Graphene joins the international fight against COVID-19
Graphene face shields in Mexico
Antonio Miramontes, CEO of Energia Fusion (Graphenemex) located in Mexico City, is a pioneer in the research and development of graphene applications, who, since almost a decade, ventured into a field dominated by Asia and Europe.
Together with his team of researchers and the National Autonomous University of Mexico (UNAM), the National Polytechnic Institute (IPN), among other institutions, they have come up with a graphene face shield that has a porosity of less than five nanometers (one billionth of a meter). The diameter size of the coronavirus virus, SARS-CoV-2 is between 80 and 120 nanometers, a size so small that regular plastic isn’t able to filter, but graphene can.
These face shields have become hospital staff’s best ally in the fight against Covid-19 in Mexico, as its graphene nanotechnological barrier blocks the virus completely and avoids bacteria, fungus and virus growth on their surface.
Could a graphene coating make surgical masks easier to sterilize and re-use?
According to a team of researchers at The Hong Kong Polytechnic University (PolyU), the answer is yes. Led by Guijun Li of PolyU’s industrial and systems engineering department, the team developed a laser manufacturing process that deposits a few layers of the carbon sheet onto commercially-available non-woven masks. The coating makes the masks superhydrophobic, which reduces the chances of infectious drops adhering to them, while graphene’s strong light-absorption properties makes it possible to sterilize them with exposure to sunlight.
Health officials all around the world are recommending that citizens wear masks in public, most importantly in places where physical distancing is hard or impossible. While wearing any type of mask is better than wearing no mask at all, the consensus is that surgical masks made from nonwoven polymer fibres are among the best types available for widespread use outside hospitals.
However, such masks have limitations. While they help prevent viruses (including SARS-CoV-2) from entering the wearer’s nose and mouth via droplets generated when an infected person sneezes, coughs or talks, virus-laden droplets tend to remain on the mask, meaning that they must either be thrown away after each use or sterilized before re-use. None of these options are attractive, since polymer-based masks are difficult to sterilize even with steam, while discarding them poses an environmental challenge.
The estimated 40 million pieces of protective gear produced worldwide every day amount to a daily 15 000-tonne mountain of waste – much of which must be incinerated, adding to carbon emissions to the already difficult environmental situation the world is facing.
Li and colleagues used a new technique of their own to deposit a few layers of this graphene onto commercial surgical masks. This new process is known as dual-mode laser-induced forward transfer (LIFT), and it uses a pulsed laser beam with a pulse duration of 10 ns. This short pulse length means that the momentum of the photons is high enough to transfer the graphene without significantly increasing the mask’s temperature – an important point, Li explains, because the melting point of the polymer fibres in the mask is only 130 °C. The LIFT method is also compatible with a roll-to-roll system, meaning that it can easily be integrated with existing automated mask manufacturing production lines, he adds.
Water droplets roll off
Since the graphene is superhydrophobic, it is self-cleaning, like a lotus leaf. Indeed, water droplets freely roll off the surface of the mask before they have time to adhere to it.
Another benefit, the researchers say, is that they can sterilize their graphene-coated masks simply by exposing them to sunlight for 40 to 100 seconds. This is possible because graphene absorbs over 95% of light across the solar spectrum from 300 to 2500 nm, so the coated masks quickly increase in temperature, reaching 70°C after 40 seconds of solar illumination and over 80°C after 100 seconds. That is high enough to inactivate most types of viruses, meaning that the mask can then be reused or (if damaged) safely recycled. In contrast, masks without a graphene coating do not show this photothermal effect, since they absorb sunlight only weakly. Even after 5 minutes of solar illumination, their temperature does not exceed 50°C, Li explains.