Giuseppe Cappelletti

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO2Prepared by Ultrasound

Nanocrystalline TiO2samples were prepared by promoting the growth of a sol–gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NOxin air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p3/2region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energyper volume (Etot/V) and not the acoustic intensity or the pulsed/continuous mode.

Surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic halide at mono- and polycrystalline silver in acetonitrile

Abstract The silver surface screening effects by specifically adsorbed halide anions in the electrocatalytic reduction of a model organic bromide (acetobromoglucose) have been studied by cyclic voltammetry on controlled mono- and polycrystalline silver surfaces in acetonitrile+0.1 M tetraethylammonium perchlorate medium as a function of the concentration c X of added TEAX (X=Cl, Br, or I, TEA, tetraethylammonium). The reduction peak potentials, E p , are regularly shifted in the negative direction with increasing c X , typically tending to an asymptotic value for c X ≈0.1 M. Several literature models describing adsorption/desorption equilibria have been applied to justify the above experimental E p versus c X trends (being logarithmic in the iodide cases) for the three halides and the four silver surfaces tested.

Wettability of bare and fluorinated silanes: A combined approach based on surface free energy evaluations and dipole moment calculations

The assessment of the surface free energy (SFE) of a material permits to control and predict a large number of physicochemical properties of a solid surface and its reactivity. Here, the surface energies of a series of bare and fluorinated silanes are determined by means of different semi-empirical models on the grounds of contact angle determinations for different solvents. Literature data are also considered in order to produce a series of films with increasing SFE. Wetting envelopes (WE) are obtained for the various surfaces in order to predict the wettability of the films by numerous commonly employed solvents. The polar and disperse components of the surface energies are obtained by the Owens-Wendt-Rabel-Kaelbe (OWRK) method; the values of the polar components are compared with gas-phase dipole moments obtained by theoretical calculations employing semi-empirical Hamiltonians. The sequences of the polar components of the SFE and of the calculated dipole moments for the different molecules are strictly the same. The interplay between theoretical and experimental approaches proves efficient in predicting the behavior of different systems and it could be employed in tuning the SFE of a solid surface with respect to its final applications.

IrO2-based disperse-phase electrocatalysts: a complementary study by means of the cavity-microelectrode and ex-situ X-ray absorption spectroscopy.

In this work, IrO(2)-based powders are screened by cyclic voltammetry for the determination of the electrochemical active sites and for the qualitative evaluation of the iridium atoms speciation. All results are obtained using a cavity-microelectrode as powder holder, thus exploiting the features of this innovative tool, whose best potentialities have been recently introduced by our group. All the studied materials have been prepared by the sol-gel technique and differ in calcination temperature and method of mixing the metal oxide precursors. The electrochemical results are complemented with the information obtained by X-ray absorption spectroscopy (XAS), that give insights on the local structure of each selected sample, confirming the trends found by cyclic voltammetry and give new and unexpected insights on the powder structural features.

Nanocrystalline titanium oxide by sol–gel method. The role of the solvent removal step

TiO2 particles have been prepared by following a sol–gel preparative route using titanium(IV) isopropoxide as the starting compound. HCl was employed as the catalyst of the polycondensation reaction in the gel formation at 25 °C and at constant ionic strength. Three different series of dried precursors were obtained by: (i) evaporating the solvent in oven at 80 °C (xerogels), (ii) reaching supercritical conditions for the fluid (aerogels), or (iii) freeze drying (cryogel). All the samples were calcined at 300 and 600 °C, for the same length of time (6 h). The powders were characterized for phase composition crystallinity (XRD), surface area porosity (BET), water and solvent content (TGA). The role played by the conditions of the solvent elimination, at the end of the sol–gel reaction, in affecting the physico-chemical properties of the powders is discussed.

Electrochemically assisted deposition of transparent, mechanically robust TiO2 films for advanced applications

In recent years, titanium dioxide has received ever growing interest, thanks to its promising applications in numerous fields such as environmental remediation, H2 generation and photovoltaics. Here, transparent and mechanically robust TiO2 films are deposited by a simple and inexpensive electrochemically assisted procedure on various kinds of substrates, both conductive and nonconductive (e.g., glass slides or different metal laminas with variable surface roughness). The obtained films are uniform, crack-free and exhibit excellent chemical, mechanical, and electrochemical robustness. The obtained layers are compared to films prepared by a routine preparation technique, such as dip coating, showing much better morphological, optical, and conductive properties. The photo-activity of TiO2 can be exploited to obtain transparent spectroelectrochemical systems and to control the wetting features of the surface. Applications concerning the modulation of the wettability are presented with respect to both the antifogging and antistain properties. The photoelectrochemical properties of TiO2 films are exploited to activate a photoelectrochemical polymerization of polypyrrole onto an unconductive support. These materials are promising for numerous applications such as smart windows, antifogging mirrors, solar cells, and optically transparent electrodes.

