Formation of aggregates in nanohybrid material of dye molecules–titanate nanosheets

Photoinduced electron transfer in layer-by-layer thin solid films containing cobalt oxide nanosheets, porphyrin, and methyl viologen

The well-known layer-by-layer (LbL) method can be used to prepare solid thin films with a controlled electron transfer direction by appropriately stacking metal oxide nanosheets and functional organic ions. In this study, we prepared thin solid films consisting of cobalt oxide nanosheets (CoNSs) as the electron transfer medium, α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) as the electron donor, and 1,1'-dimethyl-4,4'-bipyridinium or methyl viologen (MV) as the electron acceptor. We investigated the photoinduced electron transfer phenomenon in these films by irradiating them with 450 nm light. Irradiating the LbL thin solid films prepared with the CoNS/TMPyP/CoNS/MV/CoNS sequence under reduced pressure led to the production of a one-electron reduction compound of MV. Hence, photoinduced electron transfer from TMPyP to MV bound to CoNSs occurred in these LbL thin solid films. However, the conduction band of CoNSs, as determined by the photoabsorption spectral and photoelectrochemical measurements, was much higher than the lowest unoccupied molecular orbital level of TMPyP. Our findings indicate that the observed equipotential photoinduced electron transfer was caused by the metallic electron conductivity of CoNSs, which show a unique charge arrangement of Co³⁺ and Co⁴⁺. Moreover, it was also found that the observed photoinduced charge separation state has a longer life-time (>5 h) under the reduced conditions.

Innovative fabrication of a Au nanoparticle-decorated SiO2 mask and its activity on surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) utilizing the well-defined localized surface plasmon resonance (LSPR) of Ag and Au nanoparticles (NPs) under resonant irradiation has emerged as a promising spectroscopy technique for providing vibrational information on trace molecules. The Raman scattering intensity from molecules close to the surface of these finely divided metals can be significantly enhanced by a factor of more than 10(6). In addition to the high sensitivity, the reproducibility of the SERS signal is also an important parameter for its reliable application. In this work, we report on the innovative and facile fabrication of a Au NP-decorated SiO2 mask coated on indium tin oxide (ITO) glass as a SERS array substrate. First, a highly ordered porous SiO2 mask with pore sizes of 350 nm in diameter and wall thickness of 60 nm was deposited on ITO glass by using spin coating. Then, Au NPs were controllably decorated into the pores of the conductive ITO glass-bottomed SiO2 mask by using sonoelectrochemical deposition-dissolution cycling (SEDDC). Experimental results indicate that the SERS effect of Rhodamine 6G (R6G) observed on this developed substrate increases with an increase in the deposition time of Au NPs in SEDDC. The corresponding optimal enhancement factor (EF) that is obtained is ca. 6.5 × 10(7). Significantly, this system achieves an optimal reproducibility under a medium-length deposition time of Au NPs in SEDDC with a relative standard deviation (RSD) of 12% for measurements of five spots on different areas. The low RSD of the SERS signal and the large EF suggest that the developed array system can serve as an excellent spectroscopy platform for practical applications in analytical chemistry.

Surface-enhanced Raman scattering on a silver film-modified Au nanoparticle-decorated SiO2 mask array

SERS of R6G absorbed on this developed array exhibits a higher intensity by ca. 30-fold, as compared with that of R6G absorbed on the Au NP-based array without the modification of Ag films.

Surface-enhanced Raman scattering-active Au/SiO2 nanocomposites prepared using sonoelectrochemical pulse deposition methods

For improving signals, reproducibility, and stabilities of surface-enhanced Raman scattering (SERS), numerous technologies have recently been reported in the literature. However, the fabrication processes are usually complicated. It is well-known that nanoparticles (NPs) of Au and SiO(2) are SERS active and inactive materials, respectively. In this work, a simple synthesis route based on sonoelectrochemical pulse deposition (SEPD) methods has been developed to synthesize effectively SERS-active Au/SiO(2) nanocomposites (NCs) with an enhancement factor of 5.4 × 10(8). Experimental results indicate that pH value of solution and addition of SiO(2) NPs before and after oxidation-reduction cycles (ORCs) can significantly influence the corresponding SERS activities. Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on the developed Au/SiO(2) NCs exhibits a higher intensity by more than 1 order of magnitude, as compared with that of R6G adsorbed on Au NPs synthesized using the same method. Moreover, this improved SERS activity is successfully verified from the mechanisms of electromagnetic (EM) and chemical (CHEM) enhancements.

Surface-enhanced Raman scattering-active gold nanoparticles modified with a monolayer of silver film

As shown in the literature, electrochemical underpotential deposition (UPD) offers the ability to deposit up to a monolayer of one metal onto a more noble metal with a flat surface. In this work, we develop an electrochemical pathway to prepare more surface-enhanced Raman scattering (SERS)-active substrates with Ag UPD-modified Au nanoparticles (NPs) by using sonoelectrochemical deposition-dissolution cycles (SEDDCs). Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on these Ag UPD-modified Au NPs exhibits a higher intensity by ca. 12-fold magnitude, as compared with that of R6G adsorbed on unmodified Au NPs. The prepared SERS-active substrate demonstrates a large Raman scattering enhancement for R6G with a detection limit of 2 × 10(-14) M and an enhancement factor of 5.0 × 10(8). Also, the strategy proposed in this work to improve the SERS effects by using UPD Ag based on SEDDCs has an effect on the smaller probe molecules of 2,2'-bipyridine (BPy).