Microporous sulfides

The microporous sulfides are synthesized hydrothermally in the presence of alkylammonium templating agents. The GeS4-based composihons include one or more framework-incorporated metals Mn, Fe, Co, Ni, Cu, Zn, Cd and Ga. Over a dozen novel shuctures were reported which have no analogs in the microporous oxides. Ozin et al. have extended this work to a large number of microporous sulfides and selerhdes [53]. It should be noted that the microporous sulfides and selenides are prone to shucture collapse upon calcinahon to remove the template species. 

O.M. Yaghi, Z. Sun, and D. Richardson, Directed Transformation of Molecules to Solids Synthesis of a Microporous Sulfide from Molecular Germanium Sulfide Cages. J. Am. Chem. Soc., 1994, 116, 807-808. 

Encapsulation in Y zeohte was also the method chosen to immobihze Mn complexes of C2-symmetric tetradentate hgands (Fig. 24) [75]. These materials were used as catalysts for the enantioselective oxidation of sulfides to sulfoxides with NaOCl. The lack of activity when the larger io-dosylbenzene was used as an oxidant was interpreted as an indication that the reaction took place inside the zeolite microporous system. Both the chemo- and enantioselectivity were dependent on the structure of the sulfide. (2-Ethylbutyl)phenylsulfide led to better results than methylphenylsulfide, although in all cases the enantioselectivity was low (up to 21% ee). 

Fukishi and Hiiro [222] determined sulfide in seawater by this technique. The method is based on the generation of hydrogen sulfide by the addition of sulfuric acid to the water sample. The gas permeated through a microporous polytetrafluoroethylene (PTFE) tube, and was collected in a sodium hydroxide solution. The carbon dioxide in the permeate was removed by adding a barium cation-exchange resin to the sodium hydroxide solution. Injection into the... 

Kameyama, T., M. Dokiya, K. Fukuda and Y. Kotera. 1979. Differential permeation of hydrogen sulfide through a microporous vycor-type glass membrane in the separation system of hydrogen and hydrogen sulfide. Separ. Sci. Technol. 14(10) 953-957. 

In the late 1980s Bedard et al. reported the discovery of microporous metal sulfides, based on germanium (IV) and Sn (IV) sulfide frameworks [52]. 

Bedard, R.L, Wilson, S.T., Vail, L.D., Bennett, J.M., and Flanigen, E.M. (1989) The next generation synthesis, characterization, and structure of metal sulfide-based microporous solids, in Zeolites Facts, Figures, Future (eds... 

The radius in the micropore and hence the constricted diffusivity in the micropore are functions of position in the micropore x, location of the microsphere in the pellet ra, and time due to the deposition of the metal sulfide. The micropore radius R at time t is determined by the deposition... 

Concurrently with the work on carbon dioxide and hydrogen sulfide at General Electric, Steigelmann and Hughes [27] and others at Standard Oil were developing facilitated transport membranes for olefin separations. The principal target was the separation of ethylene/ethane and propylene/propane mixtures. Both separations are performed on a massive scale by distillation, but the relative volatilities of the olefins and paraffins are so small that large columns with up to 200 trays are required. In the facilitated transport process, concentrated aqueous silver salt solutions, held in microporous cellulose acetate flat sheets or hollow fibers, were used as the carrier. 

The replacement of framework anions (i.e. with chalcogens (e.g. S ) represents a more recent approach for generating microporous materials. The efforts to make microporous chalcogenides began with germanium or tin sulfides. However, germanium or tin sulfides do not form microporous materials similar to all-silica polymorphs of zeolites. It was later found that the incorporation of low-valent cations such as Mn + into the Ge-S composition helped to generate 3D frameworks. 

Enzel et al. [37] applied AFM to nanoporous semiconductors based on tin (IV) sulfide and tin (IV) selenide. The surface structure of these materials displayed regular patterns of micropores, in agreement with expectations from the crystallographic projections of their bulk structures. AFM studies of silica have dealt with, e.g., amorphous silica gels [38] or... 

R. van Slooten, M. J. Bojan and W. A. Steele, Computer Simulations of the High-Temperature Adsorption of Methane in a Sulfided Graphite Micropore, Langmuir 10 (1994) 542-548. 

Later, Yaghi et al.[32] proposed an alternative route for the synthesis of these sulfides, in which crystals were obtained from the diffusion of an aqueous solution of the 3d metal into a solution of R-Ge4S10 complex at room temperature. In 1997, Martin and Greenwood133 successfully prepared a new class of microporous metal chlorides, named CZX-n, under solvothermal conditions (160°C) in benzene solution. The framework of CZX-1 is isostructural with the aluminosilicate sodalite (SOD), while CZX-2... 

R. Bedard, S. T. Wilson, L. D. Vail, J. M. Bennett, and E. M. Flanigen, The Next Generation Synthesis, Characterization and Structure of Metal Sulfide-based Microporous Solids. Stud. Surf. Sci. Catal., 1989, 49, 375-387. 

The history of mesoporous material synthesis is unintentionally or intentionally duplicating the development of zeolites and microporous molecular sieve. It starts from silicate and aluminosilicate, through heteroatom substitution, to other oxide compounds and sulfides. It is worth mentioning that many unavailable compositions for zeolite (e.g., certain transition metal oxides, even pure metals and carbon) can be made in mesoporous material form. 

It is too ideal for one Cd4S4 nanocluster to occupy one sodalite cage. In the treatment of zeolite with H2S many mesoporous defects will be produced, and these mesoporous defects may accommodate larger cadmium sulfide clusters. Therefore, in the microporous crystal with a particular structure, there may exist many different cadmium sulfide particles with various sizes. However, the content of these cadmium sulfide clusters located defects is usually limited, and, as a result, they have little effect on the electronic spectral properties of the composite. Detailed composition and structural analysis indicates that the nanoclusters contain not only Cd and S, but also O. In fact, these clusters can be written as Cd4(S,0)4. 

Besides cadmium sulfide, other semiconductor particles can also be loaded in zeolite microporous crystals. Moller et al. prepared cadmium sulfide nanoparticles in zeolite Y through a similar approach.[117] Nevertheless, structural analysis indicates that the formed cluster particles are actually rather complex, and apart from cadmium sulfide clusters, there exist other nanoclusters such as Cd404 or Cd202Se in the channels of zeolite Y. These nanoclusters are not isolated, and they strongly interact with the framework oxygen of the zeolite. 

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