Browsing by Subject "Porous materials."
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Item Open Access Covalently functionalized MSNs as potential photosensitizing agents for PDT(2011) Türkşanlı Kaplan, MervePhotodynamic therapy (PDT) is a novel approach for the treatment of some cancers and other non-malignant diseases. PDT aims to kill cancer tissue by the generation of singlet oxygen as a result of excitation of the photosensitizer (PS) by illuminating with a light source at a certain wavelength. Mesoporous silica nanoparticles are promising in PDT issue due to their chemical inertness, biocompatibility, lowtoxicity, hydrophility and ease of surface modification. We have synthesized and characterized novel boradiazaindacene (BODIPY)-based PS that is covalently attached to the pore of mesoporous silica nanoparticles (MSNs). We have observed that near infrared absorbing photosensitizer attached MSNs successfully generate cytotoxic singlet oxygen.Item Open Access Formation of pyrene excimers in mesoporous organically modified silica thin films for visual detection of nitroaromatic explosives(2013) Beyazkılıç, PınarPyrene is a polycyclic aromatic hydrocarbon compound. Pyrene has been extensively applied as probing and sensing molecule because of excimer fluorescence which is formed upon interaction of two pyrene molecules in close proximity. In this thesis, we prepared porous thin films with bright pyrene excimer fluorescence and demonstrated their application in visual and rapid detection of nitroaromatic explosive vapors. The fluorescent films were obtained by physically encapsulating the pyrene molecules in the mesoporous organically modified silica (ormosil) networks which were synthesized via a facile template-free sol-gel method. Formation and stability of pyrene excimers were investigated in both porous and nonporous ormosil thin films. Excimer emission was found to be significantly brighter and more stable in porous films compared to nonporous films. The excellent stability of the pyrene excimers in the porous films is due to the nanoscale confinement of pyrene molecules in the porous ormosil network. We studied the nitroaromatic explosive sensing performances of the pyrene doped porous films. Films exhibited a rapid and visible fluorescence quenching when they were exposed to TNT vapor. Fluorescence quenching efficiency of an approximately 100 nm thick porous film was calculated to be 55.6% after exposure to TNT vapor for 30 seconds revealing a rapid sensing behavior. Fluorescence quenching of the films can be easily observed under UV light enabling naked-eye detection of nitroaromatic explosives. A selective quenching was observed in the excimer emission against vapors of nitroaromatic molecules; trinitrotoluene (TNT), dinitrotoluene (DNT) and nitrobenzene (NB) among various aromatic and nonaromatic compounds. Furthermore, quenched excimer emission of the films can be recovered by simply washing the films with water. It is shown that the films can be reused for at least five times after washing. To this respect, pyrene doped ormosil thin films can be presented as facile materials for nitroaromatic explosive sensing applications.Item Open Access Investigation of lithium salt-nonionic surfactant mesophases and their applications in solar cells as gel electrolyte(2013) Barım, GözdeSome salts and some nonionic surfactants self-assemble together into lyotropic liquid crystalline (LLC) mesophases. The salt can be either in aqueous solution phase or in its molten phase in the self-assembly process. Concentrated aqueous solutions of lithium salts (LiCl, LiBr, or LiI) and pluronics (triblock copolymers, such as P65, P85, P103, or P123) or 10-lauryl ether (C12H25(CH2CH2O)10OH, denoted as C12EO10) type nonionic surfactant mesophases were investigated in this thesis work. The LLC mesophases are well ordered between 5.0 and 25.0 salt/pluronics and 2.0 and 10.0 salt/C12EO10 mole ratios, and remain stable for months under the ambient conditions. The water molecules remain as the hydrates under open atmosphere in the LLC mesophases of lithium salts-nonionic surfactants. The lithium salt-pluronic LLC mesophases are birefringent and have a hexagonal mesophase in a broad range of salt concentrations. The unit cell of the mesophases increases and a transition from the hexagonal to a cubic mesophases occurs upon increasing the salt content of the media. Moreover the LLC mesophases are ordered and stable up to 25.0 salt to pluronic mole ratio. At higher salt content, one can observe either a disordered phase or co-existence of salt crystals and mesophase. There is a big demand on the gel electrolytes for dye sensitized solar cells (DSSC) in order to overcome solvent problems caused by liquid electrolytes. The LLC mesophases of LiI, LiCl and LiBr salts with 