High-performance nanocomposites of high-surface-area (HSA) g-CN and TiO-WO-BiO/SiO (g-CN/TSBW) were successfully synthesized and evaluated for their photocatalytic degradation of organic dyes in aqueous solution under visible light irradiation. The photocatalysts were characterized using XRD, N adsorption-desorption, FE-SEM, EDS, HR-TEM, FTIR, Raman spectroscopy, UV-Vis DRS, and PL spectroscopy. The study investigated the effects of g-CN content, photocatalyst loading, dye concentration and type, solution pH, scavengers, and oxidants on the photocatalytic degradation process. The g-CN photocatalyst, with a high surface area of approximately 100 m/g, exhibited a combined adsorption and photocatalytic degradation effect for rhodamine B (RhB) removal. Notably, nearly 100% RhB degradation was achieved using 1 g/L of the optimized 50% g-CN/TSBW heterojunction photocatalyst with an initial RhB concentration of 10 mg/L after only 20 min of visible light exposure. This high performance resulted from the synergistic effect of combining g-CN with TSBW, facilitated by the formation of a type II heterojunction between TiO and g-CN, which effectively suppressed the recombination of photoinduced charge carriers. Trapping experiments provided mechanistic insights into RhB photocatalytic degradation, revealing the significant contribution of superoxide radicals (•O). Based on these trapping experiments, a plausible photocatalytic reaction mechanism was proposed. Finally, the recyclability of the 50% g-CN/TSBW heterojunction photocatalyst was also demonstrated.