Study addresses main bottlenecks of photocatalysis
A multi-Institutional team from the Indian Institutes of Technology (IIT), Mandi and Delhi, and Yogi Vemana University have replicated the structure of a leaf in a low-cost inorganic catalyst to enable light-induced production of green hydrogen and ammonia.
The team was led by Venkata Krishnan, Associate Professor, School of Basic Sciences, IIT Mandi.
Pioneering Armenian chemist Giacomo Ciamician had challenged the scientists of his day to imagine using sunlight to produce chemicals much like plants do in photosynthesis in 1912. In the 1970s, researchers showed the possibility of harvesting the sun’s light energy to produce chemicals through the use of special light-activated materials called photocatalysts, thus heralding what is now known as the photocatalysis era. Since then, many photocatalysts have been discovered to bring about light-enabled reactions for various purposes, and studies are ongoing in many areas of photochemical synthesis to discover new photocatalysts and improve existing ones for better performance.
“We have been interested in improving the efficiency of photocatalytic processes for the production of hydrogen and ammonia, because these two substances are industrially important,” Krishnan said.
Hydrogen is a green energy source and ammonia is the backbone of the fertiliser industry. Both hydrogen and ammonia are being manufactured through processes that consume large amounts of energy in the form of heat and also release greenhouse gases. The use of photocatalysis in the production of these two chemicals can save not only energy and costs, but also have significant environmental benefits.
The researchers have addressed the main bottlenecks of photocatalysis — poor light absorption, photogenerated charge recombination and the need for catalytically active sites to use sunlight effectively to drive chemical reactions. They have improved the properties of a low-cost photocatalyst, calcium titanate through an approach called ‘defect engineering’ and shown its efficacy in producing green hydrogen and ammonia in two light-driven reactions.
“We were inspired by the light-harvesting mechanism of leaves and replicated the surface and internal three-dimensional microstructures of the leaf of the Peepul tree in the calcium titanate to enhance the light-harvesting properties,” Krishnan said. This helped improve the efficiency of light absorption. In addition, the introduction of defects in the form of oxygen vacancies helped to solve the problem of the recombination of photogenerated charges.