Surface-Enhanced Raman Scattering on Semiconducting Oxide Nanoparticles: Oxide Nature, Size, Solvent, and pH Effects

Abstract

Semiconducting oxide nanoparticles have proven to be excellent in detecting extremely low-concentrations of molecules through surface-enhanced Raman scattering (SERS) effects. While the enhancement of the Raman activities arises from a large increase in polarizability due to charge transfer from the molecule to the semiconducting nanoparticle, little is known about how the oxide composition, nanoparticle size, solvent, or pH affects the observed Raman activities. In the current study, we examine these effects by carrying out extensive computational investigations of semiconducting TiO2, SnO2 and Fe2O3 nanoparticles and their complexes with both catechol and dopamine. An increase in the size of the oxide cluster or a decrease in the pH of the system under observation leads to enhanced Raman activities; the variation of the activities in different solvents is very much dependent on the nature of the vibrational modes. The marked increase in the Raman activities of molecules adsorbed on SnO2 or Fe2O3 over that of molecules adsorbed on TiO2 seems to indicate that these oxide nanoparticles would be useful substrates for SERS sensors. Our results also indicate that the Raman activities of some of the TiO2 modes are magnified upon adsorption of molecules, which concurs with some very recent experimental observations. All these results are consistent with a recently proposed theoretical model of SERS on semiconducting substrates. Further, this work has implications on the development of molecular sensing, dye-sensitized solar cells, and photocatalysis.

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

“…59,[61][62][63][64][65][66][67][68][69] This level of theory has been found to yield reliable geometries and vibrational frequencies for a number of first-row transition metal systems. [70][71][72][73][74] Nonetheless, in light of recent studies indicating the improved performance of the BP86 and TPSS functionals in describing transition metal containing systems, the geometries and energies of 2 were also calculated using these functionals and the larger TZVPP basis sets. [75][76][77] These results are shown in Table S4 which indicate that the B3LYP/6-31G* level of theory is reliable for the systems investigated in this study.…”

Anatase nanoparticles surface modified with fused ring salicylate-type ligands (1-hydroxy-2-naphthoic acids): A combined DFT and experimental study

“…Several papers have investigated CT complex formation between catecholate [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] and salicylate [27,[36][37][38]40,41] type ligands and colloidal TiO 2 nanoparticles (d $ 45 Å), where the binding of modifiers induces the surface reconstruction of the nanoparticles. Recently, combined theoretical (DFT) and experimental studies were performed, mainly on catecholate-type molecules as surface modifiers of rutile [32] and anatase [33][34][35] TiO 2 nanoparticles, reporting different adsorption geometries.…”

Direct observation of p,p′‐dimercaptoazobenzene produced from p‐aminothiophenol and p‐nitrothiophenol on Cu2O nanoparticles by surface‐enhanced Raman spectroscopy

“…[38] Since then, the enhanced Raman signal of adsorbed molecules on different nanostructure based on Cu 2 O material has been investigated. [39][40][41] Raman enhancement on semiconductors was currently believed to be mainly induced by chemical mechanism, [49,50] in which chargetransfer effect between molecule and substrate semiconductors was considered as the major resource for surface enhancement. For Cu 2 O substrate, the electromagnetic effect might also play a role because a weak E-field enhancement near the roughed surface was found and attributed to lightning rod effect according to earlier study.…”