Polyvinylidene Fluoride Substrate Research Articles

Cracked-earth-like titanium carbide MXene membranes with abundant hydroxyl groups for oil-in-water emulsion separation

Membrane separation technology is one of the best methods to deal with wastewater released from oil spills and industrial wastewater. Therefore, we designed and prepared hydroxyl-rich titanium carbide MXene materials and filtered them onto a commercial polyvinylidene fluoride substrate membrane to obtain a cracked-earth-like MXene membrane with abundant hydroxyl groups and excellent underwater wettability. The underwater oil contact and sliding angles were approximately 157° and less than 3°, respectively. Moreover, the membrane effectively separated a variety of surfactant-stabilized stable emulsions with a high permeation flux of up to 6385 L m−2h−1 bar−1 and offered adequate performance after five cycles of the separation experiment. Additionally, the membrane exhibited remarkable resistance toward corrosive chemicals without any decrease in its underwater wettability performance. For example, the membrane was used to separate the emulsions containing alkali, salt, and acid. This study provides a new strategy to resolve the oily wastewater disposal problem by fabricating a cracked-earth-like MXene membrane with abundant hydroxyl groups.

PVDF-TiO2 core-shell fibrous membranes by microwave-hydrothermal method: Preparation, characterization, and photocatalytic activity

A polyvinylidene fluoride (PVDF) - titanium dioxide (TiO2) core-shell composite nanofibrous membrane (CNM) with photocatalytic activity was obtained from the microwave-assisted hydrothermal treatment of an electrospun PVDF membrane. The effects of the precursor solution acidity, the heating temperature, and the treatment time on the structure and the photocatalytic performance were investigated. The CNM obtained from a 2 M precursor acidic solution showed the presence of nanofibers (NFs) with a proper core-shell structure, wherein a TiO2 smooth shell was uniformly covering the electrospun PVDF NFs core. The TiO2 crystallographic phase was found to be temperature-dependent, with the highest anatase content observed at 120 °C. The mean PVDF-TiO2 NFs diameter measured from SEM images and the TiO2 fraction of CNM calculated from TGA results showed an accumulation of TiO2 on the PVDF NFs surface as heating temperature and treatment time increased. The photo-oxidation capability of the as-prepared CNMs was evaluated by the photocatalytic decomposition of aqueous methyl orange solution at room temperature under UV-C irradiation. PVDF-TiO2 CNM exhibited a stable performance after five cycles of the MO degradation due to a strong connection between the TiO2 layer and the PVDF substrate. The implemented approach has been demonstrated to be a feasible method for the synthesis of core-shell PVDF-TiO2 fibrous membrane. The influence of hydrothermal process parameters on the structure and final properties of PVDF-TiO2 CNM was revealed through a detailed mechanism investigation.

Facile preparation of polyvinylidene fluoride substrate supported thin film composite polyamide nanofiltration: Effect of substrate pore size

Polyvinylidene fluoride (PVDF) is rarely used as substrate membrane for thin film composite polyamide (PA) nanofiltration (NF) membrane due to its hydrophobic surface pushes water away during interfacial polymerization. According to Jurin's law, the pressure of membrane surface pushed water away is inversely proportional to the radius of membrane pore. In this study, a series of commercial PVDF membranes with pores ranging from 25 to 450 nm were used as substrates in a traditional interfacial polymerization. This preparation process does not need any pre-modification on substrate or specific equipment. It was found that the PVDF substrate pore size greatly influences the morphologies and surface properties of the corresponding TFC PA NF membrane. Only when a PVDF substrate has moderate pore size, such as 50 and 100 nm, could a continuous and defect-free PA layer will be formed, as verified through SEM characterization. The TFC membrane prepared with the PVDF substrate of 100 nm exhibits a 27.0 L m-2 h-1 bar-1 pure water permeance, and a 96.2% Na2SO4 rejection. The facile and effective method demonstrated in this study provides a new thought for the preparation of PVDF substrate supported PA NF membrane.

Continuous in situ portable SERS analysis of pollutants in water and air by a highly sensitive gold nanoparticle-decorated PVDF substrate.

