Nanoporous Substrates Research Articles

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900 °C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

Effect of Microstructure Control of Thin Film Yttria Stabilized Zirconia Electrolyte for Solid Oxide Fuel Cells by Adjusting Oblique Angle and Target Substrate Distance of Sputtering Process

In the present study, thin film yttria stabilized zirconia (YSZ) electrolyte was fabricated for solid oxide fuel cells via radio frequency (RF) magnetron sputtering with variation in oblique angle and target substrate distance (TSD). Growth tendencies were differentiated through adjusted oblique angle and TSD during sputtering, thereby microstructure of YSZ was changed. Electrochemical behavior of microstructure-controlled thin film YSZ was investigated by means of applying YSZ to anodic alumina oxide (AAO) based solid oxide fuel cells (SOFC). On nanoporous AAO substrates, Pt anode, YSZ electrolyte, and Pt cathode were deposited serially all through sputtering. For depositing thin film YSZ electrolyte, oblique angle and TSD were differentiated into four cases each, while thickness was set to be equal. YSZ thin films were evaluated using FESEM, AFM, FIB-SEM, XRD, and XPS. Electrochemical performance was investigated through i-V plot and EIS.

Single-Nanometer Changes in Nanopore Geometry Influence Curvature, Local Properties, and Protein Localization in Membrane Simulations

Nanoporous surfaces are used in many applications in intracellular sensing and drug delivery. However, the effects of such nanostructures on cell membrane properties are still far from understood. Here, we use coarse-grained molecular dynamics simulations to show that nanoporous substrates can stimulate membrane-curvature effects and that this curvature-sensing effect is much more sensitive than previously thought. We define a series of design parameters for inducing a nanoscale membrane curvature and show that nanopore taper plays a key role in membrane deformation, elucidating a previously unexplored fabrication parameter applicable to many nanostructured biomaterials. We report significant changes in the membrane area per lipid and thickness at regions of curvature. Finally, we demonstrate that regions of the nanopore-induced membrane curvature act as local hotspots for an increased bioactivity. We show spontaneous binding and localization of the epsin N-terminal homology (ENTH) domain to the regions of curvature. Understanding this interplay between the membrane curvature and nanoporosity at the biointerface helps both explain recent biological results and suggests a pathway for developing the next generation of cell-active substrates.

Single-step coating of polyethylenimine on gradient nanoporous phenolics for tight membranes with ultrahigh permeance

Ultrafiltration membranes with relatively small pores are highly expected in various separation cases. As a flexible manner to efficiently tighten the pores, post modification provides a robust platform for preparing the desired membranes. However, the endeavor to pursue high permselectivity of the membranes has been made by paying close attention to the modification layers while the effects of the substrate membranes are generally overlooked. In this work, tight membranes with ultrahigh permeance were produced by coating polyethylenimine (PEI) on gradient nanoporous phenolic substrates. Cationic PEI was tightly deposited on the negatively charged phenolics via electrostatic deposition, thus reducing the effective pore sizes to ∼2.6 nm through a single-step coating. The gradient porous nanostructures still remained after PEI coating in the phenolic membranes. The coated membranes exhibited ∼4–45 times higher permeance than counterparts with similar rejections. As the cationic PEI was distributed on the membrane surface and pore wall after coating, the positively charged membranes thus produced were able to efficiently separate cationic dyes from water.

Effect of substrate topography for graphene-based humidity sensors

Chemical vapor deposition graphene (CVDG) and electrochemical exfoliated graphene (ECG) were transferred and spin-coated on the nanoporous alumina substrate (NS) and flat alumina substrate (FS) to investigate the effect of substrate topography for graphene-based humidity sensors. The electrical resistance change of two graphene types on different substrate topography could be measured to estimate the environmental relative humidity. The relationship between graphene types, substrate topography, wettability, and humidity sensing performance was studied and discussed. The results of the water contact angle of CVDG on NS/FS and ECG on NS/FS were 77.0 ± 5.0°, 88.8 ± 4.9°, 55.9 ± 7.0°, and 59.8 ± 3.2°, respectively. The response, linearity and hysteresis characteristics of four graphene-based humidity sensors were measured and estimated. The ECG on NS humidity sensor shows the best performance in regards to the response, linearity and hysteresis.

