Dual Role of Au nanoparticles in the Catalytic Formation of an Amorphous Polynuclear Peroxo Complex and Surface Enhanced Resonance Raman Scattering

Abstract

We report the catalytic formation of bridged polynuclear peroxo complex of Co(II) and 2-picolylamine (2-PA) in aqueous alkaline medium on the surface of Au nanoparticle. The reaction followed sigmoidal kinetics both in absence and presence of the Au nanoparticle with an order of magnitude higher rate constant in the presence of nanoparticle. Importantly, using UV-Vis spectroscopy, mass spectrometry and surface enhance resonance Raman scattering (SERRS), we conclude the formation of peroxo complex with 2-PA acting as a monodentate ligand. The absorbance of the polynuclear complex at 595 nm and the extinction maximum of (agglomerated) the Au nanoparticles at 750 nm provided the right opportunity to pursue SERRS using 632.8 nm laser excitation. Density functional theoretical calculation indicated that the lowering of HOMO-LUMO energy gap of 2-PA bonded to the nanoparticle surface helped catalyze the reaction.

Simultaneous Sensing of H2O, D2O and HOD through Peroxo Vibrations

“…Bridged polynuclear peroxo complex of Co(II) and 2‐picolylamine (2‐PA) was synthesized following a reported procedure [27] . Briefly, in the basic medium (pH∼11), Co(II) was reacted with 2‐PA to form the peroxo complex with the appearance of a peak at 595 nm in the UV‐Vis spectrum (Figure S1 in the Supporting Information) – owing to the charge transfer from peroxo group to Co(III) center [27] . The absorption at 595 nm of the product complex enabled attaining resonance Raman (RR) condition when the excitation wavelength was 632.8 nm [27] .…”

“…Briefly, in the basic medium (pH∼11), Co(II) was reacted with 2‐PA to form the peroxo complex with the appearance of a peak at 595 nm in the UV‐Vis spectrum (Figure S1 in the Supporting Information) – owing to the charge transfer from peroxo group to Co(III) center [27] . The absorption at 595 nm of the product complex enabled attaining resonance Raman (RR) condition when the excitation wavelength was 632.8 nm [27] . The formation and structure of the product polynuclear peroxo species is shown in Scheme 1 [27] …”

“…The absorption at 595 nm of the product complex enabled attaining resonance Raman (RR) condition when the excitation wavelength was 632.8 nm [27] . The formation and structure of the product polynuclear peroxo species is shown in Scheme 1 [27] …”

“…Since the SERRS spectra were of superior quality and better resolved, quantitative analyses of them recorded in the presence of different H 2 O/D 2 O solvent mixtures were made. The significant observations with respect to the vibrational peaks are summarized in Figure 3D [27,29–32] . Since the extended peak shift was a result of the combined effect of adding extra mass to the peroxo “oscillator” and the coupling between the O−O and adjoining O⋅⋅D/O⋅⋅H hydrogen bonds, [29,30] a brief account of the results based on hydrogen bonding between the metal complex and the solvent (H 2 O/D 2 O) is presented in Figure 4.…”

“…This was pursued via the synthesis of a bridged polynuclear peroxo complex in the solvent mixture of H 2 O and D 2 O in absence and in the presence of Au nanoparticles. The absorption peak of the complex at 595 nm generated resonance Raman condition at the laser excitation wavelength of 632.8 nm [27] . We observed that the Raman peak of the peroxo bond was differently affected by the interaction with H 2 O, D 2 O or HOD as a result of hydrogen bonding.…”