Muge Sari Yilmaz

Thermal behavior and dehydroxylation kinetics of naturally occurring sepiolite and bentonite

Sepiolite and bentonite have a wide range of industrial applications based on their physicochemical properties such as surface area, thermal behavior, chemical composition, and mineralogic composition. The thermal behavior and kinetics of naturally occurring sepiolite and bentonite were determined in order to give an idea about the potential use of naturally occurring clay minerals in possible applications. Naturally occurring sepiolite and bentonite samples were heated to the temperature that was achieved at the end of the dehydroxylation process. Mineralogic and thermal characteristics of raw and heat treated samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen adsorption/desorption analyses. Changes in the structure following heat treatment were used for the evaluation of the dehydroxylation properties of the samples. The dehydroxylation properties of the minerals are strongly affected by the crystal structure. Kinetic analyses, which were related to the dehydroxylation of naturally occurring sepiolite and bentonite, were conducted using dynamic thermogravimetry/derivative thermogravimetry analysis under nitrogen atmosphere. Flynn–Wall–Ozawa, Kissenger–Akahira–Sunose, and Friedman isoconversional methods were used to determine the activation energies of the dehydroxylation reactions of the samples. The results indicate that the activation energy of naturally occurring sepiolite showed a little variation at a particular conversion rate (0.3–0.7), while the activation energy of naturally occurring bentonite showed a significant variation within the range of variation of the conversion rate. The present study shows that the dehydroxylation reactions of naturally occurring sepiolite and bentonite were single mechanism reaction and complex mechanism reaction, respectively.

Synthesis and characterization of MCM-41 with different methods and adsorption of Sr2+ on MCM-41

Mesoporous silica MCM-41 was prepared by classical and ultrasound methods as an adsorbent for the removal of Sr2+ from aqueous solution. The physical properties of the synthesized materials were investigated by X-ray diffraction and Brunauer-Emmett-Teller analysis. The results showed that MCM-41 prepared by the classical method had higher specific surface area and pore volume than those prepared by the ultrasound method. Therefore, it was selected as an adsorbent for the investigation of adsorption isotherms and kinetics. Adsorption of Sr2+ to MCM-41 was strongly dependent on pH values. Three two-parameter (Langmuir, Freundlich, and Temkin) and two three-parameter (Redlich–Peterson and Koble–Corrigan) adsorption isotherms were employed to model the equilibrium data of Sr2+ on the mesoporous adsorbent. The results indicated that the adsorption isotherm data fitted better to the Freundlich isotherm than to the Langmuir, Temkin, Redlich–Peterson, and Koble–Corrigan isotherms. The experimental data was described very well by the pseudo-second-order kinetic model.

The removal of template from SBA-15 samples synthesized from different silica sources

Mesoporous SBA-15 was synthesized from tetraethyl orthosilicate and sodium silicate as pure silica sources and waste gold mine treatment sludge as an alternative silica source. The synthesis of SBA-15 samples were carried out by the hydrothermal method using the silica source and Pluronic P123 triblock copolymer as the structural template in an acidic medium. The synthesized materials were characterized by X-ray diffraction and nitrogen adsorption–desorption analysis. Thermal decomposition behaviors and kinetics of template from as-synthesized SBA-15 samples derived from different silica sources were investigated by thermogravimetry. The activation energies to decomposition of the template from as-synthesized SBA-15 samples were determined by Vyazovkin model-free method. The decomposition behavior of SBA-15 synthesized from waste was similar to SBA-15 synthesized from tetraethyl orthosilicate. Thermogravimetry coupled with Fourier transform infrared spectrometry analysis was applied for analysis of gaseous products evolved during thermal decomposition of synthesized samples. H2O, CO2, CH2, and CH3 were the main gaseous products released.

Study on the dehydration kinetics of tunellite using non-isothermal methods

The thermal behavior of tunellite has been examined by using thermal analysis data at different heating rates. Coats–Redfern, Horowitz–Metzger, Piloyan–Novikova, Doyle, and isoconversional Ozawa kinetic models have been used for the non-isothermal dehydration kinetic investigation of the mineral. The kinetic parameters are computed using the above-mentioned models for all dehydration stages. In addition, structural characterizations of tunellite are analyzed by using an X-ray diffractometer, an inductive coupled plasma-optical emission spectroscopy, Fourier transform infrared spectroscopy, and a scanning electron microscope.

Dual antimicrobial effects induced by hydrogel incorporated with UV-curable quaternary ammonium polyethyleneimine and AgNO3.

