Characterization of a chlorine resistant and hydrophilic TiO2/calcium alginate hydrogel filtration membrane used for protein purification maintaining protein structure.

The development of membranes for protein purification has stringent requirement of disinfection resistance, low protein adsorption and anti-fouling, without changing protein structure. In this study, hydrophilic titanium dioxide (TiO2)/calcium alginate (TiO2/CaAlg) hydrogel membranes were prepared by a simple ionic cross-linking method. The effects of the porogenic agent polyethylene glycol (PEG) concentration, the molecular weight of PEG, and the concentration of TiO2 on the filtration properties were systematically investigated. The TiO2/CaAlg membrane exhibited excellent bovine serum albumin (BSA) rejection and anti-fouling properties. The mechanical properties and surface energy of the TiO2/CaAlg membrane were significantly improved. The chemical bonding mechanism of TiO2 and NaAlg was investigated by molecular dynamic simulation. The TiO2/CaAlg membrane had good chlorine resistance and could be disinfected or cleaned with sodium hypochlorite. The TiO2/CaAlg hydrogel membrane loaded with polyhydroxybutyrate (PHB) nanofibers maintained high flux (136.7 L/m2h) and high BSA rejection (98.0 %) at 0.1 MPa. The results of circular dichroism and synchronous fluorescence indicated that the secondary structure of BSA was maintained after membrane separation. This study provides one method for the preparation of green and environmentally friendly membrane for protein purification.

Constructing rapid water vapor transport channels within mixed matrix membranes based on two-dimensional mesoporous nanosheets.

Membrane technology is an effective strategy for gas dehumidification and fuel cell humidification. In this study, cerium fluoride oxide (F-Ce) two-dimensional (2D) mesoporous nanosheets and their composite with 1-ethyl-3-methylimidazolium dicyanamide ([Emim][DCA]) ionic liquids (ILs) (IL@F-Ce) are introduced as fillers into polyether block amide (PEBAX® 1074) to fabricate mixed matrix membranes (MMMs). The slit-shaped mesoporous structure of the nanosheets facilitates the construction of water vapor rapid transport channels in MMMs. The permeability and selectivity of water vapor for MMMs loaded with F-Ce nanosheets are greatly improved, and the performance of MMMs loaded with IL@F-Ce nanosheets are much better than the former. Particularly, the MMM with IL@F-Ce content of 4 wt.% achieves the highest H2O permeability of 4.53 × 105 Barrer, which is more than twice that of the pure PEBAX membrane, and the selectivity is increased by 83%. Thus, the MMMs based on 2D mesoporous nanosheets have considerable potential application in industrial-scale dehydration and humidification processes.

Superhydrophobic Surface-Constructed Membrane Contactor with Hierarchical Lotus-Leaf-Like Interfaces for Efficient SO2 Capture.

An organic-inorganic polyvinylidene fluoride/polyvinylidene fluoride-silica (PVDF/PVDF-SiO2) mixed matrix membrane contactor is fabricated via a facile and efficient hydrophobic modification method. The solubility parameters of the PVDF particle are precisely regulated, the PVDF particles are blended with SiO2 nanoparticles to form PVDF-SiO2 suspension, and then the suspension is introduced onto the surface of the PVDF substrate by an in situ spin coating strategy. The PVDF particles are partly etched and incorporated to construct the adhesive PVDF-SiO2 core-shell layer on the PVDF substrate, which results in a more stable PVDF-SiO2 coating layer on the substrate. The surface structure is precisely regulated by changing the etching morphology of PVDF particles and amount of doped PVDF and SiO2 particles, forming an integrated porous PVDF-SiO2 layer and constructing hierarchical lotus-leaf-like interfaces. The resultant PVDF/PVDF-SiO2 membrane contactors display the relatively regular distribution of pore size with ∼420 nm and excellent hydrophobic property with a water contact angle of ∼158°, which noticeably lightens wetting phenomena of membrane contactors. The SO2 absorption fluxes can reach as high as 1.26 × 10-3 mol·m-2·s-1 using 0.625 M of ethanolamine (EA) as liquid absorbent. The high stability of the SO2 absorption flux test indicates the excellent interface compatibility between the PVDF-SiO2 coating layer and the PVDF substrate. The versatile organic-inorganic layer exhibits super hydrophobic property, which prevents wetting of membrane pores. In addition, the membrane mass transfer resistance (H/Km) and membrane phase transfer coefficient (Km) are explored.

