Influence of some aromatic and aliphatic compounds on the rate of photodegradation of phenol in aqueous suspensions of TiO2

Abstract The influence of 3-nitrophenol, 4-nitrophenol, pentachlorophenol, ethanol, 2-propanol, ethanoic acid and ethanedioic acid on the photodegradation rate of phenol in an aqueous suspension of TiO2 (anatase) irradiated in the near-UV region was investigated. Binary mixtures of organic compound and phenol in molar ratios of 1:1 and 10:1 were used for the photoreactivity experiments performed in a batch reactor. The mineralization rate of all the mixtures was also monitored by measuring the total organic carbon (TOC) concentration. The reactivity results indicate that the photodegradation rate of phenol is mainly determined by the total amount of aromatic substrates present in the reacti…

Concerning“An Opinion on the Heterogeneous Photoreduction of N2 with H2O”: Second Letter

Sol-gel derived anatase TiO2: morphology and photoactivity

Abstract High-surface area TiO 2 (anatase) was prepared by the sol-gel method and characterized by various instrumental and analytical methods, including X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, porosimetry, specific surface area measurements, scanning electron microscopy, and titration of surface hydroxyl groups. The specimen was tested for photodegradation of phenol and nitrophenols carried out in aqueous suspension at pH = 3; photoactivity was compared with that of commercially available anatase TiO 2 . Results are discussed in terms of porosity, surface area, and availability and population of surface OH groups, consequent upon the particular method used for…

Effect of silver deposits on the photocatalytic activity of titanium dioxide samples for the dehydrogenation or oxidation of 2-propanol

Abstract Until now, the effect of the deposition of metal particles onto a powdered semiconductor oxide on its photocatalytic activity has been determined for group VIII transition metals only. In this study, AGTiO2 samples were prepared by photodeposition, characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) and tested, under band-gap illumination, using the oxidation of 2-propanol (neat liquid phase or mixed with water) in the absence or presence of molecular oxygen. The silver deposits were found to be metallic both before and after use, but the size of the particles and their distribution on the support were markedly influenced by the type …

Surface properties of iron-titania photocatalysts employed for 4-nitrophenol photodegradation in aqueous TiO2 dispersion

Iron(III) doped specimens (0.01–5% atomic Fe ∶ Ti) have been prepared by impregnating polycrystalline “home prepared” TiO2 (mainly anatase) and have been studied for photocatalytic degradation of 4-nitrophenol in aqueous dispersions. Some structural and surface properties have been studied by X-ray diffraction, specific surface area and porosity measurements and FTIR monitoring of pyridine, ammonia and methanoic acid adsorption for surface acidity and basicity. Their surface properties were compared with a corresponding series of photocatalysts prepared by a coprecipitation method. Adsorption of pyridine and ammonia indicates the presence of surface acid Lewis sites, a low concentration of …

Influence of metallic silver and of platinum-silver bimetallic deposits on the photocatalytic activity of titania (anatase and rutile) in organic and aqueous media

Abstract The influence of deposited silver upon the photocatalytic activity of titania in the rutile and anatase allotropic forms has been studied in three different reactions. The common feature found for these three reactions was an electron transfer from illuminated TiO 2 to silver particles. In the first reaction (platinum photodeposition). it has been shown that the initial presence of metallic silver orientates the localization of subsequent Pt photodeposits with, in particular, a 100% selectivity to Pt deposition on top of silver particles or agglomerates previously deposited on anatase. In the second reaction (2-propanol oxidation), Ag deposit was found beneficial for the activity o…

Influence of platinum on catalytic activity of polycrystalline WO3 employed for phenol photodegradation in aqueous suspension

Abstract A series of polycrystalline WO3 solids loaded with platinum (0.5; 1.0; 2.0 and 3.0 wt%) were prepared and characterised by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, specific surface areas determination, X-ray photoelectron spectroscopy. XPS and X-ray results indicate that the samples loaded with Pt up to 1 wt% contained on the surface mainly Pt(2+) species, while those loaded with higher amounts contained Pt(0). Moreover, the samples were employed for a probe reaction, i.e. phenol photooxidation in aqueous suspension, and their photoactivity was compared with that of two TiO2 commercial samples, mainly in the anatase phase. All the Pt–WO3 sa…

