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UDC 541.64:547.458.81
SYNTHESIS AND STUDY OF COPPER SULFIDE (Cu18S) NANOCRYSTALS ON THE BASIS OF PHOSPHORUS CONTAINING POLYMER SORBENT (PCPS) BY CHEMICAL
ROUTE
O.O.Balayeva, A.M.Maharramov, A.A.Azizov, M.B.Muradov, N.O.Balayeva, Z.Q.Mamiyev, R.M.Alosmanov, G.M.Eyvazova, Z.A.Aghamaliyev
Baku State University Institute of Physics Azerbaijan NAS
ofeliya1989@inbox.ru
Received 05.03.2015
Synthesis of copper sulfide nanoparticles on the basis functionalized nitrile butadiene rubber (NBR-26) was carried out by the method of successive ionic layer adsorption and the reaction (SILAR). The reaction was undertaken at room temperature. The XRD records show well-formed nanocrystalline particles of copper sulfide as Cu18S with structure of cubic form. The crystallite size approximated 5 nm for Cu18S nanocrystals. The band gap of Cu18S nanoparticles is found to be 3 eV. SEM/EDX analyses showed that the synthesized materials are nanocomposites and the particle size of Cu18S is in the range of 9-12 nm. Infrared spectroscopy results illustrate that nanoparticles could grow on the -PO(OH)2 functional groups of polymer. The formed nanocrystals are quantum dots and can be used photoelectron transformation devices.
Keywords: nanocomposites, Cu18S, optical properties, scanning electron microscopy (SEM).
Introduction
Copper sulfide is a promising p-type inorganic semiconductor for opto-electronic devices such as solar cells, due to its small band gap energy and its electrical properties. The synthesis technique and parameters involved play a crucial role in controlling the morphology and stoichi-ometry of CuxS, which determines their structural, optical, and electrical properties. Low-temperature solution based techniques, such as sonochemical [1], sol-gel [2], hydrothermal [3], solvothermal [4], microemulsion [5], and elec-trodepostion [6] are commonly employed to synthesize a wide variety of copper sulfide nano-structures, including nanoparticles [7], nanotubes [8], nanowires [3], nanorods [9], nanoplates [10], and hollow spheres [11].
Nanocrystalline copper sulfide (CuxS), with two stoichiometric ratios (x =2, 1.8) was obtained by one-pot synthesis at 220, 230, 240 and 2600C in an organic solvent and amorphous CuxS was obtained in aqueous solution [12]. Ilan Jen-La Plante et al. [13] presented a simple synthetic method for the formation of cuprous sulfide (Cu2S) nanocrystals via the thermal decomposition of a single-source molecular precursor, copper bis-diethyldithiocarbamate
(Cu(II)[S2CNC4H10]2). This technique allows for large scale growth of the Cu2S nanocrystals directly on a substrate. By changing the metal center in our single-source molecular precursor complex, a variety of metal sulfide nanomateri-als including lead sulfide (PbS), cadmium sulfide (CdS), zinc sulfide (ZnS), and nickel sulfide (Ni3S2) among many other potential material combinations can be groun. Copper sulfide nanocrystals have been successfully synthesized with sulfuration of Cu-alkylamine complexes [14]. Nanocrystals obtained from oleylamine are monodispersed size Cu2S nanocrystals with a spherical shape. The morphology and chemical composition of copper sulfide nanocrystals depend on alkylamine species. Those prepared with octylamine and dioctylamine are Cu18S or Cu18S-Cu2S mixture, while that prepared with trioctylamine, which has the bulkiest hydropho-bic group, is Cu2S and smallest one [14]. Poly-crystalline Cu18S compounds were fabricated by using a combined process of mechanical alloying and spark plasma sintering [15]. Low-and high-digenite, Cu18S, has been studied by X-ray diffraction at room temperature and at temperatures up to 5000C. For the experiments the Debye-Scherrer technique was used with
buffered sulfur partial pressure at all temperatures. The crystal structures of high-digenite have been determined at 200, 300, 400 and 5000C [16]. Using CuCl2 and thiourea as the precursors, Zhao et al. described the one-step synthesis and assembly of copper sulfide nano-particles by an organic amine-assisted hydrothermal method at a mild temperature (90-1100C) [17]. The aim of this work was the synthesis and study of copper sulfide nanoparticles using cost effective and convenient stabilizing agent for gaining advanced interesting properties. In this paper we successfully prepared Cu18S/PCPS nanocomposites by successive ionic layer adsorption and the reaction (SILAR) method [18] in phosphorus containing polymer sorbent (PCPS). The reaction was carried out at room temperature. The results obtained from X-ray, SEM/EDX, UV-Vis and IR spectroscopy experiments are reported. The formed composite materials can be used as the quantum dots in pho-toelectron transformation devices.
