Single-Step Process toward Achieving Superhydrophobic Reduced Graphene Oxide.

The association of cellular toxicity with the physiochemical properties of graphene‐based materials is largely unexplored. A fundamental understanding of this relationship is essential to engineer graphene‐based nanomaterials for biomedical applications. Here, an in vitro toxicological assessment of graphene oxide (GO) and reduced graphene oxide (RGO) and in correlation with their physiochemical properties is reported. GO is found to be more toxic than RGO of same size. GO and RGO induce significant increases in both intercellular reactive oxygen species (ROS) levels and messenger RNA (mRNA) levels of heme oxygenase 1 (HO1) and thioredoxin reductase (TrxR). Moreover, a significant amount of DNA damage is observed in GO treated cells, but not in RGO treated cells. Such observations support the hypothesis that oxidative stress mediates the cellular toxicity of GO. Interestingly, oxidative stress induced cytotoxicity reduces with a decreasing extent of oxygen functional group density on the RGO surface. It is concluded that although size of the GO sheet plays a role, the functional group density on the GO sheet is one of the key components in mediating cellular cytotoxicity. By controlling the GO reduction and maintaining the solubility, it is possible to minimize the toxicity of GO and unravel its wide range of biomedical applications.

The densification process plays a critical role in determining the microstructure and performance of Ti matrix composites (TMCs). Herein, a comparative study was performed on a graphene oxide (GO)/Ti-6Al-4V composite fabricated by laser powder bed fusion (L-PBF) and spark plasma sintering (SPS). The flexible GO sheets were homogeneously decorated onto the Ti-6Al-4V powders via an electrostatic self-assembly without significantly changing the particle size or sphericity. Under high-energy laser irradiation, the GO sheets were completely dissolved into the matrix. The L-PBF-produced composite was composed of fine αʼ martensite structures due to the rapid solidification and the solute carbon atoms. In contrast, the GO was reacted with Ti matrix and completely transformed into submicron TiC particles during SPS; the composite consisted of α＋β phases with randomly dispersed TiC. Moreover, the L-PBF-produced composite exhibited a higher hardness of 481 HV as compared with the SPS-produced one of 367 HV, attributing to the fine αʼ microstructures and high residual stresses. The present work offers deep understanding on the structural evolution of GO during high-temperature densifications, and shows new insights for fabrication of high-performance TMCs with tailored microstructures.

Preparation and characterization of graphene derived from low-temperature and pressure promoted thermal reduction

Despite great recent progress, the processing of graphene oxide (GO) sheets in polymers are often one of the most challenging steps in fabricating graphene/polymer nanocomposites. The challenge is how to achieve high levels of dispersion and reduction of GO simultaneously, without any residual reducing agents in the composites. In this work, microwave irradiation is applied as a remote source to in situ reduce GO sheets embedded in the poly (vinyl alcohol) (PVA) matrix, which process maximizes the advantage of GO's solvent processability. The active response of GO to microwave irradiation allows for the uniform and selective heating of GO, leading to a minutes‐quick reduction of GO without physical damage to the polymer matrix. Significant improvements in the mechanical properties, electrical conductivities and glass transition temperatures (Tgs) of GO/PVA nanocomposites are achieved, and possible reasons for the improvements are also discussed. POLYM. COMPOS., 40:170–178, 2019. © 2017 Society of Plastics Engineers

Enhancing the electrical conductivity of in-situ reduced graphene oxide-zirconia composites through the control of the processing routine

Interest in novel energy storage and conversion methods has prompted a broad interest in potential applications of conductive, complex materials such as graphene oxide slurries. Investigating the complex rheological, material, and chemical properties of chemically exfoliated graphene oxide suspensions is a potential means to address that interest. The morphological size and clustering, rheology, and electronic conductivity are determined to characterize the properties of graphene oxide (GO) suspensions from variable centrifugation speeds. The evolution of viscosity is then analyzed under oscillatory shear, steady shear, and transient shear characteristics. The resulting microstructure is then analyzed via neutron scattering analysis and imaged with scanning electron microscopy. Small-Angle Neutron Scattering (SANS) of a 500g centrifuged GO suspension determined that particle structure is locally flat sheet-like at lengths below 100 nm, crumpled aggregates of GO sheets with surface roughness at length scales from 200 nm to 2 μm, and a dense mass fractal of overlapping GO sheets extending up to length scales of 20 μm. Increased centrifugation force of the 1000g GO suspension corresponded with lower zero-shear viscosity, yield stress, and less pronounced thixotropic behavior. Rheo-dielectric measurements were conducted on 1000g and 500g GO suspensions to determine the ohmic resistance, electronic conductivity, and specific capacitance. The more fluid-like microstructure of 1000g with smaller monodispered thinning GO sheets in suspension had lower ohmic resistance and higher electronic conductivity compared to the 500g GO suspension with more polydispersed larger aggregates. The 1000g GO suspension had the highest specific capacitance of 4.63 mF cm-2 at the highest shear rate of 700 s-1 due to the higher frequency of particle-particle collisions during shear within the network of smaller and more intrinsically conductive GO sheets to store charge. Therefore, the results of this study have implications for future studies in flowable carbon nanomaterials in flow battery and flow capacitor technologies.

