RESUMO
Aminosilane self-assembled monolayers on silicon substrates have been prepared via a gas-phase procedure based on the consecutive reactions of the aminosilane precursor and water vapor. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements have been used to characterize the aminosilane layers. For comparison, substrates modified with aminosilane through a liquid-phase procedure have been prepared and characterized by means of the same techniques. The vapor-based procedure was found to yield more uniform layers characterized by fewer and smaller aggregates as compared with liquid-treated substrates. Grazing angles reflection Fourier transform infrared measurements were carried out on the vapor-treated substrates before and after water exposure to investigate the hydrolysis of the alkoxy groups and further reaction to form siloxane bonds. The surface density of amino groups, as estimated through a colorimetric method, is very similar for vapor- and liquid-treated substrates, suggesting a similar reactivity and accessibility of the functional groups on the surface.
RESUMO
The interaction between molecular hydrogen and the alkali-metal-exchanged zeolites Na-FER and K-FER at a low temperature was investigated by combining variable-temperature infrared spectroscopy and theoretical calculations by using a periodic DFT model. The experimentally determined values of standard adsorption enthalpy, DeltaH degrees , were -6.0 (+/-0.8) and -3.5 (+/-0.8) kJ mol(-1) for Na-FER and K-FER, respectively. These results were found to be in agreement with corresponding DeltaH degrees values obtained from calculations on the periodic model. Two types of alkali-metal cation sites in FER were found: channel intersection sites and channel wall sites. Calculations showed a similar interaction energy for both site types, and similar structures of adsorption complexes. Up to two dihydrogen molecules can be physisorbed on the alkali-metal cation located on the intersection of two channels, while only one H2 molecule is physisorbed on the cation at the channel wall site. The adsorption enthalpies of H2 on alkali-metal-exchanged FER are significantly smaller than those found previously for the MFI-type zeolites Na-ZSM-5 and K-ZSM-5, which is likely due to a difference in the alkali-metal cation coordination in the two zeolite frameworks.
RESUMO
Interaction of CO with K-FER zeolite was investigated by a combination of variable-temperature IR spectroscopy and computational study. Calculations were performed using omega(CO)/r(CO) correlation method in combination with a periodic density functional theory model. On the basis of agreement between experimental and calculated results, the following carbonyl complexes were identified: (i) mono- and dicarbonyl C-down complexes on single K(+) sites characterized by IR absorption bands at 2163 and 2161 cm(-1), respectively; (ii) complexes formed by CO bridging two K(+) ions separated by about 7-8 A (dual sites) characterized by a band at 2148 cm(-1); and (iii) isocarbonyl (O-down) complexes characterized by a band at 2116 cm(-1). The bridged carbonyl complexes on dual K(+) sites are about 5 kJ/mol more stable than monodentate (monocarbonyl) CO complexes. The C-O stretching frequency of monocarbonyl species in K-FER depends on K(+) location in the zeolite, and not on K(+) coordination to the framework. A combination of theoretical calculations using a periodic density functional model and experimental results showed formation of two types of monocarbonyls. The most abundant type appears at 2163 cm(-1), and the less abundant one at 2172 cm(-1). These experimentally determined wavenumber values coincide, within +/-2 cm(-1), with those derived from theoretical calculations.
Assuntos
Algoritmos , Potássio/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Zeolitas/análise , Zeolitas/química , Adsorção , Sítios de Ligação , Carbono/química , Cátions/química , Modelos Moleculares , Oxigênio/química , TermodinâmicaRESUMO
Mesoporous silicon doped with 3.0 x 10(19) B atoms cm-3 (p(+)-type) is an insulating material which dramatically increases its electrical conductivity when exposed to traces of gaseous NO2; nitrogen dioxide chemisorption at the surface generates carriers, the population of which is readily evaluated through the intensity of IR absorption.
RESUMO
Mesoporosu (MCM-41 type) silica containing surfactant-embedded Congo Red has been prepared and tested against gas phase HCl and ammonia, as well as solutions of ionic species; it is shown that the hybrid (organic-inorganic) material is permeable to both gases and ionic species, and can act as a pH indicator and as a selective chelating agent.
RESUMO
The evaluation and prediction of the shape of asymmetric gas chromatographic peaks is important as the knowledge of the amount of tailing permits to foresee the resolution between closely eluting peaks and to select the best analytical conditions for an efficient and rapid separation. A model function was tested in order to approximate the true peak shape obtained on non-polar column by injecting different compounds. The trend of the parameters involved in the used equation has been investigated as a function of column temperature and inlet pressure. The reproduction of the symmetrical or asymmetrical shape of gas chromatographic peaks is satisfactory and the method also permits to predict the shape of peaks obtained in different conditions of temperature and pressure.
