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Thursday, 19 September 2019
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Raw materials & technologies, Raw materials, Coatings pigments

Coatings pigments: TiO2 and ZnO nanoparticles compared

Friday, 15 February 2013

Scientists have characterised three types of metal nanoparticle and assessed production of reactive oxygen species through the degradation of methylene blue.

The photocatalytic killing potential of three nanoparticle concentrations was assessed on four representative bacteria

Source: Kimberly Reinick/ Fotolia
The photocatalytic killing potential of three nanoparticle concentrations was assessed on four representative bacteria Source: Kimberly Reinick/ F...

Titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles are important photocatalysts and as such have been extensively studied for the removal of organic compounds from contaminated air and water and for microbial disinfection. Despite much research on the effect of TiO2 and ZnO nanoparticles on different bacterial species, uncertainties remain about which bacteria are more sensitive to these compounds. Very few studies have directly compared the toxicity of ZnO to TiO2under both light and dark conditions. In addition, authors investigating the photocatalytic inactivation of TiO2 and ZnO nanoparticles on bacteria have failed to investigate the reactive oxygen species (ROS) generation of the nanoparticles, making it difficult to correlate killing action with the generation of ROS.

Photocatalytic killing potential assessed

In a new study, published in the "Journal of Nanoparticle Research” (DOI: 10.1007/s11051-013-1432-9), three types of metal nanoparticle (ZnO < 50 nm, ZnO < 100 nm and TiO2) have been characterised and ROS production assessed through the degradation of methylene blue (MB). The photocatalytic killing potential of three nanoparticle concentrations (0.01, 0.1 and 1 g/L) was then assessed on four representative bacteria: two gram-positive (S. aureus and B. subtilis) and two gram-negative (E. coli and P. aeruginosa).

TiO2 nanoparticles generated more ROS

Results showed that out of the three nanoparticles tested, the TiO2nanoparticles generated more ROS than the ZnO nanoparticles, corresponding to a greater photocatalytic inactivation of three of the four species of bacteria examined. The MB decomposition results correlated well with the bacterial inactivation results with higher TiO2 nanoparticle concentrations leading to greater ROS production and increased loss of cell viability. Although producing less ROS than the TiO2 nanoparticles under ultraviolet light, the ZnO nanoparticles were toxic to two of the bacterial species even under dark conditions. In this study, no correlation between cell wall type and bacterial inactivation was observed for any of the nanoparticles tested although both gram-positive bacteria were sensitive to ROS production. P. aeruginosa cells were resistant to all types of treatment and highlight a potential limitation to the application of these nanoparticles for water treatment.

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