10-lauryl ether (C12EO10) has been considered as gel-electrolyte for the DSSC. We demonstrate that the LiI/I2 couple can be incorporated into above LLC mesophases of various lithium salt-nonionic surfactant systems. Those LLC phases, with LiI/I2 couple have been characterized by means of diffraction, microscopy, spectroscopy and conductivity measurements. The LLC mesophases diffract at small angles and do not show any phase segregation upon incorporating the LiI/I2 redox couple. The LLC mesophases of these systems are 2D hexagonal, and they remain stable under ambient conditions for months. In the LLC media, the iodide ion and iodine molecule react to produce triodide ion in the media. The iodide/triodide (I- /I3 - ) redox couples containing gel electrolytes were formed and their solar performance was investigated by using a solar simulator and a cell consisting of a dye sensitized anode (FTO-dye modified TiO2), gel-electrolyte, and a cathode (FTO-Pt nanoparticles). The LLC mesophases of various lithium saltnonionic surfactant systems with the I- /I3 - redox couple were characterized using POM (Polarized Optical Microscope), XRD (X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy) and Raman techniques. These new LLC mesophases can be used as gel electrolytes in solar cells after incorporation of redox couple into the media and display responses as good as commonly used liquid electrolytes.Item Open Access Molten Salt Assisted Self-Assembly (MASA) : synthesis of mesoporous silica-ZnO and mesoporous CdO thin films(2012) Karakaya, CüneytA series of mesostructured salt-silica-two surfactants (salt is [Zn(H2O)6](NO3)2, ZnX or [Cd(H2O)4](NO3)2, CdYand surfactants are cetyltrimethylammonium bromide (CTAB) and 10-lauryl ether, C12H25(OCH2CH2)10OH, C12EO10) thin films were synthesized by changing the Zn(II) or Cd(II)/SiO2 mole ratios. The films were prepared through spin coating of a clear solution of all the ingredients (salt, CTAB, C12E10, silica source (tetramethyl orthosilicate,TMOS, and water) and denoted as meso-silica-ZnX-n and meso-silica-CdY-n, where n is Zn(II) or Cd(II)/SiO2 mole ratios. The synthesis conditions were optimized by using the meso-silica-ZnX-1.14 and meso-silica-CdY-1.14 films and XRD, FT-IR spectroscopy, POM and SEM techniques. The stability of the films, especially in the high salt concentrations, was achieved above the melting point of salts. Slow calcination of the films, starting from the melting point of the salt to 450 oC has produced the mesoporous silica-metal oxide (ZnO and CdO) thin films, and denoted as meso-silica-ZnO-n and meso-silica-CdO-n, with n of 0.29, 0.57, 0.86, 1.14, and 1.43. The calcination process was monitored by measuring the FT-IR spectra and XRD patterns at different temperatures. Structural properties of the mesoporous films have been investigated using FT-IR spectroscopy, XRD, N2 sorption measurements, UV-Vis spectroscopy, SEM, TEM and EDS techniques. It has been found that the meso-silicaZnO-n and meso-silica-CdO-n films consist of nanocrystalline metal oxide nanoplates on the silica pore walls of the mesoporous framework. The formation of nanoplates of metal oxides was confirmed by etching the silica walls using diluted HF solution and by reacting with H2S and H2Se gases. The etching process produced CdO nanoplates without silica framework. The H2S and H2Se reactions with the CdO nanoplates or meso-silica-CdO have converted them to CdS and CdSe nanoplates or meso-silica-CdS and meso-silica-CdSe, respectively. Finally, a hypothetical surface coverage of metal oxide nanoplates has been calculated by combining the data of N2 sorption measurements, UV-Vis spectroscopy and TEM images and found that there is a full coverage of CdO and partial coverage of ZnO over silica walls in the meso-silica-CdO-n and meso-silica-ZnO-n thin films, respectively.Item Open Access Synthesis and characterization of mesoporous metal sulfide and metal selenide thin films using liquid crystalline mesophases(2012) Türker, YurdanurIn this thesis, synthesis of the mesoporous CdS and CdSe by using of liquid crystalline templating (LCT) approach has been investigated. In the first part of the thesis, the thermal and structural behavior of the [Cd(H2O)4](NO3)2/surfactant (P85 = ((PEO)26(PPO)40(PEO)26)) binary lyotropic liquid crystalline (LLC) systems have been investigated towards synthesis of the mesoporous cadmium sulfide, CdS, or cadmium selenide (CdSe) directly from the mesostructured CdS (or CdSe) thin films. However, the mesostructured CdS/P85 films (at low salt concentrations), which were obtained by reacting [Cd(H2O)4](NO3)2/P85 LLC thin films under H2S atmosphere, are not stable to calcination process and always produced bulk CdO and CdS domains over the thin films. More metal ion containing [Cd(H2O)4](NO3)2-C12EO10-CTAB