Cetyltrimethylammonium Hydroxide Research Articles

Designing mordenite zeolites with tunable distribution of acid sites in channels and nano-morphology to boost the catalytic behavior performance of dimethyl ether carbonylation

Mordenite (MOR) zeolite is an efficient catalyst for dimethyl ether (DME) carbonylation, which a key step of indirect production of ethanol from syngas. Herein, a nanosheets MOR zeolite with an ultrathin thickness of 10–30 nm can be facilely synthesized by using a commercial cetyltrimethylammonium hydroxide agent. It greatly shortened the pore length of 8-membered ring (8-MR) side pocket and more amount of Brønsted acid sites (BAS) can be exposed. More importantly, the amount of BAS in 8-MR side pockets of the MOR zeolite can be significantly increased. It should be noted that the morphology of MOR zeolite with prismatic, nanosheets, and petal-like can be obtained and precisely regulated. As a result, the conversion of DME over the nanosheets MOR zeolite is increased by nearly 2 times. Our finding proposed a novel strategy for constructing tunable nanosized morphology MOR zeolite and simultaneously directional enrichment of BAS in 8-MR channels.

Enhancing Oil Solubility of BCS Class II Drug Phenytoin Through Hydrophobic Ion Pairing to Enable High Drug Load in Injectable Nanoemulsion to Prevent Precipitation at Physiological pH With a Potential to Prevent Phlebitis

This work investigates the micellar titration of phenytoin (a weakly acidic drug) with cetyltrimethylammonium hydroxide (CTAH) to form a hydrophobic ion-pair to enhance oil solubility of phenytoin, followed by an effort to formulate nanoemulsion that could potentially prevent precipitation of phenytoin at physiological pH. The ion-pair formulated in nanoemulsion was evaluated for in vitro precipitation during serial dilution at physiological pH. The formation of ion-pair during titration was explained in context of pH-solubility data. The mathematical model successfully integrated ionization and micellization equilibria to reflect on dominant mechanisms for solubilization. The micellar phenomenon during titration was confirmed using Dynamic Light Scattering (DLS). The phase changes of the excess undissolved solids during titration were evident from X-Ray Powder Diffraction (XRPD) and Fourier Transform Infrared Spectroscopy (FTIR). This analysis confirmed the conversion of phenytoin into ionized state and its subsequent ionic interaction with CTAH forming hydrophobic ion-pair complex (HIP). The complete ion pair formation was evident at pHmax (8.8 to 9.2), and its 1:1 stoichiometry was confirmed using HPLC (Phenytoin and CTAH) and H1 NMR, hence could also be called as a lipophilic salt. The ion-pair (salt) was insoluble in water and showed remarkably high partition coefficient (log P) in octanol/water. As characterized by Hot Stage Microscopy (HSM), the melting point of the ion-pair complex was lowered to 150.8⁰C compared to the free acid (> 300οC), this was even further lowered to 81.1 °C when evaluated in castor oil. This led to approximately eight-fold higher solubility of hydrophobic ion pair (HIP) in castor oil compared to the free acid form. The high miscibility in castor oil was suitable to formulate a high drug load injectable dispersed system. This was successfully achieved with lecithin and polysorbate as emulsifiers without leaching drug into continuous phase at pH 7.4. This nanoemulsion (<300 nm, and > +30 mV zeta potential) remain stable when evaluated over a period of one month. A serial dilution study of the nanoemulsion was performed in PBS buffer, microscopic observations suggested no birefringence despite incubation at 25°C for several hours. This result indicated that Phenytoin remained strongly partitioned within dispersed oily phase with a higher drug loading when ion-paired phenytoin was used. The higher drug load could enable a small volume slow bolus injection to meet 50 mg/min or lower delivery rate criteria for Phenytoin in the clinical set up. This provided a pathway to further explore potential injectable nano-emulsion formulations that could alleviate typical phlebitis issue associated with the injectable phenytoin solution administration at physiological pH.

