Browsing by Subject "Lyotropic liquid crystals"

Now showing 1 - 11 of 11

Open Access
Assembly of molten transition metal salt surfactant in a confined space for the synthesis of mesoporous metal oxide-rich metal oxide silica thin films
(2011) Karakaya, C.; Türker, Y.; Albayrak, C.; Dag, Ö.
Uniform and homogeneous coating of mesoporous materials with an active (catalytically, photonic, electrical) nanostructure can be very useful for a number of applications. Understanding chemical reactions in a confined space is important in order to design new advanced materials. In this work, we demonstrate that an extensive amount (as high as 53 mol percent) of transition metal salts can be confined between silica walls and two surfactant domains (cetyltrimethylammonium bromide, CTAB, and lauryl ether, C12H25(OCH2CH2)10OH, C12EO10) as molten salts and then converted into sponge-like mesoporous silica–metal oxides by thermal annealing. This investigation has been carried out using two different salts, namely, zinc nitrate hexahydrate, [Zn(H2O)6](NO3)2, and cadmium nitrate tetrahydrate, [Cd(H2O)4](NO3)2, in a broad range of salt concentrations. The ZnO (or CdO) layers are as thin as about ∼1.6 nm and are homogenously coated as crystalline nano-islands over the silica pore walls.
Open Access
Effects of some transition metal salts on the synthesis of mesoporous silica
(2005) Demirörs, Ahmet Faik
Open Access
Investigation of two new lyotropic liquid crystalline systems : [Zn (formula) and [Zn (formula)
(2008) Albayrak, Cemal
The transition metal aqua complex salts (TMS) can be dissolved in oligo (ethylene oxide) type non-ionic surfactants (CnH2n+1(CH2CH2O)mOH, denoted as CnEOm) with very high salt/surfactant ratios to form lyotropic liquid crystalline (LLC) mesophases. In this study we show that addition of charged surfactants, such as cethyltrimethylammoniumbromide (CTAB) or sodiumdodecylsulfate (SDS) results a new type of LLC in which the solubility of the salts in the LC mesophase of TMS: C12EO10 is enhanced. The LC phase of a [Zn(H2O)6](NO3)2:C12EO10 is hexagonal between 1.2 and 3.2 and cubic (liquid like) above 3.2 salt/ C12EO10 mole ratios. Addition of CTAB or SDS increases the same salt/surfactant mole ratio to 8.0-9.0, which is a record salt amount for a lyotropic liquid crystalline system. The mixed surfactant mesophases have birefringent hexagonal mesophase between 2.0 and 8.0 salt/C12EO10 mole ratios The new mixed surfactant systems can also accomodate high TMSs in the presence of excessive amounts of water (35.0 water:C12EO10 mole ratio). Both systems have similar thermal properties. Izotropisation Temperature (IT) values of the new systems go down with increasing salt and charged surfactant concentrations. The mesophases are stable at high salt concentrations in the presence of high CTAB or SDS concentration in the expense of the stability of the LLC mesophase. The IT values changes from around 80o C down to 32o C with increasing composition of the LLC mesophase. The new mesophase have 2D or 3D hexagonal structure that responds to water content of the phase. A 3D hexagonal phase transforms to 2D hexagonal phase with the evaporation of excess water in both [Zn(H2O)6](NO3)2:C12EO10-CTAB-H2O and [Zn(H2O)6](NO3)2:C12EO10-SDS-H2O systems. The new mesophases were investigated using POM (Polarised optical microscope), and a hot stage under the POM, XRD (X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy) and Raman techniques. These new LLC systems are good candidates for metal containing mesostructured material synthesis due to their high salt content.
