Agatino Di Paola

A survey of photocatalytic materials for environmental remediation

Heterogeneous photocatalysis is an advanced oxidation process which has been the subject of a huge amount of studies related to air cleaning and water purification. All these processes have been carried out mainly by using TiO(2)-based materials as the photocatalysts and ca. 75% of the articles published in the last 3 years is related to them. This review illustrates the efforts in the search of alternative photocatalysts that are not based on TiO(2), with some exceptions concerning particularly innovative modifications as nanoassembled TiO(2) or TiO(2) composites with active carbon, graphite and fullerene. Papers reporting preparation, characterization and testing of binary, ternary and quaternary compounds, have been reviewed. Despite many of these photocatalysts being effective for the photodecomposition of many pollutants, most of them do not allow a complete mineralization of the starting compounds, differently from TiO(2).

Semiconducting properties of passive films on stainless steels

Abstract The semiconducting properties of passive films grown on three different stainless steels have been investigated by measuring the potential dependence of the capacitance at various frequencies and in different solutions. The results of the capacitance response indicate that the passive films behave like highly doped n-type semiconductors. A strong frequency dispersion hampers the determination of the exact value of the flat band potential of the films from the Mott-Schottky plots. Donor concentrations in the range 10 20 -10 21 cm −3 have been obtained at 1 kHz. The intersection potentials at 1/ C 2 =0 show a linear dependence on the pH.

A photoelectrochemical characterization of passive films on stainless steels

Abstract Passive films on stainless steels for sea water service have been studied by means of photocurrent measurements. Four experimental ELI (Extra Low Interstitital) ferritic stainless steels (types 25Cr-4Ni-4Mo) and a commercial superaustenitic stainless steel (type 20Cr-18Ni-6Mo-N) have been investigated. Differences in the photoelectrochemical behaviour have been attributed to the different nature of the passive films grown on ferritic or superaustenitic stainless steels. An interpretation is provided to explain the complex dependence of the photocurrent transients on the applied potential. Manuscript received 27 February 1986; in amended form 19 June 1986.

Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films

Photoactive films consisting of pure anatase, brookite or rutile TiO2 were prepared by dip coating from water dispersions obtained by using TiCl4 as the precursor under similar mild experimental conditions.

Photoelectrochemical study of the amorphous-WO3-semiconductor–electrolyte junction

The photoelectrochemical behaviour of amorphous anodic films grown on tungsten has been studied. The wavelength of the incident light is shown to influence the photoresponse of the amorphous films. The experimental results are interpreted on the basis of the semiconducting properties of the film and by taking into account the various mechanisms of transport occurring in amorphous materials. At longer wavelengths a Poole–Frenkel mechanism of electrical conduction in the non-extended states of the amorphous semiconductor is invoked in explaining the transport of photoinjected carriers. At the shortest wavelengths a ‘free-carrier-like’ mechanism of transport of the photogenerated carriers is suggested. In each case a different electrode-potential dependence of the photocurrent is obtained experimentally.

Photodegradation of lincomycin in aqueous solution

Aqueous solutions of lincomycin were irradiated with UV light in homogeneous and heterogeneous systems. Lincomycin disappeared in both systems but the presence of TiO2 noticeably accelerated the degradation of the antibiotic in comparison with direct photolysis. The rate of decomposition was dependent on the concentration of lincomycin and followed a pseudo-first-order kinetics. Photolysis involved only the oxidation of lincomycin without mineralization. Differently, the treatment with TiO2 and UV light resulted in a complete mineralization of the antibiotic. The degradation pathways involved S- and N-demethylation and propyldealkylation. The mineralization of the molecule led to the formation of sulfate, ammonium, and nitrate ions.

Tensiostatic studies on formation and breakdown of anodic oxide films on tungsten in acidic chloride solutions

Abstract The anodic behaviour of tungsten in HCl and HCl + KCl solutions has been extensively studied. For each solution, the applied voltage was increased from 1 V up to the breakdown voltage. Values of the current and open circuit voltage decays were recorded. The HCl concentration was varied from 0.05 M to 12 M while appropriate addition to KCl was made to reach assigned molarities of the Cl − ion. The results are discussed and qualitatively interpreted in terms of the different influence of the H + and Cl − ions.

Study of passive films on stainless steels by photocurrent measurements

Abstract Passive films formed on three different stainless steels have been studied by means of photocurrent spectroscopy. Differences in the photoelectrochemical behaviour have been attributed to the influence of the nickel content of the alloys and to the formation of different oxide phases.

TiO2-based photocatalysis for organic synthesis

A major aim of the contemporary chemistry is to replace old environmentally hazardous processes with new, energy efficient routes allowing to reduce or totally avoid the use and production of harmful chemicals and to maximise the quantity of raw material that ends up in the final product. This chapter gives an account of TiO2-based selective photocatalysis as a green synthetic tool for the production of organics. Some case studies of the most common transformations carried out by means of photocatalytic reactions are illustrated in a midway perspective between photochemistry and organic chemistry.

Mixed oxide/sulfide systems for photocatalysis

Mixed WO3/WS2 and ZnO/ZnS powders have been prepared by sulfidation of H2WO4 or ZnO. Photocatalytic degradation of phenol has been employed to test the photoactivity of the samples. The results indicated that the coupling of the two tungsten chalcogenides enhanced the rate of disappearance of the organic substrate. Unlikely, the ZnO/ZnS systems exhibited lower photocatalytic activitiy than pure ZnO. The different photocatalytic behaviour of the two mixed oxide/sulfide systems can be explained by a simultaneous displacement of electrons and holes between two different semiconductors.