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AZ9RBAYCAN KIMYA JURNALI № 4 2016
UDC 661.666.23: 661.669
GRAPHITE INTERCALATED COMPOUND
S.B.Aliyeva, E.M.Aliyev, R.M.Alosmanov, A.M.Maharramov, A.A.Azizov, I.A.Bunyatzadeh, G.M.Eyvazova, Z.A.Aghamaliyev
Baku State University
solmaz.aliyeva@yahoo.com
Received 24.06.2016
The article highlights the synthesis of graphite intercalated compound (PCl3-GIC) via the chlorophosphorylation process. PCl3 was used as intercalate for the synthesis of PCl3-GIC and the excess of PCl3 was removed by washing the yield using acetone. The structure of the obtained PCl3-GIC was investigated using Ultraviolet-Visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscope (SEM).
Keywords: graphite, intercalation, PCl3-GIC, UV-Vis spectroscopy, FTIR-spectroscopy, SEM.
Introduction
Synthesis of new materials with specific functional properties is especially important for the development of modern science and technology. The interest of many researchers is focused on the synthesis and study of physical and chemical properties of graphite intercalated compounds (GICs), which have a regular layered structure and high anisotropic properties [1].
Graphite is the thermodynamically stable allotropic modification of carbon. Under normal conditions, graphite is chemically inert. At sufficiently high temperatures, it combines with many substances and shows reductive properties. Graphite has a layered structure. In graphite layers, carbon atoms are linked by strong covalent bonds (sp -hybridization) and form strong, stable, honeycomb-like hexagonal ring. The graphite layers, with the interlayer distance of 3.35 A (0.335 nm), are bound together by weak van der Waals forces [2].
Just like in other layered materials the various atoms, molecules or ions can be introduced between graphite layers without destroying the system of conjugated bonds (Figure 1).
The resulting structure consists of graphite layers and the layers of atoms, ions or molecules, intercalated between those graphite layers (Figure 2) [3]. After the introduction of atoms, ions or molecules into the interlayer space of the graphite, the distance between the layers increases by several times. The obtained compounds are called GICs, the process of introduction of atoms, ions or molecules to the interlayer space of graphite is called intercalation, and chemical substances introduced to the interlayer space of the graphite are called intercalates [4].
Also, mono-GICs (one type intercalate in one interlayer space) may receive bi-intercalated (two different intercalates in different interlayer spaces) and co-intercalated (two different intercalates in one interlayer space) compounds [3].
In an intercalation reaction graphite behaves as an amphoteric compound due to its aromatic nature. It is capable of receiving electrons from electron donors and give electrons to electron acceptors. Thus, intercalation compounds are divided into two groups: acceptor and donor GICs.
Interest! ate Fig. 1. Intercalation reaction [5].
----------
First stage Second stage Third stage
Graphite layer------Iutercalate layer
Fig. 2. Structure of GICs
In the acceptor GICs, polyaromatic layers carry a positive charge and are macrocations. These compounds are formed by the introduction of halogens, metal halides, oxy-halides, Bronsted acids, and others in a graphite matrix. They have complex structures. Examples of such compounds are C9AlCl3, CsCuCh, CgAsFs, CglCl, Ci6Br2, C2oFeCl3, C ;4 HSO 4 •2H2SO4, and C24+NO 3 -3HNO3 [6, 7]. In donor GICs, the intercalat acts as an electron donor, and graphite layers are mac-roanions. This group includes GICs with alkali, alkaline earth metals and lanthanides. Examples of such compounds are C4K, C8K, C24K, C8Cs, CgBa, C8Yb, C6Eu, C8Li, and C8Ca [6].
GICs are important in terms of practical usage. Such materials can be widely used as electrode materials for lithium batteries, conductive materials, catalysts, fireproof and fire resistant materials, and adsorbents for removal of hazardous substances [5, 8, 9]. In recent years, the GICs are widely used as thermoelectric materials. Thermoelectric materials, consisting of metal alloys and chemical compounds, are able to convert heat into electricity. In the process of intercalation, graphite acquires ideal properties characteristic of the thermoelectric material. An excellent thermoelectric material should have a high electrical conductivity, low thermal conductivity, and a large Seebeck effect for the maximum conversion of heat to electrical power [5]. Seebeck effect is the occurrence of electromotive force in a closed electric circuit consisting of successively connected different types of conductors with different temperatures between the joints.
In this study, the PCl3-GIC was synthesized through the chlorophosphorylation reaction, and the obtained material was investigated using UV-Vis spectroscopy, FTIR-spectroscopy, and SEM.
Materials and methods
Materials. This study used the pure graphite powder (200 mesh, high purity -99.9999 percent (metals basis)) and chemically pure phosphorus trichloride (PCl3) and acetone (C3H6O) without their further purification.
Methods. Preparation of PCL3-GIC. The PCl3-GIC, based on graphite and PCl3, was synthesized through the chlorophosphorylation reaction in a round three-necked flask equipped with mechanical stirrer, thermometer and reflux condenser [i0, ii]. The graphite and PCl3 were taken at a weight ratio of 2:1. For the synthesis of PCl3-GIC, graphite was added to the flask, then PCl3 was added (graphite:PCl3=1g:7 ml). The reaction mixture was stirred for five hours at a room temperature (approximately 250C). The mixture was then kept in a static condition for 48 hours. After completion of the process, the liquid phase, which includes unreacted PCl3, was separated from the solid phase (PCl3-GIC). The solid phase, i.e. the PCl3-GIC was washed with acetone to remove the excess PCl3 from the yield and dried in air. After completion of the intercalation process, the amount of graphite increased by 30 percent.
