Concentration Of Graphene Oxide Nanosheets Research Articles

Graphene oxide nanosheets enhancing the photothermal response of a cellular barrier exposed to near infrared light

AbstractRecent developments in targeted photothermal therapy focus on integrating near‐infrared (NIR) light and biocompatible nanostructures. It is yet unclear if graphene oxide nanosheets (GO) can assist in the photothermal response of cellular barriers under NIR irradiation. Herein, this study investigates the photothermal response of a cellular barrier treated with different concentrations of GO under the irradiation of NIR light. The synthesized GO nanosheets show good stability in aqueous media. No toxic effects are imposed onto human umbilical vein endothelial cells (HUVECs) when the cells are treated with GO up to 20 μg/mL for 1 day. In addition, the in vitro cellular barrier model with intercellular tight junctions is formed by using HUVECs, which have a high transepithelial electrical resistance (TEER) value of 89.3 Ω · cm2. Under the irradiation of NIR light (980 nm), the photothermal response on the cellular barrier is enhanced by introducing GO, which has been verified by the decrease of TEER value and the increase in the transport of dextran. The results indicate that the thermal response of a cellular barrier exposed to NIR light is non‐linearly enhanced with increasing concentration of GO.

Graphene oxide influence in soil bacteria is dose dependent and changes at osmotic stress: growth variation, oxidative damage, antioxidant response, and plant growth promotion traits of a Rhizobium strain

Climate change events, such as drought, are increasing and soil bacteria can be severely affected. Moreover, the accumulation of emerging pollutants is expected to rapidly increase, and their impact on soil organisms, their interactions, and the services they provide is poorly known. The use of graphene oxide (GO) has been increasing due to its enormous potential for application in several areas and it is expected that concentration in soil will increase in the future, potentially causing disturbances in soil microorganisms not yet identified. Here we show the effects that GO nanosheets can cause on soil bacteria, in particular those that promote plant growth, in control and 10% polyethylene glycol (PEG) conditions. Low concentrations of GO nanosheets did not affect the growth of Rhizobium strain E20-8, but under osmotic stress (PEG) GO decreased bacterial growth even at lower concentrations. GO caused oxidative stress, with antioxidant mechanisms being induced to restrain damage, effectively at lower concentrations, but less effective at higher concentrations, and oxidative damage overcame. Under osmotic stress, alginate and glycine betaine osmoregulated the bacteria. Simultaneous exposure to PEG and GO induced oxidative damage. Plant growth promotion traits (indole acetic acid and siderophores production) were increased by osmotic stress and GO did not disturb these abilities. In the context of climate change, our findings might be relevant as they can form the premises for the implementation of crop production methodologies adapted to the new prevailing conditions, which include the presence of nanoparticles in the soil and more frequent and severe drought.

A facile synthesis of cellulose acetate reinforced graphene oxide nanosheets as proton exchange membranes for fuel cell applications

In this work, for the first time, a simple casting process is used to create an efficient and highly stable cellulose acetate (CA) based membrane with dispersive graphene oxide nanosheets (GO). The successful preparation of GO and its integration into the polymer matrix was verified by structural and morphological characterization using FTIR, TEM, SEM, and XRD. Furthermore, the impact of GO nanosheets and their content on the composite membranes' physicochemical properties is investigated. The water uptake increased up to 24% as the concentration of GO increased, while the ion exchange capacity increased threefold compared to the blank CA membrane. Additionally, increasing GO loading also enhanced the proton conductivity and the tensile strength of the developed membranes. The homogeneous CA/GO nanocomposite membranes with GO filler amounts ranging from 0.3 to 0.8 wt% were found to have excellent proton conductivity varying from 9.2 to 15.5 mS/cm compared to 6.94 mS/cm for Nafion 212. Further, as systematically studied and compared in membrane performance, the overall power density of the membrane electrode assembly (MEA) with GO content was increased up to 519 mW/cm2 compared to 401 mW/cm2 for Nafion 212 with significantly lower cost. The encouraging outcomes of this study pave the way for a simple, environmentally friendly, and cost-effective approach for developing nanocomposite membranes for application in PEMFCs.

