الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 283 |  |  |
| | | from | 283 | | |
Abstract
One goal of device science is miniaturization; hence nanotechnology has received considerable attention. The possibility that the unique properties of nanostructures will result in novel applications and devices is an enticing goal. Another reason for the great popularity of this field is that phenomena occurring on this length scale are of interest to physicists, chemists, biologists, electrical and mechanical engineers and computer scientists. Although many nano-structures such as large molecules and quantum dots are of interest, at present, one of the most active areas is the study of nanotubes.
In view of the prespective of green chemistry, we attempt to explore regenerative materials for MWCNTs synthsis with high efficiency. In this thesis a well graphitized MWCNTs were synthesized from camphor solid using alumina supported Fe, Ni, Co and TiO2 catalysts by wet impregnation method via the chemical vapor deposition (CVD) technique.
This method clearly emerges as the best one for large scale production of MWCNTs, using flowing nitrogen gas. There are many important factors that affect the yield and quality of the as-synthesized MWCNTs, including metal composition, weight of the catalyst, catalyst oxidation temperature and reaction time. These parameters are to be optimized to get the product of the desired quality. A series of experiments was performed to produce different catalysts and bimetallic catalysts which are used in MWCNTs synthesis, these catalysts are Fe/Al/700, Fe/Al/800, Ni/Al/700, Ni/Al/800, Co/Al/700, Co/Al/800, Fe-Ni/Al/700, Fe-Ni/Al/800, Ti/Al/700, Ti/Al/800, Fe-Ti/Al/700 and Fe-Ti/Al/800.
Our experimental findings show that among the types of active metals onto alumina supported investigated that the catalyst composed from iron nitrate supported onto alumina and calcined at 7000C (Fe/Al/700) is the most suitable catalyst for synthesis of MWCNTs with high amount and high quality. Large yield of MWCNTs were observed at 8500C.
MWCNT purification step removes amorphous carbon from MWCNTs, improves surface area and decomposes functional groups blocking the entrances of the pores, this done through acid treatment. Refluxing as-grown MWCNTs in a mixture of 5M of [HNO3+HCl] for 4 h at 1000C helps as-grown MWCNTs functionalized with conducting aniline polymers.
Polymers can be easily processed and fabricated into intricately shaped components without damaging MWCNTs during processing using conventinal methods and hence the manufacturing cost can be certainly reduced. Therefore, MWCNT based polymer composites (MWCNT/polymer nanocomposite) stimulates great interests and have been extensively investigated.
An attempt was done to obtain a polymer with desired properties, it is necessary to determine the optimal conditions of its synthesis as dopant concentration, monomer concentration, oxidant concentration and type through oxidative chemical polymerization of aniline monomers, its polymer is polyaniline (PANI), is one of the most studied conducting polymers owing to its environmental stability, low-cost reagent and its simple synthesis method.
The conductivity, yield and viscosity of PANI depend on various factors e.g: i) oxidizing agents, ii) aniline/oxidant molar ratio, iii) concentration of protonoic acid, iv) reaction temperature, v) polymerization time. We determined the optimal conditions for synthesis the polymer including dopant concentration [HCl]. Monomer concentration includes three types [N-methylaniline, o-Toluidine and m-Toluidine]. The oxidants are ferric chloride (FeCl3), potassium dichromate (K2Cr2O7) and ammonium peroxy disulphate ((NH4)2S2O8).
We conducted an optimization of the processing conditions for dispersing the MWCNTs through aniline derivative monomers with different weight ratios of [0.5:1, 1:1 and 1.5:1] according to the removal of organic (methylene blue) and inorganic (lead) pollutants from aqueous solution. We reached a maximum value with the weight ratio of (0.5:1) (MWCNTs:monomer).
All samples were characterized using a number of complementary techniques including elemental analysis, Fourier Transform Infrared (FTIR), High Resolution Transmission Electron Microscope (HRTEM), Scanning Electron Microscope (SEM), evaluatin of texture parameters by determination of the N2/77K adsorption isotherms which are derived by application of the BET, X-Ray Diffraction (XRD), UV-Vis absorption analysis and solubility of substituted polyaniline polymers.
Testing of the as-grown MWCNTs and their nanocomposites was achieved by the multi-point adsorption isotherms technique and applying the linear Langmuir and Freundlich isotherm models. The uptake of a standard probe molecule was tried a bulky dye ”methylene blue”(MB) and lead ions (Pb2+) from lead nitrate aqueous solutions.
The XRD diffraction pattern for the catalyst Fe/Al/700 assigned the presence of Boehmite (AlOOH) and hematite (α-Fe2O3). For the as-grown MWCNT there are two characteristic peaks at 2θ0 of 260 and 440 corresponding to interlayer spacing of nanotubes and reflection of carbon atoms, respectively.
Functionalization of as-grown MWCNTs identified by FTIR clearly showed the presence of C=C, (-COOH) at 1701.2 cm-1,C-H and –NH attached to benzene rings, C=N in quinoid structure for polymer samples. Such groups offer free active sites and consequently increase cation exchange capacity.
Surface area of the as-synthesized MWCNTs decreased after being incorporated to the polymer matrix, this is may be attributed to that polymer may block the pores and cavities of MWCNTs.
The subsequent studies of the morphology of the as-synthesized MWCNTs grown by chemical vapor deposition (CVD) revealed the tubular nanostructure. For the nanocomposites characterization, the XRD analysis revealed that polyaniline is partially crystalline separated by large amorphous region. This peak is very much sharper in MWCNTs/P-aniline nanocomposite because of much enhanced-conjugation in MWCNTs. The FTIR analysis confirmed the formation of polymer.
Morphology investigations show that polymer is polymerized between the wedges of MWCNTs as well as on the tube surfaces.
The rod and coiled like structures of MWCNTs are dispersed in the polymer matrix. The UV-Vis absorption analysis of the prepared polymers revealed the presence of benzenoid rings due to π-π* transition, appearance of charged cationic species called polarons in P-NMA, while the other 2 spectra for P-oTol and P-mTol showed a high conjugation of aromatic polymer chain.
MWCNT embedded in a polymer matrix from a distributed interface was directly related to the performance of the nanocomposite. This can be seen at liquid phase adsorption, nanocomposites samples exhibit higher adsorbing capacity for Pb2+ ranging between 111.3 and 83.33 mg/g than as-synthesized MWCNTs which exhibit an adsorption capacity of 83.33 mg/g. Removal capacity of Pb2+ from the aqueous medium seems to be governed by the functional groups and their distribution in the nanocomposite samples (nitrogen in polymer, also –OH, -COOH and -C=O onto the surface of MWCNTs).
Concerning the uptake of methylene blue (MB), it is postulated that as-grown MWCNTs-Fe/Al/700 is better adsorbent than nanocomposite samples. This can be ascribed to the larger specific surface area and pore volume than modified nanocomposites due to the pore blockage as a result of modification.
Finally, all the above results show that the obtained as-grown MWCNTs under different conditions and their nanocomposites are excellent nano-adsorbents for decontamination of both heavy metal (Pb2+) and organic dye pollutants. Camphor seems to be an excellent CNT precursor, not only in terms of ease of fabrication and high yield, but also in terms of growth control and application prospects. ”Many good things in one package”.