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Öğe Adsorption and desorption behavior of copper ions on Na-montmorillonite: Effect of rhamnolipids and pH(Elsevier Science Bv, 2009) Ozdemir, Gunseli; Yapar, SaadetIn this work, the effects of an anionic biosurfactant, rhamnolipid (RL), and pH on the adsorption and desorption of Cu(2+) ions on Na-montmorillonite were investigated. Adsorption studies were conducted through the addition of Cu(2+) to the dispersions containing pristine- and/or RL-modified clay. In the case of pristine clay, RL was also added simultaneously with the Cu(2+). The effect of pH was studied in the range between 1.0 and 8.0. The highest adsorption capacity was obtained at the pH of 4.7-4.8. Among the models including the Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms; Langmuir isotherm gave a better fit to the experimental data. The most suitable fit for the adsorption kinetics of Cu(2+) was obtained with a pseudo-second-order model. It was determined that the adsorption capacity of the pristine clay is comparable with that of the activated carbon and the modification of clay with RL causes an increase in the adsorption rate due to the distribution of clay platelets in the solution. (C) 2009 Elsevier B.V. All rights reserved.Öğe Adsorption and desorption behavior of copper ions on Na-montmorillonite: Effect of rhamnolipids and pH(Elsevier Science Bv, 2009) Ozdemir, Gunseli; Yapar, SaadetIn this work, the effects of an anionic biosurfactant, rhamnolipid (RL), and pH on the adsorption and desorption of Cu(2+) ions on Na-montmorillonite were investigated. Adsorption studies were conducted through the addition of Cu(2+) to the dispersions containing pristine- and/or RL-modified clay. In the case of pristine clay, RL was also added simultaneously with the Cu(2+). The effect of pH was studied in the range between 1.0 and 8.0. The highest adsorption capacity was obtained at the pH of 4.7-4.8. Among the models including the Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms; Langmuir isotherm gave a better fit to the experimental data. The most suitable fit for the adsorption kinetics of Cu(2+) was obtained with a pseudo-second-order model. It was determined that the adsorption capacity of the pristine clay is comparable with that of the activated carbon and the modification of clay with RL causes an increase in the adsorption rate due to the distribution of clay platelets in the solution. (C) 2009 Elsevier B.V. All rights reserved.Öğe Development of near-infrared reflective inorganic pigment dispersions in the continuous phase of solvent-binder medium(Springer, 2024) Uzunkavak, Onur; Ozdemir, GunseliCoatings containing functional pigments capable of reflecting radiation in the near-infrared (NIR) spectrum have been coveted in recent years to meet various industrial specifications. In this study, NIR reflective inorganic pigments with the chemical structure of TiO2, CoAl2O4, and (Cr,Fe)2O3 were dispersed individually in the continuous phase of organic solvents and thermosetting acrylic polyol to form ready-to-use colorants for NIR reflective coatings. A total of ten different pigments, three TiO2, three CoAl2O4, and four (Cr,Fe)2O3, were included. Resin-dispersant compatibility and solvent-pigment compatibility in potential paint formulations were tested prior to dispersion design. The ability of the developed pigment dispersions to maintain the primary particle size distributions was confirmed by stability tests, and UV-Vis-NIR spectra of fresh pigment dispersions drawn-down on steel plates were comparatively evaluated. Although the change in pigment particle size distribution after subjecting the dispersions to different temperatures was negligible, the favorable NIR reflectance obtained by certain pigment dispersions served to select the optimum pigment dispersions within dispersions of the same pigment chemistry. The ALTIRIS 800, 22-5600, and 30C941 dispersions exhibited higher reflectance in the NIR spectrum compared to other developed TiO2, CoAl2O4, and (Cr,Fe)2O3 dispersions, respectively, and supported their use in paint designs suitable to autonomous vehicles.