Omar A. Abdelrahman of the UMass Chemical Engineering (ChE) Department is part of a research team which has discovered that molecular motion can be predicted with high accuracy when confining molecules in small “nano-cages.” This theoretical method can be used for screening millions of possible nanomaterials and could improve the production of fuels and chemicals. The research was recently published online in ACS Central Science, a leading open-access journal of the American Chemical Society.
The article is also featured on the home page of the DOE science office »
The research was done by a team from the Catalysis Center for Energy Innovation, headquartered at the University of Delaware, and scientists at UMass Amherst and the University of Minnesota.
According to Newswise, a Department of Energy website, molecules in the air are free to move, vibrate, and tumble, but, if they are confined in small nanotubes or cavities, they lose a lot of motion. The total loss in motion has big implications for the ability to capture CO2 from the air, convert biomass molecules into biofuels, or to separate natural gas, all of which use nanomaterials with small tubes and pores.
“Our approach was to separate out molecular tumbling and rotating from movement in position,” said Abdelrahman, who is a co-author of the study, a UMass Amherst ChE assistant professor, and a researcher at the Catalysis Center for Energy Innovation. “We discovered that all molecules when put into nano-cages lose the same amount of movement in position, but the amount of rotating and spinning depended highly on the structure of the nano-cage.”
Newswise explained that researchers from the Catalysis Center for Energy Innovation arrived at their breakthrough when thinking about squeezing molecules into tight spaces. In the air, molecules can move up, down, and into space (three dimensions), but in a nanotube it was not clear if molecules can only move in one direction (through the tube) or two directions (on the surface of the tube). Similarly, molecules can rotate and spin in three ways, but the tube edges can prevent some or all of this motion. The amount of lost rotation was the unknown quantity.
Newswise added that the team connected molecular motion to the quantity of entropy, which combines all aspects of molecular motion into a single number. Molecules lose different amounts of entropy when they access the inside of nanoporous spaces, but it has not been clear how the structure of those nanospaces impacted the change in motion and loss in entropy.
“It might sound esoteric, but the entropy changes of molecules due to limitations of rotation and movement in position within nanopores decides whether nanomaterials will work for thousands of energy and separation technologies,” said Paul Dauenhauer, a co-author of the study who is a former ChE professor at UMass Amherst and a current University of Minnesota chemical engineering and materials science associate professor and also a researcher at the Catalysis Center for Energy Innovation. “If we can predict molecular motion and entropy of molecules, then we can quickly determine whether advanced nanomaterials will solve our most pressing energy challenges.”
Newswise also noted that the ability to predict entropy and molecular motion is connected to the recent nanotechnology boom. In the past decade, research in nanomaterials has developed millions of new technologies that can grab, separate, and react hydrocarbons from natural gas and biomass. However, each of these thousands of nanomaterials has a different size and shape, and it has been too expensive and time consuming to test these advanced nanomaterials one by one.
“This discovery really opens up the door to predicting which nanomaterials will be the breakthrough of the future,” said Dionisios Vlachos, the Catalysis Center for Energy Innovation director and University of Delaware professor. “We have invented more materials on the computer than we can ever test, and now we can rapidly determine on the computer if these will work for our energy and separation needs.” (September 2018)