Thermally exfoliated urea-derived g-C₃N₄/Ti₃C₂T_X MXene 2D/2D Schottky junctions as photocatalysts​ for the removal of pharmaceutical pollutants in aquatic matrices

In recent decades, the most common photocatalyst used in environmental applications has been TiO₂, which exhibits a large band gap and can only be photoactivated under UV light. Therefore, the scientific interest has recently focused on the development of visible-light-activated photocatalysts such as g-C₃N₄. However, the photocatalytic performance of g-C₃N₄ is significantly hindered by the rapid recombination of photogenerated charges. An interesting approach to overcome this drawback is to fabricate Schottky junctions by combining g-C₃N₄ with materials demonstrating high metallicity.

In the present study, g-C₃N₄ was synthesized by forming a urea slurry that was dried and then calcinated at 550 ^oC for 4 h (CNU). The resulting CNU was ground and calcinated again at 550 ^oC for 2 h (3×) to achieve thermal exfoliation of its stacked 2D layers (CNUex3). In addition, a quantity of CNUex3 was then subjected to protonation using an HCl solution (pCNUex3). Ti₃C₂T_X MXene was prepared via a top-down methodology using HF to achieve wet-chemical etching of the Al layers from the Ti₃AlC₂ Max Phase. Subsequently, low amounts of Ti₃C₂T_X were coupled with either CNUex3 or pCNUex3 via a simple sonication methodology to form x%-CNMX or x%-pCNMX 2D/2D Schottky junctions (x = 1, 3 or 5), respectively. The structural, morphological and optical characteristics of all the synthesized materials were investigated using various characterization techniques (PXRD, SEM, ATR-FTIR, Raman spectroscopy, DRS, etc.). Furthermore, their photocatalytic performance was evaluated through laboratory-scale experiments using the antihypertensive drug Valsartan as a model pollutant, since it is commonly detected in various aquatic matrices. The results revealed that the combination of either CNUex3 or pCNUex3 with low amounts of Ti₃C₂T_X improves their photocatalytic performance due to the successful suppression of exciton recombination as a result of the formation of a Schottky barrier at the interface of the two materials.