title: Controlled assembly of hydrogenase-CdTe nanocrystal hybrids for solar hydrogen production.
abstract: We present a study of the self-assembly, charge-transfer kinetics, and catalytic properties of hybrid complexes of CdTe nanocrystals (nc-CdTe) and Clostridium acetobutylicum [FeFe]-hydrogenase I (H(2)ase). Molecular assembly of nc-CdTe and H(2)ase was mediated by electrostatic interactions and resulted in stable, enzymatically active complexes. The assembly kinetics was monitored by nc-CdTe photoluminescence (PL) spectroscopy and exhibited first-order Langmuir adsorption behavior. PL was also used to monitor the transfer of photogenerated electrons from nc-CdTe to H(2)ase. The extent to which the intramolecular electron transfer (ET) contributed to the relaxation of photoexcited nc-CdTe relative to the intrinsic radiative and nonradiative (heat dissipation and surface trapping) recombination pathways was shown by steady-state PL spectroscopy to be a function of the nc-CdTe/H(2)ase molar ratio. When the H(2)ase concentration was lower than the nc-CdTe concentration during assembly, the resulting contribution of ET to PL bleaching was enhanced, which resulted in maximal rates of H(2) photoproduction. Photoproduction of H(2) was also a function of the nc-CdTe PL quantum efficiency (PLQE), with higher-PLQE nanocrystals producing higher levels of H(2), suggesting that photogenerated electrons are transferred to H(2)ase directly from core nanocrystal states rather than from surface-trap states. The duration of H(2) photoproduction was limited by the stability of nc-CdTe under the reactions conditions. A first approach to optimization with ascorbic acid present as a sacrificial donor resulted in photon-to-H(2) efficiencies of 9% under monochromatic light and 1.8% under AM 1.5 white light. In summary, nc-CdTe and H(2)ase spontaneously assemble into complexes that upon illumination transfer photogenerated electrons from core nc-CdTe states to H(2)ase, with low H(2)ase coverages promoting optimal orientations for intramolecular ET and solar H(2) production.
authors.affiliation: Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Brown
authors.forename: Smita
authors.initials: S
authors.lastname: Dayal
authors.forename: Xin
authors.initials: X
authors.lastname: Ai
authors.forename: Garry
authors.initials: G
authors.lastname: Rumbles
authors.forename: Paul W
authors.initials: PW
authors.lastname: King
mesh_terms: D000327:Adsorption; D019187:Cadmium Compounds / Q000378:metabolism*; D046969:Clostridium acetobutylicum / Q000201:enzymology; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008958:Models, Molecular; D053758:Nanoparticles; D012993:Solar Energy; D013691:Tellurium / Q000378:metabolism*
chemical_list: D019187:Cadmium Compounds; D007506:Iron-Sulfur Proteins; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase; D013691:Tellurium; C028337:cadmium telluride