Controllable Pore Diameters Research Articles

Thin film growth into the ion track structures in polyimide by atomic layer deposition

High-aspect ratio porous structures with controllable pore diameters and without a stiff substrate can be fabricated using the ion track technique. Atomic layer deposition is an ideal technique for depositing thin films and functional surfaces on complicated 3D structures due to the high conformality of the films.In this work, we studied Al2O3 and TiO2 films grown by ALD on pristine polyimide (Kapton HN) membranes as well as polyimide membranes etched in sodium hypochlorite (NaOCl) and boric acid (BO3) solution by means of RBS, PIXE, SEM-EDX and helium ion microcopy (HIM). The focus was on the first ALD growth cycles.The areal density of Al2O3 film in the 400 cycle sample was determined to be 51±3×1016at./cm2, corresponding to the thickness of 55±3nm. Furthermore, the growth per cycle was 1.4Å/cycle. The growth is highly linear from the first cycles.In the case of TiO2, the growth per cycle is clearly slower during the first 200 cycles but then it increases significantly. The growth rate based on RBS measurements is 0.24Å/cycle from 3 to 200cycles and then 0.6Å/cycle between 200 and 400cycles. The final areal density of TiO2 film after 400 cycles is 148±3×1015at./cm2 which corresponds to the thickness of 17.4±0.4nm. The modification of the polyimide surface by etching prior to the deposition did not have an effect on the Al2O3 and TiO2 growth.

Preparation and evaluation of an injectable chitosan-hyaluronic acid hydrogel for peripheral nerve regeneration

The aim of this study was to obtain the fillers in the lumen of hollow nerve conduits (NCs) to improve the microenvironment of nerve regeneration. A pH-induced injectable chitosan (CS)-hyaluronic acid (HA) hydrogel for nerve growth factor (NGF) sustained release was developed. Its properties were characterized by gelation time, FT-IR, SEM, in vitro swelling and degradation. Furthermore, the in vitro NGF release profiles and cell biocompatibility were also investigated. The experimental results show that the CS-HA aqueous solution can undergo a rapid gelation 3 minutes after its environmental pH is changed to 7.4. The CS-HA hydrogel has interconnected channels with a controllable pore diameter and with a porosity of about 80%. It has a favorable swelling behavior and can be degraded by about 70% within 8 weeks in vitro and is suitable for NGF release. The CS-HA/NGF hydrogel exhibits a lower cytotoxicity and is in favor of the adhesion and proliferation of the BMMSCs cells. It is indicated that the CS-HA/NGF will be a promising candidate for neural tissue engineering.

Preparation and characterization of injectable chitosan–hyaluronic acid hydrogels for nerve growth factor sustained release

The usage of hollow nerve conduits shows inferior recovery effect on the repair of peripheral nerve defects. In this study, a biocompatible and biodegradable pH-induced injectable chitosan–hyaluronic acid hydrogel for nerve growth factor encapsulation and sustained release was developed as the fillers in the lumen of hollow nerve conduit to reform its microenvironment for peripheral nerve regeneration. The physicochemical properties of hydrogel were characterized by gelation time, Fourier transform infrared spectroscopy, scanning electron microscopy, compressive modulus, porosity, swelling ratio, and in vitro degradation. The in vitro nerve growth factor release profiles and cell evaluation were also investigated. The results show that the structure of chitosan–hyaluronic acid hydrogel is composed of interconnected channels with a controllable pore diameter ranging from 20 to 100 µm. The hydrogel can be degraded more than 70% within 8 weeks in vitro and is available for nerve growth factor sustained release. The chitosan–hyaluronic acid/nerve growth factor hydrogel is non-toxic and suitable for adhesion and proliferation of nerve cells and capable of maintaining nerve growth factor activity. Therefore, it could be a promising intraluminal filler of nerve conduits for peripheral nerve regeneration in neural tissue engineering.

