Template Removal Process Research Articles

Improvement of solubility of celecoxib by inclusion in MCM-41 mesoporous silica: drug loading and release

Celecoxib is a poorly water-soluble nonsteroidal anti-inflammatory drug. Here we report four ordered mesoporous silica MCM-41 supports with different particle size, pore volume, and surface properties to investigate their loading capacity with celecoxib and their release abilities. Spherical MCM-41 mesoporous supports less than 50 nm in diameter were prepared and to compare the effect of the template removal process on morphology of samples, acid extraction and calcination methods were used. Moreover, nearly 500 nm sized rod-shaped MCM-41 mesoporous silica was obtained by changing the template concentration in preparation. Boron doping was performed to determine the effect of a heteroatom on the surface of mesoporous silica and adsorbance of drug molecules and release. In order to investigate the effect of polarity of solvent during drug loading, two different solvents were used: ethanol as polar solvent and hexane as nonpolar solvent. All bare and drug-loaded samples' physicochemical characterizations were performed. The release experiments were conducted in phosphate buffer solution of pH 7.4 at 37 °C. Celecoxib solubility was highly improved compared to the pure drug. The morphology and surface property differences of MCM-41 and the solvent effect in adsorption of celecoxib have been discussed, including its delivery.

Preparation of a flexible polypyrrole nanoarray and its capacitive performance

Polypyrrole nanotube embedded nanopore array (PNENA) was prepared using an independent TiO2 nanotube array template-assisted electrodeposition and template removal process. All polypyrrole nanotubes were fully embedded inside polypyrrole nanopores to form a coaxial nanoarray structure and flow-through characteristic. The PNENA thin film electrode exhibited a specific capacitance of 88.6Fg−1 in a potential range of −0.2–0.6V and a capacity retention of 67% after the 1000 cycles in 1.0M H2SO4 aqueous solution. A solid-state flexible PNENA supercapacitor was assembled using two symmetric PNENA electrodes and gel electrolyte, showing a specific capacitance of 13Fg−1 at a current density of 0.005Ag−1. This PNENA supercapacitaor also exhibited a stable capacitive performance at both planar state and bending state, showing its possibility for flexible energy storage.

Ordered mesoporous Cu–Ce–O catalysts for CO preferential oxidation in H2-rich gases: Influence of copper content and pretreatment conditions

Highly ordered mesoporous Cu–Ce–O catalysts with different Cu contents have been synthesized by using ordered mesoporous silica KIT-6 as a hard template. The mesostructural order of the negative replica is influenced by the ratio of Cu to Ce. Using XRD, HR-SEM, TEM and EDX analysis, it was found that the ordered mesostructures of the nanocomposites degenerate with increasing Cu concentration, due to CuO leaching during the template removal process and a phase separation at high Cu concentration. Cu ions can replace Ce-ion in the structure of CeO2 at Cu concentrations below 40mol%. However, the Cu concentration in the final materials is lower than expected from the ratio used in the synthesis. The activity in preferential oxidation of CO in H2-rich gases (PROX) was tested at a space velocity of 60,000mLh−1gcat−1. The activity of the mesoporous catalysts increases with the concentration of Cu and becomes stable for Cu concentrations higher than 20mol%. A CO conversion around 100 % can be attained with Cu0.20Ce0.80O2 as catalyst at 160°C. The exit CO concentration can be as low as 70ppm under these conditions. The CO2 selectivity can reach 100 % at low temperature (60 – 80°C). Direct loading of CuO on the surface of mesoporous CeO2 leads to large CuO crystals and correspondingly low activity. The influence of the pretreatment atmosphere on activity was also studied. Oxidation–reduction–reoxidation cycling can improve the catalytic activity of the catalysts.

Preparation of agglomeration-free spherical hollow silica particles using an electrospray method with colloidal templating

Studies on synthesis of hollow particles have received considerable attention because these particles can be used for wide range applications. However, current methods have problems in the agglomeration phenomena and must be proceeded in the multi-step, complicated, and time-consuming procedures. Therefore, purpose of this study is to show a new method to produce agglomeration-free hollow silica particles with spherical shape and controllable diameter (from 90 to 200nm). Different from other reports that typically used a liquid-phase synthesis method, we used an electrospray deposition followed by template removal process. Polystyrene and silica were used as models of template and host material, respectively. The prepared particles were characterized using a fourier transform infra red and a scanning and a transmission electron microscopes. Experimental results showed that size and agglomeration condition of hollow particles were controllable only by changing core diameter, electrospray flow rate, and precursor concentration. The successful and unsuccessful condition was also described.

ChemInform Abstract: Tailored Crystalline Microporous Materials by Post‐Synthesis Modification

AbstractReview: 374 refs.

Tailored crystalline microporous materials by post-synthesis modification

Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions.

