Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 8Citation - Scopus: 10Trypsin-Immobilized Silica: a Novel Adsorbent for V(iv) and V(v) Removal From Water(Water Environment Federation, 2018) Erdem Yayayürük, Aslı; Shahwan, Talal; Şanlı Mohamed, Gülşah; Eroğlu, Ahmet EminIn the present study, trypsin-immobilized silica was employed for the removal of V(IV) and V(V) ions from water. The synthesized sorbent was first characterized and then investigated for the removal of V(IV) and V(V) under various experimental conditions. The adsorption performance of the sorbent was tested as a function of pli, sorbent amount, initial vanadium concentration, contact time, and temperature. The sorption process was then investigated, both from a kinetic perspective and also in terms of isotherm models. The Langmuir adsorption isotherm was the best model to describe the sorption process. Sorption thermodynamics were spontaneous and exothermic. The proposed method was successfully applied to real samples for the removal of V(IV)and V(V) with sufficient accuracy and precision.Article Citation - WoS: 41Citation - Scopus: 40Biosorption of Cu(ii) and Pb(ii) Ions From Aqueous Solution by Natural Spider Silk(Elsevier Ltd., 2011) Pelit, Levent; Ertaş, Fatma Nil; Eroğlu, Ahmet Emin; Shahwan, Talal; Tural, H.Aside from its excellent mechanical properties, spider silk (SS) would offer an active surface for heavy metal interaction due to its rich protein structure. The present study describes the potential use of natural (SS) as a sorbent of heavy metals from aqueous solutions. Single and multi-species biosorption experiments of heavy metals by natural SS were conducted using batch and column experiments. The biosorption kinetics, in general, was found to follow the second-order rate expression, and the experimental equilibrium biosorption data fitted reasonably well to Freundlich isotherm. From the Freundlich isotherm, the biosorption capacities of Cu(II) and Pb(II) ions onto SS were found as 0.20 and 0.007mmolg -1, respectively. The results showed a decrease in the extent of metal ion uptake with lowering the pH.Article Citation - WoS: 33Citation - Scopus: 33Modification of a Montmorillonite-Illite Clay Using Alkaline Hydrothermal Treatment and Its Application for the Removal of Aqueous Cs+ Ions(Elsevier Ltd., 2006) Öztop, Bahar; Shahwan, TalalA montmorillonite-illite clay was modified using alkaline hydrothermal treatment (reflux method) and applied to the removal of aqueous Cs+ ions. The alkaline solutions were prepared by dissolving NaOH in seawater and in distilled water, and the effect of the two alkaline media on the sorption capacities of the modified clay was discussed. The modified materials were characterized using XRD, SEM/EDS, and FTIR. As a result of the modification, the original mineral was partially transformed into a zeolitic material with spherical morphology. The results showed that the modification improved the Cs+ uptake capacity of the starting clay, with the clay modified in distilled water medium demonstrating higher sorption capacity. The sorption data were adequately described using the Freundlich and Dubinin-Radushkevich isotherm models.Letter Citation - WoS: 46Citation - Scopus: 53A Characterization Study of Some Aspects of the Adsorption of Aqueous Co2+ Ions on a Natural Bentonite Clay(Elsevier Ltd., 2006) Shahwan, Talal; Erten, Hasan N.; Ünügür, S.The natural bentonite used in this study contained montmorillonite in addition to low cristobalite. The uptake of aqueous Co2+ ions was investigated as a function of time, concentration, and temperature. In addition, the change in the interlayer space of montmorillonite was analyzed using XRPD, and the distribution of fixed Co2+ ions on the heterogeneous clay surface was recorded using EDS mapping. The sorbed amount of Co2+ appeared to closely follow Freundlich isotherm, with the sorption process showing apparent endothermic behavior. The relevance of the apparent Δ Ho values is briefly discussed. Analysis of the Co-sorbed bentonite samples using SEM/EDS showed that the montmorillonite fraction in the mineral was more effective in Co2+ fixation than the cristobalite fraction. XRPD analysis demonstrated that the interlayer