Mingjing Shan

Improved hydrophilicity, permeability, antifouling and mechanical performance of PVDF composite ultrafiltration membranes tailored by oxidized low-dimensional carbon nanomaterials

Polyvinylidene fluoride (PVDF)–oxidized carbon nanotubes (OMWCNTs), PVDF–graphene oxide (GO) and PVDF–OMWCNTs–GO composite ultrafiltration membranes were prepared by solution-blending the ternary mixture of PVDF–oxidized low-dimensional carbon nanomaterials–dimethylacetamide in combination with the phase inversion method. The microscope images of the PVDF matrix microstructure showed that the composite membranes exhibited a bigger mean pore size and higher roughness parameters than pristine membranes. The contact angle of the membranes decreased from 78.5° (PVDF) to 66.8° (PVDF–OMWCNTs), 66.4° (PVDF–GO) and 48.5° (PVDF–OMWCNTs–GO). For the PVDF–OMWCNTs, PVDF–GO and PVDF–OMWCNTs–GO composite membranes, there was a 99.33%, 173.03% and 240.03% increase in permeation flux and a 21.71%, 17.23% and 14.29% increase in bovine serum albumin (BSA) rejection, respectively, compared with those of the pristine membranes. The newly developed composite ultrafiltration membranes demonstrate an impressive prospect for the anti-irreversible fouling performance in multi-cycle operations from BSA treatment. Additionally, the addition of OMWCNTs and GO increased the tensile strength of composite membranes from 1.866 MPa to 2.106 MPa and 2.686 MPa, respectively. Conspicuously, the PVDF composite ultrafiltration membranes endowed with oxidized low-dimensional carbon nanomaterials demonstrated fascinating hydrophilicity, permeability, antifouling and mechanical performance and promising application prospects owing to the rich oxygen-containing functional groups, high specific surface and synergistic effect of inorganic additive.

A facile strategy to prepare functionalized graphene via intercalation, grafting and self-exfoliation of graphite oxide

A facile method of successive intercalation, grafting and exfoliation of graphite oxide in monomers by γ-ray irradiation to obtain functionalized graphene nanosheets was reported. The monolayer percentage of functionalized graphene nanosheets was sharply increased and the agglomeration showed a significant decrease.

Nano-structure and property transformations of carbon systems under γ-ray irradiation: a review

Carbon-based materials have been used quite successfully for decades within industry sectors. Especially, the application of them in the field of aerospace has been paid lots of attention. The severe environment such as γ-rays in space, which may give rise to the formation of atomic defects, may deteriorate the performance of carbon-based devices significantly. However, in addition to the well-known cases of destroying the properties of carbon systems, recent experiments show that γ-ray irradiation can also be employed as an attractive tool for the fabrication, modification and manipulation of carbon materials. In this article, we briefly review the recent progress in our understanding of γ-ray irradiation-induced phenomena in some carbon systems with experimental results and theoretical analysis. Particular emphasis is put on the discussion of the effects of γ-rays on nanostructure and morphology of carbon fibers, graphite, carbon nanotubes, graphene and diamond, as well as the methods for tailoring their mechanical, chemical and electronic properties. Finally, we attempt to identify the future directions in which the irradiation-induced modification field is likely to develop.

Modifying graphite oxide nanostructures in various media by high-energy irradiation

The alterations of GO nanostructures after γ-ray irradiation in water, air and styrene with an absorbed dose of 200 kGy are systematically investigated. The interlayer structures of the ultimate products are confirmed to be remarkably different from each other due to the distinct changes of functional groups on single-sheets in various media. After irradiation in water, oxygen groups in graphite oxide are shown to be obviously decreased owing to the generation of reductive radicals by the decomposition of water molecules, which is reflected in the decrease of graphite oxide interlayer spacing. The interlayer distance of graphite oxide irradiated in air is found to be significantly increased, which may be attributed to the increase of the hydroxyl groups and the topological defects. However, the graphite oxide seems to be mainly exfoliated and functionalized by the intercalation of the monomers and the grafting of polystyrene chains when irradiated in styrene. It is expected that γ-ray irradiation in different media should be a promising strategy for manipulating nanostructures and properties of graphite oxide for improving its applicability in fields of composites, catalysts and sensors.

Role of a gradient interface layer in interfacial enhancement of carbon fiber/epoxy hierarchical composites

To improve the interfacial properties of carbon fibers/epoxy composites, we introduced a gradient interphase reinforced by graphene sheets between carbon fibers and matrix with a liquid phase deposition strategy. Interlaminar shear strength and flexural strength of the composites are both improved. The interfacial reinforcing mechanisms are explored by analyzing the structure of interfacial phase with linear scanning system of scanning electron microscope and atomic force microscope. Results indicate that carbon element shows a graded dispersion in the interface region and a gradient interface layer with the modulus decreasing from fibers and matrix is found to be built. To verify the effect of gradient interphase on the interfacial properties of composites, the mixture of carbon fiber/graphene/epoxy is sonicated before curing to disperse graphene sheets in matrix homogeneously. As a result, gradient interphase structures are disappeared and interfacial performance of composites is found to be weakened. The role of gradient interface layers in enhancing interfacial performances is further proved from a different angle.

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.

Effects of ion irradiation on carbon nanotubes: a review

Ion irradiation with energetic particles can successfully be used for changing the properties of carbon nanotubes (CNTs) by functionalising, connecting, and creating defect structures in the CNTs. In this paper, we focus on the recent progress in our understanding of ion-irradiation-induced phenomena in CNTs. The production of defects (vacancies and interstitials) and the structural change of CNTs were reviewed. The ion induced modification of the properties was illustrated and the factors such as the substrate, the circumstance of the ion and the temperature which affect the defects and the properties of the ion-irradiated CNTs were also briefly investigated. By summarising the predecessors’ research, we point out the issues which still lack complete investigating and further outline the most promising ways of using beams of energetic particles for CNT-related nano-engineering.

Synergetic improvement of mechanical properties and surface activities in γ-irradiated carbon fibers revealed by radial positioning spectroscopy and mechanical model

The relationship between microstructures, surface activities, and mechanical properties of γ-irradiated carbon fibers has been evaluated quantitatively. X-ray photoelectron spectroscopy combined with argon ion sputtering indicated that the outer-surface part (∼10 nm) was functionalized and disordered by the grafting reaction; this led to an increase in the surface activity and loss of mechanical properties of γ-irradiated carbon fibers. The degree of covalent cross-linking between subsurface layers of graphene (∼1.5 μm) showed a more notable increase than that of the core (∼4 μm); this indicated that the sub-surface was mainly responsible for improvement in the tensile strength of γ-irradiated carbon fibers. Increases of 15.5% (argon) and 13.3% (epoxy chloropropane) in tensile strength were achieved. Moreover, interfacial shear strength of a single fiber in matrix increased by 19.15% (argon) and 75.03% (epoxy chloropropane). Therefore, this spatially resolved study paved a meaningful way to understand the relationship among microstructures, surface activities, and mechanical properties of γ-irradiated carbon fibers.