Functionalized Graphene Oxide Nanosheets Research Articles

Mechanical Properties and Thermal Conductivity of Epoxy Resin Reinforced with Functionalized Graphene Nanosheets and Woven Glass Fabric

The reinforcing effects of functionalized graphene sheets (FGSs) on thermosetting epoxies are examined to understand the feasibility of these FGSs–epoxy nanocomposites in composite applications. The nanocomposites are prepared by compression molding with different graphene contents (0, 1, and 3 wt%) and different chemical treatments including FGSs and reduced graphene oxide (RGO) nanosheets. In addition, two silane molecules (octyltriethoxysilane [OTES] and glycidoxypropyltrimethoxysilane [GPTMS]) are used as coupling agents. Morphological analysis shows that the use of functionalized graphene oxide nanosheets in woven glass fabric/epoxy nanocomposites significantly improves the dispersion distribution of graphene nanosheets inside the matrix and increases their interfacial adhesion. The results reveal that the nanocomposites containing functionalized graphene nanosheets show the most promising improvement in terms of thermal and mechanical properties. In particular, Young's modulus increases by up to 17% and 25% with only 3% of functionalized graphene oxide using OTES and GPTMS, respectively. The result of the water droplet contact angle of the nanocomposites reinforced by graphene oxide functionalized by octyltriethoxysilane (OTES) shows an increase to a value of 105.80, indicating the super hydrophobic nature.

Functionalized graphene oxide as a nanocarrier for multiple suppressive miRNAs to inhibit human intrahepatic cholangiocarcinoma

AbstractThe restoration of suppressed miRNAs is a promising therapeutic approach for treating tumors; however, efficient delivery remains a challenge. Herein, we aimed to develop a polyethylenimine (PEI) functionalized graphene oxide nanosheets (GO‐PEI) as a suppressive miRNA delivery system to treat human intrahepatic cholangiocarcinoma (ICC). We found that the GO‐PEI complex possessed excellent transfection efficacy and acceptable toxicity. Furthermore, using our miRNA array analysis and The Cancer Genome Atlas (TCGA) dataset, we selected four miRNAs (miR‐194‐5p, miR‐125b‐5p, miR‐122‐5p, and let‐7c‐5p) that are remarkably downregulated in ICC samples compared to that in adjacent tissues. The GO‐PEI complexed with the four miRNAs (GO‐PEI‐4miR) achieved a higher miRNA transfection efficiency than Lipo2000, as verified by quantitative reverse transcription polymerase chain reaction (qRT‐PCR) assays, immunofluorescence, and flow cytometry analyses. In addition, in vitro experiments revealed that GO‐PEI‐4miR remarkably restored the repressed miRNAs, thereby significantly repressing tumor sphere formation, colony formation, drug resistance, and markedly inhibiting the target genes of these miRNAs and cancer stem cell‐related markers. Furthermore, both tumor weights and bioluminescent imaging analysis indicated that the GO‐PEI‐4miR significantly reduced tumor formation in vivo. Taken together, these results demonstrate that GO‐PEI could be a potential delivery system for multiple repressive miRNAs in ICC therapy.

Inter-capsule fusion and capsule shell destruction using dynamic covalent polymers

Herein, capsule shells containing hindered urea bonds were prepared using interfacial polymerization in an oil-in-oil Pickering emulsion stabilized by functionalized graphene oxide nanosheets.

