Environmental Engineering Reference
In-Depth Information
higher selectivity for desired reaction products, helping to eliminate wasteful secondary
reactions, and reducing energy consumption (Samorjai and McCrea, 2001). Bimetallic
alloy nano-clusters were widely used as catalyst and can control its activity, selectivity,
and stability in certain reactions, which could reduce the consumption of chemical
reagents and production of hazardous substances (Lu et la., 1999). The bimetallic nano-
clusters dispersed on inorganic oxide supports such as Al 2 O 3 , SiO 2 , TiO 2 , and MgO,
have been studied to explore the properties of metal nano-clusters and the application in
green chemistry. Film reactors with environmentally benign nanostructured
photocatalyst films have been demonstrated to be effective in the synthesis of partial
oxygenates from different precursors (Sahle-Demessie et al., 1999). As an example, field
emission displays constructed with carbon nanotubes can provide better functionality
than the conventional cathode ray tubes that contain many toxic metals (Socolof et al.,
2001). Nontoxic and energy-efficient computer monitors are replacing those made of
cathode ray tubes (CRTs). Using carbon nanotubes in computer displays may further
diminish environmental impacts by eliminating toxic heavy metals and drastically
reducing material and energy use requirements, while providing enhanced performance
for consumer needs. Newer liquid crystalline displays are smaller, do not contain lead,
and consume less power than CRT computer monitors (Socolof et al., 2001). In contrast
to conventional processes that use harsh operating conditions and toxic materials, the
processes using nanomaterials are environmentally benign with less industrial wastes.
With increased emphasis on the green process, nanomaterials have also been
developed toward adoption and implementation of sustainable processes by minimizing
the use of toxic chemicals, solvents, and energy. Nanomaterials can assist resource
saving, energize batteries, and reduce energy consumption by the use of lightweight,
high strength materials based on carbon nanotubes and metal oxide frameworks as
hydrogen storage materials. For example, carbon nanotubes have many potential
applications, including conductive and high-strength composites, energy storage and
conversion devices, hydrogen storage media, interconnects, and so on (Baughman et al.,
2002). Nanostructured electrode materials have improved the performance of lithium ion
batteries. Toshiba's researchers have used nanoparticles (in the anode) in developing a
lithium-ion battery that recharges to 80% of its capacity in one minute. A prototype of
this battery has been discharged and recharged 1000 times with only a 1% decrease in its
capacity (Booker and Boysen, 2005). Stanford researchers have found a way to store the
lithium in a forest of tiny silicon nanowires, resulting in a new nanowire battery being
able to hold 10 times the charge of existing ones that power laptops, iPods, video
cameras, cell phones, and countless other devices (ScienceDaily, 2007). Batteries that
contain nanotubes attached to the surface of the electrodes have much long shelf life
because the nanotubes keep the chemicals separate from the electrodes when the battery
is not supplying current, while a normal battery, even when not supplying current, has
some reactions going on at a low level between its internal chemicals and its electrodes
(Krupenkin et al., 2003).
Search WWH ::




Custom Search