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.
Candida albicans (C. albicans) presents serious public health risks because of its presence in water matrices and its known resistance to various antifungal drugs. Although microbial photo-deactivation has gained intensive attention over decades, the existing deactivation process is still under debate. Finding a solution for effective fungal photo-deactivation remains a challenge and necessary task. We have demonstrated that the as-synthesized nitrogen-schorl co-modified TiO2 (N-Schorl-TiO2) photocatalytic nanocomposite is highly effective in deactivating pathogenic C. albicans under visible-light irradiation. Compared to the deactivation time with the other studies, N-Schorl-TiO2 is 1.5–6 times faster. The created electric field via schorl on the N-TiO2 provides the following vital features: prolonging the process of the electron-hole pair recombination on the surface of photocatalyst, improving the photo-deactivation performance of N-Schorl-TiO2, and preventing the nanoparticles aggregation. Ultimately, N-Schorl-TiO2 enables the 2-log-decrease photocatalytic deactivation process on C. albicans with gaining abundant •OH and 1O2 in only 6 h. Core evidences of schorl modification on the N-TiO2, •OH production and morphology information using ESR, XPS, XRD, HRTEM, and SEM are provided. This is the first work that comprehensively evaluates the critical factors, i.e., photocatalyst concentration, initial yeast concentration, and light irradiance, for C. albicans photo-deactivation. Moreover, we have found that the deactivation kinetics is appropriately described by a newly developed Light-responsive modified Hom's (LMH) model, demonstrating a good prediction of photocatalyst performance on C. albicans deactivation. Overall, this study highlights a highly efficient approach for yeast or fungi pathogen deactivation using visible-light responsive N-Schorl-TiO2, and it can serve as an essential reference for applying visible-light-responsive photocatalyst in anti-fungal treatments.
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