World’s massive economic growth is undoubtedly the result of the industrial era, which began between 18th-19th century in parts of Europe and North America. With the constant need and greed of human beings, industrialization became colossal in no time and with it we have brought upon ourselves both the positive and negative aspects. Current ecological system has been under perpetual mortification, thanks to the enormous level of pollution in air, water, soil, just name it; owing to the undeniable expansion of mechanisation. Among several other consequences of the above, contamination of drinking water on our planet is one of the most pressing issues of our time. Drinking water constitutes a minuscule fraction of entire water content on earth that renders the survival of a vast majority of living organisms. Release of heavy metal ions like those of lead, mercury and cadmium from industries to water has edged disastrous fallouts in public health. This paucity of clean drinking water has directed scientists over the world to find ways to remove hazardous wastes and purify contaminated water.
Ekashmi Rathore, a graduate student in Dr. Kanishka Biswas’s Laboratory at NCU, JNCASR, have identified a novel compound for isolating lead from water. Through the traditional process of intercalation – a reversible insertion of a molecule (or ion) into materials with layered structures, Ekashmi synthesised a potassium intercalated layered compound 1 (K-MPS-1, K0.48Mn0.76PS3.H2O ) which is competent enough for efficient extraction of lead ions from water even at extremely low concentration, i.e. 1 ppb which is well below the tolerance level of lead ions in drinking water, <15 ppb as per USA-EPA 2. During intercalation of potassium ion, the interlayer spacing (van der Waals gap) between the sheets increases, creating voids at the manganese sites. In the following step, when the lead contaminated water was allowed to pass through the intercalated compound, the potassium ions were displaced and lead ions got adsorbed into the void sites of manganese, further restoring the increased gap (originally interlayer spacing at 6.45 Å, intercalation increased it to 9.40 Å, then void site occupancy by lead ions decreased it back to ~6.45 Å).
The entire process has been examined in a wide range of pH (2-12) water and works adequately great in being able to remove lead within this whole spectrum. Along with making the compound useable in various types of water content, the team has also shown its high removal capacity (~393 mg/g) of lead ions compared to earlier studies. Further data showed 97% extraction of lead ions in a matter of 4.5h and ≥99% removal within no more than 12h. The course of action being relatively swift ensures its pragmatic nature at an industrial level. They also showed the compound’s precise selectivity in terms of being able to capture and remove only lead ions from a pool of several other mono and divalent ions that are also present in water. Additionally, the compound is stable to oxidisation compared to previously tried methods and hence comes across as an advantage in materialising this reaction.
Ekashmi (left) with Dr. Kanishka Biswas (right) at Solid State Chemistry Laboratory in NCU, JNCASR.
In fact, very interestingly, when the same procedure was experimented using water from a nearby lake (Rachenahalli Lake, Bangalore), the compound (K-MPS-1) was successfully able to selectively sequester ~99% of lead ions! So, as we can see, this novel intercalated compound is able to efficiently isolate harmful lead from drinking water through its high removal capacity, its high selectivity, being able to function in a wide pH range, works even when the concentration of lead ion is very low and more importantly being stable.
Sources of heavy metal and radionuclide in water and schematic representation for the mechanism of lead ion (Pb2+) and cesium ion (Cs+ ) capture by K-MPS-1. (Mn, purple; P, blue; S, yellow; K, black; heavy metal or radionuclide, green).
Ekashmi’s alluring idea accompanied by the prudent experiments led it to a success where her work got published in The Journal of Physical Chemistry (C) 1. She also got an award by The Falling Walls Lab India 2017, following which she beautifully presented her work in Berlin the same year (check out the video). She owes this success to her mentor Dr. Kanishka Biswas for encouraging her to pursue the idea of lead removal despite the main theme of the lab being research on thermoelectric materials. Ekashmi pursued this idea further and implemented it in efficient capture and removal of Cesium, an enduring radioisotope, from water using the same compound K-MPS-1 and similar methodology used for lead isolation 3. Further research on her plate includes mercury removal from contaminated areas and development of prototypes for detection of hazardous wastes in water.
This article is authored by Manaswini Sarangi, Evolutionary Biology Laboratory, EIBU, JNCASR.
- Rathore, Ekashmi, Provas Pal, and Kanishka Biswas. “Layered Metal Chalcophosphate (K-MPS-1) for Efficient, Selective, and ppb Level Sequestration of Pb from Water.” The Journal of Physical Chemistry C121.14 (2017).
- United States Environmental Protection Agency; Drinking Water Requirements for States and Public Water Systems; https://www.epa.gov/dwreginfo/lead-and-copper-rule.
- Rathore, Ekashmi, Provas Pal, and Kanishka Biswas. “Reversible and efficient sequestration of Cs from water by layered metal thiophosphate, K0. 48Mn0. 76PS3. H2O.” Chemistry-A European Journal (2017).