Improvement of graphene oxide characteristics depending on base washing

Graphene oxide (GO) has been synthesized using Hummer’s method. This oxidation process decorates the graphene sheets by different types of functional groups, yet the harsh oxidation condition leads to introduce many of carbonaceous fragments, which decreasing GO efficiency in many faces, touched its...

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Дата:	2015
Автори:	Kabel, Kh.I., Farag, Ah.A., Elnaggar, E.M., Al-Gamala, A.G.
Формат:	Стаття
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Опубліковано:	Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України 2015
Назва видання:	Сверхтвердые материалы
Теми:	Получение, структура, свойства
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Назва журналу:	Digital Library of Periodicals of National Academy of Sciences of Ukraine
Цитувати:	Improvement of graphene oxide characteristics depending on base washing / Kh.I. Kabel, Ah.A. Farag, E.M. Elnaggar, A.G. Al-Gamala // Сверхтвердые материалы. — 2015. — № 5. — С. 45-54. — Бібліогр.: 31 назв. — англ.

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spelling	irk-123456789-1262122017-11-18T03:02:59Z Improvement of graphene oxide characteristics depending on base washing Kabel, Kh.I. Farag, Ah.A. Elnaggar, E.M. Al-Gamala, A.G. Получение, структура, свойства Graphene oxide (GO) has been synthesized using Hummer’s method. This oxidation process decorates the graphene sheets by different types of functional groups, yet the harsh oxidation condition leads to introduce many of carbonaceous fragments, which decreasing GO efficiency in many faces, touched its applications. The synthesized GO has been washed by 10 M NaOH to produce (GOn). Thereafter quality enhancement of GO has been studied by several analyses; the introduced hydroxyl and carboxyl groups into few-layer graphene (FLG) surface have been determined by Fourier transform infrared spectra (FTIR). Raman spectroscopy analysis identified the defect degree and the transition of graphite from a crystalline to an amorphous structure and vice versa. The interlayer spacings of FLG and GOn were investigated by Xray diffraction (XRD) and the thermal stability of as-received and modified materials were examined by thermal gravimetric analysis (TGA). The morphological structure was characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The various investigations confirmed that the properties of GO were improved by neutralization impact, which may pave the way to new developments in the GO-based applications. Методом Хаммера синтезувано оксид графену (ОГ). Цей процес окислення декорує площини графена різними типами функціональних груп, жорсткі умови окислення призводять також до появи великої кількості вуглецевовмісних фрагментів, які зменшують ефективність ОГ в багатьох областях його застосування. Синтезований ОГ промивали розчином 10 М NaOH для отримання (ОГ)n. Якість ОГ досліджено кількома методами: введені в малошаровий графен гідроксильні та карбоксильні групи визначали Фур’є-інфрачервоною спектроскопією, ступінь дефектності та перехід графіту з кристалічної структури в аморфну і навпаки ідентифікували Раманівською спектроскопією, відстань між шарами у малошаровому графені і (ОГ)n досліджували з використанням рентгенівської дифракції, а термостабільність вихідних і модифікованих матеріалів – термогравіметричним аналізом, морфологію структури характеризували за допомогою скануючої електронної мікроскопії і просвічуючої електронної мікроскопії високої роздільної здатності. Різні дослідження підтвердили, що властивості ОГ поліпшувалися під дією нейтралізації, що може прокласти шлях новим розробкам щодо його застосування. Методом Хаммера синтезировали оксид графена (ОГ). Этот процесс окисления декорирует плоскости графена различными типами функциональных групп, жесткие условия окисления приводят также к появлению большого количества углеродсодержащих