Preparation and characterization of Al2O3 supported TiO2 catalysts employed for 4-nitrophenol photodegradation in aqueous medium

Abstract In this paper the preparation and some bulk and surface characterizations of set of Al2O3 supported TiO2 photocatalysts are reported. The powders were home prepared by a wet impregnation method using titanium (IV) isopropylate. The impregnation was followed by thermal treatments and this procedure was repeated several times in order to obtain samples with different amounts of TiO2. The solids were characterized by X-ray diffraction, specific surface area determination, scanning electron microscopy coupled with an electron microprobe used in an energy-dispersive mode and diffuse reflectance spectroscopy. Moreover, all of them were tested as photocatalysts by using different kinds of…

Preparation and characterisation of TiO2 (anatase) supported on TiO2 (rutile) catalysts employed for 4-nitrophenol photodegradation in aqueous medium and comparison with TiO2 (anatase) supported on Al2O3

Abstract In this paper the preparation of two sets of polycrystalline photocatalysts prepared by supporting TiO2 (anatase) on TiO2 (rutile) or Al2O3 is reported. The powders were prepared by a wet impregnation method using titanium(IV) isopropylate. The impregnation was followed by thermal treatment and this procedure was repeated several times in order to obtain samples with progressively increasing amounts of TiO2 (anatase). The photocatalytic activity of all of the specimens was tested by carrying out the 4-nitrophenol photodegradation, used as a “probe” reaction, in aqueous medium and in different kinds of batch photoreactors. The solids were characterised by X-ray diffraction (XRD), sp…

Photocatalytic degradation of phenol in aqueous titanium dioxide dispersions

The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO2 (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO2 content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given.

Influence of Silver Deposits on the Photocatalytic Activity of Titania

The objectives of depositing metals over semiconductor photocatalysts are to improve the electron-hole pair separation and to increase the rate of the reduction process due to the catalytic properties of the metal itself. Most of the deposited (noble) metals that have been studied belonged to group VIII. Very few studies concerned silver deposits. In the present work, the influence of deposited silver over anatase or rutile has been followed in three different types of reactions: (i) metal deposition, (ii) oxidation, and (iii) dehydrogenation. The final solids obtained in the last reaction (Pt/Ag/TiO{sub 2}) were also used as catalysts in two other test reactions to make comparison with TiO…

MODELING OF A TiO2-COATED QUARTZ -WOOL PACKED-BED PHOTOCATALYTIC REACTOR

A fixed-bed, photocatalytic laboratory reactor aimed to degrade pollutants from water streams was designed and built. Quartz wool coated with a thin film of TiO2 was employed as the reactor filling. The photocatalyst was placed in the reactor forming a loose packing to guarantee the intimate contact among reactants, photons, and the photocatalytic surface. This reactor was employed to study the photocatalytic decomposition of a model pollutant (formic acid). A reactor–radiation–reaction model was developed, which was comprised of the reactor mass balance, radiation model, and kinetic model for the degradation of formic acid. The local superficial rate of photon absorption, which was necessa…

Photocatalytic degradation of nitrophenols in aqueous titanium dioxide dispersion

Abstract The results are reported of an investigation into the photodegradation of nitrophenol isomers carried out in aqueous titania (anatase) dispersions under various experimental conditions. We investigated the influence of various parameters on the photodegradation rate, such as the concentrations of the catalyst, dissolved oxygen and organic compound, and the presence of various anions in the dispersion. A plausible explanation is proposed for the influence of these parameters, both mechanistic and kinetic factors being accounted for. Gas chromatography and mass spectrometry were used as analytical methods in order to determine intermediate products. Spectroscopic methods (UV-vis and …

Studio di cinetiche di reazione in un reattore fotocatalitico quasi-isoattinico

Photodecomposition of adsorbed ethanoic acid over silica gel catalyst in a flow system

