g‐C ₃ N ₄ Nanosheet/ZnO Nanosponge Heterojunctions for Efficient Visible‐Light Photocatalytic Degradation of Methylene Blue

This study explores the photocatalytic performance of ZnO nanosponge (ZnO NSp), g‐C ₃ N ₄ nanosheet (g‐C ₃ N ₄ NSh), and their composite in degrading methylene blue (MB) under UV and visible‐light irradiation. ZnO NSp displayed superior activity under UV light, achieving > 99% MB removal within 30 min and exhibiting the highest pseudo‐first‐order rate constant (0.124 min ⁻¹ ), outperforming both g‐C ₃ N ₄ NSh and the composite. In contrast, under visible light, the g‐C ₃ N ₄ NSh/ZnO NSp composite achieved 98% degradation within 60 min, attributed to enhanced charge separation across the heterojunction interface. The photocatalytic efficiency was influenced by pH, with neutral to alkaline conditions favoring MB removal through improved catalyst stability and adsorption capacity. Radical scavenging experiments confirmed superoxide (O ₂ • ⁻ ) and hydroxyl (HO•) radicals as the dominant reactive species driving degradation. These results demonstrate the complementary advantages of ZnO NSp and g‐C ₃ N ₄ NSh in different irradiation regimes and highlight the promise of their composite as an efficient, solar‐responsive photocatalyst for wastewater remediation.