The increasingly serious environmental pollution worldwide has posed a great threat to the ecosystem and human health, and yet the development of portable in situ monitoring techniques that are sensitive to gaseous and water pollutants remains incomplete. Herein, we report a highly active surface-enhanced Raman spectroscopy (SERS) substrate fabricated by immobilizing gold nanoparticles (AuNPs) onto a polyvinylidene fluoride (PVDF) membrane for continuous in situ SERS detection of pollutants in water and atmosphere. 4-Mercaptobenzoic acid (4-MBA) was adopted as a probe molecule to evaluate the performance of the substrate, and the results indicate that the polymer-based flexible substrate features high sensitivity, uniformity, and repeatability. The fabricated PVDF/SERS substrate was integrated with a portable Raman spectrometer operating under both passing-by and passing-through modes. The integrated system accomplishes quantitative detection and real-time online monitoring of pH in a liquid environment with a response speed of less than 10s and the rapid SERS response to gas molecules at a low concentration within 30s. We also demonstrated the highly sensitive detection for mainstream smoke (MS) and sidestream (SS) of cigarette smoke and verified their differences in the main constituent which contributes to the harmful secondhand smoke in public. The developed portable Raman system has excellent application prospects in online liquid and gas environmental detection.

Enhanced solar-driven evaporation process via f-MWCNTs/PVDF photothermal membrane for forward osmosis draw solution recovery

Product water recovery and draw solution (DS) reuse is the most energy-intensive stage in forward osmosis (FO) technology. Sucrose solution is the most suitable DS for FO application in food and beverages. However, sucrose DS recovery by conventional pressure-driven or thermal-driven concentration techniques consumes high energy. Herein, we developed a spontaneous and sustainable solar-driven evaporation process based on a photothermal membrane for the concentration and recovery of sucrose solution. The photothermal membrane composed of multi-walled carbon nanotubes (f-MWCNTs) phtotothermal layer on a hydrophilic polyvinylidene fluoride (PVDF) substrate. The f-MWCNTs photothermal layer with rough surface and interconnected network structures not only improves the light harvesting and light-to-heat conversion performance, but also facilitates the transport of water molecules. The hydrophilic PVDF substrate can promote the rapid transport of water for adequate water supply to photothermal layer. As a result, the optimized f-MWCNTs/PVDF photothermal membrane exhibits an excellent light absorption of 95%, and a high surface temperature of 74 °C at 1 kW m−2. Besides, it realizes an evaporation rate of 1.17 kg m−2 h−1 for 5% (w/v) of sucrose solution, which is about 5 times higher than that of the natural evaporation. The designed photothermal evaporation process is capable of concentrating sucrose solution efficiently from 5% to 75% (w/v), which has great potential in FO process and juice concentration.

Facile preparation of flexible all organic PEDOT:PSS/methyl cellulose thermoelectric composite film by a screen printing process

Screen printing technology was employed to prepare flexible all organic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/methyl cellulose (MC) composite films on a polyvinylidene fluoride substrate. The influences of the contents of MC and dimethyl sulfoxide (DMSO) post-treatment on thermoelectric properties of the as-prepared PEDOT:PSS/MC composite films were investigated. The electrical conductivity of the PEDOT:PSS/MC composite films was decreased with the contents of MC increasing, whereas the Seebeck coefficient was kept almost constant. A maximum power factor of 2.1 μW m−1 K−2 was obtained at 360 K for the composite film containing 25.67 wt% MC. After the DMSO treatment, the power factor was increased to 16.2 µW m−1 K−2 at 340 K, which was ~7.7 times as that of the untreated composite film (2.1 μW m−1 K−2 at 360 K). The screen printing technology has the characteristics of easy operation and suitable for large-scale production, and therefore it is a great potential method for fabrication of flexible thermoelectric materials.