Effects of graphene oxide nanosheets in the polychaete Hediste diversicolor: Behavioural, physiological and biochemical responses

Numerous applications exist for graphene-based materials, such as graphene oxide (GO) nanosheets. Increased concentrations of GO nanosheets in the environment have the potential to have a large negative effect on the aquatic environment, with consequences for benthic organisms, such as polychaetes. The polychaete Hediste diversicolor mobilises the sediments, hence altering the availability of contaminants and the nutrients biogeochemical cycle. As such, this study proposes to assess the effects of different GO nanosheet concentrations on the behaviour, feeding activity, mucus production, regenerative capacity, antioxidant status, biochemical damage and metabolism of H. diversicolor. This study evidenced that H. diversicolor exposed to GO nanosheets had a significantly lower ability to regenerate their bodies, took longer to feed and burrow into the sediment and produced more mucus. Membrane oxidative damage (lipid peroxidation) increased in exposed specimens. The increased metabolic rate (ETS) evidenced a higher energy expenditure in exposed organisms (high use of ready energy sources – soluble sugars) to fight the toxicity induced by GO nanosheets, such as SOD activity. The increase in SOD activity was enough to reduce reactive oxygen species (ROS) induced by GO on cytosol at the lowest concentrations, avoiding the damage on proteins (lower PC levels), but not on membranes (LPO increase). This study revealed that the presence of GO nanosheets, even at the lower levels tested, impaired behavioural, physiological, and biochemical traits in polychaetes, suggesting that the increase of this engineered nanomaterial in the environment can disturb these benthic organisms, affecting the H. diversicolor population. Moreover, given the important role of this group of organisms in coastal and estuarine food webs, the biogeochemical cycle of nutrients, and sediment oxygenation, there is a real possibility for repercussions into the estuarine community.

Significant Enhancement of the Polarization Holographic Performance of Photopolymeric Materials by Introducing Graphene Oxide.

Relying on various defects and functional oxygen-containing groups on the basal planes, graphene oxide (GO) is commonly unitized for intimate mixing with a polymer matrix to fabricate high-performance nanocomposite polymeric materials with the characteristics of graphene. Herein, by introducing GO nanosheets in a phenanthraquinone-doped polymethyl methacrylate (PQ/PMMA) photopolymer, we demonstrate that the polarization holographic diffraction efficiency of nanocomposite materials can be dramatically enhanced up to nearly 10 times and the photosensitivity can also be enhanced by more than 3 times. Experimental observations reveal that the incorporation of GO nanosheets serves as a polymerization initiator not only to promote the polymerization of MMA monomers and induce the drafting behavior of the PMMA polymer on its surface but also to effectively modulate the molecular weight of the PQ/PMMA photopolymer by adjusting the doping concentration of GO nanosheets. The current study, for the first time, demonstrates that the modulation of molecular weight for PQ/PMMA photopolymers here exerts a significant impact on their holography performance. In addition, due to the strong physisorption of PQ photosensitizers onto GO nanosheets, the aggregation of PQ around GO-graft-PMMA also facilitates the formation of GO-graft-PMMA/PQ and is beneficial to the enhancement of holographic performance. The emergence of GO-graft-PMMA/PQ nanocomposite materials here is expected to fulfill the requirement of high-performance polarization-sensitive materials in the field of polarization holographic data storage and provide a facile but effective nanocomposite doping strategy to modulate the holographic performance of photopolymers from micro- and mesoscopic levels.

Evaluating the cytotoxicity of graphene oxide using embryonic stem cells-derived cells.

Graphene oxide (GO) has several potential biomedical applications and therefore cytotoxic evaluation of GO is very important. However, the two most common in vitro models for testing cytotoxicity-primary human cells and immortalized cell lines-suffer serious limitations, namely limited supplies of cells and unrealistic cellular responses, respectively. Here, we demonstrate the use of embryonic stem cell (ESC)-derived cells to study GO cytotoxicity. We tested the use of retinal pigment epithelium (RPE) cells derived from three-dimensional human ESC cultures ("ESC-RPE" cells) as a model of GO cytotoxicity by exposing them to varying concentrations of GO nanosheets. For comparison, we also performed the same test with primary human retinal pigment epithelium cells ("hRPE"), and with cells derived from a human RPE cell line ("ARPE19" cells). We found that cytotoxicity metrics (viability, apoptosis, intracellular reactive oxygen species, and mitochondrial membrane potential) were very similar in ESC-RPE cells and hRPE cells, and those in ARPE19 cells were very different. We conclude that cell models of GO cytotoxicity derived from ESCs are an excellent alternative to primary human cells, without the limitations of tissue availability.

