Synthesis Of Graphene Oxide Nanosheets Research Articles

Modified low-temperature synthesis of graphene oxide nanosheets: Enhanced adsorption, antibacterial and antioxidant properties

Herein, we report a simple, low-temperature, ecofriendly synthesis of graphene oxide nanosheets (GONs). Graphite powder was treated with KMnO4 and a concentrated H2SO4/H3PO4 mixture to synthesize GONs. The effects of various reaction conditions such as reaction time, temperature, amounts of cleaving agents (H2SO4/H3PO4), and oxidant (KMnO4) were investigated. The synthesized GONs were examined by various techniques in order to investigate their characteristics. The best results of the synthesized GONs were observed at 35 °C within 10 h of reaction time having 8:2 ratios of H2SO4/H3PO4 acid mixture. The main absorption peak in the UV–vis spectra of GONs was at 258 nm, which is due to the π-π* transition of the atomic CC bonds. The existence of stretching vibrations of C꞊O, O–H, C–H, and C–O in the Fourier transform infrared (FTIR) spectra verified the formation of GONs. Presence of a sharp peak at 2θ = 10° with an interlayer spacing distance of 0.88 nm in the observed XRD pattern revealed that the synthesized GONs were totally oxidized and that the interlayer spacing increased. The morphological investigations confirmed the formation of ultrathin, transparent, curly, and homogenous GONs. The synthesized GONs were applied as an adsorbent for the rapid uptake of four different pesticides viz.; Profenofos, Ethion, Cypermethrin, Thiamethoxam (TMX) from the pesticides spiked water samples. About 86% adsorption of Profenofos + Cypermethrin, and 50% adsorption of ethion and thiamethoxam took place within 20 min in presence of 10 mg GONs. In addition to this, the prepared GONs were tested for the antibacterial activity against four bacterial strains by agar well diffusion method. The synthesized GONs provide a significant inhibition for gram –positive (Bacillus subtilis, and Staphylococcus aureus) and gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains. Moreover, the radical scavenging activities (RSA) of GONs were also checked and compared with Gallic acid as a standard. The obtained RSA of GONs was 60% in comparison to the 80% as of the standard Gallic acid at 1000 μg/mL concentration.

Quality by design approach for the synthesis of graphene oxide nanosheets using full factorial design with enhanced delivery of Gefitinib nanocrystals

Designing drug delivery carriers is the most focused work for a material scientist. The formulator can screen the material starting from its properties to the performance of the material. The quality by design approach has simplified the path of selection of the right parameter for analyzing the process. The present investigation elaborates the use of a full factorial design model for understanding the interaction of oxidizing agents on the conversion of graphite to graphene oxide (GO). The most frequently assessable laboratory method is chemical oxidation, which is used for understanding optimum oxidation potential and nanosheet formation. The method utilizes 2 level assessments for screening reactant concentration of sulphuric acid and potassium permanganate on preprocessed graphite. In present investigation, one categorical factor is used to understand the effect of precursor size on the final product. The statistical model provides optimum oxidation conditions, using particle size, polydispersity index (PDI), and ID/IG ratio with a 95% confidence interval (p-value less than 0.05). The optimized synthesis procedure provides the least particle size of GO nanosheet of about 220.7 nm with PDI 0.289 and ID/IG ratio of 0.98. Furthermore, pulse mode ultrasonication converts Gefitinib (GF) into nanocrystals and is deposited within intricates of GO nanosheets (nGOGF). The GO and nGOGF were preliminarily characterized using optical and vibrational spectroscopy. The hydrodynamic diameter was found to be slightly increased to 237.5 nm with decreasing surface charge (−33.64 mV) after fabrication. The x-ray Photoelectron Spectroscopy (XPS) study reveals successful grafting of oxygen-containing functional groups on GO nanosheets with peak positions observed at 284–288 eV. The Transmission electron microscopic (TEM) observation supports the wrinkled structure of GO nanosheets synthesis, along with encapsulation of GF nanocrystals. The nGOGF retard the release of GF for a prolonged period of time and the rate of dissolution was increased by fold compared to pure GF.

