Edges Of Graphene Oxide Research Articles

Application of Graphene Oxide–Natural Polymer Composite Adsorption Materials in Water Treatment

Graphene is a new type of carbon material with excellent properties that has been developed in recent years. Graphene composites have potential application value in solving the problem of water pollution. In this study, we investigated the properties and performance of graphene composites prepared through polymer modification and inorganic particle doping modification. Our research focused on the composites’ ability to adsorb heavy metal ions and degrade organic compounds through photocatalysis. In this study, we prepared graphene oxide (GO) first and then grafted p-phenylenediamine onto its surface. The process was successful and yielded promising results. The aniline grafted onto the graphene oxide surface was used as anchor point for the in situ redox polymerization of aniline, and a polyaniline macromolecular chain was grafted onto the edge of graphene oxide. The structure of the composite was determined using Fourier transform infrared spectroscopy, thermogravimetry, X-ray diffraction, and Raman spectroscopy and transmission electron microscopy. The adsorption performance of Pb+ on GO-PANI composite was studied. The maximum adsorption capacity of the GO-PANI composite for Pb+ is 1416 mg/g, 2.3 times that of PANI. Graphene/polyaniline composites can be used as an excellent adsorbent for Pb2+ heavy metal ions and have great application prospects in heavy metal wastewater treatment.

Fluorination of the tertiary carbon at the edge of graphene oxide

Fluorination of the tertiary carbon at the edge of graphene oxide

Tailoring the specific crosslinking sites of graphene oxide framework nanosheets for controlled nanofiltration of salts and dyes

Graphene oxide (GO), a material that is proven to have favorable attributes in different applications is continuously being researched and employed in membrane-based separations including nanofiltration, but challenges including instability in an aqueous environment, resulting in redispersion and swelling, as well as the difficulty in controlling the ion transport are still matters for concern. In this research, we addressed these problems by covalently crosslinking GO with different monomers of the same chain lengths, including ethylenediamine (EDA), ethylene glycol (EGL), and oxalic acid (OXA) to tailor specific crosslinking site, in able to subsequently improve the stability of the membranes while tuning the d-spacing for controllable transport of ions and molecules. These membranes produced via pressure-assisted filtration were subjected to physicochemical investigations where it revealed that surface properties including hydrophilicity and charge, as well as the membrane free volume were altered and each played a crucial role in their separation performance. The nature of the crosslinker dictated the site where crosslinking happened (GO's edges or basal planes) and influenced the passage of species, especially the fast water permeation. The membrane crosslinked with OXA has displayed an excellent pure water permeability that could reach up to ∼39.6 L m−2 h−1 at a pressure of 6 bar, a rejection for Na2SO4 of around 93%, and rejection of organic dyes, methylene blue and methyl orange of >99%. Moreover, the membranes were observed to have a stable performance in various operating conditions and exhibited an outstanding antifouling property and chlorine resistance that are essential qualities needed for desalination in realistic conditions.

Ratiometric fluorescence resonance energy transfer aptasensor for highly sensitive and selective detection of Acinetobacter baumannii bacteria in urine sample using carbon dots as optical nanoprobes

Development of sensitive and selective analytical method for accurate diagnosis of Acinetobacter baumannii (Ab) bacteria in biological samples is a challenge. Herein, we developed an ingenious ratiometric fluorescent aptasensor for sensitive and selective detection of (Ab) bacteria based on fluorescence resonance energy transfer (FRET) between ortho-phenylenediamines carbon dot (o-CD), nitrogen-doped carbon nanodots (NCND) as donor's species and graphene oxide (GO) as acceptor. NCND that assembled onto the edge of graphene oxide (GO) exhibited quenched photoluminescence emission, and with the absorption of the modified o-CD with aptamer (o-CD-ssDNA) onto the graphene oxide surface the fluorescence of o-CD was efficiently quenched. The aptamer (ssDNA) as a biorecognition element is bound with A. baumannii specifically which releases the o-CD-ssDNA from GO and the recovery of the fluorescence signal of o-CD, while the fluorescence intensity of NCND only slightly altered and acted as the reference signal in ratiometric fluorescence assay. The fluorescence intensity ratio (I550 nm/I440nm) varied from 2.0 to 10.0 with the concentration of bacteria changing from 2.0 × 103 to 4.5 × 107 cfu/mL and the low detection limit of 3.0 × 102 cfu/mL (S/N = 3). The feasibility of the developed aptasensor for selective detection of A. baumannii in urine sample with satisfactory results was also demonstrated.

