Analysis of Mg2+/Li+ separation mechanism by charged nanofiltration membranes: visual simulation.

The mechanism of the nanofiltration (NF) membrane separation of Mg2+ and Li+ needs to be further investigated, but some commonly used model theories are abstract, which makes them difficult to understand. More importantly, the relationship between the membrane charge and separation performance of Mg2+ and Li+ cannot be quantitatively analyzed. It is worth studying these challenges and providing a performance boost for Mg2+/Li+ filtration applications of NF membranes. Here, various NF membranes, with the membrane volumetric charge density increasing from -4.69 to 7.02 mol · m-3, were fabricated via interfacial polymerization. For these membranes, the separation factor S Mg,Li was decreased from 0.41 to 0.20. Importantly, the visual simulation results were consistent with the experimental results as a whole. The separation factor S Mg,Li decreased with the increase of volumetric charge density, and the minimum separation factor S Mg,Li of the NF membranes was 0.20 (experiment) and 0.17 (simulation), respectively. This meant that the performance of the positively charged NF membrane was not fully developed. Furthermore, we analyzed the relationship between the membrane charge and separation performance, and visualized the simulation of the NF membrane filtration and separation.

Improvement of PVDF nanofiltration membrane potential, separation and anti-fouling performance by electret treatment.

Electret treatment was a simple method to enhance the charge-electrode properties of polyvinylidene fluoride (PVDF) materials due to the increase of space charge and polarization charge of PVDF materials. The polarization charge was due to the electric dipole orientation change in loose nanofiltration PVDF membrane, which increased the electric dipole moment and improved the polarity of surface potential. Importantly, electret charges were less affected by ambient humidity. Therefore, the electret treatment could improve the surface negative potential of loose nanofiltration PVDF membrane, so as to improve its anti-fouling performance under certain conditions. Based on the above theoretical analysis, the influence and mechanism of the electret treatment on the surface potential, morphology, structure, hydrophilicity and anti-pollution performance of PVDF membrane were studied in this manuscript. When the electret time was 7.5 min and the electret voltage was 30 kV, the surface negative potential was the highest. The content of ß phase crystals was 39.1%, which was 12.18% higher than that of untreated membrane. In addition, the surface morphology of PVDF membrane did not change significantly, but the water contact angle decreased slightly, and the pore size increased by 0.36-0.75 nm. Importantly, the flux and the rejection of dye and BSA increased to some extent, and the maximum rejection rate and water flux were increased by 10.34% and 20.25%, respectively. Through the cyclic filtration test and analysis, the anti-fouling performance of membrane was increased due to electrostatic repulsion.

Decreased cross-linking in interfacial polymerization and heteromorphic support between nanoparticles: Towards high-water and low-solute flux of hybrid forward osmosis membrane.

Realizing that one main factor affecting development of forward osmosis (FO) membrane was internal concentration polarization (ICP), graphene oxide (GO) with two-dimensional structure and oxidized carbon nanotubes (OCNTs) with one-dimensional structure were linked by oxygen-containing groups to form water channels in the polyamide layer. OCNTs and GO were used for producing reactions among oxygen-containing groups of nanoparticles and polymer chains, and oxygen-containing groups were fully exposed because GO and OCNTs restrained aggregation. Decrease of cross-linking degree for interfacial polymerization layer was confirmed due to reaction from GO/OCNTs/m-phenylene diamine/1,3,5-benzenetricarbonyl trichloride. Moreover, OCNTs formed an appropriate supporting effect for GO to improve hydrophilic properties, which was confirmed by transmission electron microscopy, scanning electron microscope and contact angle. Resulting membrane PA-GO-OCNTs showed high water flux (114 LMH and 84.6 LMH in the PRO (active layer facing draw solution) and FO (active layer facing feed solution) mode, respectively) and low solute flux (5.17 gMH and 3.4 gMH in the PRO and FO mode, respectively) under this condition that 0.5 M NaCl and deionized water were used as draw solution and feed solution respectively. It was worth mentioning that water flux of FO membrane was far higher than that in reported literatures while its structural parameter S was only 203 µm, which led to decrease of ICP.

