Concentrations Of rGO Research Articles

Biological Degradation and Biostability of Nanocomposites Based on Polysulfone with Different Concentrations of Reduced Graphene Oxide

AbstractIncreasing incorporation of rGO in the polysulfone polymer generates materials with improved chemical and mechanical stability and less prone to biodegradation at the end of the nanocomposite life cycle. The results of attenuated total reflection infrared (ATR‐IR) and mechanical strength, after exposure to wastewater influent, show that the increasing concentrations of rGO into the polymer matrix reduce changes in the nanocomposite properties. The increasing incorporation of rGO also increases growth inhibition of the wastewater microbial population on the surface of nanocomposites. Highest biofilm inhibition and material stability are observed with nanocomposites containing 3 wt% rGO. These results suggest that reduction in the material biodegradation is linked to the inhibition of biofilm growth on the nanocomposite surface due to the antimicrobial properties of rGO. This study demonstrates, for the first time, that the amount of rGO incorporated in the nanocomposite impact the biodegradability and end of life of polysulfone nanocomposites.

Microbial reduction of Ferrihydrite in the presence of reduced Graphene oxide materials: Alteration of Fe(III) reduction rate, biomineralization product and settling behavior

Although graphene-based materials have been shown to physicochemically interact with biotic or abiotic particles after entering into the environment, little is known about their impacts on biotransformation of inorganic colloids. Accordingly, the effects of different reduced graphene oxide (rGO) materials on ferrihydrite reduction were investigated by using Shewanella oneidensis MR-1 and lactate as Fe(III) reducer and electron donor, respectively. rGO at 0.5mgL−1 stimulated the transformation of ferrihydrite to magnetite, possibly by improving electron transfer. In contrast, higher concentrations of rGO (10–100mgL−1) hindered the exposure, accessibility and therefore reduction of ferrihydrite, resulting in the formation of a mixture of goethite and magnetite. The adsorption of soil humic acid by coexisting ferrihydrite and rGO resulted in further inhibition of Fe(III) reduction. On the other hand, the enhanced Fe(III) bioreduction by the less adsorbable aquatic humic acid or simpler flavin molecules was further improved by 0.5mgL−1 rGO but inhibited by 50mgL−1 rGO. Additionally, the settling stability of the rGO-mineral aggregates was altered during bioreduction, which could influence the transport and reactivity of iron mineral and the fate of associated rGO. This study improves our understanding of the impact and behavior of rGO in the environment.

Highly enhanced photocatalytic performance of Zn(1−x)MgxO/rGO nanostars under sunlight irradiation synthesized by one-pot refluxing method

The current research presents a simple, coast-effective, and one-pot refluxing method to synthesize Zn(1−x)MgxO nanostructures, which were decorated on graphene oxide (GO) sheets. In the first step, the effect of refluxing time on structure and morphology of the pristine ZnO nanostructures was investigated. X-ray diffraction (XRD) patterns indicated that the pristine ZnO nanostructures were formed after 8 h of the refluxing process. Field emission electron microscope (FESEM) images showed that stars-shape ZnO nanostructures were formed after 10 h of refluxing time. Further refluxing process for 12 h showed that morphology and structure of the ZnO nanostructures were not changed. However, after 14 h additional phases were formed. Therefore, ZnO and Zn(1−x)MgxO nanostars that were decorated on GO sheets were synthesized during 10 h. XRD patterns indicated that GO sheets were changed into reduced graphene oxides (rGO) during the refluxing process. Transmission electron microscope (TEM) images revealed that ZnO nanostars with more branches were decorated on rGO sheets. However, the TEM images showed that the morphology of ZnxMg(1−x)O/rGO nanocomposites were changed significantly with the increase of Mg concentration up to 6%. Photocatalytic performance of the products was examined under natural sunlight irradiation. The results showed that the rGO and Mg concentrations had significant roles in the photocatalytic performance of ZnO nanostars. The concentrations of Mg and rGO increased up to 4% were the optimum concentration for enhancing photocatalytic performance of Zn(1−x)MgxO/rGO nanocomposites. In addition, room temperature photoluminescence (PL) spectroscopy and photocurrent measurement results indicated that Mg and rGO with optimum concentration caused decrease of electron-hole recombination rate.

