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

Degradation of Drugs in Aqueous Medium: Photocatalytic oxidation of Lincomycin

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…

Synthesis, Characterisation and Photocatalytic Tests of Anatase Titanium Dioxide Powders Prepared Via Sol-Gel with Different Chelating Agents and under Different Gelling Pressure Conditions

Adsorption and photocatalytic degradation of acetonitrile: FT-IR investigation

Abstract The photocatalytic degradation of acetonitrile was carried out in liquid–solid regime in a batch reactor by using two types of commercial TiO 2 powders (Merck and Degussa P25) as photocatalysts. The concentration of acetonitrile and non-purgeable organic carbon (NPOC) were monitored. The initial rate of acetonitrile conversion was found higher on TiO 2 Merck than on TiO 2 P25. FT-IR spectroscopy was used to investigate the molecular features of the adsorption and photo-oxidation of acetonitrile on the two TiO 2 powders in a fully surface hydrated form. Acetonitrile was found adsorbed on Ti 4+ surface ions and hydroxyl groups for both types of TiO 2 . This interaction appeared fully…

Photocatalytic oxidation of toluene on irradiated TiO2: comparison of degradation performance in humidified air, in water and in water containing a zwitterionic surfactant

Photocatalytic degradation of toluene was carried out both in gas–solid and in liquid–solid regime by using polycrystalline samples of TiO2 Merck and TiO2 Degussa P25. For the gas–solid regime two types of continuous photoreactor were used, a fixed bed one of cylindrical shape and a Carberry type photoreactor, both irradiated by near-UV light. The inlet reacting mixture consisted of air containing toluene and water vapours. The influence of the gas flow rate and the presence of water vapour on the photocatalytic process was investigated. CO2 and benzaldehyde were the toluene degradation products detected in the gas phase by using TiO2 Merck. In the presence of water vapour this catalyst exh…

Basic Concepts in Photocatalysis

A definition of photocatalysis is suggested. The ‘redox’ and ‘photolytic’ mechanisms are explained. For the redox photocatalytic processes guidelines are given for describing the fluid-semiconductor interface. The main ideas of the ‘collective’ and of the ‘localized’ approaches are outlined. The case of oxygen photoadsorption-photodesorption onto TiO2 is briefly outlined. The thermodynamic conditions for photoreactivity are stressed.

Optical Properties and Quantum Yields Determination in Photocatalytic Suspensions

Polycrystalline TiO2 impregnated with porphyrin derivatives in the photocatalytic degradation of 4-nitrophenol

Photocatalytic degradation of organic pollutants by using polycrystalline TiO2: case studies for environment remediation

The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst

Abstract Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of th…

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 …

Comparison of Different Photocatalytic Systems for Acetonitrile Degradation in Gas-Solid Regime

An experimental method for the determination of the photon flow reflected and absorbed by aqueous dispersions containing polycrystalline solids in heterogeneous photocatalysis

An experimental method for the evaluation of the photon flow reflected and absorbed by aqueous dispersions containing polycrystalline solids is proposed. The method is based on actinometric measurements. It is shown that the values obtained are independent of the particle sizes and of the concentration of the solids at least in the experimental conditions and in the range used in the present study (particle size range: 40–500 μm; solids concentration: 0.1–2 g liter−1). The results suggest that the values obtained should be attributed to the interfaces formed between the surface of the solids and the medium. The method is applied to a photocatalytic reaction, namely to the photodegradation o…

Photocatalytic oxidation of gaseous toluene on polycrystalline TiO2: FT-IR investigation of surface reactivity of different types of catalysts

Commercial TiO 2 Merck and TiO 2 Degussa P25 powders were employed as the catalysts for the photo-oxidation of toluene. By using TiO 2 Merck benzaldehyde was found in gas phase as the main product of the toluene partial oxidation. After an initial transient period, this catalyst exhibited a high stability in the presence of water vapour in the gaseous mixture, whereas the photoproduction of benzaldehyde sharply decreases after removal of H 2 O from the feed IR spectra of the used catalyst revealed that in the absence of water vapour benzaldehyde is molecularly held on the catalyst surface. This feature was confirmed by co-adsorbing benzaldehyde and water on the fresh catalyst. By contrast, …

Selectivity of hydroxyl radical in the partial oxidation of aromatic compounds in heterogeneous photocatalysis

