Alkali-Melting-Induced g-C₃N₄ Nitrogen Defect Construction and Band Structure Regulation: Efficient Photocatalytic Dye Degradation and Solar-Driven Applications

Photocatalytic oxidation technology harnesses solar energy for pollutant mineralization, presenting significant potential for environmental applications. A critical bottleneck remains the development of high-performance photocatalysts. This study centers on the non-metallic semiconductor material graphitic carbon nitride (g-C₃N₄). To overcome the inherent limitations of pristine g-C₃N₄, including limited surface area, rapid charge carrier recombination, and inadequate active sites, it implements surface engineering strategies employing acidic (H₂SO₄) or basic (K₂CO₃) agents to modulate microstructure, introduce defect sites (cyano/amino groups), and optimize bandgap engineering. These modifications synergistically enhanced photogenerated charge carrier separation efficiency and surface reactivity, leading to efficient dye degradation. Notably, the K₂CO₃-modified catalyst (g-C₃N₄-OH), synthesized with a mass ratio of m(g-C₃N₄):m(K₂CO₃) = 1:1, achieved 92.2% Rhodamine B degradation within 50 min under visible light, surpassing pristine g-C₃N₄ (20.6%), the optimized H₂SO₄-modified sample (g-C₃N₄-HS, 60.9%), and even template-synthesized g-C₃N₄-SBA (79.6%). The g-C₃N₄-OH catalyst demonstrated exceptional performance under both visible light and natural solar illumination. Combining facile synthesis, cost-effectiveness, superior activity, and robust stability, this work provides a novel approach for developing high-efficiency non-metallic photocatalysts applicable to dye wastewater.