Anodic Alumina Membranes: From Electrochemical Growth to Use as Template for Fabrication of Nanostructured Electrodes

The great success of anodic alumina membranes is due to their morphological features coupled to both thermal and chemical stability. The electrochemical fabrication allows accurate control of the porous structure: in fact, the membrane morphological characteristics (pore length, pore diameter and cell density) can be controlled by adjusting the anodizing parameters (bath, temperature, voltage and time). This article deals with both the fabrication and use of anodic alumina membranes. In particular, we will show the specific role of the addition of aluminum ions to phosphoric acid-based anodizing solution in modifying the morphology of anodic alumina membranes. Anodic alumina membranes were obtained at −1 °C in aqueous solutions of 0.4 M H3PO4 added with different amounts of Al(OH)3. For sake of completeness, the formation of PAA in pure 0.4 M H3PO4 in otherwise identical conditions was also investigated. We found that the presence of Al(OH)3 in solution highly affects the morphology of the porous layer. In particular, at high Al(OH)3 concentration (close to saturation) more compact porous layers were formed with narrow pores separated by thick oxide. The increase in the electric charge from 20 to 160 C cm−2 also contributes to modifying the morphology of porous oxide. The obtained anodic alumina membranes were used as a template to fabricate a regular array of PdCo alloy nanowires that is a valid alternative to Pt for hydrogen evolution reaction. The PdCo alloy was obtained by electrodeposition and we found that the composition of the nanowires depends on the concentration of two metals in the deposition solution.

Real-Time Monitoring of Doxorubicin Release from Hybrid Nanoporous Anodic Alumina Structures

This work demonstrates an advanced approach to fabricate Hybrid nanoporous anodic alumina gradient-index filters (Hy-NAA-GIFs) through a heterogeneous anodization process combining sinusoidal current-density anodization and constant potential anodization. As a result, the hybrid structure obtained reveals a single photonic stopband (PSB), which falls within the absorption region of the drug molecule and the intensity of the spectrum that are far from such absorption range. The prepared structures were loaded with the doxorubicin (DOX) drug through the drop-casting method, which allows for evaluating the maximum reflectance of the relative height of the PSB with the average reflectance of the spectrum intensity. Thereafter, this property has been applied in a flow cell setup connected to a reflectance spectrophotometer where different drug-loaded samples were placed to study the behavior and kinetics of the drug release in real-time by varying two parameters, i.e., different pore length and flow rates. As such, obtained results were analyzed with a model that includes a sum of two inverted exponential decay functions with two different characteristic time releases. Overall, this study opens up several possibilities for the Hy-NAA-GIFs to study the drug kinetics from nanoporous structures.

Advanced NMR methodologies in rock core analysis

<p>¹H NMR techniques have gained extensive acceptance in petrophysics for the evaluation of fluid-saturating reservoir rocks. This thesis presents the development of new NMR methods regarding the reserves (determination of pore length scales and surface relaxivities), productivity (estimates of permeability) and recovery of fluids (resolves of saturation evolution) in rocks. Traditionally, pore lengths are evaluated from the ground relaxation eigenmodes of spin-bearing molecules in pore space. This evaluation is not straightforward since it is affected by surface relaxivity. Here, we use an approach to determine pore length from detecting the high relaxation eigenmodes, in which way the eigenvalue spectrum directly scales to the pore size distribution. Based on this, we extend this approach for the use with low-field NMR spectrometers and 2D NMR eigenmode correlation methods. Surface relaxivity can be further extracted from these 2D correlation maps, which is in agreement with an independent NMR measurement. Permeability is generally estimated from surface relaxation via empirical pore-network models. However, for heterogeneous rocks a single (or averaged) permeability value may not be adequate. Therefore, we measure surface relaxation in conjunction with MRI techniques. Permeability profiles can then be obtained from spatially resolved relaxation maps yielding local connectedness between adjacent slices. The results are confirmed by the comparison of brine-permeability measurements. MRI experiments of fluids in rocks at reservoir-like conditions may yield optimized recovery strategies of reservoir fluids. In this context we combine MRI with diffusion-relaxation correlation measurements during flooding intervals. The results provide substantial information, such as flooding front and saturation profiles of immiscible fluids discriminated by fluid type.</p>

Advanced NMR methodologies in rock core analysis

<p>¹H NMR techniques have gained extensive acceptance in petrophysics for the evaluation of fluid-saturating reservoir rocks. This thesis presents the development of new NMR methods regarding the reserves (determination of pore length scales and surface relaxivities), productivity (estimates of permeability) and recovery of fluids (resolves of saturation evolution) in rocks. Traditionally, pore lengths are evaluated from the ground relaxation eigenmodes of spin-bearing molecules in pore space. This evaluation is not straightforward since it is affected by surface relaxivity. Here, we use an approach to determine pore length from detecting the high relaxation eigenmodes, in which way the eigenvalue spectrum directly scales to the pore size distribution. Based on this, we extend this approach for the use with low-field NMR spectrometers and 2D NMR eigenmode correlation methods. Surface relaxivity can be further extracted from these 2D correlation maps, which is in agreement with an independent NMR measurement. Permeability is generally estimated from surface relaxation via empirical pore-network models. However, for heterogeneous rocks a single (or averaged) permeability value may not be adequate. Therefore, we measure surface relaxation in conjunction with MRI techniques. Permeability profiles can then be obtained from spatially resolved relaxation maps yielding local connectedness between adjacent slices. The results are confirmed by the comparison of brine-permeability measurements. MRI experiments of fluids in rocks at reservoir-like conditions may yield optimized recovery strategies of reservoir fluids. In this context we combine MRI with diffusion-relaxation correlation measurements during flooding intervals. The results provide substantial information, such as flooding front and saturation profiles of immiscible fluids discriminated by fluid type.</p>

