A Nagoya Institute of Technology group of researchers has developed a novel, easy to synthesize composite compound that enables the efficient use of solar energy to reduce carbon dioxide. The effort is to find sustainable methods of breaking down carbon dioxide in emissions.

CO2 emissions from human activities have risen drastically over the last century and a half and some see it as the primary cause of global warming and abnormal weather patterns. So, there has been considerable research focus, in a number of fields, on lowering our CO2 emissions and its atmospheric levels. One promising strategy is to chemically break down, or ‘reduce,’ CO2 using photocatalysts – compounds that absorb light energy and provide it to reactions, speeding them up. With this strategy, the solar powered reduction of CO2, where no other artificial source of energy is used, becomes possible, opening doors to a sustainable path to a sustainable future.

A team of scientists led by Drs. Shinji Kawasaki and Yosuke Ishii from Nagoya Institute of Technology, Japan, has been at the forefront of efforts to achieve efficient solar-energy-assisted CO2 reduction. Their recent breakthrough is published in Nature’s Scientific Reports.

Schematic picture of the synthesis procedure of the three-component composite of AgI, AgIO3, and SWCNTs. The photocatalytic mechanism scheme of the composite under irradiation of visible light is also shown. Image Credit: Shinji Kawasaki and Yosuke Ishii, Nagoya Institute of Technology. More images at the first link above. Click image for the largest view.

Their research began with the need to solve the limited applicability problem of silver iodate (AgIO3), a photocatalyst that has attracted considerable attention for being useful for the CO2 reduction reaction. The problem is that AgIO3 needs much higher energy than that which visible light can provide to function as an efficient photocatalyst; and visible light is the majority of solar radiation.

Scientists have attempted to work around this efficiency problem by combining AgIO3 with silver iodide (AgI), which can efficiently absorb and utilize visible light. However, AgIO3-AgI composites have complicated synthesis processes, making their large-scale manufacturing impractical. Further, they don’t have structures that offer efficient pathways for the transfer of photoexcited electrons (electrons energized by light absorption) from AgI to AgIO3, which is key to the composite’s catalytic activity.

Dr. Kawasaki said, “We have now developed a new photocatalyst that incorporates single-walled carbon nanotubes (SWCNTs) with AgIO3 and AgI to form a three-component composite catalyst. The role of the SWCNTs is multimodal. It solves both the synthesis and the electron transfer pathway problems.”

The three-component composite’s synthesis process is simple and involves just two steps:

First, encapsulating iodine molecules within the SWCNT using an electrochemical oxidation method; and then preparing the composite by immersing the resultant of the previous step in an aqueous solution of silver nitrate (AgNO3).

Spectroscopic observations using the composite showed that during the synthesis process, the encapsulated iodine molecules received charge from the SWCNT and converted into specific ions. These then reacted with AgNO3 to form AgI and AgIO3 microcrystals, which, due to the initial positions of the encapsulated iodine molecules, were deposited on all the SWCNTs uniformly. Experimental analysis with simulated solar light revealed that the SWCNTs also acted as the conductive pathway through which photoexcited electrons moved from AgI to AgIO3, enabling the efficient reduction of CO2 to carbon monoxide (CO).

The incorporation of SWCNTs also allowed for the composite dispersion to be easily spray-coated on a thin film polymer to yield flexible photocatalytic electrodes that are versatile and can be used in various applications.

Dr. Ishii is hopeful about their photocatalyst’s potential. “It can make the solar reduction of industrial CO2 emissions and atmospheric CO2 an easy-to-scale and sustainable renewable energy-based solution tackling global warming and climate change, making people’s lives safer and healthier,” he said.

The next step, the team said, is to explore the possibility of using their photocatalyst for solar hydrogen generation.


Your humble writer tries to avoid triggering climate alarmists and deniers here and stay on point. Which encourages a pointing to the Nagoya team’s worthwhile success in their photocatalyst development. Perhaps the alarming has some positive impact by driving research that will actually be of great use one day.

So before you email mail your humble writer about climate please keep in mind few points. Climate has been used for “news making” for well on 50 years. No prediction of our demise came to be or even credible evidence exists that CO2 at or about 400 parts per million is any kind of threat.

There is a known threshold of low CO2, where plants starve and then animal life starves. Its also known that over the planet’s history that CO2 has been far higher than today and life flourished. There is quite a large range where nature runs its CO2 balance. Headlines aside, there is no credible cause for worry.

But if this team’s photocatalyst cleans up effluents recycling the CO2 by offering a carbon monoxide product, we should all be very encouraging to them, indeed.


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