Fabrication of multilayer graphene oxide reinforced high density polyethylene nanocomposites with enhanced thermal and mechanical properties via thermokinetic mixing

High density polyethylene (HDPE) was compounded with thermally exfoliated graphene oxide (TEGO) by thermokinetic mixing in a short time. High shear rates during the compounding process provided high exfoliation and proper dispersion of graphene layers in the polymer matrix. Different TEGO/polymer ratios were used to get efficient melt mixing. Structural analysis by spectroscopic techniques confirmed the exfoliation of TEGO sheets and the coverage of their surfaces by HDPE chains. Furthermore, homogeneous dispersion of graphene sheets in the matrix led to the enhancement in the mechanical and thermal properties of HPDE-based nanocomposites. Especially stress concentration sites were significantly reduced by preventing the agglomeration and restacking of graphene sheets in the matrix. Therefore, the tensile modulus and strength of HDPE nanocomposite increased about 36.5% and 45.7%, respectively, with the incorporation of 2 wt% TEGO. Microscopy analysis showed the separation of graphene layers in the cross-sectional area of composite specimens. TEGO-reinforced HDPE nanocomposites showed high thermal stability compared to the neat sample

Facile synthesis of polypyrrole/graphene nanosheet-based nanocomposites as catalyst support for fuel cells

The integration of catalyst metals into the graphene-based composites can be a new way to ensure thermal and electronic conductivities of the catalyst support materials in polymer electrolyte membrane fuel cells. In this work, graphene nanosheets were synthesized via a mild and safer chemical route including three major steps: graphite oxidation, ultrasonic treatment and chemical reduction. Then, polypyrrole was coated on graphene nanosheets by in-situ polymerization to fabricate polypyrrole/graphene nanosheet-based nanocomposites as the catalyst supports. Pt nanoparticles were uniformly dispersed on the surface of nanocomposites by sonication technique

An improved technique for the exfoliation of graphene nanosheets and utilization of their nanocomposites as fuel cell electrodes

Graphene nanosheets (GNS) were separated from graphite by an improved, safer and mild method including the steps of oxidation, thermal expansion, ultrasonic treatment and chemical reduction. With this method, the layers in the graphite material were exfoliated, and high-quality GNS were produced with higher yields. Scanning Electron Microscopy (SEM) images exhibited that GNS can exist by being rippled rather than completely flat in a free standing state. The mild procedure applied was capable of reducing the average number of graphene sheets from an average value of 86 in the raw graphite to 9 in GNS. Raman spectroscopy analysis confirmed the significant reduction in size of the in-plane sp2 domains of GNS obtained after the reduction of graphite oxide (GO). BET measurements by nitrogen adsorption technique showed that the surface area of GNS was 507 m2/g [square meters/gram]. The electrical conductivity of GNS was measured as 3.96 S/cm by the four-probe method. As the oxidation time was increased from 50 min to 10 days, stacking height of graphene sheets decreased and thus the number of graphene layers decreased. The variations in interplanar spacings, layer number, and percent crystallinity as a function of oxidation time indicated how stepwise chemical procedure influenced the morphology of graphite. The percent crystallinity of GO sheets decreased down to 2% due to the change of stacking order between graphene layers and the random destruction of graphitic structure after oxidation process. For the production of advanced type of catalyst support materials, the distinguished properties of GNS were combined with the structural properties of conducting polypyrrole (PPy) by the proposed simple and low-cost fabrication technique. A precise tuning of electrical conductivity and thermal stability was also achieved by controlling the polymer thickness of randomly dispersed GO sheets and GNS by a layer-by-layer polymer coating. However, non-uniform polymer dispersion on the surface of expanded GO occurred due to the removal of oxygen functional groups on the surface during thermal expansion of GO sheets. The shortest and most effective impregnation technique of Pt catalysts on the surface of GO, expanded GO and GNS based composites was achieved by a sonication process of 2 hrs. The C/O ratios of GO, expanded GO and GNS were measured as 2.3, 6.0, and 3.2, respectively. The characterization results showed that the presence of oxygen surface groups and the amount of PPy in nanocomposites favored the Pt dispersion and hindered the aggregation of Pt particles on the support surface. As GO content increased three times larger than the amount of PPy in nanocomposite, size distribution of catalyst particles was decreased into the range of 9 nm to 16 nm. Finally, novel fuel cell electrodes made of GO, GNS and their nanocomposites were fabricated in the form of thin-films by applying drop-casting method. Then, the performance of the prepared membrane electrode assemblies was tested in a single fuel cell. Comparably better fuel cell performance was obtained when GO sheet was used as the cathode electrode due to the large amount of oxygen surface groups on the surface of GO sheets

