Improvement of photocatalytic activity in the degradation of 4-chlorophenol and phenol in aqueous medium using tin-modified TiO2 photocatalysts

In this work, we present the synthesis of TiO₂ photocatalysts modified with different % mol of tin using the sol-gel method. The materials were characterized using different analytical techniques. The Rietveld refinement, XPS, Raman and UV-Vis techniques confirm the substitution of tin in the TiO₂ structural lattice due to changes in crystal lattice parameters, the low-energy shift of the Sn 3d_5/2 orbital, generation of oxygen vacancies and the decreased band gap and increased BET surface area. The material with 1 mol% tin shows superior catalytic activity compared to the references for the degradation of 40 ppm 4-chlorophenol (3 hours of reaction) and 50 ppm phenol (6 hours of reaction). Reactions fit pseudo first order kinetics in both instances. The increase in photodegradation efficiency was attributed to the generation of energy levels below the TiO₂ conduction band caused by the incorporation of 1% mol of tin, oxygen vacancies, and the heterojunction formed between the brookite-anatase-rutile, causing inhibition of the recombination of the electron (e^-) and hole (h⁺) photogenerated species. The easy synthesis, low cost and increased photodegradation efficiency of the photocatalyst with 1 mol% tin have the potential to favor the remediation of recalcitrant compounds in water.

Improving photocatalytic reduction of 4-nitrophenol over ZrO2–TiO2 by synergistic interaction between methanol and sulfite ions

Reaction rate for 4-nitrophenol photoreduction over ZrO₂–TiO₂ increases 19 times due to the synergistic interaction between methanol and sulfite ions.

The effect of anatase crystal orientation on the photoelectrochemical performance of anodic TiO2 nanotubes

TiO2 nanotube films were prepared by anodizing Ti plates in ethylene glycol based electrolytes containing variable concentrations of ammonium fluoride and water. The morphology, optical and semiconducting properties, as well as the composition of TiO2 films were shown to be dependent on the anodizing bath composition. Among different film properties, only the preferential orientation of anatase crystals, quantified with the texture coefficient of the (004) plane, TC(004), showed the same dependence of photoelectrochemical performance on the electrolyte composition. The increased value of TC(004) was related to anatase crystals piling up in the [001] direction (normal to the plane of the Ti substrate), forming a fiber like texture structure along the tube that facilitates the transport of photogenerated electrons toward the conducting substrate.