Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Significance
Photocatalytic processes use light energy to drive chemical reactions. Light absorption facilitates the production of an excited electron/hole pair. Unlike homogenous photocatalysis, heterogenous photocatalysis is an efficient and widely recognized technology for removing environmental propellants in natural sources. In addition to this important use, heterogeneous photocatalytic technology has recently attracted growing research attention as a promising strategy for producing alternative renewable solar energy. As a green technology, it also holds application prospects in other fields like catalysis and organic synthesis. Nevertheless, the stability and efficiency of conventional photocatalysis are still challenging.
A typical selective reaction that continues to be popular is the photocatalytic oxidation of alcohol to aldehyde. Several photocatalytic systems have been developed for the selective oxidation of benzyl alcohol to benzaldehyde with satisfactory results. Most of the traditional photocatalytic systems, however, require the use of solvents, which can have other drawbacks like increased production costs and possible environmental issues. Therefore, developing a solvent-free photocatalytic system for selective oxidation of benzyl alcohol to benzaldehyde is of extreme importance.
Recently, non-noble metal-based photocatalytic systems have emerged as a promising option. However, developing a non-noble metal-based photocatalytic system remains a big challenge due to relatively low conversion of benzyl alcohol and selectivity to benzaldehyde, among other drawbacks. In addition, heterojunction photocatalysts can be used to improve catalytic efficiency by promoting the separation of photogenerated carriers. Specifically, the Z-scheme heterojunction can improve the spatial separation of photoinduced carriers, which is vital in developing a highly efficient catalytic system.
On this account, a team of researchers from Shaanxi University of Science & Technology: Dr. Xulu Jiang, Professor Weitao Wang, Professor Huan Wang, Professor Zhen-Hong He, Professor Yang Yang, Professor Kuan Wang, Professor Zhao-Tie Liu and Professor Buxing Han developed a solvent-free aerobic photocatalytic system for efficient and selective oxidation of benzyl alcohol to benzaldehyde. This selective oxidation reaction was achieved over a well-designed and Z-scheme heterojunction photocatalyst of ZnO/C3N4. Their work is currently published in the journal, Green Chemistry.
The research team reported an improved performance of the present solvent-free photocatalytic system under solvent-free irradiation conditions, resulting in exclusive oxidation of benzyl alcohol can be exclusively oxidized to benzaldehyde. It achieved a higher yield of up to 99.8% using EDTA-2Na as an additive and a formation rate of 16633 µmol g-1h-1 at room temperature. This was attributed to the remarkably higher photocatalytic activity and selectivity compared to the existing systems based on noble and non-noble metal-based photocatalysis.
The authors examined and discussed in detail the associated photocatalytic mechanism. The mechanism involved the generation of ·O2– from O2, which could be enhanced by the heterojunction through the photogenerated electrons. Furthermore, it was worth noting that under solvent-free conditions, the water formed during the reaction process played a critical role in suppressing the activity and selectivity. In addition to benzyl alcohol, the application scope of the present solvent-free photocatalytic system could be extended to oxidizing allylic, benzylic, aliphatic and heterocyclic alcohols to their corresponding aldehydes.
In summary, the study by Shaanxi University of Science & Technology researchers presented a non-noble metal photocatalyst of ZnO/C3N4 based on Z scheme heterojunction. This system proved more efficient and robust compared to existing photocatalytic systems, with the ability to achieve high yield under solvent-free conditions. The solvent-free photocatalytic system proved to be an efficient and green strategy. In a statement to Advances in Engineering, the authors stated that it would contribute to commercial and large-scale oxidation of alcohols to aldehydes.
Reference
Jiang X., Wang W., Wang H., He Z.-H., Yang Y., Wang K., Liu Z.-T., & Han B. (2022). Solvent-free aerobic photocatalytic oxidation of alcohols to aldehydes over ZnOd/C3N4. Green Chemistry, 24(19), 7652–7660.
