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.