Carbon nanotube production over MCM-41 type catalytic materials via CVD method

We investigate the effects of mesoporous catalyst synthesis methods over carbon nanotube (CNT) production. Metal incorporated mesoporous catalysts were synthesized by two different microwave assisted synthesis methods. In the first method, MCM-41 mesoporous materials were synthesized with microwave radiation and then metal was impregnated into these as-synthesized MCM-41 samples. In the second method metal was added into the raw materials directly and then the mixture was treated in the microwave oven. The catalyst were tested in CVD for CNT production

Conversion of low-rank Kilyos coal to nitrogeneous fertilizers

The aim of this work is to convert the low-rank Kilyos coal to a material that could be used as a nitrogenous fertilizer. Incorporation of nitrogen into this Kilyos coal was accomplished by oxidative ammoniation, which was a two-step process involving oxidation with nitric acid followed by a treatment by ammonia. The nitrogen content of the raw coal increased from 0.8% to 8.3-9.3% after ammoniation process. Trace element concentrations in the nitro-coal, HA and OAC samples were within the acceptable ranges to be used as nitrogenous fertilizer. Therefore the oxy-ammoniated products could be considered as high-value fertilizers

Production of templated carbon nano materials, carbon nanofibers and super capasitors

i. Porous carbons are usually obtained via carbonization of precursors of natural or synthetic origin, followed by activation. To meet the requirements, a novel approach, the template carbonization method, has been proposed. Replication, the process of filling the external and / or internal pores of a solid with a different material, physically or chemically separating the resulting material from the template, is a technique that is widely used in microporosity and printing. This method has been used to prepare replica polymers [1,2] metals [3] and semiconductors [4] and other materials [5,6]. Zeolites represent an interesting case for replication processes, because the dimensions of their cages and channels are quite similar to those organic molecules that constitute the replica. If such as nanospace in a zeolite is packed with carbon and then the carbon are extracted from the zeolite framework, one can expect the formation of a porous carbon whose structure reflects the porosity of the original zeolite template. Owing to the disordered and inhomogeneous nature of the starting materials,\ud the resulting carbon has a wide and poorly controlled distribution of pore sizes. Zeolites with three-dimensional pore structures were found to be suitable as templates [7,8], whereas zeolites with one-dimensional structures were not effective [9]. These carbons obtained using zeolite templates with three-dimensional pore structures retained the shapes of zeolite particles, but did not retain their internal periodic structure. ii. Many methods have been proposed for carbon nanofiber (CNF) production, among them, we have chosen chemical vapor deposition (CVD) method for CNF synthesis because of its potential for scaling up the production and low cost[10]. Recent developments showed that alignment, positional control on nanometer scale, control over the diameter, as well as the growth rate of the carbon nanotubes (CNT) and CNFs can be achieved by using CVD[11-13]. Many catalysts supports and metal catalysts were proposed for CNF production through CVD technique. Silica (SiO2) [14], alumina (Al2O3) [15], quartz [16], titania (TiO2) or calcium oxide (CaO) [17] were used as the catalyst support because of their chemical inertness and high-temperature resistance. However, all of these support materials require harsh chemical treatment i.e. concentrated bases (NaOH) or strong acids (HF) to remove them, and these reagents may also damage the carbon nanostructure. Additionally, strong acids and bases are less desirable for large-scale production due to environmental concerns. Our goal in synthesizing CNFs is to achieve a control in tailoring the diameter, and morphology at the same time. We believe that understanding the chemistry involved in the catalyst and nanofiber growth process is the critical point to be able to produce defectless, property controlled CNFs. Thus, knowing the effect of the catalyst on CVD production of carbon nanofibers is very important for producing the desired CNFs. A very unique material, NaCl in the field of catalytic CVD process for carbon materials production, was selected as the support material which provides easy production and easy removal properties to the catalyst system. Together with the support material, the metal catalyst preparation step was differentiated from the conventional wet catalyst methods in which a liquid solution containing the catalyst in salt form is applied to the substrate via spray coating [16,18,19], spin coating [20-22], or microcontact printing [23] as well. The most active metals that were used previously in the catalytic CVD process for carbon materials production were Fe, Co [24], and Ni. The reason for choosing these metals as catalyst for CVD growth of nanotubes was the thermodynamic behavior of the metals at high temperatures, in which carbon is soluble in these metals and this solubility leads to the formation of metal-carbon solutions and therefore the desired carbon nanomaterial formation nucleates. In this study, transition metal based organometallic complex catalysts of Fe, Co, Ni and Cu were synthesized by a new approach of simultaneous synthesis of the support material and the catalyst. Therefore an easy production method for catalyst to use in CVD was developed by using only wet chemistry. iii. Electrochemically conducting polymers (ECPs) are of interest in late years and they are promising materials for realization of high performance supercapacitors, as they are characterized by high specific capacitances, by high conductivities in the charged states and by fast charge-discharge processes. The charge processes pertain to the whole polymer mass and not only to the surface. These features suggest the possibility to develop devices with low ESR and high specific energy and power. However, the long-term stability during cycling is a major demand for an industrial application of ECPs. Swelling and shrinkage of ECPs, caused by the insertion/deinsertion of counter ions required for doping the polymer, is well known and may lead to degradation of the electrode during cycling. This obstacle has been over overcome to some level by using composite materials made of carbon materials such as CNTs or activated carbons with CPs. Carbon material in the bulk both ensures a good electrical conductivity even the CP is in its insulating state and improves the mechanical properties of the electrodes. As mentioned in the earlier chapters, using carbon nanotubes, CPs, or both as composites for the active material of the supercapacitor applications comes with some disadvantages as well as the advantages. CPs although being a promising energy source for the job, lack the flexibility for insertion/deinsertion of the dopant ions resulting in shorter recycling life times than desired. CNTs are the employed to gain more flexibility however whether they are used as active materials solo, or engaged in a composite with a CP, they could not supply enough energy for the job. Therefore, the objective of this study is, to obtain a new material for supercapacitor active material; by depositing a conducting polymer, polypyrrole, on to carbon nanotubes via electropolymerization. By this method, the problem of bulk charging in conducting polymers is aimed to be overcomed. Since the coating is in magnitudes of nanometers, only surface charging will exist, which is desirable for supercapacitor applications