Öğe Encapsulation of resveratrol in rhamnolipid-zein nanoparticles using a pH-driven method: kinetic modeling on controlled release from nanoparticles(Taylor & Francis Inc, 2023) Korkut, Oya Cicek; Ozdemir, GunseliIn this study, the encapsulation of resveratrol (Res) in zein-rhamnolipid (RL) composite nanoparticles (NPs) by a pH-driven method and its relationship with the controlled release behavior of the NPs were investigated. The properties of the produced NPs were elucidated with different zein-RL mass ratios and encapsulation of different amounts of Res. The NPs had relatively high encapsulation efficiency, loading capacity, stability, and cumulative release percentages. The SEM analysis showed the spherical NPs obtained with and without Res incorporation and the FTIR study indicated the interactions of Res with zein-RL components. The NPs had relatively good stability over a wide range of pH (4-9), salt concentration (0-200 mM) (pH = 7), and Res amount (0-160 mg) (pH = 7.4). Ultrasonic and shaking water baths were used for release studies of Res from NPs with an optimum zein-RL mass ratio of 1.0:0.6 (w/w). In vitro release studies of Res under acidic (pH = 1.2) and neutral (pH = 7.4) conditions demonstrated initial rapid release followed by slow release. The highest cumulative release percentage was obtained at pH 1.2 and 7.4 with 120 mg Res encapsulated zein-RL NPs. The release of Res from the capsules was a pH-dependent process and the cumulative release profiles were considered to be slightly higher in acidic environments. Among the controlled release kinetic models, the Weibull model gave the best fit for optimum Res-loaded NPs. Release studies indicated that zein-RL NPs have the potential to be used as delivery systems for health-promoting bioactive molecules in functional foods, nutraceutical/dietary supplements, and pharmaceutical formulations.Öğe Mechanisms of para-chlorophenol adsorption onto activated carbons having different textural and chemical properties(Desalination Publ, 2017) David, Etelka; Secula, Marius Sebastian; Ozdemir, Gunseli; Mamaliga, IoanThe present study describes the adsorption behavior, mechanisms governing the process and thermodynamics of the separation of p-chlorophenol (4-CP) from aqueous solutions by several granular activated carbons (ACs). The main contribution of this work consists in bringing more insight onto the proper selection of sorbents based on the affinity between them and a specific sorbate with a special regard onto the textural and chemical characteristics of sorbents. Batch tests were conducted in order to evaluate the kinetics, equilibrium and thermodynamics of each considered adsorption system. Equilibrium data were fitted to Langmuir, Freundlich, Sips, Redlich-Peterson and Radke-Prausnitz isotherms in order to elucidate the mechanisms governing the adsorption processes. Also, the kinetics data were analyzed by means of pseudo-first-order, pseudo-second-order, and intraparticle diffusion models The best-fitted adsorption isotherm models were found to be in the order Sips > Redlich-Peterson > Freundlich > Radke-Prausnitz > Langmuir, and the pseudo-second-order model described best the behavior of the adsorption of 4-CP onto each of the five investigated ACs. The adsorption capacity of the AC was found to decrease with temperature. The process of 4-CP adsorption onto AC was spontaneous, and physical in nature and thermodynamically feasible.