The synergistic effect of nitrogen-doped titanium dioxide/mercaptobenzoic acid/silver nanocomplexes for surface-enhanced Raman scattering

We synthesized titanium dioxide (TiO 2 ) and nitrogen-doped TiO 2 nanoparticles (N-TiO 2 NPs) via a sol-hydrothermal method using ammonium chloride (NH 4 Cl) as the nitrogen (N) source. Furthermore, an N-TiO 2 /4-mercaptobenzoic acid (4-MBA)/silver (Ag) nanocomplex served as an active substrate for surface-enhanced Raman scattering (SERS) and was prepared by self-assembly. During SERS, the Raman signals of 4-MBA of the N-TiO 2 /MBA/Ag nanocomplexes exhibited higher intensity and sensitivity than pure TiO 2 /MBA/Ag, with 1% N doping in N-TiO 2 , producing the strongest Raman signals. We characterized the N-TiO 2 hybrid materials by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectra. N doping did not influence the phase of the TiO 2 crystal. The doped N entered into the crystal lattice of the TiO 2 , replacing some oxygen (O) to form Ti-O-N or Ti-N-O linkage. The results indicated that an appropriate amount of N doping could enhance the SERS performance of the TiO 2 SERS substrate via N substitution doping. These doping forms were beneficial to the molecular charge transfer (CT), and this resulted in improved SERS performance for N-doped TiO 2 NPs. We attributed this improvement to the formation of N-doping energy levels that were beneficial to the process of TiO 2 to MBA molecule CT. This work not only enriched the nonmetal-doped CT mechanism in SERS but also provided several reference values for practical applications. N-doped TiO 2 nanoparticles were synthesized. Whereafter, N-TiO 2 /MBA/Ag nanocomplexes were prepared and served as a SERS-active substrate. An appropriate amount of N doping can enhance the SERS properties of TiO 2 SERS-active substrate by nitrogen substitution doping. The nonmetal doping TiO 2 -to-molecule CT mechanism and the synergistic effect in N-TiO 2 /MBA/Ag charge transfer systems have been studied.