Thin Top Layer Research Articles

Direct-through channels of ZIF-8 composite membranes via in-situ PolyBMA sealing: Radical-induced phase transformation and dye removal efficiency

Metal-organic frameworks (MOFs)-based hybrid composite membranes are promising candidates for achieving highly efficient water purification. In this study, a facile, novel pressure-induced filtration method involving in-situ polymerization of butyl methacrylate (BMA) was proposed for sealing ZIF-8 nanoparticles on top of polyethersulfone (PES) ultrafiltration membrane support. The developed (ZIF-8+polyBMA)/PES composite membranes with thin toplayers of <1 μm present attractive water permeance (up to 31 LMH/bar) and good rejection of Congo red (99.2 %) and Methylene blue (99.1 %). The ZIF-8 particles served as direct-through channels with superior separation performance due to their high porosity and tunable pore structure, while the interstices were successfully sealed with polyBMA by in-situ polymerization, as demonstrated by SEM and dye removal experiments. It was found that the morphology of ZIF-8 transformed from a rhombic dodecahedron to two-dimensional hexagonal nanosheets during the fabrication process. We hypothesize that this surprising phenomenon is caused by the reaction of the initiators (Na2S2O5 and K2S2O8) that generate the hydroxyl and sulfate radicals attacking and transforming the Zn-MIM bond network of ZIF-8. However, insights into the structural changes need to be further investigated to understand the mechanism involved.

Tunable Assembly of Photocatalytic Colloidal Coatings for Antibacterial Applications.

In this study, evaporation-induced size segregation and interparticle interactions are harnessed to tune the microstructure of photocatalytic colloidal coatings containing TiO2 nanoparticles and polymer particles. This enabled the fabrication of a library of five distinct microstructures: TiO2-on-top stratification, a thin top layer of polymer or TiO2, homogeneous films of raspberry particles, and a sandwich structure. The photocatalytic and antibacterial activities of the coatings were evaluated by testing the viability of Methicillin-resistant Staphylococcus aureus (MRSA) bacteria using the ISO-27447 protocol, showing a strong correlation with the microstructure. UVA irradiation for 4 h induces a reduction in MRSA viability in all coating systems, ranging from 0.6 to 1.1 log. Films with TiO2-enriched top surfaces exhibit better resistance to prolonged exposure to disinfection and bacterial testing. The remaining systems, nonetheless, present higher antibacterial activity because of a larger number of pores and coating defects that enhance light and water accessibility for the generation and transport of reactive oxygen species. This work establishes design rules for photocatalytic coatings based on the interplay between performance and film architecture, offering valuable insights for several applications, including antibacterial surfaces, self-cleaning/antifogging applications, and water purification.

Contactless spectroscopy of photoactive centres in sapphire and nitride layered structures

Spectroscopy of photo-active centres in wide bandgap optical materials with absorption and emission bands in the range close to vacuum ultraviolet spectrum is complicated. In this work, the pulsed photo-ionization (PPI) transients, electron spin resonance (ESR) and proton induced luminescence spectroscopy techniques have been combined to evaluate the origin and parameters of deep centres in crystalline sapphire substrates. Additionally, the layered structures with MOCVD grown thin top layers of GaN, AlGaN and AlN on sapphire substrates were examined in order to clarify origin of emission bands related to the epilayers and sapphire. The sapphire assigned emission bands have been ascribed to the F+ centres, characterized by photo-activation energy of 4.8 eV. Prevailing of F+ centres has been confirmed by ESR spectroscopy results. The covering nitride layers of AlN, AlGaN and GaN led to appearance of the additional PPI spectral peaks ascribed to recombination on the interface between epitaxial material and sapphire substrate.

