Bimetal‐Doped ZnO‐g‐C ₃ N ₄ Nanocomposites as Advanced Photocatalysts for Rapid Solar‐Induced Xylenol Orange Dye Degradation

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This study reports the successful synthesis of Bi and Fe co‐doped ZnO‐g‐C 3 N 4 nanocomposites using a green ultrasound‐assisted hydrothermal route. The integration of Bi and Fe dopants into the hexagonal wurtzite ZnO lattice, combined with the 2D g‐C 3 N 4 nanosheet scaffold, resulted in a well‐integrated heterojunction with a narrowed optical bandgap of 2.04 eV. This electronic modification significantly enhanced visible‐light absorption and charge carrier separation efficiency. The optimized 3:1 Bi:Fe composite demonstrated exceptional photocatalytic performance, achieving 98% degradation of xylenol orange (XO) within 90 min under natural solar irradiation. The kinetic analysis confirmed a pseudo‐first‐order mechanism with an apparent rate constant of 0.0306 min −1 , which is 7.65 times higher than commercial ZnO. Scavenger trapping experiments identified hydroxyl radicals as the primary oxidative species driving the degradation process. Furthermore, the catalyst maintained high structural stability and reusability over four consecutive cycles. These results establish the Bi:Fe (3:1) ZnO‐g‐C 3 N 4 nanocomposite as a high‐performance, solar‐responsive, and eco‐friendly material for the rapid remediation of organic pollutants in wastewater.