evolution of pore order and crystallinity during calcination. The results show that when the pores are oriented parallel to ...

Single Molecule Tracking Studies of Flow-Aligned Mesoporous Silica Monoliths: Aging-Time Dependence of Pore Order

Single molecule tracking (SMT) methods are employed to characterize the in-plane alignment and order of cylindrical mesopores in flow-aligned surfactant-templated silica monoliths prepared within glass microfluidic channels. The majority of dye molecules observed in wide-field fluorescence videos of these samples exhibit one-dimensional (1D) diffusive motions. Orthogonal regression analysis of these motions provides a measure of the mesopore orientation distribution function, which in turn is used to quantify the mesopore order via a two-dimensional orientational order parameter, <P>. Mesopore organization is explored as a function of aging time between sol preparation and filling of the microfluidic channels. Channels filled well before gelation of the sol are shown to incorporate large monodomains having average pore alignment within a few degrees of the flow direction. These monodomains extend over several millimeters and yield aging-time-independent <P> values larger than ~0.80. In contrast, channels filled near the time of sol gelation yield monoliths with misaligned pores that are also more disordered, having <P> ≈ 0.35. The SMT results are compared to those from small-angle X-ray scattering anisotropy experiments; these data are consistent across the range of samples investigated. A model describing the aging-time dependence of sol organization is presented. These studies demonstrate that well-aligned mesoporous silica monoliths can be obtained by simple flow alignment procedures but that short sol aging times are required in order to achieve optimum pore organization.

Synthesis of Silica Nanotubes with Orientation Controlled Mesopores in Porous Membranes via Interfacial Growth

Silica nanotubes with mesopores perforating the wall were synthesized on the channel surface of porous anodic alumina (PAA) or polycarbonate membranes via interfacial growth. Transmission and scanning electron microscopy characterizations indicated that the mesopore orientation can be regulated from perpendicular to the wall to circling the axis when the thickness of the silica nanotube wall increases from about 15 to 40–60 nm, without any modification of the channel surface or external forces, just by optimizing the amount of the tetraethoxysilane confined in the channels of PAA. Mesopores in the silica nanotube wall arrange hexagonally when the diameter of the silica nanotubes is larger than 200 nm.

Evaporation‐Induced Alignment of Cylindrical Mesopores in TiO2 Thin Films

Hexagonally packed cylindrical mesopores that are vertically aligned at the surface of mesoporous TiO2 thin film are formed by self‐assembly of the hydrolyzed titanium alkoxides in the presence of poly(styrene‐b‐ethylene oxide) building blocks. The mesoporous thin film exhibits a high degree of lateral ordering and thermal stability. Long‐range lateral ordering and orientation of mesopores at the TiO2 film surface arise from a strong unfavorable interaction between the polystyrene and poly(ethylene oxide) building blocks, together with the cooperative assembling between the building blocks and inorganic species in association with the directionality of solvent evaporation.

Mesoporous “core–shell” adsorbents and catalysts with controllable morphology

A simple geometrical model is applied to predict the thickness of mesoporous shells over monodisperse spherical particles. As an example, mesoporous Ti-silicate nearly monodisperse particles with the “core–shell” structure, synthesized via the one-pot procedure are considered. The unique features of the materials are orientation of mesopores perpendicularly to the surface of non-porous cores and uniformity of mesoporous shells structure and thickness. This allows considering these materials as interesting catalysts for partial oxidation of bulk organic molecules with hydrogen peroxide.

Anisotropic electronic properties of Ni nanowires in oriented mesoporous silica film

The electronic behavior of Ni nanowires in an oriented mesoporous silica thin film was reported. The hybrid film was prepared using a facile method of airflow-induced mesopore orientation from silica sol solution containing Ni2+ cation, followed by H2 reduction. Because of the confinement effect, the Ni nanowires were aligned in the oriented mesochannels, which resulted in anisotropic electronic responses. Such a property would be of great importance in the design of nanodevices for advanced photoelectric applications.

Micron-Sized Phenyl-PMO Materials with a Crystalline Wall

The preparation of pure siliceous mesoporous materials with an atomic-scale crystalline wall is an illusive task even though the mesoporous material researches flourish recently because of their various intriguing applications. Periodic mesoporous organosilica (PMO) materials are nanoporous hybrid materials containing organic and inorganic moieties on the pore wall simultaneously. Single crystal-like PMO consisted of phenyl (–C6H4–) moieties was firstly reported by Inagaki et al. However, it was claimed that very strict reaction conditions such as an alkaline condition and a narrow range of molar ratio of the reactants were mandatory to produce single crystal-like phenyl-PMO materials. This rather strict synthetic condition hampers further studies to control the particle morphology and size variation of the PMO materials with intrinsically hydrophobic interior because of the constituent phenyl moieties on the wall. For example, most phenyl-PMO derivatives were prepared via quite similar reaction conditions originally proposed by Inagaki et al. Therefore, we have been interested in finding a reliable synthetic method to fine-tune their particle size and shape suitable for various advanced applications such as controlled drug delivery system, host materials for hydrophobic biomolecule encapsulation, and robust catalyst supports. We speculated that the π...π stacking interaction between two adjacent benzene moieties of different 1,4-bis(triethoxysilyl)benzene (BTEB) precursors might be strong enough to induce the single crystalline wall structure in a variety of reaction conditions unlike the original report. Therefore, we investigated various synthetic conditions such as different reactant molar ratios and precursor concentrations to prepare phenyl-PMOs having different particle size and morphology with an aforementioned single crystalline nature of the pore wall. We were particularly interested in the size control of the particles without perturbing the crystallinity of the pore wall. Herein, we describe a preliminary result of the preparation of size-controlled phenyl-PMO material with molecularly ordered pore walls. Our attempts closely relate to the literature method of preparing shape-controlled organic-functionalized micronsize MCM-41 type of hybrid silica materials. For example, an optimized reactant molar ratio is C18TMABr:BTEB: NaOH:H2O = 1.0:1.2:6.1:5644 where C18TMABr is an octadecyltrimethylammonium bromide, CH3(CH2)17N(CH3)3Br. The low relative molar ratio of C18TMABr to water was crucial to obtain small micron-size particles. The C18TMA templates of the as-made material were easily removed by an acid extraction in ethanol solution at 60 C. TEM images of the template-removed samples are shown in Figure 1. Under the low C18TMABr concentration, the products were formed as micron-size particles (average length or diameter < 3 μm) with the parallel pore direction relative to the longitudinal axis of the particle as shown in Figure 1. The mesopore orientation of the previously reported phenylPMO materials normally exhibited a perpendicular pore direction relative to the flat surface of the thin flake. In our case, however, the low surfactant concentration as well as a short period of stirring after the addition of BTEB precursors might prevent surfactant-organosilica micelles from aggregating to form large flakes. As a result, small particles with a parallel pore orientation as well as a crystal-like wall structure have been successfully obtained. Interestingly, individual nanotube-like uniform mesochannels were clearly discerned from the TEM images of Figures 1(b) and 1(c). SEM images of Figure 1 indicate the shape of particles and their size distribution. The powder XRD pattern of the template-free material, top trace of Figure 2, exhibited higher angle diffraction peaks at 2θ = 11.70, 23.36, and 35.48 which correspond to