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Summary Carboxylation of terminal alkynes with CO2 via direct C–H bond activation is a highly appealing way to capture and convert CO2 but faces great challenges and difficulty. Here, we report an efficient catalyst that is prepared simply through introduction of p-tert-butylaniline into graphite oxide powders followed by localized growth of Ag nanoparticles (NPs). The bulky nature of p-tert-butylaniline facilitates the powder exfoliation, giving rise to mass production of uniform modified graphene oxide (tert-GO) nanosheets of 4 nm in thickness. Notably, Ag/tert-GO shows excellent catalytic activity for converting alkynes regardless of containing electron-donating or electron-withdrawing groups under mild reaction conditions. The synergy of the amide linkages on tert-GO nanosheets and the supported small-sized Ag NPs is recognized as the vital role in promoting adsorption of CO2 and subsequent conversion.

Graphene oxide functionalized with oxygen-rich polymers as a pH-sensitive carrier for co-delivery of hydrophobic and hydrophilic drugs

In this work, a novel carrier based-on modified graphene oxide was designed for co-delivery of hydrophobic and hydrophilic anticancer drugs (curcumin (Cur) and doxorubicin (DOX) as the model of drugs). The hydroxyl groups at the edges of graphene oxide (GO) sheets were used as the initiation sites for growing poly(epichlorohydrin) (PCH) chains. Then, hyperbranched polyglycerol (HPG) was grafted on the hydroxyl end groups of PCH (PCH-g-HPG). Pendant chlorines in the main chain of GO-PCH-g-HPG were replaced with hydrazine. The modification of GO sheets with oxygen-rich polymers increased water solubility of graphene oxide. Doxorubicin was loaded onto the nanocarrier by covalent bonding with hydrazine pendant group and curcumin was loaded through π−π stacking with graphene oxide sheets which were partially reduced to graphene sheets during the carrier preparation. The MTT assay revealed that the carrier had low toxicity because of the presence of oxygen-rich polymers. The drug release of the carrier was investigated and a pH-sensitive behavior was observed for the release of drugs from the carrier. The cellular uptake images proved that co-encapsulation of both DOX and Cur drugs showed higher drug internalization in comparison with the single drug loaded carrier. According to the results, a combination of both drugs exhibited a synergistic behavior for chemotherapy.

Aldehyde-conjugated chitosan-graphene oxide glucodynamers: Ternary cooperative assembly and controlled chemical release

Simultaneous condensation of aromatic aldehydes (ArxCHO; x = 1–4) on chitosan biopolymer (CS) affords, after water-evaporation, structurally-conjugated aryl-functionalized CS-Arx-f films. Similarly, cooperative assembly of two-dimensional nanometric graphene oxide (GO), aromatic aldehyde and chitosan provides transparent, flexible and crack-free aldehyde-functionalized, ternary-reinforced CS-Arx-GO-f nanocomposite films. Homogenous films were obtained using ortho-hydroxybenzaldehyde Ar1 while the para-hydroxybenzaldehyde Ar4 was prone to packing inside. Textural and mechanical properties were investigated and expectedly, significant improvement was found for CS-Ar1-GO-f because of the great dispersion of the aromatic and the presence of the filler. The sensitivity of unsaturated CN imine bond to hydrolysis was explored for triggering controlled release of aromatics from the as-prepared films. All of them were found to induce a time-dependent aromatic release. It has been moreover observed that the release was significantly delayed in CS-Arx-GO-f compared to CS-Arx-f, a fact attributed to the interplay of the ring with the basal and edges of graphene oxide, through π-π stacking and additional hydrogen bonding interactions. This finding shows that beyond the conventional wisdom using fillers for improving thermal and mechanical properties, the tiny carbon sheets can act as a regulator for aldehyde release, thereby providing a way for more controlled chemical delivery from confined nanocomposites.