Abstract The photocatalytic oxidation of different benzene derivatives has been investigated in order to understand how the substituent group affects the selectivity to hydroxylated compounds. Experimental runs were performed by using TiO2 (Merck) aqueous suspensions at natural pH irradiated by near-UV light. The organic molecules used as substrate contained an electron withdrawing group (EWG) (nitrobenzene, cyanobenzene, benzoic acid, 1-phenylethanone), an electron donor one (EDG) (phenol, phenylamine, N-phenylacetamide) or both an EWG and an EDG (4-chlorophenol). The results clearly indicated that the primary photocatalytic oxidation of aromatic compounds containing an EDG gives rise main…

VOC's abatement: Photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst

Publisher Summary The photocatalytic oxidation of toluene in the presence of water was performed in the gas–solid regime at room temperature by using TiO2. It has been found that the presence of water was beneficial to achieve the almost complete photo-oxidation of toluene to CO2 and H2O, in fact, only very small amounts of benzaldehyde vapor that is the main product of toluene partial oxidation, were detected. Volatile organic compounds, VOC's, are an important class of air pollutants usually found in the atmosphere of all urban and industrial areas. Toluene is one of these compounds, and because of its noxious nature several strategies have been identified to reduce its presence in indoor…

Arbeitsmethoden und Versuche: Abschnitte 8.4.2 (Versuche 37 - 43) - 8.6

Synthesis, Characterisation and Photocatalytic Degradation of 4-Nitrophenol in Aqueous Phase by Using TiO2 Powders Prepared via Sol-Gel Method under Different Gelling Pressure Conditions

Preparation, Characterization, and Photoactivity of Polycrystalline Nanostructured TiO2 Catalysts.

Various preparations of nanostructured TiO2 starting from Ti(iso-OC3H7)4 or TiCl4 are reported. The samples were characterized by X-ray diffractometry, specific surface area and porosity determinations, scanning and transmission electron microscopy, and diffuse reflectance spectroscopy. 4-Nitrophenol photodegradation in aqueous medium was employed as a probe reaction to test the photoactivity of the catalysts. The photoactivity of some samples derived from Ti(iso-OC3H7)4 was found comparable with that of commercial powders. Calcination after the hydrolysis process was necessary to achieve crystallization of the particles before using them as photocatalysts for the reaction studied. The samp…

A Method for Determining Optical Properties and Quantum Yields of Photocatalytic Suspensions

Photocatalytic oxidatioon of acetonitrile : degradation performance in gas-solid and liquid-solid systems

Photocatalytic degradation of 4-nitrophenol in aqueous suspension by using polycrystalline TiO2 impregnated with functionalised Cu(II)-porphyrin or Cu(II)-phthalocyanine

The photocatalytic activity of polycrystalline TiO2 samples impregnated with functionalized Cu(II)- or metal-free porphyrins has been investigated. A probe reaction, i.e., 4-nitrophenol (4-NP) photodegradation in aqueous suspension, has been used. The results indicated that the presence of the sensitizers is beneficial for the photoactivity and suggest an important role of Cu(II). A comparison with similar samples impregnated with modified Cu(II)- and metal-free phthalocyanines showed that the presence of porphyrin is more beneficial both for the decomposition rate of 4-nitrophenol and for the disappearance of nonpurgeable organic carbon (NPOC). Experiments were carried out by using cutoff …

Photocatalytic oxidation of cyanide in aqueous TiO2 suspensions irradiated by sunlight in mild and strong oxidant conditions

Abstract The photocatalytic oxidation of free cyanide ions was carried out in aqueous aerated suspensions containing polycrystalline TiO2 (anatase) irradiated by sunlight. The influence of the presence of an organic compound (phenol) or of a strong oxidant (H2O2) on the photoprocess was also studied. The dependence of cyanide photo-oxidation rate on the following parameters: (1) cyanide concentration; (2) catalyst amount; and (3) phenol concentration was investigated. At the used experimental conditions, the kinetics of cyanide photo-oxidation is independent of the initial cyanide concentration and of the catalyst amount while it is affected by the phenol concentration and by the presence o…

Studio di processi fotocatalitici: dalla preparazione del fotocatalizzatore alla comprensione della cinetica e del meccanismo di reazione

