•A micro-fabricated lung cancer biomarkers analyzer was successfully developed.•The selective detection of four lung cancer biomarkers was possible with a single gas sensor.•Zeolite DaY, a highly ...porous solid, was used to concentrate lung cancer biomarkers.•The micro-system exhibited high selectivity and low limit of detection.
The analysis of exhaled volatile organic compounds (VOCs) related to lung cancer is a very promising way in medical diagnosis because it is non-invasive and much less expensive than traditional medical analysis used so far. In that sense, a silicon micro-analytical platform consisting of a micro-preconcentrator coupled to a silicon spiral gas chromatographic micro‐column was built, and a metal oxide-based gas sensor was used as a miniaturized gas detector. This micro-fabricated device was successfully tested to selectively detect low concentrations of VOCs considered as lung cancer biomarkers, within a few minutes even in presence of high concentrations of water vapor and carbon dioxide.
Coadsorption of formaldehyde and water vapors on NaX and NaY zeolites is studied at 298 K in the pressure range 0–2 hPa by manometry coupled with gas phase chromatography and calorimetry. ...Coadsorption isotherms, adsorption selectivities and coadsorption heats are measured. Results show that the coadsorption process is selective for water at low filling and for formaldehyde at high filling. The adsorption selectivity for formaldehyde over water is however too low to consider the possibility of using such adsorbents for the development of air handling units. On the other hand, a preliminary study carried out on the adsorption of formaldehyde and water in pure gas phase on a hydrophobic FAU zeolite reveals that high silica zeolites could be promising adsorbents for the capture of formaldehyde in the presence of water.
Display omitted
•Coadsorption capacities and adsorption selectivities of formaldehyde and water vapors on NaX and NaY zeolites are determined.•Adsorption of formaldehyde and water are very similar.•In the presence of water, NaX and NaY zeolites adsorb preferentially the formaldehyde only at high filling.•NaX and NaY are not efficient for trapping formaldehyde in the presence of water.•The use of hydrophobic FAU zeolite could be a possible alternative.
Equilibrium D2/H2 adsorption selectivity was determined at 77.4 K below 1000 hPa for a series of FAU type zeolites X exchanged with different cations (Li+, Na+, K+, Mg2+, Ca2+, Ba2+ and Mn2+). In ...addition NaY, DAY (dealuminated Y) and pure silica CHA and MFI zeolites were studied. Two experimental approaches were used to determine the D2/H2 adsorption selectivity: direct determination at the thermodynamic equilibrium from manometric coadsorption experiments and calculations by Ideal Adsorbed Solution Theory (IAST) from single gas adsorption isotherms. While these two approaches are not in quantitative agreement, they reveal similar trends. At low loading (<20 molec/uc) exchanged zeolites X in the selectivity diminishes with increasing cation size from 5.7 for MgX to 2.4 for KX: MgX > MnX > LiX > CaX ≈ NaX > KX ≈ BaX. In contrast, at high loading the selectivity is not influenced by the material composition being around 1.5 ± 0.2 for all studied materials. For cation-free zeolites (CHA and MFI) the latter value is observed for all loadings. The key role of cations in D2/H2 selectivity is explained by the fact that at low loading the adsorption proceeds through strong guest-cation interactions while at high loading weaker interactions are involved. Surprisingly, the selectivity in the low loading range is found to be correlated with the cation size and not with the interaction strength (estimated from the value of the Langmuir constant). This behavior of FAU type zeolites is thus different from that of MOFs or that predicted by simple theoretical models based on a one dimensional gas in a harmonic potential.
Display omitted
•D2/H2 thermodynamic selectivities for different zeolites are measured at 77.4 K.•Selectivity in pure silica zeolites does not depend on the pore size.•At high loading for all zeolites the selectivity has similar value (1.5 ± 0.2).•At low loading in FAU zeolites the selectivity is higher for small cations.•IAST predictions are in line with the values obtained from the coadsorption.
