Born in Chile in 1944, Camilo Vergara studied sociology in the United States. He then applied his training to photography as a scientific and politic tool of investigation of black ghettos. For the ...past forty years he has documented America’s most dilapidated neighborhoods, first of all Harlem, then Detroit, Chicago, Camden, and other cities. Year after year, he has used rephotography to document the abandoned districts taking pictures of the same places, using the same procedures. Vergara is the only photographer to have scientifically documented the dereliction of poor neighborhoods in the United States. This article shows how Camilo Vergara’s work developed, and what his ideas and concepts are. Eschewing the presentation of poverty in any sensational way Vergara deconstructs the political and social situations that led to such states of dereliction in the black ghetto.
Biogas and natural gas are interesting fuels with high H/C ratio. However, these gases frequently contain carbon dioxide and water which lowers the heat value of the gas and may induce corrosion. ...Therefore, the development of more efficient processes, such as membrane processes and improved adsorbents, for the separation of carbon dioxide and water from biogas and natural gas is of great importance. Zeolite ZSM-5 membranes are promising for this separation which is controlled by the adsorption and diffusion of the different species in the zeolite. Multicomponent adsorption data are therefore required for development of new membrane and adsorption processes. In the present work, the adsorption of water, carbon dioxide, and methane in a Na-ZSM-5 zeolite film at various temperatures was studied by in situ Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy for the first time. Adsorption isotherms were retrieved from the experimental data and the Langmuir model fitted the isotherms very well. Limiting heat of adsorption was determined from the Henrýs law regime and the values determined agreed well with previously reported data. A few experiments were conducted with multicomponent mixtures and the experimentally determined amounts adsorbed were compared with values predicted by the Ideal Adsorbed Solution Theory (IAST). It was found that for the binary mixture of carbon dioxide and methane there was good agreement between the experimental values and those predicted by the IAST. However, when water was also introduced, the IAST could not fully capture the adsorption behavior of the multicomponent mixture, probably because the adsorbed phase is not ideal. These findings are in line with previous reports for adsorption in zeolites. The multicomponent adsorption behavior of this system will be further investigated in forthcoming work.
The uptake and adsorption enthalpy of carbon dioxide at 0.2 bar have been studied in three different topical porous MOF samples, HKUST-1, UiO-66(Zr), and MIL-100(Fe), after having been ...pre-equilibrated under different relative humidities (3, 10, 20, 40%) of water vapor. If in the case of microporous UiO-66, CO2 uptake remained similar whatever the relative humidity, and correlations were difficult for microporous HKUST-1 due to its relative instability toward water vapor. In the case of MIL-100(Fe), a remarkable 5-fold increase in CO2 uptake was observed with increasing RH, up to 105 mg g–1 CO2 at 40% RH, in parallel with a large decrease in enthalpy measured. Cycling measurements show slight differences for the initial three cycles and complete reversibility with further cycles. These results suggest an enhanced solubility of CO2 in the water-filled mesopores of MIL-100(Fe).
Hierarchically porous metal–organic frameworks with mesoporous cages are demonstrated to behave as promising water adsorbents in energy‐efficient dehumidification. Their low temperature desorption ...properties for water with huge sorption uptakes are essential for various water sorption applications including desiccant dehumidification and fresh water production.
A reducible MIL‐100(Fe) metal–organic framework (MOF) was investigated for the separation of a propane/propene mixture. An operando methodology was applied (for the first time in the case of a MOF) ...in order to shed light on the separation mechanism. Breakthrough curves were obtained as in traditional separation column experiments, but monitoring the material surface online, thus providing evidences on the adsorption sites. The qualitative and quantitative analyses of FeII and, to some extent, FeIII sites were possible, upon different activation protocols. Moreover, it was possible to identify the nature and the role of the active sites in the separation process by selective poisoning of one family of sites: it was clearly evidenced that the unsaturated FeII sites are mainly responsible for the separation effect of the propane/propene mixture, thanks to their affinity for the unsaturated bonds, such as the CC entities in propene. The activity of the highly concentrated FeIII sites was also highlighted.
Modus operandi: A reducible Fe‐based metal–organic framework (MOF) was investigated for the separation mechanism of a hydrocarbon mixture by using an operando methodology (see figure). Monitoring the material surface under gas flow, the nature and the role of the active sites were identified: the unsaturated FeII entities were highlighted as being mainly responsible for the separation effect of the propane/propene mixture.
