Chemical Quenching of Singlet Oxygen and Other Reactive Oxygen Species in Water: A Reliable Method for the Determination of Quantum Yields in Photochemical Processes?

Abstract

The production of singlet oxygen in aqueous solutions by photosensitizers (PS) grafted on silica was evaluated using the widely‐known singlet oxygen quencher, furfuryl alcohol (FFA). Although reliable data could be obtained when working with some of the water‐soluble PS in homogeneous solution, strong diffusion effects prevented the measurement of accurate singlet oxygen quantum yields of the silica materials. Moreover, when electron‐transfer reactions were possible and produced other reactive oxygen species (ROS), FFA oxidation did not result from singlet oxygen production but from electron transfer steps, as, for example, with TiO2 or with anthraquinone derivatives. Some literature data on singlet oxygen quantum yields with aqueous semiconductor suspensions in the presence of FFA have thus to be considered with care. Other issues were also raised with selective quenchers for other ROS such as hydroxyl radicals or superoxide radical anions and emphasize significant artefacts mainly arising from adsorption effects. The results obtained with anthraquinone derivatives confirmed its ubiquitous photochemical behavior and appeared as complex as that of the water‐soluble anthraquinone‐2‐sulfonate AQ2S. In any case, the covalent grafting of PSs on silica allows tuning the oxidative properties of the material. It also makes possible the efficient production of singlet oxygen by water‐insoluble PS, such as cyanoanthracene derivatives, in aqueous solutions.

Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics

“…Specifically, (1) VA is excited to the singlet state ( 1 P*) and rapidly undergo intersystem crossing to the triplet state ( 3 P*). The VA in the triplet state can then participate in an electron transfer reaction with water to give the reduced radical anion, which can react with dissolved oxygen to form superoxide anion (O 2 •– ) (). − Then, the O 2 •– formed will convert NO 2 or NO to nitrite (R5). (2) The excited photosensitizer generates reducing radical intermediates to directly react with NO 2 to produce HONO/NO 2 – (). − ,,,,− To explore the role of dissolved O 2 in the secondary formation of nitrite, we measured nitrite production from the solutions of 200 mM nitrate (AN and SN) with 5 mM VA at pH = 8 under N 2 -saturated condition.…”

Synthesis of flower-like MoS2/CNTs nanocomposite as an efficient catalyst for the sonocatalytic degradation of hydroxychloroquine

“…Likewise, the deactivation of 1 O 2 using L-histidine [56] and furfuryl alcohol [57] can be explained using Eqs. (13) , (14) : …”

Mechanism for the photodegradation of 9,10-dibutoxyanthracene in the presence of air

“…Since photodecomposition proceeds in the presence of air, it was suggested that 1 is consumed for the formation of EPO, thereby indicating that compound 1 likely plays two roles, namely the generation and capture of singlet oxygen. However, the photodecomposition of 1 was suppressed in air in the presence of additives (Fig 2 ), including FFA [20], TEDA, BHT [21], and TEMP [16], which are all compounds used to detect and capture singlet oxygen. Decomposition was suppressed by the addition of these compounds, thereby indicating the involvement of singlet oxygen in the photodecomposition of 1.…”

“…In particular, when TEDA was added, ~90% of 1 remained. TEDA catalytically traps singlet oxygen, while FFA, BHT, and TEMP combine with singlet oxygen and are converted to more stable compounds [20][21][22]. Since the relative concentrations of FFA, BHT, and TEMP added to 1 decrease as singlet oxygen capture progresses, the consumption of 1 is not suppressed.…”