VICKSBURG, Miss. ⸺ When Dr. Victor Medina, a research engineer with the U.S. Army Engineer Research and Development Center’s Environmental Laboratory, was designing the Decontamination Effluent Treatment System, he visited his teammates to make a request.
“He came in and said, ‘We need to create a piece of membrane material as big as my desk,’” said Dr. Chris Griggs, an ERDC-EL research chemist. “And Jose Mattei-Sosa ⸺ a chemical engineer on my team ⸺ and I looked at each other and said, ‘OK’.”
Medina’s request turned into reality this September, when a patent was issued for the method of recycling the membrane material, a graphene oxide (GO)/chitosan compound.
The DETS was designed to treat water polluted with contaminants — chemical, biological or radiological. “Fitting the DETS with membrane technology rather than granular media filtration is the best way to remove any contaminant from the water stream, especially if we don’t know what contaminant has been used, because the membrane is more selective due to the extremely small pore size.” Medina said. “If you don’t know what’s been released, the membrane provides the highest quality treatment for the effluent.”
The team chose GO for the membrane because of the unique tendency of the material flakes to self-assemble in layers, creating narrow channels in between. The water flowing through the interlayered spacing contributes to effectively removing contaminants.
Griggs explained that the GO by itself would not stay together in water, however, because it has negative charges that repel each other when hydrated, causing the material to disperse. Some positively charged material was needed to hold the GO together.
“Normally, aluminum 3+ is used, which crosslinks the GO, but we substituted another cationic, or positively charged material: the polymer chitosan, which binds the GO together,” said Griggs, who completed his doctoral dissertation on chitosan biopolymers.
The team is among the first pioneers to develop this material for a water treatment application, although they haven’t yet actually used it with the DETS. “What really distinguishes us is the scale at which we’re working. Because we were looking at it for the DETS system, we had to scale it up ⸺ making a filter membrane that was an inch or so in diameter wasn’t appropriate, we needed something that could treat 10 gallons/minute,” Griggs said. “To scale up, we had to use a lot more material, so we had to make it recyclable, because GO costs $250/gram.”
“We’re anticipating the cost of material will eventually decrease,” he said. “But right now it’s very expensive.”
The team designed the GO/chitosan membrane to be 100 percent recyclable from the very beginning. They can make the exact same product over and over again, restoring the membrane structure, the chemical content and the material’s properties. “It reduces the lifecycle cost of the GO content,” Griggs said.
“That is rare when it comes to traditional polymers because polymers and plastics crosslink in general, and when they do that’s an irreversible process. That means it will decompose before you can melt it down — basically you break the chemical bonds and they can’t be restored. They can be reused as fillers, but you’d never be able to remake the same product.
“As far as we know, our team has the largest graphene oxide membranes in the world.”
Medina, Griggs and Mattei-Sosa developed the process to recycle the composite; Medina, Griggs, Mattei-Sosa, and Brooke Petery and Luke Gurtowski, also ERDC-EL research engineers, have a second patent pending for developing the material. “This patent took two years; it was remarkably quick,” Medina said. “The other patents I’ve gotten have taken four or five years.
“The one who started this was Mattei-Sosa. He started the process, taking old GO membranes that had been used to treat contaminants, dissolved them in acid, recast them and used them to treat the same contaminant,” Medina continued. “When we compared the recorded performance from before and after recycling, the membranes were just as effective.”
The team expects other applications for this material. Griggs and Mattei-Sosa have been looking at adding it to construction materials to make them stronger. Medina has been looking at using it for decontamination, as a wipe or a coupon, to bind contaminants.
“We were able to succeed at developing this material on this scale because we were looking at it from a different lens, through the DETS program,” Griggs said. “We probably wouldn’t have gotten there if we hadn’t had that kind of mission space. We now have a recyclable product that maximizes decontamination capabilities for both the Soldier and the Nation.”