Metal organic frameworks molecular sieves

The past nearly six decades have seen a chronological progression in molecular sieve materials from the aluminosilicate zeolites to microporous silica polymorphs, microporous aluminophosphate-based polymorphs, metallosilicate and metaHo-phosphate compositions, octahedral-tetrahedral frameworks, mesoporous molecular sieves and most recently hybrid metal organic frameworks (MOFs). A brief discussion of the historical progression is reviewed here. For a more detailed description prior to 2001 the reader is referred to [1]. The robustness of the field is evident from the fact that publications and patents are steadily increasing each year. 

Up to now, a variety of non-zeolite/polymer mixed-matrix membranes have been developed comprising either nonporous or porous non-zeolitic materials as the dispersed phase in the continuous polymer phase. For example, non-porous and porous silica nanoparticles, alumina, activated carbon, poly(ethylene glycol) impregnated activated carbon, carbon molecular sieves, Ti02 nanoparticles, layered materials, metal-organic frameworks and mesoporous molecular sieves have been studied as the dispersed non-zeolitic materials in the mixed-matrix membranes in the literature [23-35]. This chapter does not focus on these non-zeoUte/polymer mixed-matrix membranes. Instead we describe recent progress in molecular sieve/ polymer mixed-matrix membranes, as much of the research conducted to date on mixed-matrix membranes has focused on the combination of a dispersed zeolite phase with an easily processed continuous polymer matrix. The molecular sieve/ polymer mixed-matrix membranes covered in this chapter include zeolite/polymer and non-zeolitic molecular sieve/polymer mixed-matrix membranes, such as alu-minophosphate molecular sieve (AlPO)/polymer and silicoaluminophosphate molecular sieve (SAPO)/polymer mixed-matrix membranes. 

Type I isotherms are characteristic of microporous solids having relatively small external surface area (activated carbons, molecular sieve zeolites, metal organic frameworks, etc.). They are usually obtained by most gases and vapors on activated carbons. 

Nanoporous materials like zeolites and related materials, mesoporous molecular sieves, clays, pillared clays, the majority of silica, alumina, active carbons, titanium dioxides, magnesium oxides, carbon nanotubes and metal-organic frameworks are the most widely studied and applied adsorbents. In the case of crystalline and ordered nanoporous materials such as zeolites and related materials, and mesoporous molecular sieves, their categorization as nanoporous materials are not debated. However, in the case of amorphous porous materials, they possess bigger pores together with pores sized less than 100 nm. Nevertheless, in the majority of cases, the nanoporous component is the most important part of the porosity. 

The search for new zeolite-like structures was initially extended to aluminophosphate-based molecular sieves,3 and these explorations produced a variety of exotic compounds with open-framework structures, which include besides metal phosphates,4 carboxylates,5 sulfates,6 selenites, and selenates.7 Growth of this area has been rapid in the past decade necessitating new editions of the Atlas of Zeolites.2 It is noteworthy that metal—organic framework (MOF) solids have been included as zeolite types in the latest edition of the Atlas of Zeolites. 

Key Words P-31 solid-state NMR, 31P CP/MAS, Ultra-fast MAS, Phosphorylated amino acids, Nucleotides, Nucleic acids, Phosphate glasses, Aluminophosphates, Molecular sieves, Catalysts, Polyoxometalate (POM), Metal-organic framework (MOF), Inclusion complexes. 

From natural zeolites to the recently discovered meso- and macro-porous materials, the ordered porous frameworks are all constructed by inorganic species. However, in the past ten years, a new family of porous compounds composed of metal-organic frameworks (MOFs) has attracted enormous attention. The main reason is that the poor thermal and chemical stability of MOFs has been somewhat improved. In addition, the discovery of some advantages of MOFs that are lacking in molecular sieves and mesoporous materials has also stimulated the research on MOFs. 

Series of Special Issues cover various aspects of microporous molecular sieves, metal-organic frameworks and ordered mesoporous materials. Synthesis principles, templating, formation mechanisms, characterization methods, functionalization strategies, and applications are discussed in excellent and comprehensive review articles and more specific research reports. 

Table 1 summarizes terms and phrases used in membrane science and technology. To have sufficiently high fluxes, the molecular sieve separation layer (zeolite, metal-organic framework) has to be in the pm-scale. Because such thin layers are not self-supporting for mechanical reasons, inorganic membranes are usually prepared as supported membranes (Fig. 1). 

Mixed matrix membranes (MMM) consist of a nanopaiticle filler like zeolite, metal-organic framework ionic liquid or carbon, in a continuous polymer phase thereby combining the molecular sieving or another property of the filler with the established processability of the polymers in one membrane. The concept of zeolite-based mixed matrix membranes is followed for more than 30 years. However, in most cases these zeolite-based MMMs did not show an improvement of the selectivity because of an imperfect embedding of the zeolite crystals into the polymer matrix as shown schematically in Fig. 19. 

Li YS, Liang FY, Bux H, Feldhoff A, Yang WS, Caro J. Molecular sieve membrane supported metal-organic framework with high hydrogen selectivity. Angew Chem Int Ed 2010 49 548-51. 

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