Browsing by Subject "Mesoporous silica"

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Open Access
The effect of cationic surfactant and some organic/inorganic additives on the morphology of mesostructured silica templated by pluronics
(Elsevier, 2008-11-01) Poyraz, A. S.; Albayrak, C.; Dag, Ö.
Tri-block copolymers (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), represented as EOxPOyEOx), pluronics (F127=EO106PO70EO106, P65=EO20PO30EO20, P85=EO27PO39EO27, P103= EO17PO55EO17, and P123 = EO20PO70EO20) and cationic surfactants (cethyltrimethylammonium bromide (CTAB)), two surfactant systems, form complex micelles that self-assemble into mesostructured particles with distinct morphology depending on the pluronic type, the concentration of the cationic surfactant and the organic-inorganic ingredients in a siliceous reaction media under acidic conditions. The CTAB-P65 and CTAB-P85 systems form spheres, CTAB-P103 and CTAB-P123 systems form wormlike particles, and CTAB-F127 system form single crystals of mesostructured silica particles under very similar conditions. However addition of various salts (such as KCI and NaNO3) into a CTAB-P103 or CTAB-P123 solution system and cyclohexane and KCI into a CTAB-P85 solution system produces the mesostructured silica spheres and wormlike particles, respectively. By controlling the hydrophilic-hydrophobic character of the pluronics, core-corona interface, by means of additives, such as small organic molecules or salts, one could obtain the desired morphology that is dictated by the shape of the micelles of the pluronic-cationic surfactant complex. The effects of the additives and the formation mechanism of those morphologies have been discussed using spectroscopy (FT-IR and Raman), diffraction (XRD) and microscopy (POM and SEM) data. (c) 2008 Elsevier Inc. All rights reserved.
Open Access
Molten Salt Assisted Self-Assembly (MASA) : synthesis of mesoporous silica-ZnO and mesoporous CdO thin films
(2012) Karakaya, Cüneyt
A 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.
Open Access
Nanostructured materials for biological imaging and chemical sensing
(2014-11) Yıldırım, Adem
In the recent years, the design and synthesis of fluorescent nanoparticles for biological and chemical sensing applications have received considerable attention due to the excellent photostability and emission intensity of fluorescent nanoparticles and the intrinsic sensitivity of fluorescence based methods. Although considerable progress has been made in their synthesis, there is still need for low-cost and high throughput methods for their widespread utilization in biological and chemical sensing applications. In addition, studies regarding their biocompatibility are necessary to identify the toxicological potential of these nanomaterials. In this context, this thesis seeks new methods for multifunctional fluorescent nanoparticle synthesis and investigates their interactions with living organisms. In addition, it reports the applications of the fluorescent nanomaterials in biological imaging, therapy and chemical sensing applications. First, we report a self-assembly method to prepare PEGylated or peptide functionalized mesoporous silica nanoparticles (MSNs) for cell labeling and drug delivery applications. The good cyto- and blood- compatibility of the functionalized nanoparticles were demonstrated. Next, we demonstrated a surfactant assisted method to synthesize ultrabright silica nanoparticles and studied their in vitro v cytocompatibility with several cell lines. We demonstrated the applications of ultrabright particles in cell labeling, chemo and photodynamic therapy and trace explosive sensing. Then, we discuss a template-free method (porosity difference based selective dissolution strategy) to prepare self-luminescent mesoporous hollow silica nanoparticles with tailored shapes. In addition, we studied the surface effects on blood compatibility of nanoparticles in detail using the MSNs possessing different surface functional groups (ionic, polar, neutral, and hydrophobic). Finally, we investigated the optical properties of polydopamine nanoparticles and showed that fluorescence of asprepared polydopamine nanoparticles can be used for sensitive and selective detection of the dopamine neurotransmitter.
Open Access
One-pot synthesis of CdS nanoparticles in the channels of mesosructured silica films and monoliths
(American Chemical Society, 2005) Tura, C.; Coombs, N.; Dag, Ö.
Cd(II)-modified mesoporous silica films and/or monoliths synthesized in one pot using a true liquid crystalline (TLC) approach have been reacted with H2S gas to produce CdS-modified mesostructured nanocomposite materials (Nano-CdS/meso-SiO2). During this process, both the TLC and the metallotropic liquid crystalline (MLC) mesophase of metal salt ([Cd(H 2O)4](NO3)2)-nonionic surfactant (CnH2n+1- (OCH2CH2)mOH, CnEOm) systems were collectively used to incorporate large quantities of metal ions into the mesoporous silica film and monoliths. The effect of the cadmium nitrate concentration on the formation and structure of the mesoporous silica has also been investigated. The results show that at low salt concentrations, the mesoporous silica is anisotropic (hexagonal); however, at high salt concentration, the structure is isotropic (cubic or disordered). The freshly prepared CdS nanoparticles are reactive toward the surface acids that form during the H2S treatment. These surface acids also promote the degradation of the CdS nanopaticles. However, the CdS particles in the mesopores can be stabilized by washing out the acid sides or aging the samples for a period of time before the H2S reaction. The optical absorption edge of the CdS nanoparticle in the pores is sensitive to the composition and structure of the host. In this context, the materials were characterized using FTIR, micro-Raman, UV-visible absorption spectroscopy, POM, TEM, and PXRD techniques.