New fuel cell electrodes made from graphene nanosheets and their nanocomposites

The production of novel catalyst support materials could open up new ways to enhance the catalytic activity by reduced catalyst loadings. Nanocomposites composed of conducting polymers reinforced with graphene nanosheets (GNS) or graphite oxide (GO) sheets can be potential fuel cell electrodes as an alternative to commercial fuel cell electrodes

Utilization of functionalized graphene and its nanocomposites as a catalyst support in fuel cells

The production of novel catalyst support materials could open up new ways in order to enhance the catalytic activity by reduced catalyst loading. At this point, nanocomposites composed of conducting polymers like polypyrrole (PPy) reinforced with GNS are being considered as catalyst support for fuel cell applications. In the present work, the effect of chemical properties of graphite oxide (GO) sheets, GNS and their nanocomposites on catalyst size, dispersion and surface chemistry was investigated in detail to fabricate novel catalyst support materials

Surface modifications of graphene-based polymer nanocomposites by different synthesis techniques

With the appropriate surface treatments, graphene sheets can be separated from graphite material and the layer-to-layer distance can be extended. In the present work, graphene nanosheets (GNS) were separated from graphite by an improved, safer and mild method including the steps of oxidation, thermal expansion, ultrasonic treatment and chemical reduction. For the production of advanced polymer nanocomposites, the distinguished properties of GNS were combined with the structural properties of conducting polypyrrole by the proposed simple and low-cost fabrication technique. The changes in surface morphologies and surface functional groups were estimated by controlling the polymer coating on graphite oxide (GO) sheets, expanded GO and GNS

Layer-by-layer polypyrrole coated graphite oxide and graphene nanosheets as catalyst support materials for fuel cells

For the production of advanced type of catalyst support materials, the distinguished properties of graphene nanosheets were combined with the structural properties of conducting polypyrrole by the incorporation of graphene nanosheets into a polymer matrix by the proposed simple and low-cost fabrication technique. A precise tuning of electrical conductivity and thermal stability was also achieved by controlling the thickness of randomly dispersed graphene nanosheets by a layer-by-layer polymer coating. Initially, graphene nanosheets were fabricated in large quantities via a mild chemical synthetic route involving graphite oxidation, ultrasonic treatment and chemical reduction. Then, polypyrrole/graphene nanosheet composites with improved conductivity, thermal stability and high surface area were synthesized by in situ polymerization with the different pyrrole feed ratios. Although graphite oxide sheets have electrically insulating property, partially oxidized graphite oxide was also utilized as conductive fillers in polymer matrix. However, polypyrrole/graphene nanosheet composites have better electrical conductivity than polypyrrole/graphite oxide composites

Layer-by-layer polypyrrole coated graphite oxide and graphene nanosheets as catalyst support materials for fuel cells

For the production of advanced types of catalyst support materials, the distinguished properties of graphene nanosheets were combined with the structural properties of conducting polypyrrole by the incorporation of graphene nanosheets into a polymer matrix by the proposed simple and low-cost fabrication technique. A precise tuning of electrical conductivity and thermal stability was achieved by controlling the polymer thickness of randomly dispersed graphene nanosheets. Initially, graphene nanosheets were fabricated in large quantities via a mild chemical synthetic route involving graphite oxidation, ultrasonic treatment, and chemical reduction. Then, polypyrrole/graphene nanosheet composites with improved conductivity, thermal stability, and high surface area were synthesized by in situ polymerization with the different pyrrole feed ratios. Although graphite oxide sheets have electrically insulating property, partially oxidized graphite oxide was also utilized as conductive fillers in polymer matrix. However, polypyrrole/graphene nanosheet composites have better electrical conductivity than polypyrrole/graphite oxide composites

Upcycled graphene nanoplatelets integrated fiber-based Janus membranes for enhanced solar-driven interfacial steam generation †

The increasing demand for drinking water and environmental concerns related to fossil fuels have given rise to the use of solar energy in water desalination. Solar-driven interfacial steam generation is a promising method for water purification, particularly in remote areas. Janus membranes, featuring bilayer hydrophobic/hydrophilic structures, offer high functionality and have attracted significant interest in this field. This study explores the integration of novel graphene nanoplatelets (GNP) derived from waste tire pyrolysis through upcycling as a photothermal source in Janus membranes. The membranes consist of polyacrylonitrile (PAN) nanofibrous membranes for water supply and polymethyl methacrylate (PMMA)/graphene nanoplatelets (GNP) nanofibrous membranes for light harvesting. The effects of GNP content and layer thicknesses on photothermal activity, water transport, and overall evaporation rate were analyzed experimentally and numerically. The results showed that a decrease in membrane thickness led to a 19% to 63% enhancement in evaporation rate, highlighting the importance of optimizing membrane design for efficient water desalination