Experimental part
Synthetical nitrile butadiene rubber (NBR) was purchased from Voronej synthetic rubber factory in the Russian Federation. The phosphorus trichloride (PCl3) has been used from Volgograd chemical industry's product. Powder X-ray diffraction patterns of the samples were recorded by using of Bruker D2 Phaser Advance X-ray diffractometer with CuX«-irradiation (X = 1.54060 A), UV-Vis absorption spectra and IR spectra were reflected whereby SPECORD 250 PLUS-223G1020 and Cary Eclipse Spectrofluorometer (PL), respectively. SEM/EDX analysis was carried out on a Field Emission Scanning Electron Microscope JSM-7600F with Energy dispersive spectrometer X-max 50 and Electron Backscattered Diffraction System NordlysMax from Oxford Instruments.
Polymers containing -PO(OH)2 phos-phonic functional active groups were synthesized from the oxidative chlorophosphorylation reaction of NBR with PCl3 and oxygen. 10% solutions were prepared from NBR-26 with CHCl3. To carry out oxidative chlorophosphory-lation there was used an apparatus consisting of
a round four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser and a bubbler for oxygen [19]. The oxygen rate was 7 l/hour and 1:6 PCl3 was added by intervals to a stirred solution. The reaction was exothermal and the temperature was raised up to 450C in 18 hour by stirring. The phosphorus containing polymer sorbents are dark brown powder. This powder sample can be used for stabilizing the nanostructures and other powder processing.
15 ml 10-1 M of CuSO45H2O solution was prepared as precursor of the semiconductor nanoparticles. 0.05 g of PCPS powder were added to the solution and stirred at room temperature for 24 hours. Then the sample was washed to remove unexchanged Cu2+ ions. The sulphirizing of the adsorbed Cu2+ ions was carried out with 10-1 M Na2S solution. The time of sulphirizing was 3 hours. To make the reaction with the S - ion, the polymer sample adsorbed Cu2+ ions was added to 15 ml of 10-1 M Na2S solution and stirred for 3 hours with magnetic stirrer. The sample was rinsed up with distillat-ed water and this process was repeated in 5 stages and air-dried at room temperature. The nucleation process of obtained nanoparticles occurred in the first stage and the aggregation process of nanoparticles took place after first stage till 5 stages. The PCPS were used as stabilizing agent for formation of copper sulfide semiconductor nanoparticles. The sample is stable at in ambient condition.
Results and discussions
During nucleation phase, copper sulfide nuclei are formed in the first cycle by the formation of ion-coordination bond between nickel metal ions and the functional groups of polymer matrix (-PO(OH)2 and (O)PO(OH)2 groups):
R-PO(OH)2+CuSO4-5H2O+H2O^R-POO2Cu+
+2H+ +H2O (1)
or
R-PO(OH)2+CuSO4- 5H2O+H2O-—RPO(OH)OCu++H++H2O
R-PO(OH)OCu++S2-
(2)
>R-PO(OH)CuxS, the
nucleation process
CuSO4- 5H2O+Na2S • 9H2O^CuxS+ +Na2SO4. the aggregation process
(4)
Fig.1. shows the X-ray diffraction pattern of copper sulfide nanocrystals and the PCPS to be used as a reference.
29 (0)
Figure 1. XRD pattern of (a) Cu18S/PCPS nanocomposite and (b) PCPS.