Feasibility study on thin‐film PV laminates for road integration

AbstractIntegration of photovoltaics (PV) into the built environment (BIPV) and infrastructure (IIPV) is required to increase the installed capacity of PV worldwide, while still leaving sufficient area for other land uses. Although BIPV applications have proven to play a significant role in the energy transition, road integrated IIPV concepts are less developed and bring challenges in mechanical and electrical stability and safety that still need to be addressed. In this work, the feasibility of integrating thin‐film CIGS (Copper Indium Gallium Selenide) modules into road tiles is investigated. PV road stacks were produced by gluing CIGS laminates onto concrete tiles and covering them with epoxy and glass granulates to form impact‐ and anti‐skid layers. IV (current–voltage) characteristics show that, respectively, a thin and thick epoxy layer results in 2% and 6.6% relative loss in power conversion efficiency. Although a thin protective layer would be beneficial to the power conversion efficiency of road modules, raveling tests show increased risk for electrical failure when a thin top layer is used. Pull‐off tests showed that the weakest adhesive strength (0.8 N/mm2) is between the thin‐film laminate and concrete, offering sufficient adhesive strength to at least withstand light traffic loading. Raveling and wheel tracking tests show no mass loss and only minor deformation of the stack, respectively, indicating no real risk of raveling or rutting. Thermal cycling and damp heat exposure of the PV road tiles show that yellowing of the top layers can significantly reduce performance over longer periods of outdoor operation. Damp heat exposure after mechanical loading shows no indication of moisture ingress on any of the tested configurations, suggesting the proposed CIGS laminate stack is able to withstand light traffic loading. From the measurement results, it can be concluded that thin‐film CIGS modules are mechanically and electrically suitable for road integration. Power conversion efficiencies over 12% can be attained with this technology, indicating its potential for renewable energy generation in road infrastructure. Performance stability can especially benefit from alternative top layer materials that maintain high transparency over long lifetimes. Additionally, pilot tests are required to demonstrate the potential of the technology in a controlled outdoor environment.

Positively charged nanofiltration membranes with gradient structures for enhancing separation properties

Creating a gradient structure in a separation layer is an effective approach for enhancing separation performance of thin film composite membranes. Here we present the preparation of a positively charged nanofiltration membrane with a gradient structure. An inner layer consisting of a loose polyester separation layer with large pores was formed through the interfacial polymerization (IP) reaction between triethanolamine (TEA) and trimesoyl chloride (TMC). And a dense and thin top layer composed of a polyamide separation layer was obtained by secondary interfacial polymerization (SIP) reaction using polyethyleneimine (PEI) along with unreacted TMC and residual acyl chloride groups of IP reaction. The influences of TEA concentration, PEI concentration and SIP time on the physicochemical properties and separation performances of the membrane were systematically analyzed. Our results show that the presence of the gradient structure optimized mass transfer pathways and reduced mass transfer resistance, resulting in significantly improved permeability of 13.0 ± 0.5 L·m−2·h−1·bar−1 (over 3 times compared with control-PEI), high MgCl2 rejection of 91.7 ± 0.6 %, and an excellent stability and anti-fouling performance. Our work provides valuable insights and guidance for developing high-performance positively charged NF membrane with gradient structures.

Selective Quantification of Bacteria in Mixtures by Using Glycosylated Polypyrrole/Hydrogel Nanolayers.

Here, we present a covalent nanolayer system that consists of a conductive and biorepulsive base layer topped by a layer carrying biorecognition sites. The layers are built up by electropolymerization of pyrrole derivatives that either carry polyglycerol brushes (for biorepulsivity) or glycoside moieties (as biorecognition sites). The polypyrrole backbone makes the resulting nanolayer systems conductive, opening the opportunity for constructing an electrochemistry-based sensor system. The basic concept of the sensor exploits the highly selective binding of carbohydrates by certain harmful bacteria, as bacterial adhesion and infection are a major threat to human health, and thus, a sensitive and selective detection of the respective bacteria by portable devices is highly desirable. To demonstrate the selectivity, two strains of Escherichia coli were selected. The first strain carries type 1 fimbriae, terminated by a lectin called FimH, which recognizes α-d-mannopyranosides, which is a carbohydrate that is commonly found on endothelial cells. The otherE. coli strain was of a strain that lacked this particular lectin. It could be demonstrated that hybrid nanolayer systems containing a very thin carbohydrate top layer (2 nm) show the highest discrimination (factor 80) between the different strains. Using electrochemical impedance spectroscopy, it was possible to quantify in vivo the type 1-fimbriated E. coli down to an optical density of OD600 = 0.0004 with a theoretical limit of 0.00005. Surprisingly, the selectivity and sensitivity of the sensing remained the same even in the presence of a large excess of nonbinding bacteria, making the system useful for the rapid and selective detection of pathogens in complex matrices. As the presented covalent nanolayer system is modularly built, it opens the opportunity to develop a broad band of mobile sensing devices suitable for various field applications such as bedside diagnostics or monitoring for bacterial contamination, e.g., in bioreactors.