фрагментов, которые уменьшают эффективность ОГ во многих областях его применения. Синтезированный ОГ промывали раствором 10 М NaOH для получения ОГn. Затем качество ОГ исследовали несколькими методами: введенные в малослойный графен гидроксильные и карбоксильные группы определяли Фурье-инфракрасной спектроскопией; степень дефектности и переход графита из кристаллической структуру в аморфную и наоборот идентифицировали Рамановской спектроскопией, расстояние между слоями в малослойном графене и ОГn исследовали с использованием рентгеновской дифракции, а термостабильность исходных и модифицированных материалов – термогравиметрическим анализом, морфологию структуры характеризовали c помощью сканирующей электронной микроскопии и просвечивающей электронной микроскопии высокого разрешения. Различные исследования подтвердили, что свойства ОГ улучшались под действием нейтрализации, что может проложить путь новым разработкам по его применению. 2015 Article Improvement of graphene oxide characteristics depending on base washing / Kh.I. Kabel, Ah.A. Farag, E.M. Elnaggar, A.G. Al-Gamala // Сверхтвердые материалы. — 2015. — № 5. — С. 45-54. — Бібліогр.: 31 назв. — англ. 0203-3119 http://dspace.nbuv.gov.ua/handle/123456789/126212 549.21:542.943 en Сверхтвердые материалы Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Получение, структура, свойства Получение, структура, свойства
spellingShingle	Получение, структура, свойства Получение, структура, свойства Kabel, Kh.I. Farag, Ah.A. Elnaggar, E.M. Al-Gamala, A.G. Improvement of graphene oxide characteristics depending on base washing Сверхтвердые материалы
description	Graphene oxide (GO) has been synthesized using Hummer’s method. This oxidation process decorates the graphene sheets by different types of functional groups, yet the harsh oxidation condition leads to introduce many of carbonaceous fragments, which decreasing GO efficiency in many faces, touched its applications. The synthesized GO has been washed by 10 M NaOH to produce (GOn). Thereafter quality enhancement of GO has been studied by several analyses; the introduced hydroxyl and carboxyl groups into few-layer graphene (FLG) surface have been determined by Fourier transform infrared spectra (FTIR). Raman spectroscopy analysis identified the defect degree and the transition of graphite from a crystalline to an amorphous structure and vice versa. The interlayer spacings of FLG and GOn were investigated by Xray diffraction (XRD) and the thermal stability of as-received and modified materials were examined by thermal gravimetric analysis (TGA). The morphological structure was characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The various investigations confirmed that the properties of GO were improved by neutralization impact, which may pave the way to new developments in the GO-based applications.
format	Article
author	Kabel, Kh.I. Farag, Ah.A. Elnaggar, E.M. Al-Gamala, A.G.
author_facet	Kabel, Kh.I. Farag, Ah.A. Elnaggar, E.M. Al-Gamala, A.G.
author_sort	Kabel, Kh.I.
title	Improvement of graphene oxide characteristics depending on base washing
title_short	Improvement of graphene oxide characteristics depending on base washing
title_full	Improvement of graphene oxide characteristics depending on base washing
title_fullStr	Improvement of graphene oxide characteristics depending on base washing
title_full_unstemmed	Improvement of graphene oxide characteristics depending on base washing
title_sort	improvement of graphene oxide characteristics depending on base washing
publisher	Інститут надтвердих матеріалів ім. В.М. Бакуля НАН України
publishDate	2015
topic_facet	Получение, структура, свойства
url	http://dspace.nbuv.gov.ua/handle/123456789/126212
citation_txt	Improvement of graphene oxide characteristics depending on base washing / Kh.I. Kabel, Ah.A. Farag, E.M. Elnaggar, A.G. Al-Gamala // Сверхтвердые материалы. — 2015. — № 5. — С. 45-54. — Бібліогр.: 31 назв. — англ.
