Photochemical reactivity of nitrogen-doped biochars under simulated sunlight irradiation: Generation of singlet oxygen

摘要

This study explored the photochemical activity of nitrogen-doped biochars (NCMs) by investigating their role in the degradation of sulfamethazine under simulated sunlight irradiation. NCMs with different doping amounts were prepared from corn straw and urea. Results showed that nitrogen doping can notably enhance the photodegradation of SMT rather than raw char. NCMs are of photochemical activity under visible light, which was confirmed by monochromatic light experiments. Quenching experiments, ESR, pH effect, and the influence of O-2 were carried out to explore the involved oxidation mechanism in this system. Results showed that O-1(2) was the main reactive oxygen species. O-1(2) was produced from O-2 by both energy transfer and electron transfer. DFT calculations showed that pyridinic N doping can decrease the energy of intersystem crossing and thus benefit the generation of O-1(2) by triplet-triplet energy transfer. Results underscore the explicit importance of nitrogen element in photochemical reactivity of chars under simulated light irradiation even when the nitrogen content is low. It is a meaningful reminder for us to pay more attention to the assessment of the fate and transport of contaminants in the soil where it is rich in NCMs as well as the potential use of NCMs for pollutants remediation, since visible light is very abundant near the earth's surface.