Chemists from Rice University use laser-induced graphene to build self-sterilising filters
Laser-induced graphene (LIG) was developed in the laboratory of James Tour, a chemist at Rice University in Houston, Texas in 2014. Made by heating the surface of a sheet of the engineering plastic polyimide with an industrial laser cutter, LIG can be used to build super capacitors, tough composites and can even be used as an artistic medium.
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To construct a filter out of LIG, Tour’s team treated both sides of a polyimide sheet with the laser, converting some of it into graphene foam, but leaving a fine, three-dimensional lattice of the polymer as a reinforcement. They modulated the temperature of the laser between passes, forming what they refer to as a “thick forest” of graphene fibres alternating with smaller, sheets of polyimide-reinforced graphene.
In a paper in ACS Nano, the team describes how airflow through the filter construction – induced by installing it in a standard commercial vacuum air filtration system – leaves bacteria, fungi, spores, prions, endotoxins and other biological contaminants common in a hospital setting trapped within the graphene “forest”. They then utilised the conductive properties of graphene to induce resistive heating in the material, periodically raising its temperature above 350°C within a few seconds. This temperature is hot enough to kill all the pathogens, and will also decompose toxic byproducts that can feed new microorganisms and activate the human immune system.
“So many patients become infected by bacteria and their metabolic products, which for example can result in sepsis while in the hospital,” Tour said. “We need more methods to combat the airborne transfer of not just bacteria but also their downstream products, which can cause severe reactions among patients.”
“Some of these products, like endotoxins, need to be exposed to temperatures of 300 degrees Celsius in order to deactivate them,” a purpose served by the LIG filter, he said. “This could significantly lessen the transfer of bacteria-generated molecules between patients, and thereby lower the ultimate costs of patient stays and lessen sickness and death from these pathogens.”
In their paper, the team describes testing the LIG filters in a system the pulled air through at a rate of 10l per minute for 90 hours. The resistive heating killed all pathogens and destroyed all harmful byproducts. Incubating the filters for additional 130 hours revealed no subsequent bacterial growth. This, they suggest, indicates that a single LIG filter could be efficient enough to replace the double filter currently required by US federal standards in hospital ventilation systems to prevent patients being infected by airborne pathogens carried by aerosols and liquid droplets.