Ocean plastics: environmental implications and potential routes for mitigation - a perspective.

This review provides a current summary of the major sources and distribution of ocean plastic contamination, their potential environmental effects, and prospects towards the mitigation of plastic pollution. A characterization between micro and macro plastics has been established, along with a comprehensive discussion of the most common plastic waste sources that end up in aquatic environments within these categories. Distribution of these sources stems mainly from improper waste management, road runoff, and wastewater pathways, along with potential routes of prevention. The environmental impact of ocean plastics is not yet fully understood, and as such, current research on the potential adverse health effects and impact on marine habitats has been discussed. With increasing environmental damage and economic losses estimated at $US 1.5 trillion, the challenge of ocean plastics needs to be at the forefront of political and societal discussions. Efforts to increase the feasibility of collected ocean plastics through value-added commercial products and development of an international supply chain has been explored. An integrative, global approach towards addressing the growing ocean plastic problem has been presented.

Development of Stiff, Tough and Conductive Composites by the Addition of Graphene Nanoplatelets to Polyethersulfone/Epoxy Composites.

In this study, polyethersulfone (PES) was blended into epoxy resins to improve the fracture toughness of the epoxy resin without loss of mechanical properties, and then two grades of pristine graphene nanoplatelets (GnPs) were separately introduced into the PES/epoxy system to fabricate thermally conductive GnPs/PES/epoxy composites with high toughness as well as high stiffness. It was observed that the addition of GnPs obviously affected the final phase morphology by suppressing the phase separation process of the PES modified epoxy due to the increased viscosity and cure-reaction rate of PES/epoxy. The GnPs with a larger lateral dimension revealed a greater reinforcing effect, and the inclusion of 3 wt % GnPs (~5 µm in diameter) endowed the PES/epoxy matrix with a good thermal conductivity and improved the tensile, flexural, and storage modulus by 27.1%, 17.5%, and 15.6% (at 30 °Ð¡), respectively. Meanwhile, the fracture toughness was further enhanced by about 29.5% relative to the PES modified epoxy at the same GnPs concentration. The positive results suggest that the modification of epoxy resins using the PES and GnPs is an attractive approach for fabricating tougher and stiffer epoxy-based nanocomposites with multifunctional properties, which could widen the industrial applications of the epoxy resins.

Graphene nanoplatelet composite 'paper' as an electrostatic actuator.

Graphene nanoplatelets (GnP) can be made into a thin 'paper' through vacuum filtration of GnP suspension. Electrodes were fabricated from the compressed GnP paper and then by coating the surface with epoxy. The electrostatic actuator was constructed from two parallel-aligned composite papers fixed at the anode and a cathode connected to ground. The two composite papers would then separate when a voltage was applied. The GnP paper was also modified to increase surface area by introducing porosity or adding ∼10 wt% C750 (GnP with diameter less than 1 µm); or changing the relative permittivity by adding barium titanate particles; or combining these two effects by adding CNCs. Overall the output work could be significantly improved to over 400%.

Ionic liquid-assisted synthesis of Pt nanoparticles onto exfoliated graphite nanoplatelets for fuel cells.

Exfoliated graphite nanoplatelets (GnP) has been investigated as an electrocatalyst support for fuel cell applications. GnP-supported Pt catalysts were synthesized by a microwave process in the presence of room temperature ionic liquids (RTILs). Thermal-oxidation resistance of GnP and GnP-supported Pt catalysts was studied by thermogravimetric analysis and compared with a variety of other carbon nanostructures: carbon black, graphite nanofiber, single- and multiwalled carbon nanotubes. GnP showed the best thermal-oxidative stability. The results obtained from X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical testing, scanning and transmission electron microscopy showed that the RTIL synthesis method resulted in size reduction of Pt nanoparticle, improvement of Pt dispersion on GnP, and identification of the relationships between the mean size of Pt particles with increasing RTIL content. The interaction of Pt particles-GnP is stronger than that of a commercial Pt-CB, and the Pt/GnP catalysts prepared by this method have excellent electrocatalytic activity and stability for methanol oxidation.

