Road tunnel walls could soon help cut down vehicle exhaust pollution if a material developed by Japanese scientists at the National Institute of Resources and Environment in Ibaraki gains widespread acceptance.
The material, a mixture of titanium dioxide powder and activated graphite, soaks up nitrogen (NOx) and sulphur oxide (SOx) gases. These pollutants are then broken down into weak solutions of nitric and sulphuric acid when ultraviolet light from the sun is shone onto the material.
Dr Koji Takeuchi, who is leading the research team carrying out the experiments, believes the material can be incorporated into almost any surface including tunnel linings, bridges and even the walls of buildings.
Dr Takeuchi said that the use of powdered titanium dioxide, which is currently incorporated in women‚s cosmetics at a whitening agent, means that any surface which incorporates the material would be effectively self-cleaning.
The resulting nitric and sulphuric acid can be washed off with water and neutralised with alkali lime.
Dr Takeuchi’s group has already carried out tests using a sheet of fluorocarbon plastic coated with a thin layer of the titanium dioxide and graphite mixture. These showed that a weekly wash, even from a passing rain cloud, is all that is needed to keep the panel in top pollution-eating condition. The panel would last five years before needing replacement.
Comprehensive trails are currently on-going in Tokyo while Dr Takeuchi’s group is also working on a spray coating of the mixture that would do away with the need for specialist panels.
