Synergistic modulation of oxygen vacancies and heterojunction structure in Pd@CN@TiO2 promotes efficient photocatalytic Suzuki-Miyaura C-C coupling reactions

This paper reports a concise strategy for the controlled preparation of Pd@g-C3N4/TiO2 photocatalysts rich in oxygen vacancies. The scheme forms black TiO2 with oxygen vacancies on a carbon nitride material by in-situ growth and heat treatment, and then utilizes solvothermal reduction to load metallic palladium into the material. The composites were structurally analyzed using Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), elemental mapping, diffuse reflectance spectroscopy (DRS), and inductively coupled plasma (ICP) analysis. The results show that the oxygen vacancies in the black TiO2 materials prepared by the method reported in this paper can effectively improve the separation efficiency of the photogenerated electron-hole pairs and prolong the lifetime of the charge carriers by inhibiting charge recombination. In addition, the heterojunction structure formed between TiO2 and g-C3N4 materials also enhances the photocatalytic performance of the materials to some extent. After a simple optimization of the conditions, the Pd@g-C3N4/TiO2 photocatalyst could promote the Suzuki-Miyaura C-C coupling reactions under mild conditions (room temperature, 30 W LED lamp, lambda = 455 nm), and good biaryl yields were obtained (optimum yield = 99%). It is very noteworthy that the photogenerated electrons and holes generated by the photoexcited catalyst were confirmed to be the main active species in the photocatalytic process of the catalyst by radical trapping assay and EPR test. The Pd@g-C3N4/TiO2 material reported in this paper has excellent photocatalytic activity and stability in use, which provides a new reference scheme for wider green synthesis and catalysis.