Synthesis and characterization of mesoporous hydrocracking catalysts

Mesoporous catalysts have shown great prospective for catalytic reactions due to their high surface area that aids better distribution of impregnated metal. They have been found to contain more adsorption sites and controlled pore diameter. Hydrocracking, in the presence of mesoporous catalyst is considered more efficient and higher conversion of larger molecules is observed as compared to the cracking reactions in smaller microporous cavities of traditional zeolites. In the present study, a number of silica-alumina based mesoporous catalysts are synthesized in the laboratory. The concentration and type of surfactants and quantities of silica and alumina sources are the variables studied in the preparation of catalyst supports. The supports prepared are well characterized using SEM, EDX, and N2-BET techniques. Finally, the catalysts are tested in a high pressure autoclave reactor to study the activity and selectivity of the catalysts for the hydrocracking of a model mixture of plastics comprising of LDPE, HDPE, PP, and PS.

Controlled pore size of 3D mesoporous Cu-Ce based catalysts and influence of surface textures on the CO catalytic oxidation

In this paper, 3D Cu-Ce-Ox catalysts with controllable pore diameters were rationally designed and synthesized by a facile hard-template method. By controlling the hydrothermal synthesis time, mesoporous silica KIT-6 with different pores were prepared. Then, the 3D Cu-Ce-Ox catalysts were synthesized by nano-replication technology with KIT-6 as hard template. These catalysts expressed 3D pore structure, possessed higher pore volume and large pores, and owned more surface active sites, which were helpful for CO oxidation. When the synthesis time of KIT-6 was 24 h, this catalyst showed the highest catalytic activity. The reason was due to its relatively stronger redox ability and surface activity species. More Ce3+, Cu+ and chemical adsorbed oxygen concentration was very useful in achieving the highest catalytic performance.

Nonstoichiometry-Induced Enhancement of Electrochemical Capacitance in Anodic TiO2 Nanotubes with Controlled Pore Diameter

We report the fabrication of self-organized titania (TiO2) nanotubes (TNTs) with controlled pore diameters (140–20 nm) by anodization for the application of electrochemical capacitor electrodes. The areal capacitances obtained for 140 nm TNTs as 0.23/0.13 mF cm–2 at a scan rate of 1/5 mV s–1 and it is enhanced to 5.5/2.9 mF cm–2 (at the same scan rates) by controlling the pore diameter to 20 nm. In this study, role of pore diameter in the capacitance behavior of TNTs is explained on the basis of effective surface area and presence of oxygen vacancies/titanium interstitials. With a decrease in the pore diameter, the surface area-to-volume ratio (and hence, active surface sites) increases, which leads to greater dissociation of Ti4+ into Ti3+ under high temperature annealing and thus brings more nonstoichiometric defects like Ti3+ interstitials and oxygen deficiency within the lower dimensional TNTs. This manifests higher charge conductivity and greater electrochemical performance of TNTs with lower diamete...

A Facile Synthesis of Mesoporous Sulfonated Carbon and Its Structural Properties.

Mesoporous sulfonated carbons (SC) have been synthesized using tetraethyl orthosilicate (TEOS) as a silica source and sucrose as carbon source. The synthesized SC samples were carbonized in N₂flow at various high temperatures and then passing high purity air at room temperature. In this study, we extended the idea to deposit more oxygen functional groups into the surface of SC being high micropores for the favorable adsorption applications. The resulting materials were characterized by using XRD, BET surface area, TPD, TEM, TGA and FTIR techniques. Mesoporous SC materials with controllable pore diameters are expected to be significant to future research concerning the improvement of catalysis, supercapacitors, fuel cells and adsorption.

Highly ordered mesoporous silica loaded with dodecylamine for smart anticorrosion coatings

