Branka Kaludjerovic

Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth

The adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth was studied as a function of their concentrations and solution pH. For that purpose, pertinent adsorption isotherm data was collected at different pH values. The amount of adsorbed zinc and cadmium ions increases while the amount of adsorbed mercury remains constant with an increase in the equilibrium pH of the solution. The adsorption mechanisms of metal ions on activated carbon cloth are discussed. Under the conditions investigated, these primarily involve adsorption of monovalent cations (Zn and Cd) or precipitation of metal hydroxides (Cd and Hg) on the activated carbon cloth tested.

Characterization of Carbon Cryogel Synthesized by Sol-Gel Polycondensation and Freeze-Drying

Resorcinol-formaldehyde (RF) cryogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde and freeze-drying carried out with t-butanol. Carbon cryogels were obtained by pyrolyzing RF cryogels in an inert atmosphere. Characterization by nitrogen adsorption showed that carbon cryogels were micro- and mesoporous materials with high surface areas (500 m2/g< SBET <700 m2/g). Cyclic voltammetry experiments at various scan rates (2 to 200 mV s-1) were carried out to study the electrical double-layer charging of carbon cryogel electrodes in 0.5 mol dm-3 HClO4 solution. It has been demonstrated that the total specific capacitance can further be divided into mesoporous and microporous specific capacitance by analyzing the linear dependence of the specific capacitance (C) on the reciprocal of the square root of the potential scan rate ( ν -1/2), as well as linear dependence of the reciprocal specific charge (1/C) on the square root of the potential scan rate ( ν 1/2).

Characterization of nanoporous carbon fibrous materials obtained by chemical activation of plane tree seed under ultrasonic irradiation

An ultrasonic irradiation was applied for the impregnation by chemical agents in the chemical activation process of new type of active carbon precursor. Plane tree seed, due to the unique fibrous structure and low cost is a promising eco-friendly raw material for the preparation of activated carbon materials. Ultrasonic irradiation was used for the impregnation step allowing the chemical activation by different agents: potassium or sodium hydroxide, hydrogen peroxide and pyrogallol. The porous structures were examined by nitrogen adsorption/desorption isotherms at 77 K and electrochemically by cyclic voltammetry. The textures of these materials were observed by scanning electron microscopy. The application of ultrasonic irradiation in the impregnation step increased surface area of the final material more than two times in comparison to the material which impregnation in the activation process was by conventional stirring. Ultrasonic irradiation enhances the chemical activation process and the activated carbon fibrous materials with nanoporous structure were obtained by impregnation of seeds with alkaline hydroxides. Total surface areas of these samples were 976 m(2) g(-1) and 1130 m(2) g(-1). These fibers have total specific capacitance as high as 125 F g(-1) and 53 F g(-1) which major fraction in both cases originate from internal micropores structure.

Analysis of the Interaction of Pulsed Laser with Nanoporous Activated Carbon Cloth

Interaction of pulsed transversely excited atmospheric (TEA) CO2-laser radiation at 10.6 μm with nanoporous activated carbon cloth was investigated. Activated carbon cloth of different adsorption characteristics was used. Activated carbon cloth modifications were initiated by laser pulse intensities from 0.5 to 28 MW/cm2, depending on the cloth adsorption characteristics. CO2 laser radiation was effectively absorbed by the used activated carbon cloth and largely converted into thermal energy. The type of modification depended on laser power density, number of pulses, but mostly on material characteristics such as specific surface area. The higher the surface area of activated carbon cloth, the higher the damage threshold.

Modification of Carbon Cloth by Interaction with Pulsed TEA CO2 Laser

The interaction of a Transversely Excited Atmospheric (TEA) CO2 laser (pulse duration less than 2 μs) with carbon and activated carbon cloth was investigated. The investigations have shown that carbon cloth had been physically modified by the TEA CO2 laser. The type of modification strongly depends on laser working regime, such as energy density of the laser beam, etc. The morphology transformations induced by interaction with TEA CO2 laser beams resulted in different specific surface area of activated carbon cloth. Also, laser interaction induced minor changes in crystallographic structure parameters.

Laser interaction with carbon-type materials

It is well known that application of stimulated light may influence phase modifications and changes of carbon structure. These effects of laser irradiation, in different working regimes and atmospheres, are widely investigated for fullerenes and diamond structure, but for many other carbon materials, are not. In the presented experiments, we treated by Q-switch ruby and Nd3+ YAG laser beams different carbon clothes, produced by pyrolysis (T <EQ 1000 degree(s)C) of cellulose materials in inert atmosphere. The materials are interesting for many applications, including medical. The laser pulse energy was of order of 0.1 - 1 J, in one, or multi-pulse regime. Focused and unfocused beams were used to induce damages and oxidation of sample surfaces. the damages were analyzed by scanning electron microscopy and specific area is measured by Brunauer, Emmet and Teller method, before and after the interaction. Materials exhibited differences in the damaging level and the fiber breaking thresholds. Mechanisms of laser interaction leading to oxidation of carbon type materials are discussed, and the necessary experimental conditions for intended changes are analyzed.

Interaction of laser beams with carbon textile materials

Purpose – The purpose of this paper is to present the results of interaction occurring during the exposition of some specific carbon textile materials obtained in laboratory conditions to beams of various laser types. Design/methodology/approach – Carbon fabric materials – fiber, felt and cloth – obtained from different precursor materials and prepared at various process conditions (oxidized, partially carbonized, carbonized, graphitized), were exposed to pulses of various lasers (Nd3+: YAG, alexandrite, ruby). Findings – Depending on the laser power, plasma and destructive phenomena occurred. In the case of an interaction between a Nd3+: YAG laser beam and specimens of thickness in millimeter range, the authors have estimated the threshold of the energy density for drilling and discussed the possible models of the interaction. Research limitations/implications – The results have implications in the estimations of quality as well as in the improvement of material processing, giving some new light to the c...

Electrooxidation of Hydrogen on Nanostructured Pt/C Catalysts for Polymer Electrolyte Fuel Cells

Mesoporous carbon cryogel synthesized by sol-gel polycondensation and freeze-drying with specific surface area (BET) of 517 m2 g-1 was used as a catalyst support. Pt/C catalysts were prepared by a modified ethylene glycol method (EG). Transmission electron microscopy (TEM) images show that the dispersion of the catalyst is very uniform with a mean particle size of about 2.65 nm. Hydrogen oxidation reaction (HOR) was studied on Pt/C catalyst in 0.5 mol dm-3 HClO4 acid solution. It has been found that HOR appears as a reversible two-electron direct discharged reaction (Tafel slope for this reaction is ≈30mV dec-1) and that Pt/C catalyst exhibits a very high catalytic activity. However, the corresponding value of the exchange current density obtained by dividing the exchange current by the active surface area of Pt particles has the same order of magnitude as those for the HOR in acidic solution at single crystal and polycrystalline Pt.