Adsorption behavior of 6-Mercaptonicotinic acid on self-assembled gold nano-substrates explored by SERS combined with theoretical calculations

Nanoporous Au-Ag shell with fast kinetics: integrating chemical and plasmonic catalysis

Nanoporous noble metals and alloys are widely utilized as efficient catalysts, because they have high surface-to-volume ratios for sufficient active sites and induce molecule polarization through plasmon excitation as well. Herein, we demonstrate one approach to fabricate nanoporous Au-Ag shell. Such material represents the dual functions serving as efficient catalysts and high-performance surface-enhanced Raman scattering substrate. In situ spectrum acquisition can track the conversion of p-nitrothiophenol to 4, 4'-dimercapto-azobenzene at ambient temperature. In particular, as a result of chemical catalysis of Ag elements and strong plasmon-molecule coupling, catalytic kinetics of nanoporous Au-Ag shell is 79.2-123.8 times faster than Au nanoparticles (NPs), and 2.2-3.3 times faster than Ag NPs. This investigation offers a route to design superior catalysts to integrate chemical and plasmonic catalysis.

Conformations of 2-thiouracil in the aqueous solution and its adsorption behavior on the gold substrates explored by DFT calculations and experimental methods

2-Thiouracil, a thio-derivative of uracil, may appear in various tautomeric forms due to the different positions of protons. In this paper, the adsorption behavior and conformations of 2-thiouracil on the gold substrates are inspected by means of surface-enhanced Raman scattering (SERS) and density functional theory (DFT) calculations. The results indicate that all the enhanced bands are assigned to in-plane vibration modes. Besides, most of the bands related to N and S atoms are significantly enhanced and have obvious shifts in the SERS spectra. Furthermore, the CO stretching band at 1695 cm(-1) also appears in the SERS spectra. The theoretical SERS spectra of 2TU-Au₄ and 2TU2-Au₄ complexes agree well with the experimental SERS spectra of 2-thiouracil at 0.04 mM. Meanwhile, we calculate that the binding energies for 2TU2-Au₄ and 2TU-Au₄ are ca. 70 and 50 kcal/mol, respectively. Those results above imply that the 2TU and 2TU2 conformers can exist stably in the aqueous solution and both of them are vertically chemisorbed on the gold surfaces. For the 2TU, it is adsorbed on the gold surfaces through N1H position and the sulfur atom. While the 2TU2 adsorbed on the gold substrates through the N1 site and its deprotonated sulfur atom.