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Lect 4 carbon age
 
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Prof. Dr. Mohamed Khedr

Prof. Dr. Mohamed Khedr
Dean of Beni Swef Faculty - postgraduate studies for Advanced Sciences

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    Lect 4 carbon age Lect 4 carbon age Presentation Transcript

    • Carbon Age Prof. Mohamed Khedr Faculty of Postgraduates for advanced Sciences, Beni-Suif University
    • Carbon Melting point: ~ 3500oC • Atomic radius: 0.077 nm • Basis in all organic componds • 10 mill. carbon componds •
    • Nanocarbon • • • • • • • • • Fullerene Tubes Cones Carbon black Horns Rods Foams Nanodiamonds Graphene M. Khedr, A. Farghali, A. Moustafa and M. Zayed, International Journal of Nanoparticles, 2009, 2, 430-442. M. Khedr, K. Abdel Halim and N. Soliman, Materials Letters, 2009, 63, 598-601.
    • Carbon black Large industry - mill. tons each year • Tires, black pigments, plastics, dry-cell batteries, UV-protection etc. • Size: 10 – 400 nm
    • Fullerene ”The most symmetrical large molecule” • Discovered in 1985 - Nobel prize Chemistry 1996, Curl, Kroto, and Smalley • C60, also 70, 76 and 84. - 32 facets (12 pentagons and 20 hexagons) - prototype Epcot center, Paris ~1 nm Architect: R. Buckminster Fuller
    • Graphene…….!!! •• It's so strong of paper but a million times thinner. This “Imagine a piece that It would take something is how thick an elephant, balanced on a pencil, the size of graphene is. to break through a sheet of graphene the • Imagine a material stronger than diamond. This is how thickness of ais. strong graphene piece of paper. • Graphene is the strongest, yet thinnest possible material you can imagine.
    • Allotropes of Carbon Diamond, graphite, lonsdalerite, C60, C70, carbon, amorphous carbon, carbon nanotube
    • What are carbon nanotubes? • Tubes with walls made of carbon (graphite) • Nanometers in diameter • Up to tens of micrometers in height • Extremely good strength and field emission properties
    • Classification of CNs: single layer • Single-wall Carbon nanotubes (SWNTs,1993) – one graphite sheet seamlessly wrapped-up to form a cylinder – typical radius 1nm, length up to mm (10,10) tube (From Dresselhaus et al., Physics World 1998) (From R. Smalley´s web image gallery)
    • Classification of CNs: ropes • Ropes: bundles of SWNTs – triangular array of individual SWNTs – ten to several hundreds tubes – typically, in a rope tubes of different diameters and chiralities (From R. Smalley´s web image gallery) (From Delaney et al., Science 1998)
    • Classification of CNs: many layers • Multiwall nanotubes (Iijima 1991) – russian doll structure, several inner shells – typical radius of outermost shell > 10 nm (From Iijima, Nature 1991) (Copyright: A. Rochefort, Nano-CERCA, Univ. Montreal)
    • Why Carbon nanotubes so interesting ? • Technological applications – – – – conductive and high-strength composites energy storage and conversion devices sensors, field emission displays nanometer-sized molecular electronic devices • Basic research: most phenomena of mesoscopic physics observed in CNs – – – – – – ballistic, diffusive and localized regimes in transport disorder-related effects in MWNTs strong interaction effects in SWNTs: Luttinger liquid Coulomb blockade and Kondo physics spin transport superconductivity
    • Important History • 1991 Discovery of multi-wall carbon nanotubes by S. Iijima • 1992 Conductivity of carbon nanotubes J. W. Mintmire, B. I. Dunlap and C. T. White • 1993 Structural rigidity of carbon nanotubes G. Overney, W. Zhong, and D. Tománek • 1993 Synthesis of single-wall nanotubes by S Iijima and T Ichihashi • 1995 Nanotubes as field emitters By A.G. Rinzler, J.H. Hafner, P. Nikolaev, L. Lou, S.G. Kim, D. Tománek, P. Nordlander, D.T. Colbert, and R.E. Smalley • 1997 Hydrogen storage in nanotubes A C Dillon, K M Jones, T A Bekkendahl, C H Kiang, D S Bethune and M J Heben • 1998 Synthesis of nanotube peapods B.W. Smith, M. Monthioux, and D.E. Luzzi • 2000 Thermal conductivity of nanotubes Savas Berber, Young-Kyun Kwon, and David Tománek • 2001 Integration of carbon nanotubes for logic circuits P.C. Collins, M.S. Arnold, and P. Avouris • 2001 Intrinsic superconductivity of carbon nanotubes M. Kociak, A. Yu. Kasumov, S. Guéron, B. Reulet, I. I. Khodos, Yu. B. Gorbatov, V. T. Volkov, L. Vaccarini, and H. Bouchiat
    • • Structure of carbon nanotubes Classification of nanotube models, (a) armchair, (b) zigzag and (c) chiral SWNTs.
    • Nanotube’s characteristic •Seemless cylindrical molecules •Diameter as small as 1 nm. •Length: a few nm. to serveral micron •As a monoelemental polymer: Carbon atoms only •As hexagonal network of carbon atoms •CNTs are single molecules comprised of rolled up graphene sheets capped at each end.