Light-responsive metal-organic framework sheets constructed smart membranes with tunable transport channels for efficient gas separation.

Exploring a new type of smart membrane with tunable separation performance is a promising area of research. In this study, new light-responsive metal-organic framework [Co(azpy)] sheets were prepared by a facile microwave method for the first time, and were then incorporated into a polymer matrix to fabricate smart mixed matrix membranes (MMMs) applied for flue gas desulfurization and decarburization. The smart MMMs exhibited significantly elevated SO2(CO2)/N2 selectivity by 184(166)% in comparison with an unfilled polymer membrane. The light-responsive characteristic of the smart MMMs was investigated, and the permeability and selectivity of the Co(azpy) sheets-loaded smart MMMs were able to respond to external light stimuli. In particular, the selectivity of the smart MMM at the Co(azpy) content of 20% for the SO2/N2 system could be switched between 341 and 211 in situ irradiated with Vis and UV light, while the SO2 permeability switched between 58 Barrer and 36 Barrer, respectively. This switching influence was mainly ascribed to the increased SO2 adsorption capacity in the visible light condition, as verified by adsorption test. The CO2 permeability and CO2/N2 selectivity of MMMs in the humidified state could achieve 248 Barrer and 103.2, surpassing the Robeson's upper bound reported in 2019.

Efficient CO2 Separation of Multi-Permselective Mixed Matrix Membranes with a Unique Interfacial Structure Regulated by Mesoporous Nanosheets.

A facile strategy to elevate gas separation performances of polymers is to introduce a versatile particle. In this study, the novel F-Ce nanosheets are synthesized, and then F-Ce is functionalized with 1-ethyl-3-methylimidazole thiocyanate (ionic liquids, ILs), obtaining multifunctional f-F-Ce nanosheets by the facile and environment-friendly methods. The multifunctional f-F-Ce nanosheets are incorporated into the Pebax (Pebax 1657) matrix to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The f-F-Ce nanosheets play versatile parts in elevating membrane gas separation performance. On the one hand, f-F-Ce tends to arrange horizontally and constructs a unique interfacial structure for cross-layer CO2 transport in MMMs. On the other hand, the abundant mesopores from f-F-Ce construct high-speed CO2 transport channels in MMMs and notably elevate the gas permeability. Moreover, the as-prepared MMMs separate CO2 efficiently due to the comprehensive improvements of diffusivity selectivity, solubility selectivity, and reactivity selectivity. First, the high aspect ratio of f-F-Ce provides the tortuous pathways for gas transport and generates the rigid interface between the Pebax matrix and f-F-Ce nanosheets, increasing the diffusivity selectivity. Second, SCN- groups from ILs show excellent affinity to CO2, enhancing the solubility selectivity. Third, amine groups from ILs with abundant methylimidazole generate reversible reaction with CO2 to elevate reactivity selectivity. Consequently, the f-F-Ce-doped MMMs display excellent CO2 permeability and CO2/CH4 selectivity. In particular, the MMM incorporated with 8 wt % f-F-Ce displays a CO2 permeability of 1823 Barrer and a CO2/CH4 selectivity of 35, overcoming the Robeson upper bound line (2008).

Hectogram-scale green synthesis of hierarchical 4A zeolite@CuO x (OH)(2-2x) (0 ≤ x < 1) nanosheet assemblies core-shell nanoarchitectures with Superb Congo red adsorption performance.

