Surface Of Graphene Oxide Sheets Research Articles

Molecular dynamics simulation investigation on the anti-freezing mechanisms of CSH-GS/GO interfaces

Although graphene sheet (GS) and graphene oxide (GO) are two popular additives for improving the frost resistance of concrete, unclear anti-icing mechanisms of GS/GO cross-linked on the surface of calcium silicate hydrate (CSH) has hindered the design of concrete with higher durability in cold regions. To address this issue, we perform molecular dynamics simulation to reveal the icing processes of CSH-GS/GO interfaces. It is found that CSH-GS/GO interfaces can greatly suppress the crystallization process of ice compared to the original CSH surface. The crystallization process significantly weakens the chemical connectivity between CSH and GO, leading to the separation between them and ultimately the inhibition of icing. Massive H-bonds between CSH and GO disrupt the crystallization process, which is considered as the original cause of inhibition. Additionally, freezing of the solution drives salt ions to the surface of GO sheets. The existence of weak limited water (WLW) in the critical unfreezing region is resulted from the dynamic behaviors of nanosheets and ultra-high ions concentration. This work reports the ice regulation with GS/GO and opens a new avenue for the application of 2D nanomaterials in promoting anti-freezing ability of cement-based materials.

Graphene oxide-fullerene nanocomposite laminates for efficient hydrogen purification.

Graphene oxide (GO) with its unique two-dimensional structure offers an emerging platform for designing advanced gas separation membranes that allow for highly selective transport of hydrogen molecules. Nevertheless, further tuning of the interlayer spacing of GO laminates and its effect on membrane separation efficiency remains to be explored. Here, positively charged fullerene C60 derivatives are electrostatically bonded to the surface of GO sheets in order to manipulate the interlayer spacing between GO nanolaminates. The as-prepared GO-C60 membranes have a high H2 permeance of 3370 GPU (gas permeance units) and an H2/CO2 selectivity of 59. The gas separation selectivity is almost twice that of flat GO membranes because of the role of fullerene.

A Micro-Nano Structure Formed by SiC/Graphene Oxide Self-Assembly Improves the Wear Resistance and Corrosion Resistance of an Epoxy-Based Composite Coating.

In air and railway transportation, corrosion and wear lead to the rapid failure of equipment. Epoxy (EP)-based coatings are widely used in research on the anti-corrosion of organic coatings, but their application as materials for wear resistance is limited due to their non-abrasive properties. In this study, a novel high-performance epoxy-based composite coating was developed through the self-assembly of silicon carbide (SiC) and graphene oxide (GO) and the tuning of the interfacial structure with epoxy resin. The coatings were comprehensively characterized, including their electrochemical behavior, a salt spray test, and friction and wear experiments, and the optimal addition ratio of SiC-G@GO (SiC-G@GO was prepared by the self-assembly of γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560)-modified SiC (SiC-G) on the surface of GO sheets) in the epoxy coatings was explored. Benefiting from the labyrinth effect and their rolling-friction-like microstructure, the 1 wt% SiC-G@GO/EP coating exhibits excellent wear and corrosion resistance. Compared with pure epoxy resin, the 1 wt% SiC-G@GO/EP coating increased by 4 orders of magnitude after 10 days of immersion. The average friction coefficient was 41.5% lower than that of the pure EP coating, and the wear rate was 56.6% lower. This research has positive implications for the development and application of anti-corrosion and wear-resistant organic coatings.

Synthesis, Characterization, and Dye Removal Applications of Graphene Oxide-Gold Nanocomposite

Here, we report the facile synthesis of graphene oxide/gold nanocomposite, and dye removal ability as an adsorbent was studied. Sodium citrate as a reducing agent was used to reduce Au (III) ions to the formation of gold nanoparticles on the surface of graphene oxide sheets that were prepared by Hummers’ method. Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) was used to specify nanocomposite synthesis. Adsorption dosage and contact time were investigated and explained as influencing parameters in removing methylene blue and methyl orange. In optimum conditions, the amount of adsorbent 30 mg and contact time 15 min for methylene blue and the amount of adsorbent 30 mg and contact time 25 min for methyl orange were quantitatively removed from 10 mL of wastewater. The pseudo-second-order model explained the kinetic data. Since graphene oxide/gold nanocomposite could be reused reasonably and had adsorptive properties, it tends to be produced as a modest and elective adsorbent to treat wastewater.

