Ellen Phiddian
Cosmos science journalist
Quantum materials have already changed our technology beyond recognition, and the change is only going to accelerate in the coming decades.
But is it possible to make quantum technology sustainable?
Professor Qin Li, a chemical engineer at Griffith University, says she has the evidence to show it. The key in her research is carbon – something you can get from waste biomass, wastewater, or even human hair.
Not only does it make circular quantum materials, says Li – it makes them much better.
“I think people often think quantum is a little bit blue sky,” says Li, who recently presented at the 2024 Australian Conference on Green & Sustainable Chemistry & Engineering.
“But I don’t think quantum effects are so far away from us. In fact, photovoltaics for solar energy and electric conversion, in the very beginning, was also considered as a quantum effect.”
One of Li’s pursuits is quantum dots: particles on the scale of nanometres, which emit light (fluoresce) in very precise ways. The technology is poised to improve all sorts of sectors, from medical imaging to solar power, and it won the 2023 Nobel Prize in Chemistry.
Li first became interested in quantum dots in the late 2000s, when she and collaborators made them out of carbon in the lab – almost by accident. They were aiming to make another type of material: photonic crystals.
“But then our experiments didn’t pan out as we wanted,” says Li. Instead of neatly covering the crystals, the carbon film they added formed its own tiny particles.
“We had seen a paper about carbon dots, which was published by Professor Ya-Ping Sun from Clemson University,” says Li.
“We wondered whether these could be these carbon nanodots.”
Testing confirmed it: the tiny carbon particles were emissive, meaning they were carbon-based quantum dots. What’s more, they were friendlier to the body, and more sturdy, than carbon dots that other researchers had made.
“I actually received some samples from my US collaborator, and they appeared repulsive to me, because they were dispersed in toluene,” says Li, adding that the super light-sensitive carbon dots needed to be kept in dark bottles.
“But our carbon dots appeared so stable in water.”
This made them good tools for medical research. Li started investigating their potential to label cells, something that could turn into targeted drug delivery for cancer.
The next step was changing her focus from drug development to environmental monitoring. The shift prompted her to wonder about how the carbon dots were made: they’d been using synthetic chemicals, but could they do it with waste biomass?
“Initially, I had a hesitation,” says Li. “When you use biomass, there’s always problems with the purity of your precursor.”
But after discussing the idea with a couple of collaborators, she decided to give it a shot. She engaged a PhD student to see if it was possible to make quantum dots out of human hair (the student provided the hair).
The results were extremely successful.
“We made what, at that time, was the brightest blue emitting OLED [organic light-emitting diode] and with a very low voltage, 4.2 volts to turn it on,” says Li.
The hair-derived carbon dots had properties Li couldn’t have predicted. One turned out to be very sensitive to chloroform in water. This makes it a very powerful detector for drinking water, because chloroform is a known byproduct of water disinfection.
The carbon dots could spot chloroform in wastewater at concentrations as low as 3 parts per billion. The team is now working on turning the dots into a sensor.
“Because we are using this innately impure precursor, it actually introduces some functional moieties that I normally wouldn’t have thought about,” says Li.
“So this actually gives us inspiration.”
Hair was just the beginning. The team also made carbon dots out of seaweed, sugarcane waste, and biosolids from wastewater sludge – but Li is less enthusiastic about the last one.
“We tried different synthesis methods, but one of them was microwaving, and the advice here is: do not microwave biosolids,” she says. “The whole room was stinky for many days.”
Biomass does have some downsides. The hair-derived quantum dots are different depending on whose hair is being used: blonde hair yields different dots to black hair, and treatment methods can change the result.
“Quantum dots are so small, they contain maybe 100-200 atoms,” says Li.
“Any heterogeneity would be amplified.”
The biomass-derived dots have given the team ideas, but they’ve often resorted to synthetic materials again to get consistent dots.
“The biomass contains various possibilities, and the consistency issue requires checking points,” says Li.
There are also questions around getting consistent feedstocks for biomass. “If this person is not donating their hair anymore, how can we replace that?” she says.
But the technique challenges our assumptions that waste-derived materials are always low-quality, according to Li.
“We can establish an upcycling pathway and turn the waste material into high-end, highly functional quantum materials,” she says. The hair-derived quantum dots outperformed a lot of synthetic ones.
“It’s just amazing how good quality, and how easily we can make this kind of material out of waste.”