This study presents a simple method for fabricating a highly potent dual effect antibacterial hydrogel consisting of a UV-curable cationic polyethyleneimine (QUV-PEI) and embedded silver nitrate (AgNO3). In the first part of this study, polyethyleneimine (PEI) was reacted with 3-(acryloyloxy)-2-hydroxypropyl methacrylate (ACOM) to introduce methacryl functionality onto the backbone. UV-curable PEI was further quaternized by N-methylation with methyl iodate. Hydrogels based on QUV-PEI and AgNO3were found to have impressive biocidal properties. The antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of remaining viable cells (i.e. capable of growing into colonies). In a manner depending on the QUV-PEI content in the gel formulation, up to 99±1% of Escherichia coli and Staphylococcus aureus cells sprayed on the resulting hydrogel surfaces were killed. The inclusion of AgNO3 in the QUV-PEI based hydrogel not only enhanced the antimicrobial property against adherent bacteria but also led to the inhibition of bacterial growth in suspended culture via the long-term release of Ag/Ag(+) to the surrounding media. Cytotoxicity studies on human umbilical vein endothelial cells and MTS cell lines were also performed with hydrogels. These findings confirm that hydrogels are potentially useful as antimicrobial agents in a wide variety of applications.

Conversion of fly ashes from different regions to mesoporous silica: effect of the mineralogical composition

This study reports the synthesis of mesoporous MCM-41 silica materials by the hydrothermal method using five different fly ashes from the Seyitömer (FS), Çatalağzı (FC), Tunçbilek (FT), Orhaneli (FO), and Afşinelbistan (FA) power plants in Turkey. The mesoporous materials were not obtained from FA which shows a lower Si/Al ratio and Si content. The synthesized MCM-41 samples from the other region fly ashes were characterized by X-ray diffraction, nitrogen adsorption–desorption, thermogravimetry, scanning electron microscopy, and high-resolution transmission electron microscopy analyses. The results demonstrated that the structural properties of the synthesized mesoporous materials were varied from depending on chemical compositions and mineral phase contents of the used fly ashes.Graphical AbstractMesoporous silica MCM-41 was synthesized from different region fly ashes in Turkey. All synthesized sample except FOM have ordered hexagonal MCM-41 structure. Although the Si/Al ratio in the extracted solution of FOM was high, it has low Si content. The best quality MCM-41 sample was obtained from the extracted solution of FTM which has the highest Si/Al ratio and Si content. Taking these into account, Si/Al ratio and Si amount, and thereby mineral compositions of fly ashes play a significant role in the synthesis of mesoporous molecular sieves MCM-41.

Thermal analysis applied for the removal of surfactant from mesoporous molecular sieves MCM-41 synthesized from gold mine tailings slurry

The aim of the current study is to obtain the thermal behavior and kinetic analyses of the removal of surfactant from MCM-41 synthesized from tailings slurry at different heating rates. X-ray diffraction and thermogravimetric analyses were carried out to determine the characterization of the synthesized samples. Kissinger–Akahira–Sunose and Friedman isoconversional kinetic methods were applied for the purpose of determining the kinetic analysis parameters of the decomposition of surfactant from the mesoporous molecular sieves MCM-41 under non-isothermal conditions. For the comparison of these results, MCM-41 was synthesized from a pure silica source. The thermal behaviors of MCM-41 synthesized from tailings slurry do not differ from samples synthesized from pure silica during the decomposition reactions. The kinetic analysis’ results indicate that the decomposition reactions of the synthesized MCM-41 samples had complex reaction mechanisms.

The synthesis of silica-based aerogel from gold mine waste for thermal insulation

Energy consumption and increase in the greenhouse gases are very critical problem for all countries. In order to solve this problem, researches are focused on new thermal insulation materials that are the essential part of the energy-efficient buildings. Aerogels are called ‘the best thermal insulating materials’ due to their extremely low thermal conductivity. In this study, silica-based hydrophobic aerogel was synthesized by sol–gel method via ambient pressure drying. The silica source was obtained from the gold mine waste by alkali fusion method instead of using pure and expensive silica sources such as tetraethyl orthosilicate. The synthesized aerogels were used in the production of insulating plaster with different mass percentages (1, 5, 10, and 20%) and characterized by XRD, FT-IR, contact angle measurement, TG/DTA and N2 adsorption/desorption analysis. In addition, the thermal conductivity of the aerogel-based plaster was determined by using TCi thermal conductivity analysis. The results show that addition of aerogel to plaster was decreased the thermal conductivity and when the mass percentage was 20% the thermal conductivity decreases of 63% as compared to the natural plaster without aerogel.

The Preparation of Silicon and Aluminum Alkali Extracts from Fused Turkish Coal Fly Ashes

Abstract Large quantities of solid waste generated from households, offices, shops, markets, restaurants, public institutions, industrial installations, water works and sewage facilities, construction and demolition sites, and agricultural activities. It causes environmental problems such as groundwater contamination, atmospheric and water pollution, etc. when it is disposed in landfills. Fly ash is the by-product of the coal combustion process for energy generation and remains a major problem in many parts of the world. The large amounts of fly ash are produced and the annual production of it has continued to increase. The disposal of fly ash may cause long-term adverse environmental effects. In this study, the silicon and aluminum in two different Turkish fly ashes (Afsin-Elbistan and Catalagzi) were activated by fusion with sodium hydroxide. The obtained leachates were analyzed for silicon and aluminum content by inductively coupled plasma optical emission spectrometry (ICP-OES). In addition, the mineralogical and chemical properties of these fly ashes are compared.