368 billion tons. According to statistics, this was the total amount of global carbon dioxide emissions to the atmosphere in 2022. The resulting environmental problems, such as declining air quality, rising ocean temperatures, and frequent extreme weather, have prompted researchers to continuously explore various means to improve the situation.

Direct air capture (DAC) is one of such methods, and is key to achieving carbon neutrality. By safely sequestering carbon from carbon dioxide absorbed from the atmosphere, DAC captures carbon to achieve resource recovery. To date, the low atmospheric concentration of carbon dioxide has limited DAC’s efficiency. The emergence of a new type of DAC adsorbent material may become an important turning point for the widespread application of carbon capture technology.

Professor Dong Hang of GTSI recently co-authored a research article entitled "Direct air capture (DAC) and sequestration of CO2: Dramatic effect of coordinated Cu(II) onto a chelating weak base ion exchanger", which was published by the renowned academic journal Science Advances. The paper revealed a high-capacity air CO2 capture material that can be regenerated at a temperature of less than 90°C and can use seawater as a regenerant to convert CO2 into harmless and chemically stable alkalinity for storage. The dual-mode regeneration allows for more flexibility in applications and provides a new path for using marine resources for CO2 capture and storage.

Below is Professor Dong Hang's introduction to this latest research achievement.

Polyam-N-Cu2+ Composite Material

Three-fold Increase in Carbon Dioxide Capture Capacity

To date, the adsorption capacity of most DAC materials is within the range of 1.0 to 1.5 mole CO2/kg. Further increasing the adsorption capacity is crucial to improve the economic feasibility of DAC technology.

The study found that using copper ions as a medium can significantly increase the carbon capture capacity of the amine functional group. When copper and other transition metal cations are covalently linked to chelating polymers with multiple nitrogen electron donors through Lewis acid-base (LAB) interactions, the two positive charges of copper ions are not neutralized, so the coordinated copper ions can serve as an anion exchange adsorption site. The resulting composite material with a polyamine-Cu(II) structure (Polyam-N-Cu2+) can serve as a high-capacity anion adsorbent and bind with CO2 water-soluble molecules (HCO3-/CO32-) through electrostatic and LAB interactions within a wide pH range.

Ultra-high Carbon Dioxide Adsorption Capacity

Real Seawater Regeneration Efficiency of Over 80%

Tests have shown that using hydroxide as the counterion, Polyam-N-Cu2+ exhibits ultra-high CO2 adsorption capacity at greater than 50% air humidity. The material can be regenerated using traditional amine materials' thermal regeneration method after saturation or by using chloride salt solution to wash away bicarbonate radicals through ion exchange. Therefore, seawater makes for an effective material regenerant.

The study found that using real Atlantic seawater can achieve a material regeneration efficiency of over 80%, and the washed-out CO2 can be stored in the form of bicarbonate for a long time. After seawater regeneration, the material can be reused simply by rinsing it with weak alkali solution. Since hydroxide ions are also coordinating ions, the rinsing process has a very high efficiency by replacing chloride ions with hydroxide ions and only requires a very low concentration of alkali solution. The reaction process is shown below:

The Ocean Can Serve as a Massive Carbon Sink

The Practicality of Composite Materials has Real, Positive Significance

This research shows that coordinating Cu(II) can significantly enhance the CO2 capture capacity of weak alkaline amine functional groups. The resulting composite material is chemically stable, mechanically strong, and can be repeatedly used. The significance of their findings can be summarized as follows:

1. Even in atmospheric conditions with a CO2 concentration of only 400 ppm, the capacity of Polyam-N-Cu2+ is significantly higher than other high-concentration carbon source carbon capture materials, and its adsorption capacity is almost the same as that at 100,000 ppm CO2 concentration.
    
2. The composite material provides dual regeneration modes, thermal and seawater regeneration, and the ocean can be used as a huge carbon sink to store bicarbonate.
    
3. Raw materials can be obtained from multiple manufacturing companies worldwide, so the production of Polyam-N-Cu2+ can be rapidly expanded. The practicality of this composite material has positive significance for global practices related to direct air capture (DAC).

Dr. Hang Dong has served as an Assistant Professor at GTSI and an Adjunct Professor at Georgia Tech since 2022. He focuses on developing low-carbon selection separation (LOCSS) technology to solve various environmental problems. The laboratory's current research direction includes designing new materials, processes, and devices for carbon capture, utilization, and storage (CCUS) to promote carbon neutrality and recovering resources from waste to promote the development of circular economies.

Source: IFENG Tech