Photocatalytic synthesis of Schiff base compounds in the coupled system of aromatic alcohols and nitrobenzene using CdXZn1−XS photocatalysts

Achieving green synthesis and transformation of organics is always an ambition of scientists under mild conditions. In this paper, a series of CdXZn1−XS (0 ≤ X ≤ 1) samples were synthesized by a simple wet-chemical method using cadmium nitrate, zinc nitrate and sodium sulfide as precursors, and were thoroughly characterized by many techniques, including X-ray diffraction, UV–vis absorption spectra, nitrogen adsorption-desorption isotherms, scanning electron microscopy, transmission electron microscopy and (photo)electrochemical measurements. The photocatalytic performance of the as-prepared samples was evaluated by photocatalytic synthesis of Schiff base compounds in the coupled system of benzyl alcohol and nitrobenzene under visible light irradiation. Results reveal that when X is 0.78 (Cd0.78Zn0.22S), the sample exhibits the highest photocatalytic performance. The yield of Schiff base is 55.2% under visible light illumination for 4 h, and the theoretical yields of benzaldehyde and aniline could reach 96.6% and 67.9%, respectively. The quantum efficiency (QE) of the sample with λ = 450 ± 10 nm is 15.8%. In addition, many other Schiff base compounds were also synthesized from the different coupled systems of aromatic alcohols and nitrobenzene. A possible reaction mechanism involving the oxidation of benzyl alcohol to benzaldehyde by photogenerated holes and the reduction of nitrobenzene to aniline by photoinduced electrons, followed by a condensation reaction between benzaldehyde and aniline to generate Schiff base compound was proposed. It is expected that the current work could offer an avenue to fabricate a high-performance photocatalyst used in the fields of photocatalytic selective organic transformations under mild conditions.