Formation Of Mesoporous Structure Research Articles

Preparation and Mechanism Study of Mesoporous Titania Whiskers

A simple novel procedure for the,synthesis of mesoporous titania whiskers from potassium dititanate(K_2Ti_2O_5)was reported.Nanostructure whisker was obtained via controlling mesostructure transition process of the unstable trigonal bipyramidal layered crystal structure of K_2Ti_2O_5 in a hydra- tion step.XRD,TEM and HREM results confirm the existence of nanophase KOH·nH_2O inside the inorganic framework.Removing of nanophase KOH.nH_2O by acid solution leads to the formation of mesoporous structure with the specific surface area up to 248m~2/g.The mesoporous structure of TiO_2 whiskers and fibrous morphology can be preserved by calcination at 500℃with the specific surface area of 139m~2/g and the pore diameter of 8.7nm.

Synthesis of mesoporous niobium oxophosphate using niobium tartrate precursor by soft templating method

Mesoporous niobium oxophosphate (NBP) with high specific surface area (427 m 2/g) and narrow pore size distribution (3–15 nm) has been prepared using aqueous solution of niobium tartrate complex, diammonium hydrogen phosphate as precursors and cationic surfactant, tetradecyl trimethylammonium bromide (TTBr) as an organic template. The synthesized material has been characterized by simultaneously recorded thermogravimetric and differential thermal analysis (TG–DTA), fourier transformed infrared spectroscopy (FTIR), high and low angle X-ray diffraction (XRD), N 2 adsorption–desorption isotherms, high resolution transmission electron microscopy (HRTEM), 31P solid state magic angle spinning nuclear magnetic resonance ( 31P MASNMR) spectroscopy and energy dispersive X-ray (EDX) analysis. HRTEM and XRD confirm the formation of mesoporous structure and HRTEM image indicates the formation of wormhole-like mesopores in the synthesized sample. The interaction of pyridine with niobium oxophosphate has been investigated by means of adsorption infrared spectroscopy (FTIR) which shows that both Brönsted and Lewis acid sites are present on the surface of niobium oxophosphate.

Composite templates synthesis of mesoporous titania from industrial titanyl sulfate solution under external outfields

Abstract The precursors of mesoporous titania were synthesized via supra-molecular self-assembly route induced by composite templates (CTAB/P-123) from industrial titanyl sulfate solution under ultrasonic irradiation, microwave and hydrothermal condition. The hydrolysis and polycondensation rates of TiOSO4 solution were controlled by adjusting the pH value at about 1.0. Mesoporous titania with anatase phase was obtained after templates removal by calcinations. The as-prepared powder was characterized by X-ray diffraction (XRD), N2 isothermal adsorption–desorption, HRTEM and SAD. External outfields with enhancing polar action and soft hydrothermal condition were beneficial to prepare better mesoporous TiO2. Ultrasonic vibration promoted the formation of mesoporous structure. Under microwave irradiation, mesoporous TiO2 was synthesized with BET specific surface area of 190.6 m2 g−1, average pore diameter of 2.57 nm and crystal size of 13.65 nm. And ultrasonic irradiation, microwave and hydrothermal conditions were making for forming and stabilizing the mesoporous structure.

Effect of synthesis conditions on preparation of mesoporous titania-silica by a modified sol-gel technique using a cationic surfactant

Titania-silica mesoporous materials have been synthesized by a modified sol-gel technique using a cationic surfactant. The synthesis process was studied using statistical design of experiments to achieve the best conditions for titania-silica preparation. The synthesized materials were characterized by XRD, FT-IR, SEM and surface area measurements. The XRD and SEM results showed an amorphous structure of titania-silica. The surface area measurements using nitrogen adsorption showed type-IV isotherms which indicate the formation of mesoporous structure. A high surface area can be obtained (685 m2/g). The crystal size of titania-silica calculated using Scherrer’s equation was found to be in the range 8–15 nm.

