Top Surface Layer Research Articles

Solid state dewetting of Ni-Co bilayers on sapphire during slow heating and cooling

We studied the solid state dewetting of thin Ni films and Ni-Co bilayers deposited on sapphire substrate during slow heating to several target temperatures. We demonstrated that during initial stages of dewetting and bilayers intermixing, Ni atoms from the top layer diffuse along the interface between the bottom Co layer and sapphire, simultaneously with Co atoms diffusion on the surface of Ni layer. This alloying of the top surface layer with Co slows down the rate of thermal grain boundary grooving and leads to the increase of the thermal stability of the bilayers with increasing Co content. We also observed that during intermediate stages of dewetting the regions of the untransformed film with increased thickness are dotted with small surface pores of 20–30 nm in diameter reaching to the level of as-deposited film. We related the formation and extraordinary stability of these pores with the modalities of surface diffusion of metal atoms in the presence of segregated impurities. In particular, we emphasized the role of Ehrlich-Schwoebel barrier for adatoms attachment to the edge of (111) terrace in formation of the pores. Our results indicate that the fine features of surface diffusion and surface thermodynamics, together with the presence of impurities and defects in the film lead to a rich variety of film morphologies during solid state dewetting.

Effect of stacking faults in nanograins on the tensile properties of Mg–Y–Nd–Gd–Zr alloys subjected to ultrasonic surface rolling processing

In this study, an Mg–Y–Nd–Gd–Zr alloy was subjected to ultrasonic surface rolling processing (USRP), and a deformation layer approximately 651 μm deep was observed. It shows a double-gradient microstructure as the grain size increased and the twin density decreased. The grain size at the top surface layer was refined to 147.08 nm, and several stacking faults (SFs) were observed in the nanograins. Two main types of SFs were observed, including intrinsic I1 SFs bounded by 1/6〈202¯3〉 Frank partial dislocations and intrinsic I2 SFs bounded by 1/3〈101¯0〉 Shockley partial dislocations. The SFs induced a strong hindrance to dislocation motion, improving the yield strength of the alloy. Also, the dislocation caused by SFs increased the stress concentration of the nanograins and promoted premature fracture failure at the top surface of the alloy, reducing its plasticity after USRP. In addition, the tensile fracture of the alloy changed from plastic fracture mechanism dominated by micropore aggregation before USRP to brittle fracture mechanism dominated by cleavage planes and steps after USRP.

Adsorption of Oxygen to High Entropy Alloy Surfaces for up to 2 ML Coverage Using Density Functional Theory and Monte Carlo Calculations

High-entropy alloys (HEAs) manufactured with refractory elements are candidates for high-temperature structural applications. To enhance our understanding of oxidation in these complex systems, the early stages of oxidation on the surface of Al10Nb15Ta5Ti30Zr40 were studied using density functional theory and thermodynamic modeling. Surface slabs were generated from bulk configurations sampled from equilibrium using a multicell Monte Carlo method for phase prediction. The bulk structure was found to be a single BCC phase in good agreement with experimental observations. The oxygen adsorbed with a strong preference for sites with Ti and Zr and avoided sites with Nb-Al and Nb-Ta. The surface was shown to be highly reactive to oxygen, yielding a dominating oxygen coverage of two monolayers over the temperature range of 100 to 2600 K and an oxygen pressure range of 10-30 to 105 bar. Recovering a clean surface slab was not achieved until pressures approached vacuum conditions and temperature exceeded 1900 K, demonstrating the difficulty of oxygen removal from the surface. Grand canonical Monte Carlo simulations showed that high Nb content in the top surface layer reduced the surface reactivity to incoming oxygen. Inward oxygen diffusion at low coverage was preferred in regions rich with Zr but slowed with the addition of Ti and Al. Diffusion rates drastically decreased at 1 ML, especially in the region rich with Ti and Zr, where strong metal-oxygen bonds were reported. Our results indicated that a high content of Ti and Zr increased the reactivity of the HEA surface to oxygen. The presence of Nb also enhanced the resistance to oxygen adsorption, especially when partnered with Al and Ta. Inward oxygen diffusion was likely to occur at low coverage in regions rich with Zr but could be protected against with the addition of Al and Ti. The limitations of the present work are discussed. This study may provide insights that assist with devising short- and long-term mitigation strategies against material degradation related to high-temperature oxidation.

