Metal-free Monash method removes E. coli from water

Monday, 26 October, 2020

Metal-free Monash method removes <em>E. coli</em> from water

Engineers at Monash University have devised an improved method to remove potentially deadly bacteria from water using graphitic carbon nitride and sunlight.

The international team — led by Professor Xiwang Zhang from Monash University’s Department of Chemical Engineering — combined graphitic carbon nitride with polyethylenimine (PEI) to destroy E. coli and E. faecalis from water within 45 and 60 min respectively. The team’s findings are published in the journal Applied Catalysis B: Environmental.

The photocatalyst method is low cost and metal-free, preventing secondary pollution from leached metal ions during the filtration process. If upscaled, the solar-driven method could significantly improve the treatment of large volumes of water. It also has the potential to be integrated into current solar water disinfection technology in countries with limited access to fresh water.

Professor Zhang, who is also the Director of the ARC Research Hub for Energy-efficient Separation, said integrating the photocatalyst into solar water disinfection technology could nearly ensure complete and rapid disinfection in a more sustainable way.

“Infectious diseases caused by waterborne pathogens threaten the health of people worldwide,” he said.

“Graphitic carbon nitride has gained broad attention as a metal-free photocatalyst for water disinfection. However, it has limits in its capacity to remove pathogens completely using photocatalysis.

“What we’ve been able to do is fuse graphitic carbon nitride with PEI to boost photocatalytic properties of this material and test it on waterborne bacteria.

“We discovered the PEI functionalisation can, in effect, tune the photochemical reactions on graphitic carbon nitride. We found that the positively charged PEI on graphitic carbon nitride could promote the contact between photocatalyst and bacteria cells (negatively charged surface) via electrostatic adhesion, which can enable reactive oxygen species to kill the trapped bacteria cells.”

How it works

A previous study published by the research team in ACS Catalysis found PEI on graphitic carbon nitride provided a trap site for photoinduced holes. Through this, PEI can tune the photochemical reactions to generate more reactive oxygen species for bacteria inactivation.

Through this process, PEI changes the surface charge of the composite photocatalyst to be positive — in nature, the surface of bacteria cells is negatively charged due to the specific moieties of their cell structure.

As such, the positively charged PEI on graphitic carbon nitrate can promote contact between photocatalyst and bacteria cells via electrostatic adhesion. In this way, PEI traps the bacteria cells in water. The trapped cells are then killed by the generated reactive oxygen species through photocatalysis.

Under solar light irradiation, the research team was able to remove 99.99% of E.coli from water in 45 min, and the same percentage of E. faecalis within 60 min.

“This PEI functionalisation process is simple. It can be shared with desperate communities across the world after further research is conducted on the development of photocatalysis devices,” Professor Zhang said.

Image credit: © Niels Mayer

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