We report a structural and thermodynamic investigation of the phase behavior of Ga(OH,F)-MIL-53, a gallium-based metal–organic framework (MOF) having the MIL-53 topology containing 0.7 wt % fluorine ...bonded to the metal. Despite some small structural differences, especially for the hydrated form, the overall physical chemistry behavior of Ga(OH,F)-MIL-53 is very similar to standard fluorine free Ga-MIL-53 material. A combination of in situ X-ray diffraction, in situ Fourier transform infrared spectroscopy, differential scanning calorimetry, and heat capacity measurements allowed us to establish that Ga(OH,F)-MIL-53 under vacuum (i.e., the empty material) exhibits two stable phases: a nonporous narrow-pore (np) phase favored at low temperature and a large-pore (lp) phase favored at high temperature, accompanied by a huge hysteresis effect. Structure determination of the hydrated material Ga(OH,F)-MIL-53_np_H2O obtained after synthesis, activation, and rehydration was also performed. Density functional theory calculations show that it is not a stable structure of Ga(OH,F)-MIL-53 in the absence of adsorbed water molecules. Instead, this hydrated structure is a swollen variant of the np phase, where the flexible framework has expanded to accommodate water molecules.
Adsorption on microporous solid is an alternative technique to remove mercaptans from natural gases. The present study gives equilibrium adsorption data on NaX faujasite for some pure gases ...representative of natural gas impurities (ethyl mercaptan, toluene and
n-heptane) and their binary mixtures. The first part of the paper is devoted to the adsorption of pure gases. Experimental results show that the zeolite has a high adsorption affinity for ethyl mercaptan, toluene and
n-heptane. In the second part, we examine adsorption isotherms for binary mixtures of ethyl mercaptan and toluene or
n-heptane over a large domain of composition. Coadsorption enthalpies are also determined. These experimental data allow to obtain entropies of adsorbed phases and adsorption selectivities. The analysis of coadsorption data indicates that the zeolite preferentially adsorbs ethyl mercaptan over a large domain of micropore filling and that the adsorption selectivity is related to entropic effects inside zeolite micropores. A displacement of
n-heptane by ethyl mercaptan is even observed. In contrast, toluene is preferentially adsorbed by the zeolite at high micropore filling.
The degradation in liquid water of two iron-containing MOFs MIL-100(Fe) and MIL-53(Fe) synthesized in fluoride-free conditions was studied. It was found that dispersing the MOFs in deionized water ...(1 mg/mL) results in the decrease of pH to 2.9 for MIL-100(Fe) and to 4.5 for MIL-53(Fe). Given this finding the stability of the MOFs in liquid water was characterized under two different sets of conditions: 1) reflux in water at 100 °C under obtained pH and 2) at ambient temperature under adjusted pH 7. After reflux of MIL-100(Fe) at 100 °C its XRD pattern remains unchanged, however a strong decrease of its BET surface area and appearance of α-Fe2O3 nanoparticles point out to a partial degradation of the MOF. Reflux of MIL-53(Fe) in water at 100 °C results in its partial degradation yielding H2BDC molecules intercalated in the pores of the remaining MOF particles. To study the degradation of MIL-100(Fe) and MIL-53(Fe) under adjusted pH 7 at room temperature the solids were dispersed in water and then NaOH solution was added in order to maintain a constant pH value. It was found that under such conditions the frameworks of both materials collapse yielding poorly crystallized 6-line ferrihydrite. This finding suggests that the notion of “stability in deionized water” frequently used for MOFs needs to be completed by specifying the exact pH value at which the tests are realized.
Display omitted
•Degradation of fluoride-free MIL-100(Fe) and MIL-53(Fe) in liquid water was studied.•Dispersion of MOFs in deionized water results in pH decrease.•Reflux of both MOFs at 100 °C under acidic conditions results in partial decomposition.•At room temperature and constant pH 7 the structure of studied MOFs collapses.