Contact damage tolerance of alumina-based layered ceramics with tailored microstructures.

This work demonstrates how to enhance contact damage resistance of alumina‐based ceramics combining tailored microstructures in a multilayer architecture. The multilayer system designed with textured alumina layers under compressive residual stresses embedded between alumina–zirconia layers was investigated under Hertzian contact loading and compared to the corresponding monolithic reference materials. Critical forces for crack initiation under spherical contact were detected through an acoustic emission system. Damage was assessed by combining cross‐section polishing and ion‐slicing techniques. It was found that a textured microstructure can accommodate the damage below the surface by shear‐driven, quasi‐plastic deformation instead of the classical Hertzian cone cracking observed in equiaxed alumina. In the multilayer system, a combination of both mechanisms, namely Hertzian cone cracking on the top (equiaxed) surface layer and quasi‐plastic deformation within the embedded textured layer, was identified. Further propagation of cone cracks at higher loads was hindered and/or deflected owed to the combined action of the textured microstructure and compressive residual stresses. These findings demonstrate the potential of embedding textured layers as a strategy to enhance the contact damage tolerance in alumina ceramics.

Formation of a Stable Surface Oxide in MnBi2Te4 Thin Films.

Understanding the air stability of MnBi2Te4 thin films is crucial for the development and long-term operation of electronic devices based on magnetic topological insulators. In the present work, we study MnBi2Te4 thin films upon exposure to the atmosphere using a combination of synchrotron-based photoelectron spectroscopy, room-temperature electrical transport, and atomic force microscopy to determine the oxidation process. After 2 days of air exposure, a 2 nm thick oxide passivates the surface, corresponding to the oxidation of only the top two surface layers, with the underlying layers preserved. This protective oxide layer results in samples that still exhibit metallic conduction even after several days of air exposure. Furthermore, the work function decreases from 4.4 eV for pristine MnBi2Te4 to 4.0 eV after the formation of the oxide, along with only a small shift in the core levels, indicating minimal doping as a result of air exposure. With the oxide confined to the top surface layers, and the underlying layers preserved, it may be possible to explore new avenues in how to handle, prepare, and passivate future MnBi2Te4 devices.

Extensive Roof Greenery as a Response to Heat Islands: Some Problems

Abstract Extensive roof greenery is one of the ways to reduce the extent and impact of urban heat islands. A prerequisite is the correct design and operation of both the structural and vegetation part of a roof. If adequate maintenance, especially irrigation of the greenery, cannot be ensured, the use of extensive roof greenery can also be counterproductive. The case study to be presented deals with problems of a flat roof with extensive greenery above an underground garage under Central European climate conditions. Infrequent irrigation leads to extremely high temperatures of the substrate in the summer and makes the purpose of this roof pointless. The contribution analyzes the reason for the failure of the vegetation part of the roof, which was claimed to be maintenance-free, points out fire safety issues, and suggests improvements that might be considered in similar cases. At the present time, which is marked by the climate change crisis, there is great societal pressure to build green roofs. However, if it is not possible to ensure their perfect functionality, it is perhaps better to use classically proven types of roofs, but with greater reflectivity of the top layer surface.

