Friday, May 8, 2015

MIT Engineers Repair Graphene Water Filters by ALD

Here is an interesting story from on "How Engineers Repaired One-Atom Thick Graphene Filters"

(Image courtesy MIT News)

Graphene seems to be the next big thing in water filtration as scientists look to create ultrathin membranes to filter out contaminants. Only problem is, defects in the making of one-atom thick membranes are a common occurrence, causing leaks.

In a two-step process, engineers have successfully sealed leaks in graphene. First, the team fabricated graphene on a copper surface (top left) — a process that can create intrinsic defects in graphene, shown as cracks on the surface. After lifting the graphene and depositing it on a porous surface (top right), the transfer creates further holes and tears. In a first step (bottom left), the team used atomic layer deposition to deposit hafnium (in gray) to seal intrinsic cracks, then plugged the remaining holes (bottom left) with nylon (in red), via interfacial polymerization. (MIT News)

Hope is not lost though as engineers have found a way to repair the cracks and holes, filling them with a combination of chemical deposition and polymerization techniques.

The first of the two techniques used, addresses the smaller intrinsic defects. Using a process called “atomic layer disposition,” the team placed the graphene membrane in a vacuum chamber, pulsing in a hafnium containing chemical that normal does not interact with graphene.

In this scenario the chemical sticks to openings in the graphene, attracted to the area’s higher surface energy.

After several rounds of applied atomic layer deposition, the hafnium oxide successfully filled in the graphene’s nanometer-scale intrinsic defects.

This solution quickly unveiled a new issue, as the team realized it would require too much time to fill in the membranes larger defects.