The research team discovered light energy can be used to change dinitrogen (N2), a molecule made of two nitrogen atoms, to ammonia (NH3), a compound of nitrogen and hydrogen. The researchers hope the newly discovered, light-driven chemical process that creates ammonia can lead to future developments that will enhance global agricultural practices while decreasing the dependence of farmers on fossil fuels.
Traditionally there have been two main ways to transform nitrogen, the most common gas in Earth’s atmosphere, for use by living organisms:
- One is a biological process occurring when atmospheric nitrogen is “fixed” by bacteria found in the roots of some plants like legumes and then converted to ammonia by an enzyme called nitrogenase.
- The second, called the Haber-Bosch process, is an industrial method developed a century ago changing N2 to ammonia in a complex chain of events requiring high temperatures and pressures. The Haber-Bosch process requires the significant use of fossil fuels and results in a corresponding hike in greenhouse gas emissions.
Led by NREL research scientist Paul King, the new paper appears in the April 22 issue of Science. CU-Boulder co-authors include Assistant Professor Gordana Dukovic of Department of Chemistry and Biochemistry, former doctoral student Molly Wilker, now a faculty member at Luther College in Iowa, and current doctoral student Hayden Hamby.
The team showed nanocrystals of the compound cadmium sulfide can be used to harvest light, which then energizes electrons enough to trigger the transition of N2 into ammonia.
“The key was to combine semiconductor nanocrystals that absorb light with nitrogenase, nature’s catalyst that converts nitrogen to ammonia,” said Dukovic. “By integrating nanoscience and biochemistry, we have created a new, more sustainable method for this age-old reaction.”
Fertilizers and environmental protection
Developing a better environmental footprint concerning the development and use of various fertilizers is a fundamental challenge facing the international agricultural industry.
As reported by Scientific American, many synthetic chemicals used to produce fertilizers are petroleum-based. While these fertilizers have allowed farmers and gardeners to exercise greater control over the plants they want to grow by enriching the immediate environment and warding off pests, these benefits have come with environmental costs, such as the runoff pollution of many streams, rivers, ponds, lakes, and coastal areas.
“When the excess nutrients from all the fertilizer we use runs off into our waterways, they cause algae blooms sometimes big enough to make waterways impassable. When the algae die, they sink to the bottom and decompose in a process that removes oxygen from the water. Fish and other aquatic species can’t survive in these so-called “dead zones” and so they die or move on to greener underwater pastures.”
This discovery might pave the way for sounder fertilizer-manufacturing methodologies which have a safer environmental impact.
“Using light harvesting to drive difficult catalytic reactions has the potential to create new, more efficient chemical and fuel production technologies,” said NREL Research Scientist Katherine Brown. “This new ammonia-producing process is the first example of how light energy can be directly coupled to enzymatic N2 reduction, meaning sunlight or artificial light can power the reaction.”
Image via University of Colorado