Catalytic Activities of Low‐Coordinated Ce for Methane Conversion

AbstractIn heterogeneous catalysis, the catalytic activity of an active center strongly correlates with its coordination number. In this work, density functional theory calculations corrected by on‐site Coulomb interactions were conducted to investigate the catalytic performances of the CeO4‐terminated reconstructed CeO2(100) (CeO4‐t) and the Ca‐doped CeO4‐t surfaces. The undoped CeO4‐t surface contains single 4‐fold coordinated Ce (Ce4c) sites on its top surface layer, and the Ca‐doped CeO4‐t surface can expose even lower‐coordinated 3‐fold Ce (Ce3c) sites. We found that the empty 4f states of the single Ce3c sites on the Ca‐doped CeO4‐t surface have much lower energies than that of the single Ce4c sites on the undoped CeO4‐t surface, which can effectively boost the reduction of Ce4+ to Ce3+. We further studied the selective oxidation of CH4 to CH3OH on the two surfaces and found that the isolated nature combined with the strong electron‐reservoir character of the single Ce3c site makes it highly desirable for the selective activation of the first C−H bond of CH4, while the subsequent C−H bond cleavage step is less affected by such low‐coordinated Ce and the CH3OH formation becomes more facile on the Ca‐doped CeO4‐t surface, giving rise to the high activity and selectivity of the Ca‐doped CeO4‐t surface toward the selective oxidation of CH4 to CH3OH.

Fabrication of Polyethersulfone (PES) Membrane Incorporated with Graphitic Carbon Nitride (g-C3N4) Nanoparticles in Palm Oil Mill Effluent (POME) Wastewater Treatment

Backed by the evolution in the nanotechnology field, membrane modified with nanoparticles as an additive has become increasingly prominent nowadays. The enormous potential of graphitic carbon nitride (g-C3N4) photocatalyst in wastewater treatment has been disclosed extensively. In this study, 4 Polyethersulfone (PES) membranes with different concentration of g-C3N4nanoparticles as additive were fabricated and their performances were investigated. Scanning Electron Microscopy (SEM) analysis showed that the membrane top surface layer was getting denser with the higher g-C3N4nanoparticles concentration which subsequently decreased the membrane mean pore size, porosity and flux. However the membrane with higher additive concentration was demonstrated a better improvement in anti-fouling properties where the flux recovery ratio (FRR) of the membranes showed an uptrend movement from 23.43% (membrane without additive) to 64.64% (membrane with 6 wt.% of additive). The enhancement of COD and colour removal rate from 61.50 % to 66.50 % and 78.75 % to 83.75 % was also observed in this study where the finding has signified the increased g-C3N4 nanoparticles concentration was constructive in PES membrane modification.

Investigation of Spray and Roll to Roll Coated Gas Diffusion Electrode Surface & Bulk Properties Using Microscopy and Spectroscopy

Further development of large-scale manufacturing capabilities for the most critical component in polymer electrolyte membrane fuel cells (PEMFC), the membrane electrode assembly (MEA) is needed. Advances in MEA manufacturing capabilities could reduce one of the major cost factors associated with MEA production, the platinum group metal (PGM) catalysts currently used at the cathode electrode for PEMFCs. While spray coating methods have been prevalently used at lab-scale for MEA fabrication, it is desirable to move towards roll-to-roll (R2R) techniques to enable scalable production. Gas diffusion electrode (GDE) based MEAs are easier to manufacture in a R2R fashion than catalyst coated membrane (CCM) based MEAs, since the catalyst layer is deposited directly on the gas diffusion media (GDM) without inducing the PEM swelling observed via other fabrication routes.1 Understanding interfacial properties of these electrodes is important for optimization of electrochemical performance and fabrication procedures employed for wide-scale manufacturing of PEM electrodes.Key surface properties such as surface morphology and surface chemistry, as well as the bulk electrode nanostructure and composition were analyzed for a variety of GDEs with catalyst layers (CLs) prepared by R2R and spray coating methods using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectroscopy (EDS). The R2R-coated GDEs were fabricated using the slot die and microgravure coating methods on the same GDM substrate (Freudenberg H23C8) and they were made with both alcohol- and water-rich ink solvent ratios. The ultra-sonic spray coated GDEs were fabricated using both SGL 29BC and H23C8 GDM. In some cases, the spray coated GDEs had an additional amount of ionomer added, referred to as ionomer overlayer.2,3 The water-rich slot die R2R-coated GDE and the spray-coated GDE with an additional ionomer overlayer achieved the highest performance from this set of GDEs. Additionally, these GDEs showed the highest ionomer content measured by both XPS and SEM-EDS and shared a similar level of low surface roughness, implying the differences in composition and performance result from the different coating processes. Interestingly, STEM-EDS didn’t reveal a higher ionomer concentration in these samples, suggesting that these fabrication methods enrich the top surface layer without a significant impact on the bulk electrode. It was also found that the different microporous layer (MPL) surface properties inherent to a specific GDM influence the electrode morphological properties such as surface roughness as well as surface chemistry. The differences in MPL porosity lead to a unique surface ionomer enrichment degree and morphology at the CL surface that will interface with the membrane. These CL surface properties that are in contact with the membrane are hypothesized to be the reason for the improved performance metrics despite fabricating the GDE based MEAs under the same conditions. This work improved the knowledge of how a change in just one material component, or varying the fabrication process, can lead in some cases to vast differences and in others to subtle changes in initial performance, while also demonstrating the effectiveness of multiple characterization techniques towards identifying processing-property-performance trends. Mauger, S. A., Neyerlin, K. C., Yang-Neyerlin, A. C., More, K. L. & Ulsh, M. Gravure Coating for Roll-to-Roll Manufacturing of Proton-Exchange-Membrane Fuel Cell Catalyst Layers. Journal of The Electrochemical Society 165, F1012–F1018 (2018).Wang, M. et al. Impact of Microporous Layer Roughness on Gas-Diffusion-Electrode-Based Polymer Electrolyte Membrane Fuel Cell Performance. ACS Applied Energy Materials 2, 7757–7761 (2019).Mauger, S. A. et al. Fabrication of high-performance gas-diffusion-electrode based membrane-electrode assemblies. Journal of Power Sources 450, (2020).