Nanosized Cu2O/PEG400 Composite Hollow Spheres with Mesoporous Shells

The nanosized Cu2O/PEG400 composite hollow spheres (HSs, 50−80 nm in diameter) with mesoporous shells of ∼15−20 nm were synthesized by a poly(ethylene glycol) (PEG)-assisted wet-chemical method. In the hollow nanostructures, the polymer content was ca. 18.1 wt %, and the mean size of the component nanocrystals and the pore diameter were ca. 5 and 3.8 nm, respectively. In the fabrication process of hollow structures, poly(ethylene glycol 400) (PEG-400) molecules self-assemble to form micelles which act as templates for the formation of the hollow structures. PEG also acts as a reducing agent, solvent, and complexing agent. The formation of mesoporous structures is due to the oriented-aggregation of composite nanoparticles. The nanosized-composite HSs exhibited peculiar photoluminescence (PL) phenomenon with strong peaks at 414 and 436 nm and weak ones at 454, 570, and 637 nm. Furthermore, the HSs showed excellent adsorption ability for methyl orange (MO) because of their composite and mesoporous shell structures.

Electrosynthesis of mesoporous Pt–Au alloy electrode for direct methanol fuel cell

Mesoporous Pt–Au alloy films were successfully fabricated on ITO-coated glass from an aqueous mixture of H 2PtCl 6 and HAuCl 4 by electrodeposition method using proper amount of poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) (P123) as a templating agent. For comparison, nonporous Pt and mesoporous Pt were electrodeposited. Crystallinity of synthesized film was investigated by X-ray diffraction (XRD) analysis, and film composition was determined by energy dispersive X-ray spectroscopy (EDS). Scanning electron microscopy (SEM) was utilized to examine surface morphology and it was observed that the addition of P123 affected the particle growth, resulting in a significant change of surface morphology. The mesoporous structure was confirmed by transmission electron microscopy (TEM), and it was concluded that the formation of mesoporous structure strongly depended on electrodeposition conditions, such as deposition voltage, deposition time, temperature and P123 concentration. Compared with pure Pt electrodes, mesoporous Pt–Au film showed higher catalytic activities and stability for methanol oxidation.

Synthesis of well-ordered mesoporous titania powder with crystallized framework

Pure well ordered mesoporous TiO2 powder materials with crystallized frameworks were synthesized by carefully controlling the hydrolysis process of Ti precursor during self-assembly and the aging processes. A complete morphological characterization of the sample was performed using XRD, TEM, and N2 sorption isotherms. The resulted powder indicates well crystallization with two phases: anatase with main phase and the other, rutile; the SAXRD shows a peak at 0.8°, which indicates ordered mesoporous structure's formation. The thick frameworks (7 nm) and the narrow pore size distribution with the peak size within mesoporous size (5 nm) suggest the meoporous structure as well. In addition, CuO doped mesoporous TiO2 with even better ordered mesostructure were also reported in this work.

A Mechanistic Study of the Formation of Mesoporous Structures from in Situ AC Conductivity Measurements

The purpose of this work is to study the kinetics of self-assembly in the formation mechanism of anionic templated mesoporous solids (AMS-n) during the first few seconds of the synthesis as well as to demonstrate the use of alternating ion current (AIC) conductivity measurements to follow the self-assembly in complex hybrid systems. The formation of different AMS-n caged-type mesostructures through the delayed addition of the silica source is demonstrated and explained in terms of the interaction between the co-structure-directing agent (CSDA) and the oppositely charged surfactant headgroup regions. Our findings, supported by transmission electron microscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dynamic light scattering (DLS) measurements, and powder X-ray diffraction suggest that the interaction of the CSDA with the surfactant headgroup occurs within seconds after its addition to the synthesis gel leading to interaction between the polymerizing CSDAs and the oppositely charged micelle and to an increase in the micelle-CSDA aggregate size. Both DLS and AIC measurements agree that this process occurs within the first 1000 s after addition of the CSDA to the synthesis gel at room temperature. In addition to the mechanistic study it was found that the intermediate materials are comprised of a three-layer entity. Time-dependent 29Si MAS NMR studies reveal that an organo-silica layer forms around the micelles prior to a condensed outer inorganic shell of silica.

