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Nanoporous membrane filters out tiny biomolecules

Published online 29 September 2015

Scientists make highly porous membrane using copolymers for separating molecules from a solution.

Biplab Das

Scientists synthesize block copolymer membranes with pore sizes smaller than 3 nm — a feat considering that, previously, the smallest pore size made was around 15 nm. 

These nanoporous membranes, which self-assemble and are formed by copolymers, are used to remove micropollutants from wastewater. 

The research team from King Abdullah University of Science and Technology (KAUST) has made the highly porous membrane by adding different amounts of two block copolymers - polystyrene-b-poly(4-vinylpyridine) and polystyrene-b-poly(acrylic acid) into a mixture of organic solvents such as dimethylformamide, dioxane and acetone1 . 

To measure the actual pore size, the scientists filtered solutions of biomolecules such as protoporphyrin IX and lysine through the membranes. While water and lysine passed through the membrane, protoporphyrin IX was rejected. 

Studies have shown that protoporphyrin IX and lysine have diameters of 1.47 nm and 0.9 nm, respectively, indicating that the effective pore diameter of the membrane was even smaller than 1.5 nm. 

Such exceptionally small pore sizes aid water transport — faster than similar commercial counterparts, the researchers say.

“By using the two blended block copolymers, it would be possible to decrease the membrane pore size below 5 nm, opening avenues for molecular separations in pharmaceutical industries,” says principal investigator Klaus-Viktor Peinemann. 


  1. Yu, Haizhou et al. Self-assembled asymmetric block copolymer membranes: bridging the gap from ultra- to nanofiltration. Angew. Chem. Int. Ed. 54, 1–6 (2015).