Electrodeposited Polycrystalline Silver Electrodes: Surface Control for Electrocatalysis Studies

An advantageous procedure is developed, allowing preparation of electrodeposited silver electrodes of highly controlled polycrystalline surface (characterized by both electrochemical techniques and SEM), to be employed as cathodes for interphase and electrocatalysis studies. Such electrodes, tested in halide adsorption experiments in parallel with the more demanding single-crystal and polycrystalline silver rod ones, acting as a reference, perform competitively in terms of both reproducibility and stability. The same experiments allow further evaluation of the surface roughness factors of the electrodeposited silver electrodes, based on (i) the Parsons–Zobel criterion and (ii) the comparison of their capacitance minima with those of the (110) single-crystal ones, both approaches resulting in very good agreement with the standard UPD and capacitive methods.

3D Mass Spectrometry Imaging Reveals a Very Heterogeneous Drug Distribution in Tumors

Mass Spectrometry Imaging (MSI) is a widespread technique used to qualitatively describe in two dimensions the distribution of endogenous or exogenous compounds within tissue sections. Absolute quantification of drugs using MSI is a recent challenge that just in the last years has started to be addressed. Starting from a two dimensional MSI protocol, we developed a three-dimensional pipeline to study drug penetration in tumors and to develop a new drug quantification method by MALDI MSI. Paclitaxel distribution and concentration in different tumors were measured in a 3D model of Malignant Pleural Mesothelioma (MPM), which is known to be a very heterogeneous neoplasm, highly resistant to different drugs. The 3D computational reconstruction allows an accurate description of tumor PTX penetration, adding information about the heterogeneity of tumor drug distribution due to the complex microenvironment. The use of an internal standard, homogenously sprayed on tissue slices, ensures quantitative results that are similar to those obtained using HPLC. The 3D model gives important information about the drug concentration in different tumor sub-volumes and shows that the great part of each tumor is not reached by the drug, suggesting the concept of pseudo-resistance as a further explanation for ineffective therapies and tumors relapse.

Time effects on the stability of the induced defects in TiO2 nanoparticles doped by different nitrogen sources

N-doped TiO2 samples are claimed to be the most promising among the so-called second-generation photocatalysts, but their success in photocatalysis is still under debate. In this study, N-doped TiO2 nanocrystals are obtained by a simple, quick, and effortless procedure, starting from titanium alkoxide as the precursor for the sol–gel route, with the N source being either inorganic (NH3) or organic (triethylamine, urea). Structural, morphological, and optical characterizations are compared with electron paramagnetic resonance (EPR) data to give an integrated picture of such materials. No literature data on the “aging” features in the dry state of the fresh calcined samples on the EPR and diffuse reflectance spectra (DRS) measurements are reported. Our N-doped TiO2 powders show different stabilities of paramagnetic and optical signals. The photocatalytic activity is tested, toward the degradation of ethanol in aqueous media, under both visible and UV irradiation, in this latter case resembling the same trend of the paramagnetic species decay.

Designing materials by means of the cavity-microelectrode: the introduction of the quantitative rapid screening toward a highly efficient catalyst for water oxidation

In this paper, we introduce the concept and the methodology of quantitative rapid screening (QRS) of catalysts. It is based on the use of the cavity-microelectrode (C-ME), a tool that hosts a known amount of powder and can be filled and emptied quickly, thus allowing the quantitative, rapid, fine characterization of different materials. Here, C-MEs are used for selecting a suitable material to be used as electrocatalyst for the oxygen evolution reaction (water oxidation) in acidic environment, a key process for the majority of the industrial electrolytic applications including the production of high purity hydrogen. A matrix of materials, each having the same low iridium oxide content, is quantitatively screened for finding the most promising one. C-MEs allowed us to measure the effective number of active Ir sites and their surface concentration. The success of this strategy is proven by the good performance of the “best” material when tested in a proton exchange membrane water electrolyzer, that allowed high hydrogen fluxes at a low cell potential (∼4000 dm3 h−1 m−2 at less than 1.9 V).