    • Nanotube’s characteristic • Young’s modulus of elasticity ~ 1 TPa (Tera = 1012) • Tensile strength > 60 GPa (Steel ~ 2 GPa) • Conductivity of CNTs ~ 109 A/cm2 (Copper 106 A/cm2 )
    • Applications Lithium Ion Batteries Ultra Capacitors Charge Storage M. Khedr, M. Bahgat, M. Radwan and H. Abdelmaksoud, Journal of materials processing technology, 2007, 190, 153-15 M. Bahgat, M. Khedr, M. Nasr and E. Sedeek, Metallurgical and Materials Transactions B, 2007, 38, 5-11
    • Applications Plasma TV Flat screen displays M. Bahgat, M. Khedr, M. Nasr and E. Sedeek, Materials science and technology, 2006, 22, 315-320. M. Khedr, M. Bahgat, M. Nasr and E. Sedeek, Colloids and surfaces A: Physicochemical and engineering aspects, 2007, 302, 517-524.
    • Applications • Vacuum tubes - Nobel prize 1906, Thomson. • Semiconductor, Sibased - Nobel prize 1956, Shockley, Bardeen, and Brattain. - 2000, Kilby. IBM, 1952. Transistor M. Hessien and M. Khedr, Materials research bulletin, 2007, 42, 1242-1250. K. S. Abdelahalim, A. M. Ismail, M. H. Khedr and M. F. Abadir, in First Afro-Asian Conference on Advanced Material Technology, Nov. 13-16, Cairo - EGYPT, Editon edn., 2006.
    • Applications Electric devices K. Abdel Halim, M. Khedr, M. Nasr and A. El-Mansy, Materials research bulletin, 2007, 42, 731-741. M. Khedr, M. Sobhy and A. Tawfik, Materials research bulletin, 2007, 42, 213-220.
    • Applications 2 H2(g) + O2(g) → 2 H2O (l) + energy Mg2NiH LaNi5H 3.16 wt% 6 H2 (liquid) H2 (200 bar) 1.37 wt% Hydrogen storage M. H. Khedr, A. A. Farghali and A. Abdel-Khalek, Journal of analytical and applied pyrolysis, 2007, 78, 1-6. A. A. Farghali, M. H. Khedr and A. A. Abdel Khalek, Journal of materials processing technology, 2007, 181, 81-87.
    • Applications Atomic Force Microscopy M. Khedr, A. Omar and S. Abdel-Moaty, Materials Science and Engineering: A, 2006, 432, 26-33. M. Khedr, A. Omar and S. Abdel-Moaty, Colloids and surfaces A: Physicochemical and engineering aspects, 2006, 281, 8
    • Current Applications • Carbon Nano-tubes are extending our ability to fabricate devices such as: • Molecular probes • Pipes • Wires • Bearings • Springs • Gears • Pumps
    • Structural clothes: waterproof tear-resistant compat jackets: that use carbon nanotubes as ultrastrong fibers and to monitor the condition of the wearer. concrete: They increase the tensile strength, and halt crack propagation. polyethylene: Researchers have found that adding them to increases the polymer's elastic modulus by 30%. sports equipment: Stronger and lighter tennis rackets, bike parts, golf balls, golf clubs, golf shaft and baseball bats. space elevator: This will be possible only if tensile strengths of more than about 70 GPa can be achieved. Bridges: For instance in suspension bridges (where they will be able to replace steel), or bridges built as a "horizontal space elevator".
    • buckypaper- a thin sheet made from nanotubes that are 250 times stronger than steel and 10 times lighter that could be used as a heat sink for chipboards, a backlight chemical nanowires: Carbon nanotubes additionally can also be used to produce nanowires of other chemicals, such as gold or zinc oxide. These nanowires in turn can be used to cast nanotubes of other chemicals, such as gallium nitride. computer circuits: A nanotube formed by joining nanotubes of two different diameters end to end can act as a diode. conductive films: A 2005 paper in Science notes that drawing transparent high strength swathes of SWNT is a functional production technique are developing transparent, electrically conductive films of carbon nanotubes to replace indium tin oxide(ITO) in LCDs, touch screens, and photovoltaic devices.
    • electric motor brushes: Conductive carbon nanotubes have been used for several years in brushes for commercial electric motors. They replace traditional carbon black, which is mostly impure spherical carbon fullerenes. light bulb filament: alternative to tungsten filaments in incandescent lamps. magnets: MWNTs coated with magnetite optical ignition: A layer of 29% iron enriched SWNT is placed on top of a layer of explosive material such as PETN, and can be ignited with a regular camera flash. solar cells: GE's carbon nanotube diode has a photovoltaic effect. Nanotubes can replace ITO in some solar cells to act as a transparent conductive film in solar cells to allow light to pass to the active layers and generate photocurrent. superconductor: Nanotubes have been shown to be superconducting at low temperatures. ultracapacitors: MIT is researching the use of nanotubes bound to the charge plates of capacitors in order to dramatically increase the surface area and therefore energy storage ability. displays: One use for nanotubes that has already been developed is as extremely fine electron guns, which could be used as miniature cathode ray tubes in thin high-brightness low-energy low-weight displays. transistor: developed at Delft, IBM, and NEC.
