Facile two-step synthesis of yttrium-doped g-C ₃ N ₄ for enhanced photocatalytic degradation of methylene blue with self-cleaning properties

In this study, porous graphitic carbon nitride (g-C₃N₄) with different yttrium (Y) doping ratios are synthesized using a facile two-step pyrolysis method, yielding Y/g-C₃N₄-1, Y/g-C₃N₄-2, Y/g-C₃N₄-3, and Y/g-C₃N₄-4. These synthesized materials are used for the photocatalytic degradation of methylene blue (MB). Among the synthesized combinations, Y/g-C₃N₄-3 showed the highest photocatalytic activity (99%) under visible light. It exhibited pseudo-first-order kinetic behavior (<i>k</i> = 0.0439 min^-1, <i>R</i> ² = 0.999, <i>t</i> _1/2 = 15.78 min) for MB degradation, outperforming the other materials. In tap water, Y/g-C₃N₄-3 achieved a 90% degradation efficiency for the target dye. The total organic carbon (TOC) removal reached 87%, further reinforcing its effectiveness. Electrochemical impedance spectroscopy (EIS) was performed, where a smaller semicircle for Y/g-C₃N₄-3 indicated lower charge transfer resistance and improved carrier mobility. To identify reactive species, a radical scavenger experiment was performed, revealing holes (h⁺) as the primary reactive species, while ˙OH, e^-, and ˙O₂ ^- played a minor role in MB degradation. The optimized photocatalyst was coated on the fabric surface using the drop-casting method to evaluate its self-cleaning properties. This work highlights the promising potential of rare earth metal doping as a versatile strategy for synthesizing high-performance g-C₃N₄-based photocatalysts.