PHOTODEGRADATION PATHWAY OF BISPHENOL S BY TITANIUM DIOXIDE UNDER UVA IRRADIATION

Abstract

Plastic pollution has emerged as a significant global challenge in recent years. It is estimated that 5-10% of the worldwide plastic production ends up in the oceans annually1. In 2020, Malaysia’s plastic consumption amounted to 148 thousand metric tons, with an annual per capita of 16.78 kg2. The “Malaysia Roadmap Towards Zero Single- Use Plastics 2018-2030” was introduced as a three-phase national plan to eliminate single-use plastics3. However, existing plastic waste can snowball into an environmental crisis, as plastic and microplastic waste release various additives during fragmentation. Among these additives, Bisphenol S (BPS) has been identified as an emerging pollutant with the potential to adversely affect humans and animals. Therefore, the removal of this analog from wastewater is essential. This study evaluated the effectiveness of titanium dioxide (TiO2) in photodegrading BPS in an aqueous solution under UVA light while elucidating the photodegradation pathways. Key photodegradation parameters, including the initial pH of the solution, photocatalyst dosage, and illumination period, were optimized. UV-visible spectrophotometer results showed that at an initial concentration of 5 mg/mL, complete photodegradation of BPS occurred within 180 minutes under UVA exposure. Kinetic study showed that the photodegradation process followed the Langmuir-Hinshelwood kinetic model, with a rate constant of 0.0133 min-1. High-performance liquid chromatography (HPLC) analysis identified a single intermediate persisting in the solution after 180 minutes of photodegradation. However, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis detected four distinct photodegradation peaks and elucidated their formation pathways, revealing a complex degradation pathway. Overall, this study provides valuable insights into the photocatalytic degradation of BPS using TiO2 under UVA irradiation. HPLC and LC-MS/MS analyses confirmed that while BPS undergoes significant degradation under UVA light in the presence of TiO2, its degradation products persist as intermediate in the solution.