    • Chemical air pollution filter: Future applications of nanotube membranes include filtering carbon dioxide from power plant emissions. biotech container: Nanotubes can be opened and filled with materials such as biological molecules, raising the possibility of applications in biotechnology. hydrogen storage: Research is currently being undertaken into the potential use of carbon nanotubes for hydrogen storage. They have the potential to store between 4.2 and 65% hydrogen by weight. water filter: Recently nanotube membranes have been developed for use in filtration. This technique can purportedly reduce desalination costs by 75%. Mechanical oscillator: fastest known oscillators (> 50 GHz). nanotube membrane: Liquid flows up to five orders of magnitude faster than predicted by classical fluid dynamics. slick surface: slicker than Teflon and waterproof.
    • Properties unusual current conduction mechanism: that make them ideal components of electrical circuits. Currently, there is no reliable way to arrange carbon nanotubes into a circuit. The major hurdles that must be jumped for carbon nanotubes to find prominent places in circuits relate to fabrication difficulties. The production of electrical circuits with carbon nanotubes are very different from the traditional IC fabrication process. The IC fabrication process is somewhat like sculpture - films are deposited onto a wafer and pattern-etched away. Because carbon nanotubes are fundamentally different from films, carbon nanotube circuits can so far not be mass produced. atomic force microscope in a painstaking, time-consuming process. Perhaps the best hope is that carbon nanotubes can be grown through a chemical vapor deposition process from patterned catalyst material on a wafer, which serve as growth sites and allow designers to position one end of the nanotube. place the nanotubes from solution to determinate place on a substrate. Even if nanotubes could be precisely positioned, there remains the problem that, to this date, engineers have been unable to control the types of nanotubes—metallic, semiconducting, single-walled, multi-walled—produced. A chemical engineering solution is needed if nanotubes are to become feasible for commercial circuits.
    • Production Methods • Arc discharge • Laser ablation • Chemical Vapor Deposition (CVD)
    • Arc–Discharge Process • High-purity graphite rods under a helium atmosphere. • T > 3000oC • 20 to 40 V at a current in the range of 50 to 100 A • Gap between the rods approximately 1 mm or less •Lots of impurities: graphite, amorphous carbon, fullerenes Arc-discharge apparatus
    • Laser Ablation Process • Temperature 1200oC • Pressure 500 Torr • Cu collector for carbon clusters • MWNT synthesized in pure graphite • SWNT synthesized when Co, Ni, Fe, Y are used • Laminar flow • Fewer side products than Arc discharge Laser ablation apparatus
    • CVD in Gas Phase Process • Catalysts: Fe, Ni, Co, or alloys of the three metals • Hydrocarbons: CH4, C2H2, etc. • Temperature: First furnace 1050oC Second furnace: 750oC • Produce large amounts of MTWNs
    • Comparison of Nanotube Production Technology
    • The CVD method has been reported to be the most selective in CNTs formation It can produce relatively large amounts of CNTs at lower cost because it proceeds under mild conditions. The CVD process makes it possible to control the purity of product, the size and growth density of CNTs by regulating the reaction parameters and catalyst composition as well as by modifying . The CNTs can also be readily isolated using chemical means (HCl, HNO3, and HF), or ultra-sound treatment and heating. it suitable for large area, irregular-shaped substrates and multiple-substrate coatings, It the most widely utilized duo to their versatility, and industrial scalability
    • Controlling The yield %, and type of CNTs • The yield %, and type of CNTs deposited depends on support type ,percentage and type of metal loading, reaction temperature, time, catalyst particles size, carrier gas flow rate and finally the carbon source “ CO, CO2, CH4, C2H6, C2H4 and C2H2” • C2H2 exhibits very high carbon feed stock and very high activity in producing metal carbide compared to CH4 and CO • Finally, acetylene is more reactive than other hydrocarbons at the same reaction temperature, leading to CNTs of good quality.
    • Selecting the materials of the present study; • Ferrites have continued to attract attention over years. • As magnetic materials, Ferrites cannot be replaced by any other materials. • Ferrites are relatively inexpensive, stable and have a wide range of technological applications in the fabrication of high quality filters, high frequency circuits and operating devices. • Recently, ferrites are reported to be good catalysts for many chemical processes. Among these processes, the decomposition of CO2 was investigated as a process of both industrial and environmental importance . • Because CO2 is a a major component of the greenhouse gases, which caused the global worming, Freshly reduced copper ferrite was selected as a catalyst for the decomposition of CO2.
    • CO2 Catalytic decomposition Over freshly reduced CuFe2O4 • CO2 was allowed to decompose spontaneously to carbon at 400-600oC during the reoxidation of nano-crystallite metallic phase of Cu & Fe compacts, produced from the reduction process. • XRD analysis obtained for all samples produced from the reduction-reoxidation experiments at different temperatures indicates that all samples contain the iron austenite and magnetite phases, which reveals that CO2 decomposes during the reoxidation process to carbon and oxygen forming the austenite and magnetite. • Deposited carbon was detected by C-analysis. • Carbon in the form of Nano-tubes was detected by SEM. • For more evidence, carbon nano-tubes were isolated by suspention in acetone, TEM was used to prove the formation of Carbon Nano- 200 nm
    • Production of carbon nanotubes using nanosized metallic iron
    • • A catalyst of the composition 40%Fe2O3:60%Al2O3, was prepared by wet impregnation method A certain amount of nanosized iron oxide powder was mixed with Al2O3 powder and stirred for 1 hrs at 60 oC. The impregnate was then dried in an oven at 100 oC for 3 hrs, calcined at 400 oC for 4 hrs in a box muffle furnace. • The catalysts was reduced at 500 oC at 1l/min in H2 flow and CNTs were synthesized at the same reduction temperature by flowing 10%C2H2:90%H2 to know the most effective crystal size of iron oxide that give the highest percentage yield of CNTs at 500 oC.