Designable ultra-stable electrode surface engineering by the electrophoretic deposition of modified graphene oxide for rechargeable batteries

Electrode material surface protection via the two-dimensional structured graphene oxide (GO) is studied in our work for rechargeable batteries by the electrophoretic deposition (EPD). However, the large number of oxygen-containing groups on the surface and edge makes GO sheets negatively charged, which EPD can only be used for anode process. Thus, we apply p-phenylenediamine (PPD) to convert the surface of GO sheets to positive electricity and successfully achieve the cathodic EPD with modified GO. When, the cathode (eg. S, LiFePO4) and anode (eg. Li, Si) with the newfangled GO coating layers are employed in a working battery, the GO can be transformed into reduced graphene oxide (rGO) due to the in-situ electrochemical reduction. Fortunately, the rGO coating layers are acquired on the electrode surfaces, which the stability, adhesion, corrosion resistance, impact resistance have been greatly improved compared to other coating methods. Ultimately, taking advantage of this rGO coating by EDP to simultaneously realize the coating protections of the electrodes can provide alternative strategies to optimize the properties of rechargeable batteries.

ZnO-CuO nanoparticles enameled on reduced graphene nanosheets as electrode materials for supercapacitors applications

The current energy crisis situation, combined with the recent development of renewable energy resources, has promoted the development of energy storage materials for supercapacitors and rechargeable metal ion batteries. In this regard, metal oxide-based two-dimensional materials such as reduced graphene oxide nanocomposites have tremendous potential for the aforementioned purpose. The ZnO-CuO/rGO nanocomposites were designed and synthesized by a simple, cost-effective co-precipitation method. The structural and morphological analysis of synthesized nanomaterials ZnO, CuO, and ZnO.CuO/rGO nanocomposites were extensively characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Rama spectra, Brunauer-Emmett-Teller (BET) surface area, and thermogravimetric analysis (TGA). The XRD pattern results of ZnO nanoparticles show wurtzite structure, copper oxide nanoparticles show monoclinic phase structure, and ZnO-CuO/rGO composites show a mixture of wurtzite, monoclinic phase, and hexagonal structure. The surface morphology of the ZnO-CuO/rGO nanocomposite shows the spherical and hexagonal-shaped ZnO-CuO nanoparticles uniformly arranged on the surface of graphene oxide sheets. The binding energy values of the nanocomposite confirm the oxidation states of Zn, Cu, C, and O elements in ZnO-CuO/rGO presented in the XPS studies. The electrochemical activity of the ZnO-CuO/rGO nanocomposite in 1 M H2SO4 electrolyte exhibits a specific capacitance of 260.7 F/g at 0.5 A/g, high energy density, and excellent cycle stability. Even after 10,000 cycles, 98.7% of the initial supercapacitance remains. These findings suggest that the ZnO-CuO/rGO nanocomposite has a bright future as an electrode material in supercapacitors.

Functionalized SPION immobilized on graphene-oxide: Anticancer and antiviral study

