Metal-free carbon nitride polymeric films for the synthesis of valuable organics using a novel mesostructured photoreactor

Abstract

Immobilised photocatalytic systems can strongly contribute to attaining more sustainable chemical processes, reducing downstream units for photocatalyst recovery and purification of the target molecules. On the other hand, it is known that this kind of photocatalytic system usually presents higher mass transfer resistance when compared with slurries and, consequently, slower kinetics. Besides, this can be even more limited for chemical synthesis using eco-friendly conditions, where combining the photocatalytic material with the best reactor design plays a fundamental role in the process efficiency. In this work, a micro-meso structured photoreactor was used to overcome these limitations, providing a large surface area per reaction volume and a higher illumination homogeneity through the entire reactor using a compact LED system. Several photocatalytic films were developed, combining different amounts of a metal-free photocatalyst (graphitic carbon nitride) with a biodegradable polymer matrix (sodium alginate). The catalytic performance was evaluated in the synthesis of aromatic aldehydes (anisaldehyde, tolualdehyde, benzaldehyde, vanillin, and piperonal from the photocatalytic oxidation of the corresponding, anisyl-, toluyl-, benzyl-, vanillyl- and piperonyl alcohols. All experimental runs were carried out under mild operation conditions, using water as solvent, room temperature and atmospheric pressure, and natural pH. The maximum performance in terms of yield was attained in the following order: anisaldehyde > tolualdehyde > piperonal > benzaldehyde > vanillin. A novel approach for photocatalytic organic synthesis with a low carbon footprint and reduced energy requirements is proposed. Moreover, the results provided in this work open a new window for the development of sustainable photocatalytic organic processes in continuous mode operation.