Incorporating Amino Acids Functionalized Graphene Oxide Nanosheets into Pebax Membranes for CO <sub>2</sub> Separation

Incorporating Amino Acids Functionalized Graphene Oxide Nanosheets into Pebax Membranes for CO <sub>2</sub> Separation

Fouling decline and retention increase of polyethersulfone membrane by incorporating melamine-based dendrimer amine functionalized graphene oxide nanosheets (GO/MDA)

Graphene oxide (GO) nanosheets were prepared using modified Hummers method and then amino-functionalized with melamine-based dendrimer amines (MDA). The resulted nanofiller (GO/MDA) was incorporated into the polyethersulfone (PES) membrane matrix with the phase inversion technique. The effects of this incorporation on membrane properties were studied in different terms including hydrophilicity, porosity, surface and cross-sectional morphology, mean pore radius, permeability, fouling resistance and nanofiltration performance. The resulted membranes presented enhanced hydrophilicity, porosity and permeability due to the presence of super hydrophilic GO/MDA nanocomposite in the membrane matrix. The pure water flux of the PES membranes under the operating pressure of 0.3 MPa was increased from 19.9 kg/m2 h for the bare PES to 38.1 kg/m2 h and 53.9 kg/m2 h for the optimum contents of GO and GO/MDA, respectively. The flux recovery ratio (FRR) was enhanced from 50.4% for the bare PES to 78.5% for the membrane containing the optimum content of GO/MDA (0.25 wt%). This membrane also presented the minimum total and irreversible fouling ratios. Nanofiltration performance of the membranes was proved with near total rejection of anionic dye reactive red 198, alongside the remarkable retention of divalent ions (77.4% and 56.4% for Na2SO4 and MgSO4, respectively) and slight retention of monovalent ion NaCl (18.9%). Eventually, the results of the present study introduced MDAs as ideal dendrimer ligands for the preparation of highly hydrophilic and antifouling nanofillers.

POSS functionalized graphene oxide nanosheets with multiple reaction sites improve the friction and wear properties of polyamide 6

Frictional and wear properties of polyamide 6 (PA6) are very important for its use as anengineering plastic. In this study, octaamino-polyhedral oligomeric silsesquioxane (POSS) functionalized graphene oxide (GO) was used to fabricate a PA6/reduced GO-POSS (rGO-POSS) nanocomposites. Compared with PA6, the PA6/rGO-POSS nanocomposites with 0.3 wt% GO-POSS has a decrease of friction coefficient by 86.36% from 0.44 to 0.06. The depth and width of the wear scar were reduced by 79.64% and 70.69%, respectively. Meanwhile, the wear rate reached the lowest and dropped by about 65.72%. The research found that GO-POSS is self-fixed in the matrix and effectively increases the interface bonding strength.

Investigation of thermo-mechanical behavior, proton transfer and methanol permeation of polymer electrolyte membrane in low sulfonated state modified with thermally stable surface functionalized graphene oxide nanosheets

Sulfonated polyether ether ketone is currently under investigation to replace the expensive Nafion® as polymer electrolyte membrane. Sulfonic acid group is hydrophilic in nature and plays a key role in proton transfer in polymer electrolyte membranes. The higher the degree of sulfonation the higher proton conductivity in sPEEK based polymer exchange membrane is achieved; however, high degree of sulfonation causes severe dimensional instability due to higher water uptake which in turn affects membrane fuel retention capabilities as well as thermo-mechanical strength. Graphene oxide nanosheets were functionalized with aryl dizonium salt of p-Aminobenzene sulfonic acid for modification of sPEEK in low sulfonated state (DS = 53%) to improve its proton conductivity and suppress fuel crossover. The functionalization was carried out to compensate for the possible dilution of proton exchangeable sites by fillers. The resulting membranes were characterized in terms of morphology, thermo-mechanical behavior, methanol permeability, water uptake, and proton conductivities. The results proved that sulfonated GO not only improved thermo-mechanical behavior of the membrane but also dramatically increased proton conductivity (47 mS cm−1) than pristine sPEEK (25 mS cm−1). The composite membranes showed highly reduced methanol crossover compared with pristine sPEEK. The electrochemical selectivity increased from 9.5 × 104 Scm−3s (pristine sPEEK) to 26.9 × 104 Scm−3s.

