Photocatalytic degradation of the antihypertensive drug Amlodipine besylate using g-C₃N₄ materials prepared and exfoliated under N₂ flow

Graphitic carbon nitride (g-C₃N₄) has emerged as one of the most promising visible-light-activated photocatalysts due to its properties that make it ideal for environmental photocatalytic applications. According to numerous studies, urea-derived g-C₃N₄ variants demonstrate optimal photocatalytic performance in the degradation of aquatic pollutants. However, the limited yield of thermal polycondensation of urea raises significant concerns regarding sustainable production. Consequently, the use of alternative common precursors that enable higher production yields, along with their optimization to achieve competitiveness with urea-derived g-C₃N₄, has recently gained considerable ground.

In the present study, g-C₃N₄ materials were synthesized via thermal polycondensation of either thiourea (CNT-N₂) or melamine (CNM-N₂), under N₂ flow (550 °C, 4 h). Subsequently, each of these bulk materials underwent two thermal exfoliation cycles (Tex1/Mex1 and Tex2/Mex2) under N₂ flow to further enhance their photocatalytic performance. The structural, morphological, and optical characteristics of all the prepared materials were investigated using multiple characterization techniques. Furthermore, their photocatalytic performance was assessed through laboratory-scale experiments utilizing the antihypertensive drug Amlodipine besylate (AML) as a representative emerging contaminant.

The results revealed that Tex2 exhibited the highest photocatalytic activity among the prepared materials due to increased S_BET, improved interfacial charge transfer, and a narrower E_g, achieving complete removal of 5 mg L⁻¹ AML within 6 min of illumination (k_PC = 0.858 min⁻¹). Furthermore, the transformation products (21 in total), the mineralization profile, and the detoxification potential of the applied process were examined. Finally, the viability of Tex2 was evaluated in real secondary-treated hospital wastewater spiked with AML. The results demonstrated that it retained a substantial portion of its photocatalytic efficacy over five photocatalytic cycles, achieving complete AML removal and more than 40% TOC reduction in all cases. Overall, this study indicates that the tuning and exfoliation of g-C₃N₄ materials under N₂ flow can substantially improve their photocatalytic performance.