Green-synthesized supported nanocatalyst for the Rhodamine 6G photodegradation: Photocatalytic activity, machine learning modeling and ecotoxicity

This study reports the synthesis and comprehensive evaluation of a novel green-supported nanocatalyst (SiO 2 /MoO 3 -NPs) for the photodegradation of Rhodamine 6G (Rh6G) dye under visible irradiation. The nanocatalyst was developed in accordance with circular economy principles, utilizing silica (SiO 2 ) extracted from agro-industrial rice husk waste (as the catalytic support), and molybdenum trioxide nanoparticles (MoO 3 -NPs) biosynthesized using the Araucaria angustifolia extract (as the photoactive phase). The nanomaterial was fully characterized by Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), Scanning Electron Microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-Ray Diffraction (XRD), N 2 porosimetry, Zeta Potential (ZP), zero charge point (pH ZCP ), Diffuse Reflectance Spectroscopy (DRS), and acid sites present onto the surface of the nanomaterial. SiO 2 /MoO 3 -NPs confirmed the presence of α-MoO 3 and β-MoO 3 phases , as well as high surface area (260 m 2 g -1 ). The photocatalytic performance was optimized using a Central Compound Rotational Design (CCRD 2 3 ), achieving an optimal Rh6G removal of 99.9% under the ideal conditions (4.2 g L -1 of SiO 2 /MoO 3 -NPs, 1.6 mg L -1 of Rh6G, and pH 7). The kinetic degradation followed pseudo first-order model ( k = 0.027 min -1 ) and demonstrated excellent photostability, maintaining high efficiency after four reuse cycles. Furthermore, the ecotoxicity evaluation showed that the nanocatalyst and the treated wastewater were non-toxic to Artemia salina and Lactuca sativa , respectively. A Machine Learning (ML) approach (Random Forest – RF model) was successfully employed to predict of the Rh6G photodegradation mechanism, identifying key intermediate products. Therefore, these results highlight the potential of this sustainable, waste-derived nanocatalyst for efficient and environmentally friendly wastewater treatment. • Nanocatalyst (SiO 2 /MoO 3 -NPs) was bioynthesized using Araucaria angustifolia extract. • The optimized catalyst performance achieved a 99.9% removal of the Rhodamine 6G dye. • Random Forest model was successfully employed to predict the degradation mechanism. • SiO 2 /MoO 3 -NPs and treated wastewater were non-toxic ( A. salina and L. sativa ).