الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 262 |  |  |
| | | from | 262 | | |
Abstract
Summary and Conclusions
Nanomaterials have attracted developing interest due to their specific structure and various properties. Nanostructured materials have promising applications in the fields of industrial catalysis and green chemistry areas as wastewater treatment. Fe2O3/MgO system has been used as a catalyst and as an adsorbent material. The formula xFeMgO will be used throughout this work to represent the different composites where x refers to the molar % Fe3+. The molar ratios were 1, 2, 5, 10, 25 and 50 % Fe2O3 on MgO. xFeMgO nanomaterials were synthesized using three different methods, impregnation FeMgOIM, coprecipitation methods where one used ammonium hydroxide FeMgON as the precipitating agent and the other urea FeMgOU and finally FeMgOSG which was prepared by sol-gel method. All the prepared nanomaterials were calcined at 500°C for 3 h. yCuFeMgOIM samples were prepared by impregnation and y describes 1, 3, 5 and 7 % molar ratios of CuO. The prepared catalysts were used for carbon nanotubes CNTs and carbon nanofibers CNFs synthesis via a catalytic chemical vapor deposition (CCVD) technique at atmospheric pressure. The prepared catalysts were used also to catalyze the ethanol conversion using flow method within the temperature range of 200 - 400°C, at atmospheric pressure. All synthesized nanomaterials were used as adsorbents in order to remove two organic dyes (Remazol Red RB-133 and methylene blue MB) from wastewater. The prepared catalysts were characterized by XRD, SBET, and TEM while the obtained CNTs and CNFs were characterized by SEM and TEM tools.
The main conclusions that can be drawn from the obtained results are in the following:
1- All FeMgO and CuFeMgO samples consist of periclase MgO phase as a major phase, while Fe2O3 and MgFe2O4 phases appeared in samples having a high extent of Fe2O3 loadings. The obtained degree of ordering and the calculated value of the lattice constant of MgO phase decreased by adding of Fe2O3 and increased by increasing the amount of added CuO. Poorly crystalline MgO and MgFe2O4 phase were detected in FeMgON catalyst while Fe2O3 phase with a moderate degree of crystallinity was detected in FeMgOU solid. The smallest crystallite size, MgO-lattice constant, and crystallinity were obtained in FeMgOU and FeMgON samples.
2- Increasing the amount of Fe2O3 on the MgO support from 2 to 10 mol% followed by calcination at 500°C leads to a negligible decrease in BET surface area and total pore volume. Nevertheless, increasing the Fe2O3 loading to 25 mol% leads to a significant increase in surface area and total pore volume and a decrease in the average pore radius. CuO-doping led to a decrease in SBET and total pore volume and an increase in the pore radius. SBET values for 0.10FeMgO nanomaterials prepared with different methods obeyed the following order:
FeMgON > FeMgOSG > FeMgOU > FeMgOIM.
3- The EDS results proved the presence of Fe, Mg and O elements and were very close to the nominal wt% of 0.10FeMgOIM. TEM of FeMgO and CuFeMgO showed presence aggregates of uniform spherical shapes and uniform cubic nanoparticles, respectively.
4- The catalytic properties of FeMgO and CuFeMgO towards ethanol conversion showed that: the total ethanol conversion and the ethylene selectivity increases with increasing Fe2O3 loadings until 10 mol%. The 0.10FeMgOIM catalyst exhibited the highest ethanol conversion and the ethylene selectivity (dehydration) while the highest acetaldehyde selectivity (dehydrogenation) was obtained with increasing iron oxide loading. 0.10FeMgOU and 0.10FeMgOIM catalysts exhibited the highest ethanol conversion at the low and high reaction temperature, respectively while 0.10FeMgOSG exhibited the lowest activity (big aggregates). 0.10FeMgOU is the most selective catalyst to acetaldehyde (due to formation ferrite). Nanosized Fe3+ ions and medium strength basic active sites [Mg(M)–O] with high density promotes acetaldehyde formation.
The catalytic activity of all CuFeMgOIM catalysts increased progressively with reaction temperature until 325°C then slightly decreased while in case of pure 0.10FeMgOIM catalyst its catalytic activity increases continually with reaction temperature. 100% dehydrogenation selectivity (acetaldehyde production) was obtained by CuO doping.
5- SEM and TEM showed a well-dispersed CNTs having high purity, clean appearance and good morphology fully covered the surfaces of 0.10FMgOSG and few from CNTs are observed over 0.10FMgOIM after CVD reaction at 600°C. The diameters of CNTs depend on the sizes of the associated catalyst particles. High dense of CNTs are observed in both 0.10FMgON and 0.10FMgOU. The tips of CNTs over 0.10FeMgON are opened. In this way, these CNTs are grown by the root-growth mechanism. On the contrary, the tips of CNTs over 0.10FeMgOU are closed and contain the catalytic particles enclosed, so these CNTs are grown by the tip-growth mechanism. High dense of CNFs are observed over 0.07CuFMgOIM.
6- Preliminary experiments showed the tendency for FeMgO and CuFeMgO catalysts to remove Remazol Red RB-133 dye from wastewater. Carbon nanotubes and carbon nanofibers accumulated on the surface of catalyst masked the catalyst basic sites, which facilitate Methylene Blue dye removal from the wastewater by adsorption process. Remazol Red RB-133 removal was completed over FeMgO nanomaterial after 1h and extends to 1.5 h over CuFeMgO surfaces while over FeMgOSG takes only 25 min. The dye removal % was greater at lower iron oxide loading. The microporous 0.10FeMgOIM adsorbent was found to possess the highest removal efficiency of the dye and potentially lowering capital, and operational costs for practical applications.
7- The order of the adsorption capacity of the prepared nanomaterial was 0.10FeMgOIM > 0.10FeMgOSG > 0.10FeMgOU > 0.10FeMgON. This behavior is highly dependent on surface area and pores structure. The 0.10FeMgOSG adsorbent was found to possess the highest removal efficiency of the dye. Also, the adsorption capacity and removal percentage decreased by increasing the CuO dopant amounts. The kinetic study showed that the rate constant values of RR dye adsorption over various FeMgO samples are pseudo-first-order.
8- Methylene blue adsorption onto most of CNTs/FeMgO nanomaterials were completely removed by adsorption after 1h. However, the removal takes 40 min in the case of CNTs/FeMgOU solid. The efficiency of MB dye removal follows the odor CNTs/FeMgOU > CNTs/FeMgOIM > CNTs/FeMgON > CNTs/FeMgOSG. This behavior may be due to the shape of CNTs produced over each nanomaterial where the diameter of CNTs/0.10FeMgOU is the biggest one that may increase the rate of MB dye adsorption capacity.
9- Methylene blue adsorption onto CNFs/CuFeMgOIM nanomaterials with different CuO loadings were completely removed after 2-5 min. While in the case of undoped solid, the complete removal takes 60 min. For CNFs over 0.07CuFeMgOIM nanomaterial, the removal efficiency of the dye was 95.45% at only 1 min and reaches 98.63% after 5 min. This may be due to the improvement of the diameter of CNFs growth and its surface area.
10- The kinetic study showed that the rate constant values of adsorption MB dye over CNTs/FeMgO and CNFs/FeMgO of CuO-doped samples obeyed pseudo-second-order kinetics with the intraparticle diffusion model while in case of CNTs/0.01FeMgOSG and CNFs/0.03CuFeMgOIM samples the adsorption followed pseudo-first-order kinetically.