Photocatalytic degradation of formaldehyde by diffuser of solar light pipe coated with nanometer titanium dioxide thin films

The even and transparent nanometer TiO2 thin films named DegussaP25 as photocatalysis deposited on the surface of diffusers of solar light pipe were prepared by sol-gel processing. The rugged side of the diffusers of solar light pipe was coated evenly with DegussaP25 solution for the quality of 1.75 g. The experiments had showed that when the coated side was away from the sun the lighting degree may be reduced compared with that facing the sun. The average reduction was only 3.03%, which would not have a significant impact on lighting. Diffusers are important parts of a light pipe which can diffuse light evenly to the place needed to be illuminated. The experiments showed that in a sunny summer day under the direct sunlight, the solar light pipe combined with photocatalysis could reduce the formaldehyde volume fraction in a box of 0.1 m(3) from 1.0x10(-6) to 0.16x10(-6). After 1 h of photodegradation the formaldehyde volume changed from 1.0x10(-6) down to 0.1x10(-6) with faster and more complete degradation of formaldehyde. The rate of degradation under cloudy and partly cloudy conditions was slower than that under sunny conditions. It was slower in winter than in summer under sunny conditions. The experimental results also showed that the performance of photocatalysis combined with diffusers of light pipe had better effect in a small space. The performance in large space, such as open space, will be the next work in the future, which will be a great challenge.