series	Сверхтвердые материалы
work_keys_str_mv	AT kabelkhi improvementofgrapheneoxidecharacteristicsdependingonbasewashing AT faragaha improvementofgrapheneoxidecharacteristicsdependingonbasewashing AT elnaggarem improvementofgrapheneoxidecharacteristicsdependingonbasewashing AT algamalaag improvementofgrapheneoxidecharacteristicsdependingonbasewashing
first_indexed	2025-07-09T04:33:37Z
last_indexed	2025-07-09T04:33:37Z
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fulltext	ISSN 0203-3119. Сверхтвердые материалы, 2015, № 5 45 UDC 549.21:542.943 Kh. I. Kabel, Ah. A. Farag, E. M. Elnaggar, A. G. Al-Gamala (Cairo, Egypt) drkhalid1977@yahoo.com Improvement of graphene oxide characteristics depending on base washing Graphene oxide (GO) has been synthesized using Hummer’s method. This oxidation process decorates the graphene sheets by different types of functional groups, yet the harsh oxidation condition leads to introduce many of carbonaceous fragments, which decreasing GO efficiency in many faces, touched its applications. The synthesized GO has been washed by 10 M NaOH to produce (GOn). Thereafter quality enhancement of GO has been studied by several analyses; the introduced hydroxyl and carboxyl groups into few-layer graphene (FLG) surface have been determined by Fou- rier transform infrared spectra (FTIR). Raman spectroscopy analysis identified the defect degree and the transition of graphite from a crystalline to an amorphous struc- ture and vice versa. The interlayer spacings of FLG and GOn were investigated by X- ray diffraction (XRD) and the thermal stability of as-received and modified materials were examined by thermal gravimetric analysis (TGA). The morphological structure was characterized by scanning electron microscopy (SEM) and high resolution trans- mission electron microscopy (HRTEM). The various investigations confirmed that the properties of GO were improved by neutralization impact, which may pave the way to new developments in the GO-based applications. Keywords: oxidation, graphene oxide, few-layer graphene, carbona- ceous fragments, electrostatic stabilization. INTRODUCTION Graphene, one of the allotropes of elemental carbon (carbon, car- bon nanotube, fullerene, diamond) [1, 2], is a planer monolayer carbon atoms ar- ranged in two-dimensional (2D) honeycomb lattice with a Carbon–Carbon bond length of 0.142 nm [3]. It can be divided into three different types: single-layer graphene (SLG), bi-layers graphene (BLG) and few-layer graphene (FLG) [4]. Graphene has received a worldwide attention due to its exceptional charge trans- port, thermal, optical and mechanical properties; it can be synthesized by several methods as micromechanical cleavage, chemical vapor deposition (CVD), and reduction of graphite oxide to graphene. The functionalization of graphene im- proves its dispersibility and enhances its functions in various applications [5]. Gra- phene oxide (GO) can be obtained by liquid phase oxidation of graphene sheets. Chemically, both graphite oxide and GO have similar or identical structures, both possess stacked structures with chemicals on their basal planes and at their edges [1]. The only difference between them is the number of stacked layers; GO possess a monolayer or just a few stacked layers (≤ 10), while graphite oxide (> 10) [1, 6]. In general, the liquid phase oxidation of graphene was developed several dec- ades ago by Brodie [7], Staudenmaier [9] and Hummers et al. [10]. The Hummers method is generally more used in current research, it has shorter reaction time and absence of highly toxic gas ClO2 [11]. The disadvantage of the Hummers method © KH. I. KABEL, AH. A. FARAG, E. M. ELNAGGAR, A. G. AL-GAMALA, 2015 www.ism.kiev.ua/stm 46 is the contamination by excess permanganate ions, which should be removed by treatment with H2O2 [12], followed by washing several times through a membrane. The Hummers method uses a combination of potassium permanganate and sul- furic acid to obtain (manganese heptoxide) as (according to equations) below. KMnO4 + 3H2SO4 → K+ + MnO3 + + H3O+ + 3HSO4 –; (1) MnO3 + + MnO4 – → Mn2O7. (2) GO is heavily oxygenated, highly hydrophilic, and readily exfoliated in