Flexible and Freestanding MoS2/Graphene Composite for High-Performance Supercapacitors.

Two-dimensional atomically thick materials such as graphene and layered molybdenum disulfide (MoS2) have been studied as potential energy storage materials because of their high specific surface area, potential redox activity, and mechanical flexibility. However, because of the layered structure restacking and poor electrical conductivity, these materials are unable to attain their full potential. Composite electrodes made of a mixture of graphene and MoS2 have been shown to partially resolve these issues in the past, although their performance is still limited by inadequate mixing at the nanoscale. Herein, we report three composites via a simple ball-milling method and analyze supercapacitor electrodes. Compared with pristine graphene and MoS2, the composites showed high capacitance. The as-obtained MoS2@Graphene composite (1:9) possesses a high surface area and uniform dispersion of MoS2 on the graphene sheet. The MoS2@Graphene (1:9) composite electrode has a high specific capacitance of 248 F g-1 at 5 A g-1 in an electrochemical supercapacitor compared with the other two composites. Simultaneously, the flexible symmetric supercapacitor device prepared demonstrated superior flexibility and a long lifespan (93% capacitance retention after 8000 cycles) with no obvious changes in performance under different angles. In portable and wearable energy storage devices, the current experimental results will result in scalable, freestanding hybrid electrodes with improved, flexible, supercapacitive performance.

Insight into thermo-mechanical enhancement of polymer nanocomposites coated microsand proppants for hydraulic fracturing.

The present work reports the fabrication of ultra-high strength microsand proppants (100 mesh) through a polymer nanocomposite dual coating approach and gives insight into their thermo-mechanical reinforcements. The dual coating can be of 3D-cross-linked poly(styrene-methyl methacrylate)/divinylbenzene) (PS-PMMA/DVB) porous network and thermally cross-linked epoxy with graphene nanosheets. The inner layer of PS-PMMA/DVB was prepared using bulk polymerization of styrene (S) and methyl methacrylate (MMA) at 70 °C with a free radical initiator azobisisobutyronitrile (AIBN). The outer layer was prepared by mixing epoxy resin, a cross-linker, and commercial graphene (CG) followed by thermally curing the mixture. The dual-coated microsand proppants exhibited enhanced mechanical characteristics of elastic modulus (E) as high as 7.78 GPa, hardness (H) of 0.35 GPa, and fracture toughness (Kc) of 3.19 MPa m1/2 along with largely improved thermal properties. Moreover, the dual-coated microsand proppants exhibit a very high-stress resistance up to 14000 psi, and to the best of our knowledge, this is the highest stress resistance value attained for the modified sand-based proppants so far.

Microwave Irradiation Synthesis and Characterization of Reduced-(Graphene Oxide-(Polystyrene-Polymethyl Methacrylate))/Silver Nanoparticle Nanocomposites and their Anti-Microbial Activity.

Herein, we report a facile process for the preparation of styrene and methyl-methacrylate copolymer nanocomposites containing reduced graphene oxide and silver nanoparticles ((R-(GO-(PS-PMMA))/AgNPs)) by using (i) microwave irradiation (MWI) to obtain R-(GO-(PS-PMMA))/AgNPs and (ii) the in situ bulk polymerization technique to produce RGO/AgNPs-(PS-PMMA). Various characterization techniques, including FT-IR, XPS, Raman spectroscopy, XRD, SEM, HR-TEM, DSC, and TGA analysis, were used to characterize the prepared nanocomposites. The Berkovich nanoindentation method was employed to determine the hardness and elastic modulus of the nanocomposites. The results showed that the MWI-produced nanocomposites were found to have enhanced morphological, structural, and thermal properties compared with those of the nanocomposites prepared by the in situ method. In addition, the antibacterial activity of the prepared nanocomposites against the E. coli HB 101 K-12 was investigated, whereby an inhibition zone of 3 mm (RGO/AgNPs-(PS-PMMA) and 27 mm (R-(GO-(PS-PMMA))/AgNPs) was achieved. This indicates that the MWI-prepared nanocomposite has stronger antibacterial activity than the in situ-prepared nanocomposite.

Li-Ion Capacitor Integrated with Nano-network-Structured Ni/NiO/C Anode and Nitrogen-Doped Carbonized Metal-Organic Framework Cathode with High Power and Long Cyclability.

