Insights on non-exhaust emissions: An approach for the chemical characterization of debris generated during braking.

Up to 50 % of total PM2.5 emissions are due to particles derived from the automotive sector, and both exhaust and non-exhaust emissions contribute to the pollution of urban areas. Fuel incomplete combustion, or lubricant degradation due to high temperatures during the combustion process, are responsible for exhaust emissions. The non-exhaust ones concern brakes, tires and road surface-wear emissions and road resuspension contribution. The present study aims to provide a methodological approach for a detailed chemical characterization of wear friction products by means of a large array of techniques including spectroscopic tools, thermogravimetric analysis (TGA), chromatography, morphological and elemental analysis. The dust sample derived from the wear of a brake pad material was collected after a Noise & Vibration Harshness (NVH) test under loads similar to a Worldwide Light vehicle Test Procedure (WLTP) braking cycle. The TGA shows that only a small fraction is burned during the test in an oxidizing environment, testifying that the sample consists mostly of metals (more than 90 %). Fe exhibits the highest concentrations (50-80 %, even in the form of oxides). Also other kinds of metals, such as Zn, Al, Mg, Si, S, Sn, Mn, occur in small quantities (about 1-2% each). This finding is confirmed by X-ray diffraction (XRD) analysis. The organic fraction of the debris, investigated by means of Raman spectroscopy, has an evident aromatic character, probably due to oxidative phenomena occurring during the braking cycle test. Noteworthy, the extraction of the dust sample with organic solvents, revealed for the first time the presence of ultrafine particles (UFPs), even in the range of few nanometers (nanoparticles), and polycyclic aromatic hydrocarbons (PAHs), recognized as highly toxic compounds. The simultaneous presence of toxic organic carbon and metals makes of concern the non-exhaust emissions and mandatory a deep insight on their structure and detailed composition.

Urban biowaste-derived sensitizing materials for caffeine photodegradation.

Caffeine-photosensitized degradation has been studied in the presence of bio-based materials derived from urban biowaste after aerobic aging. A peculiar fraction (namely bio-based substances (BBSs)), soluble in all the pH range, has been used as photosensitizing agent. Several caffeine photodegradation tests have been performed, and positive results have been obtained in the presence of BBSs and H2O2, without and with additional Fe(II) (photo-Fenton-like process). Moreover, hybrid magnetite-BBS nanoparticles have been synthesized and characterized, in order to improve the sensitizer recovery and reuse after the caffeine degradation. In the presence of such nanoparticles and H2O2 and Fe(II), the complete caffeine degradation has been attained in very short time. Both homogeneous and heterogeneous processes were run at pH = 5, milder condition compared to the classic photo-Fenton process.

Influence of surface functionalization on the hydrophilic character of mesoporous silica nanoparticles.

We report the synthesis and surface functionalization of MCM-41-like mesoporous silica nanoparticles (MSNs) with spheroidal shape and particle size of 141 ± 41 nm. The success of surface functionalization with aminopropyl and sodium ethylcarboxylate groups (giving amino-MSN and carboxy-MSN, respectively) was ascertained by infrared spectroscopy and ζ potential measurements. The former showed the decrease of surface silanol groups and the corresponding appearance of signals related to NH2 bending mode (δNH2) at 1595 cm(-1) and COO(-) stretching (νas and νsym) at 1562 and 1418 cm(-1). The latter showed a change in surface charge, in that the isoelectric point (IEP) changed from pH 3-4.5 to 8.5 when the MSN was functionalized with the amino groups, while carboxy-MSN showed a more negative charge in the whole pH range with respect to MSN. The hydrophilic character of the prepared materials was ascertained by quantitative microgravimetric measurements, allowing the calculation of the average isosteric adsorption heat (q[combining macron]st). This was found to be 51 ± 3 kJ mol(-1), 61 ± 4, and 65 ± 3 kJ mol(-1) for MSN, amino-MSN, and carboxy-MSN samples, respectively. The increase in q[combining macron]st after functionalization can be ascribed to the specific interaction of water molecules with the functionalizing agents, in agreement with a higher basicity with respect to silanol groups. Moreover, the possibility of multiple H-bonding interactions of water molecules with the carboxylate anion is put forward to account for the higher water uptake with respect to parent MSN.

Gas-phase phenol methylation over Mg/Me/O (Me = Al, Cr, Fe) catalysts: mechanistic implications due to different acid-base and dehydrogenating properties.

This contribution reports about an in situ FT-IR investigation and the catalytic reactivity of Mg/Me(3+) mixed oxides (Me = Cr, Fe, or Al; Mg/Me = 2, atomic ratio) in the gas-phase methylation of phenol with methanol. It is the second of two papers concerning the mentioned systems, and its purpose is twofold: to confute the classic and not accurate theory concerning the reaction mechanism, and to propose a novel interpretation based on the combined use of catalytic tests and in situ molecular spectroscopy. Results here reported highlight that: (i) the reaction mechanism in phenol methylation, when catalysed by basic systems, is not a classical electrophylic substitution, as generally reported in the literature, but proceeds through the formation of formaldehyde as an intermediate, and (ii) the catalytic behaviour in respect to both methanol and phenol reactants is strictly dependent on catalyst features. Although all investigated systems exhibit a basic-type behaviour with regard to phenol, which dissociates to yield an adsorbed phenolate species, the distribution of phenolic compounds obtained with the Mg/Al/O catalyst was that typically observed with acid catalysts, with prevailing formation of anisole when the reaction was carried out below 350 degrees C and of mono and poly-C-alkylated compounds when the reaction temperature was above 350 degrees C. On the contrary, the reactivity shown by both Mg/Fe/O and Mg/Cr/O systems was that reported in the literature as typical of mixed oxides possessing basic features. The extent of methanol decomposition into light compounds was maximum in the case of Mg/Fe/O catalysts, because of the pronounced redox behaviour typical of Fe(3+) species, whereas neither methanol dehydrogenation nor decomposition were ever observed with Mg/Al/O up to 400 degrees C. Reactivity tests and spectroscopic experiments hinted for methanol dehydrogenation to formaldehyde as the first step in the ring-methylation of phenol with Mg/Cr/O and Mg/Fe/O: in that case, o-cresol and 2,6-xylenol were the only reaction products. But, with Mg/Al/O systems, for which no methanol dehydrogenation occurred, the formation of anisole was due to the synergistic effect of stronger basic features and the presence of Lewis acidic sites, that facilitate the reaction between phenol and methanol after activation over the two different types of catalytic sites.