Light-output enhancement of InGaN light emitting diodes regrown on nanoporous distributed Bragg reflector substrates

Utilising our novel wafer-scale electrochemical porosification approach which proceeds through the top surface by means of nanoscale vertical etching pathways, we have prepared full 2 inch wafers containing alternating solid GaN and nanoporous GaN (NP-GaN) layers that form distributed Bragg reflectors (DBRs), and have regrown InGaN-based light emitting diode (LED) heterostructures on these wafers. The NP-GaN DBR wafer is epi-ready and exhibits a peak reflectance of 95% at 420 nm prior to growth of the LED heterostructure. We observe a 1.8× enhancement in peak intensity of LED electroluminescence from processed devices, and delayed onset of efficiency droop with increased injection current.

Evaluation of on-Body Performance of a Sweat-Based Lactate Sensor from Low Volumes of Passive Eccrine Sweat

Lactate is a critical biomarker that can be used to monitor physical performance in sports medicine and restricted oxygen supply to tissues during anaerobic respiration for diagnosing clinical conditions such as hypoxia, cystic fibrosis, and ischemia. Recent advances have been made towards understanding accessible human biofluids to non-invasively monitor biomarkers that reflect the state of the body. Passive eccrine sweat is a potential candidate containing valuable information due to its ease of access, collection, and analysis. Literature studies have shown clinical correlations between sweat lactate and blood lactate levels which confirm that there is value in investigating sweat lactate for investigating clinical conditions. Existing wearables devices monitor only digital biomarkers to track heart rate and physical activity, however, there is no information obtained on human health status which can be understood by probing biochemical markers. The motivation of this study is to demonstrate on-body, low-volume detection of lactate in passive eccrine sweat. An electrochemical biosensor fabricated on a flexible, nanoporous substrate that can wick sweat is placed on the subject’s lower back and is utilized to detect and quantify sweat lactate levels. Label- free AC- based electrochemical impedance spectroscopy (EIS) is the signal transduction technique used to report the impedance in response to the lactate present in the passive body sweat. Prior to on-body testing, the functionality and the metrics of the lactate sensor in detecting sweat lactate within the physiological relevant ranges (5- 60mM) will be tested in controlled lab- environment to build a calibration response of curve of mapping impedance ranges to the lactate level for dynamic reporting of lactate concentrations when placed on-body. Sensor metrics obtained in human sweat from current bench top testing have yielded a 1mM as the lower limit of detection and a dynamic range of 1- 100mM. The on-body impedance response profiles produced corresponding to the lactate levels in continuous, real- time detection mode on integration with portable electronics will allow for translation into wearable biosensing applications.

Dynamics of Liquid Transfer from Nanoporous Stamps in High-Resolution Flexographic Printing.

Printing of ultrathin layers of polymeric and colloidal inks is critical for the manufacturing of electronics on nonconventional substrates such as paper and polymer films. Recently, we found that nanoporous stamps overcome key limitations of traditional polymer stamps in flexographic printing, namely, enabling the printing of ultrathin nanoparticle films with micron-scale lateral precision. Here, we study the dynamics of liquid transfer between nanoporous stamps and solid substrates. The stamps comprise forests of polymer-coated carbon nanotubes, and the surface mechanics and wettability of the stamps are engineered to imbibe colloidal inks and transfer the ink upon contact with the target substrate. By high-speed imaging during printing, we observe the dynamics of liquid spreading, which is mediated by progressing contact between the nanostructured stamp surface and by the substrate and imbibition within the stamp-substrate gap. From the final contact area, the volume of ink transfer is mediated by rupture of a capillary bridge; and, after rupture, liquid spreads to fill the area defined by a precursor film matching the stamp geometry with high precision. Via modeling of the liquid dynamics, and comparison with data, we elucidate the scale- and rate-limiting aspects of the process. Specifically, we find that the printed ink volume and resulting layer thickness are independent of contact pressure; and that printed layer thickness decreases with retraction speed. Under these conditions, nanoparticle films with controlled thickness in the <100 nm regime can be printed using nanoporous stamp flexography, at speeds commensurate with industrial printing equipment.

In-situ growth of zinc-aluminum-layered double hydroxide on nanoporous anodized aluminum bar for stir-bar sorptive extraction of phenolic acids

The present study is the first report in case of in-situ preparation and application of Zn-Al layered double hydroxide coated anodized aluminum stir bar for stir bar sorptive extraction approach. An anodized aluminum bar was electrochemically prepared and used as nanoporous substrate for in-situ growth of LDH without adding any aluminum precursor. The prepared anion exchange sorbent has been explored for the extraction of three organic acidic compounds including p-hydroxybenzoic acid, 3.4-dihydroxybenzoic, gallic acid from grape juice and nonalcoholic beer samples. In addition, the capability of the prepared bar for the extraction of quercetin was also investigated. After SBSE, phenolic acids were quantified through reversed-phase high-performance liquid chromatography-diode array detection. Plackett–Burman design was employed for screening the experimental factors. The effective factors were then optimized using Box Behnken design (BBD). Under optimum conditions, the linearity range of the method was between 0.2 and 200 μg L−1 and the coefficient of determination (r2) was higher than 0.9945. Relative standard deviations for intra- and inter-day precision of the analytes at 50 μg L−1 were 3.4–3.8% and 4.1–4.5%, respectively. Batch-to-batch reproducibility at the concentration level of 50 μg L−1 was 4.6–5.1% (n = 3); the limits of detection were between 0.06 and 0.26 μg L−1 and so were the enrichment factors between 46 and 50. Different samples of juice such as commercial and natural white and red grape, cranberry and beer were satisfactorily analyzed in order to investigate the method capability in real sample analysis.

