Inactivation of pathogens by visible light photocatalysis with nitrogen-doped TiO2 and tourmaline-nitrogen co-doped TiO2

Four types of pathogens, namely, Staphylococcus aureus (S. aureus, gram-positive bacteria), Escherichia coli (E. coli, gram-negative bacteria), Mycobacterium avium (M. avium, mycobacteria), and Candida albicans (C. albicans, fungi), are common microorganisms that cause serious human health issues. However, searching for an efficient material for inactivating pathogens via visible light driven photocatalysts remains a challenge. An attempt was made to compare the photocatalytic performance using nano-sized nitrogen-doped titanium oxide (N-TiO2) and tourmaline-nitrogen-co-doped titanium oxide (T-N-TiO2) for inactivation of pathogens under visible light irradiation. S. aureus was used to compare the photocatalytic inactivation performance of N-TiO2 and T-N-TiO2. The findings showed that photocatalyst dosage, initial microbial concentration, and visible light intensity are the key factors affecting photocatalytic inactivation process for both photocatalysts. A 2-log-inactivation of S. aureus under 7.25 mW/cm2 visible light irradiation via T-N-TiO2 was achieved within 3 h, which is shorter than the inactivation via N-TiO2 (4 h). TEM observations had proved that both visible-light-induced photocatalysis could cause severe damage to the cell membrane. The results of electron paramagnetic resonance also indicated that more hydroxyl radicals generated in the T-N-TiO2 photo-inactivation system allowed a better inactivation performance of the visible-light-induced T-N-TiO2. This is the first work exploring that Light-responsive Modified Hom's model (LHM) is able to simulate photocatalytic inactivation of S. aureus. T-N-TiO2 composite was firstly evaluated for its efficacy of photocatalytic inaction of S. aureus, E. coli, and M. avium, and an increasing order of time was required for complete inactivation as follows: S. aureus < E. coli < M. avium < C. albicans. We have found that the inactivation efficiency of tested pathogens using T-N-TiO2 is the highest as compared with literature works. Overall, T-N-TiO2 exhibits a better inactivation efficiency than that of N-TiO2 in all the tested pathogens.