63 research outputs found
Being and responsibility
No full textDrawing on Levinas, the author seeks to explore the question of being and responsibility, as a relation between ontology and ethics, from the perspective of a meta-position that would enable a critique of the classical West European ontological tradition with its strongly cosmocentric, anthropocentric, and egocentric character. The main purpose of the paper is to examine whether there is in West European thought a possibility to found the ethics of responsibility on overcoming the ontology of being. More precisely, the author seeks to show that in contemporary Western philosophy the significance and validity of the classical ontological principle are declining when it gets separated from the ethos of philosophy itself. Moreover, a gradual shift from the impersonal being to the ontology of the personality takes place. This ontology of the personality is grounded in the Other. It withdraws from the game of consciousness which represents being. The personality thus understood, in Levinas' words, carries within itself vested responsibility, because in the personality there lie the infinite and transcendence
Silver Deposition on Chemically Treated Carbon Monolith
No full textCarbon monolith was treated with HNO(3), KOH and H(2)O(2). Effects of these treatments on the surface functional groups and on the amount of silver deposited on the CM surface were studied by temperature programmed desorption (TPD) and atomic absorption spectrometry (AAS). As a result of chemical treatment there was an increase in the amount of surface oxygen complexes. The increase in the amount of silver deposit is proportional to the amount of surface groups that produce CO under decomposition. However, the high amount of CO groups, decomposing above 600 degrees C, induces the smaller Ag crystallite size. Therefore, the high temperature CO evolving oxides are, most likely, the initial centers for Ag deposition.7th Seminar of Young Researchers, Dec 22-24, 2008, Belgrade, Serbi
Characterisation of surface oxygen groups on different carbon materials by the Boehm method and temperature-programmed desorption
No full textThe surface characteristics of different carbon materials: activated carbon, carbon felt, glassy carbon and a porous carbon monolith were investigated. The specific surface area was examined by the BET method with N2 adsorption, the amount and the type of surface oxygen groups by Boehm titration as well as by temperature-programmed desorption (TPD). By comparing the results obtained using BET analysis with those of TPD and the Boehm method, it was found that the number of surface groups was not proportional to the specific surface area. The total amount of oxygen groups, obtained by TPD, is higher than the amount obtained by Boehm’s method for porous samples. The inconsistencies between these results originate from the fact that the Boehm method is limited to the determination of acidic and basic groups, whereas TPD provides information on the total number of all surface oxygen groups. In addition, the presence of porosity could reduce the solvent-accessible surface in the Boehm method. The TPD profiles of CO evolution showed the presence of a low temperature maximum, below 650 K, which originates from CO2 reduction on the carbon material surface
A TPD-MS study of glassy carbon surfaces oxidized by CO2 and O2
No full textThe temperature-programmed desorption (TPD) method combined with mass spectrometric (MS) analysis has been applied to investigate the surface properties of carbon materials. The apparatus consisting of a temperature-programmed furnace and a quadrupole mass spectrometer was constructed in order to characterize the surface of differently treated glassy carbon samples. In this work, samples of glassy carbon exposed to air, CO2 and O2 were examined. The desorption of H2O, CO and CO2, as major products, indicated the presence of different oxide groups. The amount of these groups for all samples was calculated. It is concluded that oxidation affects the nature and the amount of the surface oxide groups and contributes to their increased stability
Mass spectrometry analysis of polychlorinated biphenyls: chemical ionization and selected ion chemical ionization using methane as a reagent gas
No full textIn the present paper a quadrupole ion trap mass spectrometer, coupled with a gas chromatograph, was used to compare the electron impact ionization (EI) and chemical ionization (Cl) technique, in terms of their selectivity in polychlorinated biphenyls (PCBs) quantitative analysis. The experiments were carried out with a modified Varian SATURN III quadrupole ion-storage mass spectrometer equipped with Varian waveform generator, coupled with a gas chromatograph with DB-5 capillary column. The disadvantage of using EI in the analysis of PCBs congeners is the extensive fragmentation of the molecular ion. The main fragmentation pattern recorded in the EI mass spectra of PCBs was the loss of a chlorine atom from the molecular ion. Therefore the fragment-ion signal overlapped with the molecular-ion cluster of lower mass congener. The fragmentation reactions of PCBs are suppressed if methane is used as a reagent gas for chemical ionization, but fragment ions are also present in the spectrum as an obstruction for quantitative analysis. The most selective method for PCBs quantitative analysis appears to be Cl with mass-selected C2H5+ ions from methane, which results in a mass spectrum with a negligible amount of fragment ions
Application of carbonized hemp fibers as a new solid-phase extraction sorbent for analysis of pesticides in water samples