Lipid-derived cetyltrimethylammonium salts as renewable phase change materials for thermal energy storage

The investigation of lipid-derived salts containing ionic bonds is an attractive subject for thermal energy storage applications since the presence of different high-chain fatty acid tails and ionic bond in the backbone represent a new approach for phase change materials. In the present study, four different lipid-derived cetyltrimethylammonium salts were synthesized via a simple acid-base reaction between cetyltrimethylammonium hydroxide and lauric, myristic, palmitic, stearic acid. Nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, and Fourier transform infrared analyses techniques have been used for characterization of the resultant structures. Phase change temperatures, enthalpies, and thermal endurances of the synthesized lipid-derived salts were determined by using differential scanning calorimeter and thermogravimetric analyzer. Differential scanning calorimeter analyses revealed that these salts can store and release thermal energy between 145 and 170 kJ/kg at onset melting temperatures between 98 and 108 °C. Besides, thermogravimetric analyses indicated that they have thermal decomposition onset temperatures above 200 °C and they can easily withstand an exothermic process up to 150 °C. Based on the reported data, it can be stated that the investigated lipid-derived salts are suitable for utilization as renewable phase change materials for moderately high temperature thermal energy storage applications. This paper represents the first example in the literature reporting the thermal properties of lipid-derived salts as a new group of phase change materials. • Thermal properties of lipid-derived cetyltrimethylammonium salts. • New group of organic PCMs containing ionic bond in the backbone. • Suitable for moderately high temperature heat transfer and thermal energy storage applications. • PCMs with enthalpy between 145 and 170 kJ/kg at onset melting temperatures between 98 and 108 °C.

Nanoporous Vesicular Membranes of Amphiphilic Polymers Containing Trans / Cis Isomers

Nanoporous Vesicular Membranes of Amphiphilic Polymers Containing <i>Trans</i> / <i>Cis</i> Isomers

Synthesis of Nanocrystalline Mordenite Zeolite with Improved Performance in Benzene Alkylation and n‐Paraffins Hydroconversion

AbstractNanocrystalline mordenite (MOR) zeolites were hydrothermally synthesized in a single step with commercial cetyltrimethylammonium (CTA) hydroxide as the sole organic template, while the aluminum source was varied in a typical synthesis gel. CTA can effectively reduce the crystal growth of MOR zeolites, in some cases selectively in the a‐ and b‐directions of the unit cell. These nanocrystalline MOR zeolites do not only have a larger external surface area than their bulk counterparts prepared without CTA, but the Brønsted acid sites in the side‐pockets are also more accessible. The combination of the use of CTA and AlCl3 ⋅ 6H2O afforded the best‐performing catalyst with much improved activity in benzene alkylation and hydroconversion of n‐hexadecane (n‐C16). Modifying MOR synthesis with CTA hydroxide is a cheap and effective method to open up the one‐dimensional micropore system of mordenite, increasing the catalytic performance in hydrocarbon reactions.

Substitution of Cetyltrimethylammonium for OSDA Cations During B-SSZ-70 Zeotype Synthesis and Its Influence on Delamination

We investigated the substitution of structure-directing agent diisobutylimidazolium hydroxide with cetyltrimethylammonium hydroxide (CTA+OH−) surfactant in the synthesis gel of layered-zeotype-precursor B-SSZ-70(P). At low substitution levels, CTA+ interacts with the external-zeotype surface, where it assembles. At higher surfactant amounts, CTA+ intercalation occurs, leading to swelling of the precursor material, as evidenced by powder X-ray diffraction. Characterization of adsorbed CTA+ cations by 13C MAS NMR spectroscopy demonstrates unique broad resonances in the intercalated layers, which represent a more rigid environment than in the external-surface assemblies. At still higher CTA+ substitution levels in the synthesis gel, we observe the formation of amorphous mesoporous silica. We attempted to delaminate materials synthesized with varying CTA+ substitution levels using mild conditions, in which the conventional sonication step is replaced with an easy-to-scale high-shear mixing, and in which the use of halide reagents, which are corrosive and have been required in the past, is also avoided. Our data demonstrate that synthesis of a swollen material per se is not essential as an intermediate for delamination, and that layered zeolite precursor swelling can actually undermine zeolite delamination. Our results instead point to the CTA+ external-surface assemblies as facilitating ease of SSZ-70 delamination under these mild conditions. When calcined and functionalized with grafted titanium centers, the delaminated materials are highly active and selective olefin epoxidation catalysts with organic hydroperoxides, showing a 40% higher epoxide conversion than a catalyst prepared from conventional B-SSZ-70.

