Heya!
Daniel here,
Firstly, quick shout-out to our REU researchers working on solar membrane desalination, I just read about your current progress in a Rice article: http://news.rice.edu/2017/06/19/freshwater-from-salt-water-using-only-solar-energy-2/?utm_source=LinkedIn&utm_medium=SolarSalt&utm_campaign=LinkedIn%20links Looks very promising. And it was very nice to see Dr. Li there in the article.
I’d like to report some of my own progress as well.
Since I have altered my project to some degree, I have also updated my problem statement. As follows:
MCDI technology is a wonderfully power-efficient method for deionizing/desalinating water for drinking and other uses. However, we are currently limited in our ability to remove ions selectively from a solution, without removing a different species. Although CDI desalinization has been studied by leading research facilities with increased attention within the past 10 years, not a whole lot of progress has been made in the selectivity of the procedure, given that the majority of adsorbent materials used for CDI do not discriminate between differing ionic species to a significant degree. I plan to tackle the challenging lack of selectivity by incorporating substances into our current MCDI polymer membranes that have been theorized – or preferably observed through other tests and applications – to be ionically selective. I will change the composition of our current polymer membranes to accommodate these substances.
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We are currently acquiring, modifying, and preparing to test a handful of selectively adsorptive materials, integrating them into our current MCDI desalination configuration. I have attempted the first of my selective electrodes, an activated carbon electrode coated with a composite polymer membrane consisting of poly(vinyl alcohol) crosslinked with sulfosuccinic acid combined with a (hopefully) ionically selective ingredient, Sodium Alginate. During the coating process, we noted a large amount bubbling on contact between the activated carbon and the Na-alginate coating, although the coating itself appeared smooth and properly viscous prior to the flow-coating. We hypothesize that this occurrence may be the product of over-drying the activated carbon layer before coating with the polymer. We will redo the experiment tomorrow morning with that in mind.
Other than that, we are currently looking into a few other selective reagents that may yield interesting results when used in our MCDI cell. These substances included the aforementioned layered metal sulfide (KMS-1), Chitosan polysaccharide, and a couple of others.
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One of the most unique things about the pre-screening research process in which I must engage in before blowing my supply stipend to purchase chemicals is this: 90% of the time, there is no academic journal that can tell me: “Yes, this substance will probably work in your configuration.” There are often no answers. No one has tried what you are about to do. One of the frustrations, but also the beauty of research. At times, one can only make a solid, educated guess, do a little thinking+engineering to reduce costs and losses, and give it a shot.
Sometimes it works. Most times, though, you’re cleaning wasted cross-linked polymer out of the glassware whilst inwardly thumping your head on the nearest Field Emission-Scanning Electro Microscope.
Thoroughly enjoying the process!
More soon,
Daniel S. Cana