Published:
Author: Emily Flinchum
An illustration of the Earth made of blue denim and stiching.
“Indigo dye is cost-effective and readily available, offering a viable alternative to traditional heat-based methods of CO2 capture,"—Yayuan Liu, assistant professor of chemical and biomolecular engineering. (image created by Dall-E 3)

The dye responsible for giving your favorite jeans their iconic blue color might also be a game-changer in the fight against climate change. In a new study, scientists at Johns Hopkins Whiting School of Engineering and the Samsung Advanced Institute of Technology’s Air Science Research Center describe a method of harnessing this popular pigment to combat atmospheric carbon dioxide.

The team has developed a way to leverage the chemical properties of indigo, a blue coloring agent extracted from a shrub native to tropical areas, and electricity to remove CO2 from the atmosphere. They say their electrochemically mediated carbon capture (EMCC) method—described in Advanced Functional Materials—is scalable and shows promise for real-world applications, such as factories and power plants. The article is “Indigo as a Low-Cost Redox-Active Sorbent for Electrochemically Mediated Carbon Capture.”

“Our tests showed that this indigo-based system works at 80% of the best possible efficiency when tested in a simulated environment similar to a factory’s exhaust stream,” said Krish Jayarapu, first author of the study and an undergraduate in the Whiting School’s Department of Chemical and Biomolecular Engineering. “The chemical properties of indigo allow the dye to grab onto CO2 when electricity is applied, which means electrons are added to the system. It releases CO2 when the current is reversed, or when electrons are removed. Using electricity for carbon capture, such as in this process, could allow it to integrate as a plug-and-play unit with existing renewable energy sources.

Laboratory setup labeled with the following components:Mass Flow Controllers: These are devices used to control the flow rate of gases in the experiment.
CO2 Sensor: This sensor detects and measures the concentration of carbon dioxide.
Inlet: The point where gases enter the capture device.
Capture Device: The main device used in the experiment to capture or process the gases.
Outlet: The point where gases exit the capture device.
The setup is connected with various tubes and electrical wires, indicating a controlled experiment to measure or manipulate gas flow, particularly focusing on carbon dioxide.

Fixed-bed cell

Though the current device is a bench-scale prototype, its modular design, flexible performance, simple operating system, and reliance on low-cost materials, including indigo, highlight its potential to be a cost-effective and versatile alternative to expensive heat-based methods for industrial carbon capture, they say.

“Indigo dye is cost-effective and readily available, offering a viable alternative to traditional heat-based methods of CO2 capture,” said Yayuan Liu, principal investigator of the study, assistant professor of chemical and biomolecular engineering, and an associate member of the Ralph O’Connor Sustainable Energy Institute. “Free from the limitations of complex equipment, the electrochemically mediated carbon capture method can be utilized in various settings, from small devices to large industrial systems. Moreover, the electrical process helps move us closer to the best possible efficiency for capturing carbon.”

Jayarapu’s research was funded in part by the department’s Elnora Streb Muly Research Award, which supports undergraduate chemical and biomolecular engineering students in tackling practical industry problems.

Diagram illustrating a setup for a CO2 capture experiment, including the following elements:MFC (Mass Flow Controllers): Devices regulating the flow of gases.
Gas Cylinders: One containing 100% N2 and the other with 20% CO2.
CO2 Sensor: Measures the concentration of CO2.
Capture Device Components:
Wingnuts, acrylic plates, steel mesh, indigo layer, carbon paper separator, LFP (likely Lithium Iron Phosphate), and rubber gaskets, all assembled with screws.

CO2 separation performance in a fixed-bed cell.

Other co-authors of the study include Anmol Mathur, Xing Li, Andong Liu, and Lingyu Zhang—all from Johns Hopkins’ Department of Chemical and Biomolecular Engineering— as well as Jaeeun Kim, Hyunah Kim, and Su Keun Kuk of the Air Science Research Center.