Theoretical insight into adsorption and dissociation of water on NiCr binary alloy surfaces: Early-stage oxidation mechanism

The effects of alloy surface composition and pre-adsorbed oxygen on the behaviors of H2O over Ni–Cr binary alloy surfaces were investigated by using the first-principles method. The surface energies and work functions for a series of Ni–Cr (111) alloy surfaces with different Cr concentrations were addressed to track the surface reactivities. An enhancement effect on the surface reactivity from Cr doping in the top-surface layer (TSL) of nickel substrates was identified. The locations of Cr in the TSL dramatically promoted exothermic adsorption of H2O and its decomposed products, including OH, O, and H. The calculated potential dissociation pathways further demonstrated that the successive dissociation of H2O molecules was substantially triggered in the presence of Cr doping in the TSL. By contrast, the Cr doping in the sub-surface layer hindered the dehydrogenation of H2O with a relatively higher energy barrier for OH dissociation. Moreover, with pre-adsorbed oxygen atoms closer to Cr, the first elementary step of H2O dissociation was easily fostered, whereas the OH dissociation was hindered. The Cr doping and O pre-adsorption accelerated the dissociation of H2O, which plays a critical role in the initial oxidation of nickel-based alloys in water- or oxygen-bearing environments.

Surface segregation of 3 mol % yttria-doped tetragonal zirconia particle studied by atomic-resolution scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy

Atomic structure of the surfaces in commercial 3 mol % yttria-doped tetragonal zirconia (TZP) nano-particulate powders were studied by atomic resolution scanning transmission electron microscopy (STEM), and the surface segregation of Y were investigated by STEM energy-dispersive X-ray spectroscopy (EDS) at atomic scale. STEM-EDS observations revealed that the Y cations tend to segregate on the top surface layer, forming a monolayer segregation structure. Static lattice calculations revealed that the surface segregation of Y is energetically favorable. These results indicate that Y surface segregation occurs in the TZP powders, which might partially account for the grain boundary segregation in the sintered body of TZP ceramics.

Elemental Analysis of Popular Zinc Rich Rice Varieties using ESEM and ICP-OES

A comparative study was carried out for elemental composition of grains of eight popular rice genotypes. The Environmental Scanning Electron Microscope (ESEM) setup was used to explore type and quantity of surface elements in various layers of rice grains. The main constituents are carbon and oxygen, with elements like Al and Si being prominently found on the husk. Rice kernels serve as staple food. We found that the top surface layer of whole rice kernel is rich in carbon compared to oxygen, but oxygen content increased in the internal area of kernel (endosperm in broken kernel) in all test genotypes. Further, our ESEM results showed that the husk of grain consists of more elements than the seed part. Though most of the above rice varieties are Zn and/or Fe rich, the ESEM facility could not identify them. ICP-OES analysis revealed Nagina-22 and R-RHZ-7 as highly zinc and iron rich rice varieties respectively. The knowledge of elemental composition of husk and whole kernel may pave the way for their effective uses in biofortification programme and as such for use as food, animal feed and industrial purposes.

