Synthesis Of Microporous Materials Research Articles

Semirigid Highly Conjugated Zirconium-Organic Framework for the Capture of Micropollutants and Solar-Light Photodegradation.

Micro-organic pollutants, particularly organic dyes and personal care products (PPCPs), are widely present in wastewater, and thus pose a serious risk to human health. The capture and solar-light photodegradation of micro-organic pollutants are highly challenging tasks, which require the design and synthesis of microporous materials with specific structures. As we know, organic dyes and PPCPs can be absorbed via π-π* stacking. In this paper, an iron-based metal-organic framework (Fe-UiO-68-terNap) containing semirigid conjugated aromatic ligands is prepared for the capture and solar-light photodegradation of multiple water contaminants. UiO-68-terNap was synthesized based on ternaphthalene with π-π* stacking, which would increase the adsorption capacities of organic micropollutants in wastewater. Additionally, the formation of Fe-O-Zr enhances the charge-separation ability resulting in the successful degradation of micropollutants in 240 min. The novel material has been elucidated by single-crystal X-ray diffraction and Fe K-edge XANES, which provide key insights at a molecular level for the design of novel materials for the capture and photodegradation of organic micropollutants.

Nano-sized AlPO4-5 Crystals: Synthesis and characterization

Molecular sieves and zeolites are materials whose crystalline frameworks form nanometer or subnanometer pores. A variety of different crystal structures are known having a range of pore sizes. Because the pore sizes are usually smaller than 2 nm, they are classified as microporous materials. Synthesis of microporous materials is usually conducted by the high temperature treatment (80-200 °C) of aqueous synthesis gels. The process of heating aqueous mixtures to elevated temperatures for crystallization is typically described as hydrothermal synthesis. A hydrothermal treatment has been used to synthesize nano-sized AlPO4-5 (AFI) crystals. The treatment involved three main steps: (1) to prepare a synthesis gel and let it get well mixed, then filling autoclave with the gel and sealing it; (2) crystallization at 180 ◦C for 6 h; and (3) Calcination at 600 ◦C for 4 h to separate template materials. The crystals have been structurally characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX). The analyses show an acceptable fitness to the referred pattern. The SEM analysis and Scherer equation revealed that the size of the obtained AlPO4-5 crystals was about 65 nm.

Synthesis of Microporous Materials and Their VSC Adsorption Properties

Oral malodor is caused by volatile sulfur compounds (VSC) such as hydrogen sulfide (H2S), methyl mercaptan and dimethyl sulfide produced in mouth. VSC induces permeability of mucous membrane and oral malodor formation. Thus, the adsorbent which highly adsorbs VSC should be useful for health in mouth and may prevent teeth from decaying. The microporous material, hydrotalcite, was synthesized by a wet method, and the H2S adsorption was studied. The samples, identified by powder X-ray diffraction method, were put into glass flask filled with H2S gas. The initial concentration of H2S was 30 ppm. The change in concentrations of H2S was measured at rt, and the amount of H2S absorbed on the hydrotalcite for 24 h was 300 micro L/g. The samples were taken out from the above glass flask and put into a pyrolysis plant attached to gas chromatography-mass spectrometry to determine the amount of H2S desorbed from samples. Only 3 % of H2S was desorbed when heated at 500 °C. H2S in water was also found to adsorb into hydrotalcite, which was confirmed by the headspace gas chromatography with flame photometric detector. The hydrotalcite material should be expected to be an adsorbent material, useful for health in mouth.

