Ultra-precise “POMBarens” screen out larger molecules (red) and let through only 1nm species (green), enabling sharp molecular sorting. | Photo credit: CSIR-Central Salt and Marine Chemical Research Institute, Bhavnagar
Imagine trying to filter sand from pebbles with a fishing net: it won’t work because the holes are too big and uneven. In chemistry, separating molecules that are nearly the same size is equally difficult. But a new study from IIT-Gandhinagar offered a solution: a synthetic membrane capable of distinguishing between molecules with sub-nanometer precision.
At the heart of the solution is a type of cluster called a polyoxometalate (POM). The researchers focused on a cluster called P8, which has a crown-like structure. Think of it as a small, hard doughnut. The hole in its center is exactly 1 nm wide.
The fixed size is ideal for a filter because it never changes, unlike the flexible, uneven holes in standard plastic filters.
The finding is significant because precise separation is essential for water purification, carbon capture and the production of certain drugs.
The study was published in Journal of the American Chemical Society on January 13.
POM clusters themselves form brittle crystals that are difficult to use as filters. Instead, the researchers attached “tails” made of alkyl chains to them. The tails acted as shock absorbers and glue, allowing the clusters to self-assemble into large and flexible thin films called POMembranes.
When the tails were too short, they could not fill all the space between the donut clusters, leaving gaps between the donuts. The longer tails on the other side packed tightly and completely filled the gaps.
The length of the tail also determined how the filter worked. In the short-tailed version, called Q4, water and molecules could flow through both the donut holes and the gaps between them. This made the filter work faster, but less accurately. In the long-tailed versions, Q7 and Q10, the gaps were blocked, forcing all liquid to pass through the 1 nm holes in the center of the P8 clusters. So the POMBrane was a very precise sieve.
In tests Q7 and Q10 blocked molecules larger than 1 nm and let smaller ones through. They were also able to separate molecules that differed in mass by only 100-200 daltons, which is about 10 times better than current membranes.
“These membranes are flexible, stable at different acidity levels and can be produced in large sheets,” CSIR-Central Salt and Marine Chemical Research Institute principal scientist and study co-author Ketan Patel said in a report. “This combination is essential if membranes are to be widely used in industry.”
Published – 02 Feb 2026 09:00 IST