Free Pores Research Articles

Adsorption and diffusion behavior of CO2/N2 in coking coal matrix based on molecular simulation: Considering the effects of moisture and temperature

The moisture content and temperature of coal has a significant impact on the efficacy of inert gases (CO2/N2) in inhibiting coal spontaneous combustion (CSC). Therefore, this study explores the changes in microporous structure, adsorption capacity, heat of adsorption as well as energy distribution and diffusion of CO2/N2 at varying moisture contents (1%–5%) and temperatures (303–343 K). The results demonstrate that water molecules gradually transform large pores in the microporous structure into multiple smaller pores, thus reducing the volume proportion of free pores. The adsorption of CO2/N2 is constrained by the pre-adsorbed water molecules occupying the adsorption sites. Both temperature and moisture exert similar effects on gas adsorption capacity, with higher levels of both reducing the adsorption capacity. Notably, temperature rise is associated with an increased heat of adsorption for the gas molecules. Under moisture effects, there is an observable positive relationship between the gas diffusion coefficient and the adsorption capacity. Conversely, there is a negative correlation with temperature. At low moisture content, CO2/N2 injection is enhanced. High temperatures reduce the effectiveness of CO2/N2 in preventing CSC, while heat can only be exchanged by diluting the oxygen concentration. These results provide crucial insights into the adsorption behavior of CO2/N2 at different temperatures and moisture contents.

Multi-mode luminescence anti-counterfeiting and visual iron(Ⅲ) ions RTP detection constructed by assembly of CDs&Eu3+ in porous RHO zeolite

Carbon dots (CDs)-based composites have shown impressive performance in fields of information encryption and sensing, however, a great challenge is to simultaneously implement multi-mode luminescence and room-temperature phosphorescence (RTP) detection in single system due to the formidable synthesis. Herein, a multifunctional composite of Eu&CDs@pRHO has been designed by co-assembly strategy and prepared via a facile calcination and impregnation treatment. Eu&CDs@pRHO exhibits intense fluorescence (FL) and RTP coming from two individual luminous centers, Eu3+ in the free pores and CDs in the interrupted structure of RHO zeolite. Unique four-mode color outputs including pink (Eu3+, ex.254 nm), light violet (CDs, ex.365 nm), blue (CDs, 254 nm off), and green (CDs, 365 nm off) could be realized, on the basis of it, a preliminary application of advanced information encoding has been demonstrated. Given the free pores of matrix and stable RTP in water of confined CDs, a visual RTP detection of Fe3+ ions is achieved with the detection limit as low as 9.8 μmol/L. This work has opened up a new perspective for the strategic amalgamation of luminous guests with porous zeolite to construct the advanced functional materials.

Nitrogen-Rich Covalent Organic Polymer for Metal-Free Tandem Catalysis and Postmetalation-Actuated High-Performance Water Oxidation.

Development of high-performing catalytic materials for selective and mild chemical transformations through adhering to the principles of sustainability remains a central focus in modern chemistry. Herein, we report the template-free assembly of a thermochemically robust covalent organic polymer (COP: 1) from 2,2'-bipyridine-5,5'-dicarbonyl dichloride and 2,4,6-tris(4-aminophenyl)triazine as [2 + 3] structural motifs. The two-dimensional (2D) layered architecture contains carboxamide functionality, delocalized π-cloud, and free pyridyl-N site-decked pores. Such trifunctionalization benefits this polymeric network exhibiting tandem alcohol oxidation-Knoevenagel condensation. In contrast to common metal-based catalysts, 1 represents a one of a kind metal-free alcohol oxidation reaction via extended π-cloud delocalization-mediated free radical pathway, as comprehensively supported from diverse control experiments. In addition to reasonable recyclability and broad substrate scope, the mild reaction condition underscores its applicability in benign synthesis of valuable product benzylidene malononitrile. Integration of 2,2'-bipyridyl units in this 2D COP favors anchoring non-noble metal ions to devise 1-M (M: Ni2+/ Co2+) that demonstrate outstanding electrochemical oxygen evolution reaction in alkaline media with high chronoamperometric stability. Electrochemical parameters of both 1-Co and 1-Ni outperform some benchmark, commercial, as well as a majority of contemporary OER catalysts. Specifically, the overpotential and Tafel slope (280 mV, 58 mV/dec) for 1-Ni is better than 1-Co (360 mV, 78 mV/dec) because of increased charge accumulation as well as a higher number of active sites compared to the former. In addition, the turnover frequency of 1-Ni is found to be 6 times higher than that of 1-Co and ranks among top-tier water oxidation catalysts. The results provide valuable insights in the field of metal-free tandem catalysis as well as promising electrochemical water splitting at the interface of task-specific functionality fuelling in polymeric organic networks.