Template synthesis of boron nitride nanotubes over iron impregnated mesoporous silica MCM-41 by chemical vapor deposition technique

BN nanotubes were successfully grown over iron impregnated MCM-41 at a relatively low temperature of 750oC for 1 hour by CVD technique. BN nanotubes were obtained after the purification procedure including HCl and HNO3 treatments to remove impurities. SEM image showed the formation of nano-fibrous network BN structures in the diameter range of 20 nm to 40 nm. Both XRD and FTIR characterization results supported the formation of h-BN and c-BN nanostructures. Oxidative TGA results indicated that the synthesized BN nanostructures were thermally stable at temperatures higher than 550oC. Hydrogen storage measurements via IGA showed that BNNTs could adsorb 0.85 wt% hydrogen which was two times larger than for commercial CNTs

cu-mcm-41 ve ni-mcm-41 tipi katalitik malzemelerin sentezlenmesi ve karakterizasyonu

M.S. - Master of Scienc

Microwave assisted synthesis of MCM-41 and diffusion of organic solvents in porous media

Microwave assisted synthesis of mesoporous molecular sieves is a promising method due to several advantageous over conventional hydrothermal method such as more uniform heating, homogeneous nucleation and shorter crystallization times. The effect of microwave power and synthesis time on the structure of MCM-41 were discussed using XRD, N2 physisorption, SEM, TEM techniques. The optimum reaction time and microwave power was determined after the trial of several combinations. The obtained products were compared with the ones synthesized by hydrothermal method. MCM-41 obtained from microwave assisted synthesis was used in the diffusion experiments of organic solvents. The diffusion coefficients, mode of transport and activation energies of organic solvents into the porous channels of MCM-41 were investigated in 24-28 ˚C temperature range. As the molecular weight of the organic solvents increased, diffusion coefficients decreased, the activation energy for diffusion increased, and the time necessary to reach equilibrium was increased