Synthesis of graphene oxide nanosheets decorated by nanoporous zeolite-imidazole (ZIF-67) based metal-organic framework with controlled-release corrosion inhibitor performance: Experimental and detailed DFT-D theoretical explorations

For the first time, the zeolite-imidazole (ZIF-67) framework, a new subfamily of metal-organic frameworks (MOFs), is synthesized on the graphene oxide (GO) platform. Co2+ (as a central atom) and 2-methylimidazole (as organic ligands) were assembled to fabricate ZIF-67/GO NPs for providing epoxy-based anti-corrosion coatings with both active (self-healing) and passive (barrier) performance. Also, the ZIF-67/GO NPs were modified by 3-Aminopropyl triethoxysilane (APS) to improve the particles compatibility with the epoxy matrix and control their solubility in saline media. The FE-SEM, FT-IR, UV–Vis, Raman, TGA, and low-angle XRD techniques were used to prove the successful ZIF-67 particles growth onto the GO platforms. Tafel (potentiodynamic) polarization test demonstrated that the ZIF-67/GO@APS NPs could protect the surface of steel through mixed anodic/cathodic type (O2 reduction/Fe oxidation) mechanisms and the corrosion current density of the iron sample decreased to 1.41 µA·cm−2. Interestingly, the epoxy coatings containing ZIF-67/GO and ZIF-67/GO@APS particles revealed long-term corrosion protection durability and outstanding self-healing anti-corrosion performance, which were well studied via EIS, salt spray, cathodic delamination, and pull-off techniques. The impedance value at the lowest frequency for the coating containing ZIF-67/GO@APS after 50 days decreased from 10.7 Ω·cm2 to 10.2 Ω·cm2 that showed the lowest reduction among the studied samples.

Microfluidic-Oriented Synthesis of Graphene Oxide Nanosheets toward High Energy Density Supercapacitors

Graphene oxide (GO) has aroused worldwide interests in recent years because of perfect solubility, easy processing nature, and intriguing mechanical properties. However, safety risk, high pollution, and low synthesis rate involved in the synthesis process of GO limit its practical applications. In this work, we propose a new strategy to efficiently produce the high-quality GO based on microfluidic synthesis technology. By use of the H2SO4/H3PO4/graphite hybrid microdroplet as the microreactor, the exfoliation and oxidation of graphite can be confined in a microscale reaction environment, indicating the enhanced reaction kinetics, high reaction rate (reaction time of 2 h), and minimum safety risk. Notably, the microfluidic synthesis of GO has nearly the same chemical structure when compared with the Hummers method. More importantly, the rGO fibers processed from GO solutions possess a high specific capacitance of 716.2 mF cm–2 (23.86 F g–1) and an energy density of 14.5 μWh cm–2 (0.53 Wh kg–1), which can enduringly power a smart watch. These versatile strategies open a promising access to the fast synthesis and commercial applications of graphene.

Biobased alkyd/graphene oxide decorated with β–MnO2 nanorods as a robust ternary nanocomposite for surface coating

