Introduction - Nanotechnologies for Water Environment Applications - page 4

binding, nanoclay polymer composites, nanomembranes and photocatalyst for water
purification, new dental composites, etc. The third generation is between 2015 and 2045
with various assembly techniques, networking being at the nanoscale and new
architectures. 3-D nanosystems and molecular nanosystems will be realized during this
period, which will revolutionize both human and natural ecosystems. For example,
many engineered systems such as energy, transportation security systems may be totally
different by then. Most of the Grand Challenges identified by the National
Nanotechnology Initiative will be solved (NNI, 2000). While it seems that some of
these are a long way off, these changes will come faster than what we believe.

1.3 Environmental Applications

Although NMs promise to revolutionize many of our industries, the near term
uses are in environmental remediation and green chemistry applications, which include
(but not limited to): treatment and remediation of contaminated sites (e.g., soil,
sediment), water and wastewater; nanocatalyst- or nanotechnology-enabled
environmental benign nanomanufacturing and green process/engineering; energy and
power; as well as environmental detection and monitoring with sensor/sensor networks.
Chapters 4-15 cover the status of current knowledge of these applications. This section
briefly outlines some of these applications and the recent development/trend.

It is difficult to track when NMs were first used for environmental applications.
The NP-based catalytic converter placed in the exhaust manifold of automobiles since
the early 1970's may be viewed as the earliest success applications of nanocatalyst
(Larsen, 2005). Some studies of synthesizing NPs for environmental remediation
occurred in early 1990s (e.g., Dr. Klabunde synthesized several different nanocrystalline
metal oxides during that time. See Glavee et al., 1995). Since 1996, zero-valent NPs
(NZVI) have been used for environmental remediation of different sites contaminated by
inorganic and organic pollutants. Applications of NZVI evolved into several different
directions for research and applications. One is to develop different zero-valent metals
such as zero-valent aluminum and bimetallic NPs. For example, bimetallic Fe/Al NPs
can prevent the formation of a passive layer at the iron surface, and thus, maintain the
reactivity of iron. Bimetallic Cu/Al NPs can dechlorinate dichloromethane that can't be
degraded by bimetallic or conventional NZVI. Another direction is to develop magnetic
Fe (or Fe related) NPs for easier separation after their use. These magnetic NPs can be
used for sediment remediation and efficient drug delivery. The third direction is to
modify the surface properties by coating the NZVI (or other NPs) with different
chemicals with different functional groups. The surface-modified NPs may have much
higher stability or can be used to target underground pollutants [e.g., non-aqueous phase
liquids (NAPLs)] or to improve the traveling distance of NPs. Research on the second
and third direction often tangle with each other and with other areas (e.g., making