Image: University of Manchester
Graphene can take on at least three distinct technology approaches for producing clean water, according to Miao Yu, a professor at University of South Carolina and founder of UK-based G2O Water Technologies Ltd. as he explained to The Graphene Council last year in a interview.
In that interview, Yu said the first approach of the three is to use graphene in the creation of functional coatings. The second approach involves producing lamellar structures with nano-channels, which requires using fine layers of alternating types of materials. G2O Water is doing a bit of both of these approaches by creating a functional coating that can be applied to today’s polymer water membranes, and also creating scalable fabrication of lamellar structures of graphene oxide.
The third approach is to allow selective permeation through structural defects of single-layer graphene or graphene oxide. A group at MIT is probably the most notable example of the use of this approach in a technique they reported on three years ago.
All of these approaches to using graphene in water applications is taking on increased interest after news came out last week that researchers from the University of Manchester have developed a graphene oxide membrane that in addition to filtering out small particles has small enough pores that it can filter out salt ions. This approach, which was published in the journal Nature Nanotechnology, falls into the approach taken by the MIT researchers.
The Manchester researchers have managed to overcome a key problem in this approach when the membranes swell up after being immersed in water for some time, allowing smaller particles to continue to pass through.
“Realization of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” said Rahul Nair, a professor at the University of Manchester and one of the co-authors of the research, in a press release. “This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes.”
Of course, the imprimatur of the University of Manchester on anything to do with graphene suddenly makes this latest research noteworthy. However, the final arbiter on whether this graphene approach or the others like it for either desalinating or purifying water remains squarely on the industry.
While the mainstream press--like the BBC--has seemingly ignored all other efforts for using graphene in the desalination or purification of water--setting up the Manchester research as a kind of first in the field--the trade press has been a bit more circumspect.
The publication Water & Wastewater International (WWi) has a pretty thorough assessment of the latest Manchester research and how it stacks up to other efforts for desalinating water using graphene.
While WWi remains pretty sanguine about the general prospects of using graphene for water desalination, they get some expert opinions that characterizes this latest research as something of a long shot at this point.
Graeme Pearce, principal at Membrane Consultancy Associates (MCA) told WWi in an interview: "The development at the University of Manchester aims to produce a membrane with a highly controlled character, free from defects. Given the materials used, longevity should also be good. The challenge will be whether the membrane can be effectively used with the current form factor (the spiral wound element mounted in series in long pressure vessels) and using current process design concepts.
"Alternatively, the membrane might be better exploited by a completely different approach to process design, which would be high risk and slow to introduce, but might have a much greater long term impact if the improved membrane can be exploited more efficiently."
He added: "The key issue would be to demonstrate both performance and longevity in the first instance and then establish what features of the current approach to desalination plants limit the benefits of a new membrane and what can be done to remove these impediments."
It turns out that the technology of G2O Water technologies might have the inside track at this point, according to Pearce.
He added: "This preserves the form factor and should be more easily adopted by the industry. The development is still early stage and the longevity of the coating has yet to be established, but the approach appears to be promising and initial results on performance enhancement have been encouraging. This is more likely to allow a radical optimization of existing practice rather than the potentially more revolutionary but higher risk development from Manchester."