Removal of paracetamol (acetaminophen) by photocatalysis and photoelectrocatalysis. A critical review

Abstract

Paracetamol (PCT) is widely used as an antipyretic and analgesic drug by animals and humans, and it is detected in most natural waters and wastewaters because it is not completely removed by conventional methods in wastewater treatment plants. Since it is toxic to living beings such as microorganisms, algae, and fishes, powerful methods for its removal from the aquatic environment need to be developed. Over the last years, many research works have shown the effectiveness of photocatalysis (PC) and photoelectrocatalysis (PEC) to remediate waters contaminated with PCT. This article presents a critical and comprehensive review of such studies up to June 2022. Once the fundamentals of both techniques have been described, the review summarizes the fast removal and low mineralization of PCT by PC with pure TiO2 under UV light to further remark the better performance achieved with UV than visible light using TiO2-based nanocomposites. The treatments with other photocatalysts like pure ZnO, ZnO-based nanocomposites, WO3-based, bismuth-based, and g-C3N4-based with UV or visible light are summarized as well. Commercial and synthesized materials used for each class of these photocatalysts are described, considering their nature, composition, and band gap potential. The effect of pH and/or components of the aqueous matrix are examined, showing a lower degradation in natural waters and real wastewaters than in pure water, The different photocatalytic mechanisms proposed to originate reactive oxygen species from the photogenerated electron/hole pairs in the semiconductors are explained, along with the oxidation products detected. The PEC treatments are analyzed from the nature and composition of the photoanode, light irradiated, and electrical properties of the photoelectrochemical cells to produce the reactive oxygen species for PCT destruction. The larger drug decay with hybrid PEC + PEF treatments under sunlight is finally remarked.