Counter Cation Dependent and Stimuli Responsive Supramolecular Polymers Constructed by Calix[4]pyrrole Based Host–Guest Interactions

Carboxylate tethered calix[4]pyrroles in the form of their tetrabutylammonium (TBA) and cetyltrimethylammonium (CTA) salts were synthesized via an acid base reaction between the corresponding carboxylic acid functionalized calix[4]pyrrole and tetrabutyl‐ or cetyltrimethylammonium hydroxide. The host–guest recognition motif based on these calix[4]pyrrole macrocycles and tethered carboxylate units was employed to construct novel A–B type supramolecular polymers from low molecular weight monomers in chloroform. These supramolecular polymers were found to be dependent on the counter cation in terms of the properties of supramolecular polymers. 1H‐, DOSY‐, NOESY‐NMR spectroscopic analyses, viscosity measurements, and SEM results were used to characterize supramolecular polymers and revealed that the CTA cation becomes a direct part of supramolecular polymer via cation–π interactions between the ammonium part of CTA and carboxylate‐bound calix[4]pyrrole, effecting the overall properties of supramolecular polymers such as viscosity, gel formation, and drawing fibers. Additionally, reversible pH‐ and thermo‐responsiveness of the supramolecular polymers were demonstrated for the first time for an anion recognition induced calix[4]pyrrole based supramolecular polymer.

Removal Properties of Anionic Dye Eosin by Cetyltrimethylammonium Organo-Clays: The Effect of Counter-Ions and Regeneration Studies.

The organo-clays (OCs) were prepared by a cation exchange reaction between surfactant (cetyltrimethylammonium, C16TMA) from different counterions (Bromide, Chloride, and Hydroxide). The effect of the counterions was investigated on the physico-chemical properties of the prepared organo-clays. The highest uptake of organic cations (1.60 mmol/g) was achieved using cetyl trimethylammonium bromide solution and the lowest value (0.93 mmol/g) was obtained after modification with cetyl trimethylammonium hydroxide solution starting from the same initial ratio of mmol/g of clay greater than 2.40. The arrangement of C16TMA cations within the interlayer space was assumed to be perpendicular with a tilt angle of 32° to the plane of clay sheets instead of being parallel to the clay surface using C16TMAOH solution at the same ratio. Different techniques were used to characterize these materials. The thermal stability of these organ-clays was investigated using an in-situ X-ray diffraction (XRD) technique. The decomposition of the surfactant moiety occurred at temperatures higher than 215 °C and was accompanied with a shrinkage of the basal spacing value to 1.42 nm. These materials were applied in the removal of an acid dye “eosin.” The removed amount of eosin depended on the initial concentrations and the content of surfactants in the organo-clays. The removal of eosin was found to be an endothermic process. The maximum amount of 90 mg/g was achieved. The preheated treatment temperature of two selected OCs did affect the removal properties of eosin. A progressive reduction was observed at temperatures higher than 200 °C. The regeneration of spent OCs was studied and acceptable removal efficiency was maintained after 4 to 6 cycles depending on the used initial concentrations.

Determination of various inorganic anions and organic acids in the atmospheric particulate matter using capillary zone electrophoresis with indirect UV detection

ABSTRACTCapillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (n = 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions.

Surfactant-regulated fabrication of gold nanostars in magnetic core/shell hybrid nanoparticles for controlled release of drug

Core-shell nanostructured materials, which are of great interest for fundamental research and industrial applications, have properties that can be enhanced by combining component superstructures. Here, we report the new construction of magnetic core-shell gold nanostars (AuNSs) for controlled release of drug. The AuNSs were successfully embedded intact between an inner silica layer and outside mesoporous silica layer to create magnetic core/shell hybrid nanoparticles by using a base cationic templating surfactant, cetyltrimethylammonium hydroxide (CTAOH). The core-shell nano-composites containing AuNSs exhibit the characteristics including high magnetization, mesoporous nanostructure, photothermal properties and low in vitro toxicity, showing the potential applications for drug delivery and controlled release.

