Porous manganese oxide garnished with gold
nanoparticles removes volatile organic compounds from air and breaks
them down.
In addition to nitrogen oxides and sulfur oxides,
many volatile organic compounds (VOCs) in air contribute to smog and
high ozone levels, as well as potentially damaging human health.
Clean-air laws are thus rightly continuing to become stricter. Most
modern air-purification systems are based on photocatalysts,
adsorbents such as activated charcoal, or ozonolysis. However, these
classic systems are not particularly good at breaking down organic
pollutants at room temperature. Japanese researchers have now
developed a new material that very effectively removes VOCs as well as
nitrogen- and sulfur oxides from air at room temperature. As they
report in the journal Angewandte Chemie, their system involves a
highly porous manganese oxide with gold nanoparticles grown into it.
In addition to nitrogen oxides and sulfur oxides,
many volatile organic compounds (VOCs) in air contribute to smog and
high ozone levels, as well as potentially damaging human health.
Clean-air laws are thus rightly continuing to become stricter. Most
modern air-purification systems are based on photocatalysts,
adsorbents such as activated charcoal, or ozonolysis. However, these
classic systems are not particularly good at breaking down organic
pollutants at room temperature. Japanese researchers have now
developed a new material that very effectively removes VOCs as well as
nitrogen- and sulfur oxides from air at room temperature. As they
report in the journal Angewandte Chemie, their system involves a
highly porous manganese oxide with gold nanoparticles grown into it.
To prove the effectiveness of their new catalyst,
the research team headed by Anil K. Sinha at the Toyota Central R&D
Labs carried out tests with acetaldehyde, toluene, and hexane. These
three major components of organic air pollution play a role indoors as
well as out. All three of these pollutants were very effectively
removed from air and degraded by the catalyst - significantly better
than with conventional catalyst systems.
One secret to the success of this new material is
the extremely large inner surface area of the porous manganese oxide,
which is higher than all previously known manganese oxide compounds.
This large surface area offers the volatile molecules a large number
of adsorption sites. Moreover, the adsorbed pollutants are very
effectively broken down. There is clearly plenty of oxygen available
for oxidation processes within the manganese oxide lattice.
Degradation on the surface is highly effective because free radicals
are present there. Presumably, oxygen from air dissociates on the gold
surface to replace the consumed oxygen atoms in the lattice structure.
This process only works if the material is produced in a very specific
manner: The gold must be deposited onto the manganese oxide by means
of vacuum-UV laser ablation. In this technique, a gold surface is
irradiated with a special laser, which dislodges gold particles
through evaporation. These gold particles have unusually high energy,
which allows them to drive relatively deep into the surface of the
manganese oxide. This process is the only way to induce sufficiently
strong interactions between the little clumps of gold and the
manganese oxide support.
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