UV-Vis analysis. UV-Vis studies of the graphite (Figure 3) and PCl3-GIC (Figure 4) were investigated using Specord 210 Plus UV-Vis spectrophotometer in the wavelength range of 190-1.100 nm [12].
Fig. 3. UV-Vis spectra of graphite in powder form.
Fig. 4. UV-Vis spectra of PCl3-GIC in powder form.
FTIR analysis. FTIR measurements of the graphite (a) and PCl3-GIC (b) were calculated using Varian 3600 FTIR spectrophotometer in the wave number range of 400-4.000 cm-1 [12, 13].
SEM analysis. SEM analysis was applied on the graphite and PCl3-GIC using Field Emission Scanning Electron Microscope JSM-7600F with an energy dispersive spectrometer, X-max 50 and electron backscattered diffraction system NordlysMax from Oxford Instruments [14].
Results and discussions
UV-Vis analysis. Figures 3 and 4 show the UV-Vis spectra of graphite and PCl3-GIC in powder form, respectively.As shown in Figure 4, after the chlorophosphorylation process, some of the observed signals in the UV-Vis spectrum remained unchanged, some of them changed, and new other signals were observed. The bands at ~230 nm in graphite (a) and PCl3-GIC (b) are produced by the collective tc^-tc* electronic transition of the condensed aromatic
rings in the graphite layer [12, 15]. After the chlorophosphorylation reaction, the signals at ~343, ~462 and 487 nm disappear. In general, the signals observed in graphite and PCl3-GIC samples show n^-rc* and tc^-tc* electronic transitions [15].
FTIR analysis. FTIR spectra of graphite (a) and PCl3-GIC (b) are shown in Figure 5. As it can be seen in Figure 5, the graphite (a) shows a band at ~1.584 cm-1 due to the adsorbed water molecules and a strong peak at ~3.450 cm-1 characteristic to the crystal water associated with potassium bromide (KBr) used for preparation of infrared (IR) specimen [16].
After the chlorophosphorylation process, some of the observed signals in the spectrum remained unchanged, some of them changed and new other signals were observed. The peak at ~1.654 cm-1 is attributed to the existence of a C=C bond in pure graphite and PCl3-GIC [13, 17]. PCl3-GIC shows a peak at ~407 and ~603 cm-1, corresponding to -PCl and -PCl2 groups, respectively [12].
SEM analysis. The SEM micrographs of graphite (a) and PCl3-GIC (b) are shown in Figure 6. After the intercalation process, the structure of graphite changed and exhibited a tendency to form agglomerates [14].
155 150 145 14.0 13.5 130 125 120 11.5
11.0 10 5 10.□ 9.5 9.0
3500 3000 2500 2000 1500 1000 500
Wavenumber
Fig. 5. FTIR spectra of graphite (a) and PQ3-GIC (b).
Fig. 6. SEM of graphite (a) and PCl3-GIC (b).
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QRAFiT iNTERKALYASiYA EDiLMi§ BiRLO§MO
S.B.Oliyeva, E.M.Oliyev, R.M.Alosmanov, A.M.Mah3rramov, A.O.Ozizov, LA.Bünyadzada,
G.M.Eyvazova, Z.O.Agamahyev
Tadqiqat i§i xlorfosforla§ma reaksiyasi ila qrafit interkalyasiya edilmi§ birla§manin (PCl3-QiB) sintezim hasr edilmi§dir PCl3-QiB-in sintezi ügün PCl3 interkalyat kimi istifada edilmi§ va interkalyasiya reaksiyasina daxil olmayan PCl3 molekullan reaksiya mahsulunu asetonla yumaqla kanarla§dmlmi§dir. PCl3-QiB-nin strukturu ultrabanöv§ayi-görünan (UB-Gör.)-spektroskopiya, infraqirmizi (iQ)-spektroskopiya va skanedici elektron mikroskopiya (SEM) analiz metodlari ila tadqiq edilmi§dir.
Agar sözlar: qrafit, interkalyasiya, PCl3-QiB, UB-Gör.-spektroskopiya, lQ-spektroskopiya, SEM.
ИНТЕРКАЛИРОВАННОЕ СОЕДИНЕНИЕ ГРАФИТА
С.Б.Алиева, Э.М.Алиев, Р.М.Алосманов, А.М.Магеррамов, А.А.Азизов, И.А.Буниятзаде,
Г.М.Эйвазова, З.А.Агамалиев
Исследование посвящено синтезу интеркалированного соединения графита (РС13-ИСГ) реакцией хлорфосфорилования. Для синтеза РС13-ИСГ в качестве интеркалята использован РС13, непрореагировавшие молекулы которого были удалены промыванием продукта реакции - ацетоном. Структура полученного РС13-ИСГ исследована методами ультрафиолетовой видимой (УФ-Вид.)-спектроскопии, инфракрасной (ИК)-спектроскопии и сканирующей электронной микроскопии (СЭМ).
Ключевые слова: графит, интеркаляция, PCls-ИСГ, УФ-Вид. -спектроскопия, ИК-спектроскопия, СЭМ.