REPRESENTATION OF THE SPECIFIC SURFACE AREA OF A POROUS MEDIUM BY STATISTICAL CONTINUOUS MONOMIAL FUNCTIONS

Удельная поверхность пористых сред является важным геометрическим параметром в расчетах процессов пищевых систем и оборудования для их переработки. Расчетные формулы процессов тепло- и массообмена в настоящее время содержат осредненные значения геометрических параметров, получаемые в эксперименте. Использование формул удельной поверхности по осредненным характеристикам пористой среды существенно ограничивает точность и надежность расчетов. Получены непрерывные одночленные по всему диапазону размеров сообщающихся пор расчетные формулы удельной поверхности, основанные на функции распределения плотности вероятности размеров сообщающихся пор разных модельных конфигураций в полиразмерной дисперсной (несцепленной) и связной (сцепленной) пористых средах для двух видов исходных формул удельной поверхности, различных видов модельных поперечных сечений и длины пор. Проведен их сравнительный анализ. Установлено, что на расчет удельной поверхности влияет моделируемая длина пор. Вид поперечного сечения не влияет на расчет удельной поверхности. Полученные формулы позволяют вычислять удельную поверхность для ансамбля отдельных размерных групп пор и в целом для всей совокупности их размеров. Приведен пример расчета по полученным формулам. The specific surface area of porous media is an important parameter in the calculations of the processes of food systems and equipment. The calculated formulas of the heat and mass transfer processes currently contain the averaged values of the geometric parameters obtained in the experiment. The use of formulas the specific surface area based on the averaged characteristics of a porous medium significantly limits the accuracy and reliability of calculations. Continuous monomial calculated formulas for the specific surface and based on the function of the probability density of the size distribution open pores ware obtained. Their comparative analysis is carried out. It was found that the transverse shape is not reflected in the formulas for the specific surface area, but the simulated pore length does. The specific surface area formulas allow calculating the specific surface area for an ensemble of separate size groups of pores and, in general, for the entire set of their sizes. An example of calculation by the obtained formulas is given.

3D microstructure and critical current properties of ultra-fine-grain Ba(Fe,Co)2As2 bulk superconductors

In iron-based superconductors, randomly oriented grain boundaries have a strong influence on the transport properties via intrinsic weak-link and flux pinning mechanisms. Herein we report the critical current density (Jc) and the three-dimensional microstructure of polycrystalline bulk Co-doped Ba122 superconductors, with highly dense grain boundaries (grain size smaller than 50 nm), produced by high-energy milling. Three-dimensional electron microscopy revealed that the anomalous growth of secondary particles (aggregation) and the inter-aggregation structures were significantly different in the samples with finer grains, which may have extrinsically limited Jc. These important microstructural features were quantified as two parameters—local thickness and total pore length—by reconstructing the three-dimensional structure of the superconducting phase using the adaptive thresholding method. The results obtained in this study suggest that understanding and controlling the microstructural formation process by sintering are instrumental for improving the Jc properties of 122 polycrystalline materials consisting of ultrafine grains.

Gamze Kaya GERMINATION, STOMATAL AND PHYSIOLOGICAL RESPONSE OF ROCKET (Eruca sativa L.) TO SALINITY

The response of rocket (Eruca sativa L.) to salinity stress was tested for several germination and physiological parameters during seedling development. Two rocket cultivars (Ilıca and Istanbul) and various salinity stresses of 0, 5, 10, 15 and 20 dS m–1 created by NaCl were used in the study. Germination percentage (GP), mean germination time (MGT), germination index (GI), germination stress tolerance index (GSTI), stomata morphology, chlorophyll content (SPAD value), leaf dry matter, relative water content (RWC), cellular injury (CI) and cell membrane stability (CMS) were evaluated. Results showed that high salinity stresses led to a decrease in GP, GI and GSTI index, while MGT increased. Salinity reduced stoma length and pore length. Under saline conditions, leaf dry matter, chlorophyll content and CMS increased, while RWC decreased. Also, CI was enhanced by salinities over 10 dS m–1. It was concluded that lower CMS, CI and RWC, and greater dry matter and chlorophyll were considered as salinity tolerance at the seedling stage of the rocket, and Istanbul was more tolerant to salinity than Ilıca.

Anthrax toxin translocation complex reveals insight into the lethal factor unfolding and refolding mechanism

Translocation is essential to the anthrax toxin mechanism. Protective antigen (PA), the binding component of this AB toxin, forms an oligomeric pore that translocates lethal factor (LF) or edema factor, the active components of the toxin, into the cell. Structural details of the translocation process have remained elusive despite their biological importance. To overcome the technical challenges of studying translocation intermediates, we developed a method to immobilize, transition, and stabilize anthrax toxin to mimic important physiological steps in the intoxication process. Here, we report a cryoEM snapshot of PApore translocating the N-terminal domain of LF (LFN). The resulting 3.3 Å structure of the complex shows density of partially unfolded LFN near the canonical PApore binding site. Interestingly, we also observe density consistent with an α helix emerging from the 100 Å β barrel channel suggesting LF secondary structural elements begin to refold in the pore channel. We conclude the anthrax toxin β barrel aids in efficient folding of its enzymatic payload prior to channel exit. Our hypothesized refolding mechanism has broader implications for pore length of other protein translocating toxins.