The XRD pattern at 29=200 in reference system (PCPS) has an obvious broad peak which commonly corresponds to the amorphous polymer materials. However, it is clearly observed from the XRD data that copper sulfide nanocrystals have been accurately formed as Cu18S in modified polymer matrix and demonstrate four mean peaks at 2 9 value of 28, 33, 47, 56 and 58.50 appropriate to the (111), (200), (220) and (222) planes, respectively which corresponds to the typical Cu18S nanocrystaline with cubic structure having lattice constant of a=b=c=5.9315 and alpha=betta=gamma=900 comparing with the database of the JCPDS-24-0061. The average diameter of Cu18S nano-crystallite is calculated by the Debye-Scherer's equation [20]:
aA
D =
p cos 0 '
where, D is the particle diameter of nanocrys-tallite, a constant (0.9), X the X-ray wavelength (1.5418 A), p is the half-width of the diffraction peak. The average size of nanoparticles Cu18S after five cycles of reaction was estimated 5 nm.
Optical absorption study of materials provides useful information to analyze some features concerning the band structure of materials. The optical absorption spectra of the samples were studied at room temperature (250C) using UV-vis absorption spectroscopy. Fig.2 shows the dependence of (ahv) on hv for obtained na-noparticles.
>
Eg,sV
Figure 2. hv dependence of (ahv)2 of PCPS a and Cu 8S/PCPS b.
The straight-line behavior testifies a direct transition of the band structure. It is well known that in case of semiconductors the band gap between the valence and conduction band increases as the size of the particle decreases in the nanosize range. In addition, the steep absorption edges observed indicate the uniform particle size and morphology with fairly good crystallinity. The band gap energy of Cu18S nanocrystals shows 3 eV.
The calculation of the band gap was carried out by using the dependence (aAv)2 on hv:
a -
hv ("v - ^ n
where a is the absorption coefficient, hv is the energy of the photon, Eg is the band gap energy. The band gap of Cu1.8S nanocrystals is 3 eV after five cycles of reaction which is greater than the values for bulk crystals of Cu18S. This is connected to quantum-dimensional effects in nanoparticles [18]. The Cu18S crystallites possess well-defined, broad optical, which have obvious blue shift, compared with microscale Cu18S crystallites in previous reports [15].
The surface morphological characterization by scanning electron microscopy (SEM) of Cu1.8S/PCPS is shown in Fig.3 and Fig.4.
Figure 3. SEM image of Cu18S/PCPS nanocomposite.
Figure 4. SEM image of sample and the C, S and Cu maps of same area.
The spherical shape is observed for the sample and it is in agglomerated state. The average particle size determined from the figure is in the range of 9-12 nm, which is slightly higher than the value obtained from XRD analysis. This is due to coalescence of smaller crystallites to form larger particles to lower Gibb's free energy. The structure was found to be compact and covered by the polymer material surface.
Fig. 5 shows the EDX results of the polymer-matrix composites Cu18S/PCPS. It proves that, the Cu1.8S nanoparticles were formed into the polymer sorbent and the phosphorus peak shows that the formation of nanoparticles goes on the phosphorus containing functional active groups. Element ratio of copper and sulphur in obtained copper sulfide nanoparticles depends on the time of sulphirizing.
The IR spectroscopy characteristic of functionalized nitrile rubber (PCPS) (a), nanocomposite material Cu18S/PCPS (b) and PCPS/Cu2+(c) are shown in Fig.6.
3000 2000
Wavenumber, cm-1
Figure 5. EDX results of the CuS/PCPS nanocomposite.
Figure 6. IR spectroscopy of PCPS (a), CuL8S/PCPS (b) and PCPS/Cu2+(c).
The broad band at 2100 and 2191 cm-1 can be assigned as the O-H stretching peak of the -OPO(OH)2 group formed by the chloro-phosphonation reaction of the polymer. Upon the formation of Cu18S nanoparticles this peaks have been disappearing. The peak of PO3 - at 977 cm-1 (Fig. 6a) shifts to 941 cm-1 (Fig. 6b) upon the formation of Cu18S nanoparticles.
Two new bands at about 993 and 619 cm-1 are also seen in the PCPS-copper sulfides spectra. Dixit et al. [22] attributed these bands to the existence of CuxS (x=1.8, 2) in the product. Any band due to copper sulfide is not observable in the IR spectra as the compound is not IR-active. The spectrum of nitrile group C=N has a characteristic absorption band in the range of 2245 cm-1. But in the PCPS spectra this characteristic absorption band is shown with low intensity.
