Recently, photocatalysis attracts great attention for a broad range of antimicrobial applications, such as water and air disinfection, safe food processing and packaging, and so on. Graphitic carbon nitride (g-C3N4) holds promise for antimicrobial applications because it is visible-light-responsive and thus reactive under indoor lighting (in contrast to TiO2 that is only reactive under ultraviolet light irradiation), it is synthesized from inexpensive, earth-abundant precursors (e.g., urea, melamine), it is chemically and thermally stable under harsh environment, and its properties are highly tunable for improving photocatalytic performance. g-C3N4 is believed to inactive a broad range of microorganisms under indoor lighting, because of material excitation by photons, production of reactive oxygen species (ROS) and holes, and subsequent attack of the microorganisms with these highly reactive oxidants. The objective of our study is to develop and evaluate g-C3N4 for the inactivation of planktonic bacteria and biofilms, and understand the mechanism of inactivation. g-C3N4 powder was first prepared via thermal polycondensation of melamine, cyanuric acid, and barbituric acid, and g-C3N4 coupons were fabricated from the powder via a hydraulic press. Our preliminary results showed 2-log inactivation of E. coli, a probe bacterium, with the presence of g-C3N4 powder under the irradiation of white light emitting diodes (LEDs) for 2 h, however negligible inactivation was observed in the control experiments without the g-C3N4 powder or without light irradiation. S. epidermidis was selected as a probe microorganism for developing biofilms on the g-C3N4 coupons (in 0.1 TSB for 2-5 days), under the dark condition and white LED irradiation. The S. epidermidis biofilms were then stained with BacLight Live/Dead stain to test the efficacy for biofilm inactivation. Confocal laser scanning microscopic results indicated that a thick, live biofilm was developed in the dark condition (ca. 60-80 μm) but a thin layer of dead cells were observed under white LED irradiation. Future study will explore the development and eradication of biofilms on the g-C3N4 coupons under a range of environmental conditions (e.g., temperature, pH, light intensity, medium concentration), and the key properties of g-C3N4 and oxidative species for biofilm control will also be identified. Our study will provide a new avenue for the antimicrobial applications with visible-light-responsive photocatalysts.

Antimicrobial applications of visible-light-responsive photocatalysts

253rd National Meeting (2017)

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