Raman spectroscopy study of the transformation of the carbonaceous skeleton of a polymer-based nanoporous carbon along the thermal annealing pathway

We report a multi-wavelength Raman spectroscopy study of the structural changes along the thermal annealing pathway of a poly(furfuryl alcohol) (PFA) derived nanoporous carbon (NPC). The Raman spectra were deconvoluted utilizing G, D, D′, A and TPA bands. The appropriateness of these deconvolutions was confirmed via recovery of the correct dispersive behaviours of these bands. It is proposed that the ID/IG ratio is composed of two parts: one associated with the extent of graphitic crystallites (the Tuinstra–Koenig relationship), and a second related to the inter-defect distance. This model was used to successfully determine the variation of the in-plane size and intra-plane defect density along the annealing pathway. It is proposed that the NPC skeleton evolves along the annealing pathway in two stages: below 1600 °C it was dominated by a reduction of in-plane defects with a minor crystallite growth, and above this temperature growth of the crystallites accelerates as the in-plane defect density approaches zero. A significant amount of transpolyacetylene (TPA)-like structures was found to be remaining even at 2400 °C. These may be responsible for resistance to further graphitization of the PFA-based carbon at higher temperatures

Micro/Mesoporous Activated Carbons Derived from Polyaniline: Promising Candidates for CO₂ Adsorption

A series of activated carbons were prepared by carbonization of polyaniline at different temperatures, using KOH or K₂CO₃ as activating agent. Pure microporous or micro/mesoporous activated carbons were obtained depending on the preparation conditions. Carbonization temperature has been proven to be a key parameter to define the textural properties of the carbon when using KOH. Low carbonization temperatures (400–650 °C) yield materials with a highly developed micro- and mesoporous structure, whereas high temperatures (800 °C) yield microporous carbons. Some of the materials prepared using KOH exhibit a BET surface area superior to 4000 m²/g, with total pore volume exceeding 2.5 cm³/g, which are among the largest found for activated carbons. On the other hand, microporous materials are obtained when using K₂CO₃, independently of carbonization temperature. Some of the materials were tested for CO₂ capture due to their high microporosity and N content. The adsorption capacity for CO₂ at atmospheric pressure and 0 °C achieves a value of ∼7.6 mmol CO₂/g, which is among the largest reported in the literature. This study provides guidelines for the design of activated carbons with a proper N/C ratio for CO₂ capture at atmospheric pressure

Immersion calorimetry: molecular packing effects in micropores

Repeated and controlled immersion calorimetry experiments were performed to determine the specific surface area and pore-size distribution (PSD) of a well-characterized, microporous poly(furfuryl alcohol)-based activated carbon. The PSD derived from nitrogen gas adsorption indicated a narrow distribution centered at 0.57±0.05 nm. Immersion into liquids of increasing molecular sizes ranging from 0.33 nm (dichloromethane) to 0.70 nm (α-pinene) showed a decreasing enthalpy of immersion at a critical probe size (0.43–0.48 nm), followed by an increase at 0.48–0.56 nm, and a second decrease at 0.56–0.60 nm. This maximum has not been reported previously. After consideration of possible reasons for this new observation, it is concluded that the effect arises from molecular packing inside the micropores, interpreted in terms of 2D packing. The immersion enthalpy PSD was consistent with that from quenched solid density functional theory (QSDFT) analysis of the nitrogen adsorption isotherm

Pore size distributions derived from adsorption isotherms, immersion calorimetry, and isosteric heats: a comparative study

We compare the pore size distribution of a well-characterized activated carbon derived from model-dependent, adsorption integral equation (AIE) methods with those from model-independent, immersion calorimetry and isosteric heat analyses. The AIE approach applied to nitrogen gave a mean pore width of 0.57 nm; the CO2 distribution exhibited wider dispersion. Spherical model application to CO2 and diffusion limitations for nitrogen and argon were proposed as primary reasons for inconsistency. Immersion enthalpy revealed a sharp decrease in available area equivalent to a cut-off due to molecular exclusion when the accessible surface was assessed against probe kinetic diameter. Mean pore width was identified as 0.58 ± 0.02 nm, endorsing the underlying assumptions for the nitrogen-based AIE approach. A comparison of the zero-coverage isosteric heat of adsorption for various non-polar adsorptives by the porous test sample was compared with the same adsorptives in contact with a non-porous reference adsorbent, leading to an energy ratio or adsorption enhancement factor. A linear relationship between the energy ratio and probe kinetic diameter indicated a primary pore size at 0.59 nm. The advantage of this enthalpy, model-independent methods over AIE were due to no assumptions regarding probe molecular shape, and no assumptions for pore shape and/or connectivity

Financial Analysis of Company

Import 29/09/2010Bakalářská práce „Finanční analýza podniku“ se zabývá obecnou charakteristikou finanční analýzy, vymezením její základní problematiky, jejími přístupy a metodami. Teoretická část zdůrazňuje pojetí finančního zdraví podniku, z metod poukazuje především na analýzu poměrových ukazatelů a soustavy ukazatelů. Praktická část se věnuje aplikaci vybraných metod na konkrétních příkladech a zároveň interpretuje jejich vypovídací schopnost.The thesis „Financial Analysis of Company“ deals with the general characteristics of the financial analysis, and determinates its fundamental problems, its approaches and methods. The theoretical section highlights the concept of the financial health of company; among the available methods, it highlights the analysis of financial ratios and system indicators. The practical part deals with the application of selected methods to specific examples, while interpreting their explanatory power.Prezenční634 - Katedra ekonomiky a managementu v metalurgiivelmi dobř