MSc Thesis Title: Solar photocatalysis as disinfection technique: catsalysts preparation and inactivation assessment of bacterial pathogens
Tuesday 17 July 2018, at:12:00, Venue: Hall Κ2. Α11
Examination Committee
- Assistant Professor Danae Venieri (advisor)
- Assistant Professor Paraskevi Panagiotopoulou
- Professor Evan Diamadopoulos
Abstract:
In order to meet today’s water quality standards researchers are focused on finding sustainable and effective disinfection techniques. In this context, the objective of this thesis is the synthesis and characterization of Ν-TiO2 photocatalysts and the investigation of their disinfection potential, in terms of Escherichia coli, Pseudomonas aeruginosa and Bacillus cereus inactivation in aqueous samples under artificial sun light.
N-TiO2 photocatalysts were synthesized by a sol-gel method using various nitrogen precursors (urea, triethylamine -TEA and NH3). Characterization results showed that the obtained materials exhibited narrow band gaps and improved visible light response. The photocatalytic activity depends highly on the type of microorganism tested but in all cases N-TiO2 catalysts performed higher bacterial inactivation compared to the pure titania samples. The relative bactericidal activity of the catalysts followed the order N-TiO2 (UREA)> N-TiO2 (NH3) ~N-TiO2 (TEA)> (synthesized)TiO2> TiO2-P25. The Gram-negative indicators E. coli and P. aeruginosa were readily inactivated reaching reduction rates up to 6 Log within 60 min of treatment at an initial concentration of 106 CFU mL-1 and a catalyst concentration of 50 mg L-1. Concerning B. cereus though, a well-known resistant pathogen, N-TiO2 exhibited different activity with a maximum of a 4 Log reduction after 60 min of treatment, at a smaller initial concentration of 105 CFU mL-1 and the same catalyst concentration. Complete inactivation was achieved only in the presence of N-TiO2 (TEA) in 60 min irradiation and after increasing the catalyst loading up to 100 mg L-1. No substantial reactivation after disinfection was observed for all three indicators.
Increasing TEA concentration for the preparation of the of the catalysts from 25 to 89% did not improve catalysts optical characteristics and therefore did not enhance the process. Operating conditions, like catalyst concentration, nitrogen precursor and especially, bacterial species defined the disinfection efficiency up to certain extend.
Solar photocatalysis with N-TiO2 catalysts may be effective disinfection technology if the operational conditions are established in relation to the microbial content in water, which includes opportunistic pathogens such as P. aeruginosa and B. cereus
