Separating gases is a critical process in many industries, from medical oxygen and nitrogen production to carbon capture and natural gas purification.
However, this process is often energy-intensive and costly.
Wei Zhang, a chemistry professor at the University of Colorado Boulder, explains, “For example, separating oxygen and nitrogen requires cooling air to very low temperatures until it liquefies.
Then, by slowly warming it, the gases evaporate at different temperatures and separate out. This method is very energy-intensive and expensive.”
Most gas separation methods rely on porous materials that let specific gases pass through. The problem is these materials are usually rigid and only work for certain types of gases. Introducing different gases often makes them ineffective.
However, in a recent study published in the journal Science, Zhang and his team have developed a new type of porous material that can adapt to and separate various gases.
This material combines rigidity with flexibility, allowing size-based gas separation at a much lower energy cost.
“Our goal is to make technology better and more sustainable,” says Zhang.
Traditionally, gas separation materials have been rigid and specific to certain gases. This rigidity helps define the pores and directs the gases, but it also limits the number of gases that can pass through due to different molecule sizes.
Zhang and his research group spent years developing a porous material with a flexible component. This flexibility allows the material to adjust its pore size, making it adaptable to multiple gases.
“We found that at room temperature, the pore is relatively large, allowing most gases to pass through,” Zhang explains. “As we increase the temperature to about 50 degrees Celsius, the flexible component starts to move more, causing the pore size to shrink. Larger gases are blocked out. At 100 degrees Celsius, only the smallest gas, hydrogen, can pass through.”
The material is made of small organic molecules and resembles zeolite, a porous, crystalline material mainly composed of silicon, aluminum, and oxygen. “It’s a porous material with highly ordered pores, like a honeycomb,” says Zhang.
The researchers used a technique called dynamic covalent chemistry, focusing on the boron-oxygen bond. This bond can break and reform repeatedly, allowing the material to self-correct and maintain its structure.
“We wanted to create something tunable, responsive, and adaptable. The boron-oxygen bond fit well because of its flexibility and reversibility,” Zhang says.
Developing this new material took time. Zhang notes, “Making the material is easy. The challenge was understanding its structure—how the bonds form and how the angles within the material align. We had promising data but couldn’t immediately explain it.”
To overcome this, the team focused on a small-molecule model with the same reactive sites as their material to understand its structure better.
Zhang emphasizes the importance of scalability, as industrial applications would require large amounts of the material. “The building blocks are commercially available and inexpensive, making this method highly scalable. It could be adopted by industry when the time is right.”
The team has applied for a patent and continues researching other building block materials to expand the approach. Zhang also sees potential collaborations with engineering researchers to integrate the material into membrane-based applications.
“Membrane separations generally require much less energy, making them more sustainable in the long run,” Zhang says. “Our goal is to improve technology to meet industry needs sustainably.”
This innovative material could revolutionize gas separation processes, making them more efficient and less costly, benefiting various industries and the environment.
