Efficient removal of contaminants like oil and toxic dyes from water sources is an issue of global importance. Oil spills can be devastating to both the environment and the economy because cleanup is costly and damage to the ecosystem is sometimes irreparable.
Marine oil spills are typically contained and removed using booms and skimmers, or chemicals are dumped into the water to break down the oil and speed up natural biodegradation — processes that can be expensive, time consuming, and not always 100 percent effective.
Toxic dyes — common water pollutants in the textile industry — tend to escape conventional wastewater treatment because of their chemical properties.
To address these problems, NYU Abu Dhabi scientists have come up with a new way to remove toxic contaminants from water they believe could be more efficient and less costly than current methods.
They have developed the first calixarene based superhydrophobic, porous material that repels water and attracts oil and dye kind of like a sponge. They call it CalP.
Dinesh Shetty, lead researcher and chemist at NYUAD, said CalP — a light brown powder — “offers a new way to remove toxins from water sources and can absorb up to seven times its weight of oil from an oil and water mixture.”
The basic material has been around for decades, he explained, but this is the first porous organic calixarene-based polymer synthesized in the lab for the purpose of purifying water.
Ali Trabolsi, NYUAD assistant professor of chemistry, said CalP is able to remove “oil from water so efficiently, in just minutes, because it has several distinct properties:
- it floats, has high surface area, and low density;
- it has pores both from calixarene cavity and hypercrosslinked 3D structure that collect toxins inside;
- the material is superhydrophobic which means it repels water and it has an excellent ability to absorb a range of pollutants.”
Lab experiments were conducted using two types of oil: used engine oil and commercial grade crude oil.
After being placed on top of an oil-water mixture the light brown powder quickly absorbed the oil and turned dark brown. Complete absorption of the oil happened in about five minutes.
Its ability to absorb oil so quickly leads the researchers to believe that this process of removing contaminants from water is potentially more efficient than other similar methods because the results are “significantly higher than most absorbent materials reported to date, including commercial activated carbon.”
Further experiments using different types of dyes — anionic and cationic — had the same impressive results and are especially promising because dyes are chemically designed to withstand degradation.
In one test, about 80 percent of toxic dye poured into a glass of water was absorbed within five minutes and the rest was completely gone after just 15 minutes.
Another distinct quality of CalP is that it can be washed and reused to absorb oil products over and over again with the same efficiency, potentially reducing the cost of cleaning large oil spills.
“It’s an important part of our discovery,” said Ilma Jahovic, NYUAD chemistry major and student researcher, “because we found it was very easy to regenerate the material” even after it was soaked in oil or dye. “We did multiple cycles and its efficiency was maintained.”
“Other similar materials can be reused but require cleaning at high temperatures and it’s expensive,” she explained, whereas this material requires only mild washing with diethyl ether, ethanol, or a light acidic solution.
The next step in the research is to improve the absorption efficiency of oil products even further, and find ways to make production cheaper. CalP could also be used to further other areas of petroleum research such as gas separation to make cleaner fuel, added Jahovic.
The material is not yet practical for cleaning large oil spills, she stressed, because “we are only at gram scale” in the lab environment.