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Preparation of Graphene by Using an Intense Cavitation Field in a Pressurized Ultrasonic Reactor
Chemistry - A European Journal
Abstract
A new and efficient method to produce a large quantity of high-quality and non-oxidized graphene flakes from powdered natural graphite by using a high-intensity cavitation field in a pressurized ultrasonic reactor is demonstrated. TEM and selected-area electron diffraction (SAED) confirmed the ordered graphite crystal structure of graphene. Atomic force microscopy (AFM) was used to examine the thickness of the graphene sheets. The delamination (exfoliation) of natural graphite in the liquid phase depends on the physical effects of ultrasound, which break down the 3D graphite structure into a 2D graphene structure. The prepared graphene is of high purity and without defects because no strongly oxidizing chemicals are used and no toxic products result. TEM shows that graphene nanosheets were produced with sizes in the range of tens to hundreds of square nanometers; these nanosheets were smooth and without any ripples and corrugations. High-resolution TEM (HRTEM) and SAED analysis confirmed that the products were graphene nanosheets.
... In this work, we studied the effect of graphene-derived precursors with different amounts and distribution of functional (oxygencontaining) groups on the preparation and permeation properties of graphene-based membranes. In the first step, three types of graphene-derived precursors were synthesized; two types of GO, denoted GO-1 and GO-2 synthesized via the classic Hummers' method [29] and the method previously published by our group [30,31], respectively, and one type of carboxylated GO (GO-COOH) [32,33]. The content of functional groups was determined for the precursors, as they enable interactions with molecules of penetrating gases and water vapor. ...
... Two types of GO were prepared under different reaction conditions using synthetic protocols already described before [29][30][31]. The first synthetic route producing GO-1 is a modified Hummers' method [29] and uses a much higher concentration of oxidation agents (graphite oxidation with KMnO 4 in a 9:1 mixture of concentrated H 2 SO 4 /H 3 PO 4 acids) than the second method leading to GO-2. ...
... The second difference is that the GO-1 is prepared directly from the synthetic graphite. In contrast, the second type of graphene oxide (GO-2) is prepared from the exfoliated synthetic graphite (elemental analysis C 99.40 %, H 0.01 %) prepared using a high-intensity ultrasound in a pressurized stainless-steel batch reactor [30]. Due to the formation of the exfoliated graphite in the first step of GO-2 production, the subsequent oxidation can be done under much milder conditions using smaller amounts of oxidation agents (60 mL H 2 SO 4 , 10 mL H 3 PO 4 , and 3 g KMnO 4 ) [31] compared to GO-1. ...
The gas and water vapor permeabilities of graphene-based membranes can be affected by the presence of different functional groups directly bound to the graphene network. In this work, one type of carboxylated graphene oxide (GO-COOH) and two types of graphene oxide synthesized i) under strong oxidative conditions directly from graphite (GO-1) and ii) under mild oxidative conditions from exfoliated graphene (GO-2) were used as precursors of self-standing membranes prepared with thicknesses in the range of 12–55 μm via slow-vacuum filtration preparation method. It was observed that the permeabilities for all tested gases decreased in order GO-2 > GO-1 > GO-COOH and depended on both the arrangement of graphene sheets and their functionalization. The GO-1 membrane with a high content of oxygen-containing groups showed the best performance for water vapor permeability. The GO-2 membrane with a thickness of 43 μm exhibited a disordered GO sheet morphology and, therefore, unique gas-separation performance towards H2/CO2 gas pair, showing high hydrogen permeability while keeping extremely high H2/CO2 ideal selectivity that exceeds the Robeson 2008 upper bound of polymer membranes.
... The 0.2 g portion of h-BN was suspended in 100 mL water and exposed to an intense cavitation field in a pressurized reactor for 5 min. The pressure of 6 bar was set by means of an air compressor [15] to improve ultrasonic energy transfer to the suspended solid. ...
... The method of ultrasound exfoliation of the layered materials was used for graphene and inorganic analogues of graphene (IAG) exfoliation. The process is based on the experience from the exfoliation of other layered materials, such as graphite [15], mineral molybdenite [26], tungstenite, and g-C 3 N 4 . ...
... dye + HO • → degraded products (15) In Figure 7). The calculated degradation rate constants (min −1 ) are shown in Table 2 , and P25 ( = 0.047 min −1 ) [58]. ...
h-BN-TiO
2
nanocomposites were synthesized by the thermal hydrolysis of titanium peroxo-complexes in the presence of exfoliated h-BN. The bulk h-BN was prepared by annealing mixture of boric acid and urea, and high intensity ultrasound was used for its exfoliation. The prepared samples were characterized by X-ray powder diffraction (XRD), infrared spectroscopy, Raman spectroscopy, electron spin resonance (ESR), high resolution electron microscopy, BET surface area, and BJH porosity measurement. The UV-Vis diffuse reflectance spectroscopy was employed to estimate band-gap energies. The photoinduced charge on the surface of h-BN-TiO
2
nanocomposites was visualized using electric force microscopy (EFM). The photocatalytic activity was determined by azo dyes Orange II and Reactive Black 5 photobleaching. The highest rate constant
k
= 0.0762 min
−1
and 0.0164 min
−1
, under UV and visible light irradiation, respectively, showed sample denoted TiP050BN with moderate concentration of h-BN.
... Delamination of layered minerals [26] by ultrasound was successfully used for the preparation of exfoliated mica [27] and kaoline [28] under atmospheric pressure. Pressurized batch ultrasonic reactors were also used to exfoliate graphite to graphene [29], which then served as the precursor for the composite materials of graphene-anatase [30] and graphene oxide-anatase [31]. It can then be theorized that the exfoliation of IAGs using power ultrasound in an environment of strong polar aprotic solvents in a pressurized batch reactor could be achieved through this procedure. ...
... A portion of 0.75 to 1 g of the bulk sample was suspended in 120 ml of appropriate aprotic solvent (N-methyl-2-pyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide) and exposed to an intense cavitation field in a pressurized batch ultrasonic reactor for 20 min. The pressure of 6 bar was set in the reactor by means of an air compressor [29]. The exfoliation led to the formation of stable suspensions in the hydrophobic (organophilic) solvents. ...
... After exfoliation, wider interlayer spacings were expected, as was observed in the exfoliation of graphite [29]. However, as is evident from Additional file 1: Table S1, the value of d 002 , depending upon the number of layers, decreases to a value of approximately 0.31 nm. ...
High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.
... Delamination of layered minerals [26] by ultrasound was successfully used for the preparation of exfoliated mica [27] and kaoline [28] under atmospheric pressure. Pressurized batch ultrasonic reactors were also used to exfoliate graphite to graphene [29], which then served as the precursor for the composite materials of graphene-anatase [30] and graphene oxide-anatase [31]. It can then be theorized that the exfoliation of IAGs using power ultrasound in an environment of strong polar aprotic solvents in a pressurized batch reactor could be achieved through this procedure. ...
... A portion of 0.75 to 1 g of the bulk sample was suspended in 120 ml of appropriate aprotic solvent (N-methyl-2-pyrrolidone, N,N-dimethylformamide, or dimethyl sulfoxide) and exposed to an intense cavitation field in a pressurized batch ultrasonic reactor for 20 min. The pressure of 6 bar was set in the reactor by means of an air compressor [29]. The exfoliation led to the formation of stable suspensions in the hydrophobic (organophilic) solvents. ...
... After exfoliation, wider interlayer spacings were expected, as was observed in the exfoliation of graphite [29]. However, as is evident from Additional file 1: Table S1, the value of d 002 , depending upon the number of layers, decreases to a value of approximately 0.31 nm. ...
High intensity ultrasound exfoliation of a bulk layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN) and graphitic carbon nitride (g-C3N4) in liquids leads to the breakdown of the 3D graphitic structure into the 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.
... GO was prepared by a method that was reported in our previous studies [34][35][36]. ...
... The nanoparticles consisted of a mixture of platelet particles with the "flower-like" texture [39]. The HRSEM image (see the Fig. 2B) shows a graphene-oxide with the "sheet-like" structure, which was prepared by intense cavitation in the presence of a mixture of acids [34]. As can be seen from the Fig. 2C, in the case of nanocomposite these plates are formed by graphene oxide nanosheets covered by MnO 2 layer. ...
Abstract Graphene oxide/MnO2 nanocomposite was prepared by thermal hydrolysis of potassium permanganate (KMnO4) and 2-chloroacetamide aqueous solutions with graphene oxide (GO) suspension. The synthesized samples were characterized by specific surface area (BET) and porosity determination (BJH), X-ray Diffraction (XRD) and high-resolution electron microscopes (HRSEM, HRTEM). These nanocomposites were used in an experimental evaluation of their adsorption activity with nerve agent simulants dimethyl methyl phosphonate (DMMP) and triethyl phosphate (TEP) in aqueous media. The nanocomposites exhibited enhanced adsorptive degradation ability compared to pure manganese oxide (MnO2) and GO. The GO amount in the nanocomposites affected their degradation activity substantially. The best adsorption efficiency was observed for samples with moderate GO amount. Three methods were used to observe the mechanism of the nerve-agent simulants deactivation: Gas chromatography with mass spectrometry (GC–MS), High-Performance Liquid Chromatography (HPLC) and in situ Infrared spectroscopy (FTIR). It was shown that the hydrolysis on the surface of prepared nanocomposites yields volatile primary alcohols (methanol and ethanol) as the main hydrolysis products.
... However, this method suffers from the problems of low yield and being timeconsuming [14]. Applying pressure on a liquid exfoliation system can add a pushing force to the intercalating molecules, and thus promote the intercalation rate and exfoliation efficiency [15,16]. The supercritical fluids intercalation-exfoliation method is a special type of liquid exfoliation technique. ...
... During the production process, both making the initial cracks on the side of the stacked graphite layers, and intercalating scCO 2 molecules into the interlayers through cracks required the assistance of ultrasonic cavitation. The ultrasonic cavitation threshold is determined by the system pressure and was quite high in this 16 MPa system. Therefore, when the output power of the ultrasonic generator was too low to meet the required energy demand, ultrasonic cavitation hardly occurred. ...