Functionalized graphene oxide nanosheets with unique three-in-one properties for efficient and tunable antibacterial applications

Developing antibiotics-independent antibacterial agents is of great importance since antibiotic therapy faces great challenges from drug resistance. Graphene oxide (GO) is a promising agent due to its natural antibacterial mechanisms, such as sharp edge-mediated cutting effect. However, the antibacterial activity of GO is limited by its negative charge and low photothermal effect. Herein, the amino-functionalized GO nanosheets (AGO) with unique three-in-one properties were synthesized. Three essential properties (positive charge, strong photothermal effect, and natural cutting effect) were integrated into AGO. The positive charge (30 mV) rendered AGO a strong interaction force with model pathogen Streptococcus mutans (330 nN). The natural cutting effect of 100 µg·mL−1 AGO caused 27% loss of bacterial viability after incubation for 30 min. Most importantly, upon the near-infrared irradiation for just 5 min, the three-in-one properties of AGO caused 98% viability loss. In conclusion, the short irradiation period and the tunable antibacterial activity confer the three-in-one AGO a great potential for clinical use.

Hydroxyl group functionalized graphene oxide nanosheets as additive for improved erythritol latent heat storage performance: A comprehensive evaluation on the benefits and challenges

Graphene oxide (GO) nanosheets were employed as the additive to make composites of erythritol, a promising medium-temperature PCM candidate. GO nanosheets modified with hydroxyl groups were applied to improve the dispersion stability of the composites. A systematic characterization on the latent heat storage performance was performed for both pure and composite erythritol, in order to identify the benefits and challenges of the composites. It was found that the thermal conductivity is increased by nearly twice and the degree of supercooling was lowered from ~64 °C to ~48 °C at the loading of 1.0 wt% GO nanosheets (the maximum loading tested). The addition of GO nanosheets also leads to an increase of the retrievable latent heat during crystallization, from ~187 kJ/kg to ~225 kJ/kg at the same loading, by increasing the crystallinity. However, the introduction of GO nanosheets can also lead to a rise in the dynamic viscosity of erythritol. As a result, the crystallization rate is slowed down and accordingly, the duration of crystallization becomes 62% longer when the loading reaches 1.0 wt%. In addition, favorable dispersion stability of the erythritol composites is observed, and their melting point (~117 °C) remains almost unchanged during 50 melting-crystallization cycles. Functionalized GO nanosheets have been shown to be an efficient additive for improving the performance of erythritol, but a trade-off analysis on the loading would be required to achieve the best overall performance.

Exploring the antioxidant effects of peptides from almond proteins using PAni-Ag-GONC conjugated trypsin by improving enzyme stability & applications

Functionalized graphene oxide nano-sheets (PAni-Ag-GONC) were prepared and employed as carrier for covalent immobilization of trypsin. This low cost setting, which involves loading of high amount of enzyme on the matrix, displayed significantly enhanced thermo-stability and pH resistance. The nano-composite (NC) bound trypsin preserved 90% of activity whereas native trypsin retained only 44% of activity after 60 days of storage at a temperature of 4°C. Immobilized trypsin conserved 80.5% of activity even after its ten repeated uses. Almond protein hydrolysates prepared by native and conjugated enzyme was investigated for antioxidant activities and found that peptides resulted from NC bound trypsin displayed increase in radical scavenging activity (i.e. around 30% and 37% scavenging activity observed, respectively by native and NC bound trypsin from same concentration of peptides). This strategy provides a new approach for production of potential biopeptides which may be incorporated in drugs and functional food industries applying PAni-Ag-GONC based biocatalysis. Chemical compoundsTrichloroacetic acid (PubChem CID: 6421); Tris (hydroxymethyl)aminomethane (PubChem CID: 6503); Glycine (PubChem CID: 750); and 2,2′-diphenyl-1-picrylhydrazyl (PubChem CID: 74358); Nα- Benzoyl-DL-arginine 4-nitroanilide hydrochloride (PubChem CID: 2724371); Ammonium sulphate (PubChem CID: 6097028).