water producing stable dispersion consisting mostly of a single layer of GO [5]. The dis- tribution of oxygen-containing functional groups on graphene oxide structures have been studied using 13C NMR [13, 14]. Lerf–Klinowski suggested that, when oxy- gen located in the carbon basal plane as hydroxyl and epoxy groups compose sp3 hybridization. In addition, when oxygen located at the sheet edges as carbonyl and carboxyl it enhances sp2 hybridization [7, 15, 16]. The ratio of sp2/sp3 in GO may provide novel properties that can be useful in various applications such as chemical sensors and biosensors, super capacitors, energy storage, nanocomposites, elec- tronic and optoelectronic devices, and so on [5, 17]. The oxidation process can cut the graphitic layers into smaller fragments called ‘oxidation fragments’ [18]. These fragments are not removed from the sample in conventional treatments; however, they can be successfully removed by an aqueous base washing [19]. In this article, we oxidized FLG powders to GO using modified Hummer’s method as well as removing the oxidized fragments and contaminating metal by highly concentrated base washing to produce GOn. The morphological structure of GO was studied using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The order of crystallinity was meas- ured by X-ray diffraction (XRD). The defects on the surface of GO were detected by Raman spectroscopy. The thermal stability was determined by thermal gravim- etric analysis (TGA). The efficient of the oxidation process was observed by Fou- rier transform infrared spectra (FTIR). EXPERIMENTAL Materials Rods of graphene, provided by VEB Elektrokohle Lichtenberg, REKIPRO (Germany), were crushed in 20–25 µm using Retsch ball mill PM400 (Germany), sulfuric acid (98 %), hydrochloric acid (37 %) and potassium permanganate were purchased from Sigma-Aldrich Co. (Germany). Hydrogen peroxide (30 % v/v) and sodium nitrate were purchased from (El Nasr Company for Intermediate Chemi- cals, Egypt). Synthesis of graphene oxide and NaOH wash Graphene oxide was synthesized from the natural graphite powders using Hummer’s et al. method [10]: 1 g of FLG, 1 g of NaNO3 and 46 ml of concentrated H2SO4 were mixed together in three necked flask equipped with a magnetic stirrer and thermometer in an ice bath for about 30 min at 0 °C. Then 3 g of KMnO4 was added to the suspension carefully to prevent the temperature exceed 20 °C. The ice bath was removed and the temperature of the suspension raised to about 35±3 °C, where it was mentioned under stirring for 30 minutes to become pasty brownish gray in color. The thickened paste was stirred slowly with 46 ml of de-ionized water and the temperature increased to 98 °C, the color of the suspension changed to brown, it was kept stirring for 30 minutes. Finally, it was further diluted with ISSN 0203-3119. Сверхтвердые материалы, 2015, № 5 47 approximately 140 ml of warm water and treated with 10 ml of H2O2. The acidic suspension was neutralized by 82 ml of 10 M NaOH. The suspension was filtered, resulting yellowish-brown filter cake which washed with de-ionized water for sev- eral times. Then the filter cake was treated with 3 % HCl (1M) solution to regener- ate the functional groups [20], it was dispersed and washed with deionized water for several times. The resulting sample was dried by lyophilization using (vacuum desiccator) to avoid the aggregation of graphene oxide during the drying process [21, 22]. Instruments X-ray diffraction (XRD) analysis was performed on an X-ray diffractometer from PANlytical company model (X’Pert Pro) 2Ө range from 5o–90o conditions 40 mA, 40 kV, and wave length of Copper Kα1 at 1.54 Å. The (FTIR) Fourier transform infrared spectrum (400–4000 cm–1) was measured the addition of car- boxyl and hydroxyl groups on the graphene surface using (Thermo Fisher Scien- tific; Nicolet iS10 FTIR spectrometer, USA), the sample was mixed with pure KBr as the background, then the mixture was dried and compacted into a transparent tablet for measurement. The Raman analysis was investigated by laser as an excita- tion source at wavelength 532 nm, using dispersive Raman spectrosmeter (Senterra, Bruker, Germany), the