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Alkene epoxidation using the Mukaiyama process involving O2 and a sacrificial aldehyde, as the first step of the global alkene oxidative carboxylation, does not necessarily require a metal catalyst.

W–S–N-tri-doped TiO 2 photocatalysts (WSNTiO 2 ) were prepared by a simple sol–gel method. Tungstic acid, sodium sulfate and urea were used as tungsten, sulfur and nitrogen sources, respectively. The morphology and microstructure characteristics of the photocatalysts were evidenced by means of XRD, BET, TEM, SEM and UV–vis DRS techniques. The XRD results show that the main crystal phase of samples is anatase. It was also found that the tri-doping of TiO 2 increases its BET specific surface area from 95 to 121 m 2 ·g −1 . Besides, it was shown that tri-doping narrows the band gap of TiO 2 effectively, which has greatly improved the photocatalytic activity in the visible light region. The photocatalytic activity of tri-doped TiO 2 powders was compared to that of bi-doped ones through the degradation of Congo Red (CR) under visible irradiation. Thus, the prepared 0.5% W–N–S–TiO 2 heat treated at 450 °C showed the best photocatalytic activity compared to the prepared pure TiO 2 , Degussa P25, and co-doped samples (WNTiO 2 and WSTiO 2 ). In particular, a Congo Red degradation rate of approximately 99% was reached after only 35 min of visible light irradiation in the presence of 0.5% of WNSTiO 2 . Total organic carbon (TOC) removal of CR was up to 72% and confirmed its significant mineralization in the presence of 0.5% of WNSTiO 2 photocatalyst.

Anatase TiO 2 nanorod photocatalysts were prepared following a two-step procedure, consisting first in the alkaline hydrothermal treatment at 150 °C for 24 h of commercial Aeroxide TiO 2 P25, and a subsequent calcination at a temperature between 350 °C and 700 °C. The final calcination led to the transformation of dried TiO 2 (B) nanotubes into pure anatase TiO 2 nanorods, together with a decrease in surface area as well as with the maintain of both one-dimensional morphology and anatase phase with the temperature increase. In the case of the methanol degradation, an optimum in terms of performances was obtained for TiO 2 nanorods calcined at 500 °C, with a surface area of 122 m 2 /g. This resulted from balanced physicochemical properties with increasing the temperature, with the increase in TiO 2 crystallinity, beneficial for lowering the recombination rate, and the decrease in surface area, associated to the increase in the anatase crystallite size, that lower both adsorption capacity of TiO 2 nanorods and ability to produce OH radicals. By contrast, the optimum in terms of conversion or sulfur removal rate was observed for nanorods calcined at 380 °C in the more rarely studied photocatalytic oxidation of H 2 S, for which the accumulation at the surface of sulfates as ultimate reaction products deactivates the photocatalyst. Indeed, TiO 2 nanorods calcined at a lower temperature of 380 °C suffered from a strongly less marked deactivation than the Aeroxide TiO 2 P25 reference and nanorods calcined at lower as well as at higher temperatures. They might take advantage of a higher surface area of 219 m 2 /g for overcoming their detrimental lower crystallinity and thus improving their resistance to deactivation, by allowing the storage of larger amounts of poisoning sulfates.

A series of W-modified TiO2 (W–TiO2) photocatalysts were synthesized by a simple sol–gel method. The new photocatalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis-diffuse reflectance spectroscopy (DRS), and Brunauer, Emmett and Teller (BET) surface area analyzer. The photoactivity of the W–TiO2 photocatalysts was evaluated by the photocatalytic oxidation of Congo red (CR) dye. It was found that the average size of the prepared photocatalysts is 10 nm. Moreover, they have high surface areas (∼ 216 m2 g−1) and their light-absorption extends to the visible region compared to pure TiO2. The effects of W-loading and of the calcination temperature of the prepared photocatalysts on their photocatalytic activity were also studied. The obtained results show that the W0.5–TiO2 photocatalyst calcined at 350 °C is much highly photoactive than non-doped or highly doped TiO2. The enhanced photocatalytic activity of the weakly doped TiO2 may be attributed to the increase in the charge separation efficiency and the presence of surface acidity on the W0.5–TiO2 photocatalyst.

Hybrid TiO2–hydroxypropyl methyl cellulose (TiO2–HPMC) nanophotocatalysts were prepared by a simple in situ synthesis. The weight ratios of HPMC-to-TiO2 were 5, 10 and 20%, respectively. The as-prepared nanocomposites were characterized by XRD, XPS, UV–vis DRS, ATG and BET surface area analysis. Surface morphology was assessed by the means of SEM. The photocatalytic degradation of 4-nitrophenol (4-NP) in neutral aqueous solution under visible light irradiation was examined to evaluate the efficiency of the hybrids in comparison to pure TiO2. The results indicated that the in situ hybridization of TiO2 with HPMC significantly increases its specific surface area and extends its light absorption range to the visible region. Consequently, TiO2–HPMC nanocomposites were photocatalytically much more active than pure TiO2. Moreover, the TiO2–HPMC hybrids were found to be sufficiently photostable after five experimental runs.