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.

Photocatalytic activity of Ag/Al2O3-Gd2O3 photocatalysts prepared by the sol-gel method in the degradation of 4-chlorophenol

The photocatalytic activity in the degradation of 4-chlorophenol (4-ClPh) in aqueous medium (80 ppm) using 2.0 wt% Ag/Al2O3-Gd2O3 (Ag/Al-Gd-x; where x = 2.0, 5.0, 15.0, 25.0 and 50.0 wt% of Gd2O3) photocatalysts prepared by the sol-gel method was studied under UV light irradiation. The photocatalysts were characterized by N2 physisorption, X-ray diffraction, SEM, HRTEM, UV-Vis, XPS, FTIR and fluorescence spectroscopy. About 67.0% of 4-ClPh was photoconverted after 4 h of UV light irradiation using Ag/γ--Al2O3. When Ag/Al-Gd-x photocatalysts were tested, the 4-ClPh photoconversion was improved and more than 90.0% of 4-ClPh was photoconverted after 3 h of UV light irradiation in the materials containing 15.0 and 25.0 wt% of Gd2O3. Ag/Al-Gd-25 was the material with the highest efficacy to mineralize dissolved organic carbon, mineralizing more than 85.0% after 4 h of UV light irradiation. Silver nanoparticles and micro-particles of irregular pentagonal shape intersected by plane nanobelts of Al2O3-Gd2O3 composite oxide were detected in the Ag/Al-Gd-25 photocatalyst. This material is characterized by a lowest recombination rate of electron-hole pairs. The low recombination rate of photo-induced electron-hole pairs in the Ag/Al-Gd-x photocatalysts with high Gd2O3 contents (≥15.0 wt%) confirmes that the presence of silver nanoparticles and microparticles interacting with Al2O3-Gd2O3 composite oxide entities favors the separation of photo-induced charges (e- and h+). These materials could be appropriate to be used as highly efficient photocatalysts to eliminate high concentrations of 4-ClPh in aqueous medium.

Photocatalytic Degradation of Phenol Using Al2O3-SnO2 Mixed Oxide

Al2O3 and SnO2 mixed oxide were obtained by the coprecipitation method at different Sn4+ contents, from the urea hydrolysis at 95 degrees C using nitrate salt as metal precursor. The studies of X-ray diffraction and reflectance diffuse UV-Vis spectroscopies and N2 adsorption-desorption show important changes. The photocatalytic efficiency test for the mineralization of phenol was determined from UV-Vis spectroscopy. The Al2O3-SnO2 mixed oxide with 10% mol of Sn4+ improved the photocatalytic activity in the elimination of phenol under UV light irradiation, where the photodegradation rate was 2 times more active than Al2O3 unmodified and 1.4 times more active than the reference photocatalyst TiO2-P25. The high activity observed was discussed as a function of the small particle size of SnO2.

Photocatalytic degradation of 2,4-dichlorophenol with MgAlTi mixed oxides catalysts obtained from layered double hydroxides

MgAl and MgAlTi mixed oxides were obtained from the thermal treatment of LDH materials synthesized by the sol-gel method; these materials were characterized by N2 physisorption, XRD, UV-vis, XPS, EDS-SEM and TEM techniques. According to the results, Ti was incorporated in the LDH layer when content in the material was low. The MgAl and MgAlTi mixed oxides were evaluated in the photo-degradation of 2,4-dichlorophenol (2,4-DCP) in the presence of UV light. A superior efficiency in the photo-degradation of 2,4-DCP, in comparison with the Degussa P-25 TiO2 reference catalyst was observed, reaching a total decomposition of the 2,4-DCP molecule in less than 60 min. According to the results, Ti was incorporated in the LDH layer when the content in the material was low. The MgAl and MgAlTi mixed oxides were evaluated in the photo-degradation of 2,4-dichlorophenol (2,4-DCP) in the presence of UV light. A superior efficiency in the photo-degradation of 2,4-DCP with the MgAl and MgAlTi mixed oxides, in comparison with the Degussa P-25 TiO2 reference catalyst was observed, reaching a total decomposition of the 2,4-DCP molecule in less than 60 min.