The progressive and fatal outbreak of some diseases such as cancer and coronavirus necessitates using advanced materials to bring such devastating illnesses under control. In this study, graphene oxide (GO) is decorated by superparamagnetic iron oxide nanoparticles (SPION) (GO/SPION) as well as polyethylene glycol functionalized SPION (GO/SPION@PEG), and chitosan functionalized SPION (GO/SPION@CS). Field emission scanning electron microscopic (FESEM) images show the formation of high density uniformly distributed SPION nanoparticles on the surface of GO sheets. The structural and chemical composition of nanostructures is confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. The saturation magnetization of GO/SPION, GO/SPION@PEG and GO- SPION@CS are found to be 20, 19 and 8 emu/g using vibrating sample magnetometer. Specific absorption rate (SAR) values of 305, 283, and 199 W/g and corresponding intrinsic loss power (ILP) values of 9.4, 8.7, and 6.2 nHm2kg−1 are achieved for GO/SPION, GO/SPION@PEG and GO/SPION@CS, respectively. The In vitro cytotoxicity assay indicates higher than 70% cell viability for all nanostructures at 100, 300, and 500 ppm after 24 and 72 h. Additionally, cancerous cell (EJ138 human bladder carcinoma) ablation is observed using functionalized GO/SPION under applied magnetic field. More than 50% cancerous cell death has been achieved for GO/SPION@PEG at 300 ppm concentration. Furthermore, Surrogate virus neutralization test is applied to investigate neutralizing property of the synthesized nanostructures through analysis of SARS-CoV-2 receptor-binding domain and human angiotensin-converting enzyme 2 binding. The highest level of SARS-CoV-2 virus inhibition is related to GO/SPION@CS (86%) due to the synergistic exploitation of GO and chitosan. Thus, GO/SPION and GO/SPION@PEG with higher SAR and ILP values could be beneficial for cancer treatment, while GO/SPION@CS with higher virus suppression has potential to use against coronaviruses. Thus, the developed nanocomposites have a potential in the efficient treatment of cancer and coronavirus.

A Facile Fabrication of CdSe/ZnS QDs-Block Copolymer Brushes-Modified Graphene Oxide Nanohybrid with Temperature-Responsive Behavior.

In this paper, we described a straightforward one-step chemical method for the synthesis of semiconductor quantum dots(QDs)—block copolymer brushes functionalized graphene oxide(GO) fluorescence nanohybrids. The azobenzene-terminated block copolymer poly(N-isopropylacrylamid)-b-poly(styrene-co-5-(2-methacryoylethyloxymethyl)-8-quinolinol)(PNIPAM-b-P(St-co-MQ)) was modified on the surface of GO sheets via host–guest interactions between β-cyclodextrin-modified GO and azobenzene moieties, and simultaneously CdSe/ZnS QDs were integrated on the block copolymer brushes through the coordination between 8-hydroxyquinoline units in the polymer brushes and CdSe/ZnS QDs. The resulting fluorescence nanohybrid exhibited dual photoluminescence at 620 nm and 526 nm, respectively, upon excitation at 380 nm and LCST-type thermo-responsive behavior which originated from the change in the PNIPAM conformation in the block copolymer brushes of GO sheets.

Green Approach Using RuO2/GO Nanocomposite for Low Cost and Highly Sensitive pH Sensing

Rapid and inexpensive monitoring the real-time status of food products using pH sensors is critical for food quality and safety to determine if pathogens are present and growing. A promising material for pH sensors is ruthenium dioxide (RuO2) due to its chemical stability and excellent performance including: high sensitivity, low drift and hysteresis, and good selectivity. Furthermore, graphene oxide (GO) provides an electrode with large surface area, and good electrical properties. In this work, the in situ sol-gel deposition of RuO2 nanoparticles on the surface of GO as a facile, cost-effective, and environmentally friendly approach is used for the fabrication of a flexible pH sensor. The as-synthesized GO-RuO2 nanocomposites with a low volume were applied on the surface of screen printed carbon paste. The obtained GO-RuO2 nanocomposite pH sensor achieved high pH sensitivity (55.3 mV pH−1) in the pH range of 4–10, up to 4 times higher than the unmodified carbon electrode. The increased sensitivity of the modified electrode could be attributed to the uniform anchoring of small, crystallized RuO2 nanoparticles on the surface of GO sheets, resulting in synergistic effects between them. It also shows low drift (0.36 mV h−1) and low hysteretic width (0.8 mV). Considering the novel method of deposition and also sensing material with the cost-effective green synthesis approach, as well as excellent pH sensing properties, GO-RuO2 can be considered as a promising material for production of high-performance electrochemical pH sensors for food quality monitoring.

Grafting macromolecular chains on the surface of graphene oxide through crosslinker for antistatic and thermally stable polyethylene terephthalate nanocomposites.

