When porphyrins meet 2D materials: spectroscopic and photocatalytic properties

Abstract

Since its discovery, graphene has gained considerable interest from scientists all over the world. For more than one decade, the scientific community has been spending notable amounts of intellectual and financial resources to study its properties, which paves a way towards the commercialization of graphene, other 2D materials and a manifold of their derivatives. In this review, the spectroscopic properties of porphyrin-functionalized 2D materials are comprehensively discussed, followed by an extensive presentation of state-of-the-art achievements in photocatalysis based on such composite/hybrid materials. The primary focus is on the fundamental understanding of the structure–property–performance relationship as well as its importance in the future target-oriented design and fabrication of photocatalysts with tailored properties. After a short introduction, different design strategies for the fabrication of porphyrin (Por)-functionalized graphene-based materials (GBMs) (covalent vs. non-covalent assemblies) are systematically summarized. Then, the photocatalysis-relevant properties of the composites are thoroughly discussed based on the experimental results provided by steady-state absorption spectroscopy (ground-state properties) and time-resolved absorption and emission spectroscopies (excited-state properties). The importance of appropriate data analysis, with particular respect to the photoemission processes, is brought to attention. Subsequently, the photocatalytic behavior towards hydrogen generation, CO₂ reduction and pollutant degradation of Por and GBM hybrids are comprehensively reported and fundamental mechanisms of light-driven catalytic processes in such systems, together with efficiency-limiting steps, are highlighted. The role of spectroscopy as a very powerful tool that enables the determination of key photophysical properties essential for light-driven catalysis is emphasized. Finally, recent advances with respect to 2D materials beyond graphene and their assembly with Por as promising photocatalysts are presented. We believe that this review, which comprehensively presents the knowledge gained to date regarding composites based on 2D materials with porphyrins as promising photocatalysts, will stimulate further efforts of researchers to tackle the remaining challenges and contribute to taking a decisive step towards the commercialization of these photocatalysts in the future.