Role of thickness and intercalated water in the facile reduction of graphene oxide employing camera flash.

Graphene oxide (GO) is a potential precursor for the bulk production of graphene as the synthetic route is simple and cost-effective. Typically, reduction of GO is a time-consuming process and involves either toxic/hazardous reducing agents or high temperature treatment. Herein, we report the role of intercalated water and thickness of GO films towards the reduction of GO employing simple camera flash. A fast, simple and single camera flash instantaneously causes the deoxygenation reaction of GO without employing hazardous/toxic chemical reductants at room temperature. Successful reduction of GO employing camera flash has been verified via XRD, Raman and UV-vis spectroscopic analyses. Flash-reduced graphene shows a relatively high conductivity value of 740 S m(-1) with a C/O ratio of around 9.5. Intercalated water molecules facilitate the reduction by electron-hole pair formation. It has also been found that the intercalated water facilitates the reduction of GO up to a certain film thickness. However, the intensity of light passing through to the backside of a too thick film decreases significantly, causing incomplete reduction.

Cellulose-nanofiber-reinforced poly(lactic acid) composites prepared by a water-based approach.

The difficulty of dispersing cellulose nanofibers (CNFs) in hydrophobic polymers such as poly(lactic acid) (PLA) remains a major obstacle to the expansion of cellulose nanocomposite applications. In this work, we employed the solvent evaporation technique commonly used for drug microencapsulation to suspend PLA in water as microparticles. The suspension of the microparticles was easily mixed with the CNFs prepared by high-pressure homogenization. Water removal by membrane filtration produced CNF sheets filled with the particles. Compression molding of the stacked sheets resulted in nanocomposites with good CNF dispersions. Increases in the modulus and strength (up to 58% and 210%, respectively) demonstrated the load-bearing capability of the CNF network in the composites.

Surface chemistry of electrospun cellulose nitrate nanofiber membranes.

Electrospinning is a rapidly developing technology that provides a unique way to produce novel polymer nanofibers with controllable diameters. Cellulose nitrate non-woven mats of submicron-sized fibers with diameters of 100-1200 nm were prepared. The effects of processing equipment collector design void gap, and steel drum coated with polyvinylidene dichloride (PVDC) were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers. The fibers collected were free from all residual solvents and could undergo oxygen plasma treatment to increase the hydropholicity.

Electron and phonon transport in Au nanoparticle decorated graphene nanoplatelet nanostructured paper.

Monodispersed Au nanoparticles are synthesized on the surface of exfoliated graphene nanoplatelets (GNP) in the presence of polyethyleneimine (PEI) with microwave assisted heating. A highly structured layered Au/GNP "paper" with good flexibility and mechanical robustness is prepared by vacuum assisted self-assembly. The thermal and electrical conductivity of the hybrid paper with and without the Au nanoparticles are investigated after different experimental processing conditions including thermal annealing and cold compaction. Annealing effectively decomposes and removes the adsorbed PEI molecules and improves thermal contact between Au/GNP particles, whereas cold compaction reduces porosity and induces stronger alignment of the Au/GNP within the hybrid paper. Both approaches lead to improvement in electrical and thermal conductivity. It is also found that adjacent GNP particles are electrically connected by the Au nanoparticles but thermally disconnected. It is believed that phonons are scattered at the Au/GNP interfaces, whereas electrons can tunnel across this interface, resulting in a separation of electron and phonon transport within this hybrid paper.

Electrospun cellulose nitrate nanofibers.