    • • The effect of growth temperature on the percentage yield was also examined for iron oxide with crystal size 35 nm by carrying out the acetylene decomposition reaction at temperature 400, 500, 600 and 700 oC. • The synthesized CNTs were cooled in H2 flow and the weight of deposited CNTs was detected using weight gain technique. • C, % = (W1 – W2) / W2 ]*100 • where W2 is the initial weight of the catalyst (Fe ) and W1 is the weight of carbon deposited and catalyst. • The structure and morphology of the synthesized CNTs were characterized using XRD and HTEM
    • 250 200 Carbon yield (%) Samples of nanosized iron oxides (supported in alumina) were reduced at 500 oC and subjected to H2/C2H2 flow to get the most effective crystal size of the catalyst that give the highest percentage yield of CNTs. The highest percentage yield (228 %) was found for samples with average crystal size of 35 nm. 150 100 35 nm 100 nm 150 nm 50 0 0 5 10 15 20 25 30 35 Time (min.) Effect of crystal size of iron oxide catalyst on the Carbon yield%
    • (a) • TEM analysis of the produced CNTs over iron produced from the complete reduction of iron oxide with crystal size 35nm .Graphitic structures with a central channel (CNTs) of internal diameter 53-93 nm and its length is about 1-10 µm and CNTs were formed with a helix and curved shape structure. • The presence of catalytic nanoparticles at the tip of the produced CNTs suggests that the TEM images of CNTs produced from the decomposition of CNT production occurred via tip-acetylene over freshly reduced iron oxide with crystal size 35 nm at 500 C. growth mechanism 1µm (b ) 200 nm o
    • • TEM image of carbon produced from the decomposition of acetylene over the iron produced from the complete reduction of iron oxide with crystal size 150 nm shows that A nonhomogeneity of the carbon products was observed (amorphous carbonaceous 0.5µm structures) were observed in the sample. It was also observed that iron particles were kept in TEM images Carbon produced from the decomposition of acetylene over freshly reduced iron oxide with crystal carbon capsules. size 150 nm at 500 C • Generally, when metallic iron particles increase in size, the formation of nonselective forms of carbon is favored. o
    • 60 50 intensity (a.u ) 40 ( a) 30 20 10 0 100 80 Intensity (a.u ) XRD patterns of the catalysts after acetylene decomposition shows that there are two major peaks, one is near 2θ = 26o Minor asymmetric peak near 43.5o indicating the well graphitized nature of the CNT. The other peaks are due to catalytic impurities, metallic iron phases and support (Al2O3 ). These results suggest that the growth mechanism of carbon nanotube was the tip growth mechanism. ( b) 60 40 20 0 20 30 40 50 60 70 80 2-Theta scale XRD patterns of iron oxide catalyst with average crystal size 35 nm after decomposition of acetylene at (a) 500 oC (b) 600 oC
    • A series of decomposition experiment were carried out at 400-700 oC using the iron produced from the reduction of iron oxide samples with lowest crystal size (35 nm). Two modes of decomposition rate can be observed. The first one at lower decomposition temperature, 400 and 500 oC, where the percentage yield 220 % and 228 % was recorded, respectively. Increasing the temperature to 600 and 700 oC increase in the decomposition rate and percentage yield of 426 and 407 % were observed at 600 and 700 oC, respectively. 500 450 400 Carbon yield (%) Carbon yield (%) 400 350 300 300 200 o o 400 oC 500 oC 600 oC 700 C 100 250 0 200 350 0 400 450 500 550 600 650 700 750 5 10 15 20 25 30 35 Time (min.) o Decomposition temperature ( C) the relation ship between the acetylene decomposition temperature and the carbon yield % over freshly reduced iron The effect of temperature on the catalytic decomposition of acetylene over freshly reduced iron oxide with average crystal size 35 nm
    • The activation energy value was found to be (12.5 kJ mol-1) indicates that the decomposition of acetylene on the catalyst surface is probably a physisorption process. 6 Ea =12.5 kJ/ mol 5 4 ln dr/dt 3 2 1 0 -1 -2 0.001 0.0011 0.0012 0.0013 1/T (k) 0.0014 0.0015 Fig. 11: Arrhenius plot of CNTs synthesis over freshly reduced nanosized Fe2O3
    • The presence of catalytic nano particles at the tip of the produced CNTs and its appearance on the XRD- pattern suggests that the CNT production occurred via a tip-growth mechanism where the supported metals particles detach and move at the head of the growing nanotube catalytic nano particles TEM images of CNTs produced from the decomposition of acetylene over freshly reduced iron oxide with crystal size 35 nm at 500 oC.
