In this study, the treatment of wastewater coming from a river highly polluted with domestic and industrial effluents was evaluated. For this purpose, series of photocatalysts obtained by ZnO and TiO modification were evaluated. The effect of metal addition and Ti precursor (in the case of the titania series) over the physicochemical and photocatalytic properties of the materials obtained was also analyzed. The evaluation of the photocatalytic activity showed that semiconductor modification and precursor used in the materials synthesis are important factors influencing the physicochemical and therefore the photocatalytic properties of the materials obtained. The water samples analyzed in the present work were taken from a highly polluted river, and it was found that the effectiveness of the photocatalytic treatment increases when the reaction time increases and for both, wastewater samples and isolated Escherichia coli strain follow the next order Pt/TiO << ZnO. It was also observed that biochemical and chemical demand oxygen and turbidity significantly decrease after treatment, thus indicating that photocatalysis is a non-selective technology, which can lead to recover wastewater containing different pollutants.

In this study it was evaluated the methylene blue degradation over TiO 2 modified by sulfation and Au or Pt addition. These materials were synthesized by photodeposition method and then were widely characterized by different techniques. In general, it was found that Au or Pt particles size distribution can be effectively controlled modifying the deposition time. It was also found that metal particle size and dye adsorption on TiO 2 surface, are important factors influencing the methylene blue degradation rate. The highest dye degradation was obtained on Au-S-TiO 2 photocatalyst prepared by using 120 min of deposition time; the highest effectiveness of this material in the methylene blue degradation can be mainly due to a combined effect between the presence of gold nanoparticles acting as a sink for the electrons photogenerated during the catalytic reaction and the better adsorption of the dye over the S-TiO 2 surface partially covered by gold particles with the largest sizes. Keywords: Methylene blue, photodegradation, sulfated TiO 2 , M-TiO 2 , photocatalysts. ResumenEn este estudio se evaluó la degradación de azul de metileno sobre TiO 2 modificado por sulfatación y adición de Au o Pt. Estos materiales fueron sintetizados a través del método de fotodeposición y caracterizados usando diferentes técnicas. En general, se encontró que la distribución de tamaño de partícula de Au o Pt se puede controlar efectivamente modificando el tiempo de fotodeposición. Se encontró también que factores como el tamaño de partícula metálica y la adsorción del colorante sobre la superficie del TiO 2 influencian de manera importante la velocidad de degradación del azul de metileno. La mayor degradación del colorante se obtuvo usando el fotocatalizador Au-S-TiO 2 preparado con un tiempo de deposición de 120 min; la alta efectividad de este material en la degradación del azul de metileno se debe principalmente a un efecto combinado entre la presencia de partículas de oro que actúan como colectores de los electrones fotogenerados durante la reacción catalítica y a la mejor adsorción del colorante sobre la superficie del S-TiO

The extensive production of coal fly ash by coal combustion is an issue of concern due to its environmental impact. TiO2-zeolite composites were synthesized, at low cost, using recycled coal fly ash from a local thermoelectric power plant to produce the zeolite using the hydrothermal method. TiO2 was loaded by means of the impregnation method using ethanol and titanium isopropoxide between 8.7 and 49.45 wt% TiO2. The samples were characterized by X-ray diffraction, Raman, electron spin resonance, high-resolution transmission electron microscopy, N2 adsorption-desorption, doppler broadening of annihilation radiation, and diffuse reflectance techniques, and the photocatalytic activity of the composites was evaluated according to the degradation of methyl orange under UV light. The results show that TiO2 crystallizes in the anatase phase with a Ti3+ oxidation state, without post-treatment. TiO2 particles were located within the pores of the substrate and on its surface, increasing the surface area of the composites in comparison with that of the substrates. Samples with TiO2 at 8.7 and 25 wt% immobilized on hydroxysodalite show the highest degradation of methyl orange among all studied materials, including the commercial TiO2 Degussa P25 under UV light.

Au-ZnO nanomaterials were tested in photodegradation reactions performed under UV-Visible light; Phenol,  Catechol and Hydroquinone were selected as target molecules, and it was found that Hydroquinone is the most sensitive molecule to be degraded under illumination. The Au addition significantly increases the photocatalytic activity of ZnO in the degradation of the phenolic compounds and the Au content is an important factor influencing the physicochemical properties of the nanomaterials synthesized and therefore the effectiveness of the photocatalytic treatment. The highest effectiveness in the phenolic compounds elimination was achieved by using ZnO modified by the addition of 2 wt.% of gold, this is due to the highest absorption of this material in the visible region of the electromagnetic spectrum. By HPLC analyzes, it was determined that the degradation route of the phenolic compounds depends on the photocatalyst employed in the catalytic reaction and on the substrate to be degraded, thus, Phenol degradation takes place by formation of more intermediate compounds than the observed in Catechol or Hydroquinone photodegradation.

The aim of the present work was to evaluate the effectiveness of a heterogeneous photocatalyst based on TiO2 in the treatment of coal mining drainage which contains a variety of heavy metals and high concentration sulfates and sulfides. The photocatalytic behavior of the commercial reference Sigma Aldrich and the different materials synthesized using the Sol-gel methodology with surface modifications using sulfation and fluorination processes were analyzed. To find a possible correlation between the physicochemical properties of photocatalysts and their behavior, a characterization was carried out using X-Ray Diffraction (XRD), X-Ray Fluorescence spectrometry (XRF), Fourier transform infrared spectroscopy (FT–IR), UV–Vis diffuse reflectance Spectra (UV-Vis DRS), N2 physisorption, X-ray photoelectron spectroscopy (XPS), and particle size analysis. Results indicated that the modification of the TiO₂ prepared in the laboratory using sulfation and fluorination allowed the successful control of the physicochemical properties of this oxide. However, commercial TiO2 showed the greatest effectiveness in removing metals such as: Fe, Cu, Cr, and As after a photocatalytic reaction for a maximum of 1 hour under continuous nitrogen flow and a light intensity of 120 W/m2.