Ultralow concentration of graphene oxide nanosheets as oil-based lubricant additives

The nano-lubricant can largely enhance the tribological property of base oil, while the higher addition will cause a serious aggregation of nanoparticles. In this paper, the hexadecane-based oil (16C) with ultralow concentration of graphene oxide (GO) nanosheets as lubricant additives were successfully prepared by phase transfer method. The tribological behavior of the hexadecane with different concentration of GO has been investigated by subjecting it to macroscopic ball-on-disc friction tests using SRV-4 tribometer. The steady-state coefficients of friction (COF) of 16C with 10 mg/L GO were ca. 0.146. Based on the tribological tests and analysis of the wear scar, a lubrication mechanism was proposed. It is believed that the adsorption of GO nanosheets on the lubricated surfaces of both the ball and disk is the key to reduce friction and wear. The proper addition of GO nanosheets can easily enter into the contact area and efficiently protect the surface of the sample from wear.

Graphene Oxide Nanosheet-Composited Poly(N-isopropylacrylamide) Hydrogel for Cell Sheet Recovery

Cell sheet engineering technique has been applied to treat various tissues without the use of a traditional scaffold. To date, methods for the cell sheet harvesting depend mostly on grafted poly(N-isopropylacrylamide) (pNIPAAm) thin layers, while the native pNIPAAm hydrogel, which possibly presents the easiest way to prepare thermo-responsive materials, is not suitable for the cell sheet harvesting due to its low cell attachment. In this study, the graphene oxide (GO) nanosheet was utilized as an additive to enhance the bio-compatibility of the pNIPAAm hydrogel. Different concentrations of GO nanosheets were added to prepare GO/pNIPAAm composite hydrogels through the in-situ free radical polymerization with polyethylene glycol dimethacrylate (PEGDA) as a cross-linker. The results indicated that the physical properties of the composite hydrogels had little difference with that of the native pNIPAAm hydrogel. However, the cell attachment, proliferation and detachment behaviors on the composite hydrogel surface were greatly enhanced. Monkey fibroblast COS7 cells attached and proliferated better on the GO/pNIPAAm composite hydrogel, while intact COS7 cell sheets could be harvested from the composite hydrogels by simply lowering the temperature. In contrast, the cells appeared as clusters on the native pNIPAAm hydrogel. Furthermore, when HeLa and COS7 cells were seeded successively onto the micropatterned GO/pNIPAAm hydrogel, there could be the formation of a patterned HeLa/COS7 cell layer. The geometrically patterned GO/pNIPAAm hydrogel may provide an easy-to-prepare material for releasing patterned cell sheets compared to the specific cell-adhesive proteins reported to make patterned cell layers.

An eco-friendly triboelectric hybrid nanogenerators based on graphene oxide incorporated polycaprolactone fibers and cellulose paper

In this research, an eco-friendly triboelectric nanogenerator (TENG) with high output performance based on poly(caprolactone) (PCL)/graphene oxide (GO) and cellulose paper was developed. PCL/GO fibrous layers consisting of various concentrations of GO nanosheets (0, 0.5, 1, 2, 4 and 8 wt%) were fabricated using a cost-effective and simple electrospinning approach. Moreover, the role of GO concentration as well as the topography, thickness, and size of friction layers on the triboelectric performance was investigated. We realized that PCL/4 wt% GO-cellulose paper produced an open circuit voltage, current density and maximum power density up to 120 V, 2.5 mA/m2 and 72.5 mW/m2, respectively. Results demonstrated that this open circuit voltage was 33% greater than that of flat PCL/4 wt% GO layer, confirming the role of the fibrous structure to promote charge density accumulation. Moreover, a 98% increase in the open circuit voltage was calculated for the TENG containing PCL-4 wt% GO with the dimension of 4 × 4 cm2. The output of triboelectric nanogenerator, driven by human hand tapping, was enough to light up at least 21 blue-light-emitting diodes (LEDs) continuously. This higher performance was attributed to the formation of nanopores and strengthened negative charges on PCL from the fibrous structure and oxygen functional groups of GO, respectively. We believed that the suggested triboelectric nanogenerator with high performance, low-cost and easy fabrication process, as well as biocompatibility, has the potential to be applied for eco-friendly power sources to resolve the electronic waste issue and for self-powered biomedical devices.

