True Liquid Crystal Templating Research Articles

Mechanisms and Intermediates in the True Liquid Crystal Templating Synthesis of Mesoporous Silica Materials

Mesoporous silica materials (MSMs) produced by true liquid crystal templating (TLCT) are often considered as direct inverted replicas of the initial lyotropic liquid crystal (LLC) phase. However, the predictive design of tailor-made MSMs requires the full knowledge of the TLCT process, which is still incomplete. Here, we tackle this issue by monitoring the structural evolution during the templating process by small-angle X-ray scattering, showing that after the addition of the silica source the reaction mixture is first isotropic and then an intermediary liquid crystal phase appears, which is the key to the success of the templating process, namely the formation of ordered MSMs. We analyze the structure and the formation dynamics of this intermediary phase and present a simple theoretical model, which allows us to connect the structural parameters of the initial LLC and the MSM. These results provide an enhanced understanding of the TLCT process and are an important step toward the predictable synthesis of new MSMs in the future.

Facile and Direct Preparation of Ultrastable Mesoporous Silica with Silver Nanoclusters: High Surface Area.

We report the successful direct synthesis of an ultrastable mesoporous silicon dioxide framework containing silver nanoclusters using a modified true liquid crystal templating method. Our modification produced an extraordinary material with a high average Brunauer‐Emmett‐Teller specific surface area of 1785 m2 g−1 – the highest reported surface area to date – and an ultrastable mesoporous structure, which has been stable for nine years so far. This method eliminates the need for reduction of silver oxide into metallic silver and restricts the growth of silver clusters. The silver nanoclusters, with an average size of 1 nm, occupy the pores and walls of the framework. Analysis of the material using nitrogen adsorption/desorption method, high‐resolution transmission electron microscopy, X‐ray diffractometry, energy‐dispersive X‐ray diffractometry, X‐ray photoelectron spectroscopy, and scanning electron microscopy is discussed herein.

Mesoporous NiO/Al-SBA-15 catalysts for solvent-free deoxygenation of palm fatty acid distillate

Abstract A series of 5 wt% NiO/Al-SBA-15 catalysts were prepared by wet impregnation of ordered, mesoporous Al-SBA-15 supports (Si/Al molar ratios spanning 5–75) synthesised by a true liquid crystal templating (TLCT) method. The catalytic activity of the resulting catalysts was studied in the solvent-less, hydrogen-free deoxygenation (DO) of palm fatty acid distillate (PFAD), using a semi-batch reactor at 350 °C. 27Al and 29Si MAS-NMR was used to quantify the speciation of framework and extra-framework Al as a function of Si:Al ratio, before and after NiO functionalisation; TEM and XRD confirmed the formation of 9–10 nm NiO nanoparticles in all cases. NiO/Al-SBA-15 catalysts exhibited excellent catalytic activity for PFAD deoxygenation, with hydrocarbon yields reaching 86% and a selectivity to the diesel fraction (C11 C17) of 91%.

Mesoporous silica prepared by modified true liquid crystal templating method with high thermal stability and 10-year shelf life

We prepared mesoporous silicon dioxide with high thermal stability via modified true liquid crystal templating (TLCT). The structure of this material could withstand multiple calcination processes at 570 °C for 104 h. The material is sturdy, and it has maintained the mesoporous structure for 10 years so far. Further, it has a high Brunauer–Emmett–Teller (BET) surface area (1280 m2 g−1), exceeding 1000 m2 g−1, which was the maximum surface area produced by the original TLCT method. The material was characterized by employing the N2 sorption method, X-ray diffraction analysis, high-resolution transmission electron microscopy, X-ray photoelectron spectrometry, and 29Si magic angle spinning-nuclear magnetic resonance analysis. The 29Si MAS-NMR of the solid sample revealed that the Q4 value [Si(SiO)4] increased in direct proportion to the heat treatment duration, indicating that the condensation process continued even after multiple heat treatments. This also means that our material not only is thermally stable but also continues to improve with multiple heat treatments. Therefore, our mesoporous material is promising for use as a host in nanoparticle/cluster gusset synthesis that requires heat treatments and as an absorbent of sulfur compounds in oil products.