Enhancing filtration flux and antifouling performance of PVDF membrane constructed from semi-interpenetrating network and block copolymers

Organic fouling causes the filtration property and serve life decrease of the PVDF membrane and is the challenge for filtration applications. Therefore, it is an urgency desire to construct a PVDF membrane with good filtration and antifouling for researchers. To this end, a based PVDF and poly(N-isopropyl acrylamide)(PNIPA) semi-interpenetrating network polymer was synthesized and used as membrane matrix for preparing semi-interpenetrating network/block copolymers blend membrane. The membrane composition, structure and performance were systematically characterized and investigated by FTIR spectrum, XPS, SEM, contact angle instrument and the other experimental techniques etc. Results indicate that the prepared membrane contains PVDF, PNIPA and block copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b- poly(ethylene oxide) (F127) components, shows a porous cross section comprising a thin top surface layer with small pores, a finger-shape lower layer and a sponge-shape pore bottom layer. When the membrane are used for the filtration of bovine serum albumin(BSA) in aqueous solution at 25 ℃, the rejection can exceed 95.0% at a high flux of 307 L/(m2·h·bar). Simply raising filtration temperature to 60 °C, the flux can reach 606 L/(m2·h·bar) while the rejection barely changes, significantly improving the filtration ability of the membrane. Furthermore, the flux can recover above 93% of the original value after a BSA filtration and a subsequent water washing. Undoubtedly, the prepared membrane displays great potential for filtering BSA aqueous solution and the reason can be ascribed to the synergy between PNIPA and F127 of the membrane.

Development of tuneable polyamine top layer for nanofiltration with high stability in bleach and at extreme pHs

State-of-the-art membranes for nanofiltration are thin film composite membranes, comprising of a thin top layer on top of a porous support. Many separation processes in organic chemistry involve extreme conditions, e.g. aggressive solvents, solvent-water mixtures or extreme pH, e.g. in acid mine drainage or in Cleaning-in-Place cycles. However, the most commonly used thin film composite membranes are polyamides, typically prepared by reaction of a tri(acyl chloride) and a diamine, often trimesoyl chloride and m-phenylenediamine, respectively, which cannot withstand these extreme conditions. This study aims at preparing chemically much more robust membrane based on polyamine. As diamine, 1,2-Diaminocyclohexane is used, due to its high reactivity and in order to mimic PIMs, following its rigidity and twisted structure. Analogous to trimesoyl chloride, 1,3,5-tri(bromomethyl)benzene was used. Unfortunately, no reproducible membranes could be achieved. This was solved by increasing the number of functional groups of the bromomethyl benzene from three to four, resulting in a membrane with both very good separation performance (e.g. 99.6 % Rose Bengal rejection at a permeance of 1.03 L m−2 h−1.bar−1) and excellent stability in extreme conditions (i.e. bleach and pH <1, >13). Additionally, the formed polyamine membrane is pH-responsive and can be adjusted to the application by post-treatment, i.e. further crosslinking or quaternization.