Öğe Modeling of single and binary adsorption of lead and cadmium ions onto modified olive pomace(Desalination Publ, 2019) Uzunkavak, Onur; Patterer, Maria Silvina; Medici, Franco; Ozdemir, GunseliThis study deals with the evaluation of the single and binary removal of Pb2+ and Cd2+ from aqueous solutions using HNO3 modified olive pomace (N-OP). For the specific binary adsorption behavior, a renovative isotherm model was developed based on the additivity of the single adsorption contributions of Pb2+ and Cd2+ calculated from the binary data. The effect of the initial metal ion concentration, pH, ionic strength, and temperature on the adsorption of the single Pb2+ and Cd2+, and their binary adsorption were investigated using batch experiments at the optimum conditions. The N-OP displayed maximum adsorption capacities of 64 mg g(-1) for Pb2+ and 20.5 mg g(-1) for Cd2+ from the single metal ion solutions using 1.0 g L-1 N-OP. The results were best fitted with the Langmuir model for Pb2+ and the Radke-Prausnitz model for Cd2+ adsorption at 25 degrees C. The reusability of the N-OP was confirmed with desorption studies. The thermodynamic study revealed that the adsorption of Pb2+ was exothermic and that of Cd2+ was an endothermic process. The existence of Cd2+ in a binary solution increased the Pb2+ removal while that of Pb2+ reduced the Cd2+ removal with N-OP. This behavior may contribute to a selective removal of the heavy metal ions from their mixture.Öğe Preparation and characterization of copper and zinc adsorbed cetylpyridinium and N-lauroylsarcosinate intercalated montmorillonites and their antibacterial activity(Elsevier, 2020) Ozdemir, Gunseli; Yapar, SaadetThe main objective of the present study was the preparation and characterization of new cationic/anionic surfactants and Cu2+/Zn2+ modified montmorillonites and the evaluation of their potential applicability as antibacterial agents for topical applications. To evaluate the antibacterial activity of Cu2+ and Zn2+ by synergistic effect, as well as to reduce the well-known toxicity of these metal cations; cetylpyridinium (CP) and N-lauroylsarcosinate (SR) intercalated montmorillonite (Mt-CP-SR) was used as the host material. in addition to their role to capture the metal cations and inhibit their release in any contact medium, these surfactants also increase the efficacy of the material due to their antibacterial properties. the effect of surfactant loading on the adsorption behavior of the metal cations onto the Mt-CP was investigated using SR in two different concentrations, namely 0.7 and 1.0 CEC of sodium montmorillonite (Mt-Na). the samples prepared were characterized using SEM, ATR-FTIR, zeta potential, and XRD analyses and they were subjected to antibacterial tests using the "Standard Method Under Dynamic Contact Conditions" on the Gram positive S. aureus, and Gram negative E. coli. As confirmed with desorption and characterization studies, the addition of Cu2+/Zn2+ onto the Mt-CP-SR yielded double adsorbed amounts compared to that of the Mt-CP, which indicated that Cu2+/Zn2+ bound to SR- interacted with the Mt surface. in contrary of Zn2+ caused no considerable change in the antibacterial effect of the host, Cu2+ addition enhanced the antibacterial activity. the produced antibacterial agents have the potential use in dyes, polymer composites, personal care products, and topical medicinal applications.Öğe Preparation and characterization of sodium lauroyl sarcosinate adsorbed on cetylpyridinium-montmorillonite as a possible antibacterial agent(Elsevier Science Bv, 2017) Yapar, Saadet; Ates, Mustafa; Ozdemir, GunseliAn organo-montmorillonite was synthesized to generate a two-level antibacterial agent. The material (Mt-CP-SR) was prepared through the adsorption of sodium lauroyl sarcosinate (SR) on montmorillonite modified with cetylpyridinium (Mt-CP) and its structure was characterized by conducting ATR-FTIR, XRD, and SEM analyses. The results of the ATR-FTIR analyses indicated that SR on the surface could be detected when its amount exceeded the CEC of the Mt. The XRD analyses revealed that the adsorption of CP and SR causes the separation of Mt layers into smaller stacks. The adsorption and desorption study of SR onto and from 0.7 CEC Mt-CP were investigated to determine the amount of SR adsorbed at varying initial SR concentrations and the amount of SR released when diluted with water. Around 140 mg of SR could be loaded on one gram of the Mt intercalated with 170 mg of CP. The results indicated that desorption of SR from the surface is gradual and SR and CP have strong interactions on the montmorillonite (Mt) surface. The