Structurally controlled layered Ni3C/graphene hybrids using cyano-bridged coordination polymers

The wide range of oxygen-containing functional groups on the basal planes and edges of graphene oxide (GO) facilitate the anchoring of active metal ions on its surface. Previously, we have shown that these active centers allow the in situ crystallization of cyano-bridged Ni-based coordination polymers (Ni-CP) as nanoflakes on the surface of GO sheets (Angew. Chem. Int. Ed., 2016, 55, 8426). Here, in this work, by extending our previous concept, we demonstrate that Ni-CP-coated GO sheets can be made to self-assemble to form various multi-layered hybrid structures (Ni-CP/GO) by controlling the composition ratios. Ni3C/rGO with the original morphology was successfully prepared by converting the Ni-CP to Ni3C in the space between the graphene sheets by thermal treatment in an inert atmosphere. The electrochemical analyses reveal that the optimized Ni3C/rGO hybrid exhibits superior electrocatalytic performance for the oxygen reduction reaction (ORR) with good durability and stability.

Temperature-responsive and piezoresistive performances of poly(N- isopropylacrylamide)-grafted reduced graphene oxide smart fiber

In this work, temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) was covalently grafted onto the edge of graphene oxide (GO) sheets through a facial method cross-linked by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide in aqueous solution at room temperature. Then, the dispersion was wet spun to form a GO composite fiber. Scanning electron microscopy images suggest that severe edge distortions occur in PNIPAm-g-rGO hybrid fibers, indicating the covalent attaching of PNIPAm molecules onto the edge of graphene sheets. The PNIPAm-g-rGO fibers showed more favorable and improved electrical property than the pristine rGO fibers. Moreover, the coil-to-globule transition of the end-grafted PNIPAm chains was partially restricted by graphene sheets in the composite fiber, thereby causing the elevation of the phase transition temperature. Switching test of temperature-responsive versus electrical conductivity function has proved that the observed temperature-induced electrical conversion of the fibers was highly reversible and reproducible. Simultaneously, the composite fiber exhibited higher piezoresistive sensitivity compared with neat fiber. This smart fiber has shown remarkable potential for intelligent strain sensors, textiles, actuators, wires and on/off switches.

Graphene oxide edge grafting of polyaniline nanocomposite: an efficient adsorbent for methylene blue and methyl orange.

Polyaniline (PANI) chains were grafted at the edge of graphene oxide (GO) sheets by in-situ chemical oxidation polymerization. The obtained GO-PANI composite was used for the adsorption of cationic methylene blue (MB) and anionic methyl orange (MO) dyes from aqueous solutions. The structure of the GO-PANI composite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electronic micrograph (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potentials. GO-PANI exhibited a high adsorption capacity for MB (962 mg/g) and MO (885 mg/g) compared with other reported absorbents, which was due to adsorption through strong π-π stacking and anion-cation interactions. The nanocomposite could be recycled five times without significant loss in removal abilities for MB (87.8%) and MO (75.0%), respectively. GO-PANI composite is a promising adsorbent for the adsorption of anionic and cationic dyes from aqueous solutions.

Enhanced Field Emission of Graphene Oxide Sheets Sustained by Ni Nanoparticles

Graphene oxide is expected to be used as effective field emitter due to its unique geometry and electrical properties. However, electron field emission has only been accomplished from the edges of graphene oxide. In this paper, a different structure is proposed, in which graphene oxide was deposited on Al sheet covered with Ni nanoparticles, and high-density sharp prominences were formed on the surface of graphene oxide. Because of the enhanced local electric field produced by sharp prominences, the properties of graphene oxide field emission improved remarkably. The final results show that the graphene oxide emitter cathodes demonstrate a low-threshold field of 0.97 V/μm, and a high current density of 1 mA/cm2 is obtained under an applied field of 1.51 V/μm.