Oxidation properties of quaternary Zr-based diboride thin films grown by hybrid high-power impulse/DC magnetron co-sputtering

Sputter-deposited transition metal diborides are subject of increasing attention for protective hard coatings. However, they suffer from high brittleness and rapid oxidation. Alloying with Ta increases their toughness, but their oxidation resistance requires further enhancement. Here, the influence of adding Si on the microstructure, mechanical, and oxidation properties of quaternary Zr1−(x + y)TaxSiyBz thin films grown by hybrid high-power impulse/DC magnetron co-sputtering (ZrB2-DCMS/Ta-HiPIMS/Si-DCMS) is studied. The layers are deposited at two different conditions of Ta-target HiPIMS powers and frequencies (30 W/100 Hz and 60 W/200 Hz series) with Si-target DCMS powers PSi = 0, 10, 15, and 20 W, while the ZrB2-target DCMS power is maintained constant at 200 W. For the 30 W/100 Hz series, x decreases from 0.20 to 0.15, y increases from 0 to 0.22, and z decreases from 2.0 to 1.8 by increasing PSi. The Ta/metal ratio remains constant at x = 0.3 for the 60 W/200 Hz series, while y increases from 0 to 0.1, and z decreases from 1.7 to 1.4. All layers show columnar growth and crystallize in a hexagonal-diboride structure, but crystal orientations change by increasing PSi. The 60 W/200 Hz series have much denser microstructure than the 30 W/100 Hz series. The 60 W/200 Hz series have high hardness values (≥35 GPa), while the hardness of the 30 W/100 Hz series significantly decreases from ∼37 to ∼21 GPa as a function of PSi. Zr0.7Ta0.3B1.7 has markedly better high-temperature oxidation resistance than Zr0.8Ta0.2B2.0 due to the formation of protective B-containing oxide scales. Alloying with Si considerably decreases the oxidation rate of the 30 W/100 Hz series owing to the formation of oxide scales containing a ZrSiO4 phase with a thin Si oxide top layer; however, the oxidation rate increases for the 60 W/200 Hz series as these quaternary alloys do not contain sufficiently high B and Si to form oxidation protective barriers.

Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures

Surface enrichment in Al, Si, and Cr can greatly improve high temperature oxidation resistance of many alloys. Al, Si, and Cr coatings are commonly applied via simple slurries or more complex pack cementation processes. Due to the high melting point of Cr, the deposition of Cr-based diffusion coatings by the slurry technique has proved challenging, and to date, Cr has mostly been applied by pack cementation. Here, a novel Cr-Si coating process via the slurry technique is described which has been developed and then demonstrated on two Ni-based superalloys, Rene 80 and Inconel 740H. The addition of Si to the slurry lowers the melting point via a Cr-Si eutectic and enables the formation of a liquid phase during heat treatment. Through this Cr-Si slurry coating process diffusion layers enriched by Cr and Si of about 150 µm were achieved. Oxidation behavior was studied through isothermal exposures at 900 °C for 1000 h in lab air. Uncoated Rene 80 and IN740H both showed formation of a Ti-containing Cr2O3 scale below a thin TiO2 top layer. Underneath the external scale a zone of internally oxidized Al grew over the exposure time and reduced the load-bearing cross-section progressively. In comparison, the Cr/Si-coated samples did not show internal Al oxidation, but a slow-growing Si-rich oxide film underneath the external Cr2O3 scale. This subscale represents an additional oxygen diffusion barrier. Thus, the weight gain during exposure for the coated samples was significantly lower than for the uncoated materials.

Tribological Behaviour of Low Temperature Plasma Assisted Carburized 316 L Steel Produced by L-PBF Technique

Austenitic stainless steels produced by Laser Powder Bed Fusion (L-PBF) are interesting materials because of their excellent corrosion resistance. Due to their relatively low hardness, the tribological response of these materials is poor, which limits their use in applications where control of wear degradation is important. Nevertheless, low-temperature plasma-assisted carburisation is an interesting process for improving the wear resistance of austenitic stainless steels, as has been observed for wrought materials. In fact, the increase in hardness is guaranteed by a surface layer of expanded austenite (S-phase) with a thin top layer of amorphous carbon. In this work, AISI 316 L, produced by the L-PBF technique, was carburised using 5 different plasma gas mixtures (by varying the CH4/H2 ratio) at 475°C for 7 hours. The samples obtained were then subjected to a detailed microstructural characterisation in order to obtain information on surface modification. The morphological features of the surface were examined by SEM observations in top view and in cross-section. The tribological performance was evaluated by pin-on-flat tests (alumina sphere as counter-material) with 2 different applied loads and a stroke length of 5 mm. Friction coefficient, wear rate (stylus profilometer) and wear mechanisms (SEM) were also evaluated. Preliminary results show an increase in wear resistance of all plasma treated materials compared to the untreated material. The improved tribological performance was discussed in relation to the abrupt increase in surface hardness.