mesostructured films produced vast amount of HNO3 under the H2S atmosphere and caused decomposition of CdS back to their nitrates. To overcome above problems, a polymerizing agent, such as titania or silica precursors have been added to salt/surfactant LLC mesophase. Both titania and silica overcame the collapse of the mesophase by rigidifying the structure into mesostructured solid and also by providing stability for a thermal removal of nitrates from the medium. For this investigation, both [Cd(H2O)4](NO3)2 and [Zn(H2O)6](NO3)2 salts and P123 ((PEO)20(PPO)70(PEO)20) and C12EO10-CTAB couple have been used. Well-ordered mesostructured Cd(II) titania films have been obtained up to 15.0 Cd(II)/P123 mole ratio for a 60 mole ratio of Ti(IV)/P123 by spin or dip coating of a mixture of 1-butanol-[Cd(H2O)4](NO3)2-P123-HNO3-Ti(OC4H9)4. Exposing the mesostructured Cd(II)-TiO2 films to H2Se under a N2 atmosphere gave stable CdSe nanoparticles in the channels of the mesostructured rigid titania walls up to 25 mole % Cd(II)/Ti(IV). To further increase the metal ion (Cd(II) and Zn(II)) content in the structure, the C12EO10-CTAB-salt mesophase has been employed. The two surfactant-salt systems, in the presence of a titania precursor, produced sponge like mesoporous CdTiO3 and Zn2TiO4 films up to a mole percent of 57 and 86, respectively, upon calcination. Exposing the mesoporous CdTiO3 to H2S or H2Se atmosphere at RT produced homogeneously distributed CdS or CdSe nanocrystallites on the nanocrystalline TiO2 pore walls, respectively. The reaction of mesoporous Zn2TiO4 with H2Se produced stable ZnSe nanocrystallites on the nanocrystalline TiO2 pore walls. The conversion of titania from CdTiO3 to an anatase and brookite phase under H2S and H2Se atmosphere, respectively, and from Zn2TiO4 to a rutile phase under H2Se were observed for the first time. Adding a silica precursor to the two surfactants (C12EO10-CTAB)-salt mesophase produced mesostructured salted-silica, and its calcination produced sponge-like mesoporous silica-metal oxide (dumped meso-SiO2-CdO and mesoSiO2-ZnO) thin films. Up to ~100 % and ~50 % surface coverage could be achieved by CdO and ZnO as nano-islands over the SiO2 pore walls. Exposing the mesoporous SiO2-CdO and SiO2-ZnO thin film precursors to H2S and H2Se at RT enabled the synthesis of mesoporous SiO2-CdS, SiO2-CdSe, SiO2-ZnS, and SiO2- ZnSe thin films. The MS or MSe nanoflakes could homogenously cover the pore walls of mesoporous silica by retaining the pore morphology of the MO precursors. The H2S and H2Se reactions are slow and can be monitored using UV-Vis absorption spectroscopy and EDS to elucidate the reaction mechanism and kinetics. These data showed that the reaction starts from the top surface of the MO domains and proceeds until Si-O-M bond break. Finally, the SiO2 walls were removed from the meso-SiO2-CdS and meso-SiO2-CdSe films through etching in a dilute HF solution to produce mesoporous CdS (meso-CdS) and mesoporous CdSe (meso-CdSe). Surface of the meso-CdS has been modified using PEI (polyethyleneimine) and photoluminescent meso-CdS were obtained.Item Open Access Synthesis of mesoporous silica particles controlling the CTABr-pluronic assembly(2009) Poyraz, Altuğ SüleymanIn the synthesis of mesoporous silica materials, self-assembly of a charged surfactant (cetyltrimethylammoniumbromide, CTABr) and a pluronic (PEOx-PPOy-PEOx where PEO is CH2CH2O and PPO is CH(CH3)CH2O) into micelles have key. By controlling the hydrophilic-hydrophobic character of the CTABr-Pluronic micelles, mesoporous silica particles can be synthesized with different morphologies (sphere, wormlike, crystal-like etc.). The particles generally have 2D hexagonal mesostructure with a high surface area (as high as 800 m2 /g). Shape of the micelles as well as the morphology of the particles depend on the hydrophobic nature of the pluronic surfactant and the CTABr amount. The CTABr amount is carefully adjusted to control the morphology and structural order of the particles. The self-assembly of the CTABr-Pluronic micelles and silica species has been achieved by adjusting pH of the synthesis medium to 1.0 in order to produce mesoporous particles with a distinct morphology and mesostructure. Nature of the CTABr-Pluronic micelles can be influenced by adding organic and inorganic additives to the reaction media. The effect of the lyotropic (F- , SO4 2- and Cletc.) and hydrotropic (NO3 - , SCNetc.) anions on the micellization of P85 has been first investigated in the aquoues media using UV-Vis Spectroscopy and ethyl orange dye. Then these inorganics and organic (Benzene) additives, in the synthesis of mesoporous silica, have been used to control the micellization of the CTABr-P123 couples as well as the morphology and the pore structure of the silica particles. Highly