Abstract The photodecomposition of ethanoic acid adsorbed on silica gels from various sources was studied at wavelengths greater than 300 nm. The experiments were carried out in a flow apparatus. A few photoreactivity tests using acetone or ethanol were also performed. The photodecomposition of ethanoic acid and acetone produced mainly carbon dioxide and methane, in the ratio 2:1, and traces of ethane and methanol. Adsorbed ethanol was not affected at all by the radiation. Infrared and UV-vis reflectance spectra of ethanoic acid adsorbed on silica gels as well as UV-vis reflectance spectra of acetone and ethanol adsorbed on silica gels were recorded. The spectra show the presence of a varie…

Concerning “An Opinion on the Heterogeneous Photoreduction of N2 with H2O”

Photolysis of Adsorbed Phases: Ethanoic Acid-Insulators and Semiconductors Systems. Influence of Acid-Base Properties.

The paper reports the results of experiments in which the photodecomposition of adsorbed ethanoic acid (and in few cases of adsorbed acetone and ethanol) was carried out by using several silica gel samples, whose properties were modified by adding oxidic dopants as γ-Al2O3, which is acidic in character, and MgO, which is mainly basic. Also the related system MgO-Al2O3 was investigated. Few IR spectra on selected pure specimens and on specimens containing adsorbed ethanoic acid were recorded with the aim of following the variation of the surfaces-adsorbate interaction with the variation of the acid-base properties. It was also of interest to compare the photoreactivity of insulators and semi…

Photoassisted Mechanisms in Heterogeneous Catalysis: The Role of Surface OH in the Decomposition of Ethanoic Acid on Magnesium Oxide

The photodecomposition of adsorbed ethanoic acid was studied on a number of pure and mixed insulator and semiconductor systems having a wide range of acid-base features. MgO appeared to be much more active than any other oxide when oxygen was not present in the reactant mixture. On the basis of infrared, U.V.-Vis. reflectance and photoluminescence data it is suggested that in this case the surface hydroxy-groups which are known to absorb at wavelengths longer than 300 nm are involved in the photodecomposition process.

Diffusional kinetics of metalliding zinc into solid copper

The process of incorporation of zinc into a copper cathode has been experimentally studied in a molten salt system at 381±2° C and at various current densities. The process is shown to be kinetically controlled by the diffusion of Zn into the solid matrix. A galvanostatic pulse titration technique has been used to determine the chemical diffusion coefficient at various alloy compositions, and an exponential relationship has been found between the diffusivity and the third power of the zinc concentration in the alloy. This relationship was then used in the diffusion equation within the solid matrix and a numerical integration was performed. Very good agreement was found between the calculate…

Pila elettrochimica per la trasformazione di energia elettromagnetica in energia elettrica e relativo sistema per la produzione di energia elettrica

Photocatalytic oxidation of phenol on TiO2 powders. A Fourier transform infrared study

Abstract In the present paper a detailed investigation of a well known photoreaction, i.e. phenol photodegradation in the presence of TiO2, has been carried out. The Fourier transform infrared (FT-IR) technique has been used to characterize the catalyst surface and to follow the photoprocess by “in situ” measurements in a gas—solid regime, simulating the aqueous liquid—solid regime in which this photodegradation reaction has been usually carried out. The influence on the photoprocess of the surface hydroxylation of the catalyst has been investigated and the presence of some reaction intermediates has been revealed by FT-IR. The experimental results have demonstrated that the chosen gas—soli…

Influence of hydrogen peroxide on the kinetics of phenol photodegradation in aqueous titanium dioxide dispersion

Abstract The influence of hydrogen peroxide on the phenol photodegradation rate under near UV radiation was investigated in homogeneous and heterogeneous systems: the heterogeneous systems were aqueous dispersions of titanium dioxide (anatase). The hydrogen peroxide photodecomposition reaction was also investigated for all the systems used. The highest rate of phenol photodegradation was observed in the heterogeneous system for the contemporary presence of hydrogen peroxide and oxygen. The rate equations for phenol photodegradation and hydrogen peroxide photodecomposition for both systems were obtained. A mechanistic model able to explain the main experimental results is also proposed.