Scanning Tunneling Microscopy Investigation of Nano-Structured alpha-K5PW11(M center dot OH2)O-39(M = Mn-II, Co-II, Ni-II, and Zn-II) Keggin Heteropolyacid Catalyst Monolayers

作者：Choi Jung Ho; Kang Tae Hun; Bang Yongju; Yoo Jaekyeong; Jun Jin Oh; Song In Kyu^*

来源：Journal of Nanoscience and Nanotechnology, 2014, 14(11): 8873-8878.

DOI：10.1166/jnn.2014.9945

• Heteropolyacid
• Scanning Tunneling Microscopy
• Tunneling Spectroscopy
• Negative Differential Resistance
• Oxidation Catalysis

Nano-structured alpha-K5PW11(M center dot OH2)O-39 (M = Mn-II, Co-II, Ni-II, and Zn-II) Keggin heteropolyacids (HPAs) were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) measurements in order to elucidate their redox property and oxidation catalysis. HPA molecules formed two-dimensional self-assembled monolayer arrays on highly oriented pyrolytic graphite (HOPG) surface. Furthermore, HPAs exhibited a distinctive current voltage behavior referred to as negative differential resistance (NDR) phenomenon. The measured NDR peak voltage of HPAs was correlated with the reduction potential and the absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. NDR peak voltage of HPAs appeared at less negative voltage with increasing reduction potential and with decreasing UV-visible absorption edge energy. The correlations strongly suggested that NDR phenomenon was closely related to the redox property of HPAs. Vapor-phase oxidation of benzyl alcohol to benzaldehyde was carried out as a model reaction to track the oxidation catalysis of HPAs. NDR peak voltage appeared at less negative voltage with increasing yield for benzaldehyde.

• 出版日期2014-11