Vincenzo Vaiano

Photocatalytic Degradation of Organic Dyes under Visible Light onN-Doped Photocatalysts

This study was focused on the application of white and blue light emitting diodes (LEDs) as sources for the photocatalytic degradation of organic dyes in liquid phase with visible light. The photocatalytic activity of N-doped titanium dioxide, synthesized by direct hydrolysis of titanium tetraisopropoxide with ammonia, was evaluated by means of a batch photoreactor. The bandgap energy of titanium dioxide was moved in the visible range from 3.3 eV to 2.5 eV. The visible light responsive photocatalysts showed remarkably effective activity in decolorization process and in the removal of total organic carbon. Methylene blue was also used as a model dye to study the influence of several parameters such as catalyst weight and initial concentration. The effect of dye on the photocatalytic performance was verified with methyl orange (MO). The results demonstrated that the right selection of operating conditions allows to effectively degrade different dyes with the N-doped TiO2 photocatalysts irradiated with visible light emitted by LEDs.

Influence of the photoreactor configuration and of different light sources in the photocatalytic treatment of highly polluted wastewater

Abstract In this study, a highly polluted wastewater from tannery industry is treated by photocatalysis using home-made N-doped TiO2 as catalyst. The doping by nitrogen of titania particles leads to a reduction in the absorption threshold from 3.2 to 2.5 eV, permitting the absorption of radiation characterized by a wavelength in the visible spectrum.Experiments were carried out by using different light sources, in particular white LEDs, blue LEDs, and UV lamps, with the aim to evaluate the process efficiency at different operating conditions. The obtained performances were compared with those using an undoped commercial TiO2 catalyst (Degussa P25).Moreover, a simplified mathematical model capable to correlate the power input of the used light sources, the geometrical properties of the reactor, and emitting sources spectra with the performances of the photocatalytic reaction was developed.

Heterogeneous Photo-Fenton Oxidation of Organic Pollutants on Structured Catalysts

Abstract In this work the photo-Fenton process for removing organic substances from wastewater was studied by utilizing LaFeO3 perovskites supported on corundum monoliths. The results showed that the heterogeneous photo-Fenton process, based on structured catalysts, allows the total mineralization of acetic acid, giving CO2 and H2O. By adding H2O2 in one time at the beginning of the reaction, it was possible to attain a degree of total organic carbon (TOC) removal between 50 to 70%. With H2O2 dosage during irradiation time, 97% of TOC removal was achieved on structured catalyst containing 10.64 wt% of LaFeO3, coupled to a best utilization of H2O2 at parity of acetic acid conversion. On the same catalyst and with similar operative conditions, by changing the model pollutant in solution, an increased TOC removal was observed after 4 hours of irradiation time, resulting 53, 62 and 95% passing from ethanol to acetaldehyde and finally to oxalic acid, respectively. These results show that suitable heterogeneous catalyst permits the removal of a wide range of substances and suggest that, starting from ethanol, a progressive oxidation occurs, in agreement with the mechanism reported for the homogeneous photo-Fenton degradation of ethanol. Nanoperovskites, well anchored to the monolithic support, permitted to conjugate the improved catalytic activity to their easy and safely manipulation and direct separation from treated effluents. The catalysts can be reutilized, and no metal leaching from the structured catalyst was observed.

Photocatalytic Ethanol Oxidative Dehydrogenation over Pt/tio2: Effect of the Addition of Blue Phosphors

Ethanol oxidative dehydrogenation over Pt/TiO2 photocatalyst, in the presence and absence of blue phosphors, was performed. The catalyst was prepared by photodeposition of Pt on sulphated TiO2. This material was tested in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. The effect of the addition of blue phosphors into the fluidized bed has been evaluated. The synthesized catalysts were extensively characterized by different techniques. Pt/TiO2 with a loading of 0.5 wt% of Pt appeared to be an active photocatalyst in the selective partial oxidation of ethanol to acetaldehyde improving its activity and selectivity compared to pure TiO2. In the same way, a notable enhancement of ethanol conversion in the presence of the blue phosphors has been obtained. The blue phosphors produced an increase in the level of ethanol conversion over the Pt/TiO2 catalyst, keeping at the same time the high selectivity to acetaldehyde.

Surface water disinfection by chlorination and advanced oxidation processes: Inactivation of an antibiotic resistant E. coli strain and cytotoxicity evaluation.

The release of antibiotics into the environment can result in antibiotic resistance (AR) spread, which in turn can seriously affect human health. Antibiotic resistant bacteria have been detected in different aquatic environments used as drinking water source. Water disinfection may be a possible solution to minimize AR spread but conventional processes, such as chlorination, result in the formation of dangerous disinfection by-products. In this study advanced oxidation processes (AOPs), namely H2O2/UV, TiO2/UV and N-TiO2/UV, have been compared with chlorination in the inactivation of an AR Escherichia coli (E. coli) strain in surface water. TiO2 P25 and nitrogen doped TiO2 (N-TiO2), prepared by sol-gel method at two different synthesis temperatures (0 and -20°C), were investigated in heterogeneous photocatalysis experiments. Under the investigated conditions, chlorination (1.0 mg L(-1)) was the faster process (2.5 min) to achieve total inactivation (6 Log). Among AOPs, H2O2/UV resulted in the best inactivation rate: total inactivation (6 Log) was achieved in 45 min treatment. Total inactivation was not observed (4.5 Log), also after 120 min treatment, only for N-doped TiO2 synthesized at 0°C. Moreover, H2O2/UV and chlorination processes were evaluated in terms of cytotoxicity potential by means of 3-(4,5-dime-thylthiazol-2-yl)-2,5-diphenylte-trazolium colorimetric test on a human-derived cell line and they similarly affected HepG2 cells viability.