Prevention in Thermal Crack Formation in Chabazite (CHA) Zeolite Membrane by Developing Thin Top Zeolite and Thick Intermediate Layers.

Chabazite (CHA) zeolite membranes with an intermediate layer of various thicknesses were prepared using planetary-milled seeds with an average particle diameter of 300, 250, 200, 140, and 120 nm. The 120 nm seed sample also contained several smaller particles with a diameter of 20 nm. Such small seeds deeply penetrated into the pore channels of the α-alumina support during the vacuum-assisted infiltration process. During the secondary growth, the penetrated seeds formed a thick intermediate layer exiting between the zeolite layer and support. A decrease in seed size increased the penetration depth of seeds and the thickness of the intermediate layer, while the thickness of seed coating and zeolite layers was decreased. CHA zeolite membranes with a thin top zeoliate layer and a thick intermediate layer showed an excellent water/ethanol separation factor (>10,000) for 90 wt.% ethanol at 70 ℃ with a total flux of 1.5 kg m−2 h−1. There was no observation of thermal cracks/defects on the zeolite separation layer. The thick intermediate layer effectively suppressed the formation of thermal cracks during heating, since the tensile stress induced in the zeolite layer was well compensated by the compressive stress on the support. Therefore, it was successfully proven that controlling the microstructure of top surface and intermediate layers is an effective approach to improve the thermal stability of the CHA zeolite membrane.

Polyurethane Electrospun Fiber Biomimetics Membrane for Constructing the Structure of Grain Layer with Good Breathability for Cattle Split Leather

The traditional thick coating on split leather does not have the ability to breathe like full grain leather. The air and water vapor permeabilities of full grain leather are well known properties due to its fiber woven structure. Simulating the fiber morphology and weaving structure of the dermis or grain layer is very important to construct a top surface layer for split leather. In this paper, a PU (polyurethane) foam layer is put first on the split to enhance the adhesion of a second application of a superfine fibrous PU resin. This foam uses well-known waterborne polyurethane foaming technology. This dried foam has good breathability because of high porosity. A superfine fiber membrane is next put atop of the foam layer by using an electro-spun polyurethane resin. This second resin imitates collagen fibers in the network structure of the leathers’ grain layer. Thus, this resultant electrospun fiber biomimetics membrane simulated the grain layer of natural leather. SEM showed the morphology and structure of this electrospun fiber biomimetic membrane to be like that of the grain layer of natural leather. The porosity and apparent density were basically the same as the grain of leather, which were 63.65% and 583.878 kg/m3 respectively. The air and water vapor permeability of the biomimetics membrane were also as high as 2250 mL·cm-2·h-1 and 8753.02 μg·cm-2·h-1 respectively. Therefore, the biomimetics membrane largely restored the ability to breathe of split leather. Thus, this method simulates the performance and structure of full grain leather and is a novel method for industrial production

Ge(001) surface reconstruction with Sn impurities

Defects play an important role for surface reconstructions and therefore also influence the substrate growth. In this work we present a first principle calculation for the Ge(001) surface without and with tin impurities incorporated into the top surface layer. By mapping the system onto an Ising-type model, with interaction constants taken from density functional theory, the stability of the surface reconstructions under the influence of different concentrations of tin impurities is explored. This approach allows us to simulate the possible phase transitions for the different surface reconstructions including the local structure around the tin impurity atoms. In addition, we compare our theoretical results with experimental STM images on clean and Sn-doped Ge(100) surfaces.

