sc5b00369_si_002.cif (26.33 kB)
Topological Analysis of Void Spaces in Tungstate Frameworks: Assessing Storage Properties for the Environmentally Important Guest Molecules and Ions: CO2, UO2, PuO2, U, Pu, Sr2+, Cs+, CH4, and H2
dataset
posted on 2015-09-08, 00:00 authored by Jacqueline M. Cole, Alisha
J. Cramer, Anita ZeidlerThe identification of inorganic materials,
which are able to encapsulate
environmentally important small molecules or ions via host–guest
interactions, is crucial for the design and development of next-generation
energy sources and for storing environmental waste. Especially sought
after are molecular sponges with the ability to incorporate CO2, gas pollutants, or nuclear waste materials such as UO2 and PuO2 oxides or U, Pu, Sr2+, or
Cs+ ions. Porous framework structures promise very attractive
prospects for applications in environmental technologies, if they
are able to incorporate CH4 for biogas energy applications
or to store H2, which is important for fuel cells, e.g.,
in the automotive industry. All of these applications should benefit
from the host being resistant to extreme conditions such as heat,
nuclear radiation, rapid gas expansion, or wear and tear from heavy
gas cycling. As inorganic tungstates are well known for their thermal
stability and their rigid open-framework networks, the potential of
Na2O–Al2O3–WO3 and Na2O–WO3 phases for such applications
was evaluated. To this end, all known experimentally determined crystal
structures with the stoichiometric formula MaM′bWcOd (M = any element) are surveyed
together with all corresponding theoretically calculated NaaAlbWcOd and NaxWyOz structures that are statistically likely to form. Network descriptors
that categorize these host structures are used to reveal topological
patterns in the hosts, including the nature of porous cages, which
are able to accommodate a certain type of guest; this leads to the
classification of preferential structure types for a given environmental
storage application. Crystal structures of two new tungstates NaAlW2O8 (1) and NaAlW3O11 (2) and one updated structure determination
of Na2W2O7 (3) are also
presented from in-house X-ray diffraction studies, and their potential
merits for environmental applications are assessed against those of
this larger data-sourced survey. Overall, results show that tungstate
structures with three-nodal topologies are most frequently able to
accommodate CH4 or H2, while CO2 appears
to be captured by a wide range of nodal structure types. The computationally
generated host structures appear systematically smaller than the experimentally
determined structures. For the structures of 1 and 2, potential applications in nuclear waste storage seem feasible.