Showing papers by "Zhong-Zhen Yu published in 2016"

High-Performance Epoxy Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding

Abstract: Light-weight and high-performance electromagnetic interference (EMI)-shielding epoxy nanocomposites are prepared by an infiltration method using a 3D carbon nanotube (CNT) sponge as the 3D reinforcement and conducting framework. The preformed, highly porous, and electrically conducting framework acts as a highway for electron transport and can resist a high external loading to protect the epoxy nanocomposite. Consequently, a remarkable conductivity of 148 S m−1 and an outstanding EMI shielding effectiveness of around 33 dB in the X-band are achieved for the epoxy nanocomposite with 0.66 wt% of CNT sponge, which is higher than that achieved for epoxy nanocomposites with 20 wt% of conventional CNTs. More importantly, the CNT sponge provides a dual advantage over conventional CNTs in its prominent reinforcement and toughening of the epoxy composite. Only 0.66 wt% of CNT sponge significantly increases the flexural and tensile strengths by 102% and 64%, respectively, as compared to those of neat epoxy. Moreover, the nanocomposite shows a 250% increase in tensile toughness and a 97% increase in elongation at break. These results indicate that CNT sponge is an ideal functional component for mechanically strong and high-performance EMI-shielding nanocomposites.

Thermally Annealed Anisotropic Graphene Aerogels and Their Electrically Conductive Epoxy Composites with Excellent Electromagnetic Interference Shielding Efficiencies

Abstract: Dispersion and spatial distribution of graphene sheets play crucial roles in tailoring mechanical and functional properties of their polymer composites. Anisotropic graphene aerogels (AGAs) with highly aligned graphene networks are prepared by a directional-freezing followed by freeze-drying process and exhibit different microstructures and performances along the axial (freezing direction) and radial (perpendicular to the axial direction) directions. Thermal annealing at 1300 °C significantly enhances the quality of both AGAs and conventional graphene aerogels (GAs). The aligned graphene/epoxy composites show highly anisotropic mechanical and electrical properties and excellent electromagnetic interference (EMI) shielding efficiencies at very low graphene loadings. Compared to the epoxy composite with 0.8 wt % thermally annealed GAs (TGAs) with an EMI shielding effectiveness of 27 dB, the aligned graphene/epoxy composite with 0.8 wt % thermally treated AGAs (TAGAs) has an enhanced EMI shielding effectiven...

Air-dried, high-density graphene hybrid aerogels for phase change composites with exceptional thermal conductivity and shape stability

Abstract: High density graphene hybrid aerogels with enhanced thermal conductivity and compressive properties are fabricated by self-assembly of aqueous mixtures of graphene oxide and high-quality graphene nanoplatelets (GNPs) followed by a convenient and cost-effective air drying process. The reduced graphene oxide sheets form an integrated three-dimensional network to accommodate GNPs, while the GNPs act as reinforcements to avoid excessive volume shrinkage of the network during the air drying process. Octadecanol is thus easily impregnated into the porous graphene network to obtain octadecanol/graphene phase change composites (PCCs) with exceptional thermal conductivities. The PCC with 12 wt% graphene exhibits a thermal conductivity of ∼5.92 W m−1 K−1 that is 26-fold higher than that of neat 1-octadecanol while maintaining a high latent heat of fusion (∼202.8 J g−1). Even when compressed by a high weight at ∼70 °C, the PCC still retains shape stability without any leakage. Such abilities to endow PCCs with exceptional shape stability and to boost their thermal conductivity by an order-of-magnitude without incurring a significant loss in the heat of fusion are important attributes in enabling their practical application as latent heat storage/release units for thermal management and thermal protection.

Hierarchical graphene–polyaniline nanocomposite films for high-performance flexible electronic gas sensors

