A marriage between 3D printer plastic and a versatile material for detecting and storing gases could lead to inexpensive sensors and fuel cell batteries, suggests new research from the US National Institute of Standards and Technology (NIST).
The versatile material is a metal-organic framework (MOF); these materials are easy to make, cost little, and some are good at picking out a particular gas from the air. Seen on a microscopic level, MOFs look like buildings under construction – think of steel girders with space between them. A particular MOF talent is allowing fluids to flow through their spaces while their girders attract some specific part of the fluid and hold onto it as the rest of the fluid flows past. MOFs are already promising candidates for refining petroleum and other hydrocarbons.
MOFs have caught the attention of a team of scientists from NIST and American University because they could also form the basis for an inexpensive sensing technology. For example, certain MOFs are good at filtering out methane or carbon dioxide, both of which are greenhouse gases. The problem is that newly made MOFs are tiny particles that in bulk have the consistency of dust. And it's hard to build a usable sensor from a material that slips through your fingers.
To address this problem, the team decided to try mixing MOFs into the plastic used with 3D printers. Not only could the resultant plastic material be molded into any shape the team desired, but it’s also permeable enough to allow gases to pass right through it, meaning the MOFs could snag the specific gas molecules the team wants to detect. But would MOFs work in the mix?
In a paper in Polymers for Advanced Technologies, the researchers show that the idea has promise not only for sensing but for other applications as well. They demonstrate that the MOFs and the plastic get along well; for example, the MOFs don't settle to the bottom of the plastic when it's melted, but stay evenly distributed in the mixture. The team then mixed in a specific MOF that's good at capturing hydrogen gas and conducted testing to see how well the solidified mixture could store hydrogen.
"The auto industry is still looking for an inexpensive, lightweight way to store fuel in hydrogen-powered cars," said NIST sensor scientist Zeeshan Ahmed. "We're hoping that MOFs in plastic might form the basis of the fuel tank."
The paper also shows that when exposed to hydrogen gas, the solid mix retains more than 50 times more hydrogen than plastic alone, indicating that the MOFs are still functioning effectively while inside the plastic. These are promising results, but not yet good enough for a fuel cell.
Ahmed said his team members are optimistic the idea can be improved enough to be practical. They have already built on their initial research in a second, forthcoming paper, which explores how well two other MOFs can absorb nitrogen gas as well as hydrogen, and also shows how to make the MOF-plastic mixtures immune to the degrading effects of humidity. The team is now pursuing collaborations with other NIST research groups to develop MOF-based sensors.
"The goal is to find a storage method that can hold 4.5% hydrogen by weight, and we've got a bit less than 1% now," Ahmed said. "But from a materials perspective, we don't need to make that dramatic an improvement to reach the goal. So we see the glass – or the plastic – as half full already."
This story is adapted from material from NIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