Enhancing the energy release performance of nanothermites through metal oxides free oxygen and pores

Efficient energy release and the large-scale preparation of thermite with high energy density are currently crucial issues in the field of explosive systems. In this study, we focused on the utilization of porous metal oxides (pMxOy) prepared through urea co-precipitation and high-temperature annealing to enhance the ignition and combustion performance of nanothermites. We compared the thermochemical reactivity, ignition, and combustion performance of nAl/pMxOy with those of nanothermites composed of nano metal oxides. We found that the use of pMxOy resulted in significantly increased the reaction exergy and reduced the activation energy of nanothermites, the energy released by the nanothermite containing pMxOy increased by up to 33.4%, while the activation energy decreased by up to 34.8%. Furthermore, the ignition and combustion results show that better semiconductor bridge ignition, pressurization, and combustion performance of nanothermites consisting of high free oxygen ratio and high porosity pMxOy. This improvement can be attributed to the enhanced contact between nAl and pMxOy, as well as the improved oxygen ionic conductivity of pMxOy. We believe that this high-performance nanothermite, which utilizes porous metal oxides exhibiting high interfacial activity, can be extensively employed in various initiating explosive devices. Notably, the simplicity of the batched preparation process further enhances its potential for practical application.

Polyamide–based membranes with nanoscale homogeneity and asymmetric structure for ultrafast ion separation

Polymeric membranes are the most practical separation technology for extracting target ionic species necessary for water purification and clean energy, but are limited by the multi-scale heterogeneity, and transient and dynamic free volume pores. Modulated interfacial polymerization techniques are emergent concepts for preparing polyamide composite membranes with reduced thickness and homogeneous pore structures to satisfy the requirements for efficient ion separation applications. Herein, N–Cyclic cation-assisted kinetically regulated interfacial polymerization strategy to generate polyamide nanofilm composite membranes with tuned pore network and asymmetric structures for water purification is reported. Experimental characterization techniques and molecular dynamic simulations revealed that the N-Cyclic cations control the kinetic diffusion behaviour of the amine monomers to the aqueous/organic interface conducing to the formation of nanofilm membranes with fine-tuned polyamide network structures. Meanwhile, the N–Cyclic cation–regulated IP process not only affords to decrease the thickness of the formed polyamide nanofilm selective layers but also effectively narrows the effective pore size of the membranes. These membranes with thinner, homogeneous and asymmetric polyamide network structures exhibit enhanced water permeance of 55.7–60.42 L m−2 h−1 bar−1, and showed Na2SO4 rejection of 99.59–99.66% and MgCl2 rejection of 98.94–98.96% in nanofiltration separations, thereby outperforming the permeance–selectivity performance of the state-of-the-art polyamide-based membranes. The membranes also exhibit improved forward osmosis performances. We envision that this research will provide insightful foundations for the molecular tuning and construction of the next-generation structurally modulated polyamide nanofilms for various applications in molecular separation and water purification.