Open Access
Investigation on lithium salt - surfactant lyotropic liquid crystalline mesophases: characterization, role of water, and electrochemical behaviors
(2021-09) Topuzlu, Ezgi Yılmaz
In this thesis, lyotropic liquid crystalline (LLC) mesophases of lithium salts (LiCl, LiBr, LiNO3, LiSCN, LiI, LiI/I2, and LiH2PO4) and 10-lauryl ether (C12H25(OCH2CH2)10OH, C12EO10) have been investigated and the LiI/I2 LLC mesophases was used as gel electrolyte in a dye sensitized solar cell (DSSC). The LLC mesophases of LiCl, LiBr, LiNO3, LiSCN, and LiH2PO4 salts were prepared in a broad range of salt concentrations and found that the mesophases of LiCl, LiBr, LiNO3, and LiSCN salts are stable between 2 and 10 salt/surfactant mole ratios. The LiI-C12EO10 samples undergo meso-crystallization over a 3 mole ratio and not investigated at high salt mole ratios. The LiH2PO4-C12EO10 LLC samples are semi stable and leach out salt crystals upon aging because they cannot hold sufficient water; the water holding capacity and stability of the LiH2PO4 mesophases can be improved by adding various amount of H3PO4 that prevents salt crystallization by increasing the water content of the mesophase. Therefore, this thesis was divided into three main chapters, the first chapter is on the role of water in the LLC mesophases of LiCl, LiBr, LiNO3, and LiSCN. The second chapter is on the LiH2PO4 LLC mesophases, and addition of H3PO4 to prevent crystal formation. And the last one is about the use of the LiI/I2 LLC mesophase as gel electrolyte in DSSCs. The mesophases were obtained by evaporating clear solutions of all ingredients. First, they were fully characterized by using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR), Raman, and UV-Vis absorption spectroscopy, X-ray diffraction (XRD), AC conductivity, gravimetric measurements, and polarized optical microscope (POM) imaging to identify structural and electrical properties and water up takes of the mesophases. The water evaporation has been monitored by gravimetric, spectroscopic, and conductivity measurements. The water evaporation rate follows a 2/3 power of the evaporated water weight. After complete water evaporation, the LiCl and LiBr systems keep a similar amount of water in their mesophases (typically 3-8 water/Li+, depending on the humidity condition). However, the LiSCN and LiNO3 systems keep a significantly lower amount of water inside their mesophase (1.5-5 water/Li+ depending on the humidity condition). Water has a critical role in forming the lithium salt-surfactant mesophases and their structural properties. To investigate the role of water, humidity-dependent measurements have been carried by using gravimetry, spectroscopy, AC conductivity, and POM techniques. The gravimetric and spectroscopic data show that the H2O/Li+ mole ratio increases linearly by 0.08-0.09 per humidity. Increasing water amount in the mesophases improves their ionic conductivities with at least a factor of two when the humidity was changed from 20 % to 40 %. The water/Li+ mole ratios, water-ion, water-water, water-surfactant, and ion-surfactant interactions strongly depend on the counter anions of the lithium salts and closely follows the Hofmeister series of anions, such that the water molecules are strongly held in the LiCl mesophase but weakly held in the LiNO3 and LiSCN. Controlling the humidity over the lithium salt-surfactant mesophases is a promising way of tuning the properties of the LLC mesophases as needed. Furthermore, mixing two different lithium salts may also improve/adjust the water amount in the gel-phases. For instance, adding LiCl to LiNO3 mesophase increases the final water content in the mesophase and, therefore, the conductivity. Controlling the water amount in the mesophase can be beneficial for the use of the lithium salt-surfactant mesophases in various electrochemical applications. The LiH2PO4 mesophase has also been extensively investigated by changing the salt/surfactant mole ratio and found out that it forms at high humidity but is unstable at lower humidity. The LiH2PO4-mesophase undergoes a phase change by leaching out first surfactant and then the salt crystals. Increasing the salt amount in the mesophase can postpone the salt crystallization but it cannot stop completely. However, the LiH2PO4 mesophases can also be stabilized by adding H3PO4 that holds an extensive amount of water. The LiH2PO4-H3PO4 mesophase forms a buffer LLC mesophase that can be used in electrochemical devices as gel-electrolytes where constant pH is needed. The LiI-I2 redox couple was also prepared in LLC mesophase, characterized by the above approaches, and used in a DSSC as gel-electrolyte. To investigate the importance of the water content in the mesophase different humidity levels were tested for gelation. It was shown that 40 % humidity is the best since it increases the efficiency of DSSC from 3.67 % to 5.36 %. Further increase in the humidity level causes dye detachment and free iodine formation; therefore, the efficiency of DSSC start to decline. Altering how to introduce dye and electrolyte over the working electrode, such as introducing dye and electrolyte simultaneously and carrying gelation at 40 % humidity, results a further increase in the cell efficiency to 7.32 %, which is the highest efficiency achieved for an LLC gel electrolyte in DSSC.