Self‐Cleaning of Interfacial Oil Between Polymer Composites with Porous Zeolite Microparticles and Their Self‐Lubrication Properties

AbstractOil stain self‐cleaning and anti‐adhesion at the contacting interface between planar surfaces is a worldwide challenge and is rarely explored. Inspired by the low adhesion of Coccinella septempunctata to rough nanoporous substrates, it is attempted to reduce adhesion between the contacting interfaces of polymer composite due to the oil stain by constructing porous structures. A facile method is proposed to fabricate porous polymer composites by adding zeolite microparticles. Zeolite microparticles are used as oil cleaner to build the self‐cleaning system. The surface morphology, the mechanical properties, the anti‐adhesion and lubrication properties of the polymer composites are studied. It is suggested that the porous structure possesses self‐cleaning and high mechanical strength in ambient conditions. In addition, the excellent anti‐adhesion behavior can be realized due to the absorption of oil stain of the porous structure in the composite. The results show that the synergistic interaction of the roughness and the oleophilic properties decrease the adhesion between two planar surfaces under the oil stain condition. The present work provides a new route for the development of anti‐adhesion materials.

Antibacterial and osteogenesis performances of LL37-loaded titania nanopores in vitro and in vivo.

Background: Many studies have shown that the size of nanotube (NT) can significantly affect the behavior of osteoblasts on titanium-based materials. But the weak bonding strength between NT and substrate greatly limits their application.Purpose: The objective of this study was to compare the stability of NT and nanopore (NP) coatings, and further prepare antibacterial titanium-based materials by loading LL37 peptide in NP structures.Methods: The adhesion strength of NT and NP layers was investigated using a scratch tester. The proliferation and differentiation of MC3T3-E1 cells on different substrates were evaluated in vitro by CCK8, alkaline phosphatase activity, mineralization and polymerase chain reaction assays. The antibacterial rates of NP and NP/LL37 were also measured by spread plate method. Moreover, the osteogenesis around NP and NP/LL373 in vivo was further evaluated using uninfected and infected models.Results: Scratch test proved that the NP layers had stronger bonding strength with the substrates due to their continuous pore structures and thicker pipe walls than the independent NT structures. In vitro, cell results showed that MC3T3-E1 cells on NP substrates had better early adhesion, spreading and osteogenic differentiation than those of NT group. In addition, based on the drug reservoir characteristics of porous materials, the NP substrates were also used to load antibacterial LL37 peptide. After loading LL37, the antibacterial and osteogenic induction abilities of NP were further improved, thus significantly promoting osteogenesis in both uninfected and infected models.Conclusion: We determined that the NP layers had stronger bonding strength than NT structures, and the corresponding NP materials might be more suitable than NT for preparing drug-device combined titanium implants for bone injury treatment.

Spin-Dependent Electronic Transport in IrMn–Co/Pd Multilayered Systems

Relation between magnetoresistance and magnetization reversal in thin multilayered IrMn–Co/Pd films deposited both on planar and nanoporous substrates is in focus of the present work. Magnetic anisotropy, exchange coupling and mechanisms of magnetic resistivity are discussed.

Single-Molecule Sensing Using Nanopores in Two-Dimensional Transition Metal Carbide (MXene) Membranes

Label-free nanopore technology for sequencing biopolymers such as DNA and RNA could potentially replace existing methods if improvements in cost, speed, and accuracy are achieved. Solid-state nanopores have been developed over the past two decades as physically and chemically versatile sensors that mimic biological channels, through which transport and sequencing of biomolecules have already been demonstrated. Of particular interest is the use of two-dimensional (2D) materials as nanopore substrates, since these can in theory provide the highest resolution readout (<1 nm of a biopolymer segment) and opportunities for electronic multiplexed readout through their interesting electronic properties. In this work, we report on nanopores comprising atomically thin flakes of 2D transition metal carbides called MXenes. We demonstrate a high-yield (60%), contamination-free, and alignment-free transfer method that involves their self-assembly at a liquid-liquid interface to large-scale (mm-sized) films composed of sheets, followed by nanopore fabrication using focused electron beams. Our work demonstrates the feasibility of MXenes, a class of hydrophilic 2D materials with over 20 compositions known to date, as nanopore membranes for DNA translocation and single-molecule sensing applications.

