Researchers from North Carolina State University revealed a low-cost method for recovering nanowires from electronic gadgets that have outlived their usefulness and repurposing them in new devices. The project is a step toward more environmentally friendly technology.
Recycling Nanomaterials
“There is a lot of interest in recycling electronic materials because we want to both reduce electronic waste and maximize the use we get out of rare or costly materials,” says Yuxuan Liu, a Ph.D. student at NC State and first author of a paper on the project. According to Liu, the team has established a method for recycling nanowires that they believe may be applied to other such nanomaterials, including noble and rare-earth elements. The research was made possible by a grant from the National Science Foundation, number 1728370.
Yong Zhu, corresponding author of the paper and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State, adds, “Our recycling technique differs from conventional recycling” He explains a scenario where a glass bottle is recycled, completely melting it down before it can be used to make another glass object. With nanowires, a network is isolated from the other components within a device. The nanowire network is then isolated from the other components, then deconstructed in solution into a collection of individual silver nanowires. They can then be combined to form a new network, which can subsequently be incorporated into a new sensor or other device.
The new recycling method takes into account a device’s whole life cycle. The first stage is to create devices that are made of polymers that are soluble in solvents that do not dissolve nanowires. The polymer matrix containing the silver nanowires is dissolved once a device has been utilized, leaving the nanowire network behind. After that, the network is placed in a different solvent and subjected to ultrasound. The nanowires are dispersed, separating them from the network.
Theory in Action
The researchers produced a wearable health sensor patch that may be used to track a patient’s temperature and hydration in a proof-of-concept demonstration. Silver nanowire networks encapsulated in a polymer substance made up the sensor. The sensors were put through their paces to ensure that they were fully working. A sensor patch is usually discarded once it has been used.
The researchers, however, learned after dissolving the polymer in water, removing the nanowire network, breaking it down into a collection of individual nanowires, and then using those nanowires to create a brand-new wearable sensor for their demonstration. While the qualities of the nanowire network degraded slightly with each “life cycle,” the researchers discovered that the nanowires could be recycled four times without affecting the sensor’s performance. They also discovered that they could improve the performance of the nanowire network after four life cycles by adding fresh silver nanowires to the mix.
Finding a low-surface-tension solvent to utilize in breaking up the nanowire network is crucial to the recycling process. They discovered that low surface tension is significant because it makes it simpler for the solvent to infiltrate into the network’s tight junctions, allowing for easier network disassembly.
When breaking up nanowire networks using ultrasound, the researchers discovered that finding the appropriate time balance is also crucial. The nanowires can be broken if the ultrasound is applied for too long. If the ultrasound isn’t applied for long enough, clumps of nanowires can form.
As long as they’re employed in the form of a network, the approach the team demonstrated may be used to recycle various nanomaterials, such as nanoparticles, carbon nanotubes, other forms of nanowires, and two-dimensional materials.
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