True liquid crystal templating of SBA-15 with reduced microporosity

Mesoporous silica SBA-15 was synthesised by the true liquid crystal templating method, yielding a material with reduced microporosity compared with that produced by the more conventional liquid crystal templating route. Further advancements allow the generation of metal nanoparticle-doped SBA-15 materials with well-defined metal particle sizes, which posses potential as catalytic systems.

Ordered thiol-functionalized mesoporous silica with macrostructure by true liquid crystal templating route

Ordered thiol-functionalized mesoporous silica has successfully been synthesized via co-condensation of tetramethyl orthosilicate (TMOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) in lyotropic liquid crystalline phase of Brij 56 surfactact (C 16EO 10). In contrast to the common synthesis in micellar solution, true liquid crystal templating synthesis can easily fabricate organic-functionalized mesoporous silica with desirable macro-morphology and the loading amount of organic moieties can also be controlled well. The resultant materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), nitrogen sorption, polarized optical microscopy, Fourier transform infrared (FT-IR) spectra, differential scanning calorimetry and thermogravimetric analysis (DSC–TGA), and elemental analyses (EA). Direct evidence of the presence of chemically attached thiol groups was provided by FT-IR, DSC–TGA and EA. Adsorption measurement indicates that the materials are effective for the removal of heavy metal ions from aqueous solutions. The Hg 2+ adsorption isotherm fits Langmuir behavior, but the Type-IV adsorption isotherm for Cd 2+ was unexpectedly observed, which is probably attributed to significantly different Cd 2+ affinity ability for the thiol groups on the external surface and those lining the framework pore channels of the nanoporous adsorbent.

A systematic study of the formation of mesostructured silica using surfactant ruthenium complexes in high- and low-concentration regimes

Mesostructured silica can be prepared by surfactant templating either under conditions of low surfactant template concentration (so-called liquid crystal templating) or from a pre-formed mesophase at higher surfactant concentrations (true liquid crystal templating). In this study, the structural properties of such silica products prepared using a surfactant bipyridine complex of Ru(II) are compared with similar products templated with a conventional cationic surfactant, CTAB (cetyltrimethylammonium bromide). Templating with this ruthenium metallosurfactant leads to well-ordered mesoporous silica with catalytically active RuO2nanoparticles distributed uniformly within the silica pores.

The synthesis of mesoporous silicates containing bimetallic nanoparticles and magnetic properties of PtCo nanoparticles in silica

Using a one-pot approach employing true liquid crystal templating on neutral surfactants and simple metal salt precursors, mesostructured, mesoporous silicates have been prepared in which bimetallic nanoparticles are deposited; magnetic properties of PtCo systems so prepared are evaluated.

Fabrication and Characterization of Nanostructured Pd Hydride pH Microelectrodes

Novel pH microsensors were made by electrodepositing mesoporous Pd films onto Pt microdisks, electrochemically loading the films with hydrogen to form the alpha+beta Pd hydride phase, and then switching to the potentiometric mode to monitor pH. To create a nanostructure, the films were deposited within a molecular template formed by the self-assembly of surfactant molecules, a technique known as true liquid crystal templating. The films retain the micrometer size of the Pt microdisk but offer electroactive areas up to 900 times larger. Optimum hydrogen loading conditions were determined, and the mesoporous Pd microdisks were found to have excellent potentiometric properties. From pH 2 to 12, their potential was Nernstian, highly reproducible, very stable (+/-1.2 mV over 2 h), and without hysteresis. Their response time was better than 1 s. However, the presence of oxygen reduced their lifetime significantly, thereby requiring frequent reloading. These microelectrodes do not require calibration before and after measurements, a procedure normally essential for potentiometric pH microsensors. To our knowledge, these are the first results where nanostructured materials made by the true liquid crystal templating method have been used in the potentiometric mode; moreover, these are the first results demonstrating the application of nanostructured microdisks in the potentiometric mode.

