Research on photodegradation of formaldehyde by nanocrystalline N-TiO2 powders under visible light irradiation

The photo-degradation of formaldehyde (HCHO) by nitrogen-doped nanocrystalline TiO2 (N-TiO2) powders under visible light irradiation has been systematically investigated. Experimental results show that the degradation ratio reached up to 42.6% after 2 h visible light irradiation when the amounts of N-TiO2 powders were 0.5 g, the initial concentration of the HCHO was set at 0.98 mg/m(3), the illumination intensity was fixed at 10,000 lux, the ambient temperature was set at 26 degrees C, and the relative humidity was maintained at 33 +/- 5%. Further research shows that the degradation ratios were all larger than 40% in ten repeated cycles of photodegradation of HCHO by N-TiO2 powders. The degradation ratio was as high as 82.9% after 2 h visible light irradiation when the amount of N-TiO2 was 5 g. The degradation ratio was increased from 25.5 to 59.6% when the illumination intensity of the visible light was increased from 0 to 30,000 lux. However, the degradation ratio could not be further increased by further increasing the illumination intensity.