Effective modeling of coupled reaction and transport inside the catalytic filter wall

A new extension of 1D mathematical model describing diffusion limitation in a catalytic filter wall is proposed. Transport limitations in the flowing gas inside free pores and in the coated catalyst are considered together with a Langmuir–Hinshelwood (LH) reaction kinetics including inhibition effects. Catalytic CO oxidation is investigated as a test reaction both at low and high reactant concentrations. The computed 1D concentration profiles are compared to detailed 3D pore-scale simulations involving the structure of a real filter wall obtained from X-ray tomography (XRT) scans. The best agreement is achieved when both gas-in-pores and intra-catalyst diffusion with LH effectiveness factor are considered in the 1D model. The impact of mass transfer limitations on CO light-off curves is then simulated using a 1D+1D model of the entire monolith filter. The extended model including diffusion limitation in free pores predicts the presence of undesired reactant slip at high flow rates as observed in experiments, which was not possible with the previously published models.

Enhanced gas separation by free volume tuning in a crown ether-containing polyimide membrane

Tuning coupled free volume and pore size distribution is of great significance for membrane-based gas separation. In the present work, a polyimide membrane containing bulky -CF3 group and crown ether ring structure was developed using 4, 4′ - (hexafluoroisopropylidene) diphthalic anhydride as dianhydride monomer, 2, 2′-bis [4-(4-aminophenoxy)phenyl] -hexafluoropropanane and di(aminobenze)-21-crown-7-ether as diamine monomers. Diamine monomer with large bulky -CF3 grant the polyimide membrane more free volume, which was helpful for gas permeability enhancement. Besides, crown ether could act as a pores size distribution tuning monomer, which endowed membranes with improved gas selectivity. Results showed that the introduction of crown ether into polyimide backbone exhibited a significant impact on free volume and pores size distribution. Typically, with the increasing crown ether content, the free volume decreased, whereas the relative available free volume ratio (FAVi/FAVj) achieved a remarkable increment. It’s also worth noting that the pores size distribution was changed by copolymerization with crown ether. The intensity of macro-pore gradually decreased accompanied with an increase in micro-pore structure. As a result, the gas selectivity significantly increased. Compared the membrane without crown ether, the maximum selectivity enhancement was achieved at 30 mol% di(aminobenze)-21-crown-7-ether content. It exhibited remarkable selectivity increments about 204.8%, 198.8%, 123.2%, and 115.4% for He/CH4, H2/CH4, CO2/CH4, and CO2/N2, respectively. These results took a huge step forward which nearly hit up to the 2008 Robeson’s upper bound, especially for CO2/CH4.

Polyamide-based membranes with structural homogeneity for ultrafast molecular sieving

Thin-film composite membranes formed by conventional interfacial polymerization generally suffer from the depth heterogeneity of the polyamide layer, i.e., nonuniformly distributed free volume pores, leading to the inefficient permselectivity. Here, we demonstrate a facile and versatile approach to tune the nanoscale homogeneity of polyamide-based thin-film composite membranes via inorganic salt-mediated interfacial polymerization process. Molecular dynamics simulations and various characterization techniques elucidate in detail the underlying molecular mechanism by which the salt addition confines and regulates the diffusion of amine monomers to the water-oil interface and thus tunes the nanoscale homogeneity of the polyamide layer. The resulting thin-film composite membranes with thin, smooth, dense, and structurally homogeneous polyamide layers demonstrate a permeance increment of ~20–435% and/or solute rejection enhancement of ~10–170% as well as improved antifouling property for efficient reverse/forward osmosis and nanofiltration separations. This work sheds light on the tunability of the polyamide layer homogeneity via salt-regulated interfacial polymerization process.

Molecular insight into the diffusion/flow potential properties initiated by methane adsorption in coal matrix: taking the factor of moisture contents into account.