Selective CO2 Trapping in Guest-Free Hydroquinone Clathrate Prepared by Gas-Phase Synthesis

The most important process to make hydrogen is based on steam reforming of natural gas according to an overall reaction CH4 + 2H2O!4H2 + CO2, where after reformation of the natural gas to a CO/H2 mixture (syngas) a water-gas shift reaction results in a predominantly CO2/H2 mixture. [1, 2] Steam reforming potentially offers one technological path to extend the trend of decarbonization of the primary fossil fuel by taking advantage of the low 1:4 carbon-to-hydrogen ratio of methane compared to coal (~ 8:4) and oil (~ 2:4), provided that subsequent separation of the CO2/H2 mixture and sequestration of CO2 is cost-effective and feasible. We present here a guest-free hydroquinone (HQ) clathrate, prepared by gas-phase synthesis, which reveals unique selectivities towards CO2/CH4 and CO2/H2 mixtures. A dynamical pore-widening process allows CO2 to be adsorbed with a selectivity of 29:1 from a CO2/CH4 (50:50 v/v) mixture and with a selectivity of 60:1 reversibly stored at 7 MPa and 298 K in the presence of a CO2/H2 (50:50 v/v) mixture. This first example of a flexible hydrogen-bonded organic framework (HOF) that can reversibly and selectively absorb and store CO2 opens up a host of applications. The synthesis of microporous materials with cage-like structures, such as zeolites, clathrates and supramolecular com

Synthesis of Microporous Materials and Their Adsorptive Properties of H₂S for Dental Application

The microporous materials, Zeolite A and ZSM-5 were hydrothermally synthesized and their H2S adsorption was studied. The obtained samples were put into a separable glass flask filled with H2S gas, and the change in concentrations of H2S was measured for 1–48 h at rt. Then the samples were taken out and put into a pyrolysis plant attached to gas chromatography-mass spectroscopy to determine the amount of H2S desorbed from samples. The amount of H2S adsorbed on Zeolite A was found to be larger than that on ZSM-5. That is 46% of H2S was desorbed from Zeolite A when heated at 400 °C, while 24% of H2S was desorbed from ZSM-5. The adsorption/desorption behavior of H2S from zeolite materials could be interpreted by the electrostatic interaction between H2S and adsorbent.

ChemInform Abstract: Synthesis of Microporous Materials Using Macrocycles as Structure Directing Agents

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Supramolecular assemblies of fluoro-aromatic organic molecules as structure directing agents of microporous materials: Different effects of fluorine

We investigate the effect played by the presence of fluorine substituents in the organic molecules that act as structure directing agents during the synthesis of microporous materials, both in silica- and aluminophosphate-based compositions. We use a combination of experimental and computational approaches: first, experimental evidence is collected concerning the effect of fluorine on the structure directing ability; second, a computational study is performed with models of increasing complexity to explain the experimental results; third, whenever possible, experimental confirmation of atomic-level features emerging from the theoretical results is seeked. Different amines and ammonium ions with monofluorobenzyl groups are investigated; these aromatic molecules tend to associate through interaction of the phenyl rings, giving place to supramolecular arrangements that maximize the pore filling of the microporous structures. We have observed several effects caused by the presence of fluorine in the structure directing agents, depending on the type of molecule, the nature of the supramolecular arrangements, and the position of fluorine in the phenyl ring, which we classify into three types: (i) the presence of fluorine modifies the chemical character of the non-bonded interactions, increasing the electrostatic interactions with the microporous networks; (ii) fluorine can influence the ability to form supramolecular assemblies, required to direct efficiently the synthesis of the microporous structures; (iii) the presence of fluorine in certain positions of the aromatic rings can favour supramolecular assemblies of the organic molecules with other ions, such as fluoride or hydroxide anions, giving place to cooperative structure directing effects in the synthesis of microporous structures.

Cover Picture: Microwave Effect in the Fast Synthesis of Microporous Materials: Which Stage Between Nucleation and Crystal Growth is Accelerated by Microwave Irradiation? (Chem. Eur. J. 16/2007)

A microwave method has been used for the rapid nucleation and crystallization of microporous materials. In their Full Paper on page 4410, ff., J.‐S. Chang, S. H. Jhung et al. discuss a key issue of how the nucleation and crystal growth steps in the syntheses of microporous materials can be accelerated by microwave irradiation and how the size of the crystals obtained is affected. The cover shows crystallization curves and the size of crystals obtained according to the use of two different methods, microwave and conventional electric heating, in nucleation and crystallization steps.

