Researchers in the Netherlands, Italy and Poland have developed a new porous material that can selectively capture carbon dioxide and release it in response to visible light. Their work was published in PNAS last month.
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The work combines porous framework materials and light-responsive functional groups. Ben Feringa, who shared the 2016 chemistry Nobel Prize, and his team used 3D structures held together by rigid carbon-carbon bonds called porous aromatic frameworks (PAFs). PAFs are made through irreversible chemical reactions, making them almost impossible to destroy.
The team created the first azobenzene-containing porous material that shows bulk isomerization with exposure to visible light. The material switches between the E isomer, an extended configuration, and the Z isomer, a bent configuration.
The researchers found that irradiating the material with green light (530 nm) caused the pendant group of o-fluoroazobenzene to transform almost entirely from the E isomer to the Z isomer. In this state, the structure adsorbed up to 14% less carbon dioxide than its E isomer. Irradiation with blue light (405 nm) returned the groups to the E isomer and restored the carbon-capture capacity.
Other azobenzene-containing porous materials have only shown photoswitching on their surface, making this the first to show the switching throughout the material. The researchers used a combination of diffuse-reflectance UV/Vis, DRIFT spectroscopy and solid-state NMR spectroscopy to quantify the bulk photoisomerization.
Previously, most photoresponsive materials have required UV light, which causes the material to degrade. This system works with low-energy visible light, offering better penetration, safer operation and does not degrade the material.
Traditional porous materials are manipulated with temperature rather than light. This makes the transformation process much slower, as it can take hours for a material to cool down or heat up. Being able to manipulate the carbon capacity of the material with light makes the transformation almost instantaneous.
This new material could have applications in carbon capture, photochemical manipulation of reactions, separation technology and catalysis.