Modified ceramic membranes for the treatment of highly saline mixtures utilized in vacuum membrane distillation

Membrane Distillation processes could enable the treatment of highly saline solutions and facilitate minimal (MLD) or zero liquid discharge (ZLD) applications. Ceramic membranes can be a robust alternative to polymeric membranes if they are chemically modified to exhibit hydrophobic qualities to prevent wetting, particularly for vacuum membrane distillation (VMD). This study found that the thin top layer of asymmetrically structured ceramic membranes is robust enough for highly saline and abrasive suspensions and that TiO2 membranes outperform Al2O3 membranes in respect to the mass transport due to their larger support pore size and lower thermal conductivity. A maximum permeate flux of 35 kg/(m2 h) with exceptionally high rejections were measured in VMD using a saline brine with a concentration of 350 g NaCl per kg H2O. Furthermore, a VMD mass transfer model was successfully adopted (based on the Dusty Gas Model) to facilitate the calculation of the mass transfer through asymmetrically structured TiO2 membranes. Model deficiencies such as the underestimation of polarization effects were discussed, and correction factors integrated accordingly. This was done to establish a mass transfer modelling fundament for asymmetrical ceramic membranes used in MD that can be extended in future works and possibly serve as a tool for membrane optimization.

Nanofiltration membrane with asymmetric polyamide dual-layer through interfacial polymerization for enhanced separation performance

Thickness reduction of polyamide separation layer played an important role in permeability enhancement of thin film composite (TFC) nanofiltration membrane. However, the practical application of TFC nanofiltration membrane with ultrathin polyamide layer is still a great challenge. Herein, we proposed a strategy for preparing nanofiltration membrane with asymmetric polyamide dual-layer through interfacial polymerization. The top polyamide layer is thin, smooth and dense. The bottom polyamide layer is relatively thick, rough and porous. The thin and dense top polyamide layer enabled membrane with relatively high water permeability (18.5 ± 1 L m−2 h−1 bar−1) and Na2SO4 rejection (97.2 ± 0.8 %) performance. The thick and porous bottom polyamide layer guaranteed membrane stability. This study offers a promising strategy for polyamide composite membrane fabrication with enhanced separation performance.

Impact of soot deposits on waste gas-to-electricity conversion in a TiO2/WO3-based photofuel cell

An unbiased photo-fuel cell (PFC) is a device that integrates the functions of a photoanode and a cathode to achieve simultaneous light-driven oxidation and dark reduction reactions. As such, it generates electricity while degrading pollutants like volatile organic compounds (VOCs). The photoanode is excited by light to generate electron-hole pairs, which give rise to a photocurrent, and are utilized to oxidise organic pollutants simultaneously. Here we have systematically studied various TiO2/WO3 photoanodes towards their photocatalytic soot degradation performance, PFC performance in the presence of VOCs, and the combination of both. The latter thus mimics an urban environment where VOCs and soot are present simultaneously. The formation of a type-II heterojunction after the addition of a thin TiO2 top layer over a dense WO3 bottom layer, improved both soot oxidation efficiency as well as photocurrent generation, thus paving the way towards low-cost PFC technology for energy recovery from real polluted air.