Phosphotungstic acid supported on functionalized graphene oxide nanosheets (GO-SiC3-NH3-H2PW): Preparation, characterization, and first catalytic application in the synthesis of amidoalkyl naphthols

Grafting of 3-aminopropyltriethoxysilane (APTS) on graphene oxide (GO) nanosheets followed by reaction with phosphotungstic acid (H3PW12O40,denoted as H3PW) gave a new functionalized GO which was characterized using FT-IR, FESEM, EDX, EDX elemental mapping and ICP-OES techniques. The catalytic activity of this nanomaterial containing phosphotungstic counter-anion H2PW12O40¯ (H2PW) which was denoted as GO-SiC3-NH3-H2PW was probed in the synthesis of amidoalkyl naphthols through the one-pot, three-component reaction of β‐naphthol with various aromatic aldehydes and acetamide. The results showed a significant catalytic performance of the catalyst for this transformation in ethanol as solvent at reflux temperature, giving the corresponding products in high yields. In addition, the nanocatalyst could be easily recovered from the reaction mixture and reused many times with no significant loss of its catalytic activity.

Catalytic evaluation of newly prepared GO-SB-H2PMo as an efficient and reusable nanocatalyst for the neat synthesis of amidoalkyl naphthols

The catalytic activity of newly prepared functionalized graphene oxide nanosheets, denoted as GO-SB-H2PMo, has been investigated in the synthesis of amidoalkyl naphthols through the one-pot, three-component reaction of β‐naphthol with various aryl aldehydes and acetamide. The reactions occur under solvent-free conditions and the process is operative with various aryl aldehydes, giving the corresponding products in high yields over short reaction times. Moreover, the catalyst could be easily recovered from the reaction mixture and reused such that considerable catalytic activity can still be achieved after the fifth run.

A multifunctional thermal management paper based on functionalized graphene oxide nanosheets decorated with nanodiamond

In this study, we developed a multifunctional thermal management nanocomposite paper (NPG) consisting of cationic poly (diallyldimethylammonium chloride) (PDDA)-functionalized graphene oxide (PG) and nanodiamond (ND). Due to the functionalized reduction of graphene oxide (GO) by PDDA as well as electrostatic interactions between the positively charged PG and negatively charged ND, a three-dimensional (3D) hybrid NPG paper constructed by two-dimensional (2D) PG layers and zero-dimensional (0D) ND particles was successfully prepared via a vacuum-assisted self-assembly strategy. The resulting NPG papers were characterized by various techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) pattern and X-ray photoelectron spectroscopy (XPS). In this analogous 3D “panel-bead” structure, adjacent PG nanosheets and ND particles are bridged through electrostatic interactions, which strengthens the interface connection and reduces phonon scatterings, resulting in an effective phonon transport pathway. Thus, a superior in-plane thermal conductivity of 16.653W m−1K−1 was obtained at the mass ratio of GO:ND = 3:1 (NPG3), which is about 80 times higher than that of traditional pure polymers. In addition, the peak heat release rate (PHRR) of NPG3 paper was only 99.16 W g−1 at 439.2 °C while that of GO was 438.4 W g−1 at 210.9 °C, indicating that NPG paper possesses excellent flame retardancy. More interestingly, although the NPG3 paper has excellent insulation (electrical resistivity reaches up to 2.647 × 1011 Ω cm), the ultrafast flame alarm response was found within about 1s after the paper exposed to the flame. This design idea provides an alternative approach for preparing multifunctional thermal management nanocomposites in the future.