    • The rate is higher at the early stage then it decrease with time and still active even after 30 minutes of reaction which indicate that the catalyst is very active toward the decomposition of acetylene which is used as a source of carbon
    • Kinetics of acetylene decomposition over reduced SHF catalyst for the production of carbon nanotubes
    • • Catalyst of the composition 40SHF:60Al2O3 is prepared by wet impregnation method as follows: aqueous solutions of SHF with the required amount, was mixed with Al2O3 powder and stirred for 1 hrs at 60 oC to remove dissolved oxygen and to achieve a homogeneous impregnation of catalyst in the support. The impregnate was then dried in an oven at 100 oC for 3 hrs, calcined at 400 oC for 4 hrs in a box muffle furnace. • Approximately 50 mg of a catalyst sample was introduced in to cylindrical alumina cell closed with one end, the cell with the catalyst placed in the central region of a longitudinal furnace. • The catalyst was reduced at different temperature 500, 550, 600, and 650 oC at 1l/min in H2 flow and CNTs were synthesized via two type of experiments by flowing 10C2H2:90H2
    • E N2  H2  C2H2 Reduction & decomposition system  
    • • The synthesized CNTs were cooled in H2 flow and the weight of deposited CNTs was detected using weight gain technique. • The activity of catalyst was measured by yield % of carbon deposited which can be calculated from the following relation, C% = [W3 – (W1 – W2) / (W1 – W2)]*100. • Where W1 is the initial weight of the catalyst, W2 is the weight loss of catalyst at operating temperature, and W3 is the weight of carbon deposited and catalyst. • The structure and morphology of the synthesized CNTs were characterized using high resolution transmission electron microscopy (HRTEM)
    • Kinetics of acetylene decomposition over reduced SHF catalyst for the production of CNTs • The kinetics of synthesis of CNTs were investigated through two types of experiments, the first was done at constant reaction time 30 min and rate gas flow of 10 C2H2: 90 H2, samples were reduced at 500-650 oC and subjected to C2H2 flow at each temperature. The optimum conditions for the higher yield % were found to be 600 oC which give 262.4 yield % • The second type of experiments was done at variable decomposition temperature 500-800 oC and constant reduction temperature (600 oC). This was done at the same experimental conditions. The highest yield % was found at reduction and decomposition temperature 600 and 700 oC respectively.
    • Reaction temperature dependence for the yield % at variable reduction and decomposition temperature. yield % at (a) 500 oC, (b) 550 oC, (c) 600 oC, (d) 650 oC.
    • Not only CNTs but also CNFs a 200nm ‫ــــــــــ‬   b 500nm    TEM images of CNFs produced on SHF reduced at 600 oC by the decomposition of acetylene at 500 oC.
    • Reduction temperature ) oC ) phases content phases content (%) Crystal size (nm) 500 Sr4Fe6O13, Fe21.4O32, FeO, Fe (metal) 50 50 50 12.5 62.1 32.2 23.7 43.2 550 Fe (metal), FeO, Sr2Fe2O3 50 50 20.8 98.2 36.2 31.8 600 Fe (metal), Fe21.4O32, Fe2O3, FeO, Sr2Fe2O5, SrO 50 6.25 10.4 6.25 6.1 4.17 104 20 77.6 Crystal size and the phase content for completely reduced SHF compacts as obtained from XRD analysis.
    • • The activation energies for the first and second experiments were found to be 26.3 and 5.2 kJ/mol respectively, Arrhenius plot of CNTs synthesis on reduced SHF supported on alumina at different reduction temperature.
    • Arrhenius plot of CNTs synthesis on reduced SHF supported on alumina at different decomposition temperature.
    • • Surface area measurements • The catalyst has curie temperature around 500 oC, the catalyst has different behaviors below and above these temperature. Reduction temperature 500 oC 550 oC 600 oC 650 oC Surface area (m2g-1) 76.55 64.39 77.84 57.56 Total pore volume ( Ccg-1) 0.03788 0.0319 4 0.0368 0.02699 Average pore diameter (nm) 19.79 18.91 18.76 Micro pore volume (Ccg-1) 0.08814 0.0748 9 0.08045 0.0668 Adsorption energy ( kJmol-1) 2.429 2.357 2.217 19.84 2.208 The surface area measurements for the SHF supported on alumina with the molar ratio 40 (SrFe12O19): 60Al2O3.