Cellulose nitrate nonwoven mats of submicron-sized fibers (100-1200 nm in diameter) were obtained by electrospinning cellulose nitrate solutions. Two solvent systems were evaluated. A 70:30 (wt) ratio of ethanol to acetone and a 60:40 (wt) ratio of tetrahydrofuran (THF) to N,N-dimethylformamide (DMF) were studied. The effects of the two solvent systems, and type two different collectors; void gap, and steel drum coated with polyvinylidene dichloride (PVDC), were investigated. The PVDC layer applied to the rotating drum aided in fiber harvesting. Electron microscopy (FESEM and ESEM) studies of as-spun fibers revealed that the morphology of cellulose nitrate fibers depended on the collector type and solution viscosity. When a rotating steel drum was employed a random morphology was observed, while the void gap collector produced aligned fiber mats. Increases in viscosity lead to larger diameter fibers.

Surface functionalization of electrospun nanofibers for detecting E. coli O157:H7 and BVDV cells in a direct-charge transfer biosensor.

Electrospinning is a versatile and cost effective method to fabricate biocompatible nanofibrous materials. The novel nanostructure significantly increases the surface area and mass transfer rate, which improves the biochemical binding effect and sensor signal to noise ratio. This paper presents the electrospinning method of nitrocellulose nanofibrous membrane and its antibody functionalization for application of bacterial and viral pathogen detection. The capillary action of the nanofibrous membrane is further enhanced using oxygen plasma treatment. An electrospun biosensor is designed based on capillary separation and conductometric immunoassay. The silver electrode is fabricated using spray deposition method which is non-invasive for the electrospun nanofibers. The surface functionalization and sensor assembly process retain the unique fiber morphology. The antibody attachment and pathogen binding effect is verified using the confocal laser scanning microscope (CLSM) and scanning electronic microscope (SEM). The electrospun biosensor exhibits linear response to both microbial samples, Escherichia coli O157:H7 and bovine viral diarrhea virus (BVDV) sample. The detection time of the biosensor is 8 min, and the detection limit is 61 CFU/mL and 10(3)CCID/mL for bacterial and viral samples, respectively. With the advantage of efficient antibody functionalization, excellent capillary capability, and relatively low cost, the electrospinning process and surface functionalization method can be implemented to produce nanofibrous capture membrane for different immuno-detection applications.

Multilayered nano-architecture of variable sized graphene nanosheets for enhanced supercapacitor electrode performance.

The diverse physical and chemical aspects of graphene nanosheets such as particle size surface area and edge chemistry were combined to fabricate a new supercapacitor electrode architecture consisting of a highly aligned network of large-sized nanosheets as a series of current collectors within a multilayer configuration of bulk electrode. Capillary driven self-assembly of monolayers of graphene nanosheets was employed to create a flexible, multilayer, free-standing film of highly hydrophobic nanosheets over large macroscopic areas. This nanoarchitecture exhibits a high-frequency capacitative response and a nearly rectangular cyclic voltammogram at 1000 mV/s scanning rate and possesses a rapid current response, small equivalent series resistance (ESR), and fast ionic diffusion for high-power electrical double-layer capacitor (EDLC) application.

A novel approach to create a highly ordered monolayer film of graphene nanosheets at the liquid-liquid interface.

A monolayer of ultrathin sheets of highly hydrophobic graphene nanosheets was prepared on a large area substrate via self-assembly at the liquid-liquid interface. Driven by the minimization of interfacial energy these planar shaped graphene nanosheets produce a close packed monolayer structure at the liquid-liquid interface. This monolayer film shows high electrical conductivity of more than 1000 S/cm and an optical transmission of more than 70% at a wavelength of 550 nm. Interfacial self-assembly of these nanosheets demonstrates a promising route for the application of this novel material in optoelectronics applications.

Nanometal-decorated exfoliated graphite nanoplatelet based glucose biosensors with high sensitivity and fast response.

