about 16 bar. The size of the crystals can be tuned between 30 nm and 10,000 nm.
The hexagonal ZL crystals, which typically feature approximately cylindrical morphology, can be obtained with various aspect ratios ranging from elongated to barreland disc-shaped using this method [26, 27].
It is interesting that variations of ZL synthesis procedure including studies
regarding the mechanism of formation of the crystals continue to attract interest of
researchers despite of the fact that the first synthesis goes back to the 1968 report of
Breck and Flaningen [10, 11]. The reason for this is that the large scale of different
applications under investigation demand for different specific morphologies, sizes,
and purities of the crystals and that the properties and size distribution of the
resulting crystals depend critically on small changes of the reaction conditions
which are the chemical compositions of alumina, silica, potassium hydroxide,
water, the temperature, and the reaction time. It is also influenced by stirring and
different types of additives. The parameters which influence size, morphology, as
well as size and shape distribution are still only partially understood [28–38]. Hydrothermal synthesis of high-quality ZL crystals with tunable size and morphology
using microwave heating was reported. Crystals of different length and shape have
been obtained in this manner [39].
Assembling zeolite crystals into well-defined macroscopic structures is of particular interest, considering that zeolites are ideal host materials for a large variety of
molecules, complexes, and clusters. In device chemistry, a high degree of supramolecular organization is important for attaining the desired macroscopic properties. A
possibility for achieving such organization is the controlled assembly of the ZL
crystals into oriented structures and the preparation of mono-directional materials.
3 Guests
It may be surprising, to learn how many different guest and combinations of guest
have been inserted into the 1 nm channels of ZL. Methods that have been used are
cation exchange, insertion of neutral guest from the gas phase and from an inert
solvent, pressure-supported insertion, and ship-in-a-bottle synthesis. We list the
currently known guest in Tables 1, 2, and 3. It seems that template synthesis
procedures have not been very successful for the preparation of well-defined ZL
composites.
ZL allows, through geometrical constraints, the realization of extremely high
concentrations of well-oriented molecules that behave essentially as monomers or as
very weakly interacting monomers. A 30 nm  30 nm crystal can host 5,000 guests
that occupy 2 u.c., and a 60 nm  60 nm crystal can host up to 40,000 guests of this
size. It is convenient to introduce a parameter bearing information on the dye
concentration but based on the purely geometrical (space-filling) properties of ZL
as a host (i.e., showing to what extent the ZL channels are filled with guests). The
loading or occupation probability p of a guest-ZL composite is defined by Eq. (3):
6
G. Calzaferri
The hexagonal ZL crystals, which typically feature approximately cylindrical morphology, can be obtained with various aspect ratios ranging from elongated to barreland disc-shaped using this method [26, 27].
It is interesting that variations of ZL synthesis procedure including studies
regarding the mechanism of formation of the crystals continue to attract interest of
researchers despite of the fact that the first synthesis goes back to the 1968 report of
Breck and Flaningen [10, 11]. The reason for this is that the large scale of different
applications under investigation demand for different specific morphologies, sizes,
and purities of the crystals and that the properties and size distribution of the
resulting crystals depend critically on small changes of the reaction conditions
which are the chemical compositions of alumina, silica, potassium hydroxide,
water, the temperature, and the reaction time. It is also influenced by stirring and
different types of additives. The parameters which influence size, morphology, as
well as size and shape distribution are still only partially understood [28–38]. Hydrothermal synthesis of high-quality ZL crystals with tunable size and morphology
using microwave heating was reported. Crystals of different length and shape have
been obtained in this manner [39].
Assembling zeolite crystals into well-defined macroscopic structures is of particular interest, considering that zeolites are ideal host materials for a large variety of
molecules, complexes, and clusters. In device chemistry, a high degree of supramolecular organization is important for attaining the desired macroscopic properties. A
possibility for achieving such organization is the controlled assembly of the ZL
crystals into oriented structures and the preparation of mono-directional materials.
3 Guests
It may be surprising, to learn how many different guest and combinations of guest
have been inserted into the 1 nm channels of ZL. Methods that have been used are
cation exchange, insertion of neutral guest from the gas phase and from an inert
solvent, pressure-supported insertion, and ship-in-a-bottle synthesis. We list the
currently known guest in Tables 1, 2, and 3. It seems that template synthesis
procedures have not been very successful for the preparation of well-defined ZL
composites.
ZL allows, through geometrical constraints, the realization of extremely high
concentrations of well-oriented molecules that behave essentially as monomers or as
very weakly interacting monomers. A 30 nm  30 nm crystal can host 5,000 guests
that occupy 2 u.c., and a 60 nm  60 nm crystal can host up to 40,000 guests of this
size. It is convenient to introduce a parameter bearing information on the dye
concentration but based on the purely geometrical (space-filling) properties of ZL
as a host (i.e., showing to what extent the ZL channels are filled with guests). The
loading or occupation probability p of a guest-ZL composite is defined by Eq. (3):
6
G. Calzaferri