Delicate design of hierarchical nanoarchitectures has become a highly effective strategy to develop novel adsorbents with improved adsorption capacity. Herein, hectogram-scale green fabrication of hierarchical 4A zeolite@CuO x (OH)(2-2x) (0 ≤ x < 1) nanosheet assemblies core-shell nanoarchitectures (4A-Cu-T, T was the calcination temperature) with terrific Congo red (CR) dye adsorption performance was achieved through a simple, template-free and surfactant-free hydrothermal approach. A series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy demonstrated that all resultant adsorbents featured a core-shell structure with 4A zeolite as core ingredients and CuO x (OH)(2-2x) (0 ≤ x < 1) nanosheet assemblies as shell components. The adsorption experimental results pointed out that 4A-Cu-300 with a maximum adsorption capacity of 512.987 mg g-1 showed the best adsorption performance amongst all as-prepared adsorbents, and the adsorption capacity of shell component-CuO x Cu(OH)(2-2x) (0 ≤ x < 1) nanosheet assemblies was calculated up to 3685.500 mg g-1. The shell thickness and phase ratio of CuO and Cu(OH)2 in CuO x (OH)(2-2x) (0 ≤ x < 1) nanosheet assemblies played key roles in improving the adsorption capacity. The successive tests suggested that the "carbon deposition" resulted in the decreased adsorption capacity of first-regenerated adsorbents, but little variance in adsorption performance among regenerated samples demonstrated the good stability of such adsorbents. This work unlocks a method for the rational design of high-performance adsorbents via delicate decoration of poor-performance materials with nanosheet assemblies, which will endow the non-active materials with enhanced adsorption properties.

A porphyrin-based optical sensor membrane prepared by electrostatic self-assembled technique for online detection of cadmium(II).

An optical sensor membrane was prepared by electrostatic self-assembled technique for online detection of cadmium ion (II) (Cd(II)). The optical indicator 5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin p-toluenesulfonate (TMPyP) was adsorbed on a hydrolyzed polyacrylonitrile (PAN) membrane by electrostatic attraction and further immobilized through layer-by-layer deposition of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) on the membrane surface. The electrostatic self-assembly of polyelectrolytes on the membrane is influenced by pH and salt concentration of polyelectrolytes. The optical sensor membrane shows distinct color and spectral response to Cd(II) under static and flow-through conditions based on the coordination of TMPyP with Cd(II). A faster detection of Cd(II) is achieved at higher feed concentration of Cd(II) or appropriate lower immobilization capacity of TMPyP on the membrane. The flow-through detection is also influenced by the flow rate; higher flow rate led to faster response to Cd(II) during filtration. Compared with the static process, the flow-through conditions are more conducive to faster analysis of ppb level concentration of Cd(II) (10-3 mg L-1) due to a promoted mass transfer and filtration enrichment. Hence, the development of the optical sensor membrane in this study demonstrated the prospect to make membranes multifunctional with advantages for online chromatic warning in addition to adsorption/rejection of heavy metal ions in the solutions that are treated.

Enhanced hydrolysis of cellulose by catalytic polyethersulfone membranes with straight-through catalytic channels.

The aim of this study was to prepare sulfonated graphene oxide/polyether sulfone (GO-SO3H/PES) mixed matrix membranes (GPMMMs) with high porosity and straight-through catalytic channels by segregation and used for dynamic and continuous hydrolysis of cellulose. The high porosity and segregation increased the exposure of catalysts synergistically and the formative GO-SO3H enriched, straight-through catalytic channels had higher catalytic performance, enhancing the diffusion of hydrolytic products. Dynamic hydrolysis of cellulose is more efficient than static hydrolysis due to the enhanced contact between cellulose and catalysts achieved by the extra driving forces, and the further degradation of produced saccharides was suppressed due to the high freedom of products. The TRS reached 98.18% after 1 h at 150 °C with a catalyst/cellulose mass ratio of 1:5. More importantly, the immobilization of GO-SO3H by PES improved its stability and reusability at high reaction temperature. This strategy provides guidance to the design of high-performance catalytic membranes.

Manipulation of Grafting Location via Photografting To Fabricate High-Performance Ethylene Vinyl Alcohol Copolymer Membrane for Protein Separation.

