Browsing by Author "Vassileva P."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Adsorption of Ag+ ions on hydrolyzed lignocellulosic materials based on willow, paulownia, wheat straw and maize stalks(2016-05-01) Vassileva P.; Radoykova T.; Detcheva A.; Avramova I.; Aleksieva K.; Nenkova S.; Valchev I.; Mehandjiev D.In the present work, the adsorption of Ag+ ions on hydrolyzed plant biomass (willow, paulownia, wheat straw and maize stalks) was investigated. Chemical analyses were performed to establish the composition of the obtained materials. Adsorption mechanism, adsorption sites and specific surface areas of these materials were examined by BET analysis, IR spectroscopy, XPS and EPR. The effects of contact time, acidity of initial solutions and Ag+ ion concentrations were followed. Pseudo-first-order, pseudo-second-order and intra-particle diffusion models were used to analyze kinetic data. In all cases, the adsorption was significantly affected by the pH value. Different types of adsorption isotherms of Ag+ ions (either Langmuir or Freundlich) were registered depending on the adsorbing material. The adsorption mechanism is complex, and the process passes through different stages as clustering of Ag+ ions and formation of elemental Ag. The maximal adsorption capacities varied from 2.05 to 6.07 mg g−1. The obtained results revealed that the examined waste lignocellulosic materials are promising adsorbents for Ag+ ions.Item Adsorption properties of a nanostructured hybrid material containing aluminium towards some metal ions(2011-10-01) Detcheva A.; Vassileva P.; Georgieva R.; Voykova D.; Gerganova T.; Ivanova Y.In the present work the adsorption of some transition metal ions from aqueous solutions on a silica-based nanostructured hybrid material modified by aluminium was investigated. The novel organic-inorganic material was synthesized via a sol-gel method through hydrolysis and co-condensation reactions. Its structure was characterized by means of SEM, XRD and FTIR. Based on the data obtained the most probable cross-linking mechanism for the derived xerogel was proposed. The characterization of its texture parameters was carried out by low-temperature adsorption of nitrogen. The adsorption properties of this material with respect to Cu(II), Cr(III) and Pb(II) ions from single-component aqueous solutions and multi-component aqueous solutions containing also Cd(II) and Fe(III) were evaluated. The effect of contact time, acidity of initial solutions and metal ion concentrations was investigated using the batch method. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. In all cases the adsorption was significantly affected by the pH value. Equilibrium modelling data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models. Best fit was observed for Langmuir model, which showed determination coefficients greater than 0.992 for all ions studied. The maximum adsorption capacities for single- and multi-component adsorption were calculated. © Versita Sp. z o.o.Item Calcareous clays: Phase composition and adsorption capacity for heavy metal ions(2019-01-01) Mihailova I.; Vassileva P.; Mehandjiev D.The purpose of this study was to investigate the prospective use of calcareous clay in its natural state and after thermal treatment for removal of heavy metals from aquatic environment. The study included 6 natural products from clay deposits in Bulgaria, five of which were calcareous clays and the sixth one was an iron-rich clay. The structural characterization of the samples was carried out using inductively coupled plasma optic emission spectrometry, X-ray powder diffraction analysis, Fourier-transform infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The clay minerals contained in the samples were identified as illite, chlorite, kaolinite and smectite. Quartz, calcite and feldspar were identified in the samples too. The thermal treatment has led to changes in the phase composition of clays as a result of partial dehydration and decomposition of minerals. There was an increase in the adsorption capacity of the calcareous clays relative to the metal ions of Cu(II) and Zn(II) after thermal treatment, regardless of the reduction of their specific surface area, which is determined by the increase of the adsorption centers upon thermal treatment.Item Silica-based organic-inorganic hybrid materials as potential adsorbents for Hg(II) ions(2013-12-17) Velikova N.; Vueva Y.; Ivanova Y.; Salvado I.; Fernandes M.; Vassileva P.; Georgieva R.; Detcheva A.In the present study four functionalized mesoporous silica materials denoted as BIS-1, BIS-2, BIS-3 and BIS-4 have been synthesized through a simple co-condensation of bis-[3-(trimethoxyosilyl)propyl] amine (BTPA) and tetraethyl orthosilicate (TEOS). The influence of the BTPA amount on the structural and adsorption properties of the resultant materials was investigated. The novel hybrid materials have been characterized by FT-IR, BET, 13C CP MAS NMR and elemental analysis. The adsorption properties of mesoporous organic-inorganic materials containing amine functional groups, regarding Hg(II) ions were studied by the batch method. Experiments were carried out in acidic media. The material BIS-3 exhibits highest adsorption capacity for mercury ions. Kinetics of Hg (II) adsorption on BIS-3 was investigated. Equilibrium experimental data for BIS-3 were fitted to linear Langmuir and Freundlich models. All studied hybrid materials could be successfully used for effective removal of mercury ions from acidic aqueous solutions.Item Synthesis, characterization and adsorption properties of nanostructured hybrid materials modified by boron and zirconium(2012-10-01) Georgieva R.; Vassileva P.; Detcheva A.; Voykova D.; Gerganova T.; Ivanova Y.The adsorption properties of two new nanostructured hybrid materials containing B 2O 3 and ZrO 2 were studied. The new organic- inorganic materials were synthesized via a sol-gel method. As a modifying agent, a quantity of 10 wt.% Zr(OPr) 4 or B(OCH 3) 3 was added. The structure of the hybrid materials was investigated by means of (Fourier transform infrared spectroscopy (FTIR), x-ray diffractometry (XRD), scanning electron microscopy (SEM), (atomic force microscopy (AFM) and nuclear magnetic resonance spectroscopy (NMR). Based on the obtained data, the most probable cross-linking mechanism for the derived gels was proposed. The characterization of texture parameters of both materials was carried out with the use of low-temperature adsorption of nitrogen. Adsorption of Cu(II), Fe(III), Cr(III), Cd(II) and Pb(II) ions on both materials was investigated using multi-component solutions with different concentrations and acidity by means of the batch method. Kinetics of adsorption was also investigated. Pseudo-first order, pseudo-second order and intraparticle diffusion models were used to analyze kinetic data. The adsorption was significantly affected by the pH value. Equilibrium data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models and maximum adsorption capacities were calculated. © Versita Sp. z o.o.