Spinning 'turnstiles' inside a membrane let water through 44% faster while blocking 90% more ethanol

Researchers at the University of Queensland have built a membrane that moves water faster while blocking unwanted molecules more precisely, UQ said on 30 October. The work, with partners in Australia, the UK and China, was published in Science.

Beating a trade-off between speed and precision

Filtration membranes usually face a trade-off: membranes that let liquids through quickly tend to be less selective, and selective ones tend to be slow. “Overcoming this trade-off has been one of the biggest challenges in membrane science,” said Professor Xiwang Zhang, director of the UQ Dow Centre for Sustainable Engineering Innovation.

Turnstiles in the nanochannels

The membrane's nanochannels are less than one nanometer wide; the researchers call them molecular highways. The team introduced self-rotating ammonium ions into the channels, which made them dynamic instead of static. In tests separating water from ethanol, water transport rose by about 44%, ethanol transport fell by 90%, and separation accuracy improved tenfold compared with a standard filtration membrane.

“The self-rotating molecules are like a turnstile that help us regulate molecular traffic accurately.” — Professor Xiwang Zhang, University of Queensland

“Essentially we have upgraded the highways so that we get the best of both worlds: speed and selectivity,” Zhang said. The work was carried out with Dr. Zhuyuan Wang of UQ and collaborators from the University of Edinburgh, Monash University, the University of Melbourne, Nanjing Tech University, Nanjing University and the Australian Synchrotron.

From the lab to industry

The researchers see uses in industrial separations, chemical purification, resource recovery, carbon dioxide utilization, environmental protection and sustainable fuel production. For now it is a laboratory result; Zhang said the next step is to translate it into practical applications, and UQ did not give a timeline. More stories about new materials are collected under materials science.