Intracellular localization and toxicity of graphene oxide and reduced graphene oxide nanoplatelets to mussel hemocytes in vitro

Recently, graphene materials have attracted tremendous research interest due to their unique physicochemical properties that hold great promise in electronics, energy, materials and biomedical areas. Graphene oxide (GO) is one of the most extensively studied graphene derivatives. In order to improve GO electrical properties, nanoplatelets are chemically reduced, thus increasing nanoplatelet conductivity. This reduced GO (rGO) shows different properties and behavior compared to GO. Graphene-based wastes are expected to end up in the marine environment. Here we aimed to assess the potential toxic effects of GO and rGO to marine organisms by using in vitro assays with mussel (Mytilus galloprovincialis) hemocytes. Cells were exposed to a wide range of concentrations (up to 100mg/L) of GO (with and without polyvinylpyrrolidone-PVP as stabilizing agent: GO and GO-PVP) and rGO with PVP (rGO-PVP) to assess cytotoxicity and cell membrane integrity. Then, cells were exposed to sublethal concentrations of GO and rGO-PVP to assess their subcellular distribution through transmission electron microscopy (TEM) and to evaluate their effects on ROS production. GO, GO-PVP and rGO-PVP showed low and concentration-dependent cytotoxicity. rGO-PVP (LC50=29.902 and 33.94mg/L depending on the origin) was more toxic than GO (LC50=49.84 and 54.51mg/L depending on the origin) and GO-PVP (LC50=43.72mg/L). PVP was not toxic to hemocytes but increased bioavailability and toxicity of nanoplatelets. At TEM, GO and rGO-PVP nanoplatelets caused invaginations and perforations of the plasma membrane, which agrees with the observed decrease in cell membrane integrity. Nanoplatelets were internalized, at a higher extent for rGO-PVP than for GO, and found in the cytosol and in endolysosomal vesicles of hemocytes. Both GO and rGO-PVP increased ROS production at the highest sublethal concentration tested. In conclusion, GO, GO-PVP and rGO-PVP are not highly toxic to mussel cells but they cause membrane damage and their toxicity is ROS-mediated. Finally, in vitro assays with mussel hemocytes are sensitive tools to detect toxic effects of graphene-based nanomaterials.

Graphene oxide and graphene nanosheet reinforced aluminium matrix composites: Powder synthesis and prepared composite characteristics

The preparation and properties of reduced graphene oxide (rGO) and graphene nanosheets (GNSs) reinforcement of aluminium matrix nanocomposites (AMCs) are reported. For the rGO-AMCs, commercial colloidal GO was coated onto aluminium powder particles and then reduced via thermal annealing. For the GNS-AMCs, graphene exfoliated from graphite through ultrasonication and centrifugation was coated onto aluminium particle surfaces via dispersion mixing, filtering and drying. Pure aluminium and aluminium composites with various reinforcement concentrations of rGO and GNS were cold compacted into disc-shaped specimens and sintered in inert atmosphere. The mechanical properties and microstructure were studied and characterised via Vickers hardness, X-ray diffraction, density measurement, and scanning electron microscopy. The reinforcements were uniformly distributed onto the aluminium particle surfaces before and after consolidation within the composites. The relevant factors for the powder metallurgy process (compaction pressure, density, and sintering conditions) were optimised. Increased levels of increased hardness were recorded, over baseline compacted and sintered pure aluminium samples, prepared under identical experimental conditions, of 32% and 43% respectively for the 0.3wt.% rGO-Al and 0.15wt.% GNSs-Al composites. The process developed and presented herein provides encouraging results for realising rGO-AMC and GNS–AMC nanocomposites via low cost cold powder compaction and sintering metallurgy techniques.