laser spot size was 1 µm and the temperature of the sample was maintained at room temperature. The thermal stability was assessed by the thermal gravimetric analysis (TGA) (SDT Q600 V20.5 Build 15) in the temperature range of 20–850 °C (10 °C /min) under a nitrogen atmosphere. The shape and the surface morphology of the samples was analyzed using high resolu- tion transmission electron microscope (HRTEM), of JEOL JEM-2100F, Japan at 200 kV. The samples were sonicated to dispersing the aggregation of the graphene sheet, carried out on ultrasonic bath (Sonic Star, 50 kHz, 300 W). A Waterproof CyberScan Series 310 pH meter was used for measuring pH during the experiment. RESULTS AND DISCUSSION FTIR characterization FTIR spectra of FLG and GOn samples are shown in Fig. 1. In Fig. 1 (curve 1), the appearance of two strong peaks at 1601 cm–1 referred to conjugation system (C=C–C) stretching [23]. In Fig. 1 (curve 2), the peak at 1054 cm–1 referred to aliphatic stretching of (C–O), the peak at 1161 cm–1 referred to stretching ether system (C–O–C), the peak at 1601 cm–1 referred to stretching conjugation system (C=C–C), the peak at 1725 cm–1 referred to carbonyl group (C=O), the peak at 2918 cm–1 referred to bending and stretching of methylene group (–CH2–) and broad band at 3340 cm–1 are attributed to vibration of a hydroxyl group (O–H) [2, 24]. The FTIR observed that the oxidation process was successfully occurred, a new groups as hydroxyl, carboxyl and epoxy have been introduced into the gra- phene layers. XRD analysis The XRD analysis was used to characterize the crystallinity and purity of the oxidized FLG (GO) after high concentration base washing. The XRD patterns of the pristine FLG and GOn are shown in Fig. 2. Their interlayer spacing (d), 2θ diffraction and the relative intensity have been illustrated in Table 1. The XRD pattern of graphitic substrate shows peak at 2θ = 26.53° (002) corresponding to an interlayer spacing (d) = 3.33 Å. The FLG appeared broad peaks at 2θ = 25.53° (002) and 45.89° (100) which are attributed to graphene sheet material correspond- www.ism.kiev.ua/stm 48 ing, (d) = 3.48 Å and 1.83 Å respectively [2, 25]. After oxidation using 3 g KMnO4 results in the following changes, the peak of graphene sheets becomes narrow and shifted in the lower diffraction angle at 2θ = 22.56° corresponding to (d) = 3.94 Å, meaning that the interlayer distance increases and the structure was modified. The XRD pattern shows the feature peak at a lower diffraction angle 2θ = 10.85° corre- sponding to (d) = 8.15 Å, confirmed oxidation of FLG to GO. After washing with high concentration NaOH the XRD pattern shows a new peaks were appeared, attributed to the structural deformation, which occurred by the decomposition of epoxy groups to hydroxyl groups and –ONa [26]. 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm –1 0 20 40 60 80 1 2 T ra ns m it ta nc e, % Fig. 1. FTIR spectra of FLG (1) and GOn (2). 10 20 30 40 50 60 70 80 90 Diffraction angel 2θ, deg 1 2 In te n si ty , ar b. u n it s Fig. 2. XRD of FLG (1) and GOn (2). Raman analysis Raman spectroscopy is a standard nondestructive tool to characterize carbona- ceous materials, especially to distinct ordered and disordered crystallinity of the structures of carbon. From Fig. 3 we can show that, the main features of the graph- ite materials are G band at about 1575 cm–1, D band at about 1345 cm–1. The G ISSN 0203-3119. Сверхтвердые материалы, 2015, № 5 49 band represents a first order scattering of E2g mode, while the D band is the evi- dence for the presence of defects in the graphite material [26, 27]. The last impor- tant band is the overtone band of the D band (2D band) which appears at 2705 cm–1 [28]. The stacking order of the graphite layers along the c-axis were assessed by the 2D band, where the intensity of 2D band displays for SLG, BLG and FLG as descending order [29, 30]. Table 1. Interlayer spacing d, 2θ diffraction and relative intensity of GOn and FLG Sample 2θ d, Å Relative intensity, % 26.53° 3.33 100.00 25.53° 3.48 89.00 FLG 44.43° 1.83 6.71 23.62° 3.76 100.0 22.56° 3.94 75.45 45.13° 2.00 12.54 GOn 10.85º 8.15 16.20 1000 1500 2000 2500 3000 