title: Effect of protons on the redox chemistry of colloidal zinc oxide nanocrystals.
abstract: Electron transfer (ET) reactions of colloidal 3-5 nm diameter ZnO nanocrystals (NCs) with molecular reagents are explored in aprotic solvents. Addition of an excess of the one-electron reductant Cp*2Co (Cp* = pentamethylcyclopentadienyl) gives NCs that are reduced by up to 1-3 electrons per NC. Protons can be added stoichiometrically to the NCs by either a photoreduction/oxidation sequence or by addition of acid. The added protons facilitate the reduction of the ZnO NCs. In the presence of acid, NC reduction by Cp*2Co can be increased to over 15 electrons per NC. The weaker reductant Cp*2Cr transfers electrons only to ZnO NCs in the presence of protons. Cp*2M(+) counterions are much less effective than protons at stabilizing reduced NCs. With excess Cp*2Co or Cp*2Cr, the extent of reduction increases roughly linearly with the number of protons added. Some of the challenges in understanding these results are discussed.
authors.affiliation: Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA.
authors.forename: Carolyn N
authors.initials: CN
authors.lastname: Valdez
authors.forename: Miles
authors.initials: M
authors.lastname: Braten
authors.forename: Ashley
authors.initials: A
authors.lastname: Soria
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Gamelin
authors.forename: James M
authors.initials: JM
authors.lastname: Mayer
mesh_terms: D003102:Colloids / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D011522:Protons; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D003102:Colloids; D011522:Protons; D015034:Zinc Oxide