Rosana M. Alberici

Photocatalytic destruction of VOCs in the gas-phase using titanium dioxide

The gas-phase photocatalytic destruction of 17 VOCs over illuminated titanium dioxide was investigated using a plug flow reactor with the following experimental conditions: 200 ml min−1 flow rate, 23% relative humidity, 21% oxygen and an organic compound concentration range of 400–600 ppmv. At steady state, high conversion yields were obtained for trichloroethylene (99.9%), isooctane (98.9%), acetone (98.5%), methanol (97.9%), methyl ethyl ketone (97.1%),t-butyl methyl ether (96.1%), dimethoxymethane (93.9%), methylene chloride (90.4%), methyl isopropyl ketone (88.5%), isopropanol (79.7%), chloroform (69.5%) and tetrachloroethylene (66.6%). However, the photodegradation of isopropylbenzene (30.3%), methyl chloroform (20.5%) and pyridine (15.8%) was not so efficient. Carbon tetrachloride photoreduction was investigated in the presence of methanol as an electron donor. It was observed that the presence of methanol results in higher degradation rates. No reaction byproducts were detected for all VOCs tested under the experimental set-up and conditions described. Also, long-term conversion was obtained for all tested compounds. Catalyst deactivation was detected with toluene only, but the activity was restored by illuminating the catalyst in the presence of hydrogen peroxide. The capacity of the process to destroy different classes of volatile organic compounds present in the atmosphere was demonstrated.

Ambient mass spectrometry: bringing MS into the "real world".

AbstractMass spectrometry has recently undergone a second contemporary revolution with the introduction of a new group of desorption/ionization (DI) techniques known collectively as ambient mass spectrometry. Performed in an open atmosphere directly on samples in their natural environments or matrices, or by using auxiliary surfaces, ambient mass spectrometry (MS) has greatly simplified and increased the speed of MS analysis. Since its debut in 2004 there has been explosive growth in the applications and variants of ambient MS, and a very comprehensive set of techniques based on different desorption and ionization mechanisms is now available. Most types of molecules with a large range of masses and polarities can be ionized with great ease and simplicity with the outstanding combination of the speed, selectivity, and sensitivity of MS detection. This review describes and compares the basis of ionization and the concepts of the most promising ambient MS techniques known to date and illustrates, via typical analytical and bioanalytical applications, how ambient MS is helping to bring MS analysis deeper than ever into the “real world” open atmosphere environment—to wherever MS is needed. FigureSchematic of EASI

Gas-phase destruction of H2S using TiO2/UV-VIS

Photocatalytic destruction of H2S using TiO2/UV-VIS was conducted in the gas-phase. This process showed high efficiency, reaching degradation yields of 99% at concentration ranges of 33 to 855 ppmv. Oxygen was shown to be necessary for the photodestruction of H2S. Conversion rates were small in experiments conducted under nitrogen atmosphere (17%) compared with experiments in the presence of oxygen (99%). The photocatalytic activity of TiO2 showed that at 217 ppmv, there was no loss of the activity over extended operation periods. Deactivation of the catalyst was observed only when working at higher H2S concentrations (such as 600 ppmv), and is assumed to be caused by the adsorption of the byproducts produced onto the catalyst surface. The main product in the photocatalytic destruction of H2S in gasphase detected by FTIR and for turbidimetric analysis was sulfate ions. A mass balance showed that H2S is oxidized to SO4poststaggered−2 (95% of SO4poststaggered−2 were easily recovered from the catalyst surface), and that only 0.02% of this ion was detected at the reactor effluent. Experiments carried out using the photocatalytic process to minimize noxious emission of H2S stripped from a raw sewage sample showed that this process is viable for the elimination of odor in wastewater treatment plants.

Photocatalytic degradation of phenol and chlorinated phenols using AgTiO2 in a slurry reactor

Abstract Photodegradation of phenol (PhOH), 2,4-dichlorophenol (2,4-DCP), 2,3,5-trichlorophenol (2,3,5-TCP) and pentachlorophenol (PCP) was investigated using an open upflow slurry reactor and TiO 2 (Ag-loaded) as photocatalyst. Light was provided by three 125 W high-pressure mercury lamps. Best degradation rates were obtained using 250 mg l −1 of AgTiO 2 in the presence of H 2 O 2 and a constant supply of air (1.71 min −1 ). Under this optimized condition, destruction rate constants obtained for a 1 × 10 −4 M solution of PhOH, 2,4-DCP, 2,3,5-TCP and PCP were 0.0493, 0.0430, 0.0367 and 0.0356 min −1 , respectively. Each gram of phenol required 1.70 kW for its photodestruction.

Instantaneous characterization of vegetable oils via TAG and FFA profiles by easy ambient sonic-spray ionization mass spectrometry

A fast and reliable method is presented for the analysis of vegetable oils. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to efficiently desorb and ionize the main oil constituents from an inert surface under ambient conditions and to provide comprehensive triacylglyceride (TAG) and free fatty acid (FFA) profiles detected mainly as either [TAG + Na](+) or [FFA-H](-) ions. EASI(+/-)-MS analysis is simple, easily implemented, requires just a tiny droplet of the oil and is performed without any pre-separation or chemical manipulation. It also causes no fragmentation of TAG ions hence diacylglyceride (DAG) and monoacylglyceride (MAG) profiles and contents can also be measured. The EASI(+/-)-MS profiles of TAG and FFA permit authentication and quality control and can be used, for instance, to access levels of adulteration, acidity, oxidation or hydrolysis of vegetable oils in general.