Coal seam permeability is one of the key parameters affecting coalbed methane (CBM), and plays an important role in resource evaluation and regional selection. To fully explore the diffusion/flow potential properties initiated by methane adsorption beneath diverse moisture contents (1-5%) in coal molecules. The pore size distribution and methane adsorption capacities were discussed based on Monte Carlo (MC) and molecular dynamics (MD) methods. The potential properties of diffusion/flow induced by methane adsorption were investigated using the maximum absolute adsorption capacities as benchmark. The variation patterns of the pore structure were analyzed using SEM scanning experiment to verify the results of simulation analysis. It is found that the free pores facilitate methane molecular adsorption and increase adsorption spaces; the skeleton pores restrict the flow and transport of water molecules. Reduction values in surface free energies increase at different temperatures, and released heat diffusion coefficients and permeabilities for methane molecules drop as moisture contents increase. Interestingly, however, enhancements in temperatures increase the methane molecular diffusion coefficients. The lower the activation energies, the easier they are to diffuse. Sufficiently, the optimum conditions for gas drainage of coal seam are at temperature of 293K and moisture content of 5%, indicating greater contributions to gas pressure relief for coal seam. By comparing the results of molecular simulation and SEM scanning, trend of change is basically the same. Moreover, it is explored that hydraulic measure was the most significant to the CBM stimulation technology through field engineering application. This research is expected to provide guidance for facilitating the effectiveness of gas extraction for coal seam.

Investigating NMR-based absolute and relative permeability models of sandstone using digital rock techniques

Absolute permeability determines fluid production capacity, and relative permeability determines the produced fluid types, and their accurate calculations are critical for evaluating hydrocarbon-bearing formations. In oil/gas fields, the nuclear magnetic resonance (NMR) logging tool has been widely used due to its unique advantage of directly detecting the rock pores. However, this tool cannot measure absolute permeability or relative permeability directly. There exist many approaches for estimating NMR-based permeabilities, but most of them lack the basic understandings of fluid flow characteristics in micro-pores. To investigate NMR-based absolute and relative permeability models of sandstone , we suggest three types of pores, i.e., non-flowing bound water pores , slow-flowing free water pores, and fast-flowing free water pores, and incorporate them into the permeability calculations. The digital rock technique was utilized to study fluid flow mechanisms. Lattice Boltzmann method (LBM) was applied on two constructed three-dimensional digital rocks to calculate fluid flow velocity field distributions and absolute permeabilities. From the fluid flow simulation results, it was found that bound water exists not only in small pores but also in medium-sized pores and big pores. By comparing the permeability values of digital rocks with various porosities, we demonstrated that fast-flowing free water pores have the highest contribution to absolute permeability. Five relative permeability calculation models were investigated, where we found that the best link between the T 2 spectrum and relative permeability curve was the pore size distribution index. The obtained results indicated that the traditional Coates model combined with the spectral bulk volume irreducible method and the Brooks-Corey model are high-precision models for calculating the NMR-based absolute and relative permeabilities in sandstone reservoirs. • Three fluid flow velocity-based types of pores were investigated. • Fluid flow characteristics and their impacts on permeability were analyzed. • The three-dimensional spatial distribution of bound water was studied. • The accuracies of five relative permeability calculation models were compared.

Positron Annihilation Lifetime Spectroscopic Analysis of Plastic Deformation of High-Density Polyethylene

In this paper, for the first time, positron annihilation lifetime spectroscopy, after an appropriate adaptation, was used to analyze the plastic deformation process of high-density polyethylene as a representative semicrystalline polymer. It was shown that the average size of the free volume pores of the amorphous phase in the studied strain range decreased in comparison with the undeformed polyethylene, even after the initiation of the cavitation phenomenon due to highly anisotropic, ellipsoidal shape of cavities with the aspect ratio amounting to ∼45. The mean positron lifetime was practically constant in the analyzed range of strains even after activation of the micromechanisms of plastic deformation of crystals due to the mutually compensating effects activated in the crystalline phase. A clear change of the dispersion of positron lifetime as a function of local strain was observed. This effect was correlated with the reduction of the crystallites length by the relative displacement (slips) of adjacent crystalline blocks within individual lamellae.

Review of the cardinalfishes of the genus Cercamia (Percomorpha: Apogonidae) of the Red Sea and Indian Ocean with descriptions of three new species.