In this research, a pressure reactor coupled with an ultrasonic generator was built. The intense impact force generated from high-pressure acoustic cavitation in a supercritical CO2 (scCO2)/H2O system and the superior penetration ability of scCO2 were combined to enhance the exfoliation efficiency of natural graphite. The impacts of the aqueous solution content ratio, system pressure, ultrasonic power, and surfactant addition on graphite exfoliation efficiency were studied. Under optimal conditions, the graphene yield could reach more than 50% with 93% of the graphene sheets being less than three layers, and the suspension concentration could be greater than 2.5 g/L. In this approach, from raw material feeding to the discharge of products, natural graphite was directly exfoliated into high-quality graphene sheets in a few hours with a considerably high yield and concentration by using only CO2, H2O, and ethanol. This approach should be a feasible and promising method to produce high-quality graphene on a large scale and at a low cost.
... This method exfoliation was successfully used for exfoliation inorganic analogs of graphene, MoS 2 , WSB, h-BN and h-BCN [34]. The exfoliation processes based on longitudinal and stationary ultrasonic waves take place simultaneously [35]. ...
... The measured surface area of graphene depends on many factors, but principally on the manner of preparation of a dry sample for surface area measurement [35]. The specific surface area, (see Table 1) as measured using the nitrogen-absorption Brunauer-Emmett-Teller (BET) method, decreases from 176 m 2 g À1 to $6 m 2 g À1 (see Table 1), depending on the alkaline metal used (K > Na > Li). ...
... One gram of graphite was suspended in 140 ml of ethylene glycol and sonicated for 20 min. The final product was washed with water using dialysis (Spectra/Por 3 dialysis membrane) until the conductivity of distilled water was reached ($5 lS), filtered off and dried at 105 °C [29]. ...
... In this study, graphene was prepared using an intense cavitation field in an ultrasonic pressurised batch reactor [29]. Thus prepared graphene may be converted to graphene oxide with lower concentrations of strong acids and oxidising agents, lower reaction temperature and therefore under safer conditions than by conventional purely chemical synthesis routes. ...
... So, this method is usually called ultrasonication technique of powder mixing [153]. Pressure generated during sonication forms bubbles, which break down intermittently to release massive energy that distorts the molecular/van Der Waal bonds of the CNTs and enhance their dispersion [154]. Simoes et al. [155] used ultrasonication to disperse CNTs on Al/Ni matrix with isopropanol as the PCA for 15 min. ...
High modulus of about 1 TPa, high thermal conductivity of over 3000 W/mK, very low coefficient of thermal expansion (CTE), high electrical conductivity, self-lubricating characteristics and low density have made CNTs one of the best reinforcing materials of nano composites for advanced structural, industrial, high strength and wear-prone applications. This is so because it has the capacity of improving the mechanical, tribological, electrical, thermal and physical properties of nanocomposites. So, this study is aimed at providing the latest discoveries on the tribological behavior of CNTs-reinforced composites. The composites reviewed included metal matrix composites (MMCs), polymer matrix composites (PMCs) and ceramic matrix composites (CMCs) reinforced with CNTs. Their tribological characteristics, uses, production challenges, conclusion and recommendations are presented. The work presented the best technique to disperse CNTs on matrices to avoid its agglomeration, since agglomeration is one of the major challenges in reinforcing with CNTs. It was discovered that ball milling destroys the outer walls of CNTs but recommended that ultrasonication and functionalization before ball milling eliminate this adverse effect of ball milling. In addition, it was discovered that addition of CNTs to composite matrices improved the wear resistance, reduced the wear volume, decreased the coefficient of friction (COF) and provided self-lubricating effect on MMCs, PMCs and CMCs.
... Graphene was prepared by exfoliation of 1 g natural graphite in 100 mL ethylene glycol in a high intensity cavitation field and pressure 5 bar for 20 min in a batch reactor UIP2000 (20 kHz, 2000W, HielscherUltrasonics, GmbH, Germany). The product was purified by dialysis (Spectra/Por3 dialysis membrane) in an ultrasonic bath in DEMI water [28]. ...
Zeolites have been investigated as sorbents of heavy metals from water. Since graphene oxide was already reported as promising radionuclide sorbent, we developed composite materials containing both a synthetic zeolite (type A, P or Y) and graphene oxide to be multifunctional sorbents. The extension of multifunctionality of sorbents was done by presence of third component, exfoliated graphite, to have additional properties as conductivity. The changing sorption activities of a composite was studied depending on its composition and functional modification. The composites, characterized by X-ray powder diffraction, Raman, FTIR spectroscopy and scanning electron microscopy, were tested for sorption of selected radionuclides (¹³⁴Cs⁺, ⁸⁵Sr²⁺) and heavy metals (Pb²⁺, Cd²⁺). The dependency on composition was found in connection with a high sorption of Pb²⁺ and Cd²⁺. Finally, optimized multifunctional sorbents (Gr-GO-COOH-A in ratio 40:40:20 and Gr:GO:A in ratio 25:25:50) were found to keep interesting high sorption activities for heavy metals and radionuclides with good conductivity properties.
... Graphene sheets were prepared by exfoliation of natural graphite (1 g) in a bath ultrasound reactor UIP 2000hd (2 kHz, max. 2000 W, Hielscher Ultrasonics GmbH, Germany) under a high pressure of 5 bar in ethylene glycol (100 mL) [43]. The product was purified by dialysis with Spectra/Por 3 dialysis membrane in demineralized water to stable conductivity and constant pH. ...
The graphene oxide (GO) interaction with methylene blue (MB) cationic dye was studied in an aqueous solution at different pH during MB adsorption. The mutual interaction of MB with GO surface was studied and evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The π-π and electrostatic interaction of MB with GO surface are the main types of interactions, and the XRD data show the monomeric arrangement of MB cation with GO. The GO surface functional groups and point of zero charge (PZC) were determined by acid-base titration. Suitability of zeta-potential measurement and acid-base titration method was briefly discussed. The quality of prepared GO was evaluated by Raman spectroscopy, XRD, and atomic force microscope (AFM). The experimental adsorption equilibrium data were analyzed using Langmuir, Langmuir-Freundlich, Freundlich, and Temkin isotherms. The GO maximum adsorption capacity increases with higher pH, that is ascribed to the facile interaction of negatively charged GO with positively charged MB structure.
... Cavitation is known as a phenomenon attributed to the formation, growth, and collapsing of vapor bubbles in a liquid under sudden changes in pressure. Stengle reported using an intensive cavitation field in a pressurized reactor for the direct preparation of graphene without any chemical agents [13]. The Sonication method can create cavitation in a liquid and have a great impact on a variety of chemical processes [14]. ...
A scalable manufacturing method for production of biocompatible few layered graphene (FLG) nanosheets is developed using hydrodynamic cavitation. Scalable exfoliation is induced by employing hydrodynamic cavitation and a serum albumin protein. Unlike acoustic cavitation, the primary means of bubble collapse in hydrodynamic cavitation is caused laterally, thereby separating two adjacent flakes through a shear effect. In this process Bovine Serum Albumin (BSA), a known protein, was employed to act as an effective exfoliation agent and provide desired stability by preventing restacking of the graphene layers. This method was used to study the effect of time of graphene exfoliation in a novel hydrodynamic cavitation system. The results showed that with increasing the time of exfoliation, the number of layers of graphene decreased based on the I2D/IGratio but disorder increased based on the ID/IGratio. At 3 hours the I2D/IGratio was at 0.39 and the ID/IGratio was 0.25, while at 6 hours the I2D/IGratio was 0.35 and ID/IGratio was 0.29. The results of the theoretical and computational analysis this research outlines is needed to obtain an optimized cavitation model that can be used to potentially improve graphene synthesis and quality.
... Graphene oxide and GO-contaminated materials were characterized and described by Zhao et al. [20]. The ultrapure GO was characterized in detail by Štengl [21], Ederer et al. [22,23], and Ahlinder et al. [24]. ...
Since biological applications and toxicity of graphene-based materials are structure dependent, studying their interactions with the biological systems is very timely and important. We studied short-term (1, 24, and 48 h) effects of ultrapure (GO) and Mn2+-contaminated (GOS) graphene oxide on normal human dermal fibroblasts (NHDF) and adenocarcinomic human alveolar basal epithelial cells (A549) using selected oxidative stress markers and cytokines: glutathione reductase (GR) and catalase (CAT) activity, total antioxidative capacity (TAC), and malondialdehyde (MDA) concentration, levels of vascular endothelial growing factor (VEGF), tumor necrosis factor-alpha (TNF-a), platelet-derived growth factor-BB (PDGF-BB), and eotaxin. GOS induced higher levels of oxidative stress, measured with CAT activity, TAC, and MDA concentration than GO in both cell lines when compared to control cells. GR activity decreased in time in NHDF cells but increased in A549 cells. The levels of cytokines were related to the exposure time and graphene oxide type in both analyzed cell lines and their levels comparably increased over time. We observed higher TNF-a levels in NHDF and higher levels of VEGF and eotaxin in the A549 cell line. Both types of cells showed similar susceptibility to GO and GOS. We concluded that the short-time exposure to GOS induced the stronger response of oxidative stress markers without collapsing the antioxidative systems of analysed cells. Increased levels of inflammatory cytokines after GO and GOS exposure were similar both in NHDF and A549 cells.
... This is called cavitation which causes potent waves of vibration that releases a massive energy in the cavitation field. This energy disrupts molecular interactions of the particles and facilitates their mixing [37]. Researchers have successfully employed ultrasonication in dispersing reinforcing phases on Al matrices. ...
Monolithic aluminium alloy lacks adequate mechanical and tribological properties necessary for optimal functionality in the industry. As a consequence, industrialists and manufacturers have experienced its frequent failures in service. This has necessitated the switch to Al matrix composites which possess better mechanical and tribological characteristics. Sintering has been one of the best fabrication methods of Al composites. However, for the fact that global cost of energy has risen tremendously, the conventional sintering has been replaced by much cheaper, unconventional sintering known as spark plasma sintering (SPS). Its popularity stems from its low energy consumption, short sintering time, and superior properties of products. In this paper, the progress made in the consolidation of aluminium matrix composites (AMCs) using spark plasma sintering, its prospects, and properties of their products were reviewed. Also, powder blending methods applied in SPS were considered.