Synthesis of microporous materials using macrocycles as structure directing agents

The synthesis of microporous materials has been an important element of solid state chemistry over the past years and remains so today. The emergence of possible new applications has driven interest towards synthesis of new materials. This article reviews the application of macrocycles as structure-directing agents (SDAs) in the pursuit of these important new materials.

Non-thermal calcination by ultraviolet irradiation in the synthesis of microporous materials

We describe a new photochemical method near room temperature conditions for the removal of organic structure-directing agents in the synthesis of microporous materials. The method relies on the exposure of the sample to short-wavelength ultraviolet (UV) radiation in air and the ozone environment generated by a medium pressure mercury lamp (184–257 nm). The generality of the approach has been confirmed using three test-cases of microporous materials: a high-silica synthetic zeolite, an aluminophosphate, and a Ge-substituted microporous silica. The structures and organic contents of the microporous materials before and after UV/ozone treatment were determined using a combination of X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and nitrogen adsorption isotherms. For all three cases, the UV/Ozone treatment allows complete removal of the organic template while retaining the inorganic framework. The overall integrity of the microporous materials was comparable to or better than for materials derived by thermal calcination. This method is applicable in making new materials from organic–inorganic precursors and holds promise for microporous thin films on thermally sensitive substrates and for controlled spatial patterning.

The kinetics and mechanisms of the crystallisation of microporous materials

The synthesis of microporous materials is one of the major activities in contemporary solid state chemistry. This perspective brings together the current thinking regarding the synthesis and growth mechanisms of these technologically important materials. Also reviewed are the latest experiments being utilised to probe the complex chemistry which occurs during the synthesis of these materials.

Following the Crystallization of Microporous Solids Using EDXRD Techniques

Energy dispersive X-ray diffraction (EDXRD) techniques are applied to study the development of crystalline phases during the synthesis of microporous materials. We present data for both zeolite A and AlPO-5 systems. We explore the effects of template concentration and of temperature. The measured activation energy for zeolite A of ∼58 kJ mol-1 accords well with that observed for other silicate systems. The kinetics revealed by our study accord with the nucleation/growth model of the Avrami−Erofeev treatment.

Cooperative Structure Direction in the Synthesis of Microporous Materials: Preparation and Crystal Structure of TREN-GaPO

A unique, large-pore gallium oxyfluorophosphates has been synthesized by using a combination of two structure-directing amines: tris(2-aminoethyl)amine (TREN) and pyridine. TREN−GaPO has two parallel channel systems delineated by 12- and 8-membered rings, and the organic amines are found to be ordered in these two channels.

Simulation studies on the role of templating organic molecules in the synthesis of microporous materials: 2. Modelling the electronic interaction between the templating molecules and ZSM-5

Several templating organic molecules lead to the synthesis of ZSM-5. In the previous part of this series, we attempted to bring out the common features and amplify the qualities of tetrapropyl ammonium compounds (TPA) which make it best among the lot. Here, we report the interaction of various organic molecules with a suitable cluster model of ZSM-5 framework studied by MNDO calculations. The influence of the nature of the functional group and the alkyl group on the electronic interaction is studied systematically. The orientation of the template and the actual conformation of the ‘template-framework’ complex are decided based on the X-ray crystal structure reports and the MNDO energetics. It has been shown that quantum chemical calculations could be successfully utilized for the generalised description of the importance of several complex interactions which are mutually present.

Energetics of microporous materials

The enthalpies of formation of a series of high-silica zeolites are only 8–14 kJ/mol less exothermic than that of quartz, with a very weak dependence on volume (framework density), despite a factor of two variation in those parameters. Several mesoporous silicas, with pore diameters in the range 3–5 nm, also are only 14 kJ/mol less stable energetically than quartz. Thus, in the microporous and mesoporous regime, the energy appears to level off at values only about 14 kJ/mol less stable than quartz, with the pores behaving energetically like an inert second phase. Similar trends are seen for AlPO4 zeolites, and for a dehydrated CaAl silicate zeolite. These data suggest that the synthesis of microporous materials is not limited by their energetics but by finding appropriate kinetic pathways for their formation.

ChemInform Abstract: The Opportunities of the Fluoride Route in the Synthesis of Microporous Materials

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.