space of montmorillonite was slightly modified at the end of sorption.Article Citation - WoS: 2Citation - Scopus: 4Tof-Sims Depth Profiling Analysis of the Uptake of Ba2+ and Co2+ Ions by Natural Kaolinite Clay(Elsevier Ltd., 2004) Shahwan, Talal; Erten, Hasan N.; Black, Leon; Allen, Geoffrey CharlesThe sorption behavior of Ba2+ and Co2+ ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-Å steps was performed up to a 70-Å matrix depth of the clay prior to and following sorption. The results showed that Co2+ is sorbed in slightly larger quantities than Ba2+, with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K+, Mg 2+, and Ca2+ from the clay lattice was observed to accompany enrichment with Co2+ and Ba2+ ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba2+ and Co2+ ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (±S.D.) of Ba and Co on kaolinite surface were 0.49±0.11 and 0.61±0.19, respectively, indicating a limited uptake capacity of natural kaolinite for both ions.Article Citation - WoS: 70Citation - Scopus: 82Sorption Efficiency of Chitosan Nanofibers Toward Metal Ions at Low Concentrations(American Chemical Society, 2010) Horzum Polat, Nesrin; Boyacı, Ezel; Eroğlu, Ahmet Emin; Shahwan, Talal; Demir, Mustafa MuammerChitosan fibers showing narrow diameter distribution with a mean of 42 nm were produced by electrospinning and utilized for the sorption of Fe(III), Cu(II), Ag(I), and Cd(II) ions from aqueous solutions. The ion concentrations in the supernatant solutions were determined using inductively coupled plasma-mass spectrometry (ICP-MS). The filtration efficiency of the fibers toward these ions was studied by both batch and microcolumn methods. High efficiency in sorption of the metal ions was obtained in the both methods. The effects of sorbent amount (0.10−0.50 mg), shaking time (15−120 min), initial metal ion concentration (10.0−1000.0 μg·L−1), and temperature (25 and 50 °C) on the extent of sorption were examined. The sorbent amount did not significantly alter the efficiency of sorption; however, shaking time, temperature, and metal ion concentration were found to have a strong influence on sorption. By virtue of its mechanical integrity, the applicability of the chitosan mat in solid phase extraction under continuous flow looks promising.Article Citation - WoS: 50Citation - Scopus: 53Physicochemical Characterization of the Retardation of Aqueous Cs+ Ions by Natural Kaolinite and Clinoptilolite Minerals(Elsevier Ltd., 2005) Shahwan, Talal; Akar, Dilek; Eroğlu, Ahmet EminThe aim of this study was to carry out kinetic, thermodynamic, and surface characterization of the sorption of Cs+ ions on natural minerals of kaolinite and clinoptilolite. The results showed that sorption followed pseudo-second-order kinetics. The activation energies were 9.5 and 13.9 kJ/mol for Cs+ sorption on kaolinite and clinoptilolite, respectively. Experiments performed at four different initial concentrations of the ion revealed that the percentage sorption of Cs+ on clinoptilolite ranged from 90 to 95, compared to 28 to 40 for the kaolinite case. At the end of a 1 week period, the percentage of Cs+ desorption from clinoptilolite did not exceed 7%, while it amounted to more than 30% in kaolinite, indicating more stable fixation by clinoptilolite. The sorption data were best described using Freundlich and D–R isotherm models. Sorption showed spontaneous and exothermic behavior on both minerals, with ΔH0 being −6.3 and −11.4 kJ/mol for Cs+ uptake by kaolinite and clinoptilolite, respectively. Expanding the kaolinite interlayer space from 0.71 to 1.12 nm using DMSO intercalation, did not yield a significant enhancement in the sorption capacity of kaolinite, indicating that the surface and edge sites of the clay are more energetically favored. EDS mapping and elemental analysis of the surface of kaolinite and clinoptilolite revealed more intense signals on the surface of the latter with an even distribution of sorbed Cs+ onto the surfaces of both minerals.Article Citation - WoS: 120Citation - Scopus: 127Equilibrium, Thermodynamic and Kinetic Studies for the Biosorption of Aqueous Lead(ii), Cadmium(ii) and Nickel(ii) Ions on Spirulina Platensis(Elsevier Ltd., 