... In this study, polar aprotic dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) were used for exfoliation of graphite as the sonication medium without addition of any surfactants or ionic liquids. Additionally, these solvents prevent the inverse segregation and micelle cumulation of graphenes by exposure to high-intensity ultrasound energy [29]. The mechanism of the graphite dispersions in solvents of DMSO and DMF is ascribed to restricted solvent layer near the graphene surface blocking the aggregation of graphene layers because of the existence of sterics in the chemical structure of these solvents [30]. ...
The liquid-phase exfoliation (LPE) method has been gaining increasing interest by academic and industrial researchers due to its simplicity, low cost, and scalability. High-intensity ultrasound energy was exploited to transform graphite to graphene in the solvents of dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), and perchloric acid (PA) without adding any surfactants or ionic liquids. The crystal structure, number of layers, particle size, and morphology of the synthesized graphene samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ultraviolet visible (UV–vis) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). XRD and AFM analyses indicated that G-DMSO and G-DMF have few layers while G-PA has multilayers. The layer numbers of G-DMSO, G-DMF, and G-PA were determined as 9, 10, and 21, respectively. By DLS analysis, the particle sizes, polydispersity index (PDI), and zeta potential of graphene samples were estimated in a few micrometers. TEM analyses showed that G-DMSO and G-DMF possess sheet-like fewer layers and also, G-PA has wrinkled and unordered multilayers.
... Hal dapat dilihat dari puncak yang dihasilkan oleh sampel tidak sesuai dengan standar dari software HSP. Menurut literatur, puncak dari grafena berkisar pada 2 theta dari 20-26 O , sedangkan untuk grafena oksida berkisar antara pada 2 Theta dari 24-26 O [20]. Kandungan sampel GS teridentifikasi masih merupakan grafit sesuai dengan standar ICSD nomor 98-005-3780. ...
Tempurung kelapa termasuk sampah organik, sehingga dapat digunakan sebagai sumber karbon alternatif. Grafit merupakan salah satu alotrop karbon yang memiliki struktur mirip sarang lebah yang terdiri dari banyak lapisan, sedangkan grafena hanya memiliki satu lapisan karbon. Untuk mensintesis grafena dapat menggunakan metode sonikasi dengan ukuran partikel grafit +200#, -200+230#, dan -230# serta waktu proses selama 30 dan 60 menit. Grafit didapatkan dari arang tempurung kelapa yang berwarna coklat dan berasal dari perkebunan kelapa di Banten. Setelah proses sonikasi, grafit masuk ke proses hidrotermal dengan dan tanpa gas nitrogen. Grafena oksida yang dihasilkan dikarakterisasi menggunakan Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), dan scanning electron microscopy (SEM). Berdasarkan hasil XRD, sampel yang telah sonikasi masih berbentuk grafit oksida. Hal ini didukung dengan hasil SEM yang memiliki morfologi yang berpori dan belum transparan serta tidak terdeteksinya titik 2D pada karakterisasi Raman. Pada karakterisasi FTIR, terdapat ikatan C=C. Berdasarkan karakterisasi Raman, sampel GV 24 menunjukan rasio iD/iG sebesar 0,84. Pada karakterisasi FTIR terdeteksi ikatan O-H, ikatan C-H, dan ikatan C=C. Morfologi permukaan terlihat lebih transparan dari grafit yang telah disonikasi. Berdasarkan karakterisasi Raman, sampel GH 4 menunjukan rasio iD/iG sebesar 0,84. Pada karakterisasi FTIR terdeteksi ikatan O-H, ikatan C=C, dan ikatan C-O. Morfologi permukaan lebih transparan yang menandakan bahwa grafit telah terkelupas. Hasil penelitian menunjukan bahwa semakin lama proses sonikasi dan ukuran partikel -200# +230# menciptakan lapisan yang transparan dan tipis serta menghasilkan grafena oksida setelah melalui proses hidrotermal. Coconut shell is an organic waste and can be used as an alternative carbon source. Graphite is one of the carbon allotropes which has a honeycomb-like structure consisting of many layers, whereas graphene has only single carbon layer. To synthesize graphene, sonication method used by using graphite particle size +200#, -200# +230# and -230#, and processing time of 30 and 60 minutes. Graphite was obtained from brown coconut shell charcoal and comes from coconut plantations in Banten. After the sonication process, graphite processed by hydrothermal method with and without nitrogen gas. Characterization of graphene oxide was done by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the XRD results, the sonicated sample is still in the form of graphite oxide. This is supported by SEM results that have porous morphology and are not transparent and 2D peaks are not detected in Raman characterization. In FTIR characterization, there is a C=C bond. Based on Raman characterization, the GV 24 sample shows an iD/iG ratio of 0.84. In FTIR characterization O-H bonds, C-H bonds, and C=C bonds were detected. Surface morphology looks more transparent than graphite that has been sonicated. Based on Raman characterization, the GH 4 sample shows an iD / iG ratio of 0.84. In FTIR characterization O-H bonds, C=C bonds, and C-O bonds were detected. The surface morphology is more transparent which indicates that the graphite has been peeled off. The results showed that the longer the sonication process and particle size -200# +230# creates a transparent and thin layer and produces graphene oxide after going through the hydrothermal process.
... Therefore, this presents an eco-friendly favorable method likely attractive for industrial preparation. Similar method has also been studied for the synthesis of graphene monolayers [3,4]. ...
The thickness and size-dependent characteristics of MoS2 nanosheets lead to the use of this material for basic science research and industrial applications. Until the date, scalable production of MoS2 nanosheets without the addition of any surfactant and hazardous chemicals remains challenging. Our study reports the synthesis of a few layers of MoS2 nanosheets by the use of the liquid-phase exfoliation technique. As-synthesized nanosheets were characterized by UV-Visible spectroscopy, atomic force microscopy (AFM), photoluminescence (PL) and Raman spectroscopy techniques. Our straightforward and efficient preparation directs to very strongly blue luminescing nanosheets.
... In this study, polar aprotic dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) were used for exfoliation of graphite as the sonication medium without addition of any surfactants or ionic liquids. Additionally, these solvents prevent the inverse segregation and micelle cumulation of graphenes by exposure to high-intensity ultrasound energy [29]. The mechanism of the graphite dispersions in solvents of DMSO and DMF is ascribed to restricted solvent layer near the graphene surface blocking the aggregation of graphene layers because of the existence of sterics in the chemical structure of these solvents [30]. ...
Graphene has created an increasing notice thanks to its appealing properties [1]. In this study, graphene was prepared from graphite by a very simple and easy process. The one-step protocol involves conversion of graphite to graphene by sonication in different types of solvents such dimethyl sulfoxide, N,N-Dimethyl formamide, Perchloric acid. The structures and properties of the obtained graphene samples were characterized via UV–vis absorption, and Atomic Force Microscopy spectroscopic techniques. According to the UV-vis spectrums of all graphene products give peak at 265 nm wavelengths that referring sp2 C=C bonds [2], which may be caused by the ultrasonication required for proper suspension using the solution-based process. Also, as a result of AFM analyses, it can be concluded that the obtained graphene samples contain a few layers; while G-DMSO has four layers, G-NNDMF has five layers. It can be understand that DMSO shows better effect on graphite for sonication process. The preparation protocol is simple, easy, eco-friendly.
... These results are in good agreement with published reports. [43] The images of the fiber coated with hydrogel, AgNPs and G, using and without using IL, are shown in Figure 9. It is clearly seen in Figure 9a that sample without using IL shows a more heterogeneous G particles distribution. ...
This study presents the fabrication and characterization of cotton textile fibers coated with hydrogels containing silver and Graphene or Graphene Oxide nanoparticles using 1-hexyl-3-methyl-imidazolium (HMIMPF6) ionic liquid (IL) as carbon filler dispersant. Acrylic acid/Itaconic acid (AA-IA) hydrogels are synthesized by polymerizing an acrylic acid-itaconic acid aqueous (80/20 v/v) solution and mixed with 2-2-Azobis (2-methylpropionamide) diclorohydrate, and N,N´-methylenbis (acrylamide). Then silver nanoparticles are generated throughout the hydrogel networks using in situ method by incorporating the silver ions and subsequent reduction with sodium borohydride. Then a cotton textile fiber substrate was coated with this hydrogel. Finally, graphene or graphene oxide was added to the textile substrate already impregnated with hydrogel and silver nanoparticles. In order to favor the dispersion of the carbon nano-structures in the system, an IL was used. The influence of these nanocomposite hydrogels on the properties of textile fiber were investigated by infrared spectroscopy (ATR), scanning electron microscopy (SEM), inductively coupled plasma mass spectroscopy (ICP) and antibacterial tests against Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative). The effect of each and combined fillers dispersion on antimicrobial properties were determined. Cotton fibers coated with hydrogel containing silver nanoparticles and graphene showed better results when the ionic liquid was used. Graphene showed greater antimicrobial efficiency than graphene oxide. It was proved that the textiles coated with hydrogels containing these fillers had an excellent antibacterial ability and are a good option to be used for medical applications such as wounds and burns dressing.
... GO was prepared by a slight modification of our original procedure based on high-power ultrasonication of natural graphite, which we previously employed to synthesize low-dimensional materials such as graphene [31] or MoS 2 [32] nanosheets. A more detailed procedure of the GO synthesis is given in the electronic supplementary material (ESM). ...
Two water-based methods were used to produce TiO2/graphene oxide (GO) nanocomposites with 1 and 2 wt.% GO. Both procedures exclude the use of organometallic precursors, as well as the high-pressure and high-temperature treatments, which facilitate pure and energy efficient synthesis amenable for larger scale synthesis. Nanocomposites with narrow (<10 nm) and long spindle-like (<100 nm) TiO2 nanoparticles supported on GO flakes were obtained (TiO2/GO), and their properties for reactive destruction of the organophosphorus simile chemical warfare agent (CWA) dimethyl methylphosphonate (DMMP) were investigated by in situ DRIFTS spectroscopy. Both synthesis procedures yielded highly reactive nanocomposites with markedly different properties compared to similarly prepared pure TiO2 nanoparticles. GO also induced morphology and texture changes, which were observed to have a significant impact on the adsorption and reactivity of the nanocomposites, and which were strongly related to synthesis procedure. In particular, the reduction state of GO, as measured by Raman spectroscopy, was observed to play a major role for the reactivity of the TiO2/GO nanocomposites.
