Copper nanowire spray makes existing surfaces antimicrobial
Copper has long been known for its ability to kill viruses and bacteria on contact, which is why it's often professionally coated onto commonly touched items such as doorknobs. A new copper nanowire spray may allow everyday folks to give existing surfaces the same treatment, using a spray can.
The technology is being developed via partnership between the US Department of Energy's Ames National Laboratory, Iowa State University, and the University at Buffalo. It builds upon previous Ames research, in which a copper ink was created for the printing of circuits onto flexible electronic devices.
The scientists are assessing two types of the spray, each of which has its strengths and weaknesses. One incorporates pure copper nanowire segments about 60 nanometers in width (one one-hundredth the width of a human hair), while the other utilizes copper-zinc nanowires of that same size.
In both cases, the wires are suspended in a carrier solution such as water or ethanol. Once the liquid has been sprayed onto a surface material like plastic, glass or stainless steel – then allowed to dry at room temperature– it forms a thin antimicrobial coating.
When it came to killing the SARS CoV-2 virus (which causes Covid-19), lab tests showed that copper discs covered with the coating were just as thorough as an uncoated copper disc. That said, due to the greater surface area provided by the nanowires, the coating did the job in just 20 minutes whereas the plain disc took 40.
Additionally, within the first 10 minutes, the spray that contained pure copper nanowires inactivated the virus twice as quickly as its copper-zinc counterpart. However, the copper-zinc coating remained effective for a longer period, meaning it would have to be reapplied less frequently. For this reason, the scientists believe that it is the superior choice for real-world use.
A paper on the research was recently published in the journal RSC Advances.
Source: Ames National Laboratory
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Silver is generally a better antimicrobial than copper - the tests of the two materials aren't comparable, but the silver coating had 99.9% effectiveness on viruses overnight in one paper, while viruses on copper are said to have a half-life of 0.8 hrs in the other paper -- which is basically identical. The silver coating is invisible, adheres to any surface, has a self-limiting thickness of only 10nm (making it cheap and easy to apply uniformly), is highly tenacious and durable and the silver is not used up by its antimicrobial action. The copper coating is thicker, about 1.7 microns (1700x thicker), adheres poorly (up to 1/3 removed by adhesive tape), wears out as the copper wears away, dissolves, or corrodes, and will be likely to cost 100-1000 times as much per area (roughly $1/sq. ft vs $1 /1000 sq. ft). The copper nanowire ink is conductive and will reflect radio waves, though, which the silver / tannic ink will not.
(The silver / tannic acid coating deserves the name ink, though it hasn't been called that. It reproduces the most popular recipe for permanent ink for over 1000 years, "iron-gall ink", but replacing black iron with silver.)
I remember reading that most boats put a toxic paint on and they are looking for a replacement….