We present a general study on a high performance supercapacitor based on intercalated reduced graphene oxide with carbon black nanoparticles. Graphene oxide sheets were synthesized by oxidation and exfoliation of natural graphite and were reduced using hydroiodic acid in the presence of carbon black nanoparticles. Graphene paper was fabricated by one-step procedure via simultaneous reducing and drying the aqueous solution of mixed carbon black nanoparticles and graphene oxide on a conductive substrate. Transmission electron microscopy confirmed the intercalation of carbon black nanoparticles into reduced graphene oxide sheets, preventing them from restacking during the fabrication of paper. Results confirmed that the electrochemical performance of the reduced graphene oxide paper as a supercapacitor electrode was improved by intercalation of carbon black nanoparticles into reduced graphene oxide sheets and also the assembled supercapacitor becomes more efficient with graphene oxide separator. Cyclic voltammetry of the prepared electrodes in 30 wt% KOH solution at 10 mV/s scan rate showed that adding only 5 wt% of carbon black to graphene oxide increases specific capacitance from 118 F/g to 129 F/g. In addition, the maximum specific capacitance (139 F/g) was obtained by adding 15 wt% of carbon black and that increased to 142 F/g by the use of graphene oxide paper as a separator. Furthermore, electrochemical impedance spectroscopy by Nyquist plot showed that charge transfer resistance in electrodes decreases from 18 in the reduced graphene oxide to 6 in the reduced graphene oxide paper with intercalated carbon black nanoparticles and ions diffusion occurs easier than previous.

Preparation of Ag/reduced graphene oxide reinforced copper matrix composites through spark plasma sintering: An investigation of microstructure and mechanical properties

The hydrothermal process was used to prepare Mn3O4/x%GO nanocomposites (NC’s) having different ratios of the Mn3O4 nanoparticles (NP’s) on the surface of graphene oxide (GO) sheet. SEM image showed that the Mn3O4 NP’s were distributed over the surface of GO sheet. HRTEM images exhibited the lattice fringe arising from the (101) plane of the Mn3O4 NP’s having the interplanar d-spacing of 0.49 nm decorating on the surface of GO. The electronic absorption spectra of Mn3O4/x%GO NC’s also show broad bands from 250 to 550 nm. These bands arise from the d–d crystal field transitions of the tetrahedral Mn3+ species and indicate a distortion in the crystal structure. Photo-catalytic activity of spinel ferrite Mn3O4 NP’s by themselves was low but photo-catalytic activity is enhanced when the NP’s are decorating the GO sheet. Moreover, the Mn3O4/10%GO NC’s showed the best photo-catalytic activity. This result comes from the formation of Mn–O–C bond that confirm by FT-IR. This bond would facilitate the transfer of the photoelectrons from the surfaces of the NP’s to the GO sheets. PL emission which is in the violet–red luminescent region shows the creation of defects in the fabricated Mn3O4 NP’s nanostructures. These defects create the defect states to which electrons in the VB can be excited to when the CB. The best degradation efficiency was achieved by the Mn3O4 NP’s when they were used to decorate the GO sheets in the Mn3O4/10%GO NC’s solution.HighlightsLattice fringe of Mn3O4 with an interplanar d-spacing of 0.49 nm for (101) plane.Photocatalytic activity of spinel ferrite Mn3O4 nanoparticles by itself is low.Number of photoelectrons created depends on number of Mn3O4 on a given area of GOThe bonding of the Mn3O4 to the GO sheet would be though a Mn–O–C junction.The degradation processes were accelerated by Mn3O4/10%GO nanocompositesGraphic abstract

