There are many systems that use sunlight to purify polluted water, but their output is often quite limited. But a new loofah-inspired hydrogel uses sunlight to significantly increase the amount of water it can process at one time, treating just enough water to meet a person’s daily needs.
Existing solar still-type systems use sunlight to heat dirty water to a point where it begins to evaporate. As a result, contaminant-free water vapor condenses on surfaces within the still and then drips into the collection reservoir. This is a clever setup, but it only produces potable water while the sun is shining. Still, it’s a slow process.
Materials known as temperature-responsive hydrogels offer an alternative because they absorb dirty water at low temperatures and expel it (in a purified form) when heated. According to colleagues, most such gels have closed pores, which means they cannot process water fast enough for most people’s needs.
With that limitation in mind, scientists set out to replicate the highly open-pore design of natural loofah sponges.
They started by using a water/glycol mixture as their own polymerization medium to produce the PNIPAm (poly(N-isopropylacrylamide)) hydrogels with the large, open pores they desired. Next, the scientist coated the internal pores of the gel with two of his other polymers, polydopamine (PDA) and poly(sulfobetaine methacrylate) (PSMBA).
The resulting material absorbed contaminated water at room temperature and released 70% of its water within 10 minutes when heated by simulated sunlight. This was 4x faster than previously tested. closed– Pore hydrogel. Moreover, even under lighting conditions simulating a partially cloudy sky, the loofah gel released the same amount of water within 15–20 minutes.
Xiaohui Xu / Princeton University
So how does it work in practice?
Xu shows that hydrogels are hydrophilic (attracting water) at low temperatures, but become hydrophobic (repellent) when heated. Contaminants such as organic dyes (used in lab tests) do At low temperatures they are drawn in with the water, but their molecules stick to the gel so they are not expelled when the water is released at high temperatures. Therefore, it is not drawn in in the first place.
Lab tests have also successfully used loofah hydrogel to remove contaminants such as microplastics and heavy metals. With two treatment cycles, the material was able to reduce chromium contamination from approximately 40 ppm to below the acceptable limit of 0.07 ppm for drinking water.
Yes, Xu says the loofah hydrogel can be reused by simply rinsing it with dilute acid or ethanol.
A paper on this study was recently published in the journal ACS Central Science.
Source: American Chemical Society