Open Access
Lyotropic liquid crystalline (LLC) phosphoric acid-10-lauryl ether: mesophases, proton conductivity and synthesis of transparent mesoporous hydroxyapatite thin films
(2014-06) Tunkara, Ebrima
Many salts, acids, and bases with low deliquescence relative humidity (DRH) can organize non-ionic surfactants into lyotropic liquid crystalline (LLC) mesophases that form a ready platform for the synthesis of mesoporous materials. In this study, we show that phosphoric acid (H3PO4, PA) with low DRH value can also be used as a solvent in assembling non-ionic surfactant (C12H25(OCH2CH2)10OH, C12EO10) into stable LLC mesophases within a broad range of composition (the concentration can be as high as 20 PA/C12EO10 mole ratio). The PA/C12EO10 mesophase is bi-continuous cubic phase (V1) in extremely low concentrations (2 PA/C12EO10 mole ratio), 2D/3D hexagonal phases (H1) at moderate compositions (3 to 5 PA/C12EO10 mole ratio) and micelle cubic (I1) at high, (more than 5) H3PO4/C12EO10 mole ratios, with a typical unit cell parameter of 127, 55, and 116 Å, respectively. The mesophases of the lower concentrated samples (less than 15 mole ratio) have high thermal stability, with melting points greater than 120 oC. However the melting point drops to less than 50 oC for extremely high concentrations (more than 17 PA/C12EO10 mole ratio). The LLC mesophases were also found to exhibit high proton conductivities (~10-3 S/cm) at room temperature. The proton conductivities were even higher (10-2 S/cm) at some elevated temperatures and reduced to (10-4 S/cm) at temperatures less than 0oC. The conductivity in the cubic phase is slightly higher. Both the temperature and composition-dependent conductivity obey the most accepted proton conductivity mechanisms: Grotthuss and Vehicle. We went further to show that the combination of H3PO4 and another low DRH species, such as Ca(NO3)2·4H2O also form stable mesophases; without precipitating salts, under a wide range of concentration, from 5.3/1 to 13.3/1 precursor to surfactant ratio. High acidity stabilizes both the aqueous solution as well as the LLC phases. The clear solutions obtained from the precursor-surfactant mixtures were spin coated on glass substrates (as thin as a few hundred nanometers) and calcined to form transparent nano-size mesoporous hydroxyapatite (HAp) thin films. The formation of semi-crystalline HAp in our synthetic approach is not a straight forward process; it involves the formation of some intermediate products and also requires a calcination temperature of at least 300 oC. The formation, which starts at 300 oC, is preceded by the evaporation of nitric acid and excess water molecules to the surrounding. The crystallization continues at 400 oC and completes at 500 oC, keeping the uniformity, porosity, and transparency of the films. Films of the 5.3/1 ratio, calcined at 300 oC have high surface area of up to 96 m2/g, which dropped down to 20 m2/g at 500 oC. The mesopores start collapsing at around 600 oC. The pore size, pore walls, and the pore volumes were obtained from the N2 sorption measurements and the values are 22.4 nm, 10 nm, and 0.58 cm3/g, respectively. We also investigated the effect of precursor concentration on both the pore sizes, as well as the thicknesses of the pore walls. The results showed a reduction of surface area, and also narrower pore size distribution with increasing concentration. Temperature was also observed to have the same effect on crystallinity in all the compositions studied. All the investigations on these two systems were carried out using XRD (X-ray diffraction), FT-IR (Fourrier Transform Infrared Spectroscopy), Raman spectroscopy, POM (Polarized Light Optical Microscope), N2-sorption measurements, PEIS (Potentiostatic Electrochemical Impedance Spectroscopy), TEM (Transition Electron Microscopy), SEM (Scanning Electron Microscopy) etc.
