In this work, carbonic anhydrase (CA) molecules were embedded into metal–organic frameworks (MOFs) via physical absorption and chemical bonds, which could overcome the enzymatic inactivation and the poor separation property of pristine MOF materials. And then, these nanocomposites (enzyme-embedded MOFs) as the crystal seeds were in situ grown on oriented halloysite nanotube layers to develop novel biocatalytic composite membranes. These membranes exhibited optimal separation performance with a CO2/N2 selectivity of 165.5, about 20.9 fold higher than that of the membrane without embedded CA molecules, surpassing the Robeson upper bound (2008). At the same time, the CO2 permeance increased about 3.2 fold (from 7.6 GPU to 24.16 GPU). Importantly, the biocatalytic composite membranes showed good stability and mechanical properties and were easily scalable, which could be extended to industrial applications.

•Montmorillonite (MMT) and Mg-Al hydrotalcite (HT) nanosheets were successfully prepared.•Thin-film composite membranes were developed using MMT and HT nanosheets as nanofillers.•The combination of nanosheets with organic membrane has a great potential in gas separation application.Montmorillonite (MMT) and Mg-Al hydrotalcite (HT) nanosheets were prepared via vigorous agitation and ultrasonic, respectively. In order to increase the permeability of CO2, poly (PEA-MMT-TMC)/PS and poly (PEA-HT-TMC)/PS composite membranes were prepared via interfacial polymerization by adding the dimensional (2D) inorganic nanosheets (MMT and HT) into the aqueous phase of PEA. And in consequence, the poly (PEA-MMT-TMC)/PS composite membrane showed CO2 permeability of 15.87 barrer and the CO2/N2 selectivity of 37 at 1.0 bar when the MMT concentration was 0.068 wt%. The poly (PEA-HT-TMC)/PS composite membrane also showed CO2 permeability of 15.3 barrer and the CO2/N2 selectivity of 40 at 1.0 bar when the HT concentration was 0.25 wt%. Compared with the controlled membrane (CO2 permeability: 6.9 barrer, CO2/N2 selectivity: 103), the CO2 permeability increased after incorporating the inorganic nanosheets into the membranes and maintained the pretty CO2/N2 selectivity. The addition of exfoliated MMT and HT could facilitate the gas permeation to improve the gas separation performance of the composite membranes. Also, the combination of inorganic nanosheets with organic membrane has a great potential application in the gas separation.Download high-res image (120KB)Download full-size image

•Ionic liquid (IL) intercalated graphene oxide (IGO) with fluidity is prepared.•IL increases flexibility of IGO and reinforces its interaction with polymer matrix.•3-D cross-linked IGO networks are achieved in composite membrane.•ILs enhance membrane's anhydrous conduction and fuel cell behaviors via IGO networks.•Nanoconfined effect of IGO renders enhanced IL retention and thus stable performance.Approaches for constructing efficient and stable proton transfer highways in polymer materials are urgently desirable and required for elevated-temperature polymer electrolyte membrane fuel cell (PEMFC). Herein, ionic liquid intercalated GO (IGO) with acceptable fluidity is synthesized by a facile one-pot method and then utilized to construct anhydrous transfer highways in polymer-based composite membrane. The basic-imidazole-cation-containing ionic liquid (IL) increases the flexibility of IGO and meanwhile reinforces the interaction with acidic sulfonated poly(ether ether ketone) (SPEEK) matrix, thus yielding more proportion of perpendicularly oriented IGO and the subsequent formation of 3-D cross-linked IGO networks. The IL molecules act as effective proton carrier sites along IGO networks, and in this way, efficient and long-range transfer highways for “bulk in-plane” proton conduction are constructed. SP-(25I-GO)-10% achieves the maximum conductivity of 7.29 mS cm−1 at 150 °C, 10 times higher than that of SPEEK control membrane. Meanwhile, the maximum current density and power density of SP-(25I-GO)-10% at 90 °C are 574.1 mA cm−2 and 145.1 mW cm−2, increased by 48% and 102% compared with that of SPEEK control membrane, respectively. Additionally, the nanoconfined effect of interlayer renders composite membrane enhanced IL retention ability through capillary force, consequently stable proton conduction and single cell behavior.Download high-res image (208KB)Download full-size image