Fabrication of Mesoporous Ni-8YSZ and Its Catalytic Activity for Carbon Dioxide Reforming of Methane

Mesoporous Ni-8YSZ powder was prepared by a simple route and used as catalyst in methane reforming with carbon dioxide. The mesoporous catalyst was characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, scanning electron microscopy, transmission electron microscopy, and CO2 temperature-programmed desorption. The influence of synthesis conditions on the structure of the final product was experimentally investigated and the mechanism for the formation of mesoporous structure was briefly discussed. The performance of the as-prepared samples with different pore sizes was evaluated by conducting the reforming reaction in a fixed-bed reactor under atmospheric pressure at 700 °C. The results showed that the structure of the catalyst has a strong effect on the performance of the catalyst and the mesoporous Ni-8YSZ catalyst with relatively uniform pore size distribution and small average pore diameter exhibited high activity and stability in the reforming reaction.

Synthesis and photoluminescent properties of mesoporous (MgO) x(ZnO) 1− x materials

(MgO) x (ZnO) 1− x materials have been synthesized using mesoporous carbon as template. By increasing the MgO content in the materials greater than 25%, the (MgO) x (ZnO) 1− x materials began to form the mesoporous structure. Pore size distribution curves indicated that the BJH pore diameter decreased with increasing MgO content. In photoluminescence spectra, all the samples except pure ZnO showed both the band-edge emission and the deep-level emission (green band). It was interesting to note that the UV emission peak energy ( E UV) had a red-shift of about 48 meV at the low MgO content range of 0–25%, while when the MgO content varied from 25 to 75%, the E UV displayed a blue-shift of about 36 meV to the higher energy direction. The optical band gap ( E g) of the (MgO) x (ZnO) 1− x calculated from the absorption spectra was far smaller than that in literature, and this may be related to the formation of mesoporous structure.

Effects of post-deposition chemical treatment on the formation of mesoporous titania films

Mesoporous titania films have been synthesized by a modified sol–gel method in conjunction with amphiphilic triblock copolymers. The effects of ammonia vapor treatment on the formation of mesoporous structures were investigated. Mesoporous titania films with hexagonal structures were obtained by ammonia vapor treatment. Without ammonia vapor treatment, it was found that the mesoporous structures collapse due to crystallization. The framework of mesoporous titania was found to be amorphous. Mesoporous titania films prepared by ammonia vapor treatment showed thermal stability up to 500 °C. Mesoporous samples showed better photo-catalytic activity than anatase titania films under UV-light irradiation.

Thermally Stable Amorphous Mesoporous Aluminophosphates with Controllable P/Al Ratio: Synthesis, Characterization, and Catalytic Performance for Selective O-Methylation of Catechol

Amorphous mesoporous aluminophosphates (AlPO) with P/Al molar ratio in the range 0.8-1.15 are synthesized by using the citric acid (CA) route and are systematically characterized using N(2)-adsorption, XRD, SEM, solid-state CP-MAS NMR, FT-IR, TG-DTA, CO(2)-TPD, and NH(3)-TPD. The characterization studies show that the change in P/Al ratio could affect the structure, texture, thermal stability, and surface acid-base properties of AlPO. Samples with a relatively low P/Al ratio (< or =1.0) exhibit uniform amorphous mesoporous character and high thermal stability (up to 1173 K). Partial crystallization of the AlPO framework easily occurred on the sample with higher P/Al ratio (> or =1.1), thus leading to significant decrease of surface area and formation of particle pile mesopores. Both weak acid and weak base sites are observed over AlPO materials, and the amounts of acid-base sites can be effectively controlled by adjusting the P/Al ratio. The presence of suitable interaction between citric acid and AlPO framework is critical for the formation of mesoporous structures. Both CA and PO(4) units are considered to be ligands to coordinate with aluminum ions, forming relative uniform complexes (such as CA-Al-PO(4)) in the as-synthesized AlPO materials. The mesoporous structure of AlPO materials is obtained after the rapid decomposition of citric acid. Vapor phase selective O-methylation of catechol with methanol reaction is carried out to investigate the catalytic performances of AlPO materials with different P/Al ratios. Among them, AlP(1.1)O shows the highest activity (88.4% conversion of catechol) and the highest yield of guaiacol (74.3%). The presence of suitable weak acid-base pairs may play an important role on the title reaction.