Corrosion resistance of epoxy coating on mild steel through polyamidoamine dendrimer-covalently functionalized graphene oxide nanosheets

Epoxy coating was reinforced with polyamidoamine dendrimer-reduced graphene oxide nanosheets (GO-PAMAM) to obtain a high-performance anti-corrosion system. The GO-PAMAM was characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and UV–vis analysis. Results confirmed that PAMAM molecules successfully grafted on the GO surface, resulting in the lamellae d-spacing increment. Results of electrochemical impedance spectroscopy (EIS) and salt spray test evidenced that in the presence of 0.2 wt.% GO-PAMAM the epoxy coating corrosion protection properties were effectively enhanced. It was found from the results that the PAMAM could enhance the GO particle dispersion in the epoxy through increasing the GO nanosheets interlayer space and surface hydrophilic nature reduction.

Schiff base complexes of Mo(VI) immobilized on functionalized graphene oxide nano-sheets for the catalytic epoxidation of alkenes

Mo(VI) tetradentate Schiff base complexes were covalently immobilized onto chemically functionalized graphene oxide (GO) using 3-(tri-methoxysilyl) propylamine as a coupler. The resulting heterogeneous catalysts have been characterized by FTIR, DRS, XRD, SEM, TGA, and atomic absorption spectroscopy (AAS). These catalysts were applied in epoxidation of cyclooctene and other olefins. The catalytic procedures with all catalysts were optimized for different parameters such as oxidant, solvent and temperature. Recycling results indicated that the catalysts were highly stable and maintained activity and selectivity even after being used for five cycles.

Application of modified graphene oxide – Polycaprolactone nanocomposite coating for corrosion control of mild steel in saline medium

Polycaprolactone (PCL), a non toxic biodegradable polymer has limited application in the field of corrosion. In this study graphene based nanoparticles are incorporated into PCL matrix in order to enhance its anti-corrosion performance. The influence of graphene oxide (GO) and functionalized graphene oxide (FGO) nanosheets on the corrosion protection performance of PCL coating have been investigated. GO was functionalized with 8-bromo-[1,2,4]triazolo[1,5-a]pyridin-2-amine (BTP), and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and Energy Dispersive X-ray spectroscopy (EDX). The composite coating mixture consisted of GO/FGO-PCL matrix was applied on mild steel and surface of the coated samples were examined using Contact Angle technique, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Barrier and corrosion protection performance of the coated samples were studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods in 3.5% NaCl medium. The results showed that FGO-PCL coating exhibit superior barrier and anti-corrosion properties by improving the dispersion and exfoliation of FGO in the PCL matrix. It is found that the incorporation of FGO nanosheets make PCL more hydrophobic and also provides additional adhesion strength to the polymer.

Interface engineering of mixed matrix membrane via CO2-philic polymer brush functionalized graphene oxide nanosheets for efficient gas separation

A facile method to improve CO2 separation performance of polymer is to incorporate CO2-philic particles. In this study, sulfonated polymer brush functionalized graphene oxide nanosheets (S-GO) as fillers, with sulfonated polymer brush as CO2-philic chain anchored on GO were introduced into SPEEK membrane at nanoscale level to enhance CO2 selectivity of the membrane. The S-GO enhanced the interface compatibility as shown by SEM, and the “sieve-in-a-cage” morphology in MMMs disappeared by the introduction of CO2-philic polymer brush. Benefiting from the introduction of brush at the interface, on one hand, the CO2-philic brush on S-GO helped to widen CO2 transport pathways verified by the increased radius of free volume cavity (r3) and the fractional free volume (FFV), which resulted in the increase in gas permeability. On the other hand, the addition of the polymer brush on GO increased CO2-philic sites, which imparted enhancement in the CO2 solubility selectivity. Besides, the transport of gases through the GO nanosheets created the increment in CO2 diffusion selectivity. SPEEK/S-GO MMMs showed pronounced enhancements in both CO2 permeability and CO2/CH4(N2) selectivity. Specifically, for the SPEEK/S-GO membrane doped with 8 wt% S-GO nanosheets, the CO2 permeability reached 1327 Barrer, and CO2/CH4 selectivity increased by 179% in comparison with the SPEEK control membrane, surpassing the 2008 Robeson upper bound. The distinctive virtues of polymer brush functionalized filler may be extended to fabricate a series of MMMs for efficient molecule separation.

