Introduction - Nanotechnologies for Water Environment Applications - page 7

Atomic Force Microscope (AFM) or other scanning probes, and can not only image
biochemical activity but also monitor the changes in the cell/tissue topology during the
imaging (ScienceDaily, 2005) .
Applications of nanotechnologies bring about the solution to sustainability
issues. For example, lighter-weight NMs allow us to lighten our transportation products
thereby burning less fuel, resulting in emitting fewer greenhouse gases. Substituting the
clay-polypropylene nanocomposite materials or aluminum for steel in 1-year's fleet of
vehicles in the U.S. would result in an energy savings of 50-240 thousand tera joules, a
reduction of 4-6 million tons of CO 2 equivalents of greenhouse gases released, and a
saving of 5-6 million tons of ore, and as much as 7 fewer occupational fatalities (Lloyd
and Lave, 2003). As another example, buckypaper (made from tube-shaped carbon
molecules 50,000 times thinner than a human hair) is envisioned as a wondrous new
material for light, energy-efficient aircraft and automobiles, improved TV screens, more
powerful computers, and many other products (Kaczor, 2008).
Environmental applications of NMs cover areas much broader than water
environments, such as reduction of environmental burden (the green process and
engineering, process emission control, and desulfurization/denitrification of non-
renewable energy sources, agriculture and food systems), reduction/treatment of
industries and agricultures wastes (converting wastes into valuable products,
groundwater remediation, adsorption and photocatalytic degradation, nanomembranes),
and NPS pollution control. NMs, used as catalysts, adsorbents, membranes, and
additives, show higher activities, capabilities, and superior properties due to their high
specific areas and nano-sized effects. Thus, lower quantities of NMs can be used for
reduction/treatment of environmental wastes with higher efficiencies and lower costs.
For example, carbon nanotube (CNT) membranes have been made and tested recently
for the transport of Ru(NH 3 ) 6 3+ , multiple components of heavy hydrocarbons from
petroleum, bacteria, water, ethanol, iso -propanol, hexane, and decane. The CNT
membrane (pore diameter = ~7 nm, membrane thickness = 34-126 m, density = 3.4 x
10 9 /cm 2 ) allows water flux to be 10 4 -10 5 times the flux predicted by Hagen-Poiseuille
(H-P) equation; the gas and water permeability of these CNT membranes are several
orders of magnitude higher than those of commercial polycarbonate membranes
(diameter = 15 nm), despite having pore sizes of an order of a magnitude smaller. Thus,
CNT membranes allow us to design much more efficient treatment processes for
drinking water treatment, desalinization, and wastewater treatment (e.g., secondary
sedimentation tanks can be replaced with CNT membrane modules).
Carbon nanotube and other nanocomposite materials, however, are currently very
expensive; the challenge, therefore, is to improve their production yields and lower the
costs of these materials for their use in large quantity. In some cases (e.g., emission
control of the pollutants) alternative low-cost or non-toxic NMs (such as WC x ) are used