The use of operando FTIR indicates that the high efficiency for NO2 removal from ambient air of iron-containing zeolites comes from their ability to condensate nitric acid. The NO2 removal ...performance of Fe-modified H-BEA and H-ZSM-5 has been investigated in detail by means of in situ and operando FTIR spectroscopy. The surface characterization using NO2 and NO as probe molecules revealed important contributions of redox processes involving Fe3+ -OH and/or alpha-oxygen species as well as Fe2+ -NO species. In these anhydrous conditions, the NO2 storage performance is mainly due to the disproportion of NO2 leading to NO+ and nitrate species. However, under flow and in the presence of humidity, and thus in more realistic conditions, nitrates and NO+ formation are suppressed. The main mechanism responsible for the wet NO2 removal consists in the formation of both adsorbed nitric acid and gaseous NO. According to the proposed mechanism, a strong positive water-effect is established: the total suppression of NO2 in the presence of humidity together with the formation of NO, which is less toxic than NO2 , makes the investigated zeolites promising candidates for efficient materials used in indoor air treatment. PUBLICATION ABSTRACT
An alternative activation method was developed to stabilize the Metal Organic Framework (MOF) MIL-47(V) material in the VIII oxidation state. This solid and the oxidized forms were investigated by in ...situ infrared and Raman spectroscopies, X-ray diffraction (XRD), and Complex Impedance Spectroscopy (CIS). Unlike MIL-47(VIV), MIL-47(VIII) is a flexible structure which presents μ2-hydroxyl groups acting as preferential adsorption sites for H2O or CO2. The modulation of the oxidation state of the metal center of this porous material leads to new intermediate porous solids with mixed oxidation states VIII/VIV. In these materials, the VIII and VIV centers seem to occur in close vicinity. However, the presence of VIV centers inhibits the flexibility to a large extent.
Cu-SAPO-34 (Cu-CZC) and Fe-mordenite (Fe-MOR) and their mechanical mixture (50 : 50) have been exhaustively investigated by means of operando X-ray absorption spectroscopy under NH3-SCR conditions. ...Fe K-edge XANES and EXAFS analysis revealed similar Fe-speciation in both the pure Fe-MOR catalyst and the mechanical mixture after high-temperature pretreatment and under reaction conditions. In contrast, analysis of the Cu K-edge dataset unveiled different trends in temperature-driven Cu-speciation in the pure Cu-CZC and mechanical mixture under standard NH3-SCR conditions. This difference is more evident in a low-temperature range. The presence of the Fe-MOR component in the mixed catalyst can result in the increase of NH3 and NO concentration in the proximity of Cu-sites at a low temperature regime, which facilitates temperature-driven migration of NH3-solvated mobile di-amino complexes from Cu-CZC to the MOR framework. This decreases the density of mobile CuI complexes in the entire system and results in the higher reducibility of Cu in the mixed catalyst. The obtained results help in understanding the precise speciation of the active sites in such composite catalysts and thus provide future guidance on design of such systems.
This work is focused on the application of Cu-containing zeolites as potential environmental sensors for monitoring carbon monoxide. A number of commercial zeolites with different structural ...properties (NaX, NaY, MOR, FER, BEA and ZSM-5) were modified using CuSO4, Cu(NO3)2 and Cu(OAc)2 solutions as copper sources to prepare Cu+-containing zeolites, since Cu+ forms stable complexes with CO at room temperature that can be monitored by infrared spectroscopy. Zeolite impregnation with Cu(NO3)2 resulted in the highest total Cu-loadings, while the Cu(OAc)2-treated samples had the highest Cu+/Cutotal ratio. Cu(NO3)2-impregnated MOR, which displayed the highest concentration of Cu+, was subjected to a number of tests to evaluate its performance as a potential CO sensor. The working temperature and concentration ranges of the sensor were determined to be from 20 to 300 °C and from 10 to 10,000 ppm, respectively. The stepwise CO desorption experiments indicated that the sensor can be regenerated at 400 °C if required. Additional analyses under realistic flow conditions demonstrated that for hydrophilic zeolites, the co-adsorption of water can compromise the sensor’s performance. Therefore, a hydrophobic Sn-BEA was utilised as a parent material for the preparation of an impregnated Cu-Sn-BEA zeolite, which exhibited superior resistance to interfering water while maintaining its sensing properties. Overall, the prepared Cu-modified zeolites showed promising potential as environmental CO sensors, displaying high sensitivity and selectivity under representative testing conditions.
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