The representatives of Cercamia from the Indian Ocean including Red Sea are reviewed and three new species are described: Cercamia spio n. sp., formerly known as C. eremia (Allen, 1987), is described from 14 specimens, 1733 mm SL, collected in 1015 meters from northern (Duba) to central (Jeddah) Saudi Arabia and from Jezirat Faraun, Egypt. It also has been photographed from the Gulf of Aqaba (Dahab, Egypt) and El Quseir (Mangrove Bay, Egypt). The new species is distinguished from other Indian Ocean Cercamia in having fewer developed gill rakers on lower limb (usually 11 versus usually 1213) and fewer anal-fin rays (11 versus usually 1213). Another new species, Cercamia laamu, n. sp., is described only from the Maldives and Chagos Archipelago based on five specimens 16.030.5 mm SL. It differs from all Indian Ocean Cercamia in having more greater number of the second dorsal-fin rays (10 versus usually 9), and a translucent body devoid of reddish marks versus small reddish dots and crisscross lines. The third new species, Cercamia mascarene, n. sp., is described from 40 specimens 1936 mm SL, from Rodrigues Island, Mauritius. It differs from Cercamia eremia in having a greater number of developed gill rakers on the lower limb of the first gill arch (usually 13 versus usually 12). Free neuromasts and cephalic pores are illustrated for Cercamia mascarene and free neuromasts on the body and caudal fin are illustrated for Japanese specimens of C. cf. eremia. New diagnoses are provided for Cercamia cladara, the type species of the genus, and C. eremia. A map of collection locations for species of Cercamia is presented to show the breath of known occurrences in the Red Sea and Indian Ocean. A new morphologic diagnosis is provided for Cercamia. A phylogenetic analysis of the barcoding portion of the mitochondrial COI gene, including all available sequences from members of the genus Cercamia, displays a much higher species diversity than expected, with high levels of divergence among recognized and undescribed species. A key to the described Indian Ocean species is provided.

Physical, geochemical, and clay mineralogical properties of unstable soil slopes in the Cameron Highlands

Abstract The physical, geochemical, and clay mineralogical properties are location dependent and influence landslide, yet this relationship is understudied in the Cameron Highlands. Therefore, this study demonstrates the effect of the selected physical–geochemical properties and clay mineralogy on landslide susceptibility (LS) in the Cameron Highlands, Malaysia. Seven soil samples were taken from non-landslide-affected slopes (NAS) and 13 from landslide-affected slopes (LAS), making a total of 20 samples that were analyzed. The degree of the LAS and NAS ranges from 42–80° and 30–70°, respectively. The NAS soils were characterized by lower sand, higher clay, higher organic matter content (OMC), and higher cation exchange capacity (CEC). Soils with high sand tend to have larger free pores and weak bonds, making them more vulnerable to landslides. The electrostatic charges on the clay’s surface bind the solution ions, increasing cohesion between soil particles. Also, high CEC in soils improves their stability through the binding effect resulting from the attraction between solution ions via the electrostatic surface charges of the clay in the soil. The clay mineralogy revealed the abundance of kaolinite and illite, indicating the last stage of weathering associated with the weathering of primary minerals forming the bedrock. In this study, it was demonstrated that high sand, low clay, low OMC, low CEC, and clay mineralogy of the soil were associated with slope failure in the study area.

Investigation on cavitation behavior of ultrahigh molecular weight polyethylene during stretching in wet process and dry process