TiO2 seeded on nitrogen-doped porous carbon nanofibers for superior electrochemical performance as freestanding anodes of lithium-ion batteries.

Fibrous mats piled by nitrogen-doped porous carbon nanofibers with seeded TiO2 are fabricated and punched directly into circles as lithium-ion battery anodes. The seeding structure is composed of semi-wrapped TiO2 nanoparticles on carbon nanofibers (CNFs) coated with a thin layer of carbon. Synchronously, pores with various widths are formed on CNFs. As a freestanding anode, an initial discharge capacity of 615 mAh g-1 with a coulombic efficiency of 56% is reached, and 322 mAh g-1 is obtained after 100 cycles at a current density of 100 mA g-1. This is assigned to the increasing number of active sites for the lithium ion from pores with various widths and improved conductivity originating from nitrogen doping. Superior rate performance (179 mAh g-1 at the current density of 2000 mA g-1) under various current densities compared with that of other counterparts is attributed to the structural stability originating from the seeding structure with the help of the C-O-Ti bond. An additional 800 cycles are displayed at the current density of 2000 mA g-1, and superior stability is also exhibited.

Manipulating Migration Behavior of Magnetic Graphene Oxide via Magnetic Field Induced Casting and Phase Separation toward High-Performance Hybrid Ultrafiltration Membranes.

Hybrid membranes blended with nanomaterials such as graphene oxide (GO) have great opportunities in water applications due to their multiple functionalities, but they suffer from low modification efficiency of nanomaterials due to the fact that plenty of the nanomaterials are embedded within the polymer matrix during the blending process. Herein, a novel Fe3O4/GO-poly(vinylidene fluoride) (Fe3O4/GO-PVDF) hybrid ultrafiltration membrane was developed via the combination of magnetic field induced casting and a phase inversion technique, during which the Fe3O4/GO nanocomposites could migrate toward the membrane top surface due to magnetic attraction and thereby render the surface highly hydrophilic with robust resistance to fouling. The blended Fe3O4/GO nanocomposites migrated to the membrane surface with the magnetic field induced casting, as verified by X-ray photoelectron spectroscopy, elemental analysis, and energy dispersive X-ray spectroscopy. As a result, the novel membranes exhibited significantly improved hydrophilicity (with a contact angle of 55.0°) and water flux (up to 595.39 L m(-2) h(-1)), which were improved by 26% and 206%, 12% and 49%, 25% and 154%, and 11% and 33% compared with those of pristine PVDF membranes and PVDF hybrid membranes blended with GO, Fe3O4, and Fe3O4/GO without the assistance of magnetic field during membrane casting, respectively. Besides, the novel membranes showed high rejection of bovine serum albumin (>92%) and high flux recovery ratio (up to 86.4%). Therefore, this study presents a novel strategy for developing high-performance hybrid membranes via manipulating the migration of nanomaterials to the membrane surface rather than embedding them in the membrane matrix.

Superior Mechanical Properties of Epoxy Composites Reinforced by 3D Interconnected Graphene Skeleton.

Epoxy-based composites reinforced by three-dimensional graphene skeleton (3DGS) were fabricated in resin transfer molding method with respect to the difficulty in good dispersion and arrangement of graphene sheets in composites by directly mixing graphene and epoxy. 3DGS was synthesized in the process of self-assembly and reduction with poly(amidoamine) dendrimers. In the formation of 3DGS, graphene sheets were in good dispersion and ordered state, which resulted in exceptional mechanical properties and thermal stability for epoxy composites. For 3DGS/epoxy composites, the tensile and compressive strengths significantly increased by 120.9% and 148.3%, respectively, as well as the glass transition temperature, which increased by a notable 19 °C, unlike the thermal exfoliation graphene/epoxy composites via direct-mixing route, which increased by only 0.20 wt % content of fillers. Relative to the graphene/epoxy composites in direct-mixing method mentioned in literature, the increase in tensile and compressive strengths of 3DGS/epoxy composites was at least twofold and sevenfold, respectively. It can be expected that 3DGS, which comes from preforming graphene sheets orderly and dispersedly, would replace graphene nanosheets in polymer nanocomposite reinforcement and endow composites with unique structure and some unexpected performance.