Diana Sannino

Supercritical antisolvent precipitation of nanoparticles of a zinc oxide precursor

Supercritical antisolvent (SAS) precipitation has been applied to the production of zinc acetate with the aim of evaluating the applicability of this new process to the production of controlled size nanoparticles of catalyst precursors. SAS process is based on the large volumetric expansion of the liquid solvent induced by the fast diffusion of the antisolvent inside the liquid phase. The main process parameter that controlled zinc acetate particle size and particle size distribution (PSD) was the concentration of the liquid solution. Zinc acetate nanoparticles with sizes down to 30 nm and with a mean particle size of 50 nm have been produced. The nanoparticles showed different porosities depending again on the concentration of the liquid solution. BET surface areas up to about 175 m2/g were measured using N2 adsorption.

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.

Multiwalled carbon nanotube films as small-sized temperature sensors

We present the fabrication of thick and dense carbon nanotube networks in the form of freestanding films (CNTFs) and the study of their electric resistance as a function of the temperature, from 4 to 420 K. A nonmetallic behavior with a monotonic R(T) and a temperature coefficient of resistance around −7×10−4 K−1 is generally observed. A behavioral accordance of the CNTF conductance with the temperature measured by a solid-state thermistor (ZnNO, Si, or Pt) is demonstrated, suggesting the possibility of using CNTFs as temperature small-sized (freely scalable) sensors, besides being confirmed by a wide range of sensitivity, fast response, and good stability and durability. Concerning electric behavior, we also underline that a transition from nonmetal to metal slightly below 273 K has been rarely observed. A model involving regions of highly anisotropic metallic conduction separated by tunneling barrier regions can explain the nonmetallic to metallic crossover based on the competing mechanisms of the metal...

The influence of sulphate on the catalytic properties of V2O5-TiO2 and WO3-TiO2 in the reduction of nitric oxide with ammonia

Abstract The effect of sulphate on the catalytic properties of V2O5/TiO2 and WO3/TiO2 in the selective reduction of NO with NH3 has been investigated. For both catalytic systems, the presence of sulphate results in the enhancement of catalytic activity without reduction of selectivity to nitrogen. The rate of NO reduction depends on the sulphate content, which is affected by the original composition of titania, the method of catalyst preparation and the metal oxide loading.

Performances of V2O5-based catalysts obtained by grafting vanadyl tri-isopropoxide on TiO2-SiO2 in SCR

Abstract A V2O5-based catalyst obtained by grafting vanadyl tri-isopropoxide on a TiO2-SiO2 support obtained by grafting titanium alkoxide on silica has been studied as to the selective catalytic reduction (SCR) of NO with ammonia. The performances obtained have been compared with those of other catalysts in which V2O5 was supported, respectively, on the same support by impregnating it with ammonium vanadate and on TiO2 both by grafting vanadyl tri-isopropoxide and by impregnating it with ammonium vanadate. The first mentioned catalyst turned out to be the best as to activities and selectivities. All the used catalysts and supports have been characterised using many techniques in order to explain the different performances observed. As it will be seen, activities and selectivities, in the mentioned reaction, are mainly affected by three factors that are: (i) V2O5 dispersion largely favoured by the grafting technique; (ii) the morphological properties of TiO2 surfaces that cannot be foreseen but only investigated when TiO2 is obtained by grafting titanium alkoxide on the surface of another oxide and (iii) the type of surface acidity, retaining ammonia reagent.

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.

Controlled growth of CNT in mesoporous AAO through optimized conditions for membrane preparation and CVD operation.

Anodic aluminium oxide (RAAO) membranes with a mesoporous structure were prepared under strictly controlling experimental process conditions, and physically and chemically characterized by a wide range of experimental techniques. Commercial anodic aluminium oxide (CAAO) membranes were also investigated for comparison. We demonstrated that RAAO membranes have lower content of both water and phosphorus and showed better porosity shape than CAAO. The RAAO membranes were used for template growth of carbon nanotubes (CNT) inside its pores by ethylene chemical vapour deposition (CVD) in the absence of a catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and an external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity and quality of CNTs in terms of diameter, length and arrangement (i.e. number of tubes for each channel) were optimized by investigating the effect of changing the experimental conditions for the CVD process. We showed that upon thermal treatment RAAO membranes were made up of crystallized allotropic alumina phases, which govern the subsequent CNT growth, because of their catalytic activity, likely due to their Lewis acidity. The strict control of experimental conditions for membrane preparation and CNT growth allowed us to enhance the carbon structural order, which is a critical requisite for CNT application as a substitute for copper in novel nano-interconnects.

Carbon nanotube induced structural and physical property transitions of syndiotactic polypropylene

In this paper we have studied the effect of increasing carbon multi-walled nanotube (CNT) concentration in composites of syndiotactic polypropylene (sPP) having the same crystalline form but different morphologies. The attention was focused on the form I of sPP with different degrees of perfection (in terms of percentages of chains in helical conformation, crystal dimensions and crystallinity) obtained using two different quenching temperatures from the melt, i.e. 25 and 100 °C. We observed a decreasing effect of the crystallization temperature on increasing the nanotube content up to the samples with 10% of CNT, that show a very similar structural organization independent of the undercooling. Only the amorphous phase turns out more relaxed in the samples crystallized at the highest temperature. Either the thermal or the mechanical properties are improved on increasing the CNT content in both series of samples. The electrical conductivity increases in a similar manner in both series of samples and between 1 and 3 wt% it shows a sizable step of about eight orders of magnitude, a phenomenon that can be regarded as the onset of a percolating structure for which charge transport may take place.

Successful Integration of Membrane Technologies in a Conventional Purification Process of Tannery Wastewater Streams

The aim of this work is to design and integrate an optimized batch membrane process in a conventional purification process used for the treatment of tannery wastewater. The integration was performed by using two spiral wound membrane modules in series, that is, nanofiltration and reverse osmosis, as substitutes to the biological reactor. The membrane process was designed in terms of sensible fouling issues reduction, which may be observed on the nanofiltration membrane if no optimization is performed. The entity of the fouling phenomena was estimated by pressure cycling measurements, determining both the critical and the threshold flux on the nanofiltration membrane. The obtained results were used to estimate the need of the overdesign of the membrane plant, as well as to define optimized operating conditions in order to handle fouling issues correctly for a long period of time. Finally, the developed membrane process was compared, from a technical and economic point of view, with the conventional biological process, widely offered as an external service near tannery production sites, and, here, proposed to be substituted by membrane technologies.

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.