... The synthetic routes used in this work to prepare GO differ in some aspects from the classical Hummers method [37], which typically uses concentrated strong acids and oxidants to oxidize graphite directly to GO. In our work, graphene was prepared from graphite by exfoliation in ethylene glycol using the procedure developed by Štengl et al. [38]. Then, the resulting material was converted to GO by oxidation with permanganate. ...
... As the sonication time increases, the width of the flakes reduces significantly. The deformation of graphite particle may also be caused due to the mechanical shockwaves and shear forces created by the violent collapse of bubbles during ultrasonic treatment ( Ref 39,40). As the ultrasonication time is increased, the particle tends to break the basal plane and cracks similar to Mrozowski cracks (Ref 41) may be assumed to have formed in the basal plane (indicated by arrows in Fig. 4d) which breaks the graphite sheets further to form graphite nanoparticles. ...
A novel approach to produce Al-2 vol.% graphite nanocomposites using micron-sized graphite particles has
been reported using conventional stir casting technique combined with ultrasonic treatment. Microstructural
observations indicate that the visible agglomerations and porosities are significantly reduced after
ultrasonic treatment. Transmission electron microscopy studies of ultrasonic-treated composites reveal that
the size of the graphite particles is reduced substantially and its morphology is transformed into flake type
structures. The width of the graphite flakes is reduced markedly with the increase in ultrasonic processing
time and it is found to be in the range of 100-120 nm with an aspect ratio of 8.83 after 5 min of ultrasonication.
Added to that, considerable improvement in the hardness values are noted for ultrasonic-treated
Al-2 vol.% graphite composites when compared to conventional untreated composites. The mechanism
behind the significant reduction in graphite particle size and porosity, uniform distribution of graphite
particles and hardness increments are discussed.
... As the sonication time increases, the width of the flakes reduces significantly. The deformation of graphite particle may also be caused due to the mechanical shockwaves and shear forces created by the violent collapse of bubbles during ultrasonic treatment ( Ref 39,40). As the ultrasonication time is increased, the particle tends to break the basal plane and cracks similar to Mrozowski cracks (Ref 41) may be assumed to have formed in the basal plane (indicated by arrows in Fig. 4d) which breaks the graphite sheets further to form graphite nanoparticles. ...
7 8 A novel approach to produce Al-2 vol.% graphite nanocomposites using micron-sized graphite particles has 9 been reported using conventional stir casting technique combined with ultrasonic treatment. Microstruc-10 tural observations indicate that the visible agglomerations and porosities are significantly reduced after 11 ultrasonic treatment. Transmission electron microscopy studies of ultrasonic-treated composites reveal that 12 the size of the graphite particles is reduced substantially and its morphology is transformed into flake type 13 structures. The width of the graphite flakes is reduced markedly with the increase in ultrasonic processing 14 time and it is found to be in the range of 100-120 nm with an aspect ratio of 8.83 after 5 min of ultra-15 sonication. Added to that, considerable improvement in the hardness values are noted for ultrasonic-treated 16 Al-2 vol.% graphite composites when compared to conventional untreated composites. The mechanism 17 behind the significant reduction in graphite particle size and porosity, uniform distribution of graphite 18 particles and hardness increments are discussed. 19 20
... Experimental: Graphene was prepared by exfoliation of graphite using high intensity ultrasound in a pressure reactor [1], Graphene oxide was synthesized by modified Hummer's method [2]. The carbon nanostructures (10 ug/ml) were added to EM-G3 cells and incubated 48 h at 37°C. ...
Introduction: The study results show that surfaces treated with carbon nanostructures such as fullerenes, carbon nanotubes, graphene [1] and graphene oxide in themselves exhibit antibacterial properties. Suitably functionalized carbon nanotubes, graphene and graphene oxide mainly may be used as carriers for cytostatic agents in the targeted treatment of oncological diseases.
Methods: Cells from the breast cancer cell line and lung epithelial cells were exposed to aqueous colloidal solutions of graphene oxide and single walled carbon nanotubes (SWCN), then incubated and examined the effect of graphene oxide and carbon nanotubes on viability and structural changes in cells. The bio-distribution of nanoparticles into the cell body to the subcellular level was monitored by Raman spectroscopy and high resolution transmission electron microscopy. As a model cell population for our study a clonal cell line, EM-G3 and A549 lung epithelial cells (ATCC CCL-185; American Type Culture Collection) was used. The EM-G3 line was derived from a primary lesion of human infiltrating ductal breast carcinoma. Cells were cultured in RPMI-1640 supplemented with 10% fetal calf serum and 50 mg ml gentamicin at 37°C in a humidified atmosphere with 5% CO2 [2].
Disscussion: Nanoparticles are unlike other particles able to enter biological membranes into cells, tissues and organs. They penetrate into mitochondria and cell nuclei.
Conclusion: Studies have proven the possibility of graphene and graphene oxide to induce DNA mutations and structural changes in mitochondria, even leading to cell death.
... Experimental: Graphene was prepared by exfoliation of graphite using high intensity ultrasound in a pressure reactor [1], Graphene oxide was synthesized by modified Hummer's method [2]. The carbon nanostructures (10 ug/ml) were added to EM-G3 cells and incubated 48 h at 37°C. ...
Introduction: The study results show that surfaces treated with carbon nanostructures such as fullerenes, carbon nanotubes, graphene [1] and graphene oxide in themselves exhibit antibacterial properties. Suitably functionalized carbon nanotubes, graphene and graphene oxide mainly may be used as carriers for cytostatic agents in the targeted treatment of oncological diseases.
Methods: Cells from the breast cancer cell line and lung epithelial cells were exposed to aqueous colloidal solutions of graphene oxide and single walled carbon nanotubes (SWCN), then incubated and examined the effect of graphene oxide and carbon nanotubes on viability and structural changes in cells. The bio-distribution of nanoparticles into the cell body to the subcellular level was monitored by Raman spectroscopy and high resolution transmission electron microscopy. As a model cell population for our study a clonal cell line, EM-G3 and A549 lung epithelial cells (ATCC CCL-185; American Type Culture Collection) was used. The EM-G3 line was derived from a primary lesion of human infiltrating ductal breast carcinoma. Cells were cultured in RPMI-1640 supplemented with 10% fetal calf serum and 50 mg ml gentamicin at 37°C in a humidified atmosphere with 5% CO2 [2].
Disscussion: Nanoparticles are unlike other particles able to enter biological membranes into cells, tissues and organs. They penetrate into mitochondria and cell nuclei.
Conclusion: Studies have proven the possibility of graphene and graphene oxide to induce DNA mutations and structural changes in mitochondria, even leading to cell death.
... Graphene was produced in large quantity from natural graphite (Koh-i-noor Grafite Ltd. Czech republic) using high intensity cavitation field in a pressure batchultrasonic reactor (UIP 2000hd, 20 kHz, 2000 W, Hielscher Ultrasonics GmbH) [9]. Graphene oxide was prepared by our safety method, a 60 ml of H 2 SO 4 and 10 ml of H 3 PO 4 , 1 g of graphene and 3 g of KMnO 4 were mixed in round bottom flask. ...
Background: Graphene oxide composites with photocatalysts may exhibit better properties than pure
photocatalysts via improvement of their textural and electronic properties.
Results: TiO2-Graphene Oxide (TiO2 - GO) nanocomposite was prepared by thermal hydrolysis of suspension with
graphene oxide (GO) nanosheets and titania peroxo-complex. The characterization of graphene oxide nanosheets
was provided by using an atomic force microscope and Raman spectroscopy. The prepared nanocomposites
samples were characterized by Brunauer–Emmett–Teller surface area and Barrett–Joiner–Halenda porosity, X-ray
Diffraction, Infrared Spectroscopy, Raman Spectroscopy and Transmission Electron Microscopy. UV/VIS diffuse
reflectance spectroscopy was employed to estimate band-gap energies. From the TiO2 - GO samples, a 300 μm thin
layer on a piece of glass 10×15 cm was created. The photocatalytic activity of the prepared layers was assessed
from the kinetics of the photocatalytic degradation of butane in the gas phase.
Conclusions: The best photocatalytic activity under UV was observed for sample denoted TiGO_100
Functional nanomaterial graphene and its derivatives have attracted considerable attention in many fields because of their unique physical and chemical properties. Most notably, graphene has become a research hotspot in the biomedical field, especially in relation to malignant tumors. In this study, we briefly review relevant research from recent years on graphene and its derivatives in tumor diagnosis and antitumor therapy. The main contents of the study include the graphene-derivative diagnosis of tumors in the early stage, graphene quantum dots, photodynamics, MRI contrast agent, acoustic dynamics, and the effects of ultrasonic cavitation and graphene on tumor therapy. Moreover, the biocompatibility of graphene is briefly described. This review provides a broad overview of the applications of graphene and its derivatives in tumors. Conclusion, graphene and its derivatives play an important role in tumor diagnosis and treatment.
Tremendous research efforts have recently focused on the synthesis of graphene from graphitic materials, while environmental issues, scalability, and cost are some of the major challenges to be surmounted. Liquid phase exfoliation (LPE) of graphene is one of the principal methods for this synthesis. Nevertheless, sufficient information about the mechanisms of exfoliation has yet to emerge. Here, a microreactor based on the hydrodynamic cavitation (HC) on a chip concept is introduced to exfoliate graphite in a totally green process which involves only natural graphite flakes and water. HC-treated graphitic materials were characterized by UV-Vis and Raman spectroscopy, DLS (Dynamic Light Scattering), AFM (Atomic Force Microscopy), and SEM (Scanning Electron Microscopy) analyses. The present sustainable reactor system was found to exfoliate thick and large graphite particles to nano-sized sheets (∼1.2 nm) with a lateral size of ∼500 nm to 5 μm.