The Use of Subsidence to Estimate Carbon Loss from Deforested and Drained Tropical Peatlands in Indonesia

Drainage is a major means of the conversion of tropical peat forests into agriculture. Accordingly, drained peat becomes a large source of carbon. However, the amount of carbon (C) loss from drained peats is not simply measured. The current C loss estimate is usually based on a single proxy of the groundwater table, spatially and temporarily dynamic. The relation between groundwater table and C emission is commonly not linear because of the complex natures of heterotrophic carbon emission. Peatland drainage or lowering groundwater table provides plenty of oxygen into the upper layer of peat above the water table, where microbial activity becomes active. Consequently, lowering the water table escalates subsidence that causes physical changes of organic matter (OM) and carbon emission due to microbial oxidation. This paper reviews peat bulk density (BD), total organic carbon (TOC) content, and subsidence rate of tropical peat forest and drained peat. Data of BD, TOC, and subsidence were derived from published and unpublished sources. We found that BD is generally higher in the top surface layer in drained peat than in the undrained peat. TOC values in both drained and undrained are lower in the top and higher in the bottom layer. To estimate carbon emission from the top layer (0–50 cm) in drained peats, we use BD value 0.12 to 0.15 g cm−3, TOC value of 50%, and a 60% conservatively oxidative correction factor. The average peat subsidence is 3.9 cm yr−1. The range of subsidence rate per year is between 2 and 6 cm, which results in estimated emission between 30 and 90 t CO2e ha−1 yr−1. This estimate is comparable to those of other studies and Tier 1 emission factor of the 2013 IPCC GHG Inventory on Wetlands. We argue that subsidence is a practical approach to estimate carbon emission from drained tropical peat is more applicable than the use of groundwater table.

Severe plastic deformation-produced gradient nanostructured copper with a strengthening-softening transition

Low-excess energy twin boundary can effectively stabilize the conventional grain boundary. It has been reported that deformation-activated nanotwins in nanograined metals produced by severe plastic deformation techniques can significantly enhance mechanical-thermal stability. However, fabrication, structural evolution, and the effect of grain size and twin thickness on the mechanical stability of nanograined-nanotwinned metals, where both the grain size and twin thickness reach the nanometer scale (especially grain size is lower than 40 nm), remain unclear. In this study, a gradient nanostructured layer containing a nanograined-nanotwinned sub-layer region and an extremely refined twin-free nanograined top surface layer with grain size as small as ~10 nm is achieved on copper by using an ultrahigh-strain rate single point diamond turning technique. High-resolution transmission electron microscope observations, atomistic molecular dynamic simulations, and nanoindetation tests were performed to reveal the size-dependent mechanisms of grain refinement and hardness along the gradient direction. The propensity of deformation multifold twinning is increased firstly in large-size nanograins and then decreased once grain size is below ~48 nm, finally replaced by detwinning to form extremely fine twin-free nanograins at the topmost surface layer. In other words, both the zero-macrostrain-induced deformation multifold twinning and symmetry-breaking-based detwinning processes can continuously refine nanograins along the gradient direction. Critical grain sizes for deformation multifold twinning and detwinning are discussed. Interestingly, a Hall-Petch strengthening-softening transition is discovered at a critical grain size of ~30 nm in the gradient nanostructured layer. The softening mechanisms are elucidated to be attributed to the twin thickness effect on deformation mode in nanograined-nanotwinned structures and the pure grain boundary-mediated plasticity in extremely fine twin-free nanograins. A series of critical twin thicknesses for softening in nanograins with different grain sizes are discussed; that is, the smaller the grain size is, the smaller the critical twin thickness will be. This study offers the potential for understanding and developing stable nanostructured metals.

