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.

Recent studies have shown that chlorophyll sensitization can improve the performance of semiconductors like TiO₂ in photocatalytic reactions and light-harvesting technologies, such as solar cells. Faced with the search for renewable energy sources and sustainable technologies, the application of this natural pigment has been gaining prominence. The present work addresses some of the main possibilities of chlorophyll-TiO₂ combination, presenting the most relevant aspects affecting chlorophyll extraction and TiO₂ sensitization.

O presente trabalho mostra a classificação dos catalisadores na classe de nanomateriais já estabelecida, visto que, grande parte de suas propriedades, como por exemplo, tamanhos de poro e de partícula do metal disperso são determinados em escala nanométrica. Catalisadores sintetizados pelo método sol-gel têm mostrado avanços na obtenção de nanomateriais. Para tanto, técnicas como o S-TPR e a MET foram utilizadas para caracterizar o tamanho das partículas de cobre no catalisador (na ordem de 23 nm, caracterizando-o como um nanomaterial) e a técnica de MEV e EDS foram utilizados para o estudo da morfologia (que muda com o processo de calcinação do material), da topografia e da composição do material obtido (Cu, Zn, Al e O foram identificados em proporções correspondentes à esperada durante o preparo). É importante destacar que o oxigênio foi identificado devido à ausência de uma câmara de redução no equipamento de MEV utilizado.

The effluent treatment from the packaging industry, particularly color removal, is strongly influenced by process interferences. High concentrations of dyes often make water reuse unfeasible. In this context, the present work aims to study the clarification of the dye used in the packaging industry by the photocatalytic process. Niobium was used as a catalyst, which was characterized by different techniques. Before verifying the catalytic activity in the industrial effluent, tests were performed with synthetic dye solutions. As a characterization result, it was possible to identify typical characteristics of the semiconductor. The results with the synthetic effluent indicated that the photocatalytic reaction was adequate for the decolorization of the solution. The optimized conditions indicated pH conditions without adjustments (4.2) and a catalyst concentration of 1.0 g L⁻¹, obtaining a decolorization of 98%. Tests with industrial effluent revealed that the optimum conditions were also obtained with an unadjusted pH (6.2) and catalyst concentration of 6.0 g L⁻¹, obtaining, however, 42% discoloration. This result highlights the influence of the organic load and other interfering factors such as additives. However, the process is promising in the clarification of the effluent, which possibly, with a 42% reduction in color, can be reused in the process generating water sustainability. A curve adjustment was proposed to determine the best conditions obtained for both synthetic and industrial effluents.

Photocatalytic reduction of Cr(VI) using Nb₂O₅-based catalysts has been reported; however, Ag-promoted Nb₂O₅ remains scarcely explored. In this context, the present study describes the performance of Ag/Nb₂O₅ catalysts in removing Cr⁶⁺ under various experimental conditions. The catalyst was studied, maintaining the nominal metallic load of 5% Ag. To optimize the process, the following operating conditions were analyzed: pH, catalyst concentration, calcination temperature, additive, air bubbling, photolysis, and additive (hole scavenger). The results obtained indicated that the 5%Ag/Nb₂O₅ catalyst achieves a higher photoreduction rate than bare Nb₂O₅. Optimization of process parameters showed that the scavenger inhibits chromium adsorption on the catalytic surface. Optimal conditions observed in the tests were as follows: solution pH of 2, with hole scavenger addition, in the absence of oxygen, using a catalyst concentration of 1 g L⁻¹, and a calcination temperature of 300 °C (resulting in a poorly crystalline Nb₂O₅ phase). Photolysis in the presence of sodium formate reduced Cr⁶⁺; however, the reduction was slower. In the quenching tests, the radical scavengers that most influenced the reduction of Cr⁶⁺ were silver nitrate (e⁻ scavenger) and oxalate (h⁺ scavenger). Oxalate was the only one to reduce the total chromium concentration in the solution.