Conclusion
In summary, nano-sized Cu18S semiconductor particles were synthesized into phosphorus containing polymer sorbent by SILAR method. By the X-ray diffraction (XRD) study we have determined the crystallite size and structural properties of nanoparticles. Cu18S nanoparticles exhibit cubic structure and the size of Cu18S nanoparticles are found to be about 5 nm. The band gap of Cu18S nano-particles is 3 eV. The SEM/EDX analyses showed that the synthesized materials are nanocomposites and the particle size of Cu18S is in the range of 9-12 nm. The IR spectroscopy of polymer-matrix composites Cu18S/PCPS have demonstrated that lots of functional active groups in polymer sorbent have been disappearing, because of the sorption processes by copper ions went intensive and most of functional active groups were undergone to expensing for the formation of copper-sulfide nanoparticles.
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FOSFORSAXLAYAN POLÍMER SORBENT OSASINDA MÍS SULFÍD (Cu18S) NANOKRÍS TALLARININ
KÍMYOVÍ yolla síntezí VO TODQÍQÍ
O.O.Balayeva, A.M.Mah3rramov, A.A.Ozizov, M.B.Muradov, N.O.Balayeva, Z.Q.Mamiyev, R.M.Alosmanov,
G.M.Eyvazova, Z.A.Agamahyev
Funksionallaçmiç nitril kauçuku NK-26 asasinda mis sulfid nanohissaciklarinin sintezi ardicil ion qatinin adsorbsiya va reaksiyasi metodu ila aparilmiçdir. Reaksiya otaq temperaturunda qoyulmuçdur. Rentgen toz diffraktometrindan alinan naticalara asasan kubik formada mis sulfidin (Cu18S) nanokristallik hissaciklari formalaçmiçdir. Cu18S nanokristal-lannin ôlçûsû 5 nm-dir. Qadagan olunmuç zolagin eni 3eV-dur. Skanedici elektron mikroskopu va enerji-dispersion rentgen spektroskopiya (SEM/EDX) analizi göstarir ki, sintez olunmuç materiallar nanokompozitdirlar va Cu18S his-saciklarinin ôlçûsû SEM-a göra 9-12 nm tartibindadir. infraqirmizi spektroskopiya (ÍQ) naticalarina göra nanohissa-ciklar polimerin -PO(OH)2 funksional qruplannda amala galmiçdir va polimer sorbentdaki bir çox funksional qruplar bu sababdan itmiçdir. Alinmiç nanokristallar kvant nöqtalar olub fotoelektronikada istifada oluna bilar.
Açar sözhr: nanokompozithr, Cu18S, optiki xassahr, skanedici elektron mikroskopu, (SEM).
ХИМИЧЕСКИЙ СИНТЕЗ И ИССЛЕДОВАНИЕ НАНОЧАСТИЦ СУЛЬФИДА МЕДИ (Cu18S) НА ОСНОВЕ ФОСФОРСОДЕРЖАЩЕГО ПОЛИМЕРНОГО СОРБЕНТА
О.О.Балаева, А.М.Магеррамов, А.А.Азизов, М.Б.Мурадов, Н.О.Балаева, З.Г.Мамиев, Р.М.Алосманов, Г.М.Эйвазова, З.А.Агамалиев
Синтез наночастиц сульфида меди на основе функционализированного каучука СКН-26 осуществлен методом последовательных адсорбции ионного слоя и реакции (ПАИСР). Реакция проведена при комнатной температуре. Данные рентген-порошкового диффрактометра показывают формирование нанокристаллов Cu18S в кубической форме. Размер кристаллитов - 5 нм. Ширина запрещенной зоны наночастиц Cu18S - 3 эВ. Анализ РЭМ/ЭРС показал, что синтезированные материалы являются нанокомпозитами, и размеры частиц Cu18S находятся в диапазоне 9-12 нм. Результаты ИК-спектроскопии показывают, что наночастицы образованы на функциональной группе -PO(OH)2 полимера. Полученные нанокристаллы являются квантовыми точками и могут быть применены в фотоэлектронике.
Ключевые слова: нанокомпозиты, Cu1.8S, оптические свойства, растровый электронный микроскоп (РЭМ).
AЗЕPБAЙДЖAHCKИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 2 2015
