Hole-scavenging in photo-driven N₂ reduction catalyzed by a CdS-nitrogenase MoFe protein biohybrid system

The light-driven reduction of dinitrogen (N₂) to ammonia (NH₃) catalyzed by a cadmium sulfide (CdS) nanocrystal‑nitrogenase MoFe protein biohybrid is dependent on a range of different factors, including an appropriate hole-scavenging sacrificial electron donor (SED). Here, the impact of different SEDs on the overall rate of N₂ reduction catalyzed by a CdS quantum dot (QD)-MoFe protein system was determined. The selection of SED was guided by several goals: (i) molecules with standard reduction potentials sufficient to reduce the oxidized CdS QD, (ii) molecules that do not absorb the excitation wavelength of the CdS QD, and (iii) molecules that could be readily reduced by sustainable processes. Earlier studies utilized buffer molecules or ascorbic acid as the SED. The effectiveness of ascorbic acid as SED was compared to dithionite (DT), triethanolamine (TEOA), and hydroquinone (HQ) across a range of concentrations in supporting N₂ reduction to NH₃ in a CdS QD-MoFe protein photocatalytic system. It was found that TEOA supported N₂ reduction rates comparable to those observed for dithionite and ascorbic acid. HQ was found to support significantly higher rates of N₂ reduction compared to the other SEDs at a concentration of 50 mM. A comparison of the rates of N₂ reduction by the biohybrid complex to the standard reduction potential (E^o) of the SEDs reveals that E^o is not the only factor impacting the efficiency of hole-scavenging. These findings reveal the importance of the SED properties for improving the efficiency of hole-scavenging in the light-driven N₂ reduction reaction catalyzed by a CdS QD-MoFe protein hybrid.