Among the many potential applications of graphene and graphene-based materials, their use as protective films or as additives in coatings for corrosion protection has seen an increased level of interest in the last decade. Much of this interest is motivated by the need to implement additional functionalities, to enhance anti-corrosion performance and to ultimately extend the service life of metallic structures. Pristine graphene films, with their impermeable nature allied to flexibility and mechanical strength, appear as particularly attractive candidates for barrier films against corrosive agents, while graphene-based materials such as graphene oxide and reduced graphene oxide offer a wide range of opportunities for their dispersion in polymeric matrices for composite anti-corrosive coatings. Simultaneously, considerable progress in the development of scalable graphene and graphene-based materials production techniques has been made during the last several years. Currently, a broad range of graphene materials with different morphologies and properties is available, making the need for an adequate fit between the production method and the desired application even more evident. This review article aims to give the reader a general overview of the recent trends in both the production of graphene and graphene-based materials, and their implementation in different anti-corrosion solutions. Moreover, the present work provides a critical look on this subject, highlighting the areas in need of further exploration.
Graphene and two-dimensional (2D) materials have experienced an outstanding development in the last few years. The confinement of the carriers and the improved electrostatic control in the thin channels of fabricated devices have demonstrated surprising results in terms of electrical, photonic, and mechanical properties. However, these properties are still dependent on the fabrication process. Thickness, roughness, scalability, mobility, or defect density are closely related to the specific synthesis method. In this chapter, we describe the main synthesis methods for the fabrication of graphene and other 2D materials with extraordinary properties. Potentially, the van der Waals interaction between 2D crystals offer a platform for alternating disparate atomic layers in both vertical and lateral fashion, creating hybrid heterostructures with a variety of exciting physical phenomena in increasingly sophisticated devices.
Liquid Phase Exfoliation (LPE) method has been gaining increasing interest by academic and industrial researchers due to its simplicity, low-cost, and scalability. High intensity ultrasound energy was exploited to transform graphite to graphene in the solvents of dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), and perchloric acid (PA) without any surfactants or ionic liquids. The crystal structure, number of layers, particle size, and morphology of the synthesized graphene samples were characterized by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Ultraviolet visible (UV–vis) spectroscopy, Dynamic Light Scattering (DLS), and Transmission Electron Microscopy (TEM). XRD and AFM analyses indicated that G-DMSO and G-DMF have few layers and G-PA has multilayers. The layer numbers of G-DMSO, G-DMF, and G-PA were determined as 9, 10, and 21, respectively. By DLS analysis, the particle sizes of graphene samples were estimated in a few micrometers. TEM analyses showed that G-DMSO and G-DMF possess sheet-like fewer layers and also, G-PA has wrinkled and unordered multilayers.
The carbon nanomaterials and congeners, e.g., graphene or graphene oxide (GO), dispose of numerous unique properties, which are not necessarily intrinsic but might be related to a content of impurities. The oxidation step of GO synthesis introduces a considerable amount of metallic species. Therefore, large-scale purification is an actual scientific challenge. Here we describe new purification technique (salt‑washing), which is based on three consecutive steps: (a) aggregation of GO sheets with NaCl (b) washing of the aggregates and (c) removing of the salt to afford purified GO (swGO). The considerably improved purity of swGO was demonstrated by ICP and EPR spectroscopy. The microscopic methods (TEM with SEAD, AFM) proved that the salt-washing does not affect the morphology or concentration of defects, showing the aggregation of GO with NaCl is fully reversible. The eligibility of swGO for biomedical applications was tested using fibroblastic cell cultures. The determined IC50 values clearly show a strong correlation between the purity of samples and cytotoxicity. Although the purification decreases cytotoxicity of GO, the IC50 values are still low proving that cytotoxic effect is not only impurities-related but also an intrinsic property. These findings may represent a serious limitation for usage of GO in biomedical applications.
In this work, experiments and molecular dynamics (MD) simulations are carried out to explore the synergistic effect of supercritical CO2 (scCO2) and organic solvent on intercalation and exfoliation of graphene. Experimental characterizations via transmission electron microscopy, atomic force microscopy and Raman spectroscopy indicate that by combining scCO2 and organic solvent (N-methylpyrrolidone, NMP) few layer graphene is successfully exfoliated from graphite, among which over 30% is 1–4 layers, 55% is 5–8 layers. Systematic experiments have shown that compared with pure scCO2 or NMP, the mixed scCO2 and NMP can significantly increase the amount of graphene and reduce the exfoliation time, and the optimum volume fraction of NMP is 25%. Parallel MD simulations indicate that the scCO2 molecules first diffuse into the interlayer of graphite, and then the larger NMP molecules insert as wedges and further expand interlayer spacing, promoting intercalation and exfoliation. The iteration of scCO2 diffusion and NMP wedge can generate a positive feedback to improve the exfoliation productivity and efficiency. This work explores the synergistic effect of scCO2 and NMP on exfoliation of graphene, which may provide useful insights for exfoliation of other two dimensional materials.
The past decades have witnessed rapid advances in two dimensional (2D) materials as they carry a stellar set of unique properties over their bulk counterparts. Two families of 2D materials, namely, layered 2D materials and nonlayered 2D materials, have garnered considerable attention. Layered 2D materials have been widely used in electronic devices, catalysis, and bioelectronics due to their tunable energy band structure, superlative physical and chemical properties. By contrast, dangling bonds on the surface of non-layered 2D materials and intrinsic crystal distortion render them with abundant active sites for use in energy storage and photodetectors. In the context, the ability to effectively exfoliate 2D materials is the key to these applications. This review highlights the recent developments pertaining to exfoliation techniques applicable to 2D layered and non-layered materials and the corresponding exfoliation mechanisms. In particular, some emerging exfoliation techniques are emphasized. Subsequently, how these exfoliation techniques facilitate the applications of 2D materials in electronic devices, catalysis, lithium ion batteries, and supercapacitors is summarized. Finally, an outlook is provided with an aim to lay out the promising future research directions on 2D materials produced by exfoliation approaches.
Since the first intercalation of layered silicates by using supercritical CO2 as a processing medium, considerable efforts have been dedicated to intercalating and exfoliating layered two‐dimensional (2D) materials in various supercritical fluids (SCFs) to yield single‐ and few‐layer nanosheets. Here, recent work in this area is highlighted. Motivating factors for enhancing exfoliation efficiency and product quality in SCFs, mechanisms for exfoliation and dispersion in SCFs, as well as general metrics applied to assess quality and processability of exfoliated 2D materials are critically discussed. Further, advances in formation and application of 2D material–based composites with assistance from SCFs are presented. These discussions address chemical transformations accompanying SCF processing such as doping, covalent surface modification, and heterostructure formation. Promising features, challenges, and routes to expanding SCF processing techniques are described. Here, recent advances in exfoliation and modification of layered two‐dimensional (2D) materials in various supercritical fluids (SCFs) are highlighted. The motivating factors for enhancing exfoliation efficiency and product quality in SCFs, mechanisms for exfoliation and dispersion in SCFs, as well as general metrics applied to assess quality and processability of exfoliated 2D materials are critically discussed.
Solar light-induced photodecomposition of organophosphorus simile warfare agent dimethyl methylphosphonate (DMMP) on the surfaces of TiO2/graphene oxide (GO) nanocomposites was studied by in situ DRIFT spectroscopy. Nanocomposites containing 1 and 2 wt.% GO, respectively, were prepared by two different aqueous methods. All nanocomposites were shown to effectively adsorb and partly dissociate DMMP as shown by the formation of surface coordinated methoxy groups. Solar light illumination induced rapid decomposition of the adsorbed species to yield variously ionic and surface coordinated formate and carbonate species as the main intermediate products. Both the kinetics of adsorbed species decomposition and the formation of various intermediates were strongly affected by the presence of GO, as compared to pure TiO2 nanoparticles. The two synthesis routes yielded nanocomposites with different degree of reduction of GO that correlated with their reactivity towards DMMP adsorption and photodegradation. Upon illumination, rapid depletion of water was observed on the TiO2/GO nanocomposites and was attributed to a water splitting reaction, which competed with the DMMP photo-oxidation reaction.
Research and development in graphene synthesis have been rapidly growing the past few years because of their extraordinary physical, mechanical, thermal, electrical and optical properties. Graphene flakes, one of the most popular form of graphene, can be used for many applications such as conductive inks, nanofluids, supercapacitors, composites etc. Synthesis of graphene flakes is indeed in the path to reach the large-scale production even if cost of production and efficiency are required to be further improved. This review sheds light on the recent advancements of graphene flake synthesis and it gives a comprehensive analysis of the synthesis methods. Keys for further improvements are proposed based on the mechanisms involved in the graphene flake formation.
The simple method for preparation of nanocomposites of graphene oxide or carboxylated graphene oxide on polystyrene matrix and graphene oxide on PA66 matrix were developed and structures of nanocomposites were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The nanocomposites were investigated for radiostrontium removal from aqueous solutions. The Sr(II) sorption was dependent on pH and ionic strength at pH < 7. The Sr(II) equilibrium data were fitted by Freundlich and Langmuir models. The nanocomposites prepared were evaluated as suitable for the radiostrontium removal from contaminated wastewater.
The PtCo-graphene/carbon dots/graphene (PtCo/GCG) electrocatalyst was prepared on a glassy carbon electrode via electrodeposition of PtCo nanoparticles onto the sandwich-structured graphene/carbon dots/graphene (GCG) composite. The obtained PtCo/GCG electrocatalyst has been characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and also electrochemical measurements. Structure characterization indicates that the PtCo/GCG catalyst has good layered graphene morphology, with PtCo nanoparticles uniformly dispersed between the graphene layers. Electrochemical results indicate that PtCo/GCG catalyst has much better electrocatalytic activity and stability toward methanol oxidation when compared with PtCo/graphene and Pt catalysts. The improved performance is mainly owing to the embedding of carbon dots into the graphene layers, and the synergistic effect between Pt and Co nanoparticles. Carbon dots effectively adsorbed onto graphene layers, which increase the electrical conductivity, enhance the dispersion of PtCo nanoparticles, and subsequently enlarge the reactive surface area with more active sites.
