Generation of singlet oxygen catalyzed by the room-temperature-stable anthraquinone anion radical

Anthraquinones-based photocatalysis: A comprehensive review

In recent years, there has been significant interest in photocatalytic technologies utilizing semiconductors and photosensitizers responsive to solar light, owing to their potential for energy and environmental applications. Current efforts are focused on enhancing existing photocatalysts and developing new ones tailored for environmental uses. Anthraquinones (AQs) serve as redox-active electron transfer mediators and photochemically active organic photosensitizers, effectively addressing common issues such as low light utilization and carrier separation efficiency found in conventional semiconductors. AQs offer advantages such as abundant raw materials, controlled preparation, excellent electron transfer capabilities, and photosensitivity, with applications spanning the energy, medical, and environmental sectors. Despite their utility, comprehensive reviews on AQs-based photocatalytic systems in environmental contexts are lacking. In this review, we thoroughly describe the photochemical properties of AQs and their potential applications in photocatalysis, particularly in addressing key environmental challenges like clean energy production, antibacterial action, and pollutant degradation. However, AQs face limitations in practical photocatalytic applications due to their low electrical conductivity and solubility-related secondary contamination. To mitigate these issues, the design and synthesis of graphene-immobilized AQs are highlighted as a solution to enhance practical photocatalytic applications. Additionally, future research directions are proposed to deepen the understanding of AQs' theoretical mechanisms and to provide practical applications for wastewater treatment. This review aims to facilitate mechanistic studies and practical applications of AQs-based photocatalytic technologies and to improve understanding of these technologies.

Impact of Reactive Oxygen Species Scavenging on the Intermediate Production of Anthracene and Anthraquinone in Fresh versus Saltwater Environments

While salinity can alter the photodegradation of hydrophobic organic compounds (HOCs), the cause of their altered kinetics in seawater is not well understood. Because HOC intermediate photoproducts are often more toxic than their parent compounds, characterizing the generation of intermediates in saline environments is needed to accurately predict their health effects. The present study investigated the influence of salinity on the generation of anthraquinone through the photolysis of anthracene and the generation of anthrone and 1-hydroxyanthraquinone from the photolysis of anthraquinone as well as their reactivities with hydroxyl radicals. This was conducted by measuring the photolysis rates of anthracene and anthraquinone and characterizing their product formation in buffered deionized water, artificial seawater, individual seawater halides (bromide, chloride, and iodide), dimethyl sulfoxide, furfuryl alcohol, and solutions of hydrogen peroxide. Salinity enhanced the persistence of anthraquinone by a factor >10 and altered its product formation, including the generation of the suspected carcinogen 1-hydroxyanthraquinone. In part, this was attributed to reactive oxygen species (ROS) scavenging by the seawater constituents chloride and bromide. In addition, anthraquinone and its hydroxylated products were found to be moderately to highly reactive with hydroxyl radicals, further illustrating their tendency to react with ROS in aqueous environments. The present study emphasizes the importance of considering the effects of salinity on organic contaminant degradation; it can significantly enhance the persistence of HOCs and alter their intermediate formation, subsequently impacting chemical exposure times and potential toxic effects on estuarine/marine organisms. Environ Toxicol Chem 2023;42:1721-1729. © 2023 SETAC.