Tertiary amine mediated aerobic oxidation of sulfides into sulfoxides by visible-light photoredox catalysis on TiO2 † †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc01813g Click here for additional data file.

The selective aerobic oxidation of sulfides into sulfoxides on TiO2 under visible-light irradiation was accomplished through synergistic catalysis with triethylamine.


Reagents and solvents:
All of the reagents used were obtained from commercial suppliers such as Sigma-Aldrich, Alfa Aesar and TCI, etc. The solvents were supplied by Merck or Fischer Scientific. All the regents and solvents are of the highest purity and used without further purification.
General procedure for the oxidation of sulfide: In a typical reaction, 40 mg of Degussa P25 TiO2, 0.3 mmol of thioanisole and 0.01 mmol of triethyamine were added to 5 mL of CH3OH in a Pyrex vessel. After the reaction mixture was stirred for 30 min in dark to reach adsorption equilibrium, O2 was purged into the Pyrex vessel to raise the initial pressure to 0.1 MPa. The reaction mixture was magnetically stirred at 800 r/min and illuminated with λ>400 nm visible light irradiation in an air-conditioned room to warrant the reaction temperature constantly at 25  C. At the end of reaction, the TiO2 photocatalyst particles were separated from the reaction mixture by filtration and the products were quantitatively analyzed by gas chromatography (GC) equipped with a flame ionization detector (FID) using chlorobenzene as the internal standard. The structure of products were confirmed by comparison with the retention time with standard samples and further confirmed by gas chromatography-mass spectrometry (GC-MS).

Instrumentation and conditions:
Light source: The reaction was irradiation with an Asahi Spectra MAX-303 300 W Xenon light source using a UV-VIS mirror model. In this mirror model, the irradiating wavelength range is 270 nm-650 nm, thus the possible heating of the reaction medium the infrared light is completely excluded. Additional Asahi Spectra longpass cutoff filters (>400 nm) are used to control irradiation wavelength range during the reaction. The reaction medium was maintained at room temperature throughout the experimental process.

UV-Vis:
The UV-visible absorption spectra of the solid samples were recorded on a Shimadzu UV 2550 UV-visible Spectrophotometer with a diffuse reflectance measurement accessory.

XPS:
X-ray Photoelectron Spectroscopy (XPS) were measured by an ESCALAB250XI. The incident radiation was Mg Kα X-ray (1253.6 eV) at 400 W and a charge neutralizer was turned on for acquisition. The binding energy of N1s was corrected by C 1s peak (284.8 eV) from residual carbon. with high pure He as the carrier gas.

DFT calculation:
The first-principle calculations were performed using the Vienna ab initio simulation package (VASP) [1] that based on the density functional theory. The projector augmented wave (PAW) [2] method was used to describe the electron-ion interaction and the exchange correlation between electrons was described by the generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof (PBE) form. We used a cutoff energy of 500 eV for the plane-wave basis set. Spin polarization was allowed for all systems. The volume of the supercell was fixed but all the internal freedoms were fully relaxed. For the bulk rutile and anatase TiO2, the (4×4×6) and (6×6×2) k-mesh within the Monkhorst-Pack scheme were used respectively. Lattice relaxation was continued until the forces on all the atoms were converged to less than 10 −2 eV Å -1 . The lattice constants reproduced from GGA-PBE computations, as well as the theoretical and experimental values from the literatures are listed in Table S1. Our results are in good agreement with both the previous DFT results and experimental results.