Graphene oxide (GO) is a promising precursor to produce graphene-family nanomaterials for various applications. Their potential health and environmental impacts need a good understanding of their cellular interactions. Many factors may influence their biological interactions with cells, and the lateral dimension of GO sheets is one of the most relevant material properties. In this study, a model bacterium, Escherichia coli ( E. coli ), was used to evaluate the antibacterial activity of well-dispersed GO sheets, whose lateral size differs by more than 100 times. Our results show that the antibacterial activity of GO sheets toward E. coli cells is lateral size dependent. Larger GO sheets show stronger antibacterial activity than do smaller ones, and they have different time- and concentration-dependent antibacterial activities. Large GO sheets lead to most cell loss after 1 h incubation, and their concentration strongly influences antibacterial activity at relative low concentration (<10 μg/mL). In contrast, when incubating with small GO sheets up to 4 h, the inactivation rate of E. coli cells continues increasing. The increase of small GO sheet concentration also results in persistent increases in their antibacterial activity. In this study, GO sheets with different lateral sizes are all well dispersed, and their oxidation capacity toward glutathione is similar, consistent with X-ray photoelectron spectroscopy and ultraviolet-visible absorption spectroscopy results. This suggests the lateral size-dependent antibacterial activity of GO sheets is caused by neither their aggregation states, nor oxidation capacity. Atomic force microscope analysis of GO sheets and cells shows that GO sheets interact strongly with cells. Large GO sheets more easily cover cells, and cells cannot proliferate once fully covered, resulting in the cell viability loss observed in the followed colony counting test. In contrast, small GO sheets adhere to the bacterial surfaces, which cannot effectively isolate cells from environment. This study highlights the importance of tailoring the lateral dimension of GO sheets to optimize the application potential with minimal risks for environmental health and safety.

Light-induced oxygen sensing using ZnO/GO based gas sensor

This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

Unveiling a novel mechanism: Reduction of graphene oxide by Lysinibacillus sp. through secretion of l-ascorbic acid

Graphene oxide (GO) and reduced graphene oxide (rGO) synthesised from GO, has a promising future in fields ranging from electronics to energy technologies[1]. GO may be synthesized by the modified Hummer’s method[2], where a mixture of potassium permanganate and concentrated sulfuric acid forms the ground pillar for the oxidation of graphite to GO. rGO can be synthesized by a broad range of methods, with the chemical and the thermal reduction routes being very common[3]. The synthesis mechanism of GO by the modified Hummer’s method is still unknown, even though the active oxidizing species dimanganese heptoxide has been suggested as the main redox active specie[4]. The mechanism of the thermal reduction of GO to rGO is also unknown. We present results from i n situ synchrotron X-ray diffraction (XRD) experiments of syntheses and thermal reduction of GO. The in situ synthesis of GO was performed by placing a mixture of permanganate and sulphuric acid in a capillary next to graphite. The synthesis was then initiated by gently pushing the fluid mixture into the powder with N2 gas. The in situ XRD of the GO synthesis showed how the oxidation reaction proceeds in three separate stages, as seen in Figure 1. The first stage was the dissolution of potassium permanganate, followed by an intercalation stage and subsequent formation of crystalline material. The GO 001 diffraction peak was observed early during the synthesis, in the second stage, and the intensity of the 001 diffraction increased during the third stage. The in situ XRD results of the thermal reduction of GO to rGO showed a dependence on the temperature ramping and addition of diamond powder. Syntheses were measured at 1, 5, 10, 20 and 50 °/min temperature ramps. The syntheses were performed in a capillary with GO being heated by a hot air blower under constant N2 flow. Three stages were observed for the reduction process; a GO stage, an amorphous stage and a rGO stage. The change in stage was defined from the changing of the d-value of the initial 001 GO peak, see Figure 2. The initial GO diffraction pattern changed during the heating and more diffraction peaks were observed. The results showed that the nature of the rGO material depends heavily on both temperature and additives. These in situ XRD studies revealed the crystalline intermediates and final product of synthesis by a modified Hummer’s method and the diffractional change during the thermal reduction of GO. The stages observed for both syntheses illuminate how important it is to consider the experimental parameters dependent on the application; they might even have to be optimized separately. As the future use of GO and rGO is expanding and the commercialization of these products are enhanced, the syntheses mechanisms may be of increasing interest. [1] M. Segal, Nat Nano, 4 (2009) 612-614. [2] Hummer and Offeman, J. Am. Chem. Soc. (1958) 1339-1339 [3] Pei and Cheng, Carbon (2012) 3210-3228 [4] Dreyer, Park, Bielawski and Ruoff, Chem. Soc. Rev. (2010) 228-240 Figure 1

Field electron emission from protruded GO and rGO sheets on CuO and Cu nanorods