Nanoscale Porous Materials for Water Treatment: Advances and Challenges - Nanotechnologies for Water Environment Applications - page 316

host pore size, making it difficult for its removal. Hence, mesoporous zeolitic materials
which have a slightly bigger pore sizes (250 nm) have been developed since 1990s. In
general, such mesoporous zeolite single-crystal catalysts are shown to be both more
active and more selective than conventional zeolite catalysts. The superior catalytic
properties are ascribed to have improved mass transport in the mesoporous zeolite
crystals. Thus, mesoporous zeolite single-crystal catalysts combine the high acidity,
shape-selectivity, and hydrothermal stability of zeolites with efficient mass transport
(Christensen et al., 2003). A brief review on zeolites and molecular sieve syntheses has
been reported by (Davis and Lobo, 1992). Similar reviews on microporous and ordered
mesoporous materials syntheses and their applications as catalysts have also been
reported (Corma, 1997). Recently, NPM including zeolites have been reviewed
concerning their catalysis, hydrogen storage, waste water treatment, among others
(Logar and Kaui, 2006).
Figure 11.1 XRD patterns of the zeolite samples synthesized at room temperature for 44
(trace a), 73 (b), and 240 h (c). The inset shows the TEM micrograph of the 44-h
product, where the lattice fringes of 10-15 nm zeolite crystals embedded in an
amorphous matrix can be seen (Valtchev et al., 2005).