Characterization of organo-kenyaites: thermal stability and their effects on eosin removal characteristics

ABSTRACTOrgano-kenyaites were prepared from a cetyltrimethylammonium hydroxide (C16TMAOH) solution and solid sodium kenyaite (Na2Si22O45.10H2O) mixture. The effect of the initial cetyltrimethylammonium solution on the structure of the intercalated materials was investigated by CHN analyses, X-ray diffraction (XRD), thermogravimetric analysis, SEM, and 29Si and 13C solid NMR techniques. For C16TMAOH concentration 0.25 mM, the Na+ cations were fully exchanged. Initial C16TMAOH concentrations higher than 0.25 mM had little effect on the intercalated amount of C16TMA+ cations. The organic cations content reached a plateau of 0.66 mmol/g. The arrangement model of C16TMA+ cations corresponded to a tilt of the organic cations to the silicate layers with an angle of 42° as deduced by XRD studies. The C16TMA+ cations exhibited mainly trans-configuration of the methyl chains, as was shown by solid 13C NMR. The thermal stability of the organo-silicates was studied using in situ FTIR and in situ XRD in the range 25–450°C. The C16TMA-kenyaites were stable at temperatures below 200°C. They collapsed at higher temperatures due to the decomposition of the intercalated surfactants. These organo-kenyaites were used to remove the acidic dye molecule, eosin. The removal tests were performed at varying conditions of initial dye concentrations, organic content in the organo-kenyaites and heating temperatures. In general, the organic modification improved the removal capacity of the Na-kenyaite from 2 mg of eosin/g to 60 mg of eosin/g, and this capacity was related to the organic contents and the calcination temperatures of the organo-kenyaites.

Quantitative analysis of micellar effect on the reaction rate of alkaline fading of phenolphthalein

Quantitative treatment of the kinetic data of the reaction between phenolphthalein dianion and hydroxide ion in aqueous solutions containing variable concentration of various surfactants is presented. Following surfactants are used: Brij-35 (nonionic), sodium n-dodecyl sulfate (anionic), cetyltrimethylammonium bromide (cationic) and 3-(dimethyl-n-dodecylammonio)-propansulfonate (zwitterionic). The quantitative treatment is carried out basing of Piszkiewicz’s, Berezin’s, and Pseudophase Ion-Exchange (PIE) models. It is revealed that the Berezin’s model is a more applicable one for describing the effect of nonionic, anionic, and zwitterionic micellar systems. The values of the corresponding kinetic parameters are discussed. The effect of cetyltrimethylammonium hydroxide on the reaction is also examined and quantitatively described by the PIE model. The research of systems based on a cationic surfactant shows previously unknown effect called by us as “diverting influence”.

Synthesis of MCM-48 granules with bimodal pore systems via pseudomorphic transformation of porous glass

It was shown in previous publications that porous glasses can be transformed into MCM-41 materials with monomodal or bimodal (hierarchical) pore systems. In this study we describe the synthesis of MCM-48 granules with a bimodal pore structure via pseudomorphic transformation of porous glasses. Due to the cubic network of the MCM-48 structure, such materials are characterized by an improved mass transfer inside the pores compared to the 2 dimensional MCM-41 pore system. This represents an advantage for applications as catalyst support. Porous glass granules (100–200 μm particle size) with a pore diameter of 150 nm and a pore volume of 1.44 cm3/g were used as starting materials. The transformation process was controlled via different concentrations of cetyltrimethylammoniumhydroxide (CTAOH). The products were characterized by nitrogen adsorption, mercury intrusion, x-ray diffraction, scanning electron microscopy and light microscopy. The results confirmed the successful synthesis of MCM-48 particles with a hierarchical pore structure. The starting pore system with 150 nm diameter disintegrated during the transformation process because of the formation of MCM-48 clusters. A new pore system with approximately 3000 nm in diameter was formed among these clusters. A cavitation effect was observed during nitrogen adsorption/desorption measurements. This indicates that some parts of the starting pore system were entrapped by MCM-48 clusters. This can be explained with the higher concentration of the surfactant solution during transformation of the starting glass into the MCM-48 phase, which leads to a higher solubility and mobility of the silica source. Furthermore, the dependence of the quality of synthesized MCM-48 concerning geometry and structure of the starting materials was investigated by transformation of AEROSIL® 200. Due to the particulate and non-porous character of this starting material just a minor cavitation effect was observed during the physisorption measurements.

One-Step Synthesis of Hierarchical ZSM-5 Using Cetyltrimethylammonium as Mesoporogen and Structure-Directing Agent.

