In a heterostructure photocatalyst, a proper co-catalyst plays an important role, which is essential for achieving high efficiency in photocatalyst systems for treating organic pollutants. Carbonaceous nanomaterials are recognized as the most effective, economical, and environmentally friendly cocatalyst for various semiconductor-based heterostructure photocatalysts. CNf would be the best carbonaceous semiconducting material to form a heterogeneous photocatalyst. The heterostructure of CNf/CdS nanoflowers is prepared by a solvothermal route and probed for visible-light decomposition of the rhodamine B (RhB) dye. CNf provides a large surface area for dye adsorption, acts as a sink for photogenerated electrons from the semiconductor CdS, and improves the utilization of visible light. As a result, CNf as a co-catalyst significantly improved the photocatalytic performance of semiconductor-based organic pollutant removal systems. The plausible degradation mechanism of RhB is determined on the basis of the scavenger study. The intermediates formed during photodegradation were detected by LCMS analysis. The probable pathway of RhB degradation to CO2 and H2O is presented in this report.