Photocatalytic Oxidation of Acetonitrile

Oxidación Fotocatalítica de Acetonitrilo en Regimen Gas-Sólido y Líquido-Sólido

Study on a photocatalytic membrane reactor for water purification

Abstract Some results obtained in a photocatalytic membrane reactor, to be used for degradation of toxic organic species dissolved in water, are reported. The catalyst, TiO 2 P25 Degussa, was immobilised by means of a flat sheet polymeric membrane and 4-Nitrophenol (4-NP) was used as a model molecule to evaluate the reactor performance. A preliminary investigation of the stability, under UV irradiation, of some eligible polymeric membranes was carried out by using scanning electron microscopy (SEM), optical microscopy (OM), determinations of water permeation flux (WPF) and total organic carbon (TOC). These tests showed that commercial membranes made of fluoride + PP (FS 50 PP-Dow), polysulp…

Photocatalytic degradation of toluene in aqueous suspensions of polycrystalline TiO2 in the presence of the surfactant tetradecyldimethylamino-oxide

The heterogeneous photocatalytic method has been used for carrying out the toluene oxidation in synthetic aqueous solutions containing also a zwitterionic surfactant, i.e. tetradecyldimethylamino-oxide (C 14 DMAO). A batch photoreactor with immersed lamp and two kinds of polycrystalline TiO 2 catalysts were used. The results indicate a substantial increase of the toluene degradation rate in the presence of the surfactant; the complete photo- oxidation of toluene was achieved in a few hours of irradiation at the used experimental conditions; at higher irradiation times also C 14 DMAO was completely degraded. The main intermediates of toluene degradation were p-cresol (4-methyiphenol) and ben…

Studio della Fotodegradazione di Antibiotici in Ambiente Acquoso

Polycrystalline TiO2 Powders Impregnated with Porphyrins Used for the Photocatalytic Degradation of 4-Nitrophenol

"Caratterizzazione ottica di sospensioni acquose di fotocatalizzatori utilizzati in processi di abbattimento di inquinanti organici

Photodegradation kinetics of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of polycrystalline titanium dioxide

The photodegradation process of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of irradiated TiO2 (anatase) powder has been investigated. A batch photoreactor with immersed lamp irradiating in the near-UV region has been used for carrying out the reactivity experiments. For each substrate the influence of the initial concentration of organic compound and of pH on the degradation rate has been investigated. The main intermediates and the end products have been identified and determined, the total mass balance being satisfied. The kinetic modelling of the series of reactions occurring in the system has been satisfactorily carried out with a Langmuir-Hinshelwood rate law. T…

Degradazione Fotocatalitica Eterogenea di Acetonitrile e Toluene in Regime Gas-Solido e Liquido-Solido

Elementi di Chimica

Structural Changes of Titanium Oxide Induced by Chromium Addition as Determined by an X-Ray Diffraction Study

Abstract An X-ray diffraction study has been carried out on a series of polycrystalline TiO 2 (anatase) catalysts containing Cr(III) at different atomic concentrations (0.2-5.0 at. %), prepared by a co-precipitation method. Analysis of the variation of the unit cell parameters of chromium-doped anatase with respect to pure anatase has allowed us to estimate the solubility limit for the system at around 1.4 at. %. There is no evidence for the existence of a separate crystalline chromium oxide phase. Temperature effects on the cell parameter and on the anatase-rutile transformation rate were also analyzed. An increase in temperature produced release of the chromium from the solid solution. At…

Preparation characterization and photocatalytic activity of polycrystalline ZnO/TiO2 systems. 1. Surface and bulk characterization

Polycrystalline ZnO/TiO2 solids have been prepared with four different methods using home prepared TiO2 (anatase) or TiO2 (rutile) as supports and Zn(NO3)2·6H2O or Zn(CH3COO)2·2H2O as precursors for ZnO. The bulk and surface properties of the samples were investigated by means of TG-DTA, XRD, TEM, SEM-EDAX, XPS, BET surface area determination, and porosity measurements. XRD and TEM results indicate that no significant defect structures exist in any of the samples. The ZnO crystallinity and its enrichment on the surface of TiO2 particles were dependent on the preparation method. The surface areas generally decrease by increasing the amount of ZnO except when ZnO from Zn(CH3COO)2·2H2O was sup…

Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of phenol

The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and co…

Photodegradation of Lincomycin in aqueous TiO2 suspension by using artificial or solar light

