Novel way to make fertiliser with sunlight

Scientists have developed a new, eco-friendly method to produce ammonia, the main ingredient of fertiliser, using sunlight.

The researchers discovered that 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 new 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, researchers said.

The researchers from US Department of Energy's National Renewable Energy Laboratory (NREL) and University of Colorado Boulder (CU-Boulder) showed that nanocrystals of the compound cadmium sulfide can be used to harvest light, which then energises electrons enough to trigger the transition of N2 into ammonia.

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 that occurs 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 that changes 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, resulting in a corresponding hike in greenhouse gas emissions.

"The key was to combine semiconductor nanocrystals that absorb light with nitrogenase, nature's catalyst that converts nitrogen to ammonia," said Gordana Dukovic at CU-Boulder.

"By integrating nanoscience and biochemistry, we have created a new, more sustainable method for this age-old reaction," Dukovic said.

"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," said Brown. The research appears in the journal Science.