Wavenumber, cm –1 1 2 R am an in te ns it y Fig. 3. Raman spectra of FLG (1) and GOn (2). The oxidation process has changed the structure of the graphene lattice due to introducing of different functional groups at the basal plane and also at the edges. The G band of GOn is shifted towards a higher wave number at about 1600 cm–1 related to the formation of sp3 carbon atoms in the graphene lattice [31]. The inten- sity of D band of GOn is lower than pristine FLG, due to the high concentration base washing lead to eliminating the amorphous carbon. The relative intensity I(D)/I(G) is very useful to detect efficiency of oxidation and purification processes. We can observe that I(D)/I(G) of FLG and GOn are 0.82 and 0.62, respectively, the relative intensity is decreased due to removal of amorphous carbon and other impu- rities using high concentration NaOH that leads to diminishing the D band value. A careful inspection of Raman spectra observed that, the overtone 2D band disap- www.ism.kiev.ua/stm 50 peared in GOn due to the breakage of the stacking order along the c-axis during the oxidation process [17]. The morphology and crystallinity analysis Figure 4 shows the SEM images of FLG and GOn. It can be seen that the ap- pearance of the surface is more flat and straight due to the layers of graphene were arranged in order due to the strong layer–layer interaction (Van der Waals force) and the sample is looking black [2], as these appear in images (see Figs. 4, a, b) of the original FLG. On the other hand, from Figs. 4, c, d we can show that, the sur- face and edge of GOn were rough and wrinkled. This indicates that the regular lamellar structure of FLG has been distributed after the oxidation process; the wrinkle was caused because the distribution of hydrogen bonds is non-uniform, which formed between hydroxy groups. The oxidation process has been trans- formed the arranged layer structure to a worm-like structure with many apertures by widening and exfoliation along the c-axis of a graphite crystal. 100 μm 10 μm a b 100 μm 10 μm c d Fig. 4. SEM analysis of (a) graphitic layer-layer interaction for FLG; (b) the magnification of the image (a); (c) appearance of wrinkles on the surface of GOn after base washing; (d) the magnifica- tion of the image (c). The morphological structure and the crystalline kind of FLG and GOn were characterized by HRTEM. Figure 5 shows that the samples consist of layers with different transparences, it may be attributed to the number of layers existed in the aggregated structure [17]. From Fig. 5, a it can be observed that the bulk morphol- ogy of FLG compressed of many graphite layers and it is completely dark. On the contrary, the image of GOn (see Fig. 5, b) becomes highly transparent due to pos- ISSN 0203-3119. Сверхтвердые материалы, 2015, № 5 51 sessing high amounts of oxygenated content after oxidation process, which makes suitable for exfoliation of graphite layers into a monolayer or just a few layers of GO after ultrasonication. Also, after oxidation a reduction in the dimensions of graphitic sheets has been observed. 100 μm 100 μm a b Fig. 5. HRTEM of FLG (a) and GOn (b). TGA analysis The thermal behaviors of pristine FLG, GO and GOn were examined by thermal gravimetric analysis (TGA) in dry air, to find the efficient graphitic matter oxida- tion and possible structural damage. The TGA curves and data are shown in Fig. 6 and Table 2. The pristine FLG has started to lose weight at 46.6 °C (7.6 %) related to the physical adsorbed moisture, the sharpness weight loss at 650 °C due to the combustion of the carbon backbone to carbon dioxide [26]. The GO powder exhibit three steps of weight loss that start at 58.4°C (17 %) related to the physical ad- sorbed moisture, the second and the last weight loss at 258 °C (40 %) and Temperature, °C 650 °C 1 2 W ei gh t, % 3 71.1 °C 235 °C 708 °C Fig. 6. TGA analysis of FLG (1), GOn (2), GO (3). www.ism.kiev.ua/stm 52 590 °C (64 %), which are ascribed to the removal of oxygenated functional groups and carbon combustion to CO2, respectively. The GOn powder after high concen- tration base washing exhibit three steps of weight loss starting at 71.1 °C (11.3 %) related