Nowadays, the rapid development of lithium-ion batteries (LIBs) leads to an urgent demand for the separator with excellent mechanical and electrochemical performances. In this work, the ultra-high molecular weight polyethylene (UHMWPE)/liquid paraffin (LP) gel film and the film after extraction of LP are prepared respectively. Due to the identical crystalline structure but different content of free volume pores, the pore formation mechanism during stretching in wet process and dry process could be accurately distinguished by scanning electron microscope and in-situ small-angle X-ray scattering. It is found that since the free volume pores in amorphous phase of UHMWPE have been filled with LP, the cavitation phenomenon is suppressed completely during stretching in wet process. The porosity of membrane after biaxial stretching is just relative to the LP content instead of the draw ratio and a unique laminated structure is created along the thickness direction. On the contrary, after extraction of LP, the free volume pores in amorphous region could act as nuclei to initiate intensive cavitation effect in dry process, leading to the significant increase of pore size and porosity of membrane with the draw ratio. Furthermore, the separator made from dry process displays better electrochemical performances but worse mechanical properties than that obtained from wet process. Therefore, it is reasonable to believe that the LIBs separator with optimal pore structure and excellent properties could be developed by combining the advantages of dry process and wet process.

Studying the in vitro corrosion response of nanostructured TaN coatings in Hank's physiological solution

AbstractThe goal of this research is to determine the effect of N2 pressure to argon pressure on the microstructural analysis and corrosion behavior of nanostructured TaN deposited coatings using a reactive DC‐magnetron sputtering (RDCMS) technique. The samples coated microstructure was studied by the X‐ray diffraction (XRD) and scanning electron microscope (SEM), and elemental distribution was studied using energy‐dispersive X‐ray spectroscopy (EDS). To investigate the corrosion behavior of nanostructured TaN coatings, the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests were performed in Hank's physiological solution. The results of different tests revealed that the coating with a content of 17.6% PN2/PAr consisted of hexagonal and orthorhombic TaN phases and had denser microstructure and free pores. This coating showed superior corrosion behavior in comparison to the other ones. Also, the corrosion resistance of this coating raised by increasing the time of immersion from 48 to 168 h.

Heterogeneous evolution of pore structure during loess collapse: Insights from X-ray micro-computed tomography

The pore structure is an important feature of loess fabric and significantly influences the hydraulic properties. The evolution of pore structure during loess collapse has been extensively investigated but some aspects are still not well understood. In this study, the 3D pore structure evolution within the same loess sample was characterized using X-ray micro-computed tomography in combination with an in-house collapse test set-up. The loess pore space consists of two distinct pore categories: constricted pores and free pores. The former can be assessed only through smaller pores while the latter are generally channel-like in shape. We extracted constricted pores and free pores from the tomography images and our results show that they behave differently during the collapse. The constricted pores were not destroyed during the collapse and many of them maintain well their sizes and shapes. On the other hand, the channel-like free pores were typically closed up and had a more important contribution to the overall porosity reduction. Our results demonstrate that the pore structure evolution associated with loess collapse is not only related to pore size, but also closely linked to pore morphology (i.e. constricted/free pores). The outcome of this work provides new insights into the loess collapse process and serves to better understand the underlying mechanism of fabric collapse.

Morphological, microstructural and mineralogical dataset of bauxite over Mainpat plateau from a part of Deccan traps, Surguja district, Chhattisgarh

In this study, we present the main findings from microstructural and mineralogical studies and their implications for the genesis of bauxite/laterite in Mainpat plateau. Megascopic studies showed reddish laterite to off-white bauxite. Strong hydrolytic action formed small oolites and large pisolites with sizes of 1–2 cm in diameter. Pisolites and oolites were elliptical, circular, and as broken pieces. Matrix of gibbsite and hematite was found in petrographic observations. Morphological characteristics include pisolitic, oolitic, lamellar, and euhedral gibbsite. Microstructures discovered were spongy gibbsite, flower-like crystals, elongated gibbsite, and framework type. Crystals of gibbsite were found to be predominant with partially crystallized ilmenite and hematite as subordinate phases. Scattered bauxite crystals made free pores for passage of solutions enhancing leaching conditions. Al, Ti, Fe, Si, Cu and Zn were identified as significant components; out of which, Al and Ti have the highest concentration. The samples have high alumina constitutes of 61.45% and 65.40% with a low iron content of 6.66% and 5.61%. High Ti content of 19.38% and 17.55% might be due to strong hydrolytic action during the alteration of basalt to bauxite. Low Si content of 2.68% indicates strong leaching activity. XRF analysis showed that the samples have undergone strong lateritization. XRD examination of bauxite/laterite revealed a mixture of minerals like gibbsite, boehmite, goethite, hematite, and anatase. Enrichment in boehmite shows in situ weathering. The study aims to extract the genesis and depositional characterization of bauxite through its morphological, microstructural, and mineralogical properties.

