Inorganic-bacterial biohybrids for efficient solar-driven nitrogen fixation

Abstract

The integration of microbial nitrogen (N2) fixation with photochemical processes using inorganic light-absorbing nanomaterials is a burgeoning field in sustainable energy production. Here, we explore the synergistic combination of inorganic semiconductor nanowires (NWs) with whole-cell microorganisms to create an inorganic-bacterial biohybrid system. Specifically, we employ Cu2O@TiO2 NWs with a core/shell structure to harness sunlight and generate photoexcited electrons. Azotobacter vinelandii, serving as a biocatalyst, adsorbs onto these NWs and facilitates the reception of photoexcited electrons, thereby enhancing the efficiency of the photoelectrochemical N2 fixation reaction (PEC-NRR). The biohybrid system achieves an impressive ammonia (NH3) yield of (1.49 ± 0.05) × 10-9 mol s-1 cm-2 (5.36 ± 0.18 μmol h-1 cm-2). The enhancement in NH3 synthesis within the Cu2O@TiO2 NWs/A. vinelandii biohybrid is attributed to the increased concentrations of nicotinamide adenine dinucleotide-hydrogen (NADH) and adenosine 5’-triphosphate (ATP), as well as the overexpression of N2-fixing genes like nifH and nifD within the nitrogenase enzyme complex. This study underscores the potential of inorganic-bacterial biohybrid systems in solar-chemical conversion, paving the way for more diverse and functional approaches to harnessing solar energy for sustainable chemical production. Converting atmospheric nitrogen (N2) to ammonia (NH3) is challenging. Here, the authors develop a photoelectrochemical biohybrid system for fixing N2 into NH3, which consists of Cu2O/TiO2 nanowires and the N2-fixing diazotroph Azotobacter vinelandii.