Photobiocatalytic Conversion of Solar Energy to NH3 from N2 and H2O under Ambient Condition

Abstract

Abstract Several methods and catalysts have been investigated for eco-friendly ammonia (NH3) production under mild conditions in the past few decades. NH3 is important chemical fertilizer and now expecting as H2 carrier, and mainly synthesized by Haber-Bosch process under severe conditions (400 ℃, 20MPa). In contrast, nitrogenases, biocatalyst can activate N2 and H2O to form NH3 under ambient conditions in nature with a low synthesis rate. Herein we first reported photobiocatalytic NH3 production by the combination of cyanobacterial Anabaena variabilis as a whole-cell biocatalyst coupled with TiO2 as a photocatalyst in the existence of glycerol as a sacrificial reagent and viologens as an electron transfer mediator. Comparing with natural system, the formation rate of NH3 from a combination with inorganic photocatalyst was much increased by ca. 20.86 times. Biocatalytic reactions revealed that only reduced MV•+ passed into whole cells and transfer electrons to nitrogenase efficiently for NH3 production. The amount of intracellular [MoFe]-nitrogenase was increased in cyanobacteria cultivated in a nitrogen-deficient Allen & Arnon medium. The complete hybrid system produced NH3 with a maximum rate of 3.3 µM·g-1·h-1. This study is the first demonstration of the sustainable technology for solar-to-NH3 conversion as an energy carrier for a future carbon-neutral energy society.