Effect of metal catalyst and tailoring the conditions for cnf/cnt growth through cvd

In this study, high-temperature acetylene gas was delivered to the reactive sites of matrix-supported transition metal catalysts by means of a chemical vapor deposition (CVD) apparatus, yielding carbon nanofibers (CNF) and nanotubes (CNT). A principle feature that delineated this pyrolysis-induced polymerization from prior studies lay in the method used to support the nanoscale transition metal catalysts. In particular, sodium chloride, a byproduct of the catalyst synthesis, was deliberately retained and exploited in subsequent manipulations for the reason that it performed remarkably well as a support medium. In comparison to typical silica and alumina-based support media, a non-porous sodium chloride medium clearly revealed major operational advantages in the matter of fabricating carbon species such as nanorods and nanotubes. In particular, pyrolysis could be conducted at temperatures spanning 500°C to 700°C without observing any agglomeration and subsequent sintering of the catalyst. The root cause of the high stability of these catalytic nanoparticles was not elucidated conclusively but it appeared to be related to the segregating effect of the support matrix, which could arise initially by the direct interaction between mobile chloride ions and the catalyst surface, and subsequently via encapsulation of each catalyst particle, by the growing polymeric species. The other noteworthy peculiarity of sodium chloride as a support material lay in its markedly different morphology, which could be characterized as microcrystalline and non-porous, with catalytic particles dispersed throughout the medium as opposed to remaining surface-pendent. While somewhat counter-intuitive, the zero-porosity of this matrix did not pose any apparent drawbacks in the matter of fabricating carbon nanofibers or nanotubes. In fact, the catalytic effectiveness of many transition metals particles was comparable or better than those of the prior art, whose effectiveness typically rests on utilizing a highly-porous and high-surface support medium with an interconnected morphology. High catalytic activity appeared to be promoted by the fact that the sodium chloride matrix became mobile and acetylene-permeable at elevated temperatures, the most important evidence originating from electron micrographs, which clearly indicated carbon-coated catalysts encased entirely in sodium chloride. In comparing several transition metal oxides, the most active catalyst was clearly nickel-based. The activity of the nickel catalyst did not appear to strongly depend on the ligand used in its fabrication but there was certainly a catalytic dependency on the size of the particle. Kinetic analyses of catalysts indicated that carbon-carbon bond formation was not reaction limited. Rather, the mass transfer of carbon units within the bulk or its chemisorption dynamics was in fact rate limiting, in agreement with literature studies on related systems. It followed to reason that the superior performance of nickel over other transition metal oxides was directly related to its stronger chemisorptivity of carbon species. Reaction rate versus flow rate measurements yielded a pseudo rate constant of zero for all catalyst types, implying that acetylene was saturating under the conditions of reaction. At prolonged reaction times, all catalysts lost their activity. While the possibility of catalyst poisoning could not be ruled out, other indications suggested that poor mass transfer of either the feedstock or the growing product were the likely cause. The morphology of carbon nanotubes were relatively typical whereas the morphology of nanofibers were subject to great variability, often ranging from straight rods to nanocoils to Y-junction or second order nanotubes on nanofiber structures. A hierarchy of the rules that governed the course of growth was not clearly established in this study but the major cause of this diversity appeared to be directly related to the shape, surface properties and the chemistry of the catalyst. Two other important parameters appeared to be the gas flow rate and the pyrolysis temperature. A final merit of employing the sodium chloride support technology was related to its preparative generality and practicality, particularly in view that it could enable the synthesis of metal catalysts and polymeric carbon species while precluding some common drawbacks such as toxicity, harsh experimental manipulations, and high cost. Even the quantitative recovery of catalyst could be facilitated by dissolution of the salt support in water, followed by filtration. It follows to reason that further development and fine-tuning of this novel and non-porous support technology can instigate a new class of support materials and can potentially open the door to the synthesis of carbon-based nanostructures with truly unusual physico-chemical traits

Carbon nanotube and nanofiber growth on Zn based catalysts

In this study, acetylene gas was delivered to a catalyst network consists of NaCl-support and Zn nanoparticles in a temperature range of 500-700°C by means of a chemical vapor deposition (CVD). A principle feature that delineated this CVD study from prior studies lay, first in the method used to support the catalyst and secondly the choice of the catalyst metal. In particular, NaCl was deliberately retained and exploited in subsequent manipulations for the reason that it performed remarkably well as a support medium. The catalytic activity of Zn towards production of CNT/CNFs appeared to be promoted as a result of using molten ionic substrate

Trace elements in Turkish biomass fuels: Ashes of wheat straw, olive bagasse and hazelnut shell

