Recent Advances in Photocatalytic Degradation of Caffeine: Overview of the Mechanism and Photocatalysts

Caffeine, a widely consumed stimulant, has emerged as a recurring and persistent contaminant in aquatic environments, including surface water, groundwater and wastewater effluents. Its continuous presence poses ecological risks due to its bioactivity and resistance to conventional treatment methods. This study aims to investigate the potential of photocatalysis as a novel and sustainable approach for the effective degradation of caffeine in water systems. Photocatalysis employs semiconductor materials that, under suitable light irradiation, generate reactive oxygen species capable of breaking down organic pollutants into nontoxic end products. The review investigates a range of photocatalysts, including traditional metal oxides like TiO₂ and ZnO, as well as advanced materials such as doped semiconductors, graphene-based composites and graphitic carbon nitride, which exhibit superior performance due to enhanced light absorption and efficient charge carrier dynamics. Enhanced performance is observed in heterojunction and doped systems, as fluorinated TiO₂-based composites have achieved over 90% efficiency under UV and solar light, while Cu-doped graphitic carbon nitride has achieved 98.7% caffeine removal under sunlight. Key findings highlight that factors such as catalyst dosage, initial caffeine concentration, pH and light intensity significantly affect the degradation efficiency. The results demonstrate that optimised photocatalytic systems can achieve the complete mineralisation of caffeine with high efficiency and environmental compatibility. Although removal efficiencies are substantial, limitations such as the development of toxic intermediates, energy consumption and challenges in scaling up to industrial levels remain. Future perspectives emphasise the need for a comprehensive evaluation of process scalability and environmental safety, including monitoring for the formation and fate of degradation intermediates, as well as advancements in eco-friendly catalyst synthesis approaches.