title: Unraveling the enhanced photocatalytic activity and phototoxicity of ZnO/metal hybrid nanostructures from generation of reactive oxygen species and charge carriers.
abstract: An effective way for promoting photocatalytic activity of a semiconductor is deposition of noble metal nanoparticles (NPs) onto it. In this paper, we deposited Ag and Pd onto ZnO NPs to form ZnO/Ag and ZnO/Pd hybrid nanostructures. It was found that both Ag and Pd nanocomponents can greatly enhance the photocatalytic activity and phototoxicity of ZnO toward human skin cells. Using electron spin resonance spectroscopy with spin trapping and spin labeling techniques, we observed that either deposition of Ag or Pd resulted in a significant increase in photogenerated electrons and holes and production of reactive oxygen species including hydroxyl radicals, superoxide, and singlet oxygen. We compared the enhancing effects of Ag and Pd and found that Pd is more effective than Ag in promoting the generation of hydroxyl radicals and holes and the photocatalytic activity of ZnO. Conversely, Ag is more effective than Pd in enhancing electron transfer and the generation of superoxide and singlet oxygen. The mechanism underlying the differences in the effects of Ag and Pd may be related to differences in Fermi levels for Ag and Pd and band bending accompanied by effects on Schottky barriers. The results of these studies provide information valuable for designing hybrid nanomaterials having photocatalytic and photobiological activities useful for applications such as water purification and formulation of antibacterial products.
authors.affiliation: Key Laboratory of Micro-Nano Materials for Energy Storage and Conversion of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University , Xuchang, Henan 461000, P. R. China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: He
authors.forename: Haohao
authors.initials: H
authors.lastname: Wu
authors.forename: Wayne G
authors.initials: WG
authors.lastname: Wamer
authors.forename: Hyun-Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Jiwen
authors.initials: J
authors.lastname: Zheng
authors.forename: Huimin
authors.initials: H
authors.lastname: Jia
authors.forename: Zhi
authors.initials: Z
authors.lastname: Zheng
authors.forename: Jun-Jie
authors.initials: JJ
authors.lastname: Yin
mesh_terms: D002384:Catalysis / Q000187:drug effects / Q000528:radiation effects; D004583:Electrons; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D008027:Light; D053768:Metal Nanoparticles / Q000633:toxicity* / Q000648:ultrastructure; D010165:Palladium / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000737:chemistry*; D012834:Silver / Q000633:toxicity*; D012867:Skin / Q000166:cytology; D013816:Thermodynamics; D014961:X-Ray Diffraction; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D017382:Reactive Oxygen Species; D012834:Silver; D010165:Palladium; D015034:Zinc Oxide
keywords: ESR; ZnO/Ag; ZnO/Pd; photocatalytic; phototoxicity; reactive oxygen species