Lithium-ion capacitors (LICs) represent a new type of energy-storage devices, which have combined merits of high energy density Li-ion battery and high power density supercapacitor. Nevertheless, one significant challenge for LICs is the imbalanced kinetics between the fast capacitive cathode and relatively slow intercalation anode that limit the energy-storage performance. Here, the asymmetric LIC devices were developed based on a nitrogen-doped, carbonized zeolitic imidazolate framework (ZIF-8) cathode and a three-dimensional, nano-network-structured, conversion reaction-based Ni/NiO/C anode. These nanostructures associated with both the cathode and anode enable rapid electron and ions transport in the LIC devices, which allows the asymmetric LICs to be operated on either high energy mode (energy density of 114.7 Wh/kg at power density of 98.0 W/kg) or high power mode (power density of 60.1 kW/kg at energy density of 17.6 Wh/kg). The device also exhibited long-term cycle stability with 87% capacitance retention after 12 000 cycles. These results demonstrate that the rational design of nanoporous electrode structures can deliver a balanced, high-performance-activated cZIF-8|Ni/NiO/C-based lithium-ion capacitor.

Directed Self-Assembly of Star-Block Copolymers by Topographic Nanopatterns through Nucleation and Growth Mechanism.

Exploring the ordering mechanism and dynamics of self-assembled block copolymer (BCP) thin films under confined conditions are highly essential in the application of BCP lithography. In this study, it is aimed to examine the self-assembling mechanism and kinetics of silicon-containing 3-arm star-block copolymer composed of polystyrene (PS) and poly(dimethylsiloxane) blocks as nanostructured thin films with perpendicular cylinders and controlled lateral ordering by directed self-assembly using topographically patterned substrates. The ordering process of the star-block copolymer within fabricated topographic patterns with PS-functionalized sidewall can be carried out through the type of secondary (i.e., heterogeneous) nucleation for microphase separation initiated from the edge and/or corner of the topographic patterns, and directed to grow as well-ordered hexagonally packed perpendicular cylinders. The growth rate for the confined microphase separation is highly dependent upon the dimension and also the geometric texture of the preformed pattern. Fast self-assembly for ordering of BCP thin film can be achieved by lowering the confinement dimension and also increasing the concern number of the preformed pattern, providing a new strategy for the design of BCP lithography from the integration of top-down and bottom-up approaches.

Fabrication of Mesoporous Polystyrene Films with Controlled Porosity and Pore Size by Solvent Annealing for Templated Syntheses.

Herein, we aim to develop a facile method for the fabrication of mesoporous polystyrene (PS) films with controlled porosity and pore size by solvent annealing. A PS polymer film is solvent-annealed using N,N-dimethyl formamide (DMF) vapor for the development of phase separation, followed by rapidly cooling to the preset cryogenic temperature. Subsequently, a nonsolvent (methanol) is introduced to extract the crystalline DMF from the DMF-swollen PS, giving mesoporous PS with a network structure after the removal of DMF. The porosity of the mesoporous PS films can be controlled by the degree of swelling. Most interestingly, the phase separation between PS and DMF at the thin-film state under solvent annealing can be regulated by the annealing time through the spinodal decomposition, giving the development of nanonetwork structure with controlled structural features (i.e., framework size and interframework spacing) at invariant porosity. Consequently, after the removal of DMF, mesoporous PS films with controlled porosity and pore size can be obtained and then used as a template for the fabrication of a variety of nanoporous inorganics by templated syntheses, such as nanoporous SiO2, TiO2, and Ni, providing a cost-effective way to fabricate a range of nanoporous materials with controlled porosity and pore size as well as large specific surface area for aimed applications.

Hydrophilic polymer nanofibre networks for rapid removal of aromatic compounds from water.

Hydrophobic mesoporous polymer nanofibre networks were converted to hydrophilic ones by a mild sulfonation reaction. The resultant mesoporous polystyrene with a large free surface area effectively captured water-soluble dye molecules and allowed aromatic compounds to rapidly permeate into the internal binding sites.

Flash freezing route to mesoporous polymer nanofibre networks.

There are increasing requirements worldwide for advanced separation materials with applications in environmental protection processes. Various mesoporous polymeric materials have been developed and they are considered as potential candidates. It is still challenging, however, to develop economically viable and durable separation materials from low-cost, mass-produced materials. Here we report the fabrication of a nanofibrous network structure from common polymers, based on a microphase separation technique from frozen polymer solutions. The resulting polymer nanofibre networks exhibit large free surface areas, exceeding 300 m(2) g(-1), as well as small pore radii as low as 1.9 nm. These mesoporous polymer materials are able to rapidly adsorb and desorb a large amount of carbon dioxide and are also capable of condensing organic vapours. Furthermore, the nanofibres made of engineering plastics with high glass transition temperatures over 200 °C exhibit surprisingly high, temperature-dependent adsorption of organic solvents from aqueous solution.