In this paper, several TiO2 materials doped with zirconia precursor (0.7, 1.4, 1.6 and 2.0 mol%) were synthesized by an easy aqueous sol-gel synthesis at ambient temperature. This method consisted in the peptization of the TiO2 colloid in presence of HNO3. The corresponding pure TiO2 material was also synthesized for comparison. The performances and the physicochemical properties of these materials were compared to the well-known Evonik P25 photocatalyst.The physico-chemical characterizations showed that nano-crystalline anatase-brookite particles were produced with the sol-gel process, with higher specific surface area than P25 (~ 200 m 2 g -1 vs. 47 m 2 g -1 ). All samples presented a higher visible absorption than P25. The XPS spectra showed that all the samples were doped with nitrogen and that mixed TiO2-ZrO2 oxide materials were obtained when doping with zirconia precursor.Photoactivity was evaluated through the degradation of p-nitrophenol in water. On the one hand, under UV/visible light, the ZrO2 doping increased the degradation efficiency of the pure TiO2 catalyst due to a better charge separation in the mixed TiO2-ZrO2 oxides. The activity of the sample with the highest dopant content was even higher than the one of P25. On the other hand, under visible light, all samples were much more efficient than P25. This activity shift towards visible range was due to the N-doping of the catalysts, with a slight improvement for the doped ones.Finally, the feasibility of producing films starting from an aqueous suspension of the photocatalyst was assessed on P25, pure TiO2 and the best doped material. The photoactivity of these films, evaluated on the degradation of methylene blue under UV-A light, showed that the sample with the highest dopant concentration had an efficiency 4 times higher than pure TiO2 and 20 times higher than P25.

A screening study on seven photocatalysts was performed to identify the best candidate for pharmaceutical products degradation in water. Photocatalysts were deposited as thin films through a sol-gel process and subsequent dip-coating on glass slides. The efficiency of each photocatalyst was assessed through the degradation of methylene blue first, and then, through the degradation of 15 different pharmaceutical products. Two main types of synthesis methods were considered: aqueous syntheses, where the reaction takes place in water, and organic syntheses, where reactions take place in an organic solvent and only a stoichiometric amount of water is added to the reaction medium. Photocatalysts synthesized via aqueous sol-gel routes showed relatively lower degradation efficiencies; however, the organic route required a calcination step at high temperature to form the photoactive crystalline phase, while the aqueous route did not. The best performances for the degradation of pharmaceuticals arose when Evonik P25 and silver nanoparticles were added to TiO2, which was synthesized using an organic solvent. In the case of methylene blue degradation, TiO2 modified with Evonik P25 and TiO2 doped with MnO2 nanoparticles were the two best candidates.

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An eco-friendly photocatalytic coating, active under a cost-effective near-visible LED system, was synthesized without any calcination step for the removal of organic pollutants. Three types of doping (Fe, N and Fe + N), with different dopant/Ti molar ratios, were investigated and compared with undoped TiO2 and the commercial P25 photocatalyst. Nano-crystalline anatase-brookite particles were successfully produced with the aqueous sol-gel process, also at a larger scale. All samples displayed a higher visible absorption and specific surface area than P25. Photoactivity of the catalyst powders was evaluated through the degradation of p-nitrophenol in water under visible light (>400 nm). As intended, all samples were more performant than P25. The N-doping, the Fe-doping and their combination promoted the activity under visible light. Films, coated on three different substrates, were then compared. Finally, the photoactivity of a film, produced from the optimal N-Fe co-doped colloid, was evaluated on the degradation of (i) p-nitrophenol under UV-A light (365 nm) and (ii) rhodamine B under LED visible light (395 nm), and compared to undoped TiO2 film. The higher enhancement is obtained under the longer wavelength (395 nm). The possibility of producing photocatalytic films without any calcination step and active under low-energy LED light constitutes a step forward for an industrial development.

In this study, pure ZnCo2O4 and SnO2/ZnCo2O4 mix photocatalysts have been synthesized by the sol-gel process with three different SnO2 loading percentages (10, 20, and 30 wt %). Their photocatalytic activities were assessed on the degradation of organic pollutants in water under visible illumination. The structural, morphological, and optical properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR), nitrogen adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), and UV–Visible diffuse reflectance measurements. The results have shown that the materials are composed of a crystalline ZnCo2O4 matrix with a decrease in crystallite size with the amount of SnO2. Weakly crystalline SnO2 is also observed for loaded samples. The specific surface area is modified with the loading ratio. The evaluation of the photoactivity of the samples under visible light for the degradation of p-nitrophenol has highlighted that all materials are highly photoactive under visible light thanks to heterojunction between the two oxides. An application test has been conducted on a dye, congo red, showing the same tendencies. An optimal amount of SnO2 loading is observed for the sample containing 20 wt % of SnO2. A comparison with commercial Evonik P25 showed that the materials developed in this work have five to six times better efficiency under visible light, leading to a promising photocatalyst material.

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TiO2 prepared by a green aqueous sol–gel peptization process is co-doped with nitrogen and zirconium to improve and extend its photoactivity to the visible region. Two nitrogen precursors are used: urea and triethylamine; zirconium (IV) tert-butoxide is added as a source of zirconia. The N/Ti molar ratio is fixed regardless of the chosen nitrogen precursor while the quantity of zirconia is set to 0.7, 1.4, 2, or 2.8 mol%. The performance and physico-chemical properties of these materials are compared with the commercial Evonik P25 photocatalyst. For all doped and co-doped samples, TiO2 nanoparticles of 4 to 8 nm of size are formed of anatase-brookite phases, with a specific surface area between 125 and 280 m2 g−1 vs. 50 m2 g−1 for the commercial P25 photocatalyst. X-ray photoelectron (XPS) measurements show that nitrogen is incorporated into the TiO2 materials through Ti-O-N bonds allowing light absorption in the visible region. The XPS spectra of the Zr-(co)doped powders show the presence of TiO2-ZrO2 mixed oxide materials. Under visible light, the best co-doped sample gives a degradation of p-nitrophenol (PNP) equal to 70% instead of 25% with pure TiO2 and 10% with P25 under the same conditions. Similarly, the photocatalytic activity improved under UV/visible reaching 95% with the best sample compared to 50% with pure TiO2. This study suggests that N/Zr co-doped TiO2 nanoparticles can be produced in a safe and energy-efficient way while being markedly more active than state-of-the-art photocatalytic materials under visible light.