Controlled synthesis and investigation of the mechanism of formation of hollow hemispherical protrusions on laurate anion-intercalated Zn/Al layered double hydroxide hybrid films

Films of laurate (La) anion-intercalated zinc–aluminum layered double hydroxides (ZnAl–La–LDHs) with hollow hemispherical protrusions on the surface of the hybrid film have been conveniently prepared by an ion-exchange reaction of a nitrate-containing LDH film previously grown in situ on a porous anodic alumina/aluminum (PAO/Al) substrate. No template is required to form the hemispherical protrusions, thus avoiding a complicated template removal process. The dimensions, morphology, and resistance to bursting of the hollow hemispherical protrusions can be easily tuned by varying the experimental conditions such as sodium laurate concentration, reaction time, and reaction temperature. The evolution of the hollow protrusions was investigated by scanning electron microscopy (SEM), and a “bubble template-reconfiguration assembly” mechanism, in which air bubbles on the film surface act as a template, has been proposed to explain their formation. When the ion-exchange reaction was carried out on a film that had been treated by ultrasound to eliminate surface air bubbles, no hemispherical protrusions were formed, which is consistent with the proposed mechanism.

In situ TPR removal: a generic method for fabricating tubular array devices with mechanical and structural soundness, and functional robustness on various substrates

Wire array templates have been utilized for fabricating various three-dimensional tubular structure devices, such as solar cells, batteries and supercapacitors, as well as electronic and photonic devices. It is necessary to remove the templates by using post-treatments such as wet chemical etching, decomposition, or Kirkendall approaches. However, it remains a challenge to ensure tubular structure integrity, mechanical soundness, and chemical purity during the template removal process, which affects the functional robustness of enabled tubular structure array devices. In this work, by utilizing ZnO nanorod array devices as templates and temperature programmed reduction (TPR) as the removal method, nanotube array devices made of various functional oxides have been directly converted with well-retained uniformity, structure and mechanical soundness, and chemical homogeneity on both two-dimensional (2D) planar and three-dimensional (3D) monolith device substrates. The successful examples range from binary metal oxides such as fluorite CeO2 to complex oxides like perovskite La0.8Sr0.2CoO3 (LSCO). This TPR removal method is generic, simple and rationally controllable, and can be easily expanded to the preparation of other oxides and non-oxide tubular structure devices regardless of the interfaced device substrate geometry. As a demonstration, the enabled CeO2 nanotube array devices could function as good high-temperature O2 sensors and active photocatalytic devices with good robustness.

Hollow capsules prepared from all block copolymer micelle multilayers

We introduce a novel and versatile approach for preparing hollow multilayer capsules containing functional hydrophobic components. Protonated polystyrene- block-poly(4-vinylpyridine) (PS- b-P4VP) and anionic polystyrene- block-poly(acrylic acid) (PS- b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films onto polystyrene (PS) colloids. After removing the PS colloids, the stabilities of the formed BCM hollow capsules were found to be strongly dependent on the charge density of the hydrophilic corona segments (i.e., P4VP and PAA block segments) as well as the relative molecular weight ratio of hydrophobic core (i.e., PS segments) blocks and hydrophilic corona shells. Furthermore, in the case of incorporating hydrophobic fluorescent dyes into the PS core blocks of micelles, the hairy/hairy BCM multilayers showed well-defined fluorescent images after colloidal template removal process. These phenomena are mainly caused by the relatively high degree of electrostatic interdigitation between the protonated and anionic corona block shells.

Template removal processes within individual micron-sized SAPO-34 crystals: Effect of gas atmosphere and crystal size

In situ UV–Vis micro-spectroscopy has been employed to reveal physicochemical insight in the template removal process of morpholine-containing micron-sized SAPO-34 crystals at the single particle level. The differences in UV–Vis absorption bands and the related rate of their formation and disappearance demonstrate the generation of different intermediates when the detemplation process is performed in either oxygen or nitrogen. A series of detemplation experiments in oxygen with SAPO-34 crystals ranging between 7.5 and 58 μm indicate the formation of five major Gaussian functions with band maxima at 405, 450, 505, 555 and 608 nm, building up the experimental UV–Vis absorption spectra. These Gaussian functions, assigned to different carbonaceous deposits and their precursors, demonstrate that two separate temperature trends can be distinguished. The first one is related to the formation of small organic compounds, characterized by band maxima at 405 and 450 nm, which lead to a bimodal intensity distribution at the low and high end of the heating ramp for large-sized SAPO-34 crystals, while the more extended poly-aromatic compounds, characterized by band maxima at 555 and 608 nm, generate a mono-modal distribution at intermediate heating temperatures for both small- and large-sized SAPO-34 crystals. These features provide evidence for a crystal size dependent relationship between pore blocking and the formation of small and more extended molecular compounds within SAPO-34 porous networks when performing a thermal detemplation process.

