QUANTITATIVE ANALYSIS OF CARBON NANOTUBE SUSPENSIONS, SYNTHESIS OF INORGANIC NANOSTRUCTURED MATERIALS AND THEIR CHARACTERIZATION
Tez Türü: Doktora
Tezin Yürütüldüğü Kurum: Yıldız Teknik Üniversitesi, Metalurji Ve Malzeme Mühendisliği/Malzeme, Türkiye
Tez Danışmanı: Kaya C, Kaya F.
Tezin Onay Tarihi: 2015
Desteklendiği Program: Diğer
Özet:
This thesis consists of two separate studies. Under the scope of the first study dispersion of carbon nanotubes in organic solvents was carried out and carbon nanotube reinforced iron oxide composites were produced. MWCNTs suspensions were prepared in environments where IPA is the solvent. To provide homogeneous dispersion of MWCNTs in IPA, PVP and SDBS were utilized as additives. Ultrasonic mixing and subsequent to this operation implementation of centrifugation facilitated acquiring both PVP and SDBS containing stable suspensions. Zeta potential analysis and sedimentation tests indicate that suspensions are stable. UV-Vis absorption spectroscopy was used to determine concentrations of PVP, SDBS and MWCNTs in suspensions in which information about concentration of components is lost by implementation of centrifugation. TGA was also perfomed on dried precipitates and suspensions for comparison with UV-Vis analysis results.
MWCNTs were coated on metallic substrates by means of EPD. While performing EPD with PVP containing MWCNTs suspensions, it is found that acquiring of adherence of MWCNTs on substrate surface couldn’t be established; this problem was overcome by adding magnesium ions in suspensions at certain concentrations. It is realized that UV-Vis spectroscopy can be used to estimate material quantity in coatings obtained by means of EPD. It is found that evaluation of UV-Vis spectra of suspensions before and after EPD process facilitated estimation of material quantity in coatings and at the same time it enabled calculation of coating thickness, but this technique neglects porosity in coating.
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Solvothermal synthesis was used to produce MWCNTs Fe3O4 composite materials. In composite making process prepared MWCNTs suspensions were mixed with precursors of Fe3O4 nanoparticles before synthesis. To facilitate interation between MWCNTs and Fe3O4 nanoparticles in order to provide homogeneous dipersion of components in the structure, surface of Fe3O4 nanoparticles were coated with carbon during synthesis; subsequently this interaction was examined whether it is existing or not. Glucose and ascorbic acid was used in order to prepare Fe3O4@C core-sell nanoparticles by means of solvothermal synthesis (200 °C, 12 h.). It is understood from XRD analysis that synthesized nanoparticles are Fe3O4. FTIR invesitagations revealed that glucose or ascorbic acid aided synthesis products contain carbon and OH functional groups in their structure. It is understood from the SEM investigations that nanoparticles which are obtained by the aid of glucose or ascorbic acid possess spherical morphology; however after synthesis facilitated without addition of this two materials resulted in Fe3O4 nanoparticles having octahedron shapes.
It is found that Fe3O4@C core-sell spherical nanoparticles are composed of smaller sub 100 nm sized particles. As a result of applied magnetic fields on MWCNTs- Fe3O4@C suspensions, it is shown that components separate; while Fe3O4@C nanoparticles migrate towards magnets, nanotubes remain in suspension. The reason behind phase separation is believed to be the the consequence of functional groups present on carbonized particle surfaces’. It can be also said that both SDBS and PVP do not provide sites for nanoparticles to crystallize on nanotube surfaces.
Second study of this thesis is about production and characterization of inorganic nanotubes.
Sulphur doped or pure TiO2 nanopartilces were produced by means of sol-gel process. For doping process of TiO2, starting materials of TiO2 were mixed with thiourea (CH4N2S) during sol-gel process. Titanate nanotubes were produced from TiO2 nanoparticles by hydrothermal synthesis (130 °C, 24h.) under alkali environments. It is understood from the result of TEM analysis that produced nanotubes are around 10 nm in diameter and 100 nm in length. As a result of washing with dilute acids and water, nanotubes transformed into hydrogen titanates by the removal of sodium in their structure. TEM analysis revealed that hydrogen titanate nanotubes remain intact at 350°C, but they transform into thin nanorods and nanoparticles by decomposing at 450 °C. UV-Vis absorption spectroscopy was used to assess the electron energy band gaps of nanotubes which were subjected to different processes. Apart from doping and calcination some titanate nanotubes were analyzed after H2O2 washing. It is revealed that among investigated nanotubes the lowest band gap values (3.27 eV) were obtained from H2O2 washed and subsequently calcined (350°C) samples. It is understood that band gap value of sulphur doped and subsequently calcined (350°C) nanotubes (3.31 eV) is almost the same as that of undoped and subsequently calcined nanotubes (3.30 eV). It is understood that upon washing nanotubes with H2O2, the ESR signal corresponding to SETOV diminish. Therefore, the decrease in band gap value is attributed the elemination of SETOV by H2O2.
In addition, nanotube coatings were obtained on conductive substrates by means of EPD. It is understood that butanol-TEA solvent-dispersant combination enable production of relatively stable nanotube suspensions which can be used in electrophoretic deposition processes.
Key words: Carbon Nanotube, Suspension, Quantitative Analysis, UV-Vis Absorption Spectroscopy, Electrophoretic Deposition, Fe3O4, Nanoparticle, Solvothermal Synthesis, Hydrothermal synthesis, MWCNT, TiO2, Inorganic nanotube
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