g-C3N4-based hybrid photocatalysts for removal of emerging pharmaceutical pollutants from water: recent advances, degradation pathways, toxicity assessment,and future perspectives.

Pharmaceutical pollutants (PPs) are increasingly detected in aquatic environments, raising concerns about their persistence and potential risks to human health and ecosystems. Advanced oxidation processes based on photocatalysis have been widely developed to remove PPs and mitigate their negative effects. Recently, the metal-free photocatalyst graphitic carbon nitride (g-C3N4) has received increasing attention for environmental remediation due to its good chemical stability, non-toxicity, simple synthesis, and high removal efficiency. However, the application of g-C3N4 is still limited by rapid charge recombination, low surface reactivity, and insufficient utilization of visible light. To improve its performance for environmental remediation, particularly for the degradation of PPs in water and wastewater, various g-C3N4-based hybrid photocatalysts (CN-HPs) have been developed. This review provides a critical assessment of recent advances in these hybrid photocatalytic systems for the removal of emerging pharmaceutical pollutants from aquatic environments. The findings demonstrate that CN-HPs can achieve high removal efficiencies for various pharmaceutical pollutants under laboratory conditions. Moreover, total organic carbon reduction and mineralization often require more time than the degradation process. The removal mechanisms involve superoxide radicals (•O₂-), hydroxyl radicals (•OH), and photogenerated holes (h+), which break down PPs into smaller intermediates that are then further mineralized into inorganic products such as CO2, H2O, and inorganic ions. Toxicity assessment confirmed that the degradation of PPs using CN-HPs can produce by-products with toxicity different from that of the original compounds, and high removal efficiency alone does not indicate environmental safety. Furthermore, CN-HPs also exhibited good photocatalytic activity over repeated cycles, suggesting their potential for PPs removal from wastewater. This review also discusses the limitations and future perspectives of using CN-HPs for the removal of PPs, particularly regarding their application to real wastewater, long-term environmental safety, energy efficiency, and scale-up. In addition, we highlight the importance of combining experimental studies with artificial intelligence (AI) models to optimize treatment conditions and predict the performance of CN-HPs in removing target PPs in the field.