<p>The N-deficient g-C₃N₄/Bi₃TaO₇ composite photocatalyst with upconversion capability was synthesized via electrostatic self-assembly. Under visible light, it achieved 80.7% LVFX degradation efficiency, maintaining 65% performance under long-wavelength illumination. PL characterization demonstrated strong upconversion property, with the sample emitting blue light at 470&#xa0;nm under 800&#xa0;nm near-infrared excitation. Electrochemical analysis revealed the material’s band structure and confirmed the formation of a Z-scheme heterojunction. Based on these findings, we propose a degradation mechanism: Nitrogen defect levels act as intermediate states for electron transitions, enabling electrons to reach higher energy levels. This process generates high-energy photons that subsequently activate BTO for photocatalytic reactions.</p> Graphical Abstract <p></p>