ordered particles with larger pores and various pore structures have been synthesized using lyotropic anions in the CTABr-P123 system. Furthermore, the hydrotropic anions control the CTABr content of the CTABr-P123 micelles. Increasing CTABr amount in the CTABr-P123 micelles decreases the wall thickness of the silica particles. The hydrophobic character of the micelles can also be enhanced by adding water insoluble organic additives (benzene). The silica particles, synthesized using CTABr-P123-Benzene system, are well structured, where the higher order X-ray diffraction lines can also be observed. Finally, the catalytic role of Fions on the polymerization of the silica has been studied in the CTABr-Pluronic system. Addition of Fion to the reaction medium speeds up the formation process and producing spherical and uniform mesoporous particles less than 20 minutes. The effect of each of the reaction component, Fion, CTABr and P123 molecules, to the assembly rate has also been investigated by determining the turbidity point (due to the formation of silica particles) of the solutions. A correlation between the particle size and reaction rate has also been brought out. The mesoporous silica particles synthesized in this thesis have been characterized using PXRD, FT-IR and Raman Spectroscopy, SEM, TEM and N2 sorption measurements.Item Open Access Synthesis of mesoporous silica particles using SDS-Pluronic couples(2010) Sayın, MustafaControlling the cooperative self assembly and micellization of pluronics and SDS (sodium dodecyl sulfate)are pivotal for the synthesis of mesoporous silica particles. The pH and temperature of the synthesis media, SDS/Pluronic mole ratio, TMOS (tetramethyl orthosilicate)amount, alkali salt amount of the synthesis solution are the parameters, which play significant roles on the micellization and self assembly of surfactants. The synthesis of mesoporous silica particles with distinct morphologies is possible with the precise optimizations of these parameters. In this thesis we have investigated the synthesis of mesoporous silica particles with a well defined morphology and structure using SDS-Pluronic couple as the template. The pore size can be tuned by changing the aggregation number of the surfactant molecules in the micelles, also by changing the pluronic type. The morphological control is achieved mainly by changing the pH and temperature of the synthesis media. At different temperatures and pHs, rods, spheres, muffin and ‘s’ shaped particles have been obtained. The addition of inorganic salts, such as NaNO3, NaCl, and KCl, has also effects on the morphology and meso-structure. Addition of a small amount of NaNO3 changes spherical particles to amorphous silica however, addition of large amount of NaNO3 gives well defined muffin shaped and worm-like particles. The concentration of nitrate ion also affects the pore size and wall thickness of the synthesized particles. The KCl or NaCl salts also have similar effects on the morphology of the silica particles, the morphological transitions have been observed but the role of Cl- ion is minor on the control of pore size. The SDS concentration has important effects on the micellization of pluronics, changing the SDS/Pluronic mole ratio (between 0.05 and 5.0) in the reaction media changes the structure of the mesoporous silica particles. Particularly the SDS concentration has important effects on the surface area of the synthesized particles. The surface area of the samples changes between 100 m2 /g and 700 m2 /g and the pore size of the particles changes between 3.0 and 6.0 nm by changing the SDS/Pluronic mole ratio. This ratio is also effective on the micropore amount of the samples together with mesopores. The tunable particle size (between 0.2µ to 1000µ) and morphology (spheres, rods, muffin and ‘s’ shaped.) can be achieved by changing the SDS concentration. Furthermore, the low reaction temperature (below RT) is essential for the synthesis of mesoporous silica particles in SDS-Pluronic system. However, the low temperature is a problem for micellization. This problem was overcome by using P123, which has low critical micellization concentration (CMC) and critical micellization temperature (CMT) values or by using Hofmeister ions to decrease the pluronic surfactant solubility and the CMC and CMT of the pluronics used. Decreasing solubility of the pluronics causes effective micellization of the surfactants. The well defined micelles are the templates for the synthesis of mesoporous silica particles. Overall , the effects of SDS/Pluronic mole ratio, pH and temperature of the synthesis solution, TMOS concentration, and the additives (alkali salts) have been investigated by synthesis of more than 300 samples that were analyzed using PXRD, SEM, TEM, POM, and N2 sorption techniques.