Photocatalytic degradation of methylene blue and inactivation of Gram-negative bacteria by TiO2 nanoparticles in aqueous suspension

• Published in: Food control 2013-12, Vol.34 (2), p.372-377
• Main Authors: Wang, Jiamei, Li, Can, Zhuang, Hong, Zhang, Jianhao
• Format: Article
• Language: English
• Subjects: absorption; adsorption; antimicrobial properties; Biological and medical sciences; E. coli; equations; Escherichia coli; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Gram-negative bacteria; Hygiene and safety; irradiation; Methylene blue; nanoparticles; P. aeruginosa; Photocatalytic activity; photolysis; Pseudomonas aeruginosa; TiO2; titanium dioxide
• ISSN: 0956-7135; 1873-7129
• DOI: 10.1016/j.foodcont.2013.04.046

The photocatalytic degradation of methylene blue (MB) and inactivation of Gram-negative bacteria Escherichia coli (generic) and Pseudomonas aeruginosa by TiO2 nanoparticles in aqueous suspension were studied. TiO2 resulted in significant reduction in MB absorption and a shift of MB absorption peak from 664 nm to 658 nm after a short time of irradiation. The maximum degradation of MB was observed when the concentration of TiO2 in the aqueous suspension was 0.5 g L−1. TiO2 was also very effective with inhibiting growth of both Gram-negative bacteria E. coli and P. aeruginosa, although it took more than 60 min to observe the inactivation effects. The photocatalytic inactivation toward E. coli and P. aeruginosa by TiO2 showed a similar trend with much higher effectiveness toward E. coli under the same experimental conditions. The inactivation kinetic behaviors could be explained by the modified Langmuir–Hinshelwood model, and well fitted to a pseudo-first order kinetic equation. The reaction rate constant for E. coli and P. aeruginosa were 7.768 × 106 cfu mL−1 min−1 and 5.655 × 106 cfu mL−1 min−1, respectively. The adsorption equilibrium constant for E. coli was 1.053 × 10−8 mL cfu−1, while it was 1.438 × 10−8 mL cfu−1 for P. aeruginosa. These results further demonstrate that in an aqueous system, TiO2 nanoparticles can effectively both degrade organic compounds and inhibit Gram-negative bacteria under UVA light. Compared with the degradation activity of TiO2 toward organic compounds, its antimicrobial activity against Gram-negative bacteria would be delayed by 60 min. The antimicrobial activity of TiO2 against Gram-negative bacteria could vary with bacterial species. •Photocatalytically degrading dyes and inactivating G− bacteria by TiO2 were studied.•Mathematical model was developed to describe TiO2 antibacterial effects and kinetics.•It took longer time for TiO2 to show bacterial kill than chemical degradation.•TiO2 had similar antimicrobial effects and kinetics against E. coli and P. aeruginosa.