antibacterial activity of the material was tested against E. coil, S. aureus, and P. aeruginosa. Additionally, the SR solutions and CP + SR solutions in equimolar ratios were subjected to antibacterial tests for comparison purposes. SR proved to be effective against all three bacteria and the MIC values were found as 75 mg/mL for E. coil, 37.5 mg/mL for S. aureus, and 300 mg/mL for P. aeruginosa. The MBC was 300 mg/mL for E. coil and S. aureus. The solutions of CP + SR mixtures were ineffective against P. aeruginosa, whereas, they were effective against S. aureus. The prepared Mt-CP-SR samples were found to be effective against S. aureus and E. coil. These results indicate that the material could be used in antibacterial liquid soaps, in toothpaste formulations, personal care products, and topical applications against acne, and wounds without any negative contribution to the physico-chemical and detergency properties of the materials.Öğe Preparation of cetylpyridinium montmorillonite for antibacterial applications(Elsevier Science Bv, 2013) Ozdemir, Gunseli; Yapar, Saadet; Limoncu, Mine HosgorThe antibacterial activities of cetylpyridinium-montmorillonites (CP+-Mt) were tested on Staphylococcus aureus and Pseudomonas aeruginosa. The Mt were prepared by using the five different CP+ amounts of 0.5, 0.7, 1.0, 1.5, and 2.0 times of cation exchange capacities (CEC) of Na+-Mt. Desorption of CP+ from the surface was also determined by successive adsorption-desorption experiments. The antibacterial activity tests were conducted by using Na+-Mt and CP+-Mt through the disk diffusion (Kirby-Bauer) method against the P. aeruginosa ATCC 27853, and S. aureus ATCC 29213 strains. XRD analyses of the CP+-Mt showed that basal spacing regularly increased by increasing the amount of CP+ cations. Adsorption/desorption studies revealed that desorption occurred only in 2.0 CEC CP+-Mt by dilution with water and in 1.0 CEC CP+-Mt at a pH of 2.0. Nat(+)-Mt exhibited no antibacterial activity against both bacteria. All of the CP+-Mt samples prepared were active against S. aureus, whereas they had no antibacterial activity against P. aeruginosa. Minimum inhibitory concentration (MIC) was found to be 1 mg/plate against S. aureus, determined with 0.5 CEC CP+-Mt. Because nearly no desorption of CP+ was observed, the antibacterial activity was attributed to the CP+ bound to the Mt surface. (c) 2013 Elsevier B.V. All rights reserved.Öğe Preparation of cetylpyridinium montmorillonite for antibacterial applications(Elsevier Science Bv, 2013) Ozdemir, Gunseli; Yapar, Saadet; Limoncu, Mine HosgorThe antibacterial activities of cetylpyridinium-montmorillonites (CP+-Mt) were tested on Staphylococcus aureus and Pseudomonas aeruginosa. The Mt were prepared by using the five different CP+ amounts of 0.5, 0.7, 1.0, 1.5, and 2.0 times of cation exchange capacities (CEC) of Na+-Mt. Desorption of CP+ from the surface was also determined by successive adsorption-desorption experiments. The antibacterial activity tests were conducted by using Na+-Mt and CP+-Mt through the disk diffusion (Kirby-Bauer) method against the P. aeruginosa ATCC 27853, and S. aureus ATCC 29213 strains. XRD analyses of the CP+-Mt showed that basal spacing regularly increased by increasing the amount of CP+ cations. Adsorption/desorption studies revealed that desorption occurred only in 2.0 CEC CP+-Mt by dilution with water and in 1.0 CEC CP+-Mt at a pH of 2.0. Nat(+)-Mt exhibited no antibacterial activity against both bacteria. All of the CP+-Mt samples prepared were active against S. aureus, whereas they had no antibacterial activity against P. aeruginosa. Minimum inhibitory concentration (MIC) was found to be 1 mg/plate against S. aureus, determined with 0.5 CEC CP+-Mt. Because nearly no desorption of CP+ was observed, the antibacterial activity was attributed to the CP+ bound to the Mt surface. (c) 2013 Elsevier B.V. All rights reserved.