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Published May 1994 | metadata_only
Journal Article

Photocatalytic Production of H_2O_2 and Organic Peroxides on Quantum-Sized Semiconductor Colloids


Illuminated (320 ≤ X ≤ 370 nm), aqueous suspensions of transparent quantum-sized (Q-sized) ZnO semiconductor colloids in the presence of carboxylic acids and oxygen are shown to produce steady-state concentrations of H_2O_2 as high as 2 mM. Maximum H_2O_2 concentrations are observed only with added electron donors (i.e., hole scavengers). The order of efficiency of hole scavengers is as follows: formate > oxalate > acetate > citrate. Isotopic labeling experiments with ^(18)O_2 are consistent with the hypothesis that hydrogen peroxide is produced directly by the reduction of adsorbed oxygen by conduction band electrons. Quantum yields for H_2O_2 production are near 30% at low photon fluxes. However, the quantum yield is shown to vary with the inverse square root of absorbed light intensity [Φ ∝ ((I_(abs))^(-1)½)], with the wavelength of excitation, and with the diameter of the Q-sized colloids. The initial rate of H_2O_2 production is 100-1000 times faster with Q-sized ZnO particles (D_p = 4-5 nm) than with bulk-sized ZnO particles (D_p = 0.1 µm).

Additional Information

© 1994 American Chemical Society. Received for review May 12,1993. Revised manuscript received November 29,1993. Accepted January 5, 1994. We are grateful to the EPA (815041-01-0; 815170-01-0) and ARPA (NAV5 HFMN N0001492J1901) for financial support, and we appreciate the assistance of Drs. Detlef Bahnemann, Claudius Kormann, and Peter Green in various aspects of this research.

Additional details

August 20, 2023
August 20, 2023