    • 200 nm  50nm _____ TEM images of CNTs produced on SHF reduced at 600 oC by the decomposition of acetylene at 600 oC
    • Catalyst Wt % Time (min) T ( oC) Carbon source Carrier gas Rate flow Yield % Observation Fe-Ni/ MgO 2:98 30 1000 C2H2 N2 10:90cm3min 112 Good crystallinity Fe-Ni/ MgO 2:98 60 800 C2H2 N2 10:90cm3min 104 Excellent quallity Fe-Ni/ MgO 20:80 30 800 C2H2 N2 10:90cm3min 240 High quality and density Fe-Ni/ MgO 30:70 30 800 C2H2 N2 10:90cm3min 260 High quality and density Co-Mo/ MgO 5:95 30 800 C2H2 H2 10:100sccm 6 SWNTs Co-Mo/ MgO 10:90 30 800 C2H2 H2 10:100sccm 27 Co-Mo/ MgO 40:60 30 800 C2H2 H2 10:100sccm 576 MWNTs Fe/ AL2O3 40:60 90 700 C2H2 H2 10:100sccm Low L. 2m m D. 40-50 nm Ni/ AL2O3 40:60 90 700 C2H2 H2 10:100sccm Fe –Ni/ AL2O3 40:60 90 700 C2H2 H2 10:100sccm 121 L. 4 µ m D. 20 nm Fe –Co/ CaCO3 5:95 60 700 C2H2/ C2H4 N2 30ml/min 358 Spongy and very soft Fe –Co/ MgO 5:95 60 700 C2H2/ C2H4 N2 30ml/min 229
    • Catalyst Carbon source Temperature (oC) Yield % 3Co:3Mo/SiO2 CO 800 1 1.7Co:85Mo/ MgO CO 1000 2 SWNTs 1.7Co:85Mo/ MgO CH4 1000 15 MWNTs 5Co:5Mo/ MgO CH4 1000 80% SWNTs and 20% MWNTs 1Mo:9Fe/SiO2 CO 850 40 1Mo:9Fe/SiO2 C2H4 850 SWNTs and MWNTs with a ratio of 3:7 Catalyst Reduction temperature (oC) Decomposition temperature (oC) Freshly reduced 500 500 171.3 SrFe12O19 550 550 272.3 30 supported on Al2O3 Time (min.) Carbon source C2H2 Carrier gas H2 Rate flow L/min. Yield % 10/90 600 600 367 650 650 329
    • Second Experiment Catalyst Reductio n T (oC) Freshly reduced Decompositio n T (oC) Time Carbon (min.) source Carrie Rate Yield r flow % gas L/min. supported on Al2O3 230.2 600 SrFe12 O19 500 367 600 30 C2H2 H2 10/90 700 436.9 800 180.7
    • Catalytic decomposition of acetylene over CoFe2O4/ BaFe12O19 core shell
    • • Catalyst of the composition 40 catalyst:60Al2O3 is prepared by wet impregnation method as follows: aqueous solutions of catalyst with the required amount, was mixed with Al2O3 powder and stirred for 1 hrs at 60 oC to remove dissolved oxygen and to achieve a homogeneous impregnation of catalyst in the support. The impregnate was then dried in an oven at 100 oC for 3 hrs, calcined at 400 oC for 4 hrs in a box muffle furnace. • Approximately 50 mg of a catalyst sample was introduced in to cylindrical alumina cell closed with one end, the cell with the catalyst placed in the central region of a longitudinal furnace. • The catalyst was reduced at different temperature 500, 600, 700 and 800 oC at 1l/min in H2 flow and CNTs were synthesized via two type of experiments by flowing 10C2H2:90H2
    • 1. Catalyst characterization The difference in reduction temperatures lead to difference in phases formed during reduction process at those temperatures (500-800oC). Figure 2. SEM of CoFe2O4 / BaFe12O19 core shell reduced, at different temperatures, (A) 700 oC (81 % reduction) (B) 500 oC (72 % reduction) Figure 1 . XRD patterens for CoFe2O4/BaFe12O19 core shell reduced at different temperatures (1) Iron, Fe (2) Cobalt, Co (3) Barium peroxide, BaO2 (4) Barium oxide, BaO .
    • 2. Surface area measurements Table 1. Effect of different reduction temperatures of CoFe2O4/ BaFe12O19 core shell on surface area measurements. 500 oC 600 oC 700 oC 800 oC Surface area (m2/g) 82.24 124.1 66.96 36.29 Total pore volume (cc/g) 0.040 0.0629 0.032 0.018 Adsorption energy (kJ/mol) 2.58 2.9 2.342 2.250 Average pore diameter (nm) 19.83 20.29 19.38 19.95 Micro pore volume (cc/g) 0.077 0.105 0.0712 0.0429 Surface area increases by decreasing reduction temperatures till 600oC, then any further decrease in temperatures from 600 to 500oC leads to a decrease in the surface area, as shown in Figure which shows fine structure containing microspores of sample reduced at 600oC. Figure . SEM of CoFe2O4 / BaFe12O19 core shell reduced at 600 oC.
    • 3. Effect of reduction temperature on the formation of carbon nanotubes Figure . Carbon yields (%) as a function of time at different reduction and decomposition temperatures.
    • Figure . Carbon yields (%) as a function of temperatures of CoFe 2O4 / BaFe12O19 core shell reduced, at different temperatures and decomposed the C2H2 at the same temperature.
    • Figure . TEM of CoFe2O4 / BaFe12O19 core shell reduced, at different temperatures, (a) 700 oC (81 % reduction ) (b) 800 oC (84.5 % reduction)
    • Figure 5. TEM of CoFe2O4 / BaFe12O19 core shell reduced and decomposed the C2H2 at the same temperature (a) 700 oC ( 81 % reduction and 267% carbon yield ) (b) 500 oC ( 72 % reduction and 141% carbon yield )
    •  It is supposed that acetylene decomposes at different temperatures 500800°C on the top of a supported catalyst  The dissolved carbon diffuses in the catalyst, precipitates on the rear side and forms a nanotubes  The carbon diffuses through the catalyst due to a thermal gradient formed by the heat release of the exothermic decomposition of acetylene  The formation of carbon nanotubes and formation of carbon fibers by tip growth mode
    • 4. Effect of decomposition temperature on the formation of carbon nanotubes and kinetics Figure. Carbon yields (%) as a function of temperatures of CoFe2O4 / BaFe12O19 core shell reduced, at 700oC and decomposed the C2H2 at different temperatures 500-800 oC .
