The two-line (the name is derived from the fact that when examined by X-ray diffraction, it shows two lines) ferrihydrite material is produced by self assembly of Fh nanoparticles in 1-propanol in the presence of polyoxyethylene (20) cetyl ether template. The resulting highly porous material consists of aggregated nanocrystals.

Due to its pores and arrangement of nanoparticles, this material has a large and accessible inner surface. In comparison to other iron oxide materials, it has a particularly high proportion of unsaturated and thus reactive iron centers on its surface.

These have fewer oxygen atoms as near neighbors than the iron atoms in the interior of the mineral. Such isolated iron oxide units absorb ozone especially well. Once bound to the iron, the ozone splits into an oxygen molecule (O₂) and a highly reactive oxygen atom (O), which can react with a second lone oxygen atom to form O₂.

The following aspects prompted us to consider mesoporous 2LFh (M2LFh) a judicial choice for O₃ removal: 1) it possesses high surface area and, being in the ferrihydrite (Fh) phase, a much higher percentage of iron sites are at or near the surface than in the bulk; 2) with accessible mesopores, Fh nanoparticles have the potential for high adsorption owing to an increased rate of mass transfer to the reactive iron sites, such as we recently reported for their high efficiency in rapidly removing organic contaminants in the air; and 3) as an oxyhydroxide of iron, Fh is environmentally friendly and can be applied in various sectors.

...Among a wide range of materials tested at room temperature (RT), we found M2LFh to be the most efficient candidate for O₃ removal; it showed about 95 % O₃ removal with high reproducibility.

—Mathew et al.

Ozone (O₃) is a dangerous air pollutant that is highly reactive and causes both short- and long-term adverse health effect and also disrupts plant growth. Ozone is formed when nitrogen oxide from exhaust is irradiated with UV light and releases an oxygen atom, which reacts with an oxygen molecule (O₂) to form an ozone molecule (O₃). A number of electrical devices, such as photocopiers and laser printers, also release this unhealthy gas.

The typical “ozone smell” when using older photocopiers and laser printers is not the ozone itself: it is reaction products from the ozone. Most newer devices are equipped with filters that convert the ozone. Removal of O₃ is essential for aircraft applications because O₃ is an unavoidable pollutant at high altitude and can be introduced into the aircraft cabins during the flight.

Previous materials for the elimination of ozone have a number of disadvantages: for example, some require organic additives, others do not work without expensive metals, some are far from environmentally friendly, and most are not flexible enough for wide use in a variety of applications.

Resources

• Thomas Mathew, Kenichirou Suzuki, Yasuhiro Ikuta, Yasutaka Nagai, Naoko Takahashi, and Hirofumi Shinjo (2011) Mesoporous Ferrihydrite-Based Iron Oxide Nanoparticles as Highly Promising Materials for Ozone Removal. Angewandte Chemie International Edition 50, No. 32, doi: 10.1002/anie.201102007