The graphene oxide (GO) and polyethylene terephthalate (PET) molecular chains are connected together by the two amino groups of the crosslinking agent p-phenylenediamine (PPD). The presence of macromolecular chains could make GO uniformly dispersed in the polymer matrix, improving the antistatic performance and thermal stability of the nanocomposite. In this paper, GO was prepared by the improved Hummers, method. In the first step, an amine group of PPD undergoes a nucleophilic ring-opening reaction with an epoxy group on GO. Multiple characterization methods indicate that PPD is successfully grafted to the surface of GO sheets and GO is partially reduced simultaneously. The graphene layer spacing increased from 0.81 nm for GO to 1.49 nm for grafted graphene oxide (g-GO). The number of oxygen-containing functional groups in GO is also reduced. The conductivity of g-GO at room temperature is 1.8 S cm-1, which is much higher than that of GO. In addition, the thermal stability of g-GO has also been improved. In the second step, the other unreacted terminal amino group of PPD is grafted to PET molecular chains through hydrogen bonding or amidation reactions. Antistatic and thermally stable nanocomposites were then obtained by hot pressing. Different ratios of graphene/polyester nanocomposites were obtained. At the same time, the g-GO is further thermally reduced. The thermal stability of PET/g-GO nanocomposite has been greatly improved, while the thermal stability of PET/GO nanocomposite is basically the same as that of pure PET. For the PET/g-GO nanocomposite, the residue rate has increased by nearly 10%, and the maximum thermal decomposition temperature has also increased by 11 °C. When the content of g-GO is 1.0 vol%, the bulk conductivity of PET/g-GO nanocomposite is increased by 8 orders of magnitude. However, when the content of GO is 1.0 vol%, the bulk conductivity of the PET/GO nanocomposite is only improved by 3 orders of magnitude. PET/g-GO nanocomposites exhibit good antistatic properties. The PET/g-GO nanocomposite's conductive percolation threshold is 0.61 vol%, while that of the PET/GO nanocomposite is 1.64 vol%. The electrical conductivity of the nanocomposite increases with the increase of graphene content. And the well-dispersed modified graphene can improve the electrical conductivity of the nanocomposite.

Integrating Conductive Metal–Organic Framework with Graphene Oxide to Highly Sensitive Platform for Electrochemical Sensing

AbstractThe rational selection and integration of materials play important roles in advancing electrochemical sensing. Herein, a highly sensitive electrochemical platform based on composites of graphene oxide (GO) and conductive YbHHTP metal–organic framework (HHTP = 2,3,6,7,10,11‐hexahydroxytriphenylene) for the detection of dopamine (DA) and uric acid (UA) is reported. The composites are prepared by the introduction of GO into the hydrothermal synthesis of YbHHTP. The morphology, structure, and property of the resultant GO/YbHHTP composites are characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, ultraviolet–visible spectroscopy, X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and cycle voltammetry. The results show that this in situ integration strategy facilitates the homogeneous anchoring of YbHHTP nanorods on the surface of GO sheets to achieve a considerable conductivity in the composites and fast electrochemical kinetics for probe molecules. As a result, the GO(2.0)/YbHHTP‐modified electrodes exhibit ultrahigh sensitivity in detection of DA (3.62 µA µm−1) and UA (1.97 µA µm−1) as well as excellent reproducibility, stability, and anti‐interfere ability.

Enhancement of photocatalytic by Mn3O4 spinel ferrite decorated graphene oxide nanocomposites

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

Surface Modification of Graphene and its Derivatives for Drug Delivery Systems

Nowadays, carbon-based nanostructure materials are regarded as promising carriers for drug delivery to improve the effective treatment of diseases. The formation of covalent and noncovalent molecular bonds can be used for surface modification of nano-carriers in order to manipulate their toxicity, water solubility, and cellular internalization. Graphene and its derivatives have shown important potential in drug delivery systems. Among different graphene derivatives, Graphene Oxide (GO) is the most extensively used derivative. GO sheets have possessed certain oxygen functional groups including carboxylic acid groups at the edges, epoxy and hydroxyl groups on the basal planes. The oxygen groups on the surface of GO sheets enhance their capabilities for functionalization with chemical and bioactive molecules. In this review, we highlight the recent researches about the effect of reactive sites on the surface of GO and its derivatives in drug delivery systems. Therefore, the application of GO and its derivatives have been discussed as a delivery system in cancer treatment, gene therapy, and combination therapy, followed by discussions on their related issues. Finally, the review will provide a future perspective to the applications of GO-based materials as part of drug delivery systems, and may open up new viewpoints to motivate broader interests across these interdisciplinary fields.