No full textThere is a growing interest in utilization of abundantly available materials, bio-mass or industrial byproducts, as precursors for the preparation of carbon materials. Short hemp fibers, acquired as waste from textile production, were used as low-cost precursor for production of carbon materials as a sorbent in the solid-phase extraction, for pesticide analysis in water samples. Different carbon materials were prepared by carbonization of unmodified and chemically modified hemp fibers. Activation of carbonized materials with potassium hydroxide improves sorption properties of carbonized hemp fibers by increasing the specific surface area (up to 2192 m(2)/g) and the amount of surface oxygen groups. The following parameters that may affect the solid-phase extraction procedure efficiency were optimized: different elution solvents and the pH value of pesticide solution. Extracts were analyzed by liquid chromatography-tandem mass spectrometry technique. For this study pesticides belonging to the different chemical classes were chosen. Obtained results indicate that carbonized and activated hemp fibers could be successfully applied as a solid-phase sorbent for the pesticide analysis in water samples. (C) 2012 Elsevier B.V. All rights reserved
Cd and Zn in atmospheric deposit, soil, wheat, and milk
No full textContinuous air quality monitoring in the Vojvodina district of Serbia and Montenegro has shown high levels of Cd, especially in the outskirts of large towns such as Kikinda. The construction and metal processing industries located in Kikinda have been emitting significant amounts of heavy metals into the environment. The levels of Cd and Zn were monitored in the region of Kikinda and compared to their concentrations detected in Novi Sad, the capital of Vojovodina, where emission of heavy metals originated mostly from vehicle traffic. The study was performed during the economic sanctions when industrial production decreased drastically. The consequence of that was a significant decrease of the concentration of Cd and Zn in atmospheric deposits. Data collected during 3 years indicated a direct influence of atmospheric deposits on heavy metal distribution in the chain soil-cattle feed milk. Decreased Cd concentrations of 93% in atmospheric deposits in the Kikinda region resulted in decreased Cd concentrations of 17% in cattle feeds and 13% in milk. Decreased Zn concentrations of 58% in atmospheric deposits caused reduced Zn concentrations of 30% in soil, 17% in cattle feeds, and 17% in milk. (C) 2004 Elsevier Inc. All rights reserved
Influence of different carbon monolith preparation parameters on pesticide adsorption
No full textThe capacity of carbon monolith for pesticide removal from water, and the
mechanism of pesticide interaction with carbon surface were examined.
Different carbon monolith samples were obtained by varying the carbonization
and activation parameters. In order to examine the role of surface oxygen
groups in pesticide adsorption, carbon monolith surface was functionalized by
chemical treatment in HNO3, H2O2 and KOH. The surface properties of the
obtained samples were investigated by BET surface area, pore size
distribution and temperature-programmed desorption. Adsorption of pesticides
from aqueous solution onto activated carbon monolith samples was studied by
using five pesticides belonging to different chemical groups (acetamiprid,
dimethoate, nicosulfuron, carbofuran and atrazine). Presented results show
that higher temperature of carbonization and the amount of activating agent
allow obtaining microporous carbon monolith with higher amount of surface
functional groups. Adsorption properties of the activated carbon monolith
were more readily affected by the amount of the surface functional groups
than by specific surface area. Results obtained by carbon monolith
functionalisation showed that π-π interactions were the main force for
adsorption of pesticides with aromatic structure, while acidic groups play an
important role in adsorption of pesticides with no aromatic ring in the
chemical structure
Influence of the precursor chemical composition on heavy metal adsorption properties of hemp (Cannabis Sativa) fibers based biocarbon
No full textWaste hemp (Cannabis sativa) fibers were used as sustainable and renewable raw materials for production of low-cost biocarbon sorbent for heavy metals removal. Carbon precursors of different chemical composition were obtained by oxidative and alkaline treatments of hemp fibers. Influence of lignocellulosic precursor chemical composition on hemp fibers-based biocarbon (HFB) characteristics was examined by BET surface area measurement, scanning electron microscopy and mass titration. It was found that lignin content and polymorphic transformation of cellulose increase the SBET of microporous HFBs, while hemicelluloses induce more homogeneous distribution of adsorption active sites. Heavy metal ions adsorption onto HFBs is primarily influenced by the amount of surface oxygen groups, while specific surface area plays a secondary role. Equilibrium data obtained for lead ions adsorption were analyzed by different nonlinear adsorption isotherms, and the best fitting model was chosen using standard deviation and Akaike information criterion (AICC). The maximum adsorption capacities of HFBs ranged from 103.1 to 116.3 mg Pb/g. Thermodynamic parameters showed that Pb2+ adsorption onto HFBs is a spontaneous and complex endothermic process, suggesting the coexistence of physisorption and chemisorption mechanisms. [Project of the Serbian Ministry of Education, Science and
Technological Development, Grant no. 172007 and Grant no. 172029
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