Comparative study of the photodeposition of Pt, Au and Pd on pre-sulphated TiO2 for the photocatalytic decomposition of phenol

A comparative study of the photodeposition of Pt, Au and Pd under the same experimental conditions onto pre-sulphated and non-sulphated TiO2 was performed. Morphological and surface characterisation of the samples as well as photocatalytic activity for phenol photooxidation was studied. The influence of sulphate pre-treatment on the deposits size and dispersion onto the TiO 2 surface, and photodeposition yields with the different metals were also analysed. The photocatalytic activity of the doped materials was then investigated, observing that catalytic behaviour can be correlated to physical characteristics of the samples determined by (XRD) X-ray diffraction, (XPS) X-ray photoelectron spectroscopy, (XRF) X-ray fluorescence spectrometry and (TEM) transmission electron microscopy. Sulphate pre-treatment was found to influence both the level of dispersion and the size of metal clusters on the TiO2 surface. Sulphation and metallisation of samples was found to produce a synergistic enhancement in photoactivity for the degradation of phenol. The photoactivity of the catalysts with respect to the doped metal species was ordered Pt > Pd > Au.Ministerio de Ciencia e Innovación CTQ2008-05961-CO2-01Junta de Andalucía P06-FQM-140

Influence of the strong metal support interaction effect (SMSI) of Pt/TiO2 and Pd/TiO2 systems in the photocatalytic biohydrogen production from glucose solution

Two different catalysts consisting of Pt/TiO2 and Pd/TiO 2 were submitted to diverse oxidative and reductive calcination treatments and tested for photocatalytic reforming of glucose water solution (as a model of biomass component) in H2 production. Oxidation and reduction at 850°C resulted in better photocatalysts for hydrogen production than Degussa P-25 and the ones prepared at 500°C, despite the fact that the former consisted in very low surface area (6-8 m2/g) rutile titania specimens. The platinum-containing systems prepared at 850°C give the most effective catalysts. XPS characterization of the systems showed that thermal treatment at 850°C resulted in electron transfer from titania to metal particles through the so-called strong metal-support interaction (SMSI) effect. Furthermore, the greater the SMSI effect, the better the catalytic performance. Improvement in photocatalytic behavior is explained in terms of avoidance of electron-hole recombination through the electron transfer from titania to metal particles

Nueva ruta de síntesis para el dióxido de titanio

Se obtuvo dióxido de titanio por medio de una nueva ruta de síntesis que combina la técnica solgel con reacción a presión autógena. Se ensayaron dos geles de síntesis con diferentes fuentes de titanio; una de ellas usó tetraisopropil ortotitanato empleando agua e isopropanol como estructurantes en diversas proporciones, obteniéndose en todos los experimentos TiO2 en fase anatasa. Para el segundo tipo de síntesis se empleó el tetracloruro de titanio en mezcla con sílica e isopropanol algunos de los TiO2 se obtuvieron como fase anatasa mientras que otros cristalizaron como una mezcla anatasa-rutilo en diferentes proporciones, dependiendo de las relaciones entre los precursores en la gel de síntesis. La caracterización de los materiales obtenidos se realizó por medio de DRX y UV-Vis para determinar la cristalinidad y propiedades ópticas de los materiales obtenidos

Preparación de Sistemas Óxido de Titanio/Óxido de Silicio (TiO2/SiO2) mediante el Método Solvotérmico para Aplicaciones en Fotocatálisis

Sistemas Óxido de Titanio/Óxido de Silicio (TiO2/SiO2) fueron obtenidos por anclaje de TiO2 en SiO2. El fotocatalizador TiO2 se obtuvo por alcohólisis del TiCl4 con 2-propanol y posterior cristalización a presión autógena a 200 °C, excluyendo etapas de calcinación a altas temperaturas. Se emplearon diferentes relaciones SiO2/TiCl4 para determinar su influencia en la estabilidad, propiedades y fotoactividad de los sistemas TiO2/SiO2. La actividad fotocatalítica fue evaluada por la fotodegradación de metanol en fase gaseosa. El TiO2 cristalizó como fase anatasa o como una mezcla rutilo/anatasa, dependiendo por la relación SiO2/TiCl4 inicial. Los resultados muestran que se producen materiales compuestos con alta cristalinidad del TiO2. Se encontró también que hay una fuerte relación entre la actividad fotocatalítica con las propiedades fisicoquímicas y de estas con las composiciones iniciales de síntesis

Hydrothermal preparation of highly photoactive TiO2 nanoparticles

TiO2 nanoparticles have been prepared by amine assisted sol–gel precipitation of Ti4+ aqueous solutions and further hydrothermal treatment. The effect of different starting acidic solution (nitric, chlorhydric and acetic acids) as well as the addition of triethylamine (TEA) at different pH has been widely investigated. It has been stated that different amounts of TEA could have interesting effects upon hydrothermal treatment. Surface and morphological features significantly differ from TiO2 prepared using different synthetic route. In all cases, amine precipitated TiO2 obtained exhibit high conversion values for phenol photo-oxidation reaction, being in certain conditions higher than that exhibited by TiO2 Degussa P25. The precipitation of the acetic acidified solution leads to high surface area values and well crystallized anatase with small crystallite size. In addition, this set of catalysts show the cleanest surface after the hydrothermal treatment. The conjunction of these features would be the characteristic features responsible of the best photocatalytic activity observed