Synthesis and characterization of acidic properties of Al-HMS materials of varying Si/Al ratios

HMS and Al-HMS materials with Si/Al ratio in the range 5–45 were synthesized by neutral templating pathway. The as synthesized as well as calcined samples were examined for pore size distribution, surface area and XRD. These investigations confirmed the hexagonal mesoporous structure formation at all Si/Al ratios. The TGA measurements indicated that two types of template species interacting with Si or Al could be distinguished. The acidity and acid strength distribution studies using microcalorimetric NH 3 adsorption indicated that the acidity increases with Al content in the mesoporous structure. The presence of Al in the structure creates a wide variety of acid sites of varying strengths. The heterogeneity of the sites also increases with Al content of the catalysts. The activities for cumene cracking reaction to test acidity of the materials supported the trend obtained from microcalorimetric NH 3 adsorption results.

Synergistic Effect in an Au−Ag Alloy Nanocatalyst: CO Oxidation

Au-Ag alloy nanoparticles supported on mesoporous aluminosilicate have been prepared by one-pot synthesis using hexadecyltrimethylammonium bromide (CTAB) both as a stabilizing agent for nanoparticles and as a template for the formation of mesoporous structure. The formation of Au-Ag alloy nanoparticles was confirmed by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). Although the Au-Ag alloy nanoparticles have a larger particle size than the monometallic gold particles, they exhibited exceptionally high activity in catalysis for low-temperature CO oxidation. Even at a low temperature of 250 K, the reaction rate can reach 8.7 x 10(-6) mol.g(cat.)(-1).s(-1) at an Au/Ag molar ratio of 3/1. While neither monometallic Au@MCM-41 nor Ag@MCM-41 shows activity at this temperature, the Au-Ag alloy system shows a strongly synergistic effect in high catalytic activity. In this alloy system, the size effect is no longer a critical factor, whereas Ag is believed to play a key role in the activation of oxygen.

Synthesis of MCM-41-type mesoporous materials using filtrate of alkaline dissolution of ZSM-5 zeolite

MCM-41-type mesoporous materials possessing strong Brönsted acidity originated from ZSM-5 zeolite were synthesized by using soluble aluminosilicate species containing the fragments of the structure of ZSM-5 zeolite. The thermal stability of the mesoporous structure of the obtained mesoporous material was enhanced by the post-treatment with an ammonium aqueous solution. These results suggest an important role of alkalinity of slurries on the following two processes; (1) alkaline dissolution of ZSM-5 zeolite and (2) formation of mesoporous structure. These successive processes were efficiently improved by use of a continuous-flow reactor. The mesoporous material synthesized in the continuous-flow reactor catalyzed the cracking of cumene at 523 K, while a conventional Al-MCM-41 hardly catalyzed. The mesoporous material synthesized by using the filtrate of alkaline dissolution of ZSM-5 possessed a stronger Brönsted acidity than a conventional Al-MCM-41.

The roles of acid in the synthesis of mesoporous titania with bicrystalline structure

The effects of H +/Ti molar ratio on the formation of mesoporous structure and the phase transition have been investigated, and the mesoporous titania with bicrystalline framework consisting of anatase and rutile was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area, and BJH pore size distribution.

Special Issue Ceramics Integration. Effect of Crystallization on the Formation of Mesostructured TiO2 Thin Films.

Strict control of the crystallization of TiO2 is one of the most important factors in forming mesoporous structured TiO2 thin films. Effects of the crystallization of TiO2 on the formation of mesoporous structures have been studied by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) observation and X-ray diffractometry (XRD) analysis. The obtained well-ordered mesoporous TiO2 thin films, calcined at 450°C to remove the template, are composed of a continuous non-crystalline TiO2 matrix containing TiO2 nanocrystals, whose mean size is sufficiently small to support the mesostructure. In the mean time, the mesoporous TiO2 materials that almost lose their ordered structure after calcination consist of large TiO2 crystallites (over 6 nm), and the overgrowth of TiO2 crystallites cause a collapse of the mesoporous structure.