Inspired by the rational design concept, a novel antimicrobial agent zeolitic imidazolate framework-8 (ZIF-8)/graphene oxide (GO) was synthesized and utilized as a novel and efficient bactericidal agent to fabricate antimicrobial thin film nanocomposite (TFN) membranes via interfacial polymerization. The resultant hybrid nanosheets not only integrates the merits of both ZIF-8 and GO but also yields a uniform dispersion of ZIF-8 onto GO nanosheets simultaneously, thus effectively eliminating the agglomeration of ZIF-8 in the active layer of membranes. A ZIF-8/GO thin film nanocomposite (TFN-ZG) membrane with typical water permeability (40.63 L m–2 h–1 MPa–1) allows for efficient bivalent salt removal (rejections of Na2SO4 and MgSO4 were 100% and 77%, respectively). Furthermore, the synthesized ZIF-8/GO nanocomposites were verified to have an optimal antimicrobial activity (MIC,128 μg/mL) in comparison with ZIF-8 and GO separately, which sufficiently endowed the TFN-ZG membrane with excellent antimicrobial activity (84.3% for TFN-ZG3). Besides, the antimicrobial mechanisms of ZIF-8/GO hybrid nanosheets and TFN-ZG membranes were proposed. ZIF-8/GO functionalized membrane with high antimicrobial activity and salt retention denoted its great potential in water desalination, and we suggest that ZIF-8 based crystal may offer a new pathway for the synthesis of a multifunctional bactericide.Keywords: antimicrobial; graphene oxides; in situ growth; nanofiltration; ZIF-8

Carrier-based immobilization has been developed to enhance enzymatic stability and activity, which permits the employment of enzymes in different solvents, at wide ranges of pH and temperature as well as high substrate concentrations. In this study, a novel carrier was prepared with halloysite nanotubes (HNTs) and layered double hydroxide (LDH) via a layer-by-layer (LbL) deposition process followed by an in situ growth technique. The in situ growth of LDH nanoplatelets on a HNTs support was demonstrated producing a well-defined three-dimensional architecture (HNTs@LDH). These flowerlike structural materials possess a high lysozyme immobilized amount (237.6 mg/g support) compared with individual HNTs and LDH. And such lysozyme immobilized composites (HNT@LDH–Ly) exhibit a superior antibacterial property against Escherichia coli (E. coli).Keywords: Enzyme immobilization; Halloysite nanotubes; In situ growth; Layered double hydroxide;

A facile and novel method for the fabrication of mixed matrix membranes (MMMs) has been developed, i.e., in situ synthesis of quaternized polyethylenimine (QPEI) soft nanoparticles (SNPs) followed by quaternization with bromoethane in poly(ether sulfone) (PES) casting solution. The resulting composite membranes were constructed via phase inversion method. The influences of SNPs on the morphology and performance of the hybrid membranes were systematically investigated by scanning electron microscopy, dynamic water contact angle, antifouling measurement, etc. The composite membranes exhibited a thin top layer and porous finger-like structure, which were greatly affected by in situ synthesized SNPs. Contact angle and water uptake measurements indicated that the hydrophilicity of hybrid membranes markedly improved in contrast with that of unfilled membrane. Meanwhile, the water flux of the membranes significantly enhanced due to the incorporation of SNPs. The ion-exchange capacity (IEC) value could achieve as high as 0.72 mmol g–1 with an initial PEI content of 1.5 wt %. The salts rejection of MMMs followed the order: MgCl2 > MgSO4 > Na2SO4 > NaCl, confirming that the hybrid membranes were positively charged. Meanwhile, the fouling parameters demonstrated that the composite membranes exhibited a preferable antifouling property. The newly developed membranes demonstrated an impressive prospect for the dye purification due to the high rejection of reactive dyes with a high permeation flux, as well as low multivalent ions retention. The possible separation mechanism of dyes and salts for composite membranes influenced by synthesized SNPs was also proposed in this study.Keywords: antifouling property; dyes purification; in situ synthesis; mixed matrix membranes; Polyethylenimine; soft nanoparticles;

•SiO2-PSS with various molecular weights was prepared via SI-ATRP.•Negatively charged NF membranes were fabricated by blending with SiO2-PSS.•The membranes showed a potential application in dye purification and desalination.Silica spheres in nanoscale were prepared via sol–gel method and then sodium 4-styrene sulfonate was grafted onto the surfaces of SiO2 (PSS-SiO2) by surface-initiated atom transfer radical polymerization (SI-ATRP). Then, a negatively charged loose SiO2-PSS/polyethersulfone (PES) nanofiltration membrane with high flux was fabricated via phase inversion method. FT-IR and TEM results showed that SiO2 nanoparticles were synthesized and modified successfully. GPC results further proved the “living”/controlled behavior of SI-ATRP. The morphology, hydrophilicity of the membranes were investigated by SEM, static water contact angle and water ratio. The results revealed that the surface hydrophilicity and water permeability of hybrid membranes were greatly improved after adding SiO2-PSS and thus may enhance fouling resistance to a certain extent. The salt permeation and separation of dye/salt mixture of the hybrid membranes were significantly superior to the pure PES membrane, and the order of permeation for different salt solutions was NaCl > MgCl2 > MgSO4 > Na2SO4. When the content of SiO2-PSS was 3.0 wt%, the hybrid membrane showed optimal performance with IEC value of 0.07 mmol/g and pure water flux of 269.5 L m−2 h−1 and the rejections for all types of salts declined to under 11%. The above results indicated that SiO2-PSS incorporated into PES matrix played an important role in enhancing the performance of NF membranes, which may possess a significant impact on the application in dye purification and desalination.Graphical abstract