A joint experimental and molecular simulation study was performed to investigate the adsorption of tetrachloroethene on two MFI zeolites, ZSM-5 with a Si/Al ratio of 26.5, and silicalite-1, which is ...the pure silica form of ZSM-5. Adsorption isotherms and isosteric heats of adsorption of tetrachloroethene were measured and compared to molecular simulation results. Experimental curves for both MFI zeolites show a step at loading of 4 molecules·uc−1 that was interpreted in terms of a structural change of the host framework. A thermodynamic analysis based on the osmotic ensemble scheme allowed attributing this step to a symmetry change from ORTHO (orthorhombic form with Pnma symmetry) to PARA (orthorhombic form with P212121 symmetry) of both adsorbents upon micropore filling. The adsorption mechanism was also characterized. The first tetrachloroethene molecules adsorbs in the channel intersections of the MONO (monoclinic form with P21/n11 symmetry) and ORTHO structures of silicalite-1 and ZSM-5, respectively. Then, the above-mentioned structural change from ORTHO to PARA occurs, leading to a filling of sinusoidal channels until saturation was reached, i.e. ∼8 molecules.uc-1 for silicalite-1 and 6 molecules·uc−1 for ZSM-5. In addition, simulation results indicate that the sodium cations in the ZSM-5 zeolite are located at the channel intersections during the whole adsorption process.
Carbonyl compounds are ubiquitous quality trackers that provide information about food product degradation as well as air and water pollution levels. In addition, they are used as biomarkers for ...medical diagnoses. With more user-friendly sensors, their fast detection and easy quantification are highly relevant. The synthesis, characterization, and performance assessment of a new sensor based on aniline fluorescence to monitor carbonyls in real time is reported. A cost-effective synthesis using a straightforward sol-gel process led to the construction of a nontoxic silica-based material with high porosity, which can be used with almost no sample preparation. The material exhibits a rapid (< 1 min) fluorescence decrease upon interaction with carbonyl groups. The limit of detection is as low as ca. 5 × 10−4 mol·L−1 for hexanal, while fluorescence extinction occurs at much higher concentrations (5 × 10−1·mol L−1), which enables the sensor to be used with a very broad range of detection. Real-time monitoring is possible since the fluorescence loss correlates with the concentration of carbonyl moieties. The performance was validated in simulating as well as in real media, making this sensor suitable for use in a wide range of applications.
Display omitted
•Carbonyl monitoring is crucial in many domains.•The usual techniques often require time, expensive equipment, and toxic compounds.•New fast, user-friendly and cost-effective sensors are required.•A new fluorescent sol-gel sensor for multi-analyte detection was designed.•Its performance in both modeling and real media was demonstrated.
The zwitterionic bipyridinium carboxylate ligand 1-(4-carboxyphenyl)-4,4′-bipyridinium (hpc1) in the presence of 1,4-benzenedicarboxylate anions (BDC2–) and Zn2+ ions affords three porous ...coordination polymers (PCPs): Zn5(hpc1)2(BDC)4(HCO2)2·2DMF·EtOH·H2O (1), Zn3(hpc1)(BDC)2(HCO2)(OH)(H2O)·DMF·EtOH·H2O (2), and Zn10(hpc1)4(BDC)7(HCO2)2(OH)4(EtOH)2·3DMF·3H2O (3), with the formate anions resulting from the in situ decomposition of dimethylformamide (DMF) solvent molecules. 1 and 3 are photo- and thermochromic, turning dark green as a result of the formation of bipyridinium radicals, as shown by electron paramagnetic resonance measurements. Particularly, crystals of 3 are very photosensitive, giving an eye-detectable color change upon exposure to the light of the microscope in air within 1–2 min. A very nice and interesting feature is the regular discoloration of crystals from the “edge” to the “core” upon exposition to O2 (reoxidation of organic radicals) due to the diffusion of O2 inside the pores, with this discoloration being slower in an oxygen-poor atmosphere. The formation of organic radicals is explained by an electron transfer from the oxygen atoms of the carboxylate groups to pyridinium cycles. In the structure of 3′, Zn10(hpc1)4(BDC)7(OH)6(H2O)2, resulting from the heating of sample 3 (desolvation and loss of CO molecules due to the decomposition of formate anions), no suitable donor–acceptor interaction is present, and as a consequence, this compound does not exhibit any chromic properties. The presence of permanent porosity in desolvated 1, 2, and 3′ is confirmed by methanol adsorption at 25 °C with the adsorbed amount reaching 5 wt % for 1, 10 wt % for 3′, and 13 wt % for 2. The incomplete desorption of methanol at 25 °C under vacuum points to strong host–guest interactions.
Molecular dynamics (MD) simulations have been