Light-Driven Nitrogen Fixation Via a Mediated CdS Nitrogenase System

We have been working with the enzyme MoFe nitrogenase which is capable of reducing N₂ to produce NH₃, a commodity chemical that is produced on the scale of millions of tons every year. The goal of our project is to further develop the method of using photoreactive nanoparticles to drive this reduction process. To do so, we are using CdS nanoparticles that are able to transfer excited electrons to the nitrogenase enzyme when exposed to light, ascorbic acid as an electron donor to replace these electrons, MoFe nitrogenase, and viologen as an electron transfer mediator. The kinetics of electron transfer from CdS to viologen using different ligands was investigated, and it determined electron transfer occurs more quickly with TGA ligands than ME ligands. During these reactions, the amount of ascorbic acid was also varied, and it was found that at lower levels of ascorbic acid, the rate of electron transfer increased significantly. Finally, reactions to determine how using viologen affected the yields of NH₃ and H₂ were performed by placing a solution of the following conditions under a solar simulator for 2 hours: 119 nM CdS, 112 mM Ascorbic Acid, 1.7 mM Viologen in 0.1M PB. The preliminary results showed that using viologen increased the amount of NH₃ produced but decreased the amount of H₂ produced. This likely means that viologen is altering the pathway by which NH₃ is being produced.