Assuntos
Cromatografia Gasosa/métodosRESUMO
A historical cohort mortality study conducted among 515 silicotic subjects revealed higher than expected risks for all causes [standardized mortality ratio (SMR) 1.89], respiratory tract diseases (SMR 8.89), silicotuberculosis (SMR 27.00), respiratory tract cancers (SMR 3.14), and lung cancer (SMR 3.50). Mortality from cardiovascular diseases was lower than that expected (SMR 0.51). Lung cancer risk increased with duration of occupational exposure (SMR 2.80, 2.99, and 5.02 for 14, 15-29, and 30 years of employment, respectively). Lung cancer risk was higher for the silicotics without tuberculosis (SMR 3.72) than for those with tuberculosis (SMR 2.83). Indirect adjustment for smoking habits, including number of cigarettes smoked per day, showed that smoking would have been responsible for a maximum risk of 1.77. Thus smoking may have explained 50% of the observed excess mortality from lung cancer.
Assuntos
Neoplasias Pulmonares/mortalidade , Silicose/mortalidade , Adulto , Estudos de Coortes , Intervalos de Confiança , Humanos , Incidência , Itália/epidemiologia , Neoplasias Pulmonares/epidemiologia , Masculino , Pessoa de Meia-Idade , Fatores de Risco , Silicose/epidemiologia , Fumar/efeitos adversos , Taxa de Sobrevida , Fatores de TempoRESUMO
The paper reports the synthesis of an ordered silica mesostructure of the SBA-15 type inside a macroporous bioactive glass-ceramic scaffold of the type SiO(2)-CaO-K(2)O, to combine the bioactivity of the latter with the release properties of the former, in view of local drug delivery from implants designed for tissue engineering. The standard procedure for SBA-15 synthesis has been modified to minimize the damage to the scaffold caused by the acidic synthesis medium. The composite system has been characterized by means of Scanning Electron Microscopy (coupled with EDS analysis), Small Angle X-Ray Diffraction, Thermogravimetry analysis and Infrared Spectroscopy: the formation of a well ordered hexagonal mesostructure was confirmed. Ibuprofen has been chosen as model drug. The uploading properties have been investigated of the scaffold-mesoporous silica composite as compared with the scaffold as such, and a five-fold increase in the adsorbing properties toward ibuprofen was found, due to the presence of the ordered mesoporous silica. The ibuprofen release to a SBF solution in vitro is complete in 1 day. Retention of bioactivity from the glass-ceramic scaffold after the silica mesostructure incorporation has been observed.
Assuntos
Cerâmica/química , Sistemas de Liberação de Medicamentos , Vidro/química , Dióxido de Silício/química , Alicerces Teciduais/química , Analgésicos não Narcóticos/administração & dosagem , Materiais Biocompatíveis/química , Ibuprofeno/administração & dosagem , Microscopia Eletrônica de Varredura , PorosidadeRESUMO
Silanol species in phenylene-bridged periodic mesoporous organosilica (PMO), templated via tri-block copolymer Pluronic P123 and thus characterized by large pores and amorphous wall structure, have been characterized by means of FT-IR spectroscopy. Investigation has been carried out on both the naked sample outgassed at different temperatures and the sample when interacting with molecular probes able to form H-bonding (ammonia and carbon monoxide). After outgassing at 773 K, the material shows both isolated silanols and silanols engaged in "intraframework" H-bonding with the pi-cloud of structural aromatic rings. Interaction with ammonia showed that a fraction of these species is inaccessible, being probably located inside the pore walls. Thermal treatment above 673 K causes the appearance of SiO3(OH) species formed as a consequence of the cleavage of some Si-C bonds. The presence of hydroxyls slightly more acidic than isolated silanols has been evidenced: these are interpreted as perturbed geminal species.
RESUMO
Detailed understanding of weak solid-gas interactions giving rise to reversible gas adsorption on zeolites and related materials is relevant to both, fundamental studies on gas adsorption and potential improvement on a number of (adsorption based) technological processes. Combination of variable-temperature infrared spectroscopy with theoretical calculations constitutes a fruitful approach towards both of these aims. Such an approach is demonstrated here (mainly) by reviewing recent studies on hydrogen and carbon monoxide adsorption (at a low temperature) on alkali-metal exchanged ferrierite. However, the methodology discussed, which involves the interplay of experimental measurements and theoretical calculations at the periodic DFT level, should be equally valid for many other gas-solid systems. Specific aspects considered are the identification of gas adsorption complexes and thermodynamic studies related to standard adsorption enthalpy and entropy.
RESUMO
The interaction, at a low temperature, between molecular hydrogen and the zeolite Li-FER was studied by means of variable temperature infrared spectroscopy and theoretical calculations using a periodic DFT model. The adsorbed dihydrogen molecule becomes infrared active, giving a characteristic IR absorption band (H-H stretching) at 4090 cm(-1). Three different Li(+) site types with respect to H(2) adsorption were found in the zeolite, two of which adsorb H(2). Calculations showed a similar interaction energy for these two sites, which was found to agree with the experimentally determined value of standard adsorption enthalpy of DeltaH(0) = -4.1 (+/-0.8) kJ mol(-1). The results are discussed in the broader context of previously reported data for H(2) adsorption on Na-FER and K-FER.
