A chemical compound (Meisenheimer complex) synthesised through a simple, single-step process of mixing two chemicals at room temperature has been found to be highly effective in removing fluoride and metal ions such as lead, mercury, cadmium, copper, and iron from drinking water.
The compound repels water by nature. A two-member team led by Professor Debasish Haldar from the Department of Chemical Sciences at the Indian Institute of Science Education and Research (IISER), Kolkata tested its efficiency in removing oil spills. A polystyrene sponge that absorbs water became a water-repelling material when coated with the compound and was able to absorb a wide variety of oils and organic solvents from water.
“The compound has negative and positive charged parts and this helps it absorb metal ion pollutants and fluoride from water,” says Professor Haldar.
“One gram of the compound was able to remove a large amount of lead (817 mg) and mercury (830 mg) from water and nearly half its weight of copper (451 mg) and iron (511 mg),” says Tanmay Das from IISER, Kolkata and the first author of a paper published on this in the journal ACS Omega.
The researchers tested the efficiency of the compound to absorb different metals by passing water containing 50-100 parts per million (ppm) of metal solutions through two grams of the compound mixed in 60 grams of silica gel. The absorption capacity was extremely high at around 99%.
To test the compound’s capacity to remove metal ions below the World Health Organisation’s limit, the researchers used the compound to treat water containing five ppm of copper, mercury, cadmium and iron. After 10 minutes of treatment, the concentration levels of the metals dropped to below 2 parts per billion (ppb), which is far below the WHO limit for these metals.
In the case of fluoride, water with a high concentration of fluoride (10 ppm) was treated with the compound. After 10 minutes of treatment, the fluoride concentration dropped to 10 ppb. The silica gel filter containing the compound showed equal efficiency for three cycles and has to be recycled after the third cycle.
“We are trying to commercialise it. We are already working with a company based in Chennai, which is testing the material. A water filter using our compound may become commercially available in a year’s time,” Professor Haldar says.