Culture of dental pulp stem cells on nanoporous alumina substrates modified by carbon nanotubes.

PurposeAlumina substrates are one of the commonly used scaffolds applied in cell culture, but in order to prevent formation of biofilm on the alumina substrate, these substrates are modified with carbon nanotube.MethodsThe alumina substrate was made by a two-step anodization method and was then modified with carbon nanotubes by simple chemical reaction. The substrates were characterized with FTIR, SEM, EDX, 3D laser scanning digital microscope, contact angle (CA) and surface free energy (SFE). To determine how this modification influences the reduction of biofilm, biofilm of two various bacteria, Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus), were investigated.ResultsThe biofilm on the modified substrate decreased due to the presence of carbon nanotubes and increased antibacterial properties. Dental pulp stem cells (DPSCs) were cultured onto flat alumina (FA) and nanoporous alumina-multiwalled carbon nanotubes (NAMC) substrates to examine how the chemical modification and surface topography affects growth of DPSCs.ConclusionCell attachment and proliferation were investigated with SEM and Presto Blue assay, and the findings show that the NAMC substrates are suitable for cell culture.

Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

AbstractPhotoelectrode degradation under harsh solution conditions continues to be a major hurdle for long‐term operation and large‐scale implementation of solar fuel conversion. In this study, a dual‐layer TiO2 protection strategy is presented to improve the interfacial durability between nanoporous black silicon and photocatalysts. Nanoporous silicon photocathodes decorated with catalysts are passivated twice, providing an intermediate TiO2 layer between the substrate and catalyst and an additional TiO2 layer on top of the catalysts. Atomic layer deposition of TiO2 ensures uniform coverage of both the nanoporous silicon substrate and the catalysts. After 24 h of electrolysis at pH = 0.3, unprotected photocathodes layered with platinum and molybdenum sulfide retain only 30% and 20% of their photocurrent, respectively. At the same pH, photocathodes layered with TiO2 experience an increase in photocurrent retention: 85% for platinum‐coated photocathodes and 91% for molybdenum sulfide–coated photocathodes. Under alkaline conditions, unprotected photocathodes experience a 95% loss in photocurrent within the first 4 h of electrolysis. In contrast, TiO2‐protected photocathodes maintain 70% of their photocurrent during 12 h of electrolysis. This approach is quite general and may be employed as a protection strategy for a variety of photoabsorber–catalyst interfaces under both acidic and basic electrolyte conditions.

Sandwich nanoporous framework decorated with vertical CuO nanowire arrays for electrochemical glucose sensing

Increasing demands for electrochemical glucose sensors with high overall performance have recently attracted intensive attention. Herein, we report a novel sandwich-like nanoarchitecture composed of uniform CuO nanowire array layers grown on the nanoporous Cu2O film, which was synthesized via annealing the nanoporous copper thin film obtained by dealloying Cu-based metallic glass precursors. The glucose sensor based on the newly developed CuO/Cu2O nanocomposite exhibits prominent overall electrocatalytic performance towards the oxidation of glucose with a wide linear dynamic detection range from 0.1 to 6 mM, high sensitivity up to 1.95 mA/cm2·mM, fast response time of less than 1.5 s, low detection limit of 1 μM (S/N = 3) as well as excellent selectivity. The enhanced electrocatalytic property of the nanocomposite is attributed to the high surface area originating from the in-situ grown CuO nanowire array structure and synergetic bi-continuous nanoporous Cu2O substrate. This finding not only provides promising candidates for blood glucose sensing, but also opens a new avenue to designing nanostructured catalysts for engineering applications in general.

Optimization of structural and optical properties of nanoporous silicon substrate for thin layer transfer application

A study on optical and structural properties of nanoporous silicon is presented in this paper. The samples were prepared by electrochemical etching a heavily boron doped silicon wafer in a hydrofluoric acid electrolyte and flowed by in-situ sintering in ultra-high vacuum chemical vapor deposition reactor (UHVCVD) under hydrogen atmosphere at high temperature varied between 900 and 1100 °C. The structural and morphological properties were carried out using atomic force microscopy (AFM), scanning electronic microscopy (SEM) and high resolution transmission electronic microscopy (HRTEM). The optical properties were performed using the photoluminescence Spectroscopy (PL), Time Resolved Photoluminescence (TRPL), RAMAN spectroscopy and Fourier-transform infrared spectroscopy (FT-IR). It is shown that the in-situ heating at 900 °C desorbs the native oxide from the porous layer and closes the pores forming a continuous defects-free surface at the top of porous layer. The process allows obtaining stable porous layer with enhanced structural and optical properties and also tailoring the morphological properties and the visible optical emission. This paper aims at a comprehensive determination of the physical properties of sintered porous silicon, in particular, its structural and optical properties.

