'Designer' materials found deep in Siberian permafrost
We've just discovered natural metal-organic frameworks – but scientists have been making them in the lab for decades. Belinda Smith reports.
Chemists often copy molecules from nature – think drugs derived from bacteria and plants which are refined and synthesised in the lab.
Now, the tables have turned – in a way.
A team of chemists from Canada and Russia probed the structure of rare minerals dug from the depths of Siberian coal mines and found they had the porous structure of metal-organic frameworks, or MOFs – a family of recently manmade, designer materials never before seen in nature.
While natural MOFs have been around longer than synthesised versions, the findings, published in Scientific Reports, suggest there could be many more MOFs out there waiting to be discovered and exploited in the lab.
It "completely changes the normal view of these highly popular materials as solely artificial", says study co-author Tomislav Friščić from McGill University in Canada.
Despite first being synthesised around the middle of last century, work into MOFs has boomed in the past couple of decades.
Like molecular sponges, they comprise an ordered array of atoms punctuated by large gaps that effectively trap gases. One promising use for MOFs is in carbon capture, where a MOF “scrubber” could soak up carbon dioxide from coal-fired power plant emissions.
But they’d never been seen in nature.
So when Friščić came across mention of two rare organic minerals – stepanovite and zhemchuzhnikovite – in a Canadian mineralogy journal, he was intrigued. Samples brought to the surface from drill holes 230 metres deep were chemically analysed and reported in 1963.
Friščić noticed their formulae were very similar to that of MOFs developed in the 1990s – could they have the same structure too?
So Friščić, Igor Huskić (also at McGill) and colleagues from Lomonsov Moscow State University and Saint Petersburg State University retrieved the original samples of stepanovite and zhemchuzhnikovite.
But because the minerals were largely impure – being thin veins embedded in lignite – the researchers also grew pure stepanovite and zhemchuzhnikovite crystals, yielding green and yellow-green shards respectively.
Using a technique called X-ray powder diffraction, which fires X-rays at finely crushed samples of the crystals and measures how the X-rays bounce off, they concluded that both stepanovite and zhemchuzhnikovite had the ordered honeycomb-like structure of many MOFs.
Stepanovite and zhemchuzhnikovite are pretty rare so the team is expanding their search for more abundant MOF-like minerals which may be suitable for gas capture or storage.