“Plate-anchor” shaped POSS-functionalized graphene oxide with self-fixing effect in polyimide matrix: Molecular dynamic simulations and experimental analysis

In this paper, we report an approach for synthesizing “plate-anchor” shaped polyhedral oligomeric silsesquioxane (POSS)-functionalized graphene oxide nanosheets with self-fixing effect via the amide formation. The resultant POSS-GO hybrid has excellent dispersibility in various organic solvents, such as N, N′-dimethylacetamide, pyridine, tetrahydrofuran and carbon tetrachloride. The molecular dynamics simulation (MD) indicates that the POSS-GO nanocomposites can not only react with PI resin by amidation, but also can be self-fixed in the resin through the “plate-anchor” structure, in which the GO nanosheet acts as “plate”, the POSS is considered as the “anchor”, thus being highly attractive for reinforcing polymer matrix. As expected, only 0.3 wt % addition of POSS-GO into polyimide (PI) can significantly increase the mechanical strength, thermal stability and friction and wear properties of polymer matrix. It is envisioned that the “plate-anchor” shaped composite exhibits outstanding advantages in the field of advanced materials.

Phosphomolybdic acid supported on Schiff base functionalized graphene oxide nanosheets: Preparation, characterization, and first catalytic application in the multi‐component synthesis of tetrahydrobenzo[a]xanthene‐11‐ones

New Schiff base (SB) functionalized graphene oxide (GO) nanosheets containing phosphomolybdic counter‐anion H2PMo12O40¯ (H2PMo) were successfully prepared by grafting of 3‐aminopropyltriethoxysilane (APTS) on GO nanosheets followed by condensation with benzil and finally reaction with phosphomolybdic acid (H3PMo12O40, denoted as H3PMo) and characterized using Fourier transform infrared (FT‐IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), particle size distribution, energy‐dispersive X‐ray (EDX) analysis, EDX elemental mapping, and inductively coupled plasma optical emission spectrometry (ICP‐OES). The prepared new nanomaterial, denoted as GO‐SB‐H2PMo, was shown to be an efficient heterogeneous catalyst in one‐pot, three‐component reaction of β‐naphthol, aldehydes, and dimedone, giving high yields of tetrahydrobenzo[a]xanthene‐11‐ones within short reaction times. The catalyst is readily recovered by simple filtration and can be recycled and reused several times with no significant loss of catalytic activity.

Confinement of functionalized graphene oxide in sulfonated poly (ether ether ketone) nanofibers by coaxial electrospinning for polymer electrolyte membranes

A novel cambiform-like core-shell nanofiber containing sulfonated graphene oxide core is fabricated through coaxial electrospinning method to improve proton conductivity, fuel blocking and inorganics/polymer compatibility for fuel cell applications. As induced by the strong electrostatic force, the sulfonated organosilane functionalized graphene oxide nanosheet is axially elongated to form a unique cambiform-like and highly wrinkled morphology in the core of the sulfonated poly (ether ether ketone) nanofiber, which is evidenced by the transmission electron microscopy images. It provides a forced contact and good dispersion of graphene oxide in the polymer to improve the tensile strength (approximately 2.6 and 1.8 folds of that of the blend monoaxial electrospun and cast membranes, respectively). The wrinkled graphene oxide core contains the sulfonated functional groups and micro-voids which are favorable for water uptake, making the co-spinning membrane exhibit approximately 43.2% and 33.0% increase of water uptake compared with that of the blend monoaxial electrospun and cast membranes, respectively, and thus facilitate the formation of hydrogen bond networks for proton hopping but tortuous pathways for fuel permeation. Accordingly, both lower hydrogen permeation and much higher methanol selectivity (11 folds of that of Nafion 115) are achieved in the co-spinning membrane.