Preparation of refreshable membrane by partially sacrificial hydrophilic coating

Polyvinylidene fluoride (PVDF) is widely used as a kind of water treatment membrane material, but its high hydrophobicity leads to easily being polluted by oily wastewater, which limits further development in the field of water treatment. In this paper, a simple and green strategy based on chitosan (CS) and tannic acid (TA) was taken to transform the hydrophobic PVDF membrane into superhydrophilic one. CS possessed excellent capability of antifouling but its surface binding affinity was relatively poor, while TA enjoyed wonderful surface adhesion and certain ability of absorbing water. Herein, combining the advantages of CS and TA, a special partially sacrificial coating was designed. (3-cholropropyl)trimethoxysilane (CTS) was used as a chain connecting the PVDF substrate with CS to form the first coating layer, and then TA was introduced as the second coating layer. Because of the unstable characteristic of CS coating, part of the polluted coating can be washed away by pure water with the contaminants. The modified membrane showed superhydrophilicity (the water contact angle was 17°) and underwater superoleophobicity (the underwater oil contact angle was 158°). Moreover, the initial pure water flux of modified membrane was 8579 L m−2 h−1, which was more than twice than that of pristine membrane (3057 L m−2 h−1). After the membrane was contaminated by toluene emulsion and rinsed thoroughly with pure water, the water flux recovery rate of the modified membrane reached about 98%, meaning the modified membrane possessed excellent anti-fouling and self-recovery ability. Besides, the rejection rate of toluene emulsion was 99.1%, showing the modified membrane could be used to efficiently handle the oil/water separation. During six cycles of being polluted and rinsed, the water flux recovery rate would decrease a little after each cycle, from 98% to 94.3% in the end, which demonstrated that the sacrificial layer did exist. This facile approach has great potential in practical water remediation.

Fabrication of nanofiltration membrane on MoS2 modified PVDF substrate for excellent permeability, salt rejection, and structural stability

• MoS 2 was first incorporated into PVDF substrates for fabricating novel TFN NFMs. • The TFN NFMs exhibited an enhanced water flux up to 21.5 LMH/bar. • The TFN NFMs showed a high rejection rate of 98.6% for Na 2 SO 4 . • High permeability, salt rejection, and structural stability were achieved concurrently. • The TFN NFMs exhibited a high actual seawater desalination potential ability. A thin-film composite polyamide membrane has been widely implemented in water desalination. However, the balance between permeability and selectivity by decreasing structural stability has restricted their larger-scale applications in water desalination. Here, we fabricated nanofiltration membranes (NFMs) by interfacial polymerization on polyvinylidene fluoride (PVDF) substrates modified with hierarchical flower-like molybdenum disulfide (HF–MoS 2 ). The thin-film nanocomposite (TFN) NFMs exhibited a water flux up to 21.5 LMH/bar and rejection rates of 98.6% for Na 2 SO 4 . Steric hindrance and Donnan exclusion together contributed to high salt rejection rates, as evidenced by a less polyamide layer thickness such as 56 nm and a high surface negative charge at pH 3–10. Note that the nanocomposite substrate became more porous, more hydrophilic, and rougher than the non-nanocomposite one, due to an increase in the fraction of macroporous on the surface, which was known to affect the performance of the polyamide layer. The high content of HF-MoS 2 incorporated in PVDF substrate led to enhanced hydrophilicity and, consequently, a cross-linking degree of defect-free polyamide, resulting in declines in thickness and increases in water permeability and salt rejection. Furthermore, TFN NFMs exhibited an excellent organic solvent resistance and long-term stability, indicating that HF-MoS 2 incorporation had no adverse effect but even improved their structural stability. Compared to NFMs without MoS 2 modification, NFMs with MoS 2 modification showed a better performance for desalination of real seawater and excellent anti-biofouling properties for lysozyme and bovine serum albumin. Taking together, the TFN NFMs provide high permeability and rejection rate without a decline in structural stability. Therefore, TFN NFMs were promising candidates for practical water desalination treatment.

Can Composite Janus Membranes with an Ultrathin Dense Hydrophilic Layer Resist Wetting in Membrane Distillation?

