Vertically aligned carbon nanotubes can chemically trap, store greenhouse gases more effectively than typical materials

Better trap for greenhouse gases
Snapshots of CO2 adsorption in double-walled carbon nanotube arrays (with an inner tube diameter of 2r=3 nanometers and various inter-tube distance at T=303 K and p=1 bar). Credit: Rahimi/Babu

Emissions from the combustion of fossil fuels like coal, petroleum and natural gas tend to collect within Earth's atmosphere as "greenhouse gases" that are blamed for escalating global warming.

So researchers around the globe are on a quest for materials capable of capturing and storing . This shared goal led researchers at Technische Universität Darmstadt in Germany and the Indian Institute of Technology Kanpur to team up to explore the feasibility of vertically aligned carbon nanotubes (VACNTs) to trap and store two greenhouse gases in particular: carbon dioxide (CO2) and sulfur dioxide (SO2).

As the team reports in the Journal of Chemical Physics, from AIP Publishing, they discovered that gas adsorption in VACNTs can be influenced by adjusting the morphological parameters of the thickness, the distance between nanotubes, and their height.

"These parameters are fundamental for 'tuning' the hierarchical pore structure of the VACNTs," explained Mahshid Rahimi and Deepu Babu, the paper's lead authors and doctoral students in theoretical physical chemistry and inorganic chemistry at the Technische Universität Darmstadt. "This hierarchy effect is a crucial factor for getting high-adsorption capacities as well as mass transport into the nanostructure. Surprisingly, from theory and by experiment, we found that the distance between nanotubes plays a much larger role in gas adsorption than the tube diameter does."

Typical carbon materials used in gas adsorption/desorption applications show huge hysteresis effects—in which the value of the physical property lags behind the changes in the effect causing it—due to pore size structure and distribution, so the team originally set out to "gain a deeper experimental and theoretical understanding of the fundamentals of adsorption and selectivity in carbon materials, as well as their application potential," they added.

The team chose VACNTs as a material to explore because they are created via a chemical vapor deposition process, which makes it possible to achieve a dense growth and regular tight packing of carbon nanotubes. VACNTs are "ideal model structures on which theory and experiment can be probed," said Rahimi and Babu.

Why is the dense growth and tight packing of carbon nanotubes important? "It allows our team to introduce well-defined adsorption sites that can be explored theoretically and creates an ideal symbiosis between experiment and theory," Rahimi said. "For theory, we rely on a molecular simulation method to simulate the adsorption process so it's as similar to the experiment as possible. This lets us predict what will happen in a much cheaper way, as well as explore what's happening in the experimentally studied system more deeply."

The team's most recent findings show that the gas adsorption provided by VACNTs is superior to typical adsorption materials such as porous carbon, zeolites and metal organic frameworks within the mid-pressure (30 bars) regime. "This adsorption range is important for technologically relevant processes like gas storage for automotive purposes," noted Rahimi.

As far as their future plans, the team will continue studying gas adsorption and selectivity under electrical charging conditions in VACNT structures. "Beyond this, we'll introduce specific atoms to achieve controlled elemental doping of the carbon nanotubes," she added. "This will allow us to further tune the gas selectivity. Another area we'll also explore is 'controlled nanotube openings' in such VACNTs to increase the ."


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More information: "Double-walled carbon nanotube array for CO2 and SO2 adsorption," is authored by Mahshid Rahimi, Deepu J. Babu, Jayant K. Singh, Yong-Biao Yang, Jörg J. Schneider and Florian Müller-Plathe, Journal of Chemical Physics , September 22, 2015, DOI: 10.1063/1.4929609
Journal information: Journal of Chemical Physics

Citation: Vertically aligned carbon nanotubes can chemically trap, store greenhouse gases more effectively than typical materials (2015, September 22) retrieved 18 July 2019 from https://phys.org/news/2015-09-vertically-aligned-carbon-nanotubes-chemically.html
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Oct 01, 2015
This hierarchy effect is a crucial factor for getting high-adsorption capacities as well as mass transport into the nanostructure. The origin of such effect was attributed by many scientist to be due to the dual structure which is composed of nano and micro-sized structure.However, the mechanism of such dual structure is still elusive.


Oct 01, 2015
This hierarchy effect is a crucial factor for getting high-adsorption capacities as well as mass transport into the nanostructure. The origin of such effects was attributed by many scientists to be due to the special formation of dual structure composing of nano and microsized structure. However, the mechanism responsible for such effects by the dual structure is still elusive.

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