Assuntos
Hidrogênio/química , Modelos Químicos , Modelos Moleculares , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Zeolitas/análise , Zeolitas/química , Adsorção , Simulação por Computador , Hidrogênio/análise , Lítio/análise , Lítio/química , Conformação MolecularRESUMO
The association between ozone (O3) and daily mortality was investigated in Genoa, an Italian city characterized by a Mediterranean climate and a high prevalence of elderly inhabitants. The O3 effect, adjusted for long time trend, seasonality and weather, was assessed using Poisson regression modelling, allowing for overdispersion and autocorrelation, and expressed as mean variation percent of daily mortality per 50 microg/m3 increase (MV). Significant MVs for overall (+4.0%) and cardiovascular (+7.2%) mortality were detected at 1-day lag. The effects were stronger in the warmer season (May-October). Similar estimates were found after restricting the analyses to the elderly (>or=75 years). Furthermore, in this group, higher MVs were observed for total mortality at 2-day lag. A statistically significant synergistic effect between O3 and temperature was observed for cardiovascular mortality, particularly in elderly people, with an evident increase in mortality risk above 26 degrees C (MV +30.0% for the whole population and +40.0% for the elderly, respectively). This investigation highlights the importance of taking local climatic and demographic features into account when comparing different time-series studies, and substantiates the influence of photochemical pollution on mortality trends in small urban areas.
Assuntos
Poluentes Atmosféricos/toxicidade , Poluição do Ar/efeitos adversos , Mortalidade/tendências , Ozônio/toxicidade , Fatores Etários , Idoso , Poluentes Atmosféricos/análise , Poluição do Ar/análise , Doenças Cardiovasculares/mortalidade , Efeito Estufa , Humanos , Umidade/efeitos adversos , Itália/epidemiologia , Pessoa de Meia-Idade , Ozônio/análise , Distribuição de Poisson , Sistema de Registros , Estações do Ano , TemperaturaRESUMO
A new method is demonstrated for calculating gas adsorption heats from variable-temperature infrared spectra of adsorbed molecules. By focusing on the low coverage regime, where (at equilibrium) there is only a very small fraction of molecules adsorbed, the procedure devised yields the corresponding value of adsorption enthalpy without needing to know the equilibrium pressure. Experimental measurements can thus be highly simplified, which constitutes one of the merits of the new method. Versatility for dealing with adsorption processes occurring at a low temperature, and having a small energy balance, is another favourable feature.
Assuntos
Temperatura Alta , Temperatura , Termodinâmica , Adsorção , Gases/química , Sensibilidade e Especificidade , Espectrofotometria Infravermelho/métodos , Propriedades de SuperfícieRESUMO
BACKGROUND: A historical cohort mortality study was conducted among 3984 shipyard workers assigned to ship repair, refitting, and construction in the harbor of Genoa, Italy, between 1960 and 1981. These workers were exposed to asbestos fibers, welding fumes and gases, silica dust, polycyclic aromatic hydrocarbons, and solvents. METHODS: Workers were classified in 20 different job-titles depending upon the type of activity. Standardized mortality ratios (SMRs) were computed using male residents of the Province of Genoa as the referent population. RESULTS AND CONCLUSIONS: For the whole cohort significantly increased SMRs were detected for all causes, all cancers, liver, larynx, lung, pleural and bladder cancers, respiratory tract diseases, and cirrhosis of the liver. The analysis by job-title showed increased SMRs not only for pleural cancer, but also for lung, laryngeal cancers and respiratory tract diseases in occupations entailing heavy asbestos exposure. Bladder and liver cancers and liver cirrhosis mortality also appeared to be related to occupational exposure.
Assuntos
Doenças Profissionais/mortalidade , Exposição Ocupacional/estatística & dados numéricos , Adulto , Idoso , Asbestose/etiologia , Asbestose/mortalidade , Estudos de Coortes , Seguimentos , Humanos , Indústrias , Itália/epidemiologia , Neoplasias Hepáticas/mortalidade , Masculino , Pessoa de Meia-Idade , Compostos Policíclicos/efeitos adversos , Neoplasias do Sistema Respiratório/mortalidade , Navios , Dióxido de Silício/efeitos adversos , Neoplasias da Bexiga Urinária/mortalidadeRESUMO
The study defines the epidemiological characteristics of HIV-infection in the population of Genoa and estimates the entity of AIDS-cancer association. The cohort includes 317 subjects resident in the Municipality of Genoa, aged above 14 years and notified prior to 31 December 1991 and/or dead from AIDS in the period 1988-1991. From 1984 to 1991, 44 cases of tumour were recorded. The comparison between the rate ratios found in the AIDS patients' cohort and in the general population of Genoa strengthen the significant association highlighted in literature regarding overall cancer, 26.7 (p < 0.05), and in particular, Kaposi's sarcoma, 3239.4 (p < 0.05); non-Hodgkin's lymphomas, 84.8 (p < 0.05); Hodgkin's lymphomas, 20.6 (p < 0.05). Moreover, a significant increase in the risk of testicular seminoma, 61.5 (p < 0.05) and lung cancer, 18.0 (p < 0.05) is confirmed.