Abstract: A hierarchically nanostructured graphene–polyaniline composite film is developed and assembled for a flexible, transparent electronic gas sensor to be integrated into wearable and foldable electronic devices. The hierarchical nanocomposite film is obtained via aniline polymerization in reduced graphene oxide (rGO) solution and simultaneous deposition on flexible PET substrate. The PANI nanoparticles (PPANI) anchored onto rGO surfaces (PPANI/rGO) and the PANI nanofiber (FPANI) are successfully interconnected and deposited onto flexible PET substrates to form hierarchical nanocomposite (PPANI/rGO-FPANI) network films. The assembled flexible, transparent electronic gas sensor exhibits high sensing performance towards NH3 gas concentrations ranging from 100 ppb to 100 ppm, reliable transparency (90.3% at 550 nm) for the PPANI/rGO-FPANI film (6 h sample), fast response/recovery time (36 s/18 s), and robust flexibility without an obvious performance decrease after 1000 bending/extending cycles. The excellent sensing performance could probably be ascribed to the synergetic effects and the relatively high surface area (47.896 m2 g−1) of the PPANI/rGO-FPANI network films, the efficient artificial neural network sensing channels, and the effectively exposed active surfaces. It is expected to hold great promise for developing flexible, cost-effective, and highly sensitive electronic sensors with real-time analysis to be potentially integrated into wearable flexible electronics.

Enhanced thermal conductivity and satisfactory flame retardancy of epoxy/alumina composites by combination with graphene nanoplatelets and magnesium hydroxide

Abstract: Thermally conductive epoxy composites with eco-friendly flame retardancy are prepared by using spherical alumina (Al2O3), magnesium hydroxide and graphene nanoplatelets (GNPs) as thermally conductive fillers. Highly filled alumina particles do not seriously increase the viscosity of the epoxy monomer due to their spherical shape and smooth surface and thus the compounding keeps a good processibility; The incorporation of small amounts of layered GNPs efficiently increases the thermal conductivity of epoxy/Al2O3 composites because of the synergistic effect between layered GNPs and spherical Al2O3 on forming a thermally conductive network within epoxy matrix. Interestingly, the addition of a small amount of eco-friendly magnesium hydroxide endows the thermally conductive epoxy composites with a satisfactory flame retardancy. The epoxy composite with 68% Al2O3, 7% modified GNPs (m-GNPs) and 5% magnesium hydroxide is determined as the optimum composition with a high thermal conductivity of 2.2 W/(mK), 11 times of that of neat epoxy. Its satisfactory flame retardancy is confirmed by the high limiting oxygen index of 39% and UL-94 rating of V-0 with no dripping. The compact, dense and uniform char layers derived from well-dispersed m-GNPs act as efficient barrier layers and contribute to the flame retardant properties of the epoxy composites.

Hollow Manganese Silicate Nanotubes with Tunable Secondary Nanostructures as Excellent Fenton-Type Catalysts for Dye Decomposition at Ambient Temperature

Abstract: Fast diffusion rate of ions and sufficiently exposed active sites are important for catalysts. As a superior but rarely studied Fenton-type catalyst, unsatisfactory ion diffusion rate of manganese silicate is the exact obstacle for improving its catalytic activity. Here, hierarchical manganese silicate hollow nanotubes (MnSNTs) assembled by tunable secondary structures are precisely fabricated by an efficient hydrothermal method and systematically investigated as Fenton-type catalysts for the first time. The open end and thin mesoporous walls of the hollow nanotubes help shorten the diffusion pathway of ions and enhance the mass transport. Moreover, the numerous standing small nanosheets endow MnSNTs with higher specific surface area and larger pore volume than the large nanosheets and nanoparticles, and thus expose more active sites for adsorption and catalytic decomposition. MnSNTs are highly efficient in adsorption and catalytic decomposition of cationic dyes with an excellent recycling stability. About 98.1% of methylene blue is catalytically decomposed in 45 min at an ambient temperature of 25 °C. When the temperature increases to 60 °C, only 2 min are required, with a 530% higher kinetic constant than reported.

Direct Reduction of Graphene Oxide by Ni Foam as a High-Capacitance Supercapacitor Electrode

Abstract: Three dimensional reduced graphene oxide (RGO)/Ni foam composites are prepared by a facile approach without using harmful reducing agents. Graphene oxide is reduced by Ni foam directly in its aqueous suspension at pH 2 at room temperature, and the resultant RGO sheets simultaneously assemble around the pillars of the Ni foam. The RGO/Ni foam composite is used as a binder-free supercapacitor electrode and exhibits high electrochemical properties. Its areal capacitance is easily tuned by varying the reduction time for different RGO loadings. When the reduction time increases from 3 to 15 days, the areal capacitance of the composite increases from 26.0 to 136.8 mF cm–2 at 0.5 mA cm–2. Temperature is proven to be a key factor in influencing the reduction efficiency. The composite prepared by 5 h reduction at 70 °C exhibits even better electrochemical properties than its counterpart prepared by 15 day reduction at ambient temperature. The 5 h RGO/Ni foam composite shows an areal capacitance of 206.7 mF cm–2 at...

