Browsing by Author "Yaneva Z."

Now showing 1 - 8 of 8
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    Binary adsorption of copper and sulfates on barium-modified clinoptilolite
    (2018-01-01) Lavrova-Popova S.; Yaneva Z.
    The binary adsorption of copper cations and sulfate anions by surface modified natural clinoptilolite was investigated. The efficiency of the adsorbent was studied using batch adsorption technique under different experimental conditions by varying parameters such as initial ions concentration in the aqueous solution, clinoptilolite mass and contact time. An assessment of the equilibrium and the kinetics of copper and sulfates ions sorption was made. The experimental results were fitted to the Freundlich, Baudu, and the Multilayer isotherms. It was established that the Baudu isotherm best describe the binary removal of Cu2+ and SO4 2- by modified clinoptilolite with incorporated barium ions on its surface (CLIBa). Before the clinoptilolite modification (CLI), the removal of both copper and sulfate ions was best described by Baudu and Multilayer isotherms, respectively. The removal of Cu2+ is probably due to physiosorption, while that of SO4 2- - to at least two different in nature mechanisms - complexation and adsorption. The Ba-modification of the natural clinoptilolite led to a 1.1 times decrease and 4.8 times increase of the copper and sulfate removal efficiency. The kinetics of Cu2+ and SO4 2- adsorption onto modified clinoptilolite followed pseudo second-order model which suggests that both ions were adsorbed on the CLIBa surface via chemical interaction and intraparticle diffusion mechanisms.
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    Drug mass transfer mechanism, thermodynamics, and in vitro release kinetics of antioxidant-encapsulated zeolite microparticles as a drug carrier system
    (2018-10-01) Yaneva Z.; Georgieva N.; Bekirska L.; Lavrova S.
    The aim of the present study was to develop a new vitamin E-zeolite drug carrier system, and investigate the mass transfer mechanism of the antioxidant encapsulation and release on/from the mineral matrix by thermodynamic and kinetics sorption/desorption experiments and mathematical modelling of the experimental data. The surface, morphological and spectral characteristics of the vitamin and the zeolite were determined by Boehm titration, SEM, FTIR and UV/Vis spectrophotometric analyses. Intraparticle diffusion was not the only rate-limiting mechanism, as the mixed-order kinetics model gave the highest regression coefficient (R2) and lowest SSE, MSE, RMSE, and AICC values. The thermodynamic study confirmed the endothermic nature of the spontaneous encapsulation process and increased degrees of randomness at the solid-liquid interface. The in vitro release results were best modelled by the zero-order and sigmoidal models. The results obtained are essential for the development of innovative vitamin E-carrier systems for application in human and veterinary medicine.
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    Dynamic studies of nitrophenols sorption on perfil in a fixed-bed column
    (2008-01-01) Yaneva Z.; Marinkovski M.; Markovska L.; Meshko V.; Koumanova B.
    The adsorption of two substituted nitrophenols, namely 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), from aqueous solutions onto perfil was studied using a fixed bed column. The theoretical solid diffusion control (SDC) model describing single solute adsorption in a fixed bed based on the Linear Driving Force (LDF) kinetic model was successfully applied to the investigated systems. The model parameters of solid diffusion coefficient, DS, axial dispersion coefficient, DL, and external mass transfer coefficient, kf, for the investigated systems were estimated by the means of a best fit approach. Some deviations were found between the predicted and the experimental data which reflect the fact that the assumptions of the model were not quite fulfilled for these experiments. It is necessary to adjust the values of the solid diffusion coefficient, the axial dispersion coefficient and the external mass transfer coefficient in order to obtain a satisfactory agreement between the simulated and the experimental breakthrough curves. A Biot number was used as an indicator for the intarparticle diffusion. The Biot number was found to decrease with the increase of bed depth, indicating that the film resistance increased or the intraparticle diffusion resistance decreased.
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    Flavonoids Extraction Kinetics, Antimicrobial Activity and Radical Scavenging Potential of Bulgarian Woundwort (Solidago virgaurea L.)
    (2022-02-01) Yaneva Z.; Simeonov E.; Rusenova N.; Ivanova D.; Nikolova G.; Karamalakova Y.; Chilev C.; Beev G.
    The medicinal plant woundwort (Solidago virgaurea L.) characterizes by diuretic, antimutagenic, anti-inflammatory activity and it has been applied for urinary tract, nephrolithiasis and prostate disorders treatment. The aim of the present study was to analyze the extraction kinetics of catechin, epigallocatechin and quercetin from Bulgarian woundwort extracts, to assess the antibacterial potential of the medicinal plant extracts against four bacterial strains (Staphylococcus aureus ATCC25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Bacillus cereus), their antioxidant capacity and radical scavenging potential. The concentrations of the flavonoids in the extracts obtained at different extraction conditions (solvent, temperature, extraction time) were determined by newly-developed by the scientific team RP-HPLC-PDA methodologies. The agar well diffusion method was applied to evaluate the antibacterial activity of the plant extracts. The 70% EtOH extracts at 20◦C displayed significantly higher antibacterial activity against the foodborne pathogenic bacteria S. aureus and P. aeruginosa as compared to the 70% and 98% EtOH extracts at 30◦C and 20◦C, respectively. The medicinal plant exhibited satisfactory antioxidant potential and radical-scavenging activity.