Towards fully epoxy-based thin film composite membranes for solvent-resistant and solvent-tolerant nanofiltration

Epoxy curing is a versatile chemistry that can be applied in membrane preparation, both via phase inversion and interfacial polymerization. Here, fully epoxy-based TFC membranes are demonstrated for the first time and tested for solvent-tolerant nanofiltration (STNF) applications. First, UF membranes with a retention for bovine serum albumin (BSA, ∼66000 g mol−1) of ∼40% and a water permeance of 171 L m−2 h−1 bar−1 were prepared via phase inversion by pre-curing epoxide resins (EPON™ resin 1009F and EPON™ resin SU-8) with 1,6-hexanediamine (HDA) prior to phase inversion in water. Subsequently, selective top layers were synthesized on these supports layers via interfacial polymerization (IP) or interfacial initiation of polymerization (IIP) of the same epoxy resins, resulting in a thin selective top layer of the same material. By using different amines, different epoxide ring-opening polymerizations (ROP) could be targeted. These TFC membranes were then tested for use in water-solvent mixtures and achieved a 92.8% methyl orange (MO, 327 g mol−1) retention and a permeance of 0.21 L m−2 h−1 bar−1 in a 20/80 DMF/water feed solution. Cured epoxy chemistry is known for its excellent chemical stability, making these membranes suitable for a wide variety of solvent-resistant NF (SRNF) and STNF applications.

Estimation of Root-Zone Soil Moisture in Semi-Arid Areas Based on Remotely Sensed Data

Soil moisture (SM) is a bridge between the atmosphere, vegetation and soil, and its dynamics reflect the energy exchange and transformation between the three. Among SM at different soil profiles, root zone soil moisture (RZSM) plays a significant role in vegetation growth. Therefore, reliable estimation of RZSM at the regional scale is of great importance for drought warning, agricultural yield estimation, forest fire monitoring, etc. Many satellite products provide surface soil moisture (SSM) at the thin top layer of the soil, approximately 2 cm from the surface. However, the acquisition of RZSM at the regional scale is still a tough issue to solve, especially in the semi-arid areas with a lack of in situ observations. Linking the dynamics of SSM and RZSM is promising to solve this issue. The soil moisture analytical relationship (SMAR) model can relate RZSM to SSM based on a simplified soil water balance equation, which is suitable for the simulation of soil moisture mechanisms in semi-arid areas. In this study, the Xiliaohe River Basin is the study area. The SMAR model at the pixels where in situ sites were located is established, and parameters (a, b, sw2, sc1) at these pixels are calibrated by a genetic algorithm (GA). Then the spatial parameters are estimated by the random forest (RF) regression method with the soil, meteorological and vegetation characteristics of the study area as explanatory variables. In addition, the importance of soil, climatic and vegetation characteristics for predicting SMAR parameters is analyzed. Finally, the spatial RZSM in the Xiliaohe River Basin is estimated by the SMAR model at the regional scale with the predicted spatial parameters, and the variation of the regional SMAR model performance is discussed. A comparison of estimated RZSM and in-situ RZSM showed that the SMAR model at the point and regional scales can both meet the RMSE benchmark from NASA of 0.06 cm3·cm−3, indicating that the method this study proposed could effectively estimate RZSM in semi-arid areas based on remotely sensed SSM data.

The antifouling and separation performance of an ultrafiltration membrane derived from a novel amphiphilic copolymer containing a crown ether

Amphiphilic copolymers have attracted extensive attention for the preparation of ultrafiltration (UF) membranes processed with high separation and antifouling performances. Herein, hydrophilic crown ether (dibenzo-18-crown-6-ether, DE) units were introduced into poly(p-terphenyl, isatin) (PDTI) based on a polycondensation reaction via superacid-catalysis. The copolymers showed good thermal stability and membrane-forming properties, and the UF membranes fabricated by NIPS exhibited excellent separation performance. The content of the hydrophilic DE significantly influenced the morphology structure of the UF membranes. The cross-section structure of the membranes gradually converted from finger-like pores to loose sponge pores during delayed phase separation. The water flux of membranes ascended from 130.9 LMH bar−1 to 286.6 LMH bar−1 while the BSA rejection rate decreased from 99.4% to 90.8% as the DE content increased from 10% to 30%. These changes were associated with an enhanced surface porosity, larger surface pore diameter, and thinner top layer. Moreover, increasing the DE content in the copolymer greatly improved the antifouling performance due to greater hydrophilicity. Upon increasing the molar ratio of DE to p-terphenyl from 1: 9 to 3: 7, the flux recovery rate of the membranes surged from 58.5% to 91.5% and remained >80.2% after three fouling-cleaning cycles. In addition, the surface segregation of the hydrophilic DE segment in the copolymer was confirmed by the higher oxygen element content of the UF membrane on the top surface (18.62%) than that of the polymer (13.97%). Therefore, the amphiphilic copolymer containing a crown ether synthesized by a one-pot polycondensation reaction provides an effective way for the preparation and property adjustment of UF membranes.