    • FT-IR spectra analysis at Figure , revealed four peaks at 283.48, 269.02, 256.48 and 1577.49 cm-1 that indicating the presence of multiwalled carbon nanotubes as shown in the TEM micrograph. Figure. FT-IR spectra for CoFe2O4 / BaFe12O19 core shell reduced at 700oC and decomposed the C2H2 at 600oC (a) at range from 4000-500cm -1 (b) at range from 650-150 cm-1 TEM of CoFe2O4 / BaFe12O19 core shell reduced at 700 oC and decomposed the C2H2 at 600 oC.
    • Activation energy of 2.9 kJ/mol for the reaction physisorption Arrhenius plots for CoFe2O4/BaFe12O19 core shell reduced at different temperatures 500- 800oC.
    • Catalytic decomposition of acetylene over CoFe2O4/ NiFe2O4 core shell
    • 1. Catalyst characterization The difference between reduction temperatures lead to slightly increase in the rate of reduction from 76 % at 800 oC to 71% at 500 oC, which can be attributed to grain size approximation. SEM micrograph of cobalt ferrite /nickel ferrite core shell reduced at different temperatures at final stages at 600oC. SEM micrograph of nanocrystallite CoFe2O4 /NiFe2O4 core shell reduced at 800 oC.
    • 2. Surface area measurements Effect of different reduction temperatures of CoFe2O4/ NiFe2O4 core shell on surface area measurements 500 oC 600 oC 700 oC 800 oC Surface area (m2/g) 193.8 65.09 74.79 185.7 Total pore volume (cc/g) 0.0968 0.032 0.0356 0.0690 Average pore diameter (nm) 19.99 19.67 19.08 14.87 Photomicrograph of CoFe2O4 / NiFe2O4 core shell reduced at 500 oC (X400).
    • 3. Effect of reduction temperature on the formation of carbon nanotubes Carbon yields (%) as a function of time at different reduction and decomposition temperatures.
    • 4. Effect of decomposition temperature on the formation of carbon nanotubes and kinetics Carbon yields (%) as a function of temperatures of CoFe2O4 / NiFe2O4 core shell reduced, at different temperatures and decomposed the C2H2 at the same temperature.
    • Photomicrograph of CoFe2O4 / NiFe2O4 core shell reduced at different temperatures (X40). (a)800 oC to give 76 % reduction and 153 % carbon yield. (b)700 oC to give 73 % reduction and 158 % carbon yield. (c)600 oC to give 72 % reduction and 217 % carbon yield. (d)500 oC to give 71 % reduction and 157 % carbon yield.
    • Carbon yields (%) as a function of temperatures of CoFe2O4 / NiFe2O4 core shell reduced, at 600oC and decomposed the C2H2 at different temperatures 500800 oC.
    • TEM micrograph of cobalt ferrite /nickel ferrite core shell reduced at 600oC and decomposition temperature at 700oC. TEM micrograph of cobalt ferrite /nickel ferrite core shell reduced at 600oC and decomposition temperature at 800oC.
    • FT-IR spectra analysis at Figure , revealed three peaks at 256.48, 1571.7 and 1282.43 cm-1 that indicating the presence of multiwalled carbon nanotubes as shown in the TEM micrograph. FT-IR spectra for CoFe2O4 / NiFe2O4 core shell reduced at 700oC and decomposed the C2H2 at 600oC (a) at range from 4000-500cm -1 (b) at range from 650-150 cm-1
    • physisorption Activation energy of 2.1 kJ/mol for the reaction Arrhenius plots for CoFe2O4/NiFe2O4 temperatures 500- 800oC. core shell reduced at different
    • SYNTHESIS AND MODIFICATION OF MULTI WALLED CARBON NANOTUBES (MWCNT) FOR WATER TREATMENT APPLICATIONS
    • 1- Preparation of C/S catalyst/support: The support-catalyst were prepared by wet impregnation method. A required amount of the support material (S) was milled in a ball mill for 10 hrs in order to decrease the crystallite size and increase the surface area. Calculated ratios of the metal salts (C1(NO3)and C2(NO3) were added into the ball mill with (S) and milled for another 2 hrs. The produced fine powder dispersed in a few drops of water, mixed well to get a homogeneous paste of (S), C1(NO3) and C2(NO3). The mixture was dried in oven at 120oC for 12 hrs, cooled and ground well to obtain a fine powder of C1-C2/S catalyst/support mixture
    • 2- Carbon nanotubes preparation: Approximately 0.5g of catalyst/support sample was introduced to cylindrical alumina cell closed with one end, the cell with the catalyst suspended by chain in a horizontal furnace and attached to the pan of a fully automatic sensitive (0.1 mg) balance (K) (Perciza-Swiss) to record the weight gain at all the time of the experiment. catalyst/support preheated to different operating temperature in a flow of nitrogen gas (70 ml/min). After 10 min the acetylene gas was allowed to pass over the catalyst bed with a rate of 10 ml/min for 40 min. The acetylene gas flow was stopped; the product on the alumina cell was cooled to room temperature while nitrogen flow was on. The weight of the carbon deposited along with the catalyst was noted. The percentage of carbon deposit (C%) obtained in each reaction was determined using the following relationship: C % = [W3 – (W1 – W2) / (W1 – W2)]*100 where W1 is the initial weight of the catalyst , W2 is the weight loss of catalyst at operating temperature, and W3 is the weight of carbon deposited and catalyst.