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    Kinetics of green solid-liquid extraction of useful compounds from plant materials: Kinetics coefficients and modeling
    (2018-02-23) Simeonov E.; Yaneva Z.; Chilev C.
    A mathematical model for modeling solid-liquid extraction from plants was developed. Two extraction systems, System I Nicotiana tabacum L.-water and System II Geranium sanguineum L.-water, were investigated. The effect of agitation rate on the mode of the extraction process was studied, as the limit values in the case of internal diffusion for System I and System II were determined. The kinetics of extraction for both systems at determined technological parameters (temperature and solid/liquid ratio) was experimentally investigated. The values of the partial mass transfer coefficient, k, were determined by the Regular regime method. A four-parameter empirical model for prediction of the effective diffusivity, Deff, was also presented. The model adequacy is verified with the experimental data and shows very good coincidence.
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    Linear and nonlinear regression methods for equilibrium modelling of p-nitrophenol biosorption by Rhizopus oryzae: Comparison of error analysis criteria
    (2013-01-01) Yaneva Z.; Koumanova B.; Georgieva N.
    The study assessed the applicability of Rhizopus oryzae dead fungi as a biosorbent medium for p-nitrophenol (p-NP) removal from aqueous phase. The extent of biosorption was measured through five equilibrium sorption isotherms represented by the Langmuir, Freundlich, Redlich-Peterson, multilayer and Fritz-Schlunder models. Linear and nonlinear regression methods were compared to determine the best-fitting equilibrium model to the experimental data. A detailed error analysis was undertaken to investigate the effect of applying seven error criteria for the determination of the single-component isotherm parameters. According to the comparison of the error functions and to the estimation of the corrected Akaike information criterion (AI C C), the Freundlich equation was ranked as the first and the Fritz-Schlunder as the second best-fitting models describing the experimental data. The present investigations proved the high efficiency (94) of Rhizopus Oryzae as an alternative adsorbent for p-NP removal from aqueous phase and revealed the mechanism of the separation process. © 2013 Zvezdelina Lyubenova Yaneva et al.
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    Newly Synthesized Lignin Microparticles as Bioinspired Oral Drug-Delivery Vehicles: Flavonoid-Carrier Potential and In Vitro Radical-Scavenging Activity
    (2023-04-01) Ivanova D.; Toneva M.; Simeonov E.; Nikolova B.; Semkova S.; Antov G.; Yaneva Z.
    The aim of the present study was to synthesize lignin microparticles, to evaluate their physicochemical, spectral, morphological and structural characteristics, to examine their encapsulation and in vitro release potential and behaviour towards the flavonoid morin in simulated physiological medium and to assess the in vitro radical-scavenging potential of the morin-loaded lignin microcarrier systems. The physicochemical, structural and morphological characteristics of alkali lignin, lignin particles (LP) and morin-encapsulated lignin microparticles (LMP) were determined based on particle size distribution, SEM, UV/Vis spectrophotometric, FTIR and potentiometric titration analyses. The encapsulation efficiency of LMP was 98.1%. The FTIR analyses proved that morin was successfully encapsulated in the LP without unexpected chemical reactions between the flavonoid and the heteropolymer. The in vitro release performance of the microcarrier system was successfully mathematically described by Korsmeyer–Peppas and the sigmoidal models outlining the general role of diffusion during the initial stages of the in vitro release process in simulated gastric fluid (SGF), and the predominant contribution of biopolymer relaxation and erosion was determined in simulated intestinal medium (SIF). The higher radical-scavenging potential of LMP, as compared to that of LP, was proven via DPPH and ABTS assays. The synthesis of lignin microcarriers not only provides a facile approach for the utilization of the heteropolymer but also determines its potential for the design of drug-delivery matrices.
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    Study of the mechanism of nitrophenols sorption on expanded perlite - Equilibrium and kinetics modelling
    (2012-01-01) Yaneva Z.; Koumanova B.; Georgieva N.
    The adsorption behavior of 2-nitrophenol (2-NP) and 2,4-dinitrophenol (2,4-DNP) on expanded perlite (EP) at equilibrium and kinetic conditions was investigated. The experimental equilibrium data were interpreted by Langmuir, Freundlich, Redlich-Peterson, Temkin and the multilayer isotherm models. Both the Temkin and the multilayer models gave the most satisfactory representation of the experimental data for 2-NP sorption on EP covering the whole concentration range, presuming high initial sorption rate, presence of adsorbent-adsorbate chemical interactions and multilayer adsorption, as the basic characteristics featuring the equilibrium behavior of the system studied. The experimental kinetic results were analyzed by the pseudo-first, pseudo-second order models, Bangham's model, intra-particle diffusion model, and Elovich kinetic equation. The values of the calculated rate, mass transfer parameters and correlation coefficients proved that chemisorptions/intraparticle diffusion could be outlined as the basic rate controlling mechanisms during 2-NP/2,4-DNP sorption on expanded perlite. Uptake of nitrophenols increased in the order 2-NP < 2,4-DNP.