MSGID: 1:317/3 642f9c6c   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Fully recyclable printed electronics ditch toxic chemicals for water   
    First-of-its-kind demonstration suggests a more environmentally friendly   
   future for the electronics industry is possible    
      
     Date:   
         April 6, 2023   
     Source:   
         Duke University   
     Summary:   
         Engineers have produced fully recyclable printed electronics   
         that replace the use of chemicals with water in the fabrication   
         process. By bypassing the need for hazardous chemicals, the   
         demonstration points down a path industry could follow to reduce   
         its environmental footprint and human health risks.   
      
      
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   FULL STORY   
   ==========================================================================   
   Engineers at Duke University have produced the world's first fully   
   recyclable printed electronics that replace the use of chemicals with   
   water in the fabrication process. By bypassing the need for hazardous   
   chemicals, the demonstration points down a path industry could follow   
   to reduce its environmental footprint and human health risks.   
      
      
   ==========================================================================   
   The research appeared online Feb. 28 in the journal Nano Letters.   
      
   One of the dominant challenges facing any electronics manufacturer is   
   successfully securing several layers of components on top of each other,   
   which is crucial to making complex devices. Getting these layers to   
   stick together can be a frustrating process, particularly for printed   
   electronics.   
      
   "If you're making a peanut butter and jelly sandwich, one layer on either   
   slice of bread is easy," explained Aaron Franklin, the Addy Professor   
   of Electrical and Computer Engineering at Duke, who led the study. "But   
   if you put the jelly down first and then try to spread peanut butter on   
   top of it, forget it, the jelly won't stay put and will intermix with   
   the peanut butter. Putting layers on top of each other is not as easy   
   as putting them down on their own -- but that's what you have to do if   
   you want to build electronic devices with printing."  In previous work,   
   Franklin and his group demonstrated the first fully recyclable printed   
   electronics. The devices used three carbon-based inks: semiconducting   
   carbon nanotubes, conductive graphene and insulating nanocellulose. In   
   trying to adapt the original process to only use water, the carbon   
   nanotubes presented the largest challenge.   
      
   To make a water-based ink in which the carbon nanotubes don't clump   
   together and spread evenly on a surface, a surfactant similar to detergent   
   is added. The resulting ink, however, does not create a layer of carbon   
   nanotubes dense enough for a high current of electrons to travel across.   
      
   "You want the carbon nanotubes to look like al dente spaghetti strewn   
   down on a flat surface," said Franklin. "But with a water-based ink,   
   they look more like they've been taken one-by-one and tossed on a wall   
   to check for doneness. If we were using chemicals, we could just print   
   multiple passes again and again until there were enough nanotubes. But   
   water doesn't work that way. We could do it 100 times and there'd still   
   be the same density as the first time."  This is because the surfactant   
   used to keep the carbon nanotubes from clumping also prevents additional   
   layers from adhering to the first. In a traditional manufacturing process,   
   these surfactants would be removed using either very high temperatures,   
   which takes a lot of energy, or harsh chemicals, which can pose human and   
   environmental health risks. Franklin and his group wanted to avoid both.   
      
   In the paper, Franklin and his group develop a cyclical process in which   
   the device is rinsed with water, dried in relatively low heat and printed   
   on again.   
      
   When the amount of surfactant used in the ink is also tuned down,   
   the researchers show that their inks and processes can create fully   
   functional, fully recyclable, fully water-based transistors.   
      
   Compared to a resistor or capacitor, a transistor is a relatively   
   complex computer component used in devices such as power control or   
   logic circuits and sensors. Franklin explains that, by demonstrating a   
   transistor first, he hopes to signal to the rest of the field that there   
   is a viable path toward making some electronics manufacturing processes   
   much more environmentally friendly.   
      
   Franklin has already proven that nearly 100% of the carbon nanotubes   
   and graphene used in printing can be recovered and reused in the same   
   process, losing very little of the substances or their performance   
   viability. Because nanocellulose is made from wood, it can simply be   
   recycled or biodegraded like paper. And while the process does use a   
   lot of water, it's not nearly as much as what is required to deal with   
   the toxic chemicals used in traditional fabrication methods.   
      
   According to a United Nations estimate, less than a quarter of the   
   millions of pounds of electronics thrown away each year is recycled. And   
   the problem is only going to get worse as the world eventually upgrades   
   to 6G devices and the Internet of Things (IoT) continues to expand. So   
   any dent that could be made in this growing mountain of electronic trash   
   is important to pursue.   
      
   While more work needs to be done, Franklin says the approach could   
   be used in the manufacturing of other electronic components like   
   the screens and displays that are now ubiquitous to society. Every   
   electronic display has a backplane of thin-film transistors similar to   
   what is demonstrated in the paper. The current fabrication technology   
   is high-energy and relies on hazardous chemicals as well as toxic   
   gasses. The entire industry has been flagged for immediate attention   
   by the US Environmental Protection Agency. [https://www.epa.gov/   
   climateleadership/sector-spotlight-electronics] "The performance of our   
   thin-film transistors doesn't match the best currently being manufactured,   
   but they're competitive enough to show the research community that we   
   should all be doing more work to make these processes more environmentally   
   friendly," Franklin said.   
      
   This work was supported by the National Institutes of Health   
   (1R01HL146849), the Air Force Office of Scientific Research   
   (FA9550-22-1-0466), and the National Science Foundation (ECCS-1542015,   
   Graduate Research Fellowship 2139754).   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Electronics # Graphene # Technology   
             o Earth_&_Climate   
                   # Water # Sustainability # Air_Quality   
             o Computers_&_Math   
                   # Spintronics_Research # Mobile_Computing #   
                   Computers_and_Internet   
       * RELATED_TERMS   
             o Environmental_impact_assessment o Environmental_engineering   
             o Hazardous_waste o Waste_management o Fracking o   
             Electrical_engineering o Pollution o Remediation   
      
   ==========================================================================   
   Story Source: Materials provided by Duke_University. Original written   
   by Ken Kingery. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Shiheng Lu, Brittany N. Smith, Hope Meikle, Michael J. Therien,   
      Aaron D.   
      
         Franklin. All-Carbon Thin-Film Transistors Using Water-Only   
         Printing.   
      
         Nano Letters, 2023; 23 (6): 2100 DOI: 10.1021/acs.nanolett.2c04196   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230406152644.htm   
      
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