Results
Figure 2 Hydrogen evolution curve with nanorods bound to biofilm beads.
During the period with lighting, the hydrogen production increases, until we shut off the light at points that correspond to the tips. The curve then goes downward, showing that the hydrogen concentration is lowered, an evidence of the bidirectional catalytic activity of hydrogenase. It is noteworthy that the hydrogenase shows the greatest production rate at the beginning of lighting: a transient sharp rise can be observed at the valleys. It is also obvious that each period of “light-on light-off” gives similar curves, which implies that our hydrogenase is stable.
In our experiment, we find that despite the reported affected catalytic ability of FeFe hydrogenase due to oxygen, non-strict anaerobic and short-term exposure to oxygen does not cause detrimental effects on the enzyme activity of producing hydrogen. This can be explained by the high catalytic ability and the segregation layer from the atmosphere provided by the hydrogen it produces. Meanwhile, the electron sacrificial agent VitaminC also adds to the “protection layer” of the hydrogenase in our system.
Comparing the system with biofilm and with out biofilm Figure 2 and Figure 3
Before we tested the system with biofilm-anchored CdS nanorods, we tested ones with freely-flowing CdS nanorods. The result is shown in Figure3.
During lighting period, the hydrogen production increases, until we shut off the light at points that correspond to the tips. The curve then goes downward, showing that the hydrogen concentration is lowered, an evidence of bidirectional catalytic activity of hydrogenase. The tip reached 30mV compared to the system with biofilm-anchored hydrogenase, 8mV. This lower catalytic efficiency is possibly due to the lower amount of nanorods added to the system in Figure2, since the binding of CdS to biofilm is a reaction that does not guarantee all the binding. It is also likely that the size of the microspheres on which the biofilm grow is too small for sufficient binding of all the nanorods. However, this seemingly low efficiency system has beat the efficiency of previous report this year. The efficiency calculation is in the next section.
Figure 3 Hydrogen evolution curve with free-flowing nanorods.
Another point to note between our two systems is that in the process of hydrogen generation without biofilm-anchored CdS, a stir bar with a necessary speed of 800 RPM was needed. But in Figure 2, the system with biofilm, a stir bar was not used. It is likely because the aggregates of NR have a bigger chance in colliding with
E. coli to transfer electrons.
Conclusion
In conclusion, although we did not seeAlthoughWe therefore propose this model as our final model, although further optimization of the system is still under way, including deciding on the optimized material and size the microsphere for biofilm growth.
