With increasing demands for alternative sources of fuel, extensive research has focused on discovering methods to generate renewable energy from earth abundant resources. In recent years, a wide range of inorganic nanostructures with high surface areas and tunable band gaps have been used as photocatalysts. To increase their activity, “Z-scheme” photocatalytic systems have been implemented in which multiple types of photoactive materials simultaneously oxidize water and reduce molecules upon photoillumination. In this talk, I will show recent efforts to use DNA as a structure-directing agent for well-defined photoactive donor and acceptor nanocrystals. In the first part, I will demonstrate that DNA as a structure directing agent to assemble TiO2 and Pt decorated CdS nanocrystals significantly improved water splitting as opposed to utilizing a single type of particle or simply mixing the particles in solution. Potential limitations in H2 production caused by negatively charged DNA on the Pt@CdS nanoparticles was simply fixed by controlling the amount of DNA per CdS nanorod. DNA also allowed positioning of a single or series of electron mediators site-specifically in between the two catalysts for increased H2 production. In a similar vein, I will also show some of our recent efforts in applying Z-schemes for CO2 reduction to usable fuels. In this work, DNA bases of 10, 20, 30, 40, and 80 bases were first used to position the TiO2-CdS nanocrystals with interparticle distances of ~3, ~6, ~9, ~12, and ~24 nm, respectively. As compared to either TiO2 alone, Au@CdS alone, or simple mixtures of the two, the DNA assembled TiO2-Au@CdS showed a significant (2.94-5.28 fold) increase in CO2 photoreduction, as evidenced by the generation of formate, formaldehyde, and methanol. Furthermore, we show that with this particular Z-scheme, separating the nanoparticles at 9-10 nm showed the highest yields CO2 conversion. This result was found not only for nanocrystals spaced with linear 30mer dsDNA, but also for 40mer DNA composed of both linear and hairpin DNA. Electron transfer from TiO2 to Au@CdS was achieved over DNA lengths as large as 24 nm. For comparison, a 5 kDa polyethylene glycol (PEG) spacer, which has an approximate end-to-end distance of ~11 nm, showed a very low amount of CO2 conversion. Lastly, I will also showcase our recent efforts in interfacing enzymes with semiconductor nanocrystals for driving photoassisted redox activity, in particular nitrogen fixation.

Bio-nano interfaces for renewable energy

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.