Tackling membrane wetting is an ongoing challenge for large-scale applications of membrane distillation (MD). Herein, composite Janus MD membranes comprising an ultrathin dense hydrophilic layer are developed by layer-by-layer assembling cationic polyethyleneimine and anionic poly(sodium 4-styrenesulfonate) polyelectrolytes on a hydrophobic polyvinylidene fluoride substrate. Using surfactant-containing saline water as the feed with low surface tension, experiments reveal that the number of polyelectrolyte layers, rather than surface wettability or surface charge, determines the anti-wetting performance of the composite Janus membranes. More deposited layers yield higher wetting resistance. With the aid of positron annihilation spectroscopy, this study, for the first time, demonstrates the origin of the excellent wetting resistance of the composite Janus membranes. The effective pore size of the polyelectrolyte multilayer decreases with an increase in the number of the deposited layer. The membrane with an ultrathin hydrophilic multilayer of 48 nm has a sufficiently small pore size to sieve out surfactant molecules from the feed solution via a size exclusion mechanism, thus protecting the hydrophobic substrate from being wetted by the low-surface-tension feed water. This study may pave the way for developing next-generation anti-wetting Janus membranes for robust membrane distillation.

A highly sensitive polydopamine@hybrid carbon nanofillers based nanocomposite sensor for acquiring high-frequency ultrasonic waves

Nanocomposite strain sensors have shown application prospect in a wide range of applications. However, the sensitivities of the existing nanocomposite strain sensors to high-frequency, microscope dynamic strains are rather unsatisfactory. Herein, we fabricate a highly sensitive nanocomposite sensor for acquiring micro-vibrations generated by ultrasonic waves, from polydopamine(PDA)-coated hybrid carbon nanofillers. First, multi-walled carbon nanotubes (MWCNTs) are coated by 10s nm thick viscous PDA to improve their compatibility with polyvinylidene fluoride substrates. Compared to uncoated MWCNTs, the use of 15 wt% PDA-coated MWCNTs leads to a 40% increase in sensitivity. Then, one-dimensional PDA@MWCNTs are mixed with two-dimensional single-layer graphene to enhance the geometric contact between nanofillers. The sensitivity of sensors with hybrid nanofillers far exceeds that of PDA@MWCNT sensors. Also, as the mass fraction of graphene within hybrid nanofillers expands from 33% to 66%, the sensitivity of the proposed sensor improves by approximately 120%, surpassing that of pure graphene sensors. The high sensitivity of the proposed sensor, which actually utilizes a lower graphene content, was shown to be derived from the synergy between the two types of nanofillers which are of different dimensionalities. This study presents a novel approach for optimizing the sensitivity of nanocomposite strain sensors to high-frequency micro-vibrations.

Carbonization of gradient phenolics filled in macroporous substrates for high-flux tight membranes: Toward ultrafiltration of polypeptides

Tight ultrafiltration (UF) membranes with high permeances have gained growing attention in the separation of biomacromolecules. Herein, we report the preparation of gradient carbonaceous structures filled in macroporous polyvinylidene fluoride (PVDF) substrates and their efficient separation of polypeptides. Gradient phenolics composed of nanoparticles with sizes increasing from top side to bottom side are firstly synthesized inside PVDF substrates. When soaked in concentrated H2SO4, phenolic nanoparticles are partially carbonized and foamed to form micropores while the PVDF substrate maintains intact. Thus-produced carbonaceous membranes are mechanical robust and exhibit narrowed pore sizes and enhanced hydrophilicity. Their permselectivity can be adjusted simply by changing the dosages of phenolic precursors filling into the PVDF substrates. Low dosages lead to remarkably high water permeances up to 1721 L/(m2·h·bar). At higher dosages, the membrane is tightened to show a molecular-weight-cut-off (MWCO) down to 3.7 kg/mol and high permeances several times larger than other membranes with similar MWCOs. We demonstrate that such a tight UF membrane efficiently separates polypeptides with molecular weights of only a few kg/mol (angiotensin Ⅱ and thymosin β4). Our work opens a new avenue for the synthesis of high-flux tight UF membranes with narrowed pores, enabling the precise separation and fractionation of biomacromolecules.