Abstract The development of nanoscience and technology has devoted significant attention to studies on hollow particles. Among these materials, mesoporous silica nanoparticles have recently attracted attention as potential nanocontainers due to their high stability, biocompatibility, large surface area, controllable pore diameter and easy surface functionalization. Mesoporous silica nanoparticles can uptake, store and release organic or inorganic molecules of various sizes, shapes and functionalities. The aim of this work is to study the use of mesoporous silica with hexagonally ordered (4–14 nm) for active corrosion protection of carbon steel. Mesoporous silica was characterized by X-ray diffraction (XRD), nitrogen adsorption isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mesoporous silica structures were loaded with dodecylamine and embedded into an alkyd primer with a weight load ratio of 15 wt.% of mesoporous silica. Kinetics of the release of inhibitor was evaluated by electrochemical impedance measurements in aerated 0.1 mol/L NaCl solution containing 1 wt.% of mesoporous silica at different pH values (2.0, 6.2 and 9.0). The anticorrosive performance of carbon steel coated with alkyd primer loaded with 15 wt.% of mesoporous silica with entrapped dodecylamine was demonstrated by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). Kinetics of inhibitor releasing curves showed that for pH 2.0 condition the release of inhibitor was faster in comparison to other pH conditions (9.0 and 6.2) showing that this complex porous system provides high loading capacity and efficient inhibitor release in low pH. In addition, due to the release of inhibitor during the corrosion process, well-pronounced active anticorrosion properties and self-healing were provided and confirmed by EIS and SVET measurements. Coated samples were also evaluated in a salt spray chamber and the self-healing effect was also remarkable.

Shaping quaternary assemblies of water-soluble non-peptide helical foldamers by sequence manipulation.

The design and construction of biomimetic self-assembling systems is a challenging yet potentially highly rewarding endeavour that contributes to the development of new biomaterials, catalysts, drug-delivery systems and tools for the manipulation of biological processes. Significant progress has been achieved by engineering self-assembling DNA-, protein- and peptide-based building units. However, the design of entirely new, completely non-natural folded architectures that resemble biopolymers ('foldamers') and have the ability to self-assemble into atomically precise nanostructures in aqueous conditions has proved exceptionally challenging. Here we report the modular design, formation and structural elucidation at the atomic level of a series of diverse quaternary arrangements formed by the self-assembly of short amphiphilic α-helicomimetic foldamers that bear proteinaceous side chains. We show that the final quaternary assembly can be controlled at the sequence level, which permits the programmed formation of either discrete helical bundles that contain isolated cavities or pH-responsive water-filled channels with controllable pore diameters.

Porosity Control and Transfer in Silicon Nanostructures through Electrochemical & Chemical Etching

High surface area and controlled pore diameter silicon nanostructures were prepared using a two-step etching procedure. Firstly, the experimental conditions of silicon electrochemical etching leading to the formation of high surface area porous silicon thin films were described. Thereafter, the porous silicon layers were either lifted off the substrate to collect the porous particles or subjected to metal-assisted chemical etching (MaCE) in a hydrofluoric acid - silver nitrate solution to produce high aspect ratio porous silicon nanowires with controlled pore dimensions. The consecutive electrochemical and chemical (MaCE) silicon etching procedures enabled the synthesis of porous silicon nanowires with high specific surface area (up to 460 m²/g) along with low average pore diameter (below 6.5 nm).

Biofilm formation on a TiO2 nanotube with controlled pore diameter and surface wettability

Titania (TiO2) nanotube arrays (TNAs) with different pore diameters (140 − 20 nm) are fabricated via anodization using hydrofluoric acid (HF) containing ethylene glycol (EG) by changing the HF-to-EG volume ratio and the anodization voltage. To evaluate the effects of different pore diameters of TiO2 nanotubes on bacterial biofilm formation, Shewanella oneidensis (S. oneidensis) MR-1 cells and a crystal-violet biofilm assay are used. The surface roughness and wettability of the TNA surfaces as a function of pore diameter, measured via the contact angle and AFM techniques, are correlated with the controlled biofilm formation. Biofilm formation increases with the decreasing nanotube pore diameter, and a 20 nm TiO2 nanotube shows the maximum biofilm formation. The measurements revealed that 20 nm surfaces have the least hydrophilicity with the highest surface roughness of ∼17 nm and that they show almost a 90% increase in the effective surface area relative to the 140 nm TNAs, which stimulate the cells more effectively to produce the pili to attach to the surface for more biofilm formation. The results demonstrate that bacterial cell adhesion (and hence, biofilm formation) can effectively be controlled by tuning the roughness and wettability of TNAs via controlling the pore diameters of TNA surfaces. This biofilm formation as a function of the surface properties of TNAs can be a potential candidate for both medical applications and as electrodes in microbial fuel cells.