to the physical adsorbed moisture, the second and the last weight loss at 266 °C (32.2 %) and 74 °C (57.8 %) which are attributed to the removal of oxy- genated functional groups and carbon combustion to CO2, respectively. The results observed that the thermal stability of GO and GOn are less than that of FLG attrib- uted to the oxidation process. Otherwise, the thermal stability of GOn is more sta- ble than GO due to the base washing removal of the amorphous carbon. Table 2. TGA comparison between FLG, GO and GOn Weight loss, % at temperature, °C Sample 46.6 58.4 71.1 200 235 550 708 Pristine FLG 7.6 GO 17 40 64 GOn 11.3 32.2 57.8 CONCLUSION FLG powder has been oxidized using modified Hummer’s method, the oxidized FLG (GO) has been washed by high base concentration (10 M NaOH) to enhance the removal efficiency for the carbonaceous fragments. The impact of high concen- tration base washing on the surface of GO has been studied using: XRD analysis to confirm the degree of crystalline and the interlayer spacing, XRD pattern shows new peaks appeared, lead to the interlayer spacing was increased after oxidation and base washing, attributed to the introduced hydroxyl groups increase the repul- sion between graphene sheets due to posting the same negative charge. Raman analysis shows that the amorphous carbon content was diminished after base wash- ing. GOn is more thermal stable than GO, regarding to the base washing, remove the fragment and enhance the thermal stability. Furthermore, the base washing removed the acid waste by friendly environmental method, low cost, saving the time and the quantity of water needed to eliminate the remained acid. Методом Хаммера синтезувано оксид графену (ОГ). Цей процес окис- лення декорує площини графена різними типами функціональних груп, жорсткі умови окислення призводять також до появи великої кількості вуглецевовмісних фрагментів, які зменшують ефективність ОГ в багатьох областях його застосування. Синтезований ОГ промивали розчином 10 М NaOH для отримання (ОГ)n. Якість ОГ досліджено кількома методами: введені в малошаровий графен гідроксильні та карбоксильні групи визначали Фур’є-інфрачервоною спектроскопією, ступінь дефектності та перехід графіту з крис- талічної структури в аморфну і навпаки ідентифікували Раманівською спектроскопією, відстань між шарами у малошаровому графені і (ОГ)n досліджували з використанням рентгенівської дифракції, а термостабільність вихідних і модифікованих матеріалів – термогравіметричним аналізом, морфологію структури характеризували за допомогою скануючої електронної мікроскопії і просвічуючої електронної мікроскопії високої розді- льної здатності. Різні дослідження підтвердили, що властивості ОГ поліпшувалися під дією нейтралізації, що може прокласти шлях новим розробкам щодо його застосування. Ключові слова: окислення, оксид графена, малошаровий графен, вуглецевмісні фрагменти, електростатична стабілізація. ISSN 0203-3119. Сверхтвердые материалы, 2015, № 5 53 Методом Хаммера синтезировали оксид графена (ОГ). Этот процесс окисления декорирует плоскости графена различными типами функциональных групп, жесткие условия окисления приводят также к появлению большого количества углерод- содержащих фрагментов, которые уменьшают эффективность ОГ во многих областях его применения. Синтезированный ОГ промывали раствором 10 М NaOH для получения ОГn. Затем качество ОГ исследовали несколькими методами: введенные в малослойный графен гидроксильные и карбоксильные группы определяли Фурье-инфракрасной спектро- скопией; степень дефектности и переход графита из кристаллической структуру в аморфную и наоборот идентифицировали Рамановской спектроскопией, расстояние между слоями в малослойном графене и ОГn исследовали с использованием рентгеновской дифракции, а термостабильность исходных и модифицированных материалов – термо- гравиметрическим анализом, морфологию структуры характеризовали c помощью ска- нирующей электронной микроскопии и просвечивающей электронной микроскопии высо- кого разрешения. 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Improvement of graphene oxide characteristics depending on base washing

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