Preparation and properties of porous polyimide films with TiO 2/polymer double shell hollow spheres

Without the template removal process, double shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO 2 shells. TiO 2 encapsulated hollow spheres were incorporated with the polyamic acid solutions and imidized to prepare the porous polyimide films. The final porous texture of the film depends on the as-doped arrangement and the properties of the hollow spheres. The TiO 2 shell exhibits good thermal stability and chemical resistance to prevent the collapse of hollow spheres during the polyamic acid solution/hollow particle mixing and the imidization procedures. The effects of preparation conditions on the morphology of the encapsulated hollow spheres were investigated. The dielectric constant of the porous polyimide films (pore diameter around 0.6 µm) decreased to 2.8. The influences of hollow particles on the porous textures, the dielectric and dynamic mechanical properties of the porous films were studied.

Microwave synthesis of MFI-type zeolite membranes by seeded secondary growth without the use of organic structure directing agents

This paper reports the microwave synthesis of MFI-type zeolite membranes by secondary growth of nanocrystalline silicalite seed layers in pure inorganic precursors. The inorganic precursor solutions contained SiO 2, Al 2(SO 4) 3, NaOH, and H 2O. It was found that the membrane formation and quality were sensitive to the Si/Al ratio of the precursor solution. Good quality MFI membranes were obtained from precursors with Si/Al ratios in range 111–130. The membranes had H 2/SF 6 permselectivity of >1700 and H 2 permeance >3 × 10 −7 mol m −2 s −1 Pa −1 at 23 °C when helium was used as sweeping gas. The membrane synthesis duration can be greatly shortened by microwave heating as compared to the conventional heating method. Furthermore, membranes obtained from template-free inorganic precursors exhibited higher permselectivties of H 2 over N 2, and SF 6 than the membrane synthesized with TPAOH template. The studies on small gas permeation mechanisms and BET characterization of zeolite particles suggested that the membranes derived from inorganic solutions contained minimized intercrystalline pores by avoiding the high temperature template removal process and possessed slightly smaller effective pore size likely due to trapping of SiO 2 molecular species in the zeolite microporosity.

Mesoporous Aluminophosphate Thin Films with Cubic Pore Arrangement

Mesoporous aluminophosphate thin films with 3D cubic (Im3m) pore arrangement were synthesized for the first time. Thin films were templated with block copolymer nonionic templates Pluronic F127 and F108 and deposited on a glass substrate by dip-coating. In situ SAXS investigations show the formation of a highly ordered mesostructure upon the dip-coating process, which remains stable up to at least 670 K. A cubic mesostructure was observed also by TEM. Template removal process was monitored by TG and FT-IR. A transition from an amorphous aluminophosphate gel to a well-defined aluminophosphate framework was observed by MAS NMR.

Visualizing the Crystal Structure and Locating the Catalytic Activity of Micro‐ and Mesoporous ZSM‐5 Zeolite Crystals by Using In Situ Optical and Fluorescence Microscopy

A combination of optical and fluorescence microscopy was used to study the morphology of micro- and mesoporous H-ZSM-5 zeolite crystals (17 x 4 x 4 microm) and to evaluate, in a spatially resolved manner, the effect of mesoporosity, introduced via desilication, on catalytic performance. For this purpose, the oligomerization of various styrene molecules was used as a model reaction, in which the carbocation intermediates formed in the zeolite pores act as reporter molecules. In situ confocal fluorescence measurements after the template removal process showed that the crystals generally consist of three different subunits that have pyramidal boundaries with each other. Examination of these crystals during styrene oligomerization revealed differences in the catalytic activity between the purely microporous and the combined micro- and mesoporous crystals. The introduction of intracrystalline mesoporosity limits the formation to dimeric carbocation intermediates and facilitates the transport of styrene molecules inside the zeolite volume. This leads to a more uniform coloration and fluorescence pattern of the crystals. Moreover, the oligomerization of various styrene compounds, which differ in their reactivity, provides a good way of estimating the Brønsted acid strength in a spatially resolved manner, showing a nonhomogeneously distributed Brønsted acidity over the volume of the crystals. More detailed information on the structure of the ZSM-5 crystals was revealed for mesoporous crystals during the oligomerization of 4-methoxystyrene. This reaction induced an "explosion" of the crystal leading to the formation of a complex system with at least eight different subunits. Finally, polarized-light microscopy was used to unravel the pore geometry in these individual building blocks. The observed differences in catalytic behavior between micro- and mesoporous ZSM-5 crystals are strengthened by the microspectroscopic techniques employed, which show that upon desilication the crystal morphology is affected, the product distribution is changed towards less conjugated carbocation intermediates, and that a gradient in Brønsted acid strength appears to be present.

