Hairy solution for assessing water quality

A team of researchers from Griffith University has used human hair waste to develop organic devices that test water quality.

Professor Qin Li and her team from the School of Engineering and Built Environment — in collaboration with Queensland University of Technology — synthesised highly fluorescent carbon dots from human hair waste with the ability to detect trace amounts of chloroform in water, a major by-product of water disinfection.

The carbon dots were created using a chemical-free process by heating up the hair to 180°C in an oxygen-deficient environment. The results are published in Sustainable Materials and Technology.

Carbon dots are small carbon nanoparticles (less than 10 nm in size) with varying functional groups on the surface with the ability to fluoresce when exposed to a range of chemical and biochemical contaminants. The intensity of the fluorescence changes when surface functional groups on the carbon dot interact with the particular chemical species, making them perfect for chemical sensor applications.

Professor Li said the contaminants the carbon dots target could be as unique as the individual whose hair from which they are made.

“It might sound strange, but hair is an extremely valuable waste product,” Professor Li said.

“Being rich in protein and full of carbon and nitrogen, it is an excellent precursor for transformation into useful materials like carbon dots.

“Because hair is rich in nitrogen, when we altered the thermal treatment conditions, we produce carbon dots with different nitrogen-containing functional groups on their surface which bind specific contaminants.”

Remarkably, the researchers also found that hair of different colours produced carbon dots that responded preferentially to differing pollutants.

Former Griffith University Research Fellow Dr Ehsan Eftekhari said, “The dark hair showed a high specificity for sensing chloroform pollution in water, while the blonde hair we tested was more sensitive to metal species like magnesium.”

The carbon dots derived from dark hair, with nitrogen-based sensing antennas on the surface, were able to detect chloroform in as few as three molecules per billion water molecules.

“Chlorination is a widely adopted disinfection method in water treatment used to reduce pathogen risks and waterborne diseases, but it also creates by-products that have been linked to higher cancer rates,” said study co-author Professor Fred Leusch, Chair of the Australian Water Quality Advisory Committee.

“So developing sensors to monitor the amount of chlorine used in treatment and the by-product concentrations in real time is of critical importance to public health,” he said.

The carbon dot sensors could even tell the difference between very similar chemical contaminants.

“In this study, we found the nitrogen-based sensing antennae on the carbon dots’ surface was sensitive to chloroform, but not to the chemically similar contaminant bromoform, due to the subtle difference in their electronic structures,” Professor Li said.

“I’m constantly amazed by how much biological materials can teach us on designing functional products, such as carbon dots-based nanosensors.

“Using biowaste to make carbon dots for water quality sensors, without employing any harmful solvents, makes it a sustainable technology that truly adheres to the principles of green chemistry.”

Image caption: Professor Qin Li, School of Engineering and Built Environment, Griffith University.