Chemical cleaning and membrane aging of poly(vinylidene fluoride) (PVDF) membranes fabricated via non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS)

Poly(vinylidene fluoride) (PVDF) is one of the most used membrane materials in the water industries, and the PVDF membrane can be fabricated majorly through non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS). The differences in membrane aging of NIPS-PVDF and TIPS-PVDF remain unclear. In this study, the agings of commercially available NIPS-PVDF and TIPS-PVDF membranes were investigated in the pilot-scale MBRs experiment as well as in the batch soaking tests. The raw PVDF powders in different crystalline polymorphs were also subjected to aging tests to examine the relation between PVDF polymorphous structure and aging. The results showed that the NIPS-PVDF membrane experienced more severe aging in the pilot-scale MBR experiment in comparison with the TIPS-PVDF membrane. Acid aging dislodged and eliminated the additives in the membrane, but did not attack the PVDF. NIPS-PVDF membrane was the dominant β PVDF phase, which was more susceptible to dehydrochlorination in alkaline oxide aging. The thin top layer in the asymmetric structure of the NIPS-PVDF membrane resulted in its vulnerability against alkaline oxide aging. The α PVDF phase and the symmetric structure of the TIPS-PVDF membrane contributed to its greater stability in alkaline oxide aging. Overall, the results can provide a basis for selecting a chemical cleaning strategy for PVDF membranes, and for improving the anti-aging characteristics of the PVDF in the membrane fabrication.

Ultrasonic imaging through reverberation media

Thin layered media like thermal barrier and corrosion resistant coating layers, are important components to protect and strengthen the base materials. Nevertheless, the non-destructive testing (NDT) of base materials under thin layer media are still strongly demanded. However, surface and reverberation waves propagating in the top thin layer deteriorate the ultrasonic imaging results of base materials. Particularly, they overwhelm the reflection waves of defects, making ultrasonic NDT of base materials a challenge. These waves are determined by the structural of testing objects and called structural noises. Here, a pre-process of ultrasonic total focusing method is proposed to remove the structural noises. The pre-process utilizes the different similarity characteristics of structural noises and defect signals in diagonal matrices to suppress the noises by principal component analysis. The experimental results show that it can effectively improve the SNR about 5–8 dB and reduce array performance indicators about 30–40%.

Synthesis of hierarchical LTA zeolite membranes by vapor phase transformation

Weakening the mass transfer resistance inside the selective layer of membrane can effectively increase the membrane separation performance. In this study, we introduce macropores into the conventional LTA zeolite membrane layer, resulting in an unprecedented hierarchical membrane structure. Specifically, the hierarchical LTA zeolite membranes composed of a macroporous zeolite layer and a thin dense top layer (600 nm), are fabricated on rough α-Al2O3 tubular supports by vapor phase transformation method using mesoporous silica spheres (MSPs) as the porogen in the precursor layer. The H2 (N2) permeance of the hierarchical LTA zeolite membrane is near 10 times that of the conventional LTA zeolite membrane, indicating that the hierarchical pore structure can effectively weaken the mass transfer resistance inside the selective layer of membrane. And it has good pervaporation performance for 90 wt% ethanol aqueous solution at 348 K, i.e., the flux can reach 4.54 kg m−2 h−1 with a separation factor of >10,000, which is much higher than that of the conventional LTA zeolite membrane. The preparation of LTA zeolite membranes with hierarchical pore structure using MSPs as a porogen is expected to open up a new way for the construction of zeolite membranes.