Effect of polar organic vapors on surface potential of Au nanoparticle aggregates probed by surface-enhanced Raman scattering of 2,6-dimethylphenylisocyanide

Abstract

We demonstrate by means of surface-enhanced Raman scattering of 2,6-dimethylphenylisocyanide that the surface potential of Au nanoparticle aggregates changes upon contact with polar organic vapors such as acetone and ammonia by as much as +0.16 and -0.56 V, respectively.

Effect of organic vapors and potential-dependent Raman scattering of 2,6-dimethylphenylisocyanide on platinum nanoaggregates

“…On the other hand, the cyclovoltammograms suggested that even a full monolayer of 2,6-DMPI does not protect platinum nanoaggregates completely from environmental chemicals. 19 This suggests that sodium and perchlorate ions can approach the electrode surface like specifically adsorbed ions, and thus the NC group of 2,6-DMPI can be understood to reside in an electric double layer even in a very dilute electrolyte solution. The NC stretching band should then be affected by the Stark effect.…”

“…This is understood as a consequence of the fact that even a full monolayer of 2,6-DMPI does not protect platinum nanoaggregates completely from environmental chemicals. 19 In a separate potential-dependent SERS in electrochemical environments, the NC group of 2,6-DMPI is concluded to be located within an electric double layer even in a very dilute electrolytic solution. A part of the NC peak shift observed in this work, not only in the ambient vapor but also in the electrochemical environment, is thus assumed to arise from the Stark effect, [22][23][24][25][26][27] although the major part is due to the inductive charge transfer effect from/to platinum.…”

“…18 In a separate study, we have recently confirmed by means of SERS that the surface potential of Au nanoparticles is subject to change upon contact with polar organic vapors such as acetone and ammonia. [19][20][21] The NC stretching band of 2,6-dimethylphenylisocyanide (2,6-DMPI) on Au nanoaggregates was blue-shifted from 2182 to 2188 cm À1 in the presence of acetone vapor, while it was red-shifted from 2182 to 2162 cm À1 in the presence of ammonia. 19 Consulting a separate potentialdependent SERS of 2,6-DMPI on an Au wire electrode, the blue and red-shift observed with Au nanoaggregates correspond to potential changes of Au from +0.16 to +0.32 and À0.40 V, respectively.…”

“…[19][20][21] The NC stretching band of 2,6-dimethylphenylisocyanide (2,6-DMPI) on Au nanoaggregates was blue-shifted from 2182 to 2188 cm À1 in the presence of acetone vapor, while it was red-shifted from 2182 to 2162 cm À1 in the presence of ammonia. 19 Consulting a separate potentialdependent SERS of 2,6-DMPI on an Au wire electrode, the blue and red-shift observed with Au nanoaggregates correspond to potential changes of Au from +0.16 to +0.32 and À0.40 V, respectively. These potential changes could be understood by invoking either an s-type charge transfer from Au to the unoccupied p orbital of the oxygen atom of acetone or the donation of the lone-pair electrons of ammonia nitrogen to Au nanoparticles.…”

“…These potential changes could be understood by invoking either an s-type charge transfer from Au to the unoccupied p orbital of the oxygen atom of acetone or the donation of the lone-pair electrons of ammonia nitrogen to Au nanoparticles. [19][20][21] In this work, we have examined how organic vapors would affect the SERS of 2,6-DMPI on Pt nanoaggregates, and any difference from Au nanoaggregates was interpreted on the basis of quantum chemical calculations. We found that the amount of peak shift of the NC stretching vibration is dependent to a small degree on the surface coverage of 2,6-DMPI on Pt.…”