    • 3- CNTs Purification: CNTs purification process was achieved by using Chemical oxidation method. Specific amount of the asgrown carbon nano-tubes were added to a mixture of concentrated nitric acid /sulfuric acid (3:1 by volume, respectively). The mixture is refluxed in oil bath for 4 hrs at 120 °C. After cooling to room temperature, the reaction mixture is diluted with distilled water and then filtered through a filter paper (3 μm porosity). This washing operation was repeated several times using distilled water and followed by drying in a drier at 100 °C.
    • 4-Adsorption of heavy metals and organic dyes: Adsorption experiments were performed at 298 K. Exactly 100 ml of metal or dye solution placed in a beaker and 0.1g oxidized CNTs was added to the solution and left on a magnetic stirrer for 5 min. to ensure the dispersion. At different times, 5 ml of the sample solution was withdrawn and filtered with filter paper and the change in characteristic absorption at the specific beaks measured using an ultraviolet-visible (UV-vis) spectrophotometer (Jasco 530), from which the concentration of heavy metals and dyes was inferred.
    • Results and dissections: TEM image of the as prepared CNTs synthesized at 600 oC. TEM image of the oxidized CNTs synthesized at 600 oC and refluxed in conc. Acid for 4 hrs.
    • SEM image of the oxidized CNTs synthesized at 600 oC and refluxed in concentrated acid for 4 hrs.
    • HNO3/H2SO4 MWCNT Oxidized b MWCNT schematic preparation of the functionalized carbon nanotubes. a b FTIR spectra of (a) as grown MWNT , (b) acid treated purified MWNT.
    • 3 Before adsorption After adsorption Intensity 2 1 0 200 400 600 Wave length Adsorption Mn7+ by using functionalized CNTs. 0.10 3 CrCl3 before adsorption K2CrO4 after 4.5 hrs CrCl3 after 8hrs 0.08 K2CrO4 CrCl3 after 3hrs K2CrO4 after 20 hrs 2 Intensity Intensity 0.06 0.04 1 0.02 0.00 0 -0.02 300 400 500 600 Wave length 700 800 300 400 500 600 Wave length Absorption peaks of Cr3+ and Cr6+ adsorbed by functionalized CNTs.
    • 0.5 T. Blue After adsorption 1 Methylen blue Methylen blue after adsorption 0.4 Intensity Intensity 0.3 0.2 0.0 0.0 300 0 400 500 600 700 300 800 400 500 600 700 800 Wave length Wave length Methyl green Methyl green after adsorption Intensity Intensity Bromopyrogallol red Bromopyrogallol after adsorption 300 400 500 600 Wave length 700 800 300 400 500 600 700 800 Wave length Absorption beaks of different dyes ( Tolludine blue, Methyl green, Methylen blue, Bromopyrogallol red) before and after adsorption on functionalized CNTs.
    • As-growing CNTs Acid treated Functionalized HOOC COOH C=O O=C OH HO COOH HOOC COOH Inner pores blocked Catalyst removed Adsorption increased Functional group added For nonpolar and/ or planer chemicals: Adsorption decreased. For polar chemicals : Adsorption increased. The effect of CNT functional groups on organic molecule adsorption
    • Reduction-Reoxidation System
    • Activation energies of nano cryst. copper ferrite reduction 1.5 initial meddle final log(dr/dt) 1.0 0.5 0.0 -0.5 -1.0 11 12 13 14 104/T, K-1. 15 16
    • Gas-Solid reaction mechanisms 1-Gaseous diffusion mechanism 2-Interfacial chemical reaction mechanism 3-Solid state diffusion mechanism
    • Activation energies and controlling mechanisms of the reduction process Stage Initial Ea, kJ/mol. 39.35 Controlling mechanism Interfacial chemical reaction with some contribution to gaseous diffusion mechanism Intermediate Final 65.2 55.3 Interfacial chemical reaction mechanism Interfacial chemical reaction mechanism
    • c 1 - (1-X) 1/2 1.0 0.8 0.6 0.4 0 50 100 150 200 250 time, min. 0.6 1 - (1-X) 1/2 b 0.5 0.4 0.3 0.2 1/2 [1-(1-X) ] + [X+(1-x) ln (1-X)] 0 20 40 60 80 100 120 140 time, min. 0.25 a 0.20 0.15 o 400 C o 500 C o 600 C 0.10 0.05 0.00 0 2 4 6 8 10 12 14 16 18 20 time, min.
    • CO2 Catalytic decomposition Over freshly reduced 220 nm CuFe2O4 R6O6 • CO2 was allowed to decompose spontaneously R6O5 to carbon at 400-600oC during the reoxidation of nano-crystallite metallic phase of Cu & Fe compacts, produced from the reduction process. R6O4 produced from the reduction-reoxidation experiments at different temperatures indicates that all samples contain the iron austenite and magnetite phases, which reveals that CO2 decomposes during the reoxidation process to carbon and oxygen forming the austenite and magnetite. • Deposited carbon was detected by C-analysis. • Carbon in the form of Nano-tubes was detected by SEM. • For more evidence, carbon nano-tubes were isolated by suspention in acetone, TEM was used to prove the formation of Carbon Nano- Intensity, a.u. • XRD analysis obtained for all samples R5O6 R5O5 R5O4 R4O6 R4O5 R4O4 20 30 40 50 60 2 - theta, degree 70 80