Amino-functionalized graphene oxide was reacted with isocyanate monomer to evaluate the potential application of GO-NH2 as a functional filler for the preparation of polyurethane nanocomposites. A set of advanced techniques (XRD, FTIR spectroscopy, Raman spectroscopy, and TEM) was used to characterize the functionalized samples, together with elemental analysis and XPS, which provided valuable information on the total N content and the nitrogen (chemical) speciation, respectively. In addition, a simple and fast spectrophotometric method was developed for the estimation of accessible amino groups (functional speciation). The method is based on the interaction of NH2 groups with the anionic dye acid orange 7 under appropriate conditions (pH = 3.6) and shows good precision. It can be advantageously used for the fast evaluation of the GO-NH2 reactivity with isocyanate monomer and its applicability as the polymer filler.
The preparation of dispersions of single- and few-sheet 2D materials in various solvents, as well as the characterization methods applied to such dispersions, are critically reviewed. Motivating factors for producing single and few-sheet dispersions of 2D materials in liquids are briefly discussed. Many practical applications are expected for such materials that do not require high purity formulations and tight control of donor and acceptor concentrations, as required in conventional Fab processing of semiconductor chips. Approaches and challenges encountered in exfoliating 2D materials in liquids are reviewed. Ultrasonication, mechanical shearing, and electrochemical processing approaches are discussed, and their respective limitations and promising features are critiqued. Supercritical and more conventional liquid and solvent processing are then discussed in detail. Effects of various types of stabilizers, including surfactants and other amphiphiles, as well as polymers, including homopolymeric electrolytes, nonionic polymers, and nanolatexes. Consideration of apparent successes of stabilizer-free dispersions indicates that extensive exfoliation in the absence of dispersing aids results from processing-induced surface modifications that promote stabilizing 2D material/solvent interactions. Also apparent paradoxes in “pristineness” and optical extinctions in dispersions suggest that there is much we do not yet quantitatively understand about the surface chemistry of these materials. Another paradox, emanating from modeling dilute solvent-only exfoliation by sonication using polar components of solubility parameters and surface tension for pristine graphene with no polar structural component, is addressed. This apparent paradox appears resolved by realizing the reactivity of graphene to addition reactions of solvent radicals produced by sonolysis. is accompanied by unintended polar surface modifications that nucleate attractive interactions with solvent. This hypothesis serves to define important theoretical and experimental studies that are needed. We conclude that the greatest promise for high volume and high concentration processing lies in applying methods that have not yet been extensively reported, particularly wet comminution processing using small grinding media of various types.
A graphene oxide-mesoporous birnessite-type δ-MnO2 nanocomposite (GO-MnO2) was prepared by thermal hydrolysis of suspension potassium permanganate (KMnO4), 2-chloroacetamide and with graphene oxide (GO) in aqueous solution. The prepared nanocomposites samples were characterized by Brunauer–Emmett–Teller surface area (BET) and Barrett–Joiner–Halenda porosity, X-ray Diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and high-resolution transmission electron microscopy (HRTEM) with energy dispersive x-ray spectroscopy (EDS) for create the map of elements. The degradation activity of the prepared samples was assessed from the kinetics of the stoichiometric degradation of parathion methyl (PM) in the polar solution (acetonitrile). It was shown that prepared samples were effective in decomposition of PM by cleavage of the P-O-aryl bond in the pesticide molecule. The degradation mechanism for PM on the GO-MnO2 surfaces was proposed.
Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecules and development of new biosensors owing to their improved electron transfer kinetics compared to pristine graphene. Here, we report complex electrochemical behavior and electrocatalytic performance of variously fluorinated graphene derivatives prepared by reaction of graphene with a nitrogen-fluorine mixture at 2 bars pressure. The fluorine content was simply controlled by varying the reaction time and temperature. The studies revealed that electron transfer kinetics and electrocatalytic activity of CFx strongly depend on the degree of fluorination. The versatility of fluorinated graphene as a biosensor platform was demonstrated by cyclic voltammetry for different biomolecules essential in physiological processes, i.e. NADH, ascorbic acid and dopamine. Importantly, the highest electrochemical performance, even higher than pristine graphene, was obtained for fluorinated graphene with the lowest fluorine content (CF0.084) due to its high conductivity and enhanced adsorption properties combining - stacking interaction with graphene regions with hydrogen-bonding interaction with fluorine atoms.
Since supercritical fluids possess low interfacial tension, excellent wetting of surfaces and high diffusion coefficients, they have been employed to intercalate and delaminate tightly-stacked layered materials such as silicates. In recent years, many researchers have begun to explore the possibility of using SCFs as intercalators to penetrate into the nano-gaps of graphite, and exfoliate it into graphene sheets. Although this SCFs intercalation and exfoliation approach is experimentally confirmed to be efficient and promising to produce graphene in large-scale with low-cost, it does not receive the attention it deserves. To arouse interest and reflection on this approach, this review is organized to summarize the recent progress in graphene production by SCFs technology. In this review, the process of SCFs intercalation and exfoliation method is decomposed into three stages, the mechanisms and influence factors for each stage are analyzed, the recommendations for graphene quality improvement are provided, the advantages and challenges of SCFs technology on graphene large-scale production are also summarized. Besides the ability of efficient intercalation, supercritical water or alcohol also can be used as reducing agents to produce reduced graphene oxide from graphene oxide, this SCFs reduction approach is also included in this review.
The study reported herein describes for the first time a method for producing defect-free graphene directly from its mineral ore. This was achieved by treating graphite ore in an ionic liquid containing biphasic solvent system, applying pressurized intense cavitation ultrasound. Without any graphite ore pre-treatment, large few layer thick graphene sheets, as well as micrometric layered crumpled graphene structures, were produced. This opens new opportunities for the development of graphene-based technologies.
Natural raw mineral tungstenite (WS2) was exfoliated to single-layer sheets using high intensity ultrasound. Exfoliation of bulk layered materials, such as WS2 by ultrasound is an attractive way to a large-scale preparation of mono- or few-layered crystals. To evaluate the quality of delamination, X-ray diffraction, Raman spectroscopy and microscopic techniques (TEM and AFM) were employed. The obtained exfoliated product served as a precursor for quantum dot preparation using simple refluxing in ethylene glycol. The synthesized WS2 quantum dots were characterized by photoluminescence spectroscopy and AFM microscopy. Exfoliated WS2 can thus join the group of similarly prepared single-layers of MoS2 or graphene. This journal is
With high carrier mobility and low cost, reduced graphene oxide (RGO) shows bright prospects for use in the field of thermoelectric materials. To investigate the intrinsic thermoelectric properties of RGO sheets, we prepared RGO papers which were reduced by HBr solution for 5 min, 20 min, and 60 min, respectively. Thermogravimetry analysis (TGA) and Raman analysis showed that the conjugated carbon network of graphene oxide (GO) was restored during the reduction process and the thermal stability of the RGO papers was much better than that of GO paper. The RGO paper that was reduced for 60 min and then annealed in Ar/H2 atmosphere exhibited the highest electrical conductivity of 3.22 × 105 S/m at 160°C. As the reduction degree of the RGO paper deepens, the Seebeck coefficient gradually transforms from positive to negative, indicating that the conduction type of RGO paper can be controlled by regulating the reduction degree.
Since its discovery, graphene and its oxidized form, graphene oxide (GO), have attracted interest in a wide range of technical applications. Concerns about their potential toxicity calls for scrutinized studies, but hitherto conflicting results have been reported which partly may be due to variations of synthesis and exposure procedures. Here we report on the attachment and toxicity of contamination-free graphene oxide nanoparticles (GONP) in living lung epithelial cells. The synthesis of chemically pure GONP was made by an improvement of Hummer’s method based on graphene exfoliated from graphite using high-intensity ultrasonication, resulting in two dimensional sheets with a lateral dimension in the range 200 nm to 3 µm and thickness of 0.9 nm. Confocal Raman spectroscopy combined with multivariate analysis was used to study the interaction of GONP and living cells. It is shown that overlapping Raman bands due to GONPs and biomolecules in the cells can clearly be separated with this approach. Orthogonal partial least squares discriminant analysis was used to compare spectral data collected from cells exposed to GONP with spectral data collected from non-exposed control cells, and spectral data from cells exposed to a surfactant known to induce apoptosis. Our analyses show that GONP readily attach to the cells, forming sheets which cover large fraction of the cell surfaces, and induce small chemical changes. In particular, chemical modifications of proteins and lipids in lung epithelial cells are inferred. GONPs do not, however, decrease cell viability. In contrast, enhanced cell proliferation is observed. Our results shed new light on the interactions of GO, and in contrast to some previous reports, suggest that GO is not toxic. The hyperspectral Raman spectroscopy analysis employed here should be applicable for other fields in nanomedicine as a label-free non-perturbing analytical method.
Monolayer nanosheets of h-BN and h-BCN were prepared by high intensity ultrasound in a pressurized batch reactor. Exfoliation of bulk layered materials using ultrasound is an attractive route to large-scale preparation of monolayer crystals. To evaluate the quality of exfoliation and structural properties, XRD, XPS, SAED, BET and porosity, and microscopy techniques (HRTEM, AFM) were employed. The diffuse IR and Raman spectroscopy were used to determine spectral properties. Thus, the prepared monolayer nanosheets served as a precursor for the synthesis of strong luminescent quantum dots. The BN Quantum Dots (BN-QDTs) and BCN Quantum Dots (BCN-QDTs) were characterized by AFM, photoluminescence spectroscopy and AFM particle size analysis. Our easy preparation lead to the production of very strong blue-green luminescent quantum dots.
Carbon nanotubes [CNTs] have excellent electrical, mechanical, optical and thermal properties. However, efficient dispersion of CNTs in any medium requires their functionalization. In this work, CNTs prepared from the catalytic process have been functionalized under three different conditions using the same acid oxidizing media. The effect of the reaction conditions on the CNTs, in terms of the extent of covalent functionalization has been determined by employing SEM, FTIR, XRD, Zeta meter, UV, Oxygen percentage analysis, Boehm's titration and visual dispersion as the characterization techniques . Results show that CNTs functionalized by reflux in the oxidizing acid are the best dispersed.