Catalyst deactivation in the gas phase destruction of nitrogen-containing organic compounds using TiO2/UV–VIS

Possible application of the TiO2/UV‐VIS photocatalytic process in the destruction of nitrogen-containing malodorous compounds was evaluated. Pyridine (C5H5N), propylamine (C3H7NH2) and diethylamine (C4H10NH) were photodegraded in the presence and in the absence of oxygen. Degradation of nitrogen-containing organic compounds was confirmed by mass balance taking into consideration NH4 C and NO3 ions trapped at the TiO2 surface. Photocatalytic deactivation was observed in all cases. Online mass spectrometry was used to identify byproducts in the gas phase formed during the degradation process. GC‐MS analysis of the dichloromethane-extract of aqueous species leached from the surface of deactivated catalyst, as well as pre-concentration in a Tenax column were used to identify intermediates in the gas phase. These byproducts are considered to be the major ones responsible for deactivation of TiO2.

Mass spectrometry on-line monitoring and MS2 product characterization of TiO2/UV photocatalytic degradation of chlorinated volatile organic compounds

On-line Mass Spectrometry and MS2 are applied to monitor and identify the by-products and total mineralization products of TiO2/UV photocatalytic degradation of four chlorinated volatile organic compounds (VOCs): trichloroethylene (TCE), tetrachloroethylene (TeCE), chloroform, and dichloromethane. Selected multiple ion mass spectrometry monitoring using characteristic 70 eV electron ionization ionic fragments monitors in real time the destruction of the starting VOC and the formation of by-products, i. e., the degrees of VOC mineralization, as a function of the flow and relative humidity of the carrier gas (synthetic air). Several by-products were detected: phosgene for TCE, TeCE, and chloroform; dichloroacetyl chloride for TCE; and trichloroacetyl chloride for TeCE. Cl2 and CO2 were also detected as final mineralization products of the four chlorinated VOCs. Structural characterization of by-products was accomplished via MS2 collision-induced dissociation of molecular ions or characteristic ionic fragments.

Water solubilization of ethanol and BTEX from gasoline: on-line monitoring by membrane introduction mass spectrometry

The solubilization of ethanol and the aromatic hydrocarbons benzene, toluene and the isomeric ethylbenzene and xylenes (BTEX) in water in contact with commercial samples of ethanol-containing Brazilian gasoline was monitored on-line by membrane introduction mass spectrometry (MIMS) and BTEX and ethanol concentrations in water after prolonged contact were measured by flow injection analysis (FIA) coupled with MIMS (FIA–MIMS). The cosolvent effect of ethanol, which is known to increase BTEX solubility in water, was also found to speed up BTEX solubilization as compared with ethanol-free gasoline. The ethanol cosolvent effect was also compared with that of methyl tert-butyl ether (MTBE). Chemometric multivariate analysis applied to FIA-MIMS mass spectra of the ethanol–BTEX aqueous solutions formed after prolonged contact with gasoline samples showed that identical samples cluster closely whereas small variances in BTEX composition occurring among and within the three different types of ethanol-containing Brazilian gasoline are easily detected as they cause great dispersion in the chemometric plots.

Analysis of fuels via easy ambient sonic-spray ionization mass spectrometry.

The desorption and ionization of analytes directly from surfaces or natural matrices under ambient conditions has greatly simplified chemical analysis by mass spectrometry. Among the currently available set of such techniques, easy ambient sonic-spray ionization (EASI) is one of the simplest and most easily implemented. Fuels are among the most important and most complex classes of chemical mixtures and a challenge for fast and comprehensive chemical analysis. This review summarizes the applications of EASI-MS for fast, simple and nearly sample-preparation-free analysis of various fuels, focusing in typification, adulteration and quality control.

Direct characterization of commercial lecithins by easy ambient sonic-spray ionization mass spectrometry

Commercial lecithins are composed mainly of phospholipids and triacylglycerols. The analysis of the commercial lecithins, including their fraction of phospholipids, normally involves laborious and expensive protocols. Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) is shown to be an efficient technique for the analysis of lipids. Samples of commercial lecithins including standards, refined, deoiled and modified soy lecithin were tested. Characteristic profiles of phosphatidylcholines and triacylglycerols are detected by EASI(+)-MS, whereas EASI(-)-MS provided phosphatidylethanolamines, glycophospholipids and free fatty acids profiles. Acetylated lecithins also displayed characteristic acetylated derivatives. EASI-MS data was also compared to MALDI-MS, and found to display richer compositional information. The industrial process applied to lecithin fabrication was also characterised via typical EASI-MS profiles. EASI-MS both in its positive and negative ion modes offers a direct, fast and efficient technique able to characterise commercial lecithin.