Ethylene vinyl alcohol copolymer (EVAL) membrane has great potential for applications in protein separation and purification, but the uncontrollable distribution of grafting location when membranes are modified by the grafting method limits the membrane performance. Herein, an effective strategy for controlling the distribution of grafting location was designed to fabricate a high-performance EVAL membrane via photografting. The UV intensity through the membranes was weakened when the local concentration of the photoinitiator benzophenone (BP) on the topside of the membrane increased; thus, the grafting location inside the EVAL membrane changed from homogenous to asymmetric distribution based on the UV absorbability of BP. The grafting inside the membrane pores can be promoted when the loose and porous surface of the EVAL membrane was used as the UV-facing side. More importantly, the varied distribution of grafting location played different roles on improving the membrane performance. For protein binding, the limited convection in the membrane bed was avoided, and the desorption efficiency could be improved when the grafting location enriched inside the membrane pores. For protein filtration, the antifouling properties of the EVAL membrane were enhanced when the grafting location enriched on the topside. This research offers a novel approach to achieve controllable grafting location distribution of membranes and provides a perspective to design the high-performance EVAL membranes for protein separation.

Mixed matrix membrane contactor containing core-shell hierarchical Cu@4A filler for efficient SO2 capture.

Achieving high flux membrane contactor is significantly important for hazardous gas removal. In this study, we prepared poly(vinylidene fluoride) (PVDF)-based mixed matrix membrane contactor (MMMC) that contained a core-shell hirarchical Cu@4A composite filler (Cu@4A). On one hand, the Cu@4A regulated the physical structure of MMMC, which enhanced gas permeation and thus resulted in the increment of physical SO2 absorption flux. On the other hand, Cu@4A changed the chemical environment of MMMC by remarkably increased SO2 facilitated transport sites, which elevated SO2 concentration around Cu@4A by the enhancement of adsorption and oxidation of SO2, resulting in the increase of chemical SO2 absorption flux. Moreover, the copper nanosheets on 4A helped to construct facilitated transport pathways along the Cu@4A fillers at polymer-filler interface. The results showed that Cu@4A loaded MMMC exhibited increased SO2 removal efficiency and SO2 absorption flux compared with PVDF control membrane. Specifically, the M1040 MMMC loaded with 40 wt% Cu@4A and PVDF concentration 10 wt% exhibited the highest SO2 removal efficiency and SO2 absorption flux, which was up to 73.6% and 9.1 × 10-4 mol·m-2·s-1 at the liquid flow rate of 30 L/h. Besides, the overall SO2 mass transfer coefficient (Ko) and membrane mass transfer resistance (H/Km) were investigated.

Synergistic effects of zeolite imidazole framework@graphene oxide composites in humidified mixed matrix membranes on CO2 separation.

In this study, composite nanosheets (ZIF-8@GO) were prepared via an in situ growth method and then incorporated into a polyimide (PI) matrix to fabricate mixed matrix membranes (MMMs) for CO2 separation. The as-prepared MMMs were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA) and water uptake measurements. Water uptake measurements establish the relationship between the gas permeability and water uptake of membranes and an increase in the water uptake contributes to the CO2 permeability owing to an increase in the CO2 transport channels. The MMMs exhibit excellent CO2 permeability in when compared with an unfilled PI membrane in a humidified state. The ZIF-8@GO filled membranes can separate CO2 efficiently due to the ZIF-8@GO nanocomposite materials combining the favorable attributes of GO and ZIF-8. First, the high-aspect ratio of the GO nanosheets enhances the diffusivity selectivity. Second, ZIF-8 with a high surface area and microporous structure is beneficial to the improvement of the CO2 permeability. Third, ZIF-8@GO possesses synergistic effects for efficient CO2 separation. The MMM with 20 wt% ZIF-8@GO exhibits the optimum gas separation performance with a CO2 permeability of 238 barrer, CO2/N2 selectivity of 65, thus surpassing the 2008 Robeson upper bound line.

Graphene Oxide Membranes with Heterogeneous Nanodomains for Efficient CO2 Separations.

