Ultrasonic Duration Dependent Defect Engineering and Morphological Evolution in Graphene Oxide

ABSTRACTSulfonated polyether sulfone-based cation-exchange membranes are prepared by incorporating different amounts of graphene oxide and sulfonated graphene oxide nanosheets. The graphene oxide nanosheets are synthesized according to Staudenmaier and Hummer methods and functionalized using 3-mercaptopropyl trimethoxysilane. Transport properties of nanocomposite membranes including ion-exchange capacity, transport number, and conductivity as well as their thermal stabilities are enhanced by incorporating sulfonated graphene oxide rather than graphene oxide. Also, the enhancement is more significant for the nanocomposites having functionalized graphene oxide synthesized by Staudenmaier method than those by Hummers method due to higher density of active sites in the Staudenmier graphene oxides for functionalization.

Large-scale fabrication of graphene is highly important for industrial and academic applications of this material. The most common large-scale preparation method is the oxidation of graphite to graphite oxide using concentrated acids in the presence of strong oxidants and consequent thermal exfoliation and reduction by thermal shock to produce reduced graphene. These oxidation methods typically use concentrated sulfuric acid (a) in combination with fuming nitric acid and KClO(3) (Staudenmaier method), (b) in combination with concentrated nitric acid and KClO(3) (Hofmann method) or (c) in the absence of nitric acid but in the presence of NaNO(3) and KMnO(4) (Hummers method). The evaluation of quality and applicability of the graphenes produced by these various methods is of high importance and is attempted side-by-side for the first time in this paper. Full-scale characterization of thermally reduced graphenes prepared by these standard methods was performed with techniques such as transmission and scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their applicability for electrochemical devices was further evaluated by means of cyclic voltammetry techniques. We showed that while Staudenmaier and Hofmann methods (methods that do not use potassium permanganate as oxidant) generated thermally reduced graphenes with comparable electrochemical properties, the graphene prepared by the Hummers method which uses permanganate as oxidant showed higher heterogeneous electron transfer rates and lower overpotentials as compared to graphenes prepared by the Staudenmaier or Hofmann methods. This clearly shows that the methods of preparations have dramatic influences on the materials properties and, thus, such findings are of eminent importance for practical applications as well as for academic research.

Fascinating features of 2D graphene oxide (GO) have very high potential to enhance the mechanical performance and fracture toughness of epoxy composites after successful dispersion in the epoxy matrix. The dispersion of GO in a highly viscous epoxy matrix was achieved by lateral exfoliation and longitudinal size reduction of graphene sheets. GO was synthesized via an improved Hummer's method, exfoliated through dual‐mode ultrasonication for 20, 30, and 60 min, and reduced to nanoscale (~217 to 227 nm) using high‐energy wet ball milling for 9 h. The synthesized GO and BGO were characterized using XRD, FT‐IR, Raman spectroscopy, FESEM, and TGA to confirm crystal structure, functional groups, defect density, surface morphology, and thermal stability respectively. It was observed that even at higher filler loadings of 1 wt.% of GO and BGO exfoliated for 60 min (GO60@1% and BGO60@1%), the resulting nanocomposites showed a substantial improvement in tensile strength by 39.92% and 41.91%, respectively, and modulus by 6.92% and 12.90%, respectively compared to the NE. Whereas, incorporation of GO60@1% and BGO60@1% into epoxy matrix significantly enhanced fracture toughness ( K IC ) by ~72% and ~140% respectively and the fracture energy ( G IC ) by ~322% and ~356%, respectively with respect to NE. The enhancement is attributed to the superior dispersibility of BGO, which facilitates strong and consistent interfacial interactions with the epoxy matrix, thereby improving the material's resistance to fracture. The exfoliation of GO through ball milling can be a suitable method for industries to prepare graphene‐based nanocomposites with significantly high tensile and fracture properties.

Rheology of graphene oxide suspended in yield stress fluid

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

Graphene oxide (GO) is widely explored as a functional additive in polymer composites; however, its simple physical dispersion in dental resins often leads to poor interfacial stability and limited long-term performance. Covalent functionalization may overcome these limitations by enabling chemical integration into the polymer matrix. This study presents the synthesis and FT-IR/Raman characterization of GRAPHYMERE®, a novel graphene oxide-based monomer obtained through exfoliation, amine functionalization with 1,6-hexanediamine, and transamidation with methyl methacrylate. A novel GO-based monomer, GRAPHYMERE®, was synthesized through a three-step process involving GO exfoliation, amine functionalization with 1,6-hexanediamine, and transamidation with methyl methacrylate to introduce polymerizable acrylic groups. The resulting product was characterized using FT-IR and Raman spectroscopy. Spectroscopic analyses confirmed the presence of aliphatic chains and amine functionalities on the GO surface. Although some expected signals were overlapped, the data suggest successful surface modification and partial insertion of methacrylamide groups. The process is straightforward, uses low-toxicity reagents, and avoids complex reaction steps. GRAPHYMERE® represents a chemically modified GO monomer potentially suitable for copolymerization within dental resin matrices. While its structural features support compatibility with radical polymerization systems, further studies are required to assess its mechanical performance and functional properties in dental resin applications.

