Global Dialogue on Nanotechnology and the Poor ... - Nanowerk

nanotechnology,
water, & development
[3.3.1] Nanoparticles for the Catalytic Degradation
of Water Pollutants
A catalyst is a substance that promotes the chemical reaction of
other materials without becoming permanently involved in the
reaction. Researchers are exploring how nanocatalysts such as
titanium dioxide (TiO 2) and iron nanoparticles can be used to
degrade organic pollutants and remove salts and heavy metals
from liquids. People expect that nanoelectrocatalysts will enable
the use of heavily polluted and heavily salinated water for drinking,
sanitation, and irrigation. 70 Using catalytic particles either dispersed
homogeneously in solution or deposited onto membrane structures
could chemically degrade pollutants instead of simply moving them
somewhere else. Catalytic treatment of polluted water could be
specifically targeted to degradation of chemicals for which existing
technologies are inefficient or cost prohibitive.
Researchers are experimenting with, for example, a method using
nanoscale zero-valent iron as a catalyst to remove arsenic from
groundwater. 71 Other researchers are developing an iron-storage
protein that consists of a native nano-size iron oxide core that may
serve as catalysts in (photo)chemical degradation processes of
common contaminants.
Several companies are developing applications that are already
on the market or will be soon. For instance, U.S.-based Inframat
Corporation is developing a material composed of a highly porous
nanofibrous structure that can be used to remove arsenic from
drinking water by combining a nanofibrous MnO 2 oxidative process
with a granular ferric hydroxide adsorptive process. 72 The technology
supposedly circumvents the limitations of today’s active-site
nanoparticulate materials that have a strong tendency to form
agglomerates, which limit the permeability of the reactive
constituents into and through the agglomerated mass. Another
company, EnvironmentalCare from Hong Kong, has developed
a nano-photocatalytic oxidation technology for the removal of
bacteria and pollutants from water. 73 It uses nano-coated TiO 2
filters that trigger a chemical process, which converts harmful
pollutants into the harmless end products of carbon dioxide
and water. In photocatalysis, water passing through a nanomaterial
is also subjected to ultraviolet light, leading to the destruction
of contaminants.
‘‘
Catalytic treatment of polluted
water could be specifically targeted
to degradation of chemicals for
which existing technologies are
’’
inefficient or cost prohibitive.
Another example of potentially promising research is provided by
researchers in the United States at the Universities of Illinois and
Pittsburgh and Yeshiva University who are exploring the use of
nanocatalysts to reduce pollution of oxidized contaminants
(e.g., nitrates). Presently, nitrate in drinking water is either not
removed or it is removed using ion exchange resins.The former
presents health risks, and the latter is expensive because waste
streams must still be treated when the resins are regenerated.
Nitrate is a stable and highly soluble ion with a low potential for
co-precipitation or adsorption so that removal of nitrates using
conventional water treatment is difficult.This research focuses on
identifying the most promising catalysts (e.g., bimetallic metal
catalysts such as Pd-Cu) to use for the reduction of nitrate and
other oxidized compounds and to gain fundamental understanding
of the reactivity and selectivity of these new catalytic materials. 74
Researchers at Rice University in the United States are exploring
nanocatalysts to remove tri-cholorethylene and organic aromatic
contaminants, mainly pesticides, from groundwater. 75 The researchers
suggest that although each system requires a different catalyst and
overall remediation strategy, nanoscale engineering of materials
permits the design of more efficient systems. For instance, the
researchers have developed a new way to produce high surface area
(> 250 m2/gm) nanocrystalline titania, which under UV illumination
is capable of photo-oxidizing a variety of molecules. Additionally,
ongoing work on the environmental implications of fullerenes,
particularly C 60, led these researchers to hypothesize that the oxygen
radical production capabilities of nanoscale C 60 aggregates in water
could be leveraged for degradation of contaminants.
70
“Forging Ahead:Technological Innovation and the Millennium Development Goals,”Task Force on Science,Technology, and Innovation, UN Millennium Project, November 8, 2004,
.
71
U.S. Department of Commerce,“U.S. EPA Workshop on Nanotechnology for Site Remediation,” Washington, DC, October 20 – 21, 2005,
; and L. McDowall,“Degradation of Toxic Chemicals by Zero-Valent Metal Nanoparticles – A
Literature Review,” Commonwealth of Australia, 2005, .
72
Inframat, “Description of Nanofibrous MnO2 Bird’s-Nest Superstructure Catalyst,” .
73
Nano-Fotocide, .
74
H. Xu et al.,“Structural Changes of Bimetallic PdX/Cu (1-X) Nanocatalysts Developed for Nitrate Reduction of Drinking Water,” Materials. Research Society Symposium Proceedings,
Vol. 876E, 2005, .
75
Center for Biological and Environmental Nanotechnology, “Nanocatalysts for Remediation of Environmental Pollutants,”
.
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