Simultaneous effects of temperature and vacuum and feed pressures on facilitated transport membrane for CO2/N2 separation

The facilitated transport of CO2 through an amine-containing polymeric membrane on a nanoporous PES substrate was studied at large feed-to-permeate pressure differentials that are relevant to post-combustion carbon capture. With the selective layer reinforced mechanically by incorporation of carbon nanotubes, the carrier saturation of amino groups by excessive CO2 was observed at high feed or permeate vacuum pressure. Nearly complete carrier saturation was observed at 7 atm feed pressure or a permeate vacuum near ambient pressure. At relatively low vacuum pressures, the vacuum degree and operating temperature affected the CO2 transport simultaneously. A vacuum pressure significantly lower than the water saturation pressure at certain temperature resulted in the dehydration of the selective layer, thereby a reduced CO2 permeance. This dehydration was mitigated at a moderate vacuum pressure. At the moderate vacuum pressure, the nanoporous PES substrate controlled the water permeation, leading to a sufficiently hydrated selective layer with high CO2 permeance and CO2/N2 selectivity. Overall, the membrane performed well with 0.3–0.6 atm vacuum pressures at 67 °C and a feed pressure of 4 atm, achieving the best membrane performance with a CO2 permeance of 1451 GPU and a CO2/N2 selectivity of 165.

Influence of nanoporosity on the nature of hydroxyapatite formed on bioactive calcium silicate model glass.

For hard tissue regeneration, the bioactivity of a material is measured by its ability to induce the formation of hydroxyapatite (HA) under physiological conditions. It depends on the dissolution behavior of the glass, which itself is determined by the composition and structure of glass. The enhanced HA growth on nanoporous than on nonporous glass has been attributed by some to greater specific surface area (SSA), but to nanopore size distribution by others. To decouple the influence of nanopore size and SSA on HA formation, we have successfully fabricated homogeneous 30CaO-70SiO2 (30C70S) model bioactive glass monoliths with different nanopore sizes, yet similar SSA via a combination of sol-gel, solvent exchange, and sintering processes. After incubation in PBS, HA, and Type-B carbonated HA (HA/B-CHA) form on nanoporous monoliths. The XPS, FTIR, and SEM analyses provide the first unambiguous demonstration of the influence of nanopore size alone on the formation pathway, growth rate, and microstructure of HA/CHA. Due to pore-size limited diffusion of PO43- , two HA/CHA formation pathways are observed: HA/CHA surface deposition and/or HA/CHA incorporation into nanopores. HA/CHA growth rate on the surface of a nanoporous glass monolith is dominated by the pore-size limited transport of Ca2+ ions dissolved from nanoporous glass substrates. Furthermore, with increasing nanopore size, HA/CHA microstructures evolve from needle-like, plate-like, to flower-like appearance. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 886-899, 2019.

In-situ growth of zeolitic imidazole framework-67 on nanoporous anodized aluminum bar as stir-bar sorptive extraction sorbent for determining caffeine

The objective of the present study was to develop a simple, sensitive and cost-effective sample pretreatment technique to extract and determine caffeine in different samples of beverage as well as urine. An anodized aluminum bar was electrochemically prepared and employed as nanoporous substrate for in-situ growth of crystals of the zeolitic imidazole framework-67 (ZIF-67). The above-mentioned sorbent, too, was applied as a stir bar sorptive extraction (SBSE) device along with HPLC-UV.Under predetermined experimental condition, the detection limit of the aimed method was 0.05 μg L−1 in beverages, and it was 0.1 μg L−1 in urine samples. Moreover, the linear dynamic range was 0.2–200 μg L−1 for beverages, and it was 0.5–200 μg L−1 for urine samples, too. The inter-day RSDs (10 μg L−1) were 5.3% and 5.7% respectively, and they were 5.8% and 6.1% for intra-day RSDs (10 μg L-1) in beverages and urine samples. Bar to bar reproducibility for three prepared bars equaled 6.2%. The applicability of the SBSE-HPLC-UV was investigated by determining caffeine in different samples of beverage and urine. The final range of obtained spiking recoveries was from 91.2 to104%.