Zeolite-like carbon materials

Z. Yang, Y. Xia, and R. Mokaya, Enhanced Hydrogen Storage Capacity of High Surface Area Zeolite-like Carbon Materials, J. Am. Chem. Soc., 129, 1673-1679 (2007). 

In addition to mesostructured metal oxide molecular sieves prepared through supramolecular assembly pathways, clays, carbon molecular sieves, porous polymers, sol-gel and imprinted materials, as well as self-assembled organic and other zeolite-like materials, have captured the attention of materials researchers around the globe. Clays, zeolites and sol-gel materials are still very popular because of their extensive and expanding applications in catalysis and separation science. Novel carbons and polymers of ordered porous structures have been synthesized. There are almost unlimited opportunities in the synthesis of new organic materials of desired structural and surface properties via self-assembly or imprinting procedures. 

Sorption effects in the macroscopic scale are usually used for non-continuous pumping. They contain a highly porous sorption material like activated carbon or zeolites with a huge inner surface. The sorption material is usually cooled down by liquid nitrogen. They are regenerated by heating the sorption material to temperatures of several hundred degrees Celsius after a disconnection of pump and vacuum-chamber. 

This is very likely due to their very high reactivity, making deposition difficult and unwanted side reactions probable. Because the walls have uniform thickness (<1 nm), zeolites have been used as a template for the synthesis of ordered micro porous carbon materials [127-130] and they are tested for hydrogen physisorption [131]. 

Different porous materials, including oxides (a-AlaO. , Si02, Ti02), zeolites (Na-ZSM-5, H-ZSM-5, H-beta, Na-Y, and H-USY), carbon (activated carbon, Norit, and mesoporous carbon (Novacarb from MAST Carbon Ltd.)), cement-like materials (end and tras, with low and high lime content, respectively), and catalysts (1 wt.% Pt/ALOs, 5 wt.% Pt/AbOs, and 16 wt.% Ni/AbOa) were used, as well as home-made samples (AbOs, MCM-41, and SBA-15). 

Normally, carbon materials are characterised using the DFT which assumes a slit-like pore geometry [12]. However, these zeolite templated carbons are best described by the DFT-Hybrid... 

Yang Z, Xia Y and Mokaya R (2007), Enhanced hydrogen storage capacity of high surface area zeolite-like carbon materials , J Am Chem Soc, 129, 1673. 

Very recently, Yang et al. have successfully synthesised zeolite-like porous carbon materials that exhibit well-resolved powder XRD patterns... 

Zeolites are microporous crystalline aluminosilicates with a channel-like or cagelike pore structure with pore-opening sizes in the range of 0.3 to 1.5 nm [13]. The spatially periodic pore structure and well-defined nanospaces of zeolites offer opportunities to control the nanostructure and morphology of microporous carbon materials at the nanometer level. As schematically illustrated in Figure 2.1, zeolite pores can be filled wifh a carbon precursor such as furfuryl alcohol (FA). After a proper treatment, followed by removal of the zeolite framework, a carbon nanostructure with pores replicated from the zeolite framework is obtained. Over the past decade, many zeolite templates (e.g., zeolite Y, zeolite (3, and ZSM-5) and carbon precursors (e.g., FA, phenol-formaldehyde, and sucrose) have been... 

The adsorption process consists of the concentration of chromium ions on the surface of the sorbent. In comparison with conventional methods, such as membrane filtration or ion exchange, it has significant advantages like low cost, availability, and ease of operation. A variety of natural and synthetic materials has been used as Cr(VI) sorbents, including activated carbon, biological materials, zeolites, chitosan, and agricultural or industrial wastes. Biosorption of chromium from aqueous solutions is a relatively new process that has proven very promising in the removal of contaminants from aqueous effluents. 

For industrial purposes the most important sorbents are activated carbons and zeolites which are available in a great variety of different forms (powder, pellets, fibers, membranes etc.) having different properties [1.27, 1.28]. Besides many other sorbents are investigated and synthesized today being based on either natural materials like peat or coal or natural gas and crude oil leading - for example - finally to porous polymeric materials etc. [1.26]. 

Equilibria states of pure or mixed gases adsorbed on the (external and internal) surface of porous materials like activated carbons or zeolites can be measured by using any of the basic physical properties of matter like its extensivity in space, gravity, inertia or molecular structure. An overview of these properties and resulting measurement methods is given in Table 1 below. Also, possibilities for combinations of these methods to measure gas mixture or so-called coadsorption equilibria are indicated. 

The adsorption isotherms are often Langmuirian in type (under conditions such that multilayer formation is not likely), and in the case of zeolites, both n and b vary with the cation present. At higher pressures, capillary condensation typically occurs, as discussed in the next section. Some N2 isotherms for M41S materials are shown in Fig. XVII-27 they are Langmuirian below P/P of about 0.2. In the case of a microporous carbon (prepared by carbonizing olive pits), the isotherms for He at 4.2 K and for N2 at 77 K were similar and Langmuirlike up to P/P near unity, but were fit to a modified Dubninin-Radushkevich (DR) equation (see Eq. XVII-75) to estimate micropore sizes around 40 A [186]. 

The use of FOSS polyhedra as models for silica surfaces or as secondary building units in inorganic materials such as zeolites or other porous solids is likely to increase rapidly as more is understood about the mechanisms by which the polyhedra may be constructed. It will be of particular interest to see if the larger structures such as TeoHeo or T240H240 or their derivatives (Section VII.C) and analogous to carbon structures such as Cgo or nanotubes, can be prepared. 

Nowadays synthesis of mesoporous materials with zeolite character has been suggested to overcome the problems of week catalytic activity and poor hydrothermal stability of highly silicious materials. So different approaches for the synthesis of this new generation of bimodal porous materials have been described in the literature like dealumination [4] or desilication [5], use of various carbon forms as templates like carbon black, carbon aerosols, mesoporous carbon or carbon replicas [6] have been applied. These mesoporous zeolites potentially improve the efficiency of zeolitic catalysis via increase in external surface area, accessibility of large molecules due to the mesoporosity and hydrothermal stability due to zeolitic crystalline walls. During past few years various research groups emphasized the importance of the synthesis of siliceous materials with micro- and mesoporosity [7-9]. Microwave synthesis had... 

The category of builders consists predominantly of several types of materials -specific precipitating alkaline materials such as sodium carbonate and sodium silicate complexing agents like sodium triphosphate or nitrilotriacetic acid (NTA) and ion exchangers, such as water-soluble polycarboxylic acids and zeolites (e.g., zeolite A). 

MOF-177 has been demonstrated to act like a super sponge in capturing vast quantities of carbon dioxide at room temperature. At moderate pressure (about 35 bar), its voluminous pores result in a gravimetric CO2 uptake capacity of 33.5 mmol/g, which far exceeds those of the benchmark adsorbents zeolite 13X (7.4 mmol/g at 32 bar) and activated carbon MAXSORB (25 mmol/g at 35 bar). In terms of volume capacity, a container filled with MOF-177 can hold about twice the amount of CO2 versus the benchmark materials, and 9 times the amount of CO2 stored in an empty container under the same conditions of temperature and pressure. 

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