Oxidation Prevention Properties of Reduced Graphene Oxide Mixed with 1-Octanethiol-Coated Copper Nanopowder Composites

1-Octanethiol-coated Cu nanoparticles were mixed with reduced graphene oxide (rGO) to fabricate Cu nanoinks with enhanced oxidation prevention. Graphene oxide (GO) was synthesized using modified Hummer’s method and rGO was reduced from GO using hydrazine hydrate. Copper nanoinks were fabricated with varying concentrations of rGO (Cu : rGO ratios of 100 : 1, 500 : 1, and 1000 : 1 wt.%). The coating layers on the copper nanoparticles and rGO were observed using transmission electron microscopy and characterized by X-ray photoemission spectroscopy, X-ray diffraction, and Raman spectroscopy. It was observed that surface roughness increased as the concentration of rGO in Cu patterns increased, and an optimized Cu : rGO weight ratio of 1,000 : 1 was established. After sintering, the electrical properties and corrosion resistance of copper patterns both with and without rGO were measured and monitored for 200 days. The copper pattern with rGO (Cu : rGO = 1,000 : 1) was found to maintain its initial resistivity (1.63 × 10−7 Ω·m) for 150 days. Corrosion tests were conducted to confirm the oxidation prohibition of rGO. The resistance polarization(Rp)of the copper pattern was measured to be 1.5 times higher than that of the copper pattern without rGO. Thus, rGO was shown to prevent oxidation and improve the conductivity of copper patterns.

Inhibition of Viability of the Respiratory Epithelial Cells Using Functionalized Graphene Oxide.

The viability of A549 cells, a human lung carcinoma epithelial cell line, was evaluated after exposure to graphene oxide (GO) and its derivatives (dodecylamine GO (DA-GO), reduced GO (rGO), and sodium dodecyl sulfate rGO (SDS-rGO)). A decrease in the relative amounts of C-OH bonds and an increase in the number of C-C and C-N bonds in the C 1s spectra indicated that the reduction of GO to rGO and the surface functionalization of GO has taken place. The appearance of amine stretching bands, out-of-plane C-H stretching vibrations, and S = O stretching bands in the infrared spectra indicated the formation of DA-GO, rGO, and SDS-rGO, respectively. Low concentrations (3-25 µg/mL) of GO, rGO, and SDS-rGO were found to be mildly toxic, whereas DA-GO exhibited severe dose-dependent toxicity over the same concentration range. High concen- trations (50-400 µg/mL) of GO and all its derivatives resulted in severe toxicity to the A549 cells. It is believed that surface functionality strongly affects the viability of A549 cells.

Graphene-reinforced calcium phosphate cements for bone tissue engineering

F decades, natural calcium phosphate cements (CPCs) derived from sintered animal bone have been investigated to treat bone defects. However, they have low mechanical strength as a critical limit. Graphene not only improves the mechanical properties of scaffolds but promotes osteoinduction. To this end, reduced graphene oxide-incorporated natural calcium phosphate cements (RGOCPCs) were fabricated for reinforcement of CPCs’ characteristics. The fabricated RGO-CPCs showed distinct surface properties and chemical properties according to the RGO concentration. The mechanical properties of RGO-CPCs were significantly improved compared to those of CPCs. In in-vitro studies using a mouse osteoblast cell line and rat-derived adipose stem cells, RGO-CPCs were little toxic to the both cells although high concentrations of RGO decreased the cell adhesion rate and cell viability. Western blotting, immunocytochemistry, and the Alizarin red staining assay revealed that osteoinductivity of RGO-CPCs was highly increased with the increase of RGO. We conclude that RGO-CPCs can overcome the flaws of previously developed natural CPCs and be potential candidates as bone cements for clinical application of bone repair and regeneration.

Multifunctional and environmentally friendly nanocomposites between natural rubber and graphene or graphene oxide

This work describes a green route to multifunctional nanocomposite materials composed of natural rubber (NR) latex and graphene (rGO) or graphene oxide (GO). Aqueous solutions with different concentrations of GO and rGO (prepared with the surfactant cetyltrimethylammonium bromide – CTAB) were mixed with natural rubber latex under magnetic stirring followed by sonication. The slurries obtained after casting were dried in an oven in air at 70 °C for 24 h. The nanocomposites were characterized by TEM and SEM, AFM and KFM. The thermal, electrical and mechanical properties were evaluated using TGA, resistivity measurements (four-point) and DMA. Swelling tests were performed using three solvents with different polarities: xylene, isopropanol and water. The inclusion of filler networks in the polymeric matrices provided significant improvements in the electrical, chemical and mechanical properties, in comparison to the unfilled polymer. In addition, the nanocomposites proved to be biodegradable.