In this paper, a controlled synthesis of graphene oxide nanosheets decorated with β–MnO2 nanorods (β-MnO2 NRs@GO) hybrid was reported via a facile chemical deposition system. For the first time, a biobased ternary nanocomposite series based on linseed oil alkyd filled with β–MnO2 NRs@GO hybrid was developed through a solution casting technique, applied on carbon steel as anticorrosive materials, and dried through an auto-oxidation mechanism. GO nanosheets with thickness <2 nm and β–MnO2 nanorods (NRs) with single-crystallinity, 20−30 nm mean diameter-size, <1 μm length, and exposed with [110] growth orientation of wurtzite structure were synthesized through controlled regimes. The synergetic effects of distributing different β–MnO2 NRs@GO hybrid concentrations in the alkyd matrix were studied to tune the coatings' mechanical and protective properties. The durability and thermal resistivity of the nanocomposite films were investigated. The surface and anticorrosion features of the ternary nanocomposites were studied through water contact angle (WCA), atomic force microscopy, scanning electron microscope, electrochemical analysis, and salt-fog experiment (in 5% NaCl solution). The highest reinforcing improvement with thorn-like protrusions roughness was achieved through a well-distribution of 2.5 wt% β–MnO2 NRs@GO nanofillers in the matrix. The alkyd/β–MnO2 NRs@GO (2.5 wt%) nanocomposite exhibited the highest hydrophobicity (WCA of 141°), root mean square roughness of 15.64 nm, thermal stability, and chemical resistance against 3 N NaOH solution for 24 h. Also, it showed the highest impact resistance (12.74 J), polarization resistance, and stability in a salt-fog environment for 500 h. This fascinating biobased nanocomposite coating provides a promising alternative for replacing petro-based anticorrosive surfaces for the sustainable future environment.

Graphene oxide nanosheets for treatment of mine-drainage contaminated water: The effect of phosphate functionalisation on U(VI) removal

Acid mine drainage (AMD) poses significant challenges to fresh water supplies in mining regions globally. Not only is water made too acidic for consumption, the acidic conditions also lead to the mobilization of toxic elements including uranium. Nanomaterials have been shown to be effective for the treatment of such contaminated water. In this study, we investigated the effect of phosphate functionalisation on the removal of uranyl ions from mine-drainage contaminated water. Graphene oxide (GO) nanosheets functionalised through the Arbuzov reaction were therefore synthesized and characterized for structure, elemental composition and functionalisation. Adsorptive removal of uranyl [U(VI)] ions by the nanosheets was then examined in batch studies as a factor of time, pH, U(VI) concentration, and adsorbent concentration. X-ray diffraction confirmed the synthesis of GO nanosheets from graphite, while the presence of phosphate groups in GO was confirmed by FTIR. TEM images revealed a tendency for stacking, particularly for functionalised nanosheets. Adsorption of U(VI) from solution was found to be optimal at pH 4 for both GO and GO-PO4. However, adsorption by GO-PO4 attained equilibrium earlier and was >15% higher than that of GO, effects ascribed to the phosphate functionalisation. Importantly, even in mine-drainage contaminated water (pH 2.78) GO-PO4 out-performed GO by >30%. These data suggest that functionalisation of GO nanosheets increases their efficiency in U(VI) removal from mine-drainage contaminated water by GO. We discuss the proposed mechanisms for the mode of phosphate functionalisation.

Chloramine-T/N-Bromosuccinimide/FeCl3/KIO3 Decorated Graphene Oxide Nanosheets and Their Antibacterial Activity.

In this work, we report the synthesis of graphene oxide nanosheets (GO NS) using four different oxidants, namely, chloramine-T (CAT), FeCl3, N-bromosuccinimide (NBS), and KIO3. Fourier transform infrared spectroscopy (FTIR) was used to characterize the functional groups present in the synthesized GO. The microstructure analysis was performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the morphology of GO. High-resolution transmission electron microscopy (HRTEM) studies demonstrated the nanostructure and crystalline phases of GO. The antibacterial activity of the prepared GO NS was investigated against pure cultures of Pseudomonas pneumonia and Staphylococcus aureus. The synthesized GO NS with CAT-GO (C-GO) exhibited very good antibacterial activity towards pathogens.

