Photocatalysis of H2 from alcohol reforming on gold or platinum nanoparti- cles requires semiconductor materials, such as titania, that supply electrons needed in the reduction of H+ to H2. However, this photocatalytic system requires photons that provide energy greater than the band gap of the semiconductor. The band gap of titania (∼3.2 eV) requires radiation with wavelengths shorter than 350 nm. Unfortunately, only a small fraction of the solar radiation meets this requirement. However, photosystem I (PS I) absorbs all wavelengths of visible radiation shorter than -700 nm, which is 43%-46% of the solar radiation. PS I can provide a charge-separated P700 +-FB state that is stable for ∼100 ms. Thus, PS I linked to Au or Pt nanoparticles is an alternative to titania-supported photocatalytic production of H2.In this study, PS I was covalently linked to nanoparticles using a molecular wire that enables transfer of electrons at a rate faster than that of the recombination of the charge-separated state. PS I was formed as shown in Scheme 1 (steps 1-3). This rebuilt PS I was covalently linked either to 12-nm Au or 3-nm Pt nanoparticles using 1,6-hexanedithiol as the molecular wire (Scheme 1, step 4). After illuminating with white light at an intensity of 2500 μE for 12-16 h, samples were taken and analyzed for H2. It was found that both PS I conjugated to Au and to Pt nanoparticles produced hydrogen gas (Table 1). To evaluate if H2 evolution is limited by electron transfer through the molecular wire or through the donor side reduction of P700+, cytochrome c6 (Cyt c6) was added to PS I/nanoparticle bioconjugates. The rate of hydrogen production was higher upon addition of Cyt c6 compared to the bioconjugate that used DCPlP as the electron donor. This proved that hydrogen evolution is limited by reduction of P700 +. It is also noteworthy that there was no hydrogen gas observed using wild-type PS I and in experiments lacking one or more components for bioconjugation, indicating that the light provides the necessary charge-separated state for H2 production. In addition, the electron transfer to the nanoparticle surface occurred only when the rebuilt PS I was covalently attached to the nanoparticle through 1,6-hexanedithiol, which captures the iron-sulfur cluster and connects the protein to the nanoparticle.
|Original language||English (US)|
|Number of pages||3|
|State||Published - Jun 1 2008|
All Science Journal Classification (ASJC) codes
- Molecular Biology