Effect of sunlight irradiation on photocatalytic pyrene degradation in contaminated soils by micro-nano size TiO2

The enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils by micro-nano size TiO2 in the presence and absence of sunlight was investigated. The results showed that the synergistic effect of sunlight irradiation and TiO2 was more efficient on pyrene degradation in quartz sand and red and alluvial soils than the corresponding reaction system without sunlight irradiation. In the presence of sunlight irradiation, the photooxidation (without TiO2) of pyrene was very pronounced in alluvial and red soils and especially in quartz sand. However, in the absence of sunlight irradiation, the catalytic pyrene degradation by TiO2 and the photooxidation (without TiO2) of pyrene were almost nil. This implicates that ultra-violet (UV) wavelength range of sunlight plays an important role in TiO2-enhanced photocatalytic pyrene degradation and in photooxidation (without TiO2) of pyrene. The percentages of photocatalytic pyrene degradation by TiO2 in quartz sand, alluvial and red soils under sunlight irradiation were 78.3, 23.4, and 31.8%, respectively, at 5 h reaction period with a 5% (w/w) dose of the amended catalyst. The sequence of TiO2-enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil, due to different texture and total organic carbon (TOC) contents of the quartz sand and other two soils. The differential Fourier transform infrared (FT-IR) spectra of degraded pyrene in alluvial soil corroborate that TiO2-enhanced photocatalytic degradation rate of degraded pyrene was much greater than photooxidation (without TiO2) rate of degraded pyrene. Based on the data obtained, the importance for the application of TiO2-enhanced photocatalytic pyrene degradation and associated organic contaminants in contaminated soils was elucidated.

► Synergistic effect of sunlight irradiation and TiO2 promoted degradation of pyrene. ► Micro-nano size TiO2 enhanced degradation rate of transformed pyrene. ► Soil organic matter retarded the degradation of pyrene catalyzed by TiO2. ► Sunlight is renewable energy for photocatalytic degradation of pyrene by TiO2.