We report the novel fabrication of a highly sensitive, selective, fast responding, and affordable amperometric glucose biosensor using exfoliated graphite nanoplatelets (xGnPs) decorated with Pt and Pd nanoparticles. Nafion was used to solubilize metal-decorated graphite nanoplatelets, and a simple cast method with high content organic solvent (85 wt %) was used to prepare the biosensors. The addition of precious metal nanoparticles such as platinum (Pt) and palladium (Pd) to xGnP increased the electroactive area of the electrode and substantially decreased the overpotential in the detection of hydrogen peroxide. The Pt-xGnP glucose biosensor had a sensitivity of 61.5+/-0.6 microA/(mM x cm(2)) and gave a linear response up to 20 mM. The response time and detection limit (S/N=3) were determined to be 2 s and 1 microM, respectively. Therefore, this novel glucose biosensor based on the Pt nanoparticle coated xGnP is among the best reported to date in both sensing performance and production cost. In addition, the effects of metal nanoparticle loading and the particle size on the biosensor performance were systematically investigated.

Characterization and thermophysical properties of unsaturated polyester-layered silicate nanocomposites.

The thermophysical properties of unsaturated polyester (UPE) nanocomposites reinforced by organo-montmorillonite clay nanoplatelets are reported. The organo-clay nanoplatelets were sonicated in acetone for 2 hours to be dispersed in the UPE matrix. Vacuum extraction removed not only the acetone but also the styrene present in the UPE solution. The same mechanical and thermophysical properties of UPE were regained after adding the lost amount of styrene to the UPE solution. Both delaminated and intercalated clay morphologies were observed by transmission electron microscopy. It was found that the sonication process was effective to delaminate clay nanoplatelets for more homogeneous dispersion, dependent on organic chemical modifications for clay nanoplatelets. A higher storage modulus enhancement was obtained when the organo-clay nanoplatelets were delaminated and more homogeneously dispersed. The reinforcing effect of both delaminated and intercalated clay nanoplatelets was theoretically evaluated with the Halpin-Tsai equations. It was evaluated that the aspect ratio of delaminated clay nanoplatelets was approximately 150. The increase of the storage modulus below and above the glass transition temperature was achieved without reducing glass transition temperature and Izod impact strength with increasing clay content.

Recent advances in biodegradable nanocomposites.

There is growing interest in developing bio-based products and innovative process technologies that can reduce the dependence on fossil fuel and move to a sustainable materials basis. Biodegradable bio-based nanocomposites are the next generation of materials for the future. Renewable resource-based biodegradable polymers including cellulosic plastic (plastic made from wood), corn-derived plastics, and polyhydroxyalkanoates (plastics made from bacterial sources) are some of the potential biopolymers which, in combination with nanoclay reinforcement, can produce nanocomposites for a variety of applications. Nanocomposites of this category are expected to possess improved strength and stiffness with little sacrifice of toughness, reduced gas/water vapor permeability, a lower coefficient of thermal expansion, and an increased heat deflection temperature, opening an opportunity for the use of new, high performance, lightweight green nanocomposite materials to replace conventional petroleum-based composites. The present review addresses this green material, including its technical difficulties and their solutions.

"Green" nanocomposites from cellulose acetate bioplastic and clay: effect of eco-friendly triethyl citrate plasticizer.

"Green" nanocomposites have been successfully fabricated from cellulose acetate (CA) powder, eco-friendly triethyl citrate (TEC) plasticizer and organically modified clay. The effect of the amount of plasticizer varying from 15 to 40 wt % on the performance of the nanocomposites has been evaluated. The morphologies of these nanocomposites were evaluated through X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) studies. The mechanical properties of nanocomposites are correlated with the XRD and TEM observations. Cellulosic plastic-based nanocomposites with 20 wt % TEC plasticizer and 5 wt % organoclay showed better intercalation and an exfoliated structure than the counterpart having 30/40 wt % plasticizers. The tensile strength, modulus and thermal stability of cellulosic plastic reinforced with organoclay showed a decreasing trend with an increase of plasticizer content from 20 to 40 wt %. The nano-reinforcement at the lower volume fractions (phi < or = 0.02) reduced the water vapor permeability of cellulosic plastic by 2 times and the relative permeability better fits with larger platelet aspect ratios (alpha = 150).