الفهرس 
Introduction and Literature SurveyOnly 14 pages are availabe for public view
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Abstract
Summary
Carbon nanotubes have a great attention in recent times because of their extraordinary physiochemical properties; such as electrical and thermal conductivity, flexibility, strength, sensors,. etc. Thus unique properties make nanotubes the most interesting material, as well as potentially useful for future technologies.
In the present work, MWCNTs were synthesized by atmospheric pressure chemical vapor deposition system (APCVD). bimetallic catalyst (Fe2O3-Co3O4) with MgO as a supported catalyst were required for synthesizing MWCNTs. The catalyst was prepared by the impregnation method which depends on increasing the surface area. MWCNTs were purified and functionalized by using acid treatment (conc HNO3 and conc H2SO4 with 3:1%).
The purified MWCNTs were decorated with a the three metals oxides nanoparticles(ZnO, Co3O4, CuO) via hydrothermal treatment methods. The unpurified, purified MWCNTs, and decorated MWCNTs with ZnO, Co3O4, and CuO were characterized by different interesting characterization techniques as; field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), X-ray powder diffraction (XRD), Fourier transformer infrared spectroscopy (FTIR), thermogravemtric analysis (TGA-DTA) and Raman spectroscopy.
• FESEM images showed a few nanotubes impeded with a little amount of metal catalyst. After purification, the integrity structure of MWCNTs is observed.
• The micrograph images of HRTEM confirmed the hollow-core structure of MWCNTs. It estimated the outer and inner diameter of MWCNTs in nano range. The inner and outer diameter are about 6, 25.7 nm, respectively.
• The morphology of nanocomposite ZnO/MWCNTs was characterized by HRTEM to insure the distribution of nanoparticles of metal oxide on the surface of MWCNTs. the micrograph images showed the distribution of spherical pores of ZnO nanostructure . The main average size reach about 38 nm.
• HRTEM images also confirm the homogenous distribution of Co3O4 on the surface of MWCNTs without any agglomeration on the surface of nanotubes. The average diameter is about 49nm.
• Also HRTEM images showed a high successively magnifications of monoclinic structure of small CuO crystals and have sizes in nano ranges. HRTEM images described the distribution of CuO nanoparticles on MWCNTs surface.
• The XRD pattern of the catalytic particles; showed that the diffraction peaks of support catalyst (MgO) pattern are becoming sharper. Another small peaks are assigned to Fe2O3, Co3O4. As well as, indicating to the good crystallinity structure of samples.
• The hexagonal graphite structure of MWCNTs was also confirmed by XRD patterns at 2θ=26.3ο - 44.7ο . The inner diameter of MWCNTs was obtained about 6.4 nm which is closely the same obtained from HRTEM images. Also XRD patterns confirm the crystallinity structure of ZnO, Co3O4 and CuO nanoparticles with main size equal 40, 50 and 43 nm, respectively. .
• FTIR spectra for unpurified MWCNTs showed the presence of carboxylic group on the surface of unpurified MWCNTs, which could be due to partially oxidation may occur during the manufacturing process. The spectra confirm the existence of the C=C stretching vibration of the CNTs surface which appears at 1631 cm-1.
• For purified MWCNTs; FTIR spectra confirm successful oxidation of MWCNTs and confirm the existence of carboxylic group –COOH on it is surface due to acid treatment. The results prove the well purification and functionalization process.
• FTIR spectra eastimated also the interaction between MWCNTs surface and metals oxides (ZnO, Co3O4, CuO) nanoparticles. It showed the stretching vibration at 458 cm-1 related to ZnO nanoparticles .
• Also, it was noticed that the FTIR spectra confirm the presence of Co3O4 structure on the surface of nanotubes, where The sharp bands at 668 and 560 cm-1 are related to the presence of Co+2 which refers to tetrahedral coordinate structure and Co+3 refers to octahedral coordinate. Finally, FTIR spectra estimated the bands at 447 cm-1, 606 cm-1 that related to the stretching vibration mode of Cu-O in the monoclinic structure CuO.
• Thermogravimetric analysis measurements (TGA-DTA) deduced the decomposition temperatures of both unpurified and purified MWCNTs that higher than 550οC. The results reflect the higher thermal stability of MWCNTs. TGA measurements showed the existence of a little number of metallic particles 15%, and after treatment with strong acids is about 7%. The result refers to the well purification process obtained.
• TGA-DTA analysis of ZnO/MWCNTs showed that the amount of ZnO nanoparticles influences the stability of nanotubes. Nevertheless, our sample has high quality with suitable thermal stability and all exothermic peaks before 600οc disappear. Furthermore, the TGA-DTA curves Co3O4/MWCNTs nanocomposite reveals wight loss about 40% corresponding to an exothermic at 420 οC representing the oxidation of MWNTs.
• Also, the TGA curve showed the amount of CuO nanoparticles percentage on the surface of nanotubes is about 75%. Then DTA curves gave an exothermic peak at 522οC which indicated the oxidation of MWCNTs.
• Raman spectra are showed the high energy mode that is called G graphite band (C=C). The ID/IG ratio for unpurified and purified MWCNTs samples are equal 0.85, 0.6, respectively. Thus results indicated to the high quality of MWCNTs structure.
• Raman spectra are also confirm the formation of ZnO, Co3O4 and CuO nanoparticles structure on the active sites of MWCNTs surface.
• Molecular modeling calculations is applied by using HF method at Sto-3G basis set. The method was suitable for studying the molecular structure of CNT and the interaction of CNT with ZnO,CuO and Co3O4 nanoparticles.
• molecular electrostatic potential (MESP) studies showed that the distribution of charges outside and inside CNT surface as alone and after the interaction with the three nanoparticles. The studies showed the change of colors from red to blue color (high to low energy) in case of the three nanocomposite. The results indicated to the high reactivity properties of CNT after functionalization As comparison with CNT which is neutral.
• Also, Results of calculated TDM confirm the MESP results where TDM of CNT increased due to the interaction of CNT with metal oxides. The results showed that the highest reactivity and highest dipole moment belong to CNT-Co-O as adsorb state is about 21.1 Debeye. Additionally, band gap energy results showed that CNT-Co -O as adsorb state has the lowest value of energy gap 2.26 eV.
• Molecular modeling calculations deduced that the nanocomposite Co3O4/MWCNTs is the most reactive one in comparison with the other structures. This makes CNT-Co-O suitable for sensor application.
• The nanocomposite of Co3O4/MWCNTs was studied and evaluated as a humidity sensor. The impedance was recorded with changing humidity level in the range RH% (11%-97%). and frequancy (50 HZ-1000 KHZ). The results showed the optimum frequancy at 50HZ.
• The humidity sensor revealed a good response time about 65 sec and recovery time about 275 sec. In addition to the hysteresis loop reach about 15% . The humidity sensor offers an excellent repeatability with increasing and decreasing humidity levels.