Synthesis of graphene oxide nanosheets from sugar beet bagasse and its application for colorimetric and naked eye detection of trace Hg2+ in the environmental water samples

In the present study, an analytical method was developed by using graphene oxide (GO) stabilized silver nanoparticles (AgNPs) for colorimetric and naked eye detection of trace Hg2+ in the environmental water samples. In this regard, a stable aqueous dispersion of GO has been synthesized by employing sugar beet bagasse as carbon source. Subsequently, AgNPs were decorated on the surface of as-synthesized GO by in-situ reduction of Ag+. Follow by, Hg2+ detection process was performed by consideration of the influence of several key factors including sensor stability over time, sample pH, response time, selectivity and sensitivity of the sensor. The obtained results revealed that the produced nanosensor has a good sensitivity and selectivity to Hg2+ detection with response time of 2 min with linear range of 10 to 100 µM. The sensing mechanism of analyte was based on the selective amalgam reaction between AgNPs and Hg2+. Moreover, the naked eye detection was investigated by the sensor's color changed from yellow to colorless. The detection limit of the produced sensor was 0.64 nM. This sensor was also applied to detect Hg2+ in the environmental water samples with recoveries in the range of 92.17% to 105.57%. The produced nanosensor exhibited good selectivity of Hg2+ in the presence of high concentration of other ions.

Improved features of a highly stable protease from Penaeus vannamei by immobilization on glutaraldehyde activated graphene oxide nanosheets.

In this study, we report the synthesis of graphene oxide nanosheets (GON) by a modified Hummers method. Then, a protease purified from the Penaeus vannamei shrimp was immobilized on the GON activated with glutaraldehyde. Several techniques such as SEM, DLS and FTIR were applied to characterize the different nano-structures at the different levels. The immobilization of the protease on the GON activated with glutaraldehyde did not affect the optimum pH, but significantly improved thermal stability and stability at extreme pH values, as well as activity at 90 °C. After 24 h of incubation at 90 °C, the free enzyme retained less than 10% of the activity, while the immobilized enzyme kept more than 90% of its original activity. The apparent Km and Vmax for Penaeus vannamei protease remained fairly similar after immobilization, a very relevant data considering the large size of the substrate (casein).In the hydrolysis of casein at 70 °C and in the presence of 2 M urea, the immobilized enzyme exhibited a higher activity than the free enzyme. The results indicate that the immobilization of the enzyme Penaeus vannamei protease on GON activated with glutaraldehyde increases its already high stability against environmental stresses and makes it suitable for biotechnological and industrial applications.

The performance of immobilized Candida rugosa lipase on various surface modified graphene oxide nanosheets

In this study, we have reported the synthesis of graphene oxide nanosheets (GON) and its functionalization with 2, 4, 6-trichloro-1, 3, 5-triazine (TCT) through two routes, (a) directly reaction of GON with TCT (GON-1), and (b) reaction of GON with pre-functionalized TCT with 3-aminopropyltriethoxysilane (APTS) (GON-2). Subsequently, GON, GON-1 and GON-2 have been used as supports for immobilization of Candida rugosa lipase (CRL). Several techniques such as XRD, SEM, EDS, UV–Vis, CHNS, FTIR and AFM were applied to characterize the nano-structures and success of synthesis, functionalization and CRL immobilization processes. The results corresponding to optimization of immobilization process revealed the following order for values of loading capacity, immobilization yield and leaching of CRL: GON > GON-1 > GON-2, while this order is reversed for, specific activity and recovery activity. The assessment of operational parameters represents the high storage stability and reasonable reusability for all the immobilized CRL while the pH and thermal stability of CRL@GON-2 are higher than two others. It seems the longer linker of GON-2 could more effectively prevent the unfavorable interaction between enzyme-enzyme and enzyme-product that consequently resulted the best catalytic performance, pH and thermal stability. The advantages of these supports make them suitable candidates for practical applications.

Synthesis of graphene oxide nanosheets functionalized by green corrosion inhibitive compounds to fabricate a protective system

The adsorptive behavior of Urtica Dioica (U.D) leaf extract on the graphene oxide nanosheets (GONs) was examined by experimental and density functional theory (DFT) approaches. Experimental results demonstrated the strengthened adsorption of the Urtica Dioica leaf extract on the GO sheets at acidic pH of 2, leading to the corrosion inhibition of mild steel in chloride solution. It was observed that the inhibition effects of GO-U.D sheets enhanced in the presence of Zn2+ cations in solution and coating phases. The DFT results revealed the physisorption and chemisorption of inhibitors onto GO surfaces.