Unidirectional diffusion synthesis of covalent organic frameworks (COFs) on polymeric substrates for dye separation

Covalent organic frameworks (COFs) are regarded as important candidates for the preparation of advanced membranes with remarkable performances on account of their uniform and tailorable channels and good chemical stability. The development of COFs-based membranes is burgeoning, and there remains lacking of facile and mild methods to prepare to these membranes. Herein, we report on the unidirectional diffusion synthesis (UDS) of TpPa (an imine-based COFs) on commercial polyvinylidene fluoride (PVDF) microfiltration substrates for the preparation of composite COFs-based membranes at room temperature. The p-phenylenediamine (Pa) aqueous solution and 1,3,5-triformylphloroglucinol (Tp) n-hexane solution were separately charged into the two sides of a diffusion cell. With the suitable solution pairs and molar ratio of two precursors, only Pa molecules can pass through the macropores of PVDF to react with Tp molecules at the phase interface formed by this solution pairs, leading to the in situ synthesis of TpPa layer on the top side of PVDF substrates. The membrane fabricated with a synthesized duration of 24 h exhibits a superior selectivity for dyes (>90%) and appreciable water permeance (60 L·m−2·h−1·bar−1). The permeance of the resultant membrane is ∼2–20 times higher than other reported membranes with comparable dye rejections. The UDS offers a facile and mild process to directly grow COFs on porous polymeric substrates to construct composite membranes capable of efficient separations of dye molecules.

Biocatalytic PVDF composite hollow fiber membranes for CO2 removal in gas-liquid membrane contactor

A highly efficient biocatalytic carbonic anhydrase (CA)-polydopamine (PDA)/polyethylenimine (PEI)-polyvinylidene fluoride (PVDF) (referred to as CA-m-PVDF) composite membrane was fabricated for CO2 conversion and capture in the gas-liquid membrane contactor (GLMC) process. The co-deposition of PDA/PEI with amino functional groups was employed to amine-functionalize a PVDF substrate as support for subsequent in-situ CA immobilization by cross-linking with glutaraldehyde. This enhances the enzyme stability and prolongs its lifespan, thus facilitates CO2 hydration efficiency in the GLMC process. In this work, different immobilization CA protocols were compared based on the CA activity and activity recovery. For biocatalytic CA-m-PVDF membranes, the best activity of 498 U m−2 (membrane) and a corresponding activity recovery of 31.5% were achieved (m(5 h)-PVDF as support, 0.67 (v/v)% GLU as cross-linking agent, 600 μg mL−1 CA solution, pH 8.0, temperature at 25 °C, and 24 h reaction time). By using water as absorbent with a liquid velocity of 0.25 m s−1 in a bench-scale GLMC setup, a high-efficiency CO2 absorption flux of 2.5 × 10−3 mol m−2 s−1 was obtained, which was ~165% higher than that of the non-biocatalytic m-PVDF membrane. The long-term stability test showed a good enzyme activity for CO2 hydration capacity for the CA-m-PVDF membranes during 40 days of test duration. Overall, the results achieved in this work may provide promising insights into enzyme immobilization on polymeric supports for the development of high-efficiency biocatalytic membranes for CO2 capture in GLMC applications.

Development of quercetin imprinted membranes-based PVDF substrate

Molecular imprinting becomes the most outstanding approach in providing predetermined selectivity to the molecule of interest through the introduction of artificial recognition sites within the polymer matrix. This study presents the fabrication of quercetin-imprinted membranes (QIMs) for selective extraction of quercetin through surface imprinting polymerization method. Polyvinylidene fluoride (PVDF) membrane was used as the polymer support for the thermal polymerization process to take place and subsequent removal of quercetin from resultant polymer matrix leaves behind specific cavities that are complementary to the size, shape and functionality of quercetin molecules. QIMs and non-imprinted membranes were synthesized to evaluate and characterize the differences with respect to their morphology, chemical functionality as well as their binding behaviour towards quercetin and other components. The confirmation on the presence of imprinted layer on PVDF membrane was done through FTIR, FESEM and AFM analysis. Modelling of isotherm and kinetic adsorption also was performed to provide detailed insight into the adsorption mechanism of quercetin to the membranes. Membrane selectivity test was carried out using sinensetin and rosmarinic acid as competitive components.