Photon absorption by aqueous TiO2 dispersion contained in a stirred photoreactor

We present a simple experimental method which allows the evaluation of the absorbed photon flow. The method is based on measurements of transmitted photon rates (by means of standard actinometer solutions) for different reactor thicknesses and/or catalyst concentrations. The method was applied to phenol degradation reaction carried out in a stirred batch phtotoreactor containing aqueous TiO 2 (anatase) dispersion, directly irradied by a 1,500 W Xe lamp

Photocatalytic oxidation of gaseous toluene on anatase TiO2 catalyst: Mechanistic aspects and FT-IR investigation

Abstract Photo-oxidation of toluene has been carried out in gas–solid regime by using polycrystalline anatase TiO2 as the catalyst. The reacting gaseous mixture was toluene, air and water in various molar ratios. A pyrex fixed-bed continuous photoreactor irradiated by a medium pressure Hg lamp was used for performing the photoreactivity experiments. The main oxidation product was benzaldehyde but benzene, benzyl alcohol and traces of benzoic acid, phenol and unidentified compounds were also detected. The molar conversion to benzaldehyde with respect to the initial amount of toluene was ca. 20% in the best experimental conditions. Benzene was produced only as a transient product during the f…

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 …

Decomposition of nitrous oxide upon nickel oxide-magnesium oxide solid solutions

The decomposition of N 2 O has been studied over MgO catalysts, doped with NiO and NiO + Li 2 O from 1 to 10% (atomic). For pure MgO, activity is low, but is enhanced by addition of Ni 2+ ions. The apparent activation energy is reduced from 35 kcal/mole for pure MgO, to about 18 kcal/mole. Oxygen acts as a poison, and it is chemisorbed on the catalyst. The presence of lithium greatly increases the apparent activation energy. The results are interpreted in terms of oxygen chemisorption and of its influence on the course of the reaction.

Preparation, characterisation and photoactivity of nanostructured TiO2 catalysts

ChemInform Abstract: Rate of Photon Absorption and Turnover Number: Two Parameters for the Comparison of Heterogeneous Photocatalytic Systems in a Quantitative Way

Abstract In order to correctly compare the performance of different photocatalytic systems using polycrystalline semiconductor oxides, two parameters are proposed: the rate of photon absorption (rpa) and the turnover number (tn). From these quantities the quantum yield (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline TiO2 (anatase) of different preparation methods and sources, has been used as “test reaction” in order to determine the tn, rpa and qy values.

Rate of photon absorption and turnover number: two parameters for the comparison of heterogeneous photocatalytic systems in a quantitative way

Abstract In order to correctly compare the performance of different photocatalytic systems using polycrystalline semiconductor oxides, two parameters are proposed: the rate of photon absorption (rpa) and the turnover number (tn). From these quantities the quantum yield (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline TiO2 (anatase) of different preparation methods and sources, has been used as “test reaction” in order to determine the tn, rpa and qy values.

Photocatalytic Oxidation of Drugs by Using Artificial and Solar Irradiation

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…

Heterogeneous photocatalysis: optical characterisation of polycrystalline photocatalysts for pollutant degradation in aqueous medium

Photocatalytic membrane reactors for degradation of organic pollutants in water

Abstract Different flowsheets (batch and continuous) of photocatalytic membrane reactors, to be used for degradation of organic pollutants present in water, together to some experimental results, are reported. 4-Nitrophenol (4NP) was used as a probe polluting agent and titanium dioxide in suspension was the catalyst. The photodegradation tests in the batch system were carried out without membrane changing the characteristic variables of the process (light intensity, TiO 2 concentration, 4NP concentration, O 2 concentration, pH) to find their optimum values. The batch system consisted of a water jacket thermostatted and stirred beaker irradiated from above with a UV–Vis lamp (light intensity…

Some working principles of heterogeneous photocatalysis by semiconductors

The present paper outlines some of the principles which are the working base for the photocatalytic processes: we refer to those photocatalytic processes performed using irradiated semiconductors. The steps related to the photoproduction of electron-hole pairs and their separation are discussed. It is also shown how the step of pair separation induces the formation of various chemical species, some of which are useful for the oxidation reactions. It is also shown that in order to reach a detailed description of photocatalytic processes it is necessary to have the knowledge of both the electronic and the physicochemical features of the semiconductors. The paper finally reports a case study r…

Oxidación Fotocatalítica del Acetonitrilo en Régimen Gas-Sólido y Líquido-Sólido

Hybrid processes coupling photocatalysis and membranes for degradation of organic pollutants in water