Open Access
Lyotropic liquid crystalline mesophases from acid-salt-surfactant systems: synthesis and characterization of mesoporous LiMPO4 (M=Mn(II),Fe(II),Co(II) AND Ni(II))
(2019-09) Uzunok, Işıl
This study presents the synthesis and characterization of mesoporous lithium metal phosphates (LMPs) of Mn(II), Fe(II), Co(II), and Ni(II). The LMPs were synthesized using a modified molten salt self-assembly (MASA) method. Clear and homogeneous solutions of lithium nitrate (LiNO3), transition metal nitrate ([M(H2O)6](NO3)2, phosphoric acid (H3PO4, PA), and surfactant (pluronic P123, EO20PO70EO20, where EO is ethylene oxide and PO is propylene oxide) in water were spread on a microscope slide by drop-cast coating method to from a lyotropic liquid crystalline (LLC) mesophase. The mesophases were characterized using polarized optic microscope (POM) and x-ray diffractrometer (XRD) techniques. In the mesophase, the mole ratio of the inorganic components was kept constant (1:1:1, Li(I):M(II):PA) but the inorganic ingredient (lithium salt, transition metal salt, and PA) to surfactant mole ratios were varied from 10 to 90. The mesophases are ordered and diffract at small angles in all compositions. However, the mesophases slowly undergo transformation from LLC mesophase to semisolid mesostructured particles by the hydrolysis of PA and LMP formation over time. The drop-cast coated samples were calcined to produce mesoporous LMPs. The samples were characterized using N2 adsorption-desorption, XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Attenuated total reflectance - fourier-transform infrared spectroscopy (ATR-FTIR) techniques. The LMPs are amorphous up to 400 oC but become crystalline above this temperature. The amorphous mesoporous LMPs have large Brunauer, Emmett and Teller (BET) surface area, around 30-100 m2/g but drops down to a few m2/g upon annealing at 500 oC. The SEM images show that the particle morphology depends on the inorganic/surfactant ratio in the initial mesophase. Both Mn(II) and Co(II) produce the olivine phase of LiMnPO4 (LMnP) and LiCoPO4 (LCoP), respectively, under our reaction conditions. However, Ni(II) samples need either excess lithium source or adjustment of pH of the clear solutions to form olivine phase of LiNiPO4 (LNiP). This adjustment can be done by using LiH2PO4 as the Li(I) and phosphate source in place of LiNO3 and PA. Unlike iron compound, the olivine phases of LMPs of Mn(II), Co(II) and Ni(II) were successfully obtained. In the iron case, it is difficult to keep iron in 2+ oxidation state under our reaction conditions. It undergoes an oxidation to form Fe3+ species. Therefore, mesoporous FePO4 and Li3Fe2(PO4)3 materials were synthesized, where the iron has 3+ oxidation state. Most synthesis has been carried out over glass slides that simply contain 16% of sodium. We found that our samples undergo Na+ ion-exchange reaction with the glass substrates above 300 oC. Therefore, the samples were first calcined at 300 oC over glass substrates and further annealed at higher temperatures in alumina sample holder to produce mesoporous forms. However, if the annealing step is carried over the glass slides, sodium metal phosphates (NaMPs) form in maricite phase. These samples were also characterized by XRD, SEM, TEM, and ATR-FTIR techniques. To eliminate the ion-exchange reactions, other substrates like quartz, pyrex or fluorine doped tin oxide (FTO) were used. However, notice that ion-exchange can also be performed to synthesize mesoporous maricite NaMPs as another synthesis method.
Open Access
Lyotropic liquid crystalline mesophases made of salt-acid-surfactant systems for the synthesis of novel mesoporous lithium metal phosphates
(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Uzunok, Işıl; Kim, J.; Çolak, Tuluhan O.; Kim, D.; Kim, H.; Kim, M.; Yamauchi, Y.; Dağ, Ömer
Mesoporous lithium metal phosphates are an important class of materials for the development of lithium ion batteries. However, there is a limited success in producing mesoporous lithium metal phosphates in the literature. Here, a lyotropic liquid crystalline (LLC) templating method was employed to synthesize the first examples of LiMPO4 (LMP) of Mn(II), Co(II), and Ni(II). A homogeneous aqueous solution of lithium and transition metal nitrate salts, phosphoric acid (PA), and surfactant (P123) can be spin coated or drop‐cast coated over glass slides to form the LLC mesophases which can be calcined into mesoporous amorphous LMPs (MA‐LMPs). The metal salts of Mn(II), Co(II) and Ni(II) produce MA‐LMPs that crystallize into olivine structures by heat treatment of the LLC mesophase. The Fe(II) compound undergoes air oxidation. Therefore, both Fe(II) and Fe(III) precursors produce a crystalline Li3Fe2(PO4)3 phase at over 400 °C. The MA‐LMPs show no reactivity towards lithium, however the crystalline iron compound exhibits electrochemical reactivity with lithium and a good electrochemical energy storage ability using a lithium‐ion battery test.