Exploring the effects of graphene oxide concentration on properties and antifouling performance of PEES/GO ultrafiltration membranes

In this study, asymmetric polyphenylene-ether-ether-sulfone (PEES) ultrafiltration (UF) membranes containing graphene oxide (GO) were prepared via non-solvent-induced phase separation process and N-methyl pyrrolidone was used as a solvent. The synthesis of GO was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis. The morphology of the prepared GO nanosheets was observed by field emission scanning electron microscope (FESEM) and transmission electron microscope. The membranes prepared with increasing concentrations of GO nanosheets were characterized by attenuated total reflectance-FTIR, SEM, atomic force microscopy (AFM), contact angle, and UF studies. The FTIR spectra of the GO embedded membranes reveal large amounts of –OH groups present due to the existence of GO nanosheets which improved its surface hydrophilicity. The contact angle of PEES/GO membrane was significantly lower than PEES membrane. The SEM pictures showed that PEES/GO UF membranes had a sponge-like substructure with the increased porosity and pore size. An AFM topography imaging showed that roughnesses of the modified membranes were improved compared to the pristine PEES membrane. The UF studies showed that the pure water flux ( JW) and the bovine serum albumin flux ( JP) were increased with the incorporation of GO into the blend solution. For the membrane with 0.1% GO content, JW increased by 75% and JP improved twofold which correspond to the maximum values of 186 and 113 L m−2 h−1, respectively. Furthermore, the flux recovery ratio results suggested that PEES/GO membranes have better antifouling characteristics due to the changes in membrane morphology and surface hydrophilicity.

Effect of graphene oxide nanosheets on the geotechnical properties of cemented silty soil

In the present study, the effect of graphene oxide nanosheets (GO) on the geotechnical properties of cemented soil was investigated. Various concentrations of GO (0.02, 0.05 and 0.1wt% of cement) were added to the soil to evaluate the influence of GO on the soil's compaction characteristics, consistency limits, unconfined compression strength (UCS) and direct shear parameters. The scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis were used to characterize the structure of synthesized GO and stabilized soil samples. The addition of GO decreased the plasticity and compressibility parameters of the treated soil samples. The tensile and the shear strength of the treated soil samples were increased with an increase in the GO concentration. The unconfined compressive strength was increased as the GO content increased in the cemented soil samples. The obtained results showed that the GO as a stabilizing agent has a considerable influence on the mechanical properties of stabilized soil.

O-(carboxymethyl)-chitosan nanofiltration membrane surface functionalized with graphene oxide nanosheets for enhanced desalting properties.

A novel O-(carboxymethyl)-chitosan (OCMC) nanofiltration (NF) membrane is developed via surface functionalization with graphene oxide (GO) nanosheets to enhance desalting properties. Using ring-opening polymerization between epoxy groups of GO nanosheets and amino groups of OCMC active layer, GO nanosheets are irreversibly bound to the membrane. The OCMC NF membranes surface-functionalized with GO nanosheets are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle analyzer, and zeta potential analyzer. The membranes exhibit not only higher permeability but also better salt rejections than the pristine membranes and the commercial NF membranes; besides, the desalting properties are enhanced with the concentration of GO nanosheets increasing. Furthermore, the transport mechanism of GO-OCMC NF membranes reveals that the nanoporous structure of GO-OCMC functional layer and size exclusion and electrostatic repulsion of water nanochannels formed by GO nanosheets lead to the membranes possessing enhanced desalting properties.