Because of simplicity, eco-friendly and attracting of scientific community, pure and non-metal-doped TiO$_2$ nanoparticles (NPs) photocatalysts: TiO$_2$ (T), C-TiO$_2$ (CT), N-TiO$_2$ (NT), S-TiO$_2$ (ST) and C, N, S-TiO$_2$ (CNST) were prepared by aqueous mangrove extract via sol–gel method. The materials were characterized by XRD, FTIR, UV–Vis absorption spectroscopy, BET, SEM, TEM, EDX, XPS, EIS and PEC. The results indicated that the planned photocatalysts exhibit an anatase crystal phase with a particle size in the range of 20–37 nm. The non-metal doping induces a redshift of optical absorption edge, and exhibits a strong visible light absorption. The photoluminescence intensityemission follows the order: T>CT>ST>NT>CNST, whereas the photocatalytic activity (PCA) increases in the reverse order. The PCA was assessed by photodegradation of two organic dyes, reactive blue 19 (B19) and red 76 (R76) under visible light illumination. The enhancement in visible PCA followed the order CNST>NT>ST>CT>T. The photocatalytic degradation efficiency of the dyes using the CNST sample reached 100% after 60 min of irradiation. The most active species in the photocatalytic processes are the positive holes. The solid photocatalysts were recycled five times without losing its activity. The chemical oxygen demand test confirmed that the CNST is the best photocatalyst of the investigated samples. Overall, the greenly synthesized NPs demonstrated the outstanding potential of green productfor treating contaminated water by both B19 and R76 dyes under visible light illumination.