Fengmin Jin

Flexible and planar graphene conductive additives for lithium-ion batteries

Graphene is introduced into a lithium-ion battery (LIB) as a type of novel but powerful planar conductive additive and the flexible graphene-based conducting network is characterized by a novel “plane-to-point” conducting mode with exceptional electron transport properties and unique geometrical nature (a soft and ultrathin planar structure). With a much lower fraction of graphene additives than those of commercial carbon based additives, the graphene-introduced LiFePO4 cathode shows better charge/discharge performance than commercial cases. Graphene also shows a better performance compared to carbon nanotubes, another type of novel conductive additive with similar fractions. These results present us an indication that graphene will possibly find early application as a flexible and planar conductive additive in high performance LIBs, as our further efforts have shown that a graphene-introduced battery is of better performance as compared to real commercial batteries with conventional additives.

Graphene-DNA hybrids: self-assembly and electrochemical detection performance

Graphene combines with single-stranded DNA by a self-assembly process under strong ultrasonication and in the resulting water-dispersible graphene-DNA hybrids, monolayers of globular ss-DNA molecules are adsorbed on both sides of the graphene sheets by a non-covalent π–π stacking. The cyclic voltammetry results of the graphene-DNA hybrids coated electrodes demonstrate a well-defined and nearly symmetrical redox characteristic which means an enhanced electron transfer on the electrode surface as compared to the uncoated glassy carbon electrodes. Accordingly, the coated ones show apparently better sensing performance towards hydrogen peroxide which is characterized by large detection range, rapid response and high sensitivity.

One-pot self-assembly of three-dimensional graphene macroassemblies with porous core and layered shell

The innate character of graphene, defined as the basic unit of sp2carbon materials, provides opportunities for the design and construction of carbon nanostructures with tuned properties. Here, we report a novel three-dimensional graphene macroassembly with a core–shell structure starting from reduced graphene oxides (RGO) by a one-pot self-assembly process under very mild conditions. In the presence of KMnO4, such an assembly process is initiated by low-temperature heating below 100 °C at atmospheric pressure and is totally free from a severe hydrothermal process. Such a core–shell structure is characterized by a porous core and layered membrane shell, and the macro-morphology and infrastructure of the macroassembly are well controllable and tunable. The macroassembly presented here and its self-assembly preparation directly from graphene nanosheets present the first example of the simultaneous formation of a coaxial hybrid infrastructure in a graphene-based nanostructured material, and such a core–shell structured macroassembly shows potential for use in energy storage and other applications.

Conductive graphene-based macroscopic membrane self-assembled at a liquid–air interface

Free-standing graphene-based macroscopic membranes, which are characterized by a layered structure and tunable conductivity, are prepared by a self-assembly process at a liquid–air interface. Since the preliminary results indicate that it is hard to construct macroscopic graphene membranes solely by low-temperature exfoliated graphene nanosheets (LGNs) at the liquid–air interface, graphene oxide nanosheets (GONs), as the stacking template and sticking component, are introduced into the assembly process of graphene layers to promote the formation of layer-by-layer stacking structure and help form a conductive macroscopic membrane. The conductivity of such a graphene-based membrane can be tuned by changing the GON fraction in the LGN/GON hybrid membrane.

High-performance ultrafiltration membranes based on polyethersulfone–graphene oxide composites

Graphene oxide nanosheets are employed as nanofillers to improve hydrophilicity and antifouling performance of a polymer-based membrane, resulting in high performance ultrafiltration membranes with substantially improved flux.

Shape evolution and thermal stability of lysozyme crystals: effect of pH and temperature

The properties of crystalline protein materials are closely linked to crystal shape. However, the effective strategies for the shape control of protein crystals are lacking. The conventional sitting-drop vapor-diffusion method was employed to investigate the influence of pH and temperature on the crystal nucleation behavior of hen egg white lysozyme. Moreover, the size distributions of protein crystals grown at different conditions were analyzed. Differential scanning calorimetry was employed to evaluate the thermal stability of lysozyme crystals. The results indicated that pH and temperature will affect the supersaturation and electrostatic interactions among protein molecules in the nucleation process. In particular, the crystals with different aspect ratios can be selectively nucleated, depending upon the choice of pH and temperature. Therefore, this study provided a simple method for obtaining shape-controlled lysozyme crystals and supplied some information on thermal behaviors of lysozyme crystals grown at different pH values.

Enhanced electrochemical detection performance of multiwall carbon nanotubes functionalized by aspartame

Inexpensive, non-toxic, and biocompatible materials that can disperse multiwall carbon nanotubes (MWCNTs) in aqueous solutions through a non-covalent approach while retaining their unique electronic and photonic properties are highly preferred. In this article, we introduce the use of an amphiphilic dipeptide derivative, aspartame, as an effective dispersing agent in preparing highly stable suspensions under ultrasonication. The results demonstrate that aspartame was absorbed by the nanotube surface possibly because of non-covalent π–π stacking between the aromatic group of aspartame and the CNT backbone. In addition, the resulting MWCNT/aspartame composites remained stably dispersed over a wide range of pH values. The chronoamperometric measurements of MWCNT/aspartame composite-coated electrodes for hydrogen peroxide demonstrated better electrochemical detection performance, as characterized by significantly enhanced step current, higher sensitivity, and reduced potential compared with bare electrodes.

Ultrathin carbon nanotube?DNA hybrid membrane formation by simple physical adsorption onto a thin alumina substrate

Ultrathin carbon nanotube membranes can be prepared on alumina substrates by a facile immersion-adsorption approach, which involves two steps, the first step DNA wrapping and the second step uniform adsorption of the DNA-wrapped nanotubes onto porous alumina. In this approach, DNA wrapping imparts a hydrophilic nature to the carbon nanotubes, which enhances the interaction between the nanotubes and hydrophilic porous alumina and results in the self-assembly formation of ultrathin nanotube membranes with well-controlled thickness, biocompatibility, conductivity and optical properties.

Flow Rate and Concentration‐dependent Effects of Molecular Dynamics on Elution Behaviors of Flexible Polymers in Gel Permeation Chromatography: A Multi‐angle Laser Light Scattering Study

Gel permeation chromatography (GPC) coupled with multi‐angle laser light scattering (MALLS) provides a tool to simultaneously measure the elution behavior and molecular shape of flexible polymers in their dependence on column flow rate and solute concentration. As flow rate was increased, the radius of gyration (R g) of flexible polymers first decreased a little and then increased gradually. In all cases, the values of R g, the hydrodynamic radius (R h), and ρ (R g/R h) decreased as the concentration increased. As a result, flow‐induced molecular stretch and concentration‐induced molecular shrinking for flexible polymers in the gel pores were deduced from the size‐related elution behaviors and tested by light scattering. In addition, the flow rate and concentration‐dependent effect of elution behavior parameters such as the elution volume (V e), the weight‐averaged molecular weight (M w), and polydispersity index (PI) were interpreted in terms of molecular deformation and orientations of flexible polymers.