Graphene oxide (GO) is one of the members of carbon-based nanomaterials and can be featured as graphene structure decorated with various oxygenated functional groups. Recently, various methods have been found for producing carbon-based nanomaterials with enhanced efficiency in several applications. The chemical process involves oxidizing graphite to GO using a powerful oxidizing chemical. Hummers method is one of the most known and versatile method for the production of GO nanomaterials because of its ease of application, parameter controllability and high yield. This process enables graphite oxidation and exfoliation into single- or multi-layered GO sheets. Exfoliation, the separation of graphene or graphitic layers, is a critical process in GO synthesis. Since exfoliation separates multilayered graphite oxide flakes or particles, it forms single layer GO by forcing oxidizing agents or solvent molecules between layers. The sonication process can exfoliate the oxidized layers, resulting in the formation of GO structure when the exfoliated layers consist of only one or a few layers of carbon atoms. Therefore, sonication procedure is among the key parameters of Hummers method that influences the characteristics of GO-based nanomaterials. In this study, the impact of sonication duration time and power parameters on morphological and structural characteristics of GO development was examined. For this purpose, characterization studies were performed by using Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and Raman spectroscopy analysis. The findings revealed that the increase in sonication power and time led to an increase in defects in the resulting GO structure.

Thermal and mechanical properties of graphene oxide nanocomposite hydrogel based on poly (acrylic acid) grafted onto amylose

We present a method to produce composite anodes consisting of thermally reduced graphene oxide-containing carbon nanofibers (TRGO/CNFs) via electrospinning a dispersion of polyacrylonitrile (PAN) and graphene oxide (GO) sheets in dimethylformamide followed by heat treatment at 650 °C. A range of GO (1-20 wt % GO relative to polymer concentration) was added to the polymer solution, with each sample comprising similar polymer chain packing and subsequent CNF microstructure, as assessed by X-ray diffraction. An increase from 0 to 20 wt % GO in the fibers led to carbonized nonwovens with enhanced electronic conductivity, as TRGO sheets conductively connected the CNFs. Galvanostatic half-cell cycling revealed that TRGO addition enhanced the specific discharge capacity of the fibers. The optimal GO concentration of 5 wt % GO enhanced first-cycle discharge capacities at C/24 rates (15.6 mA g(-1)) 150% compared to CNFs, with a 400% capacity increase at 2-C rates (750 mA g(-1)). We attribute the capacity enhancement to a high degree of GO exfoliation. The TRGO/CNFs also experienced no capacity fade after 200 cycles at 2-C rates. Impedance spectroscopy of the composite anodes demonstrated that charge-transfer resistances decreased as GO content increased, implying that high GO loadings result in more electrochemically active material.

Reinforcement of hydrogenated carboxylated nitrile–butadiene rubber with exfoliated graphene oxide

Interactions of graphene oxide with the microbial community of biologically active filters from a water treatment plant

Metallic coatings have been traditionally used to protect the underlying substrate against corrosion. Recent reports have illustrated that use of carbonaceous material such as graphene, graphene oxide, carbon nanotubes as additives in conventional coating have led to significant enhancement in the corrosion resistance behaviour of the composite coatings. In this talk, the author will discuss the evolution of microstructure, morphology, phase constitution and corrosion behaviour of electrodeposited ZnCo coatings as a function of the amounts of graphene oxide contained in them. The as-deposited ZnCo-graphene oxide composite coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). XRD based analysis of the coatings revealed that all the coatings contained Zn phase along with intermetallic phase (Zn10. 63Co2.34). A gradual increase in the volume fraction of the intermetallic phase was observed upon graphene oxide addition. Morphological characteristics and changes in the surface roughness were studied using SEM and AFM. A compact and smooth morphology was observed for initial graphene oxide additions while a higher graphene oxide concentration produced surface cracks due to graphene oxide agglomeration in the electrolytic bath. Weight loss measurements of control sample containing only the intermetallic phase revealed that the intermetallic was more corrosion resistant. The coatings were studied using electrochemical impedance spectroscopy (EIS) in 3.5 wt. % NaCl to understand the characteristics of corrosion product layer. Corrosion current in the coatings was found to decrease for initial graphene oxide addition while for higher additions a sudden increase in corrosion rate was observed. The impermeability of the graphene oxide and a relative increase in the volume fraction of nobler intermetallic phase lead to the initial reduction in corrosion rate. While, after an optimum graphene oxide addition which yielded the lowest corrosion rate, the incorporation of agglomerated graphene oxide lead to cracks and surface defects primarily due to non-uniform deposition. The surface morphology was analyzed using SEM after they were exposed to the electroactive media (3.5 wt.% NaCl). A continuous zinc dissolution was observed in the case of pristine ZnCo coatings while formation of pits was evident for maximum graphene oxide addition. Figure 1