Hierarchical ZSM-5 zeolite is hydrothermally synthesized in a single step with cetyltrimethylammonium (CTA) hydroxide acting as mesoporogen and structure-directing agent. Essential to this synthesis is the replacement of NaOH with KOH. An in-depth solid-state NMR study reveals that, after early electrostatic interaction between condensed silica and the head group of CTA, ZSM-5 crystallizes around the structure-directing agent. The crucial aspect of using KOH instead of NaOH lies in the faster dissolution of silica, thereby providing sufficient nutrients for zeolite nucleation. The hierarchical ZSM-5 zeolite contains mesopores and shows excellent catalytic performance in the methanol-to-hydrocarbons reaction.

Can a catanionic surfactant mixture act as a drug delivery vehicle?

Surfactants can self-assemble in dilute aqueous solutions into a variety of microstructures, including micelles, vesicles, and bilayers. Recently, there has been an increasing interest in unilamellar vesicles, which are composed of a closed bilayer that separates an inner aqueous compartment from the outer aqueous environment. This interest is motivated by their potential to be applied as vehicles for active agents in drug delivery via several routes of administration. Active drug molecules can be encapsulated in the bilayer membrane if they are lipophilic or in the core of the vesicle if they are hydrophilic. Furthermore vesicles formed by mixing of cationic and anionic surfactants (so called ‘catanionic’ systems) can be used as models for biological membranes as they have low critical micelle concentration ( cmc ) and are highly biocompatible. In this work the formation of amino acid based mixed surfactant vesicles and their stabilization and biocompatibility were studied systematically using several instrumental techniques. Binary mixtures of the anionic sodium N -alkanoyl- l -sarcosinate, SAS and cationic cetyltrimethylammonium hydroxide (CTAOH) or dodecyltrimethylammonium hydroxide (DTAOH) surfactant was found to form high surface active and strong synergistic interaction in different compositions and concentrations. • Mixture of cationic and anionic surfactants (i.e., catanionic mixture) forms stable vesicles. • The vesicles can be used for pH-triggered drug delivery. • The vesicles can entrap the drug molecules to their inner aqueous core. • The catanionic vesicles are biocompatible in nature.

Positron-Annihilation-Lifetime-Spectroscopy (PALS) for the characterization of bimodal silica-gel synthesized by pseudomorphic transformation

In this study the results of the characterization of bimodal silica-gel samples with nitrogen adsorption and Positron-Annihilation-Lifetime-Spectroscopy (PALS) are compared. The bimodal silica-gel samples were synthesized by pseudomorphic transformation of a mesoporous silica gel. A set of eight samples was generated using different volumes of 0.07 M cetyltrimethylammonium hydroxide (5–42 ml/g) to obtain bimodal pore systems with controlled proportions of 15 nm pores of the original silica-gel and 4 nm pores formed by the MCM-41 phase. The aim was to proof if it is possible to determine the pore volumes directly from the PALS experiment. The results of the PALS measurements clearly indicate the bimodal pore structure in the materials. Two individual pore systems can be detected with a good resolution. The peak area of the signals can be calculated and compared with the pore volumes determined by nitrogen adsorption. The results show a correlation between the pore volume determined by nitrogen adsorption and the peak area calculated from PALS. Some differences between the measured pore volumes of the starting material can be an indication for the formation of a closed porosity in the starting material and after the processes of pseudomorphic transformation. The PALS measurements enable a complementary characterisation of pore systems in the micro- and mesopore range. Bimodal structured porous materials can be studied and the individual pore systems are well separated. The observed correlation between intensities (respectively peak areas) from PALS and pore volumes determined by nitrogen adsorption for the different pore classes allows the direct estimation of the pore volumes by PALS via calibration and the quantification of a potential closed porosity.

A simple analytical method for determining inorganic anions and formate in virgin olive oils by capillary electrophoresis with capacitively coupled contactless conductivity detection

This paper describes a novel and simple method for determining chloride, nitrate, sulfate, fluoride, and formate in virgin olive oil (VOO) by capillary electrophoresis with capacitively coupled contactless conductivity detection. The anions were extracted from VOO by a simple ultrasound-assisted aqueous liquid–liquid extraction procedure. The anions were separated in less than 3 min with good peak resolutions using a background electrolyte composed of 15 mmol L−1 histidine solution at pH 4.0, adjusted with lactic acid, and 0.6 mmol L−1 cetyltrimethylammonium hydroxide as electrosmotic flow (EOF) modifier. Tartrate was used as internal standard (I.S.). The proposed method showed good linearity and had coefficients of determination (R2) ranging from 0.9984 to 0.9999. The limits of quantification (LOQ) were between 0.01 and 0.7 mg kg−1. Recovery tests were used to evaluate the efficiency of the extraction procedure; the recovery percentages ranged from 70.2 to 118%, with a relative standard deviation (RSD) varying from 0.7 to 19.4%. The proposed method was applied to the determination of the anions in five different commercial samples of VOO.