Preparation of nano-SiO2 modified graphene oxide and its application in polyacrylate emulsion

Graphene oxide-silica nanohybrids (GO-SiO2) were prepared using graphene oxide (GO) and tetraethyl orthosilicate (TEOS) via the sol-gel method. It was further employed to modify polyacrylate (PA) via in situ polymerization to fabricate PA/GO-SiO2 composite. The structure and properties of GO-SiO2 and PA/GO-SiO2 composite were systematically investigated. FT-IR, TG, SEM and TEM analyses indicated that GO-SiO2 nanohybrids were successfully prepared and the SiO2 particles covered the surface of GO sheets. After being modified by GO-SiO2, the main structural feature of PA still remained, and the dispersion of PA emulsion was slightly improved. DSC measurement suggested that the introduction of GO-SiO2 would slightly decrease the tensile strength of PA/GO-SiO2 composite film while improved its elongation at break, but it had no significant effect on the monomer conversion of the PA emulsion. Moreover, the thermal stability and water-resistance of the composite film could be reasonably improved. This suggests the application potential of GO-SiO2 nanohybrids in the modification of PA emulsion for leather finishing.

Tuning the Oxygen Content of Reduced Graphene Oxide and Effects on Its Properties.

The need to recover the graphene properties in terms of electrical and thermal conductivity calls for the application of reduction processes leading to the removal of oxygen atoms from the graphene oxide sheet surface. The recombination of carbon–carbon double bonds causes a partial recovery of the original graphene properties mainly limited by the presence of residual oxygen atoms and lattice defects. However, the loss of polar oxygen-based functional groups renders the material dispersibility rather complicated. In addition, oxygen-containing functional groups are reaction sites useful to further bind active molecules to engineer the reduced graphene sheets. For these reasons, a variety of chemical processes are described in the literature to reduce the graphene oxide. However, it is greatly important to select a chemical process enabling a thin modulation of the residual oxygen content thus tuning the properties of the final product. In this work, we will present a chemical-processing technique based on the hydroiodic acid to carefully control the degree of residual oxidation. Graphene oxides were reduced using hydroiodic acid with concentrations from 0.06 to 0.95 mol L–1. Their properties were characterized in detail and tested, and the results showed that their oxygen content was finely tuned from 33.6 to 10.7 atom %. This allows carefully tailoring the material properties with respect to the desired application, which is exemplified by the variation of the bulk resistance from 92 Ω to 14.8 MΩ of the film from the obtained rGO.

Exploring β-CD grafted GO nanocomposites with an encapsulated fluorescent dye duly optimized by molecular docking for better applications

Here, we have designed and synthesized β-cyclodextrin grafted Graphene Oxide based fluorescent probe with encapsulated fluorescent dye. The nanocomposites were characterized by several spectroscopic methods such as FTIR, DLS, zeta potential, UV–vis and fluorescence spectroscopy. Thermal gravimetric analysis (TGA) was employed to account for thermal stability of β-CD grafted graphene oxide nanocomposites. Nile blue molecules are well encapsulated into the cyclodextrin cavity and embedded on the surface of Graphene Oxide sheet. Molecular Docking study helps us to understand the feasibility of encapsulation process of fluorescent dye inside our synthesized nanocomposites. Various physicochemical properties like UV–vis and fluorescence spectra of composite in different solvent and photophysical properties like fluorescence quantum yield, molar extinction coefficient, stokes shift have been calculated.

Prominent adsorption of Cr(VI) with graphene oxide aerogel twined with creeper-like polymer based on chitosan oligosaccharide

Low-density aerogels with three–dimensional porous structure were synthesized using soluble chitosan oligosaccharide (COS) and graphene oxide (GO) as raw materials under mild conditions. Tetraethylenepentamine was used as the crosslinker of COS and the bridge between GO and COS, as well as the provider of functional groups. Structural characterizations revealed that crosslinked COS polymers firmly fixed on the surfaces of GO sheets and abundant amino groups homogeneously distributed in the pores. The adsorption capacity of the aerogel for Cr(VI) can reach up to 519.8 mg/g, while the adsorption efficiency for trace Cr(VI) adsorption can also reach 100% especially. The adsorption mechanism was investigated with X–ray photoelectron spectroscopy and zeta potential analysis. The superb properties suggested that the strategy of using COS as a raw material for the fabrication of adsorbents with controllable structure and form is meaningful.