Simultaneous drying and chemical modification of hierarchically organized silica monoliths with organofunctional silanes

Large, low density silica monoliths with a hierarchical organisation of macro- and periodically arranged mesopores are prepared by a true liquid crystal templating approach of an ethylene glycol-modified silane in the presence of a non-ionic block copolymer surfactant and subsequent drying of the wet gels with organosilanes. In this approach the silanes serve two functions: first, the silylation reactions allow for non-destructive drying of the monolithic gels and simultaneous extraction of the block copolymer template; second, they serve as surface functionalization agent. A variety of organofunctional silanes such as trimethylchlorosilane, 3-mercaptopropyltrimethoxysilane, phenyl-trimethoxysilane, 3-[(2,2-dimethyl-1-aza-2-silacyclopent-1-yl)dimethylsilyl]-1-propanamine, a cyclic silazane resulting in aminopropyldimethylsilyl groups on the silica surface, and (methylmethacryloyl)dimethyl-methoxysilane, has been successfully applied in the interfacial modification of the silica surface. The resulting silica monoliths were characterized with respect to their structure by SEM, SAXS, and nitrogen sorption and with respect to their chemical composition by elemental analysis, titrations and MAS-NMR spectroscopy.

Zirconia Needles Synthesized Inside Hexagonal Swollen Liquid Crystals

We report the synthesis of zirconia microneedles by the direct nucleation of particles inside a hexagonal swollen liquid crystal (SLC) (cell parameter a = 27 nm) prepared by mixing with the proper ratio, an aqueous solution of sulfated zirconium colloids, a cationic surfactant (cetylpyridinium chloride), cychlohexane as swelling agent with an oil over water ratio of 2.5 (vol.), and 1-pentanol as cosurfactant. After a slow crystallogenesis that can be enhanced by an initial induction step under moderate temperature, particles in the centimeter range can be obtained, with a very high shape ratio (over 100). These particles are made of crystalline octahydrate zirconium oxychloride containing pores of 20 nm diameter, aligned along the main axis of the liquid crystal, as the fingerprint of the oil cylinders present in the hexagonal phase. The morphology of these particles confirms that the shaping mechanism is based on true liquid crystal templating (TLCT). Further thermal treatment of these particles, after extraction from the SLC, leads to the crystallization of zirconia with the same needlelike morphology as the zirconium oxychloride.

High-activity heterogeneous catalysts prepared in one step from the mesophases of metallosurfactants

Surfactant Ru(II) complexes have been used to template mesoporous silicates using the true liquid crystal templating method, giving evenly dispersed, nanometer-sized ruthenium particles which show very high catalytic activity and selectivity in the hydrogenation of 1-hexene.

A spectroscopic study of group IV transition-metal-incorporated direct templated mesoporous catalysts. Part 2. A comparison of Ti-, Zr- and Hf-containing materials

Ti, Zr and Hf ions have been incorporated into mesoporous silica using a novel one-pot procedure based on the true liquid crystal templating (TLCT) synthesis method. The nature of the metallic sites was assessed using diffuse reflectance UV-visible, photoluminescence and FT-IR spectroscopy. In situ adsorption of oxygen and ammonia probe molecules provided information on the accessibility of optically active species.

A Spectroscopic Study of Group IV Transition Metal Incorporated Direct Templated Mesoporous Catalysts Part 1: A Comparison between Materials Synthesized Using Hydrophobic and Hydrophilic Ti Precursors

Titanium has been incorporated into mesoporous silica using novel one-pot procedures based on the true liquid crystal templating (TLCT) synthesis method. Two different Ti sources were used, one ins...

Liquid Crystal Templating of Mesoporous Materials

There is currently great interest in the use of lyotropic liquid crystals as templates for the production of mesoporous inorganic or metallic materials having uniform pore sizes in the range 20-100 Å or greater. Such materials have potential applications as catalysts, molecular sieves or electrodes, and can accommodate molecules which are too large to fit within the pores of conventional zeolites. We have investigated the structure and alignment of mesoporous materials produced using the True Liquid Crystal Templating (TLCT) method. In TLCT, the surfactant forms a lyotropic liquid crystal phase of well defined geometry and dimensions at the start of the synthesis. We have been able to produce hexagonal mesoporous coatings within capillaries, having a specific alignment of the 2-D hexagonal lattice, as probed by X-ray diffraction. We have also followed the structural kinetics of the alignment process. These TLCT mesoporous materials may be functionalized for catalytic applications.

Templating mesoporous silicates on surfactant ruthenium complexes: a direct approach to heterogeneous catalysts

Mesoporous silicas have been obtained by the true liquid crystal templating (TLCT) method, using a surfactant RuII complex as the template; on calcination, ruthenium-containing particles are deposited into the pores; the materials show high catalytic selectivity for the hydrogenation of hex-1-ene.