To investigate the synergistic effect of multi-nanofillers in a superabsorbent nanocomposite, a poly (sodium acrylate–acrylamide) superabsorbent nanocomposite incorporating graphene oxide and halloysite nanotubes (PAA-AAm–HNT–GO) was synthesized via the inverse suspension polymerization method. Graphene oxide (GO) was prepared by an improved method and halloysite nanotubes (HNTs) were modified by grafting carboxyl groups. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were carried out to examine the structure and morphology of the resulting superabsorbent nanocomposite. It was found that HNTs, GO and poly(sodium acrylate-acrylamide) (PAA-AAm) copolymers combine well with each other during the polymerization process. Meanwhile, the particle sizes of the resulting superabsorbent nanocomposite reduced to about one-tenth of the original size after the introduction of HNTs and GO. The PAA-AAm–HNT–GO superabsorbent nanocomposite exhibited a significant improvement in its water absorption and water retention abilities, due to the synergistic effect of the HNTs and GO, compared with controls, which may make it suitable for use in some special applications that demand a higher water absorption and retention capacity.

In this study, poly(4-vinylpyridine) (P4VP) was first grafted onto the surface of halloysite nanotubes (HNTs) via in situ polymerization, and then, silver ions were immobilized on P4VP via complex reaction. Finally, silver ions were reduced to silver nanoparticles (Ag NPs). Polyethersulfone (PES) ultrafiltration membranes bending with modified HNTs loaded with Ag NPs were prepared via phase inversion. FT-IR spectra and TGA results showed that HNTs were modified successfully. The contact angle data indicated that the hydrophilicity of the membranes was enhanced by the addition of modified HNTs. The permeation properties of the hybrid membranes were significantly superior to the pure PES membrane, especially when the modified HNTs content was 3%; the pure water flux of the membrane reached the maximum at 396.5 L·m–2·h–1, which was about 251.5% higher than that of the pure PES membrane, and the rejection was slightly affected by the addition of the modified HNTs. The microstructure of the membranes was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the structure of membrane was not obviously affected by addition of the modified HNTs. Antibacterial activity of the hybrid membrane was evaluated with the viable cell count method using antibacterial rate against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial rates of the hybrid membranes against E. coli and S. aureus were about 99.9% and 99.8%, respectively.

Natural halloysite nanotubes (HNTs) were modified with a silane coupling agent, N-β-aminoethyl-γ-aminopropyl trimethoxysilane (KH-792), to form a new adsorbent for Cr(VI) removal. The as-prepared product was characterized by FTIR spectroscopy, TGA, TEM, and specific surface analysis. The results showed that KH-792 was successfully grafted onto the halloysite surface. Modified HNTs exhibited a rapid adsorption rate for Cr(VI) and approached 95% of the maximum adsorption capacity within 5 min. The effects of initial Cr(VI) concentration, temperature, pH, and ionic strength on the adsorption capacity were investigated in batch experiments. The results showed that low temperature was favorable to improve adsorption efficiency, and the adsorption capacity decreased significantly with the increase of pH and ionic strength. The optimum pH was found to be 3–5. The main adsorption mechanism was considered to be electrostatic interaction between protonated amino groups on the adsorbent surface and negatively charged Cr(VI). The results above confirmed that modified HNTs had the potential to be utilized as a low-cost and relatively effective adsorbent for Cr(VI) removal.

A novel composite charged mosaic membrane (CCMM) was prepared via interfacial polymerization (IP) of polyamine [poly(epichlorohydrin amine)] and trimesoyl chloride (TMC) on the polyethersulfone (PES) support. Fourier transform infrared spectroscopy (FT-IR), environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM) and water contact angle analysis were applied to characterize the resulted CCMM. The FT-IR spectrum indicates that TMC reacts sufficiently with polyamine. ESEM and AFM pictures show that the IP process produces a dense selective layer on the support membrane. The water contact angle of the CCMM is smaller than that of the substrate membrane because of the cross-linked hydrophilic polyamine network. Several factors affecting the IP reaction and the performance of the CCMM, such as monomer concentration, reaction time, pH value of aqueous phase solution and post-treatment, were studied. The pure water flux of the optimized CCMM is 14.73 L·m−2·h−1·MPa−1 at the operating pressure of 0.4 MPa. The values of separation factor a for NaCl/PEG1000/water and MgCl2/PEG1000/water are 11.89 and 9.96, respectively. These results demonstrate that CCMM is promising for the separation of low-molecular-weight organics from their salt aqueous solutions.