Surface characterization and electrochemical properties of tantalum nitride (TaN) nanostructured coatings produced by reactive DC magnetron sputtering

In this study, TaN nanostructured coatings were successfully produced on AISI 316 L stainless steel substrates using the reactive DC magnetron sputtering method. Among all of these coating processes, the only variable factor was the percentage of partial pressure of nitrogen gas (PN2) which was attended in the sputtering process. To do this, the percentage of partial pressure of nitrogen gas was chosen in different percentages of 5%, 10% and 15%. After the coatings formation, their microstructure, chemical composition and corrosion behavior were studied. The microstructure of the samples coated was studied by the scanning electron microscope (SEM), their elemental and phase composition by energy diffraction spectroscopy (EDS), X-ray diffraction (XRD) and elemental distribution was carried out by mapping (MAP) analysis. In order to study the corrosion behavior of coatings, the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests were carried out in a simulated body fluid (Ringer's solution). Immersion time of specimens was determined 1, 24, 48 h and 7 days in Ringer's solution. The results of different tests showed that coatings containing 15% nitrogen consisted of hard orthorhombic and hexagonal tantalum nitride phases, had free pores and denser microstructure. This coating exhibited better corrosion behavior than the other two ones in all of the immersion times. The corrosion resistance of this coating also increased by rising immersion time from 1 h to 7 days. In fact, the coating containing 15% of nitrogen being immersed for 7 days with a resistance of 118.68 (MΩ.cm2), had the highest corrosion resistance.

Facile synthesis of N-doped hollow carbon nanospheres wrapped with transition metal oxides nanostructures as non-precious catalysts for the electro-oxidation of hydrazine

In the present work, N-doped hollow carbon nanospheres (N-HCNSs) is prepared by direct carbonization of polyaniline-co-polypyrrole (PACP) hollow spheres without template needing. Two different NiO nanostructures (nanosheets and nanowires) are prepared by forming a shell around the N-HCNSs via simple hydrothermal/calcination processes ([email protected] and [email protected]). The morphology and structure of the nanostructures are characterized using field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The prepared nanocomposites are used as catalysts for the electrocatalytic oxidation of hydrazine. The electrocatalytic activities of different electrodes including GCE, N-HCNSs/GCE, NiO-NPs/GCE, [email protected]/GCE and [email protected]/GCE for hydrazine oxidation are compared using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques. The obtained results revealed significantly higher electroactive surface area (ECSA), higher catalytic activity, lower over-potential and better stability of [email protected]/GCE toward the hydrazine electro-oxidation. This observation can be related to the different parameters such as the unique nanowires structure with free pores and the enlarged specific surface area, high conductivity of N-HCNSs, and the synergistic effect between NiO and N-HCNSs.

The Effect of Aqueous–Ethanol Sodium Chloride Solutions on the Selectivity and Electrosurface Properties of an Acetyl Cellulose Membrane

The electrokinetic properties and selectivity of an acetyl cellulose membrane with respect to 0.0001 mol/L sodium chloride solutions in water–ethanol mixtures have been studied. The electrical conductivity, streaming potential, and filtration and selectivity characteristics of the membrane have been measured. It has been found that, in solutions with alcohol contents of 4 and 12%, the membrane selectivity with respect to sodium chloride is increased and decreased relative to that in an aqueous solution, respectively. No correlation between the membrane selectivity and its surface charge has been observed. The membrane has been found to possess a slight selectivity (20–26%) with respect to ethanol. It has been hypothesized that the solvation enthalpy of electrolyte ions changes differently in a free solution and membrane pores at different contents of ethanol in the mixtures, thereby affecting the membrane selectivity.