Öğe SURFACE AND INTERFACE PROPERTIES OF LAUROYL SARCOSINATE-ADSORBED CP+-MONTMORILLONITE(Clay Minerals Soc, 2015) Yapar, Saadet; Ozdemir, Gunseli; Fernandez Solarte, Alejandra M.; Torres Sanchez, Rosa M.Catanionic surfactant systems are used as drug-delivery vehicles and as nanocompartments in the formation of biomaterials and nanosized particles. Clay minerals are compatible with organic tissues and also have biomedical applications. The aim of the present study was to combine the properties of catanionic surfactants and clay minerals to obtain new materials with potential uses in medicine, waste-water treatment, and antibacterial applications. The surfactants chosen to make the catanionic surfactant were cetylpyridinium (CP) and lauroyl sarcosinate (SR), which interact strongly in aqueous media and cause specific aggregations such as ion-pair amphiphiles and needle- and leaf-like structures. Aside from the aqueous solution, new ternary systems are formed with different structures and properties through the addition of montmorillonite (Mnt). The surface and interlayer structures of the different Mnt-CP-SR samples prepared by using CP and SR in amounts equal to various ratios of cationic exchange capacity of the clay mineral were studied. They were also compared with the structured surfactant aggregates formed in aqueous media. The Mnt-CP-SR samples were subjected to X-ray diffraction (XRD), thermogravimetric analyses, and zeta-potential measurements to elucidate the interlayer- and external-surface structures. The XRD analyses showed the formation of a compact structure in the interlayer region resulting from the interaction between randomly oriented pyridinium and negatively charged SR head groups. The triple interactions among the Mnt surface, CP, and SR were more complex than the double interactions between the Mnt and cationic surfactant, and the CP played a dominant role in the formation of external and interlayer surface structures regardless of the amount and order of the addition of SR. The new findings support new applications for organoclays in the fields of biomedicine, remediation of polluted water, and nanocomposite materials.Öğe Synthesis and Characterization of Non-leaching Inorgano- and Organo-montmorillonites and their Bactericidal Properties Against Streptococcus Mutans(Springer, 2022) Sahiner, Asli; Ozdemir, Gunseli; Bulut, T. Hakan; Yapar, SaadetThe direct application of heavy metal- and quaternary ammonium-based antibacterial agents can cause inconvenience such as irritation, short-term applicability, discoloration of the tissue, and environmental concerns. The immobilization of these agents on montmorillonite (Mnt) was expected to diminish these effects by hindering direct contact of the ions with the target tissues. The objective of the present study was, therefore, to prepare inorgano(I)- and organo(O)-montmorillonites (I/O-Mnt) and to determine their potential uses in such biomedical applications. Na-montmorillonite (Mnt-Na) was modified by hydrothermal and microwave irradiation methods using Cu2+/Zn2+, and quaternary ammonium and/or anionic surfactants. The effect of the structures formed by immobilization on Mnt surfaces on antibacterial activity was investigated. Quaternary ammonium surfactants were cetyltrimethyl ammonium bromide (CTAB) with a linear alkyl chain, cetylpyridinium chloride (CPC) with a single aromatic ring, and benzethonium chloride (BZT) with double aromatic rings. N-lauroyl sarcosinate (SR) was the anionic surfactant. The samples were subjected to thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Desorption tests showed that the antibacterial efficacy against Streptococcus mutans stemmed from I/O-Mnt and not from the ions released from the material surfaces to the aqueous phase. The results of the antibacterial studies showed that the existence of a linear alkyl chain and a double aromatic ring were the structural factors causing the greatest antibacterial effect. The time-kill tests revealed that Mnt-CTA, Mnt-BZT, and Mnt-CP-SR were effective against Streptococcus mutans within 5 min of contact. With the new findings, they were identified as possible selective and potent bactericidal agents and promising candidates for biomedical applications.
