18
Nanoporous Materials
A. K. Cheetham and P. M. Forster
18.1
Introduction
The scope of this chapter concerns crystalline inorganic and hybrid inorganic–
organic materials that exhibit periodic porosity in the nanometer range. The prototypic systems of the inorganic class are the aluminosilicate zeolites, which have
regular channels with diameters that range between approximately 0.3 and 1.0 nm.
Such channels are able to accommodate relatively small inorganic and organic
molecules, thereby facilitating a wide range of commercial applications as well as
fundamental studies of molecules in confined spaces. We shall explore the growing
chemical and structural diversity of such materials. Amorphous materials, such as
activated carbons, which exhibit nanoporosity on a similar length-scale, will not be
discussed. Nor shall we cover mesoporous silicas and related materials, since they
are non-crystalline.
There has been an enormous growth in the chemical diversity of openframework and nanoporous materials* during the last 20 years [1]. Prior to the
early 1980s, when the nanoporous aluminum phosphates were first reported by
Flanigen and co-workers [2], the aluminosilicate zeolites and closely related systems represented the predominant class of nanoporous materials with threedimensional crystalline structures. The extent of the change during recent years
can be judged from the fact that as many as 35 elements of the main block and
the transition series are now known to participate as major components of such
frameworks, and the number is increasing rapidly. Most are based upon oxygencontaining materials, especially phosphates, but there is a growing list of examples
based upon other chemistries, such as oxyfluorides [3], nitrides [4], sulfides [5],
and halides [6]. The range of systems has also increased in another sense: whereas
the zeolites and early AlPO 4 s were based entirely upon corner-sharing tetrahedra,
* There is much inconsistency in the literature
regarding the use of the terms ‘‘openframework’’ and ‘‘nanoporous’’. Here, we use
open-framework to refer to materials with open
architectures, and use nanoporous to refer
specifically to materials where porosity has been
demonstrated through surface area or ion
exchange experiments.
589
Nanoporous Materials
A. K. Cheetham and P. M. Forster
18.1
Introduction
The scope of this chapter concerns crystalline inorganic and hybrid inorganic–
organic materials that exhibit periodic porosity in the nanometer range. The prototypic systems of the inorganic class are the aluminosilicate zeolites, which have
regular channels with diameters that range between approximately 0.3 and 1.0 nm.
Such channels are able to accommodate relatively small inorganic and organic
molecules, thereby facilitating a wide range of commercial applications as well as
fundamental studies of molecules in confined spaces. We shall explore the growing
chemical and structural diversity of such materials. Amorphous materials, such as
activated carbons, which exhibit nanoporosity on a similar length-scale, will not be
discussed. Nor shall we cover mesoporous silicas and related materials, since they
are non-crystalline.
There has been an enormous growth in the chemical diversity of openframework and nanoporous materials* during the last 20 years [1]. Prior to the
early 1980s, when the nanoporous aluminum phosphates were first reported by
Flanigen and co-workers [2], the aluminosilicate zeolites and closely related systems represented the predominant class of nanoporous materials with threedimensional crystalline structures. The extent of the change during recent years
can be judged from the fact that as many as 35 elements of the main block and
the transition series are now known to participate as major components of such
frameworks, and the number is increasing rapidly. Most are based upon oxygencontaining materials, especially phosphates, but there is a growing list of examples
based upon other chemistries, such as oxyfluorides [3], nitrides [4], sulfides [5],
and halides [6]. The range of systems has also increased in another sense: whereas
the zeolites and early AlPO 4 s were based entirely upon corner-sharing tetrahedra,
* There is much inconsistency in the literature
regarding the use of the terms ‘‘openframework’’ and ‘‘nanoporous’’. Here, we use
open-framework to refer to materials with open
architectures, and use nanoporous to refer
specifically to materials where porosity has been
demonstrated through surface area or ion
exchange experiments.
589