Mixed α-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol

Mixed oxides, α-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared α-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)∙9H2O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV–vis diffuse reflectance spectroscopy. UV–vis diffuse reflectance spectra showed that incorporating a 5%wt. of α-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH ≈ 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a α-Fe2O3-Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6or α-Fe2O3, single or mixed. Using the system α-Fe2O3-Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the α-Fe2O3-Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV-illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the radical dotOH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals (radical dotOH).Ministerio de Economía y Competitividad CTQ2015-64664- C2-2-

A facile Shape-Controlled Synthesis of highly photoactive Fluorine containing TiO2 nanosheets with high {001} facet exposure

Surface fluorinated TiO2 materials with high {001} facet exposure were prepared by a simple and high yield preparation procedure. Faceted/fluorinated samples showed a high photocatalytic performance not only in oxidation processes, tested inphenol and Methyl Orange degradation, but also in a reduction process as Cr(VI) photoreduction. Reaction rates for these materials greatly exceeded the ones obtained for materials prepared without Fluorine addition and for commercial TiO2 Degussa (Evonik) P25 used as reference photocatalyst. A broad characterisation of the samples allowed us to estimate the percentages of different facets and the amount and form in which the fluorine is found on the surfaces. Good photocatalytic behavior can be ascribed to both high {001} facet exposure and adsorbed fluorine on the photocatalysts surfacesMinisterio de Economía y Competitividad CTQ2015-64664-C2-2-

Photocatalytic removal of patent blue V dye on Au-TiO2 and Pt-TiO2 catalysts

In this work it was studied the efficiency of a photocatalytic process for the removal of patent blue V. This dye is very difficult to remove by conventional treatments such as adsorption or coagulation therefore the photocatalytic process is a very interesting alternative for the removal this dye mainly because it does not require expensive oxidants and it can be carried out at mild temperatures and pressures. In this work it was tested the efficiency of Au-TiO2 and Pt-TiO2 photocatalysts in the Patent blue V removal. The Au-TiO2 catalysts were prepared by two different methods: chemical reduction and photochemical deposition; Pt-TiO2 catalysts were obtained only by photochemical deposition. In the synthesis of the catalysts prepared by photochemical deposition, it was evaluated the influence of some parameters, such as deposition time and the intensity of the light source over the physicochemical properties and photocatalytic activity of the materials obtained. An analysis of the effect of the catalyst dosage and initial patent blue V concentration over the dye degradation efficiency was also attempted. In general, it was observed that the presence of Au or Pt on TiO2 enhances the patent blue V photodegradation; it was found that noble metal particle size and distribution on TiO2 surface are important factors influencing the dye removal. The highest dye degradation was obtained over the Au-TiO2 catalyst prepared by photochemical deposition, using high light intensity and 15 min of deposition time during the synthesis. A discoloration and a total organic carbon (TOC) removal of 93 and 67% respectively, were obtained over this material after 180 min of UV irradiation. These values are higher than that the obtained on S-TiO2 (discoloration and TOC removal of about 25% and 3%, respectively)

Estudio de la actividad de los fotocatalizadores Pt and Au-TiO2 en la degradación de contaminantes orgánicos bajo luz visible

Pt-TiO and Au-TiO photocatalysts were prepared by noble metal photodeposition on sulfated TiO. It was observed that optical absorption, oxidation state and particle size of the metallic species (Pt or Au) play an important role in the TiO photocatalytic activity under visible-light irradiation. Photocatalytic activity of the bare TiO powder in the phenol and methyl orange degradation increased with the sulfation and metal addition. The highest degradation rate under UV-Visible and visible light irradiation was obtained on Pt-S-TiO photocatalyst; this is mainly due to the optical properties of TiO induced by platinization and also to the good distribution and low Pt particles size. It was also found that this catalyst has a good stability after two cycles of reaction in the phenol photodegradation under UV-Visible light irradiation. The Pt-S-TiO photocatalyst was also active under solar light and under the environmental conditions of the city of Tunja (Boyacá), Colombia.Los fotocatalizadores Pt-TiO2 y Au-TiO2 se prepararon por fotodeposición del metal noble sobre el TiO2 sulfatado. Se encontró que las propiedades ópticas, el estado de oxidación y el tamaño de partícula de las especies metálicas (Pt o Au) juegan un papel fundamental en la actividad fotocatalítica del TiO2 bajo luz visible. La actividad fotocatalítica del TiO2 en la degradación de fenol y naranja de metilo aumentó significativamente a través de los tratamientos de sulfatación y metalización de este óxido. La más alta velocidad de degradación bajo luz UV-Visible y visible, se alcanzó usando el fotocatalizador Pt-S-TiO2 ; esto se debe principalmente a la modificación de las propiedades ópticas del TiO2 inducidas por la platinización, también a la buena distribución y al pequeño tamaño de las partículas de Pt. Se encontró, además, que este catalizador presenta una buena estabilidad después de dos ciclos de reacción en la degradación de fenol bajo luz UV-Visible. El fotocatalizador Pt-S-TiO2 fue activo también bajo luz solar directa y bajo las condiciones medioambientales de la ciudad de Tunja (Boyacá), Colombia.Fondo Nacional de Financiamiento para la Ciencia, la Tecnología y la Innovación Fransisco José de Caldas – Colciencias 279-2016MINECO/FEDER, UE CTQ2015-64664-C2-2-