In a new study, detailed in the Journal of American Chemical Society, scientists described how a visible light-activated and single-site catalyst can convert carbon dioxide (CO2) into key molecules that can be used for making useful chemicals. The discovery reveals the possibility to convert greenhouse gas into hydrocarbon fuels, using sunlight. To find out details of the efficient reaction, the scientists used single ion of cobalt and National Synchrotron Light Source II to help decrease the energy barrier for breaking down carbon dioxide.
While converting Carbon Dioxide CO2 into simple parts like oxygen and carbon monoxide (CO) has gained various application, breaking it down would not only remove CO2 from the atmosphere but also create building blocks to make fuel, according to Anatoly Frenkel, a chemist at Stony Brook University and Brookhaven Lab. He also led the study to determine the activity of the catalyst.
As none of the earlier studies has reported solar reduction of CO2 with single ion, this research team is the first to make a single-site catalyst, Frenkel said.
Since breaking the bond of Carbon Dioxide (CO2) takes longer time period and consumes a lot of energy, the scientists set out to create a catalyst that lower the energy barrier as well as accelerate the process. Electrons are the key ingredient for breaking down the bond of CO2 which can be generated when a semiconducting material gets activated by light energy. The light then excites the electrons, making them available to the catalysts for chemical reactions.
The scientists needed to find a semiconductor material where sunlight’s natural energy would be sufficient to kick out the electrons. Further, the semiconductor must be able to bind to a catalyst made from materials abundantly found in nature. The team wanted the catalyst to be selective enough to induce the reaction of converting CO2 into CO and didn’t want electron to be used for other reactions than breaking down CO2.
They discovered that cobalt ions bind to a semiconductor consisting or carbon, nitrogen, and hydrogen atoms known as graphitic carbon nitride (C3N4) met all the requirements. Although electrons generated by C3N4 are capable of providing enough energy to reduce CO2, they don’t have long lifetime to travel to surface of the semiconductor to use for chemical reaction.
In the new study, the research team adopted a strategy to create sufficient energetic electrons for the catalyst by using water molecules as electron donor, and enhance the catalysis of for CO2 reduction. Under visible light irradiation, the catalyst worked in the breaking down of CO2, converting into CO with good selectivity.
In order to find why the experiment worked, the team used X-ray absorption spectroscopy. Then, they calculated the number of photons absorbed by the samples for individual value of the X-ray energy. It was discovered that the catalyst reducing CO2 was made of single ions of cobalt enclosed by nitrogen atoms on all sides.
The absence of cobalt-cobalt pairs was an evidence that it was in fact the single atoms of cobalt that dispersed on the surface, Frenkel said. Though the science detailed in the new study paper is still not in practical use, there are numerous possibilities for applications, he added.