Micellar effects upon the rate of alkaline hydrolysis of triflusal

The rate of hydrolysis for triflusal was measured at varying concentrations of NaOH at four different temperatures (i.e. 25, 35, 45 and 55°C). The micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltrimethylammonium hydroxide (CTAOH) and dodecyltrimethyl-ammonium bromide (DTABr) had catalytic effect on the rate of hydrolysis. CTABr, CTACl and DTABr gave maxima like curve for the rate–[surfactant] plot while CTAOH gave plateau like curve. The anionic sodium dodecyl sulfate (SDS) did not influence the rate of alkaline hydrolysis of triflusal. The non-ionic Brij-35 inhibited the rate of the hydrolytic reaction. The catalytic effect by cationic micelles was treated by applying the pseudophase ion exchange model while the inhibitive effect by non-ionic micelles has been described by using the Poisson–Boltzmann pseudophase model. The variation in kψ with the change in [surfactant] was used to determined various kinetic parameters e.g., binding constant (Ks), and micellar rate constant (km). The addition of electrolytes decreased the reaction rate in CTABr and CTAOH micelles.

Simple preparation of lotus-root shaped meso-/macroporous TiO2 and their DSSC performances

In pursuit of superior TiO2 photoanode materials for dye-sensitized solar cells (DSSCs), we prepared lotus-root shaped meso-/macroporous TiO2. The lotus-root shaped meso-/macroporous TiO2 was easily prepared by using a cetyltrimethylammonium hydroxide (CTAOH) template in aqueous solution. The crystallization of the as-prepared amorphous lotus-root shaped TiO2 was performed at 700°C in air. Crystalline anatase phase with a very small portion of rutile phase was generated after the heat treatment at 700°C and the BET surface area of crystalline lotus-root shaped meso-/macroporous TiO2 material (LR-700) was 30.0m2g−1. The wall of LR-700 displayed well-developed mesoporosity with a pore dimension of 28.3nm. Periodically arranged microscale one-dimensional (1D) macropores were also observed in the particles. The photon-to-current conversion efficiencies (η) of LR-700 photoanodes in Grätzel type DSSCs were examined. The conversion efficiency of DSSC prepared by mixing nanoparticulate Evonik P25 and LR-700 (ratio=85:150 by mass) was 28% greater compared to the reference electrode using P25. Incident photon-to-current efficiencies (IPCE) of the DSSCs were dramatically improved by employing the photoanodes composed of a mixture of P25 and LR-700 but impedance analysis indicated that P25/LR-700 mixed cells have resistances similar to the standard P25 reference cell. Thus, photovoltaic performances could be improved mainly due to the increases of dye uptake and external quantum efficiency by using a mixed photoanode composed of LR-700 and nanocrystalline P25 particles.

Organo-bentonites with improved cetyltrimethylammonium contents

AbstractOrgano-bentonites were prepared using a bentonite and an aqueous cetyltrimethylammonium hydroxide solution. The ratio of the surfactant (in mmoles) to the cation exchange capacity varied from 0.5 to 20, with 20 being the highest ratio ever reported in the literature. At high surfactant to cation exchange capacity ratios, the interlayer spacing increased to 3.75 nm due to the formation of a paraffin-type bilayer of surfactant cations, which was shown to be mainly in gauche conformations using solid state 13C CP/NMR. When the exchange reaction was carried out in a methanol-water mixture, the expansion of the organo-bentonites depended on the concentration of methanol (% by volume). The decomposition temperatures of the organic cations depended on the basal spacing of the organo-bentonites, and in situ X-ray diffraction revealed that the basal spacing of our organo-bentonites was stable up to 210°C. Above this temperature, the basal spacing shrunk to 1.47 nm due to decomposition of the surfactants.