Cyclohexane photocatalytic oxidative dehydrogenation to benzene on sulphated titania supported MoOx

Abstract The effect of sulphate on the photocatalytic properties of MoOx/TiO2 catalysts for cyclohexane photocatalytic oxydehydrogenation has been investigated with a gas-solid continuous flow reactor. Photocatalytic tests performed on anatase titania at different sulphate content, ranging from 0 to 2 wt%, have shown that only the total oxidation of cyclohexane occurs. Cyclohexane conversion to carbon dioxide at steady state conditions decreases as the sulphate load increases. Photocatalytic oxidative dehydrogenation of cyclohexane to benzene has been studied on MoO3 4.7 wt % supported on sulphated titania. The presence of sulphate species on the surface of titania enhances selectivity and yield to benzene as more as higher is the sulphate content. On the catalyst with the highest sulphate content very high selectivity to benzene was obtained, very weakly dependent of cyclohexane conversion. The selectivity properties of MoOx/TiO2 catalysts are associated to the presence of both sulphate and polymolybdate species on the titania surface.

The Effect of Sulphate Doping on Nanosized and Catalysts in Cyclohexane Photooxidative Dehydrogenation

The effect of sulphate doping of titania in promoting activity and selectivity of catalysts for the cyclohexane photooxidative dehydrogenation has been investigated in a gas-solid fluidized bed reactor. Sulphate and/or molybdate-modified titania catalysts were prepared by incipient wet impregnation of nanosized (5–10 nm crystallite size) samples. At 60% of titania surface coverage by , sulphate surface density was obtained up to 19 mol/ without formation of . The catalysts were characterized by adsorption-desorption at , micro-Raman and UV-visible reflectance spectroscopy, thermogravimetric analysis coupled with mass spectroscopy (TG-MS), and mass titration. Unsulphated and sulphated titania are both active in cyclohexane total oxidation, but sulphate doping of titania has a detrimental effect on the reaction rate. On Mo-based catalysts, polymolybdate species enabled sulphated titania to convert cyclohexane to benzene (99% selectivity) and cyclohexene, reducing at zero the formation of . Cyclohexane conversion to benzene is almost linearly dependent on sulphate surface density, resulting in enhanced yield to benzene. The enhanced photooxidative dehydrogenation activity and benzene yield by sulphate doping could be attributed to the increase of surface acidity and, as a consequence, of cyclohexane adsorption.

Oxidative dehydrogenation of ethanol over Au/TiO 2 photocatalysts

Abstract Au/TiO2 photocatalysts were used in ethanol oxidative dehydrogenation. Catalysts at gold loading ranging between 0.5-2 wt.% were synthesized by photodeposition (using different deposition times: 15 and 120 min) over an ownprepared TiO2 by sol-gel method. For reference purposes, a commercial 1 wt.% Au/TiO2 catalyst (AUROliteTM, Strem Chemicals) was also tested. Photocatalytic reactions were carried out in a gas-solid photocatalytic fluidized bed reactor. Catalytic activity depends strongly both on Au loading and on the material properties, such as particle size and distribution of metal on titania surface. Acetaldehyde was the main reaction product, with ethylene, crotonaldehyde and CO2 as by-products. An important improvement of TiO2 photoactivity was achieved for the catalyst with 0.5 wt.% gold prepared with 120 min deposition time. For an ethanol inlet concentration of 0.2 vol% at 60 °C, the maximum conversion and acetaldehyde selectivity were 82% and 95%, respectively. These values are considerably higher than those obtained over pristine TiO2 and over the commercial catalyst.

Improved Performances of a Fluidized Bed Photoreactor by a Microscale Illumination System

The performances of a gas-solid two-dimensional fluidized bed reactor in photocatalytic selective oxidation reactions, irradiated with traditional UV lamps or with a microscale illumination system based on UV emitting diodes (UVA-LEDs), have been compared. In the photocatalytic oxidative dehydrogenation of cyclohexane to benzene on MoOx/TiO2-A12O3 catalyst the use of UVA-LEDs modules allowed to achieve a cyclohexane conversion and benzene yield higher than those obtained with traditional UV lamps. The better performances with UVA-LEDs are due to the UVA-LEDs small dimensions and small-angle emittance, which allow photons beam be directed towards the photoreactor windows, reducing the dispersion outside of photoreactor or the optical path length. As a consequence, the effectively illuminated mass of catalyst is greater. We have found that this illumination system is efficient for photo-oxidative dehydrogenation of cyclohexane to cyclohexene on sulphated MoOx/𝛾-A12O3 and ethanol to acetaldehyde on VOx/TiO2.

Photo-fenton Oxidation of Acetic Acid on Supported Lafeo3 and Pt/lafeo3 Perovskites

Photo-Fenton process uses Fe as homogeneous catalyst, hydrogen peroxide and UV light to mineralize organic pollutants by the formation of highly reactive hydroxyl radicals. Several limitations to this process are present, such as the limited operational pH range to avoid oxyhydroxide sludge formation and the catalyst recovery. Heterogeneous photo-Fenton process based on structured catalyst can avoid a subsequent separation stage, overcoming these disadvantages. In this work, the comparison of performances of LaFeO3 and Pt/LaFeO3 perovskites supported on different honeycomb monoliths, made of cordierite or corundum, were studied. PhotoFenton oxidation of acetic acid ashowed that LaFeO3 supported on corundum honeycomb was more active than on cordierite monolith. The addition of Pt on catalysts did not help to increase their performance in the studied reaction. Photo-Fenton oxidation tests carried out on catalysts having different content of LaFeO3 evidenced the existence of an optimal loading of active phase.