Triangular silver nanoparticles loaded on graphene oxide sheets as an antibacterial film

Silver nanoparticles (AgNPs) are the only broad-spectrum antimicrobial nanoagents that have been used in clinical practice, although their harmful effects to the environment and mammalian cells continue to promote the development of advanced materials and effective approach. This work reports on synthesis of an antibacterial nanocomposite film formed from graphene oxide (GO) nanosheets decorated with triangular AgNPs. The AgNPs with different edge lengths were prepared by the photochemical growth process and were self-assembled on the surface of GO sheets. Our work indicated that the antibacterial activities of the composite films were amount-dependent of AgNPs, and a very low amount of triangular AgNPs in the composite films could exert effective antibacterial effect on Gram-negative bacteria Escherichia coli and Gram-positive Staphylococcus aureus.

Incorporation of silica network and modified graphene oxide into epoxy resin for improving thermal and anticorrosion properties

AbstractIn this study, the silica network and functionalized graphene oxide (GO) were incorporated into the epoxy coating systems, which was aimed to improve the thermal property and corrosion resistance of epoxy coatings. First, tetraethyl orthosilicate (TEOS) oligomers and epoxy hybrid was fabricated through sol–gel method. Then the (3‐aminopropyl) triethoxysilane (APTES) modified graphene oxide (FGO) was added into the epoxy hybrid composite to obtain anticorrosion coatings. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectrum, and X‐ray photoelectron spectrum were conducted to evaluate the structural information of GO and APTES modified GO nanosheets. The results indicated that the APTES successfully grafted onto the surface of GO sheets. Besides, TGA curves, electrochemical measurements and salt spray test were also carried out to characterize the thermal performance and corrosion resistance of GO based epoxy coatings. The TGA results revealed that the thermal performance of epoxy coating containing silica network and FGO nanofiller (ES/FGO) was significantly strengthened compared to pure epoxy. The initial degradation temperature of epoxy coating was increased from 300 to 343.7°C after incorporation of silica component and FGO. The EIS measurements demonstrated that the impedance modulus of ES/FGO was significantly higher than neat epoxy, which indicated that the corrosion resistance of epoxy was substantially strengthened after introduction of silica component and FGO. The corrosion rate and inhibition efficiency of epoxy composite coatings were also shifted from 1.237 × 10−7 mm/year and 76.6% (for neat epoxy) to 1.870 × 10−9 mm/year and 99.6% (for ES/FGO), respectively. The salt spray test also revealed that the silica and FGO can improve the corrosion resistance of epoxy coating. Additionally, the dispersion of GO sheets was also enhanced after the modification of APTES siloxane.

Photoluminescence Emission during Photoreduction of Graphene Oxide Sheets as Investigated with Single-Molecule Microscopy

Graphene oxide (GO), the oxidized state of graphene, has a similar chemical structure to graphene, except for the existence of many defects and oxygen-containing functional groups. GO could be photoreduced under light irradiation, and it is crucial to study and understand the changes of chemical structure and photoluminescence during this photoreduction process. Herein, by using single-molecule optical microscopy, the photoreduction of three different GO sheets were monitored in situ. The photoluminescence from highly oxidized GO sheets changed continuously under light irradiation, and many blinking spots showed up on this GO sheet surface. The appearance of these blinking events is highly related to the stacking of the GO sheets. Much less blinking could be observed on stacked GO sheets. It was found that the reduction speed of GO in water is much higher than that in air, and much less blinking could be observed when GO was reduced in water. Moreover, this is also highly related to the chemical structures of the GO sheets used for photoreduction. No blinking could be observed on less oxidized GO sheets. This work provides an effective approach for in situ study of the optical properties of GO sheets, boosting a deeper understanding of GO photoreduction. Moreover, this method could also be extended for in situ studying the optical properties of other materials.