Oxidative power of aqueous non-irradiated TiO 2 -H 2 O 2 suspensions: Methylene blue degradation and the role of reactive oxygen species

Abstract

I am indebted to Håvard J. Haugen, Janne Elin Reseland and Ståle Petter Lyngstadaas. I would like to thank you for the inspirational discussions, progress meetings and the encouragement to present my research outside the department. But most importantly, you backed me up when I needed it the most. You have my respect. I never thought that microbiology is fun. That was before I met Jessica Lönn-Stensrud. Thank you for showing me bakterienes forunderlige verden and for being an excellent supervisor. Thanks, Hanna Tiainen, for absolutely everything. You have been a mentor for me and I enjoyed every bit of this three-year-long roller coaster ride. Our intense discussions have been a highlight of my PhD and I would like to thank you for passing on your passion for research. Along the way, I had the privilege to work with several outstanding researchers in their field.

Antibacterial effect of hydrogen peroxide-titanium dioxide suspensions in the decontamination of rough titanium surfaces

“…TiO2 nanoparticles did not show intrinsic antibacterial properties ( Figure 3B), and hence, the delay in tRLUmax/2 is suggested to be due to the interaction between TiO2 and H2O2. The non-photocatalytic formation of oxygen centred radicals, due to the interaction of H2O2 and TiO2, has previously been shown (Fenoglio et al 2009;Sanchez et al 2013;Wiedmer et al 2016). These studies suggested that TiO2 can act as a Fenton catalyst and decompose H2O2 into oxygen centred radicals namely superoxide (O2 -• ) and hydroxyl radicals ( • OH).…”

“…One explanation for the relatively small increase in antibacterial activity may be the nature and location of the radicals formed at the H2O2-TiO2 interface. Earlier results indicated that primarily superoxide radicals (O2 -• ) are formed at this interface and the oxidative effect is limited to the proximity of the surface (Wiedmer et al 2016). Extracellular polymeric matrix (EPS) may protect bacteria from direct contact with TiO2 nanoparticles and thereby hamper the antibacterial effect.…”

“…Extracellular polymeric matrix (EPS) may protect bacteria from direct contact with TiO2 nanoparticles and thereby hamper the antibacterial effect. Further, there is evidence that O2 -• can adsorb to the metal oxide surface resulting in negative net surface charge of TiO2 in physiological pH (Anpo et al 1999;Wiedmer et al 2016). This may lead to unfavourable repulsive forces between the negatively charged TiO2 surface and the overall negatively charged bacterial wall which may further limit the bactericidal effect of formed free radicals.…”

“…The nanoparticles (Degussa P25, Evonik Degussa GmbH, Hanau Wolfgang Germany) used for H2O2-TiO2 suspensions have a primary particle size of 23 nm and consist of a mixed crystal phase of 80% anatase and 20% rutile according to the manufacturer specifications. It has also been shown that these particles occur as stable agglomerates in aqueous suspensions at physiological pH (Wiedmer et al 2016). All chemicals were purchased from Sigma Aldrich (Sigma Aldrich, St. Louis, USA) if not stated differently.…”

“…It has been shown that the antibacterial effect of H2O2 is significantly reduced for pathogens with intrinsic defence mechanisms, in particular pathogens with high catalase activity and the ability to form a protective biofilm (Gaupp et al 2012;Mah & O'Toole 2001;McDonnell & Russell 1999;Stewart et al 2000). Recent studies indicate that the oxidative power of H2O2 can be enhanced by the addition of titanium dioxide (TiO2) particles due to non-photocatalytic formation of oxygen centred radicals at the H2O2-TiO2 interface (Sanchez et al 2013;Wiedmer et al 2016). So far, only two in vitro studies have investigated the antibacterial effect of such H2O2-TiO2 suspensions with different outcome.…”