Achieving high membrane performance in terms of gas permeance and carbon dioxide selectivity is an important target in carbon capture. Aiming to manipulate the channel affinity towards CO2 to implement efficient separations, gas separation membranes containing CO2 -philic and non-CO2 -philic nanodomains in the interlayer channels of graphene oxide (GO) were formed by intercalating poly(ethylene glycol) diamines (PEGDA). PEGDA reacts with epoxy groups on the GO surface, constructing CO2 -philic nanodomains and rendering a high sorption capacity, whereas unreacted GO surfaces give non-CO2 -philic nanodomains, rendering low-friction diffusion. Owing to the orderly stacking of nanochannels through cross-linking and the heterogeneous nanodomains with moderate CO2 affinity, a GO-PEGDA500 membrane exhibits a high CO2 permeance of 175.5 GPU and a CO2 /CH4 selectivity of 69.5, which is the highest performance reported for dry-state GO-stacking membranes.

Novel affinity membranes with macrocyclic spacer arms synthesized via click chemistry for lysozyme binding.

Affinity membrane has great potential for applications in bioseparation and purification. Disclosed herein is the design of a novel affinity membrane with macrocyclic spacer arms for lysozyme binding. The clickable azide-cyclodextrin (CD) arms and clickable alkyne ethylene-vinyl alcohol (EVAL) chains are designed and prepared. By the azide-alkyne click reaction, the EVAL-CD-ligands affinity membranes with CD spacer arms in three-dimensional micro channels have been successfully fabricated. The FT-IR, XPS, NMR, SEM and SEM-EDS results give detailed information of structure evolution. The abundant pores in membrane matrix provide efficient working channels, and the introduced CD arms with ligands (affinity sites) provide supramolecular atmosphere. Compared with that of raw EVAL membrane, the adsorption capacity of EVAL-CD-ligands membrane (26.24mg/g) show a triple increase. The study indicates that three effects (inducing effect, arm effect, site effect) from CD arms render the enhanced performance. The click reaction happened in membrane matrix in bulk. The effective lysozyme binding and higher adsorption performance of affinity membranes described herein compared with other reported membranes are markedly related with the proposed strategy involving macrocyclic spacer arms and supramolecular working channels.

Enhanced interfacial interaction and CO2 separation performance of mixed matrix membrane by incorporating polyethylenimine-decorated metal-organic frameworks.

Polyethylenimine (PEI) was immobilized by MIL-101(Cr) (∼550 nm) via a facile vacuum-assisted method, and the obtained PEI@MIL-101(Cr) was then incorporated into sulfonated poly(ether ether ketone) (SPEEK) to fabricate mixed matrix membranes (MMMs). High loading and uniform dispersion of PEI in MIL-101(Cr) were achieved as demonstrated by ICP, FT-IR, XPS, and EDS-mapping. The PEI both in the pore channels and on the surface of MIL-101(Cr) improved the filler-polymer interface compatibility due to the electrostatic interaction and hydrogen bond between sulfonic acid group and PEI, and simultaneously rendered abundant amine carriers to facilitate the transport of CO2 through reversible reaction. MMMs were evaluated in terms of gas separation performance, thermal stability, and mechanical property. The as-prepared SPEEK/PEI@MIL-101(Cr) MMMs showed increased gas permeability and selectivity, and the highest ideal selectivities for CO2/CH4 and CO2/N2 were 71.8 and 80.0 (at a CO2 permeability of 2490 Barrer), respectively. Compared with the membranes doped with unfilled MIL-101(Cr), the ideal selectivities of CO2/CH4 and CO2/N2 for PEI@MIL-101(Cr)-doped membranes were increased by 128.1 and 102.4 %, respectively, at 40 wt % filler loading, surpassing the 2008 Robeson upper bound line. Moreover, the mechanical property and thermal stability of SPEEK/PEI@MIL-101(Cr) were enhanced.

Trapping bound water within a polymer electrolyte membrane of calcium phosphotungstate for efficient CO2 capture.

Calcium phosphotungstate is synthesized and utilized to fabricate a polymer electrolyte membrane for the first time. The strong hygroscopicity of both Ca(2+) and PW12O40(3-) is found to "trap" bound water within the membrane, resulting in an appealing CO2 capture performance.