Abstract Tests of degradation in a photocatalytic membrane system with the lamp immersed in the suspension inside the photoreactor have been carried out by using polycrystalline TiO2 (Degussa P25) as catalyst and humic acids, organic dyes, 4-nitrophenol as pollutants. The influence of the type of nanofiltration membrane, initial concentration of pollutant and pH on the photodegradation rate was investigated in discontinuous and continuous configurations. Two membranes were tested, i.e. NF-PES-010 (Celgard, Germany) of polyethersulphone and NTR-7410 (Nitto-Denko, Japan) of sulphonated polyethersulphone. The last one was chosen for all of the photoreactivity experiments because permeability a…

Optical Characterisation of Semiconductors Used as Photocatalysts for the Degradation of Organic Pollutans in Acqueous Medium

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…

Optical properties and quantum yield determination in photocatalytic suspensions

Knowledge of the optical properties of photocatalytic suspensions is vital for a correct comparison of their energetic efficiency. In this work, the determination of both absorption and scattering coefficients of aqueous suspensions of commercial TiO2 powders irradiated by monochromatic light was carried out by measuring only one quantity—the transmitted photon flow—as a function of the catalyst mass and by applying an asymptotic form of the Kubelka–Munk solution of the radiative transfer equation. Applying a nonlinear fitting procedure the evaluation of the actual values of absorption and scattering coefficients was carried out. The limit for optically thick media of the Kubelka–Munk equat…

Efecto de la Fotocatálisis Heterogenea y la Ozonización sobre la Oxidación del Ion Oxalato en Suspensión Acuosa de TiO2

Photocatalytic Degradation of 4-nitrophenol in aqueous suspension by using polycristalline TiO2 samples impregnated with a Cu(II)-phthalocyanine

In this paper, the preparation of polycrystalline TiO2 samples impregnated with a modified Cu(II)-phthalocyanine (TiO2–CuPc) is reported along with an investigation on the photocatalytic behavior of this system compared with bare TiO2 (both in the anatase and rutile form) and with TiO2 samples impregnated with not functionalized commercial phthalocyanine (TiO2–CuPc) or with metal free phthalocyanine (TiO2–Pc). The photocatalytic degradation of 4-nitrophenol (4-NP) was studied as a probe reaction. The presence of modified CuPc showed to be beneficial only for TiO2 (anatase) while the commercial not functionalized CuPc also slightly for both TiO2 (anatase) and TiO2 (rutile). The metal free Pc…

Preparation of polycrystalline TiO2 photocatalysts impregnated with various transition metal ions : characterization and photocatalytic activity for the degradation of 4-nitrophenol

A set of polycrystalline TiO2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and si…

Studies on various reactor configurations for coupling photocatalysis and membrane processes in water purification

General aspects and perspectives of heterogeneous photocatalysis for the treatment of polluted aqueous effluents are presented. Some experimental results obtained by using various configurations of photocatalytic membrane reactors (PMRs) are reported. The configurations studied were: (i) irradiation of the cell containing the membrane, with three sub-cases: (i1) catalyst deposited on the membrane; (i2) catalyst in suspension, confined by means of the membrane; (i3) entrapment of the photocatalyst in a PSF membrane; (ii) irradiation of the re-circulation tank and catalyst in suspension confined by means of the membrane. In the case “(i)”, a preliminary investigation of membrane stability und…

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.

Carbon and nitrogen-doped TiO2: preparation, characterisation and visible light photocatalytic activity

A method for determining optical properties of photocatalytic suspensions

Preparation characterization and photocatalytic activity of polycrystalline ZnO/TiO2 systems. 2. Surface, bulk characterization, and 4-nitrophenol photodegradation in liquid-solid regime

Electron spin resonance spectroscopy (ESR), Fourier transform infrared spectroscopy (FTIR), and monitoring of pyridine (py) and boric acid trimethyl ester (BATE) adsorption for determining surface acidity and basicity, respectively, were used to carry out further characterization of mixed ZnO/TiO2 polycrystalline solids prepared by different methods. Moreover, the powders were tested in a batch photoreactor for a probe reaction, i.e., 4-nitrophenol photodegradation in aqueous medium. ESR results indicated the presence of signals attributable to Zn+ species in ZnO/TiO2 (anatase) solids, while in ZnO/TiO2 (rutile) samples the presence of zinc induced only the formation of signals probably due…

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.

Fundamentos de Química