Cylindrical and Spherical Membranes of Anodic Aluminum Oxide with Highly Ordered Conical Nanohole Arrays

Nanoporous anodic aluminum oxide (AAO) with uniform and controllable pore diameters and periods over a wide range has been explored for various applications due to relatively easy fabrication processes. Moreover, one of the interesting possibilities afforded by the anodization process is that the anodization can take place on aluminum films with arbitrary shape, such as a section of cylinder or sphere, which has not yet been well studied or applied in nanofabrication. In this paper, we report that highly ordered conical nanohole arrays prepared by the anodization of cylindrical and spherical Al films have been fabricated. As can be seen by scanning electron microscopy (SEM), straight nanohole arrays have been grown along the radical directions of the cylindrical or spherical alumina membrane without bending or branching at all, the diameter of the conical nanoholes and the diameter change along individual channels can be tuned by changing the curvature of the membrane. These new types of templates may open new opportunities in optical, electronic and electrochemical applications.

A facile synthesis of graphene-supported mesoporous TiO2 hybrid sheets with uniform coverage and controllable pore diameters

Mesoporous TiO2 has attracted extensive research interest due to its promising application in photocatalysis, but which is inevitably diminished by the electro-hole pair recombination. The incorporation of graphene into mesoporous TiO2 can improve the properties, there are however great challenges in realizing the full potential of graphene due to its poor dispersion in organic solvents and the hard nucleation of TiO2 on its surface. Herein, we present a novel and easy approach for the synthesis of two-dimensional sandwich-like graphene-supported mesoporous TiO2 hybrid sheets with tailored morphologies, uniform coverage and controllable pore diameters and surface areas, leading to improved photocatalytic performance in comparison with bare mesoporous TiO2 spheres.

Fabrication and characterization of conductive anodic aluminum oxide substrates

Biomaterials that allow the utilization of electrical, chemical and topographic cues for improved neuron–material interaction and neural regeneration hold great promise for nerve tissue engineering applications. The nature of anodic aluminum oxide (AAO) membranes intrinsically provides delicate control over topographic and chemical cues for enhanced cell interaction; however their use in nerve regeneration is still very limited. Herein, we report the fabrication and characterization of conductive AAO (CAAO) surfaces for the ultimate goal of integrating electrical cues for improved nerve tissue behavior on the nanoporous substrate material. Parafilm was used as a protecting polymer film, for the first time, in order to obtain large area (50cm2) free-standing AAO membranes. Carbon (C) was then deposited on the AAO surface via sputtering. Morphological characterization of the CAAO surfaces revealed that the pores remain open after the deposition process. The presence of C on the material surface and inside the nanopores was confirmed by XPS and EDX studies. Furthermore, I–V curves of the surface were used to extract surface resistance values and conductive AFM demonstrated that current signals can only be achieved where conductive C layer is present. Finally, novel nanoporous C films with controllable pore diameters and one dimensional (1-D) C nanostructures were obtained by the dissolution of the template AAO substrate.

Electrochemical synthesis, characterisation, and preliminary biological evaluation of an anodic aluminium oxide membrane with a pore size of 100 nanometres for a Potential Cell Culture Substrate

In this study we investigate the electrochemical synthesis and characterisation of a nanometre scale porous anodic aluminium oxide (AAO) membranes with a mean pore diameter of 100 nm. The membranes exhibit interesting properties such as controllable pore diameters, periodicity and density distribution. These properties can be preselected by adjusting the controlling parameters of a temperature controlled two-step anodization process. The surface features of the nanometre scale membrane such as pore density, pore diameter and inter-pore distance were quantified using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). A preliminary biological evaluation of the membranes was carried out to determine cell adhesion and morphology using the Cercopithecus aethiops[African green monkey – (Vero)] kidney epithelial cell line. Optical microscopy, FESEM and AFM investigations revealed the presence of focal adhesion sites over the surface of the porous membranes. The positive outcomes of the study, indicates that AAO membranes can be used as a viable tissue scaffold for potential tissue engineering applications in the future.