2008) Şeker, Ayşegül; Shahwan, Talal; Eroğlu, Ahmet Emin; Yılmaz, Sinan; Demirel, Zeliha; Conk Dalay, MeltemThe biosorption of lead(II), cadmium(II) and nickel(II) ions from aqueous solution by Spirulina platensis was studied as a function of time, concentration, temperature, repetitive reactivity, and ionic competition. The kinetic results obeyed well the pseudo second-order model. Freundlich, Dubinin Radushkevich and Temkin isotherm models were applied in describing the equilibrium partition of the ions. Freundlich isotherm was applied to describe the design of a single-stage batch sorption system. According to the thermodynamic parameters such as ΔG°, ΔH°and ΔS° calculated, the sorption process was endothermic and largely driven towards the products. Sorption activities in a three metal ion system were studied which indicated that there is a relative selectivity of the biosorbent towards Pb2+ ions. The measurements of the repetitive reusability of S. platensis indicated a large capacity towards the three metal ions.Article Citation - WoS: 46Synthesis, Characterization and Application of a Novel Mercapto- and Amine-Bifunctionalized Silica for Speciation/Sorption of Inorganic Arsenic Prior To Inductively Coupled Plasma Mass Spectrometric Determination(Elsevier Ltd., 2011) Boyacı, Ezel; Çağır, Ali; Shahwan, Talal; Eroğlu, Ahmet EminA bifunctional sorbent, (NH2 + SH)silica, containing both amine and mercapto functionalities was prepared by modification of silica gel with 3-(triethoxysilyl)propylamine and (3-mercaptopropyl)trimethoxysilane. In addition to the bifunctional sorbent, silica gel was modified individually with the functional mercapto- and amino-silanes, and the mono-functional sorbents, namely (SH)silica and (NH2)silica, were also mechanically mixed ((NH2)silica + (SH)silica) for the sake of comparison of sorption performances. It has been demonstrated that (SH)silica shows quantitative sorption only to As(III) at two pH values, 1.0 and 9.0, while (NH2)silica displays selectivity only towards As(V) at pH 3.0. On the other hand, the bifunctional (NH2 + SH)silica possesses the efficient features of the two mono-functionalized sorbents; for example, it retains As(III) at a wider pH range, from 1.0 to at least 9.0 with the exception at pH 2.0, and it also shows quantitative sorption to As(V) at pH 3.0. This property gives the bifunctional (NH2 + SH)silica a better flexibility in terms of sorption performance as a function of solution pH. The mechanically mixed (NH2)silica + (SH)silica exhibits a similar but less efficient sorption behavior compared to the bifunctional sorbent. Desorption of both As(III) and As(V) species can be realized using 0.5 M NaOH. The validity of the proposed method was checked through the analysis of a standard reference material and a good correlation was obtained between the certified (26.67 μg L−1) and determined (27.53 ± 0.37 μg L−1) values. Spike recovery tests realized with ultrapure water (93.0 ± 2.3%) and drinking water (86.9 ± 1.2%) also confirmed the applicability of the method.Article Citation - WoS: 43Citation - Scopus: 47Aas, Xrpd, Sem/Eds, and Ftir Characterization of Zn2+ Retention by Calcite, Calcite–kaolinite, and Calcite–clinoptilolite Minerals(Elsevier Ltd., 2005) Shahwan, Talal; Zünbül, Banu; Tunusoğlu, Özge; Eroğlu, Ahmet EminIn this study, the sorption behavior of Zn2+ on calcite, kaolinite, and clinoptilolite, in addition to mixtures of calcite with kaolinite and clinoptilolite, was investigated at various loadings and mixture compositions using atomic absorption spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared techniques. According to the obtained results, within the experimental operating conditions, the sorption capacity was enhanced with increasing amount of calcite in both types of mixtures. Under neutral–alkaline pH conditions and high loadings, the order of Zn2+ retention was observed as calcite > clinoptilolite > kaolinite. The experiments on the retention of Zn2+ by pure calcite under conditions of oversaturation showed that the uptake process proceeds via an initial adsorption mechanism (possibly ion-exchange type) followed by a slower mechanism that leads to the overgrowth of the hydrozincite phase, Zn5(OH)6(CO3)2.