Nanocomposites of thermoplastic polyurethane (TPU), which were prepared using two types of functionalized graphene sheets
(FGS) of similar thickness but different sizes were examined. The percolation threshold of the nanocomposite was reduced,
evidently by increasing the particle size of the FGS. This means that the FGS with a mean particle size of 8.3 μm had a percolation
threshold at 0.39 wt% in the nanocomposite of TPU, whereas it was 1.41 wt% when the FGS size was 2.4 μm. The FGS enhanced
the modulus of TPU through a reinforcing effect but both the tensile strength and elongation at break were reduced as the
FGS content was increased. These effects of FGS on the tensile properties were more evident with a larger particle size of
FGS. The morphology and thermal properties of the nanocomposites were also examined.
Graphenes with varying number of layers can be synthesized by using different strategies. Thus, single-layer graphene is prepared by micromechanical cleavage, reduction of single-layer graphene oxide, chemical vapor deposition and other methods. Few-layer graphenes are synthesized by conversion of nanodiamond, arc discharge of graphite and other methods. In this article, we briefly overview the various synthetic methods and the surface, magnetic and electrical properties of the produced graphenes. Few-layer graphenes exhibit ferromagnetic features along with antiferromagnetic properties, independent of the method of preparation. Aside from the data on electrical conductivity of graphenes and graphene-polymer composites, we also present the field-effect transistor characteristics of graphenes. Only single-layer reduced graphene oxide exhibits ambipolar properties. The interaction of electron donor and acceptor molecules with few-layer graphene samples is examined in detail.
Electron spin resonance study of unzipped graphene nanoribbons (GNRs) reveals a specific carbon-related signal, denoted G C , at g =2.0032 , attributed to GNRs periphery centers. The signal is observed to be readily quenched upon O 2 adsorption, which appears to be fully reversible upon room temperature vacuum treatment. Its depassivation behavior, observed from 130 K onward, is well described by first-order kinetics, characterized by the dissociation energy of 0.58±0.04 eV of spread 0.11±0.02 eV . The G C signal is not sensitive to other gases, such as H 2 , He, N 2 , and Ar, pointing to a G C – O 2 physisorption interaction unique for GNRs, in agreement with theoretical insight. The G C center thus emerges as a highly selective, sensitive, and reversible O 2 sensor.
In the present work, the use of a commercial ionic liquid as a convenient
solvent medium for graphite exfoliation in mild and easy conditions without any
chemical modification is presented. To confirm the presence of few layer
graphene, its dispersion was charachterized by Raman spectroscopy, atomic force
miscroscopy and field emission electron microscopy. From the UV-Vis
characterization, a graphene concentration as high as 2.543 mg/ml was obtained,
which is the highest value reported so far in any solvent.
Electron spin resonance (ESR) investigation of graphene nanoribbons (GNRs)
prepared through longitudinal unzipping of multiwalled carbon nanotubes
(MWCNTs) indicates the presence of C-related dangling bond centers, exhibiting
paramagnetic features. ESR signal broadening from pristine or oxidized graphene
nanoribbons (OGNRs) is explained in terms of unresolved hyperfine structure,
and in the case of reduced GNRs (RGNRs), the broadening of ESR signal can be
due to enhancement in conductivity upon reduction. The spin dynamics observed
from ESR linewidth-temperature data reflect a variable range hopping (VRH)
mechanism through localized states, consistent with resistance-temperature
data.
An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers' method (KMnO(4), NaNO(3), H(2)SO(4)) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO(3), increasing the amount of KMnO(4), and performing the reaction in a 9:1 mixture of H(2)SO(4)/H(3)PO(4) improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers' method or Hummers' method with additional KMnO(4). Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers' method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers' method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the construction of devices composed of the subsequent CCG.
Methods for the Generation of Power Ultrasound Gas-Driven TransducersLiquid-Driven TransducersElectromechanical TransducersUltrasonic Apparatus Whistle ReactorUltrasonic Cleaning BathLaboratory Equipment Based on the Ultrasonic Cleaning BathDirect Immersion Sonic HornLaboratory Scale Reactors Involving Probe SystemsLarge Scale Applications Whistle SystemsLow Intensity SystemsHigh Intensity Systems Gas-Driven TransducersLiquid-Driven TransducersElectromechanical Transducers Whistle ReactorUltrasonic Cleaning BathLaboratory Equipment Based on the Ultrasonic Cleaning BathDirect Immersion Sonic HornLaboratory Scale Reactors Involving Probe Systems Whistle SystemsLow Intensity SystemsHigh Intensity Systems
SPHERICAL particles of carbon consisting of concentric graphite-like
shells ('carbon onions') can be formed by electron irradiation of
graphitic carbon materials1,2. Here we report that, when such
particles are heated to ~700 °C and irradiated with electrons, their
cores can be transformed to diamond. Under these conditions the spacing
between layers in the carbon onions decreases from 0.31 in the outer
shells (slightly less than the 0.34-nm layer spacing of graphite) to
about 0.22 nm in the core, indicating considerable compression towards
the particle centres. We find that this compression allows diamond to
nucleate-in effect the carbon onions act as nanoscopic pressure cells
for diamond formation.
High-power ultrasound can generate cavitation within a liquid and through cavitation provide a source of energy which can be used to enhance a wide range of chemical processes. Such uses of ultrasound have been grouped under the general name sonochemistry. This review will concentrate on applications in organic synthesis where ultrasound seems to provide a distinct alternative to other, more traditional, techniques of improving reaction rates and product yields. In some cases it has also provided new synthesic pathways.
By introducing polyaniline nanofibers (PaniNFs) as a stabilizer during the conversion of graphene oxide to graphene in an aqueous medium under ultrasound, the aggregation of the intermediates and products was effectively suppressed. A stable dispersion of PaniNFs and graphene (G) with a high concentration was obtained. This method represents a convenient and potential route to prepare a PaniNF-G dispersion on a large scale, which may increase the applications of graphene. Vacuum filtration of the dispersion yields a high-quality self-supporting PaniNF/G composite film, whose electrical conductivity can be increased by rinsing with hydrochloric acid.
Novel layered structures of polyaniline (PANI) doped with graphene oxide (GO) were directly prepared by adding GO aqueous solution into the emeraldine base form of PANI (PANI-EB) dissolved in a mixture solution of m-cresol and ethanol. The method is simple and inexpensive because of saving inorganic or organic acids as the dopant, opening a new way to prepare hybrid materials of PANI with GO. It was proposed that the π–π planar structure of GO and the carboxyl groups on the surface of GO are served as the template and dopant, respectively that results in the formation of the layered structures. The doping function of GO in the PANI-GO has been proved by structural characterizations and conductivity measured by a four-probe method.
A new type of graphene-based nanohybrid was prepared from graphene nanosheets and 4-(diphenylamino)benzaldehyde (TPA-CHO) through 1,3-dipolar cycloaddition. The nanohybrid was modified by platinum nanoparticles via photodeposition. The nanohybrid and its Pt modified nanocomposite were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Ultraviolet–visible absorption (UV–vis), Fourier transform infrared (FTIR), and Raman spectra confirmed that triphenylamine moiety grafted on the graphene surface. The results of fluorescence quenching and photocurrent enhancement of the triphenylamine-functionalized graphene revealed that photoinduced electron transfer from triphenylamine moiety to the graphene sheet. The investigation of using the Pt modified graphene-based nanocomposite as a photocatalyst for H2 evolution showed that under UV–vis light irradiation, the average H2 evolution rate and the quantum efficiency is 2.3 μmol h−1 and 0.45% mol E−1, respectively. This work demonstrated a potential application of an organic sensitizer covalently functionalized graphene as a novel photocatalyst in the field of solar energy conversion.
Mildly oxidized graphene oxide (MOGO) was achieved by chemical exfoliation of graphite through a modified Hummers' method. The MOGO is not only able to be stably dispersed in water at a high concentration (1 mg mL−1), but also preserves the highly crystalline structure of the conjugated carbon framework. Thus, the MOGO can be used as a low-defect precursor to prepare highly conductive graphene by chemical reduction. The electrical conductivity of hydrazine or hydriodic acid reduced MOGO was measured to be 169 or 405 S cm−1. This value is about 3 times that of the chemically converted graphene (CCG) prepared by reducing the conventional graphene oxide via Hummers' method with the same reducing agent. This work not only develops a facile route to high-throughput preparation of processable high-quality CCG, but also provides a deeper understanding of the crucial influence of the degree of oxidation of graphene oxide on the electrical properties of its reduced product.
Graphenes with varying number of layers can be synthesized by different strategies. Thus, single-layer graphene is obtained by the reduction of single layer graphene oxide, CVD and other methods besides micromechanical cleavage. Few-layer graphenes are prepared by the conversion of nanodiamond, arc-discharge of graphite and other means. We briefly present the various methods of synthesis and the nature of graphenes obtained. We then discuss the various properties of graphenes. The remarkable property of graphene of quenching fluorescence of aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements. The interaction of electron donor and acceptor molecules with few-layer graphene samples has been discussed. Decoration of metal nano-particles on graphene sheets and the resulting changes in electronic structure are examined. Few-layer graphenes exhibit ferromagnetic features along with antiferromagnetic properties, independent of the method of preparation. Graphene-like MoS2 and WS2 have been prepared by chemical methods, and the materials are characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques.
Influence of micropore volume on the value of C-constant of BET-isotherm was studied for series of different zeolites with mesoporous alumina. Results showed the great sensitivity of Cbet value on micropore content especially in the range up to about 7–12 % wt of zeolite, where it increases to extremely high, nonrealistic values (over 10002000).
