Outstanding response of carbon nitride photocatalysts for selective synthesis of aldehydes under UV-LED irradiation

The photocatalytic conversion of alcohols into the corresponding aldehydes constitutes an important reaction in organic synthesis. Optical semiconductors based on carbon nitride were prepared by thermal condensation of dicyandiamide followed by a thermal post-treatment (gCN-T) and further sonication (gCN-TS). The efficiency of these materials was evaluated on the selective conversion of different aromatic alcohols to the corresponding aldehydes, namely anisaldehyde, benzaldehyde, tolualdehyde, piperonal and vanillin. The best performance of gCN-T (1 g L-1) was found for the conversion of anisyl alcohol to anisaldehyde (> 99% conversion and selectivity in 45 min of UV-LED irradiation). The alcohol conversion and yield for aldehyde formation was related with the number, electronic nature and position of the functional groups in the aromatic ring. The use of gCN-TS, constituted by carbon nitride nanosheets, also produced > 99% conversion and selectivity towards anisaldehyde, while reducing the reaction time to 30 min and the catalyst load to 0.2 g L-1. The immobilization of gCN-TS in glass rings revealed to be a promising strategy for continuous production of aldehydes without the need of a catalyst separation step.