Construction of SiO2@MWNTs incorporated PVDF substrate for reducing internal concentration polarization in forward osmosis

This work provides a facile and effective way of incorporating SiO2@MWNTs in polyvinylidene fluoride (PVDF) substrate to alleviate the internal concentration polarization (ICP) impact of the resultant thin film composite forward osmosis (TFC-FO) membranes for the first time. The in-situ decoration of multi-walled carbon nanotubes (MWNTs) using tetraethyl orthosilicate (TEOS) as precursor was conducted, resulting in improved hydrophilicity and the excellent dispersion of synthesized SiO2@MWNTs in PVDF membrane substrates accordingly. Effects of the SiO2@MWNTs concentration on the morphologies and properties of the modified substrates, and further impact on the polyamide (PA) layer structure are investigated via various characterizations. Besides, the intrinsic separation properties and forward osmosis performance of resultant TFC-FO membranes are also systemically studied. In comparison with the control TFC membrane, SiO2@MWNT-modified TFC membranes exhibit higher water fluxes with the enhanced membrane selectivity, as indicated by the decreased JS/JV values (from 1.10 to 0.19 g/L). This work therefore presents an alternative approach to prepare TFC-FO membranes with enhanced water flux as well as increased selectivity.

Fabrication and characterization of micro-patterned PDMS composite membranes for enhanced ethanol recovery

Bio-ethanol recovery via pervaporation process has drawn growing attention in the past few decades, however, its large-scale industry application remains limited due to the relatively low separation efficiency, especially in flux. In view of this, surface patterned nonporous PDMS (Polydimethylsiloxane) composite membranes with enhanced ethanol recovery efficiency were fabricated in this work. Line and space pattern was first printed on two-layer PVDF (Polyvinylidene fluoride) substrate using phase separation micromolding followed by modified immersion precipitation. And then PDMS solution prepared with three kinds of crosslinking agents (TEOS, Tetraethyl orthosilicate; VTES, Triethoxyvinylsilane; p-TTES, p-tolyltriethoxysilane) were cast atop the as-prepared patterned substrate as selective layer. Morphology, topography and surface chemistry were thoroughly characterized and results indicated that PDMS cross linked with TEOS showed the largest pattern size, while for membranes prepared with VTES and p-TTES, pattern size appeared to be smoothed. This can be mainly ascribed to the higher steric effect introduced by vinyl and phenmethyl groups, which increased the rigidity of polymer and thereby reduced the pattern size. Pervaporation performance for both patterned and non-patterned composite membranes under varied feed concentration and temperature were also evaluated. Evidence supported that permeate flux of patterned membranes cross linked with TEOS reached 977.73 g m−2 h−1 (45 °C, 2 wt% ethanol concentration) and are generally 2.11 times as high as that of non-patterned one. In addition, although increased the permeate flux, surface patterning exerted no adverse effect on membrane selectivity. The overall findings of this work provide a promising platform for nonporous composite membrane preparation to achieve high permeate flux without losing selectivity.

Performance of a pervaporation system for the separation of an ethanol-water mixture using fractional condensation.

Polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) composite membranes were fabricated and subsequently applied in ethanol recovery from an ethanol-water mixture by pervaporation (PV) using fractional condensation. The effects of feed temperature and feed flow velocity on the pervaporative properties of PDMS/PVDF composite membranes were investigated. Scanning electron microscopy (SEM) results showed that PDMS was coated uniformly on the surface of porous PVDF substrate, and the PDMS separation layer was dense with a thickness of 1.7 µm. Additionally, it was found that with increasing feed temperature, the total flux of the composite membrane increased, whereas the separation factor decreased. As the feed flow velocity increased, the total flux and separation factor increased. Besides, the permeate vapor was condensed by a two-stage fractional condenser maintained at different temperatures. The effects of the condensation conditions on fractions of ethanol-water vapor were studied to concentrate ethanol in product. The fractional condensers proved to be an effective way to enhance the separation efficiency. Under the optimum fractional condensation conditions, the second condenser showed a flux of 1,329 g/m2 h and the separation factor was increased to 17.2. Furthermore, the long-term operation stability was verified, indicating that the PV system incorporating fractional condensation was a promising approach to separate ethanol from the ethanol-water mixture.