•SiO2 spheres were modified by poly (ionic liquid) brushes via RATRP.•Positively charged NF membranes were fabricated by incorporation of SiO2-PIL.•The membranes exhibited higher rejection for dyes and superior penetration for salts.Silica spheres modified by poly (ionic liquid) brushes, a novel positively charged nanomaterial is prepared by atom transfer radical polymerization (ATRP). A high flux positively charged loose nanofiltration membrane is fabricated via “blending-phase inversion” method. The morphology structures, hydrophilicity, thermal and mechanical properties, permeation performance of these membranes are investigated in detail. The results reveal that the hybrid membranes have enhanced surface hydrophilicity, water permeability, thermal stability, and mechanical properties. Characterization of membrane separation properties shows that the hybrid membranes possess higher salt permeability and relatively higher rejection for reactive dyes, which may open opportunities for the recycling of reactive dyes wastewater. Moreover, such hybrid membranes have an outstanding operational stability and salts concentration showed little effect on the separation properties.Download full-size image

•HNTs were firstly modified by poly (ionic liquid) brushes via RATRP.•Molecular separation membranes were fabricated by incorporation of HNTs-PIL.•These membranes possess high salt passage and organic matter removal.A positively charged nanomaterial was prepared adopting the graft polymerization of ionic liquid monomers on halloysite nanotubes (HNTs) via reverse atom transfer radical polymerization (RATRP). A novel and facile organic–inorganic hybrid molecular separation membrane was then fabricated by the incorporation of modified HNTs via phase inversion method. This hybrid membrane was investigated in terms of morphology structure, hydrophilicity, thermal, mechanical and electrical properties, and separation performances. The results revealed that the hybrid membranes represented thickened and loosened skin layer, enhanced surface hydrophilicity and water flux, as well as good thermal and mechanical properties. Most importantly, the hybrid membranes showed stabilized rejection for Reactive Black 5 (above 90%) and Reactive Red 49 (80%–90%), whereas the rejection for sorts of salts declined to below 10% indicating a potential molecular separation characteristic for dye desalination.Download full-size image

Polyethyleneimine/2-hydroxypropyl trimethyl ammonium chloride chitosan/TiO2 nanoparticles/trimesoyl chloride (PEI/HACC/TiO2/TMC) positively charged composite nanofiltration (NF) membrane using polysulfone ultrafiltration membrane as support layer and TiO2 nanoparticles as modifying agent was prepared by interfacial polymerization reaction. The separation performance of the NF membrane was tested by pure water, PEG1000 solution, salt solutions, dye solutions and mixed solutions of dye and salt. The membrane structure was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At the optimal preparation conditions of 3 wt.% PEI, 0.3 wt.% HACC, 0.9 wt.% TiO2, 1.5 wt.% TMC, reaction temperature of 20 °C and reaction time of 60 s, the NF membrane shows the high flux, the high dye rejection and the low salt rejection, which are suitable to the process of purifying raw dye.Highlights► PEI/HACC/TiO2/TMC composite nanofiltration membrane was fabricated successfully. ► HACC was used as dispersant agent of TiO2 nanoparticles. ► TiO2 was added into the nanofiltration membrane by interfacial polymerization reaction.

The magnetic composite of Fe3O4-halloysite nanotube (HNT) was prepared by chemical precipitation method. The prepared adsorbents were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and multipoint Brunauer–Emmett–Teller (MBET). The results revealed that Fe3O4 particles with diameter of 3–5 nm dispersed on the nanotube surface and formed a composite with halloysite. The Fe3O4–HNTs composite exhibited fine magnetic property (Ms = 8.47 emu/g) and could be easily separated from aqueous solution by the application of an external magnetic field. Adsorption results showed that Fe3O4–HNTs composite could maintain a high adsorption capacity for methyl violet (MV) when the pH, concentration of metal ion and temperature varied. Adsorption kinetics was best described by the pseudo-second-order model. Equilibrium data fitted well with the Langmuir isotherm. The used Fe3O4–HNTs could be regenerated by simple calcinations. The recovered adsorbents could be used again for MV removal and magnetic separation. Because of the excellent adsorption capacity at different conditions, reproducibility and separability, Fe3O4–HNTs composite is a promising candidate for removing cationic dye from waste water.Download full-size imageHighlights► The magnetic composite of Fe3O4-halloysite was prepared by chemical precipitation method. ► The composite can be separated rapidly from solution by the application of external magnetic field. ► The composite shows excellent adsorption capacity and reproducibility for methyl violet dye.