Open Access
Role of silica in the self-assembly of salt-surfactant mesophases and synthesis of mesoporous metal oxides
(2023-07) Ullah, Najeeb
In recent years, mesoporous metal oxides have attracted great attraction due to their unique optical, electrochemical, and catalytic properties. Mesoporous nickel oxide (m-NiO) is a p-type semiconductor, versatile in its application due to its high surface area, and has been investigated towards electrochromic devices, electrodes, supercapacitors, and catalysts. The electrochemical properties of NiO depend on its morphology, surface area, and particle size. In this thesis, mesoporous nickel oxide has been synthesized by combining soft templating (molten salt-assisted self-assembly method) and hard templating methods to attain a high surface area. Homogeneous aqueous solutions of nickel(II) nitrate hexahydrate ([Ni(H2O)6](NO3)2), TMOS (as silica source), and two surfactants, CTAB (charged surfactant) and C12E10 (nonionic surfactant) are stable only if a concentrated nitric acid is added before the TMOS addition. In the absence of nitric acid, TMOS hydrolyzes and condenses quickly, resulting in silica precipitation. The silica precipitation also occurs by using other salts, such as nickel(II) chloride hexahydrate, nickel(II) sulfate hexahydrate, cobalt(II) nitrate hexahydrate, and manganese(II) nitrate tetrahydrate. The silica precipitate is characterized by ATR-FTIR, small-angle, and wide-angle XRD and N2 adsorption-desorption measurements. The diffraction lines at 1.7 and 23o, 2θ, indicate the formation of mesostructured amorphous silica, in which the surfactant species fill the pores. . The silica precipitate is calcined at 450 oC for two hours to remove the surfactant completely, and characterized by ATR-FTIR, small-angle and wide-angle XRD measurements, N2- adsorption-desorption analysis and SEM-EDX techniques. The maximum surface area (1395 m2/g) is obtained from the cobalt(II) nitrate hexahydrate salt, and the EDX analysis confirms that there is no element other than silicon and oxygen in its elemental detection limit. The homogeneous, stable aqueous solutions of the nickel(II) nitrate hexahydrate ([Ni(H2O)6](NO3)2), HNO3, TMOS (as silica source), and two surfactants, CTAB (charged surfactant) and C12E10 (nonionic surfactant) solution is drop-casted on a glass slide to form a mesophase and analyzed by small-angle XRD, ATR-FTIR and POM techniques. The diffraction lines at 1.5 and 1.6o, 2θ, show the formation of ordered lyotropic liquid crystalline mesophases. The mesophases are then calcined at different temperatures (from 250 to 500 °C), to obtain m-NiO/SiO2 powders and characterized by ATR-FTIR, XRD measurements, N2- adsorption-desorption analysis, and SEM-EDX techniques. The XRD patterns show broad lines at small- and wide-angles, indicating the formation of m-NiO/SiO2 at 300 °C, where the pore-walls are made up 2.6 nm crystalline NiO coated amorphous silica . The NiO particle size (on the pore wall) grows with increasing annealing temperature, and at 500 °C, the particle size reaches 7.9 nm. This is also supported by the BET surface area that decreases at higher temperatures. At 300 °C, the BET surface area is 305 m2/g, which drops to 174 m2/g at 500 °C. However, the pore size of m-NiO/SiO2 does not responds to annealing temperature. It means that the pore walls grow in 2D space rather than 3D due to the presence of silica as a hard template. Therefore, combining the hard- and soft-templating methods can efficiently synthesize the crystalline materials with a high surface area. The m-NiO/SiO2 films can be coated over the FTO glass and calcined at different temperatures to fabricate the electrodes for oxygen evolution reaction (OER). During CV measurement, the NiO pore-walls get oxidized to NiOOH and reduced to Ni(OH)2 in the back cycle. Moreover, overpotential that is determined for the OER improves with the usage of the electrode, independent of the electrode thickness.
Open Access
Synthesis of mesoporous silica particles using SDS-Pluronic couples
(2010) Sayın, Mustafa
Controlling 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.