Ash contents of wheat straw, olive bagasse and hazelnut shells were 7.9%, 3.9%, 1.2%, respectively, which seemed to be within the average values of ash of biomass. The microstructure of ashes included smooth, polygonal, granular and molten drop structures. A large percentage of particles present in ashes are commonly 1–20 lm in size. SEM/EDS analyses performed on the major ash forming elements in different ashes indicated that Si, Ca, K and Mg and P were generally the most abundant species. Trace element levels in ash samples of various biomass types such as hazelnut shell, wheat straw, olive bagasse were analysed using ICP spectroscopy. The elements determined were some of those considered being of great environmental concern such as, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb. In all of the ashes studied Fe had the highest concentration among other trace elements, Mn was the second element that exhibited higher concentrations. The order of concentration of elements in the ashes from the highest to the lowest values was as follows: Fe > Mn > Zn > Cu > Ni > Cr > Pb > Co

Fuel supply chain analysis of Turkey

In spite of its natural sources, Turkey depends on other countries in terms of energy production, and a transfer from conventional fossil sources to sustainable energy sources is strongly necessary. Among the sustainable energy sources, biomass is the subject of this study. The characteristics, logistic aspects, environmental aspects, economical, legal and technical aspects are investigated in order to show that the possible biomass co-firing is very important for the construction of economic, sustainable and environmentally friendly energy systems

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

Research data supporting “Bio-compatible and Sustainable Optical Strain Sensors for Large-area applications”

Original or unprocessed data is provided in support of the article “Bio-compatible and Sustainable Optical Strain Sensors for Large-area applications”. The data is structured into six folders, each correlating to a specific data type presented in the published article. The folders are named according to the figures, which the contained data were taken from, except for the “supplementary” folder (data of 6 figures in one folder). All data are saved as plain text (csv format) with a file name indicating the corresponding figure and the nature of data, for example spectral data of Figure 1a would be stored in folder “fig1” with a file name of “a_spectra.txt”. fig1: Intensity values of the spectra shown in Fig 1f and their corresponding wavelength are provided. fig2: Intensity values of the spectra shown in Fig 2a-c and their corresponding wavelength are provided. fig3: Peak wavelength value shown in Fig 3b and their corresponding angle of detection are provided. fig4: Pitch values shown in Fig 4a,b and stretch ratio values shown in Fig 4c,d, and their corresponding angle of detection are provided. fig5: Normalised peak wavelength values shown in Fig 5a and their corresponding strain values are provided. supplementary: All measurement data shown in the supplementary information are provided.BBSRC David Phillips fellowship [BB/K014617/1] Isaac Newton Trust [76933], ERC [H2020 639088

Controlled, Bio-inspired Self-Assembly of Cellulose-Based Chiral Reflectors.

The self-assembly process of photonic structures made of cellulose nanocrystals is studied in detail by locally monitoring and controlling water evaporation. Three different stages during the evaporation process are identified. Spectroscopy quantifies the amount of disorder in the fabricated samples. Control of this process enables the selection of a range of different colors starting from the same suspension, providing a facile, sustainable route for the manufacture of structural color

Co-firing of biomass and other wastes in fluidised bed systems

A project on co-firing in large-scale power plants burning coal is currently funded by the European Commission. It is called COPOWER. The project involves 10 organisations from 6 countries. The project involves combustion studies over the full spectrum of equipment size, ranging from small laboratory-scale reactors and pilot plants, to investigate fundamentals and operating parameters, to proving trials on a commercial power plant in Duisburg. The power plant uses a circulating fluidized bed boiler. The results to be obtained are to be compared as function of scale-up. There are two different coals, 3 types of biomass and 2 kinds of waste materials are to be used for blending with coal for co-firing tests. The baseline values are obtained during a campaign of one month at the power station and the results are used for comparison with those to be obtained in other units of various sizes. Future tests will be implemented with the objective to achieve improvement on baseline values. The fuels to be used are already characterized. There are ongoing studies to determine reactivities of fuels and chars produced from the fuels. Reactivities are determined not only for individual fuels but also for blends to be used. Presently pilot-scale combustion tests are also undertaken to study the effect of blending coal with different types of biomass and waste materials. The potential for synergy to improve combustion is investigated. Early results will be reported in the Conference. Simultaneously, studies to verify the availability of biomass and waste materials in Portugal, Turkey and Italy have been undertaken. Techno-economic barriers for the future use of biomass and other waste materials are identified. The potential of using these materials in coal fired power stations has been assessed. The conclusions will also be reported