Environmental Engineering Reference
In-Depth Information
arsenic, chromate) from water [64-66]. The important parameter is the partition coefi-
cient of the soluble species between the hydrogel and water. We have shown that loading
conducting polymers [67] into the nanoporous hydrogel could signiicantly increase the
partition of some species (e.g., tryptophan) into the material [68].
Several materials could be used to make nanocomposites with nanoporous carbon or
nanoporous hydrogels, effectively changing the materials' properties.
2.1.2.3 Conducting Polymers
Conducting polymers are doped by counterions (anions or cations) behaving as polyelec-
trolytes that can exchange inert ions with toxic ones [69]. Additionally, since the oxidation/
reduction of conducting polymers involves ion exchange, the oxidation state depends on
the concentration of ions in solution [70]. Therefore, conducting polymers can be used for
sensing [71] and/or removal [72] of toxic ions present in water.
2.1.2.4 Nanoparticles
Metal (e.g., gold) nanoparticles constitute one of the earliest examples of artiicial nanopar-
ticles [73] and are the most extensively studied nanotechnology objects [74]. The large surface
area allows them to adsorb toxic substances present in water [75]. Metal nanoparticles have
been extensively used as electrocatalysts in fuel cell research, and have potential use in elec-
troanalysis [76] and electrochemical incineration of organic compounds [77]. PtRu catalysts
are the most active for methanol oxidation [78], likely due to the formation of Ru oxides in the
surface that are able to oxidize adsorbed poisons like CO. Such behavior would allow oxida-
tion of other organic species of analytical interest that do not present reversible redox couples
but have oxygenated groups or C-H bonds that can be irreversibly oxidized. Analogously,
harmful organic compounds can be completely oxidized by active electrocatalysts.
Metal oxide nanoparticles (e.g., magnetite, Fe
3
O
4
) strongly adsorb toxic ions (e.g., arsenite)
and can be used to remove them from water [79]. Conducting polymers can also be made
into the form of nanoparticles [80]. The high surface area and small size makes adsorp-
tion favorable and diffusion inside the particles fast. Water puriication using nanoporous
materials can be made by a variety of processes: physical [81] or chemical adsorption of
soluble species [82]; electrochemical [83], photochemical [84], or catalytic complete oxida-
tion of organics [85]; electrochemical capacitive deionization [86]; absorption of soluble
species in cross-linked polymers [87]; etc.
In the present chapter, we will describe different methods to synthesize nanoporous
materials (carbon and hydrogels), to load them with conducting polymers or nanoparticles
(metal and metal oxide), and to use them in aquatic nanotechnology.
2.2 How to Make Nanoporous Materials and Nanocomposites
2.2.1 Nanoporous Carbon
One way to form porous carbon involves producing porous precursor resins, such as RF,
which are then converted into glassy carbon by carbonization. Ambient air-drying of RF
gels gives nonporous resins (xerogels) by the collapse of the gel due to surface tension
forces at the water/air interface during drying (Scheme 2.1). To avoid that, the gels could