Surface instabilities of constrained elastomeric layers subject to electro-static stressing

Surface instabilities on the top surface of a soft elastomeric dielectric layer bonded on its bottom to a stiff substrate are investigated for two electro-static conditions: (I) a voltage difference imposed across the top and bottom surfaces of the layer which are both conducting, and (II) a voltage difference imposed across a rigid planar electrode above the layer and the conducting top surface of the layer. In the absence of surface energy, the critical voltage associated with the onset of instability of the planar state is shown to be a surface mode with any wavelength that is short compared to the layer thickness. With no layer pre-stretch and no surface energy, the uniform state in (I) has hydrostatic compression while that of (II) has hydrostatic tension, nevertheless the critical voltage is the same for both problems if the permittivity is the same for both systems. The role of equi-biaxial pre-stretch and surface energy is presented for both problems for neo-Hookean materials and for the Gent generalization. The thrust of the study is the investigation of the post-bifurcation behavior involving nonlinear interactions among the simultaneous surface modes associated with the critical voltage. The post-bifurcation response of Problem I is a crease-like mode with the top surface probing downward towards the lower surface. The opposite occurs for Problem II with the formation of a sharp ridge protruding towards the upper electrode. The bifurcation behavior is highly unstable leading to an extreme sensitivity to small imperfections. The study complements earlier work and highlights unresolved issues.

Magnetic field–influenced nanofiltration membrane blended by CS–EDTA–mGO as multi–functionality green modifier to enhance nanofiltration performance, efficient removal of Na2SO4/Pb2+/RR195 and cyclic wastewater treatment

Magnetic field–influenced nanofiltration membrane by blending of magnetic multi–functionality green modifier (CS–EDTA–mGO) was fabricated via phase inversion processes. Migration of superparamagnetic nanofiller particles into top surface layer of M6 NF–membrane by incorporating external magnetic–filed during casting phase improved the hydrophilicity, as well as formation of large pores diameters (1.57 nm) which offer a flux enhancement (84.2 kg/m2h), excellent fouling resistance (Rr of 26.4%, Rt of 39.4% and Rir of 25.0%) and highest flux recovery ratio (75.9%). The order of salt rejection for all modified NF–membranes was Na2SO4 > MgSO4 > NaCl and the efficiency of the membranes to reject salts follows the order of M6 > M4 > M0. The performance of M6 as magnetic field–influenced membrane in rejection of RR195 and MB was 21% and 42% higher than unblended membrane (M0), respectively. The highest removal efficiency of Pb2+ and Cd2+ observed for M6 (98.2% and 93.6%, respectively). M6 was more efficient in concurrent removing pollutants from mixed–solute feed. In this case, the existing of Na2SO4 enhanced the retention of RR195 from 97.2% to 99.3%. Long–term operation tests demonstrated the excellent stability of M6 for 18 h filtration with a limited reduction in rejection and water flux of single salt solution. M6 membrane has found potential application in cyclic textile wastewater treatment which the water flux was found to be constant over 3–repeated filtration cycles.

Structurally Asymmetric Porous Carbon Materials with Ordered Top Surface Layers from Nonequilibrium Block Copolymer Self-Assembly

Inorganic materials with asymmetric pore structures provide increased accessibility and flux, making them attractive for applications in energy conversion and storage, separations, and catalysis. Non-equilibrium-based block copolymer structure-directed self-assembly approaches provide routes to obtaining such materials. We report a one-pot synthesis using the co-assembly and non-solvent-induced phase separation (CNIPS) of poly(isoprene)-b-poly(styrene)-b-poly(4-vinylpyridine) (ISV) triblock terpolymer and phenol formaldehyde resols. After heat-treatment, carbon materials with asymmetric pore structures result. They have a mesoporous top surface atop a porous support with graded porosity along the film normal. The walls of the macroporous support are also mesoporous, providing an additional structural hierarchy and increased specific surface area. We demonstrate how successfully navigating the pathway complexity associated with the nonequilibrium approach of CNIPS enables switching from disordered to ordered top surfaces in the as-made organic–organic hybrids and resulting carbon materials after thermal treatments. To that end, a combination of ex situ transmission small-angle X-ray scattering (SAXS) of the membrane dope solutions, in situ grazing-incidence SAXS (GISAXS) after dope solution blading and during solvent evaporation, and scanning electron microscopy (SEM) of the final membrane structures was used. We expect the final porous carbon materials exhibiting a combination of asymmetric, hierarchical pore structures and well-defined mesoporosity throughout the material to be of interest for a number of applications, including batteries, fuel cells, electrochemical double-layer capacitors, and as catalyst supports.