Scientists at Daegu Gyeongbuk Institute of Science and Technology, Korea, have developed a novel heterostructured photocatalyst using titanium and copper, two abundant and relatively inexpensive metals, for the conversion of CO₂ into CH₄.

Under illumination for 6 hours, the optimized reduced titania-Cu₂O photocatalyst enables 0.13% photoreduction of highly diluted CO₂ with water vapors to 462 nmol g⁻¹ of CH₄ while showing excellent stability over seven testing cycles (42 h). A paper on the work is published in the journal Applied Catalysis B: Environmental.

Their cost-effective synthesis procedure, coupled with the high stability of the photocatalyst, provides an economically feasible way to convert waste carbon dioxide and water into useful hydrocarbon fuels using sunlight.

The escalating carbon dioxide (CO2) emissions and the consequent acceleration of climate change are alarming, and it has proven challenging to find feasible ways to actively reduce the concentration of CO2 in the atmosphere. What if we drew inspiration from photosynthesis, the process by which plants use sunlight to convert CO2 and water into useful chemicals?

Prof Su-Il In and his co-researchers from DGIST based their approach around the concept of “Z-scheme” charge transfer mechanism in heterostructured photocatalysts, where the interfaces between two different materials play a central role in chemical processes that resemble the electron transfers in natural photosynthesis.

They reinforced reduced titanium nanoparticles edges with dicopper oxide (Cu₂O) nanoparticles through photo-deposition, a unique yet relatively simple and inexpensive procedure.

The rich electron density of reduced titania at the interface helps neutralize positive charges, called “electron holes,” in Cu₂O, which otherwise accumulate excessively and lead to photocorrosion. Moreover, the geometric configuration of the resulting interfaces allows both materials to be exposed to the reactive medium and jointly enhance photocatalytic performance, in contrast to core–shell structures previously developed to avoid photocorrosion.

Apart from its CO₂ conversion capabilities, the proposed photocatalyst has other benefits.

Aside from showing stable performance for 42 hours under continuous operation, the proposed photocatalyst is composed of earth-abundant materials, which greatly adds to its economic viability.

Photocatalytic CO₂ reduction is applicable in processes that produce huge volumes of CO₂, like thermal power stations and industrial fermentation facilities (distilleries). Integrating this technology in such facilities will give them access to inexpensive and abundant fuel and cuts in carbon emission taxes.

—Prof In

Resources

• Shahzad Ali, Junho Lee, Hwapyong Kim, Yunju Hwang, Abdul Razzaq, Jin-Woo Jung, Chang-Hee Cho, Su-Il In (2020) “Sustained, photocatalytic CO₂ reduction to CH₄ in a continuous flow reactor by earth-abundant materials: Reduced titania-Cu2O Z-scheme heterostructures” Applied Catalysis B: Environmental doi: 10.1016/j.apcatb.2020.119344