Fabrication of a compressible PU@RGO@MnO2 hybrid sponge for efficient removal of methylene blue with an excellent recyclability

Abstract: To enhance the recyclability while maintaining the high efficiency for the removal of organic dyes, monolithic polyurethane@reduced graphene oxide@manganese dioxide (PU@RGO@MnO2) hybrid sponge with a hierarchical structure and satisfactory flexibility is fabricated by self-assembly of RGO on a PU sponge followed by uniform coating of MnO2 nanoparticles onto RGO by means of an in situ redox reaction between RGO and KMnO4. RGO acts as an ideal substrate to accommodate MnO2 nanoparticles and prevents their aggregation, whereas the numerous hydrophilic MnO2 nanoparticles play dual roles of adsorption and catalytic degradation of methylene blue (MB) dye. The resultant hybrid sponge shows a hierarchical porous structure that provides fast transport channels and abundant active sites, benefiting the diffusion and removal of MB. By enhancing the mass transfer with the help of a micro-pump, the monolithic hybrid sponge acts as a filter for dye removal. Under the dynamic mode, the adsorption efficiency of the PU@RGO@MnO2 hybrid sponge for MB (50 ppm, 30 mL) reaches 94% after 20 min, whereas it is as low as 5% under the static mode. With the assistance of H2O2, the removal efficiency of the hybrid sponge is 96% at first time under the dynamic mode, whereas it is only 14% in the static mode. The monolithic hybrid sponge is highly efficient in adsorption and catalytic degradation of MB based on an adsorption–oxidation–desorption process. Even after being used 4 times, it still maintains excellent removal efficiency and recyclability.

K2Mn4O8/Reduced Graphene Oxide Nanocomposites for Excellent Lithium Storage and Adsorption of Lead Ions

Abstract: Ion diffusion efficiency at the solid–liquid interface is an important factor for energy storage and adsorption from aqueous solution. Although K2Mn4O8 (KMO) exhibits efficient ion diffusion and ion-exchange capacities, due to its high interlayer space of 0.70 nm, how to enhance its mass transfer performance is still an issue. Herein, novel layered KMO/reduced graphene oxide (RGO) nanocomposites are fabricated through the anchoring of KMO nanoplates on RGO with a mild solution process. The face-to-face structure facilitates fast transfer of lithium and lead ions; thus leading to excellent lithium storage and lead ion adsorption. The anchoring of KMO on RGO not only increases electrical conductivity of the layered nanocomposites, but also effectively prevents aggregation of KMO nanoplates. The KMO/RGO nanocomposite with an optimal RGO content exhibits a first cycle charge capacity of 739 mA h g−1, which is much higher than that of KMO (326 mA h g−1). After 100 charge–discharge cycles, it still retains a charge capacity of 664 mA h g−1. For the adsorption of lead ions, the KMO/RGO nanocomposite exhibits a capacity of 341 mg g−1, which is higher than those of KMO (305 mg g−1) and RGO (63 mg g−1) alone.

Introduction: Toward Multi-functionality

Abstract: In this monograph, basics and advanced knowledge of different facets of polymer nanocomposites will be reviewed. This understanding will take us a step closer towards achieving truely multi-functional polymer nanocomposites. This monograph also highlights our continuous and coherent research efforts over many years on these materials.

Wear/Scratch Damage

Abstract: In 2009 and 2013, we gave comprehensive reviews on the fundamentals and advances that have been made on tribological aspects of polymer nanocomposites (Dasari et al. in Mater Sci Rep 63:31–80 and Dasari et al. in Tribology of Polymeric Nanocomposites, Butterworth-Heinemann, Elsevier, Croydon, pp 551–570). So, to avoid duplications, here, we focus only on the necessary fundamentals to explain the recent progress on the topic.

Applications and Outlook

Abstract: So far, in the previous chapters, we have only shown the potential of polymer nanocomposites to exhibit different functionalities. Herein, we will briefly review some examples of multi-functional polymer-based nanocomposites, which have been reported in the literature along with some commercial applications in different sectors.