Organic semiconductor nanostructures: optoelectronic properties, modification strategies, and photocatalytic applications

Organic semiconductors (OSCs) possess diverse chemical structures and tailored optoelectronic properties via simple chemical modifications, so increasing use of them are found in efficient visible-light photocatalysis. However, the weak chemical bonds and the poor charge behavior (e.g., low concentration of free charge carriers, low carrier mobility) intrinsic in them, always incur quite limited stability and efficiency. Therefore, the assembly of them into refined nanostructures or nanocomposites is usually proposed to enhance their optoelectronic properties, as well as the photocatalytic efficiency and reliability. Zero-dimensional (0D) nanoparticles are low in size and hence high specific surface area (SSA); One-dimensional (1D) nanostructures are usually arranged in an orderly long range thus leading to low surface defect density and increased carrier mobility; Two-dimensional (2D) nanostructures are particularly capable of enhancing the photogenerated charge utilization because of their large reaction sites and shortened charge transport length. Furthermore, the building of heterogeneous interfaces in the nanocomposites can effectively facilitate the special charge separation. All these highlight the importance of organic nanostructures in improving the photocatalytic activity and stability. Therefore, organic semiconductor nanostructures (OSNs) have been increasingly used in the photocatalytic water splitting into H2 and O2, CO2 reduction, pollutant decomposition, disinfection, etc. In this review, we first examine the important optoelectronic properties of OSNs that govern the photocatalytic processes; we then analyze different classes of OSNs and their mechanistic pathways, with an emphasis on the structure-property relationships; we also introduced various photocatalytic applications of OSNs; we lastly propose the challenges and future outlook in real use.