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
Nanoarchitectonics of mesoporous CaFe2O4 thin-film electrodes from salt-surfactant lyotropic liquid crystalline mesophases and their OER performance
(American Chemical Society, 2023-09-05) Raza, Hamid Ali; Karakaya, Irmak; Dağ, Ömer
Metal oxides of earth-abundant elements (such as Ca and Fe) are highly important for fabricating active electrodes for various electrochemical applications (such as electrocatalysis and photo-electrocatalysis). Here, we employed a molten-salt-assisted self-assembly process to fabricate CaFe2O4 thin-film electrodes on graphite rods. The roles of precursor type (nitrates and chlorides) and solvent (water and ethanol) have been addressed in the fabrication of the electrodes that are tested in oxygen evolution reaction (OER) in alkali media. The mesophases have an unusual orthorhombic structure that is likely transformed from a well-known 3D hexagonal phase by an elongation along the b-axis caused by the hydrolysis and condensation of the Fe(III) species in the lyotropic liquid crystalline media. Four sets of mesoporous electrodes with a high surface area are fabricated using nitrate and chloride precursors in aqueous media and nitrates in ethanol. The electrodes, fabricated from the chloride precursors, are not as porous as nitrates, but they display better performance in the OER. The electrodes, fabricated from ethanol solutions, outperform, are more robust, and display as low as 250, 342, and 642 mV overpotentials at 1, 10, and 100 mA/cm2 current densities with a Tafel slope of around 60 mV/dec. The electrode thickness has no role in the electrode performance and can be prepared as thin as tens of nanometers with good stability and OER performance.
Open Access
The role of charged surfactants in the thermal and structural properties of lyotropic liquid crystalline mesophases of [Zn(H2O)6](NO3)2-CnEOm-H2O
(2010) Albayrak, C.; Soylu, A. M.; Dag, Ö.
The mixtures of [Zn(H2O)6](NO3)2 salt, 10-lauryl ether (C12H25(OCH2CH2)10OH, represented as C12EO10), a charged surfactant (cetyltrimethylammonium bromide, C16H33N(CH3)3Br, represented as CTAB or sodium dodecylsulfate, C12H25OSO3Na, SDS) and water form lyotropic liquid crystalline mesophases (LLCM). This assembly accommodates up to 8.0 Zn(II) ions (corresponds to about 80% w/w salt/(salt + C12EO10)) for each C12EO10 in the presence of a 1.0 CTAB (or 0.5 SDS) and 3.5 H2O in its LC phase. The salt concentration can be increased by increasing charged surfactant concentration of the media. Addition of charged surfactant to the [Zn(H2O)6](NO3)2–C12EO10 mesophase not only increases the salt content, it can also increase the water content of the media. The charged surfactant-C12EO10 (hydrophobic tail groups) and the surfactant (head groups)-salt ion (ion-pair, hydrogen-bonding) interactions stabilize the mesophases at such salt high and water concentrations. The presence of both Br and NO 3 ions influences the thermal and structural properties of the [Zn(H2O)6](NO3)2–C12EO10–CTAB(or SDS)–H2O LLCM, which have been investigated using XRD, POM (with a hot stage), FT-IR and Raman techniques.
Open Access
Two-dimensional mesoporous vanadium phosphate nanosheets through liquid crystal templating method toward supercapacitor application
(Elsevier, 2018) Mei, P.; Kaneti, Y. V.; Pramanik, M.; Takei, T.; Dağ, Ömer; Sugahara, Y.; Yamauchi, Y.
Mesoporous vanadium phosphate (VOPO4) nanosheets have been successfully synthesized through an easy and reproducible lyotropic liquid crystals (LLC) templating approach for the first time. Using the triblock copolymer (P123) as a surfactant, VOPO4 precursor with a well-developed 2D hexagonal mesostructure can be obtained. Following complete removal of the template by calcination, crystallized VOPO4 frameworks with less-ordered mesostructure are achieved. The as-prepared mesoporous VOPO4 nanosheets exhibit superior pseudocapacitive performance (767 F g‒1 at 0.5A g‒1) by virtue of the favorable mesostructure that gives rise to abundant easily accessible redox active sites as well as reinforced charge transfer and ion diffusion properties. The charge storage mechanism of the mesoporous VOPO4 nanosheets has been experimentally demonstrated to be based on the reversible two-step redox reactions between V(V) and V(III) in acidic medium. This advantageous LLC templating strategy is expected to open up a new route for designing various mesoporous metal phosphates with superior electrochemical performance for utilization in energy storage devices.