This study describes the experimental design and optimization of the photocatalytic reaction using the immobilized catalyst Fe/Nb₂O₅ in the degradation of Triclosan and 2.8-DCDD. The techniques employed to characterize the photocatalysts were: specific surface area, average pore volume, average pore diameter, photo-acoustic spectroscopy (PAS), X-ray diffraction (XRD), and scanning electron microscopy (SEM/EDS). The reaction parameters studied were pH, catalyst concentration, catalyst calcination temperature, and nominal metallic charge. The results indicated that the immobilized Fe/Nb₂O₅ catalysts were efficient in the degradation of Triclosan and 2.8-dichlorodibenzene-p-dioxin. The catalysts with nominal metal loading of 1.5% Fe calcined at 873 K showed the highest constant reaction rate and the lowest half-life 0.069 min⁻¹ and 10.04 min. Tests in different matrices indicated that the photocatalytic reaction using aqueous solution containing Cl⁻ is faster when compared with the ultrapure water matrix.

This study describes the synthesis of an innovative nanomaterial (patent application number BR 1020210000317) composed of cobalt ferrite functionalized in niobium pentoxide CoFe₂O₄@Nb₅O₂ (CFNb), synthesized via green synthesis using tangerine peel extract. The material emphasizes the combination of a magnetic material (which allows for easy recovery after application) with niobium pentoxide (a metal which is abundant in Brazil). CFNb was applied as a catalyst for the paracetamol (PCT) degradation by photocatalysis. The new materials were characterized through surface and pore analysis (S_BET, S_EXT, S_mic, V_mic, and V_TOTAL), photoacoustic spectroscopy (PAS), zero charge point (pH_PZC, scanning electron microscopy (SEM/EDS), and X-ray diffraction (XRD). The reaction parameters studied included pH and catalyst concentration. The results indicated that the CFNb nanocatalysts were efficient in the paracetamol degradation, presenting better results in conditions of low pH (close to 2) and low catalyst concentration under irradiation of the 250 W mercury vapor lamp (greater than 28 mW·cm⁻²) at 60 min of reaction.

TiO₂-based semiconductors are formidable photocatalysts for redox reaction applications. Although N-doped TiO₂-Nb₂O₅ catalysts have already been explored in the literature, studies on their antioxidant activity are scarce, and systematic investigations on the effects of synthesis parameters over a wide range of %Nb and NH₄OH concentrations are limited. In addition, the relationship between optimal pH and %Nb has not yet been adequately explored. In the present work, the sol–gel synthesis of N-doped TiO₂-Nb₂O₅ catalysts was optimized using a design of experiments approach focused on photocatalysis, adsorption, and antioxidant applications. The samples were characterized by TGA, SEM/EDS, XRD, PZC tests, photoacoustic spectroscopy, and N₂-adsorption/desorption experiments. The salicylic acid (SA) degradation tests and DPPH radical scavenging assays demonstrated the superior photocatalytic activity (up to 72.9% SA degradation in 30 min, pH 5) and antioxidant capacity (IC₅₀ = 88.9 μg mL⁻¹) of pure TiO₂ compared to the N-doped TiO₂-Nb₂O₅ catalysts. The photocatalytic activity, however, proved to be intensely dependent on the pH and %Nb interaction, and at pH 3, the 25Nb-1N-400 catalyst promoted more significant SA degradation (59.9%) compared to pure TiO₂ (42.8%). In the methylene blue (MB) adsorption tests, the catalysts N-doped TiO₂-Nb₂O₅ showed removals at least seven times greater than TiO₂ catalysts without Nb.