Synthesis of graphene oxide nanosheets for the removal of Cd(II) ions from acidic aqueous solutions

In this study, graphene oxide nanosheets were synthesized and employed to adsorb Cd(II) in acidic aqueous solutions. Characterization techniques, such as AFM, TEM, XRD, FT-IR, Raman and Zeta potential were used to investigate the adsorbent properties. Results demonstrated that the Cd(II) removal efficiency was found to increase from 6.29% to 96.72% with the increase of adsorbent dosage from 0.02 to 2.00 g/L. The removal efficiency remained constant with further increase of the adsorbent dosage. Cd(II) adsorption was greatly enhanced with the increase of solution pH from 2.02 to 4.01. In addition, the adsorption equilibrium was attained within 120 min, and a slight decrease in solution pH was observed after the adsorption of Cd(II). The adsorption data were revealed to fit well in pseudo-second-order kinetics and Langmuir isotherm model, and the maximum Cd(II) adsorption capacity was recorded to be about 44.64 mg/g with 0.50 g/L of adsorbent dosage. Ion-exchange, electrostatic attraction and physical adsorption were found to be involved in the adsorption mechanisms of this process. Findings from this study suggested that the synthesized adsorbent could be highly effective for Cd(II) removal from acidic water environments.

Synthesis of Graphene Oxide Nanosheets via Modified Hummers’ Method and Its Physicochemical Properties

The efficient synthesis of exfoliated graphene oxide nanosheets (GO) via modified Hummers’ method was successfully carried out. The physicochemical properties of GO were determined by Fourier transform infrared spectroscopy (FTIR), UV-visible spectrophotometry (UV-vis), x-ray diffraction analysis (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The graphite was fully oxidized by strong oxidizing agent caused the oxygen-containing functional groups such as C-O-C, C=O, and COOH were introduced into the graphite layers as analyzed by Raman and FTIR. XRD pattern of GO showed 2θ of 12.0o with interlayer spacing ~ 7.37A which describe non uniform crystal structure with the addition of oxygen containing functional groups. UV-vis spectrum of GO exhibit maximum absorption peak at ~ 234 nm corresponding to the aromatic C=C bond with π-π* transition. The morphology of GO was observed to have flake-like shape and less transparent layers by TEM. The properties of synthesized GO suggest high potential in producing the high quality of graphene which is can be applied as the electrocatalyst support for direct methanol fuel cell application.

Synthesis of graphene oxide nanosheets and its application to construct a modified carbon paste electrode as a hydroxylamine electrochemical sensor

A ferrocene-derivative compound, 2, 7-bis (ferrocenyl ethynyl) fluoren-9-one (2,7-BFE), was synthesized and used to construct a modified graphene paste electrode. The electrooxidation of hydroxylamine at the surface of the modified electrode was studied using cyclic voltammetry (CV), chronoamperometry (CHA), and square wave voltammetry (SWV). Under the optimized conditions, the square wave voltammetric peak current of hydroxylamine increased linearly with hydroxylamine concentration in the range of 2.0 × 10−7 to 2.5 × 10−4 M and detection limit of 9.0 × 10−8 M was obtained for hydroxylamine. Finally, this modified electrode was used for determination of hydroxylamine in some water samples.