The term Graphite has been indiscriminately applied to many varieties of native carbon of very different properties. The graphite of New Brunswick differs but little in appearance from anthracite coal. The graphite of Greenland is not very dissimilar, but possesses rather more metallic lustre. However, among these varieties of carbon, two may be especially distinguished,—by a superior degree of metallic lustre, by their structure, and other well-defined properties. In the following paper, the term Graphite is mited to these two varieties, which may be further distinguished as "lamellar” and amorphous.” The lamellar graphite is found in great abundance in Ceylon, whence large quantities are annually imported into this country. It appears in commerce in masses, sometimes of the weight of many pounds, of a brilliant metallic lustre, and possessing a distinct fibrous structure. It is very difficult by mechanical processes to bring this graphite to a fine state of division; however, by a prolonged grinding in water, it may be reduced to minute flat plates. This graphite is associated with quartz. A deposit of the same variety of graphite has recently been discovered at Travancore. The graphite from Travancore has no fibrous structure, but is in the form of slightly coherent, minute dates. Specimens of a similar graphite have also been given to me, from Moreton Bay an Australia, in a matrix of quartz, and from Ticonderoga, in the State of New York, associated with olivine and sphene. When cast iron is dissolved in acid, a residue is eft of about 4 per cent, of carbon in the form of graphite. This graphite also consists of minute brilliant plates, and is perfectly similar in its appearance and properties to the lamellar variety of native carbon. Amorphous graphite is found in Borrowdale in Cumberland, and is also largely imported into this country from Germany, probably from Griesbach near Passau, but I am unable to speak with certainty as to the locality whence it comes. It appears as a powder of a silvery grey colour, soft to the touch, and which rubbed on paper gives a brilliant metallic streak. This graphite is much softer than the other variety, and therefore better adapted for the manufacture of pencils.
A novel high-pressure sonoelectrochemical cell has been developed in order to study the effect of pressure on cavitation and acoustic streaming in electrochemical processes. The reversible one electron reduction of a solution of Ru(NH3)63+ in aqueous 0.1 M KCl at a 25 μm diameter Pt microdisk electrode was studied under up to 60 bar pressure of argon and carbon dioxide and in the presence of ultrasound. The resulting cathodic current response was interpreted to be composed of a steady macroscopic streaming induced component and a transient spikelike component detected after the onset of the cavitation. The threshold for the cavitation process was strongly dependent on pressure and increased monotonically in the presence of argon. However, the threshold appeared at lower ultrasound power when pressurizing with carbon dioxide and even decreased at higher pressures (>40 bar) in the presence of CO2. The analysis of the observed phenomena is possible in terms of the mechanical pressure, the surface tension, and the formation of a liquid CO2 phase.
An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp2 domains of graphene nanosheets obtained after the reduction of graphite oxide.
Mn 2 O 7 —a long‐known compound, whose crystal structure has finally been elucidated: the Mn atoms are surrounded tetrahedrally by O atoms; the bridging and the terminal Mn–O bonds are, as expected, of different lengths. The Mn 2 O 7 molecules are packed in such a way that an only slightly distorted fcc arrangement results for the O atoms.
The preparation of aqueous graphene dispersions by exfoliation of pristine graphite in the presence of a wide range of surfactants is reported. High graphene concentrations, up to about 1mgmL−1, were obtained with the use of some non-ionic surfactants. The dispersions consisted of single- and few-layer graphene platelets with their basal planes virtually free of even atomic-sized (point) defects. The potential utility of such highly concentrated dispersions toward the low-cost, large-scale manipulation and processing of graphene was demonstrated by processing them into electrically conductive, free-standing paper-like films.
. Aqueous colloids of graphene oxide nanosheets were produced from exfoliation of graphite oxide using a magnetic stirrer and
heat treatment in the absence of ultrasonication. Laser particle measurements showed that the particle size distribution of
graphite oxide dispersed in de-ionized water was significantly influenced by treatment time indicating an increasing exfoliation
level of graphite oxide. Atomic force microscopy (AFM) confirmed that single-layer graphene oxide nanosheets with a thickness
of ~1 nm were obtained after 72 h of magnetic stirring and heat treatment. These findings provide a new methodology for preparation
of single-layer graphene oxide nanosheet colloids.
Layer-aligned poly(vinyl alcohol)/graphene nanocomposites in the form of films are prepared by reducing graphite oxide in the polymer matrix in a simple solution processing. X-ray diffractions, scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis are used to study the structure and properties of these nanocomposites. The results indicate that graphene is dispersed on a molecular scale and aligned in the poly(vinyl alcohol) (PVA) matrix and there exists strong interfacial interactions between both components mainly by hydrogen bonding, which are responsible for the change of the structures and properties of the PVA/graphene nanocomposites such as the increase in Tg and the decrease in the level of crystallization.
The surface-colored mica pigment is mica chemically modified by controlled homogeneous hydrolysis of sulfates mainly of transition metals, such as Ti, Cr, Fe, Co, Ni, Zn, Al, and Cu, in the presence of urea, with possible thermal after--treatment. Properties of the resulting pigment depend on granularity of mica, its degree of delamination, and on the thickness of the deposited metal oxide used after delamination. Flakes of colored mica were coated with metal oxide layers by homogeneous precipitation of metal sulfates with urea in aqueous medium at 95-98°C.
Anhydrous AlCl3 was used to increase the reducing ability of sodium borohydride (NaBH4) for removing oxygen functional groups on graphene oxide (GO) at a reaction temperature below 150 °C, which provided an extendable, mild, and controllable route for large-scale production of graphene. The influences of reducing temperature and reducing time on the electrical conductivity of reduced GO were examined. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, and elemental analysis.
Chars and activated carbons were produced from raw, HCl-washed, and HCl/HF-washed Elbistan lignites at 700 °C, 800 °C, 900 °C, and 1000 °C. The pyrolysis and activation reactions increased the BET areas (m2/g carbon) of the acid-washed samples almost 10-fold. The increase of the BET areas (m2/g carbon) by increasing the temperature of pyrolysis or activation from 700 °C to 1000 °C was explained with the burn-out of carbon which led to the development of porosity. The values of the stacking heights, Lc of HCl/HF-washed samples seemed to increase from 1.0 nm to 1.5 nm, the average number of graphene sheets increased from 2.8 to 4.4, and the lateral size of the crystallites, La, increased very faintly from 5.0 nm to 5.5 nm when the pyrolysis temperature was increased from 700 °C to 1000 °C. Activation reactions performed at the same temperature range did not change the stacking heights. The values of Lc for activated HCl/HF-washed samples stayed almost constant in the same range as for the carbonized samples within 1.0−1.5 nm. This indicated that oxidative reactions during activation did not alter the stacking heights of the crystallites significantly in the temperature range of 700−1000 °C. The results presented in the present work can be considered as indications for the development of turbostratic (fully disordered) structures in the temperature range of 700−1000 °C.
Aggregation of isolated graphene sheets during drying graphene dispersions leads to a loss of its ultrahigh surface area advantage as a two-dimensional nanomaterial. We report a metal nanoparticle-graphene composite with a partially exfoliated graphene morphology derived from drying aqueous dispersions of platinum nanoparticles adhered to graphene. Platinum nanoparticles with diameters spanning several nanometers are adhered to graphene by a chemical route involving the reduction of metal precursors in a graphene dispersion. Face-to-face aggregation of graphene sheets is arrested by 3−4 nm fcc Pt crystallites on the graphene surfaces, and in the resulting jammed Pt−graphene composite, the Pt acts as spacers resulting in mechanically exfoliated, high-surface-area material of potential interest for supercapacitors and fuel cells.
An exact derivation of the Scherrer equation is given for particles of spherical shape, values of the constant for half-value breadth and for integral breadth being obtained. Various approximation methods which have been used are compared with the exact calculation. The tangent plane approximation of v. Laue is shown to be quite satisfactory, but some doubt is cast on the use of approximation functions. It is suggested that the calculation for the ellipsoidal particle based on the tangent plane approximation will provide a satisfactory basis for future work.
A study was conducted to demonstrate a new green route for the synthesis of processable graphite oxide (GO) on a large scale. It was observed that a stable graphene suspension can be prepared quickly by heating an exfoliated-GO suspension under alkaline conditions at moderate temperatures. The main objective of the study was, to introduce functional groups to exfoliated GO by free-radical addition. It was also observed that the addition of NaOH to the GO suspension, to improve the solubility of the carboxyl-terminated alkyl free-radical, was accompanied by unexpected color change. Investigations revealed that exfoliated GO can undergo fast deoxygenation in alkaline solutions, resulting in stable aqueous graphene suspensions. The graphene suspensions obtained from synthesis showed significant long-term stability that was required for processing.
Graphene materials (GMs) as supercapacitor electrode materials have been investigated. GMs are prepared from graphene oxide sheets, and subsequently suffer a gas-based hydrazine reduction to restore the conducting carbon network. A maximum specific capacitance of 205 F/g with a measured power density of 10 kW/kg at energy density of 28.5 Wh/kg in an aqueous electrolyte solution has been obtained. Meanwhile, the supercapacitor devices exhibit excellent long cycle life along with ∼90% specific capacitance retained after 1200 cycle tests. These remarkable results demonstrate the exciting commercial potential for high performance, environmentally friendly and low-cost electrical energy storage devices based on this new 2D graphene material.
Graphene nanosheets were produced in large quantity via a soft chemistry synthetic route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. X-ray diffraction and transmission electron microscopy (TEM) observations show that graphene nanosheets were produced with sizes in the range of tens to hundreds of square nanometers and ripple-like corrugations. High resolution TEM (HRTEM) and selected area electron diffraction (SAED) analysis confirmed the ordered graphite crystal structure of graphene nanosheets. The optical properties of graphene nanosheets were characterized by Raman spectroscopy.
The specific surface area of a muscovite sample increases drastically after exposure to a LiNO3 solution, e.g., from 3.4 m2/g, corresponding to platelets of ca. 200 silicate layers, to 295 m2/g (platelets of ca. 2–3 silicate layers) after treatment at 180C under atmospheric pressure for 46 h. The efficiency of the cleavage process decreases with decreasing temperature (down to 50C). The LiNO3/H2O weight ratio is also very important: at 130C and a reaction time of 46 h, for instance, a value in the range of 1.7–1.8 leads to the highest specific surfaces. The cleaved products have the form of strong papers that disperse readily in water. During the cleaving procedure, not only the particle thickness, but also the diameter decreases. There is no evidence of damage or partial dissolution of the silicate structure after cleavage, by IR spectroscopy and yield. The use of LiCl also leads to an increase in specific surface area, but the effect is weaker than in the case of LiNO3. Treatment with some other alkaline and alkaline earth nitrates and chlorides did not increase the specific surface area of muscovite significantly.