The promising application of surface-enhanced Raman spectroscopy (SERS) was definitely based on the high quality substrates which were restricted to the rough noble metals and colloidal nanoparticle materials. However, semiconductor has become a potential substrate for the SERS investigation due to its high stability and reproducibility. It remains significant challenges in interpreting the enhancement mechanisms. Herein, broom-like ZnO nanoparticles with novel morphology and uniform size was prepared by pyrolysis of (CH 3 COO) 2 Zn. By using p-nitrophenylthiophenol (PNTP), phenylthiophenol (TP) and p-aminophenylthiophenol (PATP) as probe molecules, the SERS effect on ZnO surfaces was systematically studied under the irradiation of excitation lines with the wavelength of 532 nm and 638 nm. The different substituents in p-position of TP allowed to change the energy levels by the electron withdrawing or donating group, it was beneficial to match the energy level gap between the probe molecules and semiconductor for triggering the photon driven charge transfer. The surface enhancement factor (EF) of broom-like ZnO nanoparticles were estimated accordingly, and the contribution of non-resonance and charge transfer to SERS effect was distinguished. The results demonstrated that the surface enhancement factor was about 10 to 35 times depending on the probe molecules and excitation wavelengths. Therefore, the different enhancement origination contributed to the different molecules on the ZnO substrate. For the TP and PATP, the charge transfer from the HOMO level of molecule to CB of ZnO was achieved by the assistance of the laser photon with the appropriate energy. Moreover, the higher energy of the photon is, the stronger the SERS enhancement effect. As for the PNTP, the photon driven charge transfer was absent due to the significant change of the HOMO and LUMO level caused by the electron withdrawing group of NO 2. It revealed that the enhancement effect of PNTP molecule about 10 times was contributed by the non-resonance enhancement mechanism which was mainly due to the changes in the polarizability caused by the chemical adsorption. Comparing to the noble metal surface, the enhancement of charge transfer on ZnO was decreased with 1~2 orders of magnitude. The relatively lower rate of charge transfer in semiconductor resulted in the decrease of the charge transfer enhancement. The preliminary studies provided a novel approach for the preparation and regulation of new semiconductor SERS substrates. Keywords surface-enhanced Raman Spectroscopy (SERS); ZnO; surface enhancement factor (EF); non-resonance enhancement; photon-driven charge transfer enhancement
The activity and uniformity of surface-enhanced Raman scattering (SERS) effect has been already become the critical role for fundamental research and practical application. Herein, Au nanoparticle monolayer films (Au MLF) were fabricated based on the self-assembly of nanoparticles at the air/water interface by introduction of polyvinylpyrrolidone (PVP) as additional agent. The change of assembly duration allowed the formation of Au MLFs with different density. Due to the excitation mode and intensity of localized surface plasmon resonance (LSPR) varying with the nanoparticle density, the activity and uniformity of SERS substrate could not be taken into account at the same time. For example, loose Au MLF exhibited excellent SERS and catalytic performance but poor uniformity, while compact Au MLF held excellent uniformity and reasonable SERS and catalytic performance. It demonstrated that the intensity of SERS signal was not only relevant to the activity but also to the number of "hot spots", while the conversion rate of surface plasmon resonance (SPR) induced catalysis was only associated with the activity of "hot spots". By using the compact film with relative standard deviation of SERS intensity and SPR catalytic efficiency less than 5% and 6% as the SERS substrate, the influence of the external environment on the SPR catalytic reaction was clarified. In this paper, the effect of laser power on the efficiency and reaction rate of SPR induced catalytic reaction was investigated according to the coupling reaction of para-aminothiophenol (PATP) and decarboxylation process of 4-mercaptobenzoic acid (MBA). It was found that the increase of laser power not only improved the efficiency of SPR catalytic reaction, but also accelerated the reaction rate from the perspective of reaction kinetics due to the heat effect and hot electrons generated by SPR. The results indicated that the rate of the SPR catalytic reaction was linear with the reciprocal of the square of the laser power. It provided a new approach for the determination of the kinetic parameters of the related surface processes. Keywords surface-enhanced Raman scattering (SERS); Au monolayer film; plasmon catalyzed surface reaction; laser power; decarboxylation reaction
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.