3D porous micro/nanostructured interconnected metal/metal oxide electrodes for high-rate lithium storage

In light of the micro/nanoporous structure concept and metal oxide-based anodes of lithium ion batteries (LIBs), a novel kind of three dimensional (3D) porous micro/nanostructured interconnected (PMNI) metal/metal oxide electrode was successfully fabricated via a facile H2 gas bubble dynamic template route. Firstly, 3D porous Ni (and Cu) was electrodeposited on the stainless steel sheet by the drastic cathodic deposition, partially thermally oxidized at a low temperature in air, and finally formed 3D PMNI Ni/NiO and Cu/Cu2O. Directly, as anodes of LIBs, 3D PMNI Ni/NiO and Cu/Cu2O exhibit a high-rate capability of 675.9 and 312.8 mA h g−1 at 20C rate, respectively. High-rate lithium storage properties may be ascribed to the fact that this kind of 3D PMNI metal/metal oxide electrode provides a stable 3D scaffold, highly conductive pathway and shorter ion diffusion length. Note that the H2 gas bubble dynamic template route in the present work is a low cost, facile one-step process of formation and elimination of the template, and offers flexibility in controllable thickness and pore diameters of 3D porous structures, assuring optimization to match the characteristic kinetics of other LIBs electrodes. The strategy may open up a new way to design and optimize 3D multifunctional architectured electrodes by using suitable micro and nano dimensional sub-components.

Nanoporous α-Alumina Membrane with High Chemical Resistance Prepared by Anodizing

not Available.

Fabrication of Highly Ordered Gold Nanorods Film Using Alumina Nanopores

A simple method for fabrication of highly ordered gold nanorod film is introduced in this article. The procedure is based on thermal evaporation of gold into a porous anodic alumina film (PAA). The PPA film was fabricated by combining the hard and mild anodization. This combination effectively decreases the processing time of fabrication of highly ordered porous anodic alumina film with controlled pore diameter and length. It was found that gold nanorods configuration affected by the porous anodic alumina film structure such as pore diameter and length. Furthermore the evaporation process change the rods diameter along the nanopores via the decreasing the pore mouth during the gold deposition.

Growth and optical absorption properties of silver nanorod arrays in porous anodic aluminum oxide templates

Silver nanorod arrays have been fabricated by alternating current (AC) and pulsed direct current (DC) electrodeposition in porous anodic aluminum oxide (AAO) templates with controlled pore diameters of 19, 38, and 65 nm, respectively. The variation of their optical absorption properties with the incident angle and the nanorods length (corresponding to the electrodeposition time) has been investigated. Optical absorption spectra show that the position of longitudinal surface plasmon resonance (LSPR) peak has a small blueshift with the increase of incident angle of the excitation light. While the aspect ratio of the nanorods increases, the position of LSPR peak first redshifts and then blueshifts to a certain wavelength. Furthermore, the position of LSPR peak can be tuned, ranging from 550 nm to 900 nm, which makes it possible to couple various wavelength of excitation source to assist radiative energy transfer to the acceptor.

Selective Crystallization of Proteins Using Engineered Nanonucleants

This study reports for the first time a detailed experimental investigation of protein crystallization in engineered nanoconfined spaces with both controlled pore diameters and narrow pore size distributions. We propose a systematic approach for controlling the nucleation and crystallization of biological macromolecules based on a relationship between the protein radius of gyration (Rg) and specific pore diameter. A series of nanonucleants with ordered mesopores having narrow pore size distributions were prepared. The templates were tested for proteins ranging in molecular weight from 14 to 450 kDa. Well-formed protein crystals were obtained on only one of the five presented nanonucleants for all protein cases tested, highlighting the unique template selectivity exhibited by these nucleants. In addition, concanavalin A and catalase were both crystallized at ∼2 times lower supersaturation levels than previously reported by any known method. Our observations fully support theoretical studies that predict the enhanced thermodynamic stability of proteins in nanoconfined cavities, including specifically the importance of nucleant pore diameter with respect to protein radius of gyration. The nucleants described here could have major industrial applications for downstream separation and purification of biopharmaceuticals, as well as improved opportunities for the crystallization of complex proteins for structural determination.