Development of low mass-transfer-resistance fluorinated TiO2-SiO2/PVDF composite hollow fiber membrane used for biogas upgrading in gas-liquid membrane contactor

An inorganic-organic fluorinated titania-silica (fTiO2-SiO2)/polyvinylidene fluoride (PVDF) composite membrane was fabricated, via facile in-situ vapor-induced hydrolyzation method followed by hydrophobic modification. This low mass-transfer-resistance membrane, composing of a mesoporous layer deposited onto macroporous substrate, was designed for biogas upgrading in gas-liquid membrane contactor (GLMC) application. The surface hydroxylation was introduced to facilitate the bridging of TiO2-SiO2 nanoparticles and PVDF substrate, which resulted in a more coherent deposition of the fTiO2-SiO2 layer onto the substrate. The surface microstructure was fine-tuned by controlling the amount of doped Si precursor, forming an integrated mesoporous fTiO2-SiO2 layer. The resultant fTiO2-SiO2/PVDF composite hollow fiber membrane exhibited a tighter pore size of ~25 nm and a desired water contact angle of ~124°, which effectively prevented membrane wetting. The CO2 absorption fluxes of 8.0 and 5.6 × 10−3 mol m−2 s−1 were achieved due to the lower mass transfer resistance, by using 1 M of monoethanolamine (MEA) and sodium taurinate as absorbents with a liquid velocity of 0.25 m s−1, respectively. The long-term stability test showed a good integrity between the fTiO2-SiO2 layer and the PVDF substrate after 31-days of GLMC operation. The main benefit is the robust fluorinated inorganic layer which exhibited strong chemical resistance and high hydrophobicity, thus preventing membrane damage and pore wetting. Overall, this work provides an insight into the preparation of high–performance inorganic/organic composite hollow fiber membranes for carbon dioxide (CO2) removal in GLMC application.

Determination of stress-coefficient of magnetoelastic anisotropy in flexible amorphous CoFeB film by anisotropic magnetoresistance

Flexible magnetic devices are one of the indispensable flexible devices. However, the deformation of the magnetic devices will change the magnetic anisotropy of magnetic materials due to magnetoelastic anisotropy, which will decrease the performance of the devices. Therefore, it is essential to determine the stress-coefficient of magnetoelastic anisotropy in magnetic materials. Here, the magnetic anisotropy constants of an amorphous CoFeB film on a flexible polyvinylidene fluoride (PVDF) substrate in different stress states were quantitatively investigated by anisotropic magnetoresistance (AMR). The enhanced magnetic anisotropy of the CoFeB film at reduced temperature is due to magnetoelastic anisotropy induced by anisotropic thermal expansion of the PVDF substrate. Through fitting the AMR curves under variant fields in different stress states, the stress-coefficient of magnetoelastic anisotropy in the amorphous CoFeB film is obtained to be 170.7 × 103 erg cm−3 GPa−1.

Tight ultrafiltration membranes of mesoporous phenolic resin filled in macroporous substrates

Mesoporous polymers derived from supramolecules of phenolic resins (PRs) and block copolymers (BCPs) containing highly uniform pores with sizes down to a few nanometers, are expected to deliver promising membrane separation performances. Here we report on the preparation of mesoporous phenolic membranes exhibiting tight ultrafiltration properties through a pore-filling strategy. Solutions of PR/BCP supramolecules are filled into the macropores of polyvinylidene fluoride (PVDF) microfiltration membranes (substrates), followed by thermopolymerization to solidify the solution in the pores. Subsequently, the filled PVDF substrates are treated in hot H2SO4 to remove the BCP components, thus producing mesopores in the PR framework. The produced composite membranes are mechanical robust and ductile as mesoporous phenolic resins are tightly embedded in the pores of the PVDF matrix. The mesoscale porosity in the PR phases endow the composite membrane a tight ultrafiltration performance with the molecular-weight-cut-off (MWCO) down to 2350Da. The separation properties can be tuned simply by adjusting the dosage of supramolecule solutions used to fill the macroporous substrates. Considering the tight and uniform pore sizes and the robustness of phenolic resins, this strategy opens a new avenue to ultrafiltration membranes with low MWCOs or even nanofiltration membranes.