Ultrasound irradiation: A robust approach for direct functionalization of graphene oxide with thermal and antimicrobial aspects

Sonochemical waves as mechanochemical energy was employed to exfoliate graphite oxide and functionalized graphene oxide (GrO), through a reaction of solvent and accountable for top-down and bottom-up approach respectively. The in situ formation of ester intermediate was inferred and a polymeric surface of GrO was further functionalized with 6-Aminoindazole (6-AIND) through sonochemical nucleophilic substitution reaction. As compared to conventional method the effect of ultrasound was verified for the direct functionalization of GrO. The conventional hazardous acylation step for functionalization of GrO was deleted in ultrasound assisted formation of f-(6-AIND) GrO nanocomposite, prepared by stereoselective exploitation of carboxyl groups at edges of GrO. The characterization has ascertained a covalent attachment of 6-AIND onto GrO surface with ATR-FTIR, XPS, SSNMR, TGA, DSC, XRD, AFM, RAMAN, EDX, SEM, BET and elemental analyzer. A weight loss in TGA depicts enhanced thermal stability of f-(6-AIND) GrO and a thermally sensitive behavior. The f-(6-AIND) GrO was studied for in vitro antimicrobial activity to ensure health and environmental safety. Antibacterial activity was identified against human pathogenic gram-positive (Staphylococcus aureus; ATCC 25923) and gram-negative bacteria (Escherichia coli; ATCC 25922). The antifungal activity was observed against Candida albicans (ATCC 10231).

Star Polymer Unimicelles on Graphene Oxide Flakes

We report the interfacial assembly of amphiphilic heteroarm star copolymers (PSnP2VPn and PSn(P2VP-b-PtBA)n (n = 28 arms)) on graphene oxide flakes at the air-water interface. Adsorption, spreading, and ordering of star polymer micelles on the surface of the basal plane and edge of monolayer graphene oxide sheets were investigated on a Langmuir trough. This interface-mediated assembly resulted in micelle-decorated graphene oxide sheets with uniform spacing and organized morphology. We found that the surface activity of solvated graphene oxide sheets enables star polymer surfactants to subsequently adsorb on the presuspended graphene oxide sheets, thereby producing a bilayer complex. The positively charged heterocyclic pyridine-containing star polymers exhibited strong affinity onto the basal plane and edge of graphene oxide, leading to a well-organized and long-range ordered discrete micelle assembly. The preferred binding can be related to the increased conformational entropy due to the reduction of interarm repulsion. The extent of coverage was tuned by controlling assembly parameters such as concentration and solvent polarity. The polymer micelles on the basal plane remained incompressible under lateral compression in contrast to ones on the water surface due to strongly repulsive confined arms on the polar surface of graphene oxide and a preventive barrier in the form of the sheet edges. The densely packed biphasic tile-like morphology was evident, suggesting the high interfacial stability and mechanically stiff nature of graphene oxide sheets decorated with star polymer micelles. This noncovalent assembly represents a facile route for the control and fabrication of graphene oxide-inclusive ultrathin hybrid films applicable for layered nanocomposites.

Modeling the physisorption of bisphenol A on graphene and graphene oxide

The physisorption of bisphenol A (BPA) on pristine and oxidized graphene was studied theoretically via calculations performed at the PBE-D3 level (including dispersion force corrections). Three stable conformations of BPA on graphene were found. A lying-down configuration was energetically favored because the presence of π-π stacking and dispersion forces increased interactions. In addition, the adsorption of BPA on the edges of graphene oxide was enhanced when adsorption occurred on carboxyl and carbonyl groups, whereas the adsorption strength decreased when adsorption occurred on hydroxyl groups. The highest physisorption strength was obtained on the surface of graphene oxide due to the presence of π-π stacking and dispersion forces (which provided the greatest contribution to the adsorption energy) as well as hydrogen bonds (which provided a smaller contribution), indicating that oxidized graphene is a better candidate than pristine graphene for BPA removal. On the other hand, an increase in electrophilicity was observed after the physisorption of BPA in all systems (with respect to graphene and BPA in their isolated forms), with the adsorbent acting as the electron acceptor. Finally, molecular dynamics simulations performed using the PM6 Hamiltonian showed that the adsorption of BPA on graphene is stable.