Ultralow temperature synthesis and improved adsorption performance of graphene oxide nanosheets

In this article, we first report an ultralow temperature (−60°C) synthesis of graphene oxide nanosheets (GONs), which is achieved via the reduction reaction of tetrachloroethylene (C2Cl4) and potassium in liquid ammonia solution at atmospheric pressure. The as-obtained multilayer GONs with a high quality exhibit a low C/O atomic ratio of approximately 2:1, indicating that GONs are rich in the oxygen-containing functional groups. In order to improve their adsorption property, GONs are reduced at 500°C for 2h in flowing N2, which results in the successful preparation of graphene nanosheets (GNs) with a high C/O atomic ratio of approximately 32:1. GNs show high specific surface area (508m2/g), high adsorption capacity (Qe=148.36mg/g, Co=180mg/L), and rapid adsorption rate (>96%, 10min) of organic dye rhodamine B (RhB) from water, suggesting that GNs have potential environmental applications as alternatives to commercial materials in wastewater treatment for the removal of organic dye. Compared with the reported methods to prepare GONs, our techniques have attractive advantages, such as low reaction temperature and being friendly to environment.

Synthesis of graphene oxide nanosheets by electrochemical exfoliation of graphite in cetyltrimethylammonium bromide and its application for oxygen reduction

An electrochemical method is reported for the production of graphene oxide (GO) and graphene nanosheets using the following steps: electrochemical intercalation of cetyltrimethylammonium bromide (CTAB) into graphite followed by the electrochemical exfoliation of a CTAB-intercalated graphite electrode. These electrochemical processes yield a stable colloidal GO/CTAB suspension. Then, exfoliated GO was used as a precursor at cathodic potentials (completely reduced potential: −1.5 V) by cyclic voltammetry or cronoamperometry. The colloidal GO/CTAB suspension and electrochemically reduced graphene oxide (RGO) nanosheets have been carefully characterized by spectroscopic and electrochemical techniques in comparison to the stable colloidal graphene/sodium dodecyl sulfate suspension. Particularly, FTIR spectra indicate that a variety of the oxygen-containing functional groups have been produced from the graphite plane by electrochemical oxidation. UV-vis spectra of GO/CTAB suspensions show that a large amount of GO is obtained after successive electrochemical intercalation and exfoliation processes. Finally, the straightforward synthesis of RGO/CTAB composites provide a low-cost and high performance for oxygen reduction reaction (ORR), which is also a promising strategy for the synthesis of various GO/cationic surfactants composites.

Facile and fast synthesis of graphene oxide nanosheets via bath ultrasonic irradiation

For the first time, this work reports a facile sonochemical route in the synthesis of graphene oxide nanosheets (GO) via oxidation of graphite (G). The synthesis of GO was carried out in a fast way under ultrasonic bath irradiation (GO-U). In comparison, the synthesis of GO via classical method (GO-C) was done under the same conditions as ultrasonic method. The products were completely different and the oxidation did not happen the same as way as ultrasonic method. Furthermore, GO was synthesized based on classical approach that most commonly used (GO-C′), not under the same conditions as ultrasonic method. The GO sheets were characterized using UV–Vis, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscope (TEM), thermal gravimetry (TG), and Raman spectroscopy techniques. The XRD confirms that the spaces between GO-U and GO-C′ sheets were higher than graphite. Also, XRD indicated that the GO-U has fewer sheets rather than GO-C′. The TEM observations were confirmed the synthesis of nanosheets. The UV–Vis results were shown the absorption peaks at 230nm for GO-U and GO-C′, at 245nm for GO-C, and at 255nm for G. The blue shift in GO-U with respect to G and GO-C can be interpreted based on the higher character of sp3/sp2 in GO-U than G and GO-C. The FT-IR presents the oxygenated functional groups on graphene oxide sheets. A reduction in size of the in-plane sp2 domains was observed by Raman spectrum. The BET analysis for G, GO-U and GO-C′ confirmed that GO-U has a highest specific surface area among all the samples. Therefore, the ultrasonic bath method even with low intensity has a fundamental role in the synthesis of graphene oxide nanosheets and it is relatively fast, simple, cost-effective and efficient as compared to the classical method.

Fast and facile microwave-assisted synthesis of graphene oxide nanosheets

A fast and facile microwave-assisted method was developed for preparing GO.