Intergrowth Structure of Zeolite Crystals as Determined by Optical and Fluorescence Microscopy of the Template‐Removal Process

Growing together: The template-removal process in a series of zeolite crystals has been mapped by a combination of in situ optical and fluorescence microscopy. Three-dimensional spatial distribution of light-absorbing and -emitting species allowed visualization of the architecture of zeolite intergrowths.

Freestanding nanowire arrays from soft-etch block copolymer templates.

Nanoporous poly(4-fluorostyrene) templates on gold-coated silicon/silicon oxide substrates were prepared by the electric field alignment of poly(4-fluorostyrene)-b-poly(d,l-lactide) block copolymer thin films followed by mild degradation of the polylactide phase using dilute aqueous base. Electrochemical deposition of nanowires was accomplished using a protocol for the preparation of copper oxide. Freestanding nanowires were observed after removal of the template by either simple dissolution of the poly(4-fluorostyrene) or by treatment with UV irradiation. The annealing time, the electric field strength used to align the block copolymer films, and the template removal method are shown to influence the freestanding nanowire arrays. The "soft-etch" method described is generally useful for the preparation of templates and nanostructures that are sensitive to more aggressive template removal processes.

Porosity of mesoporous silica thin films: Kinetics of the template removal process by ellipsometry

Mesoporous silica (MPS) films were prepared by the sol–gel route using the acid-catalysed procedure starting from tetraethoxysilane. Three different organic templates, Brij56, Pluronic F127 and CTAB have been tested. The dependence of porosity on the organic template, the surfactant/Si molar ratio and on the calcination temperature and annealing time is investigated using spectroscopic ellipsometry for real time monitoring of the pore formation kinetics. We show that the template removal is a fast process already occurring at temperatures as low as 160 °C, and that development of porosity is characterized by a saturating behaviour. Furthermore, the higher the organic content in the starting hybrid material, the higher the porosity in the final SiO 2 film. Finally, data show that a porosity as high as 58% can be achieved, and that the most stable SiO 2 mesoporous materials are obtained using the Brij56 template.

Silica Structures Templated on Fibers of Tetraalkylphosphonium Salt Gelators in Organogels

Phosphonium cations (18(n)RP(+)) consisting of three or four n-octadecyl chains and R = PhCH(2) or C(m)H(2)(m+1) (m = 1-5 or 12) when n = 3 and with iodide, bromide, chloride, fluoride, or perchlorate anions are used to gelate and polymerize solutions of 2-10 wt % tetraethyl orthosilicate in ethanol, benzene, tetrahydrofuran, and dimethyl sulfoxide using acid or base catalysis and under hydrolytic or nonhydrolytic conditions. These are the simplest low-molecular-mass organic gelator structures of which we are aware that have been able to template silica. The silica objects that are obtained after the hydrolytic sol-gel process include porous, spherulitic, and tubular objects in the size range of several micrometers to tens of nanometers. Their specific shapes and sizes depend on the specific conditions of the hydrolytic sol-gel process, including the nature of the catalyst. The electrostatic interaction between silicate intermediates and gelator strands is the driving force for templating. The template effect is strongly influenced by several factors, including (1) the competition between silicate/solvent and silicate/template interactions, (2) the period of the sol-gel process, (3) the hardness of the anion of the gelator salt, (4) the surface tension of the solvent, (5) and the sequence of drying and template removal processes. The nature of the R group influences the stability of the molecular gels but appears to have little effect on the silica morph obtained. In addition, it is shown in one case, where a direct comparison is possible, that the fibers of one of our phosphonium salts are a much more efficient template for silica than those of the corresponding ammonium salt (with its "harder" cationic center). The specific nature of the objects and the conditions under which they can be formed are discussed.

One-Step Preparation of MgO Hollow Spheres and Hexagonal Cylinders via Zn Template

Polycrystalline hollow spheres and single crystalline hexagonal cylinders of MgO have been fabricated by chemical vapor deposition using ZnO and Mg as the starting materials. The Zn produced during the chemical reaction serves as template material, and vaporization of which leads to the formation of the hollow structures. The presence of trace amount of Si in the source material is identified to be critical for the existence of the stable MgO hollow structures, which otherwise would be damaged during the Zn template removal process. The same principle can be readily adopted in many other material systems and result a variety of hollow structures for catalyst, sensor and medical applications.

Direct synthesis of palladium-containing mesoporous carbon

Palladium-containing mesoporous carbon materials with high surface area, large pore volume and narrow pore size distribution have been synthesized by a simple one-step sol–gel technique followed by a carbonization and template removal processes. These materials contain uniformed pores with 2.2 nm average pore diameter and surface areas larger than 1500 m 2/g. The palladium content of these materials can be precisely controlled during the sol–gel process. Compared with the commercially available activated carbon supported palladium catalysts, these materials exhibit improved catalytic activities for Heck reaction of iodobenzene and styrene.