The aminated graphene oxide (GO) was prepared by the functionalization of pristine GO with ethylenediamine and then dispersed into the poly(amic acid) (the precursor of polyimide [PI]) solution followed by the chemical imidization to successfully fabricate the PI/amine‐functionalized GO mixed matrix membranes (MMMs) using in‐situ polymerization method. Chemical structure and morphology of the GO before and after amine modification were characterized by scanning electron microscopy, Raman spectrum, Fourier transform infrared, and X‐ray photoelectron spectroscopy. Scanning electron microscopy indicated that fine dispersion of GO throughout PI matrix was achieved, which indicates that the in‐situ polymerization approach can enhance the interfacial interaction between the GO and the PI matrix, and then improve the dispersion of carbon material in the polymer matrix. Compared with the conventional solution mixture method, the MMMs prepared with in‐situ polymerization method showed excellent CO2 permeability and CO2/N2 selectivity. The MMMs doped with 3 wt.% aminated GO exhibited maximum gas separation performance with a CO2 permeability of 12.34 Barrer and a CO2/N2 selectivity of 38.56. These results suggest that the amino groups on GO have strong interaction with the CO2 molecules, which can significantly increase the solubility of polar gas. Our results provide an easy and efficient way to prepare MMMs with good mechanical behavior and excellent gas separation performance.

ABSTRACTThe mechanical and functional properties of polyacrylonitrile (PAN) nanofibers are significantly influenced by molecular orientation, yet achieving high orientation remains a significant challenge. In this paper, graphene oxide (GO)/PAN nanocomposite fibers were fabricated using electrospinning technology. By manipulating the flow shear field and tensile shear field, nanocomposite fibers with varying degrees of orientation were obtained. The structural evolution was characterized using scanning electron microscopy (SEM), Fourier‐transform infrared spectroscopy (FTIR), Raman spectroscopy, and X‐ray diffraction (XRD). SEM analysis revealed controlled fiber diameter distribution and morphological alignment. FTIR and Raman spectroscopy analysis confirmed strong interfacial interactions between GO sheets and PAN molecular chains, with the flow shear effects dominating orientation control over tensile shear. Under a needle length of 150 mm, an injection speed of 0.2 mm/min, a spinning voltage of 15 kV, and a drum speed of 100 r/min, the incorporation of GO increased the CN group orientation factor from 0.1655 to 0.2389, the crystallinity from 44.57% to 48.42%, and the crystallite size from 4.04 nm to 4.81 nm. This study provides a novel strategy for developing highly oriented GO/PAN nanocomposite fibers, offering new insights for the advancement of high‐performance fiber materials.

We report the first use of spark plasma sintering (SPS) as a single-step process to achieve superhydrophobic reduced graphene oxide (rGO). It was found that SPS was capable of converting smooth and electrically insulating graphene oxide (GO) sheets into highly electrically conductive rGO with minimum residual oxygen and hierarchical roughness which could be well retained after prolonged ultrasonication. At a temperature of 500 °C, which is lower than the conventional critical temperature for GO exfoliation, GO was successfully exfoliated, reduced, and hierarchically roughened. rGO fabricated by only 1 min of treatment at 1050 °C was superhydrophobic with a surface roughness (Ra) 10 times as large as that of GO as well as an extraordinarily high C:O ratio of 83.03 (atom %) and water contact angle of 153°. This demonstrates that SPS is a superior GO reduction technique, which enabled superhydrophobic rGO to be quickly and effectively achieved in one single step. Moreover, the superhydrophobic rGO fabricated by SPS showed an impressive bacterial antifouling and inactivation effect against Escherichia coli in both aqueous solution and the solid state. It is envisioned that the superhydrophobic rGO obtained in this study can be potentially used for a wide range of industrial and biomedical applications, such as the fabrication of self-cleaning and antibacterial surfaces.