Chemistry / Kimya

Permanent URI for this collectionhttps://hdl.handle.net/11147/4072

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Author: search.filters.author.Shahwan, TalalEnd date: 2009

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  • Research Project
    Bazı toksik metal iyonlarının kalsit ve aragonit mineralleri ile etkileşimi sonucu oluşan karbonatların oluşum kinetikleri ve morfolojik karakteristiklerinin spektroskopik ve mikroskobik tekniklerle incelenmesi
    (TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2006) Shahwan, Talal; Eroğlu, Ahmet Emin; Tunusoğlu, Gözde; Altay, Özge; Yılmaz, Sinan
    [No Abstract Available]
  • Article
    Citation - WoS: 13
    Citation - Scopus: 15
    Synthesis of Poly-2 Methacrylate-Montmorillonite Nanocomposite Via in Situ Atom Transfer Radical Polymerization
    (Cambridge University Press, 2008) Oral, Ayhan; Shahwan, Talal; Güler, Çetin
    The poly-2-hyroxyethyl methacrylate (PHEMA)/clay nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. To produce organically modified montmorillonite (MMT) that has ATRP initiator moiety, a new catalyst that consists of quaternary ammonium salt moiety and an initiator moiety was synthesized. This initiator was intercalated into the interlayer spacing of the MMT. The polymerization reaction was carried out in a mixed solvent system consisting of methyl ethyl ketone and 1-propanol at 50 °C, using the initiator that has been already synthesized with a copper bromide catalyst. The 2, 2′-bipyridyl (bpy) complex was used as ligand. The products were characterized via Fourier transform infrared, nuclear magnetic resonance (1H NMR, 12C NMR), transmission electron microscopy, x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. © 2008 Materials Research Society.
  • Other
    Corrigendum To “modification of a Montmorillonite–illite Clay Using Alkaline Hydrothermal Treatment and Its Application for the Removal of Aqueous Cs+ Ions” [j. Colloid Interface Sci. 295 (2006) 303–309]
    (Elsevier Ltd., 2006) Öztop, Bahar; Shahwan, Talal
    Unfortunately, we noticed that Ref. [8], which was cited three times in our article, was mistakenly not cited also in the experimental part as the reference on which we based our hydrothermal treatment process. In light of this, the first paragraph of the experimental section (pages 303 and 304) should read...
  • Article
    Citation - WoS: 33
    Citation - Scopus: 33
    Modification 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, Talal
    A 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: 46
    Citation - Scopus: 53
    A 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: 69
    Citation - Scopus: 77
    Morphosynthesis of Caco3 at Different Reaction Temperatures and the Effects of Pdda, Ctab, and Edta on the Particle Morphology and Polymorph Stability
    (Elsevier Ltd., 2007) Altay, E.; Shahwan, Talal; Tanoğlu, Metin
    Facile precipitation of CaCO3 was performed using aqueous solutions of CaCl2 with Na2CO3 over a wide range of mixing and aging temperatures. The precipitation process was then repeated in the presence of PDDA, CTAB, and EDTA at the mixing temperatures of 30 °C, 50 °C, 70 °C, and 90 °C. The presence of these additives was seen to greatly suppress the formation of aragonite. Among these additives, EDTA was the one that showed the most prominent effects on particle morphology of CaCO3. The sequence of pH adjustment appeared to be a critical factor for the additive functionality.
  • Article
    Citation - WoS: 21
    Citation - Scopus: 21
    Retention of Aqueous Ba2+ Ions by Calcite and Aragonite Over a Wide Range of Concentrations: Characterization of the Uptake Capacity, and Kinetics of Sorption and Precipitate Formation
    (The Geochemical Society of Japan, 2007) Tunusoğlu, Özge; Shahwan, Talal; Eroğlu, Ahmet Emin
    The uptake of aqueous Ba2+, ions by abiogenic calcite and aragonite was studied over a wide range of concentration; 1.0 × 101, 5.0 × 101, 1.0 × 102 5.0 × 102, 1.0 × 103, 5.0 × 104, and 1.0 × 104 mg/L. The uptake process was characterized using ICP-AES, XRPD, SEM/EDS, and FTIR techniques. Up to the initial concentration of 5.0 × 102 mg/L, the uptake of Ba2+ ions was fast and obeyed Lagergren's kinetic model. The equilibrium data were adequately described using Freundlich isotherm model. The overgrowth of BaCO3 (witherite) took place at higher concentrations, in a kinetically slow process and enhanced the uptake of Ba2+ ions. Quantitative XRPD was used to evaluate the fractions of precipitated BaCO3 on calcite and aragonite minerals and monitor their variation with time. At all the studied concentrations, aragonite showed higher removal capacity of Ba2+ and faster uptake kinetics than did calcite. The precipitated crystals appeared to predominantly possess olivary-like morphology with an average particle size of 1-2 μm. EDS was used to reveal the elemental quantities of Ba and Ca after BaCO3 formation on calcite and aragonite surfaces. FTIR spectroscopy was employed to analyze the vibrational modes in carbonate mixtures upon incorporation of Ba2+ by sorption and precipitation mechanisms.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Study of the Scavenging Behavior and Structural Changes Accompanying the Interaction of Aqueous Pb2+ and Sr2+ Ions With Calcite
    (The Geochemical Society of Japan, 2005) Shahwan, Talal; Zünbül, B.; Akar, Dilek
    The uptake of Pb2+ and Sr2+ ions from aqueous solutions by calcite was studied at various initial concentrations and pH conditions using the batch method under ambient conditions. XRPD, SEM/ EDS, AAS/AES, and DRIFT techniques were used in characterizing the sorption process. The results indicated that the retention mechanism of Ph2+ and Sr2+ ions ranged from ion incorporation to precipitate overgrowth (cerussite, hydrocerussite for Pb, strontianite for Sr) depending on the concentration and pH conditions. The calcite structure seemed to be entirely vanishing upon formation of cerussite and hydrocerussite while partial dissolution of calcite occurred upon strontianite formation. The formation of precipitates showed rapid kinetics, and equilibrium seemed to be reached within about an hour from the start of mixing. SEM analysis showed that cerussite, hydrocerussite, and strontianite had columnar prismatic-like, tabular hexagonal-like, and needle-like morphologies. Based on a nine-month observation period, dry samples of hydrocerussite seemed to show more morphological stability than cerussite. EDS analysis indicated that Pb2+ sorption is more favored than that of Sr2+, particularly in the phase of precipitate overgrowth. DRIFT analysis indicated a change in the symmetry of the carbonate groups in calcite matrix upon uptake of Pb2+ and Sr2+ cations.
  • Article
    Citation - WoS: 19
    Citation - Scopus: 21
    Kinetic and Thermodynamic Investigations of Strontium Ions Retention by Natural Kaolinite and Clinoptilolite Minerals
    (Walter De Gruyter Gmbh, 2005) Akar, Dilek; Shahwan, Talal; Eroğlu, Ahmet Emin
    The current study was devoted to the determination of various thermodynamic and kinetic parameters resulting from the fixation of Sr2+ by natural samples of kaolinite and clinoptilolite minerals. The sorption process followed pseudo second order kinetics, with faster sorption on kaolinite compared to clinoptilolite, where the uptake is affected by intraparticle diffusion. Freundlich and Dubinin-Radushkevich isotherm models described the data more adequately than Langmuir model, and clinoptilolite showed a higher strontium sorption capacity than kaolinite. Thermodynamically, the activation energy of Sr2+ sorption by kaolinite and clinoptilolite were respectively, -8.5 and -18.4 kJ/mol. The sorption process on both minerals was spontaneous and endothermic at all the studied concentrations, with ΔH° being 11.3 and 9.8 kJ/mol, for sorption on kaolinite and clinoptilolite, respectively. The findings of this study were compared with those of an earlier study on the uptake of Cs+ by the same minerals.
  • Article
    Citation - WoS: 27
    Citation - Scopus: 29
    Characterization of Sr2+ Uptake on Natural Minerals of Kaolinite and Magnesite Using Xrpd, Sem/Eds, Xps, and Drift
    (Walter De Gruyter Gmbh, 2005) Shahwan, Talal; Erten, Hasan N.
    The sorption behavior of Sr2+ ions on natural minerals rich in kaolinite and magnesite was studied using SEM/EDS, XPS, XRPD, AAS/AES and DRIFT techniques. Quantitative analysis of the XPS data shows that magnesite is more effective in Sr2+ uptake than kaolinite. DRIFT spectra and XRPD patterns indicate that the structures of both minerals were not affected upon Sr2+ sorption. Intercalation of DMSO in kaolinite lamellae aiming at increasing the interlayer space did not significantly enhance the sorption capacity of the clay towards Sr2+ probably due to the lack of a negative charge on the accessible sites. EDS mapping indicated that while the sorbed Sr is equally distributed on surface of natural kaolinite, it was associated - to a larger extent - with the regions richer in Mg in the case of natural magnesite. Comparing the uptake mechanisms of natural magnesite with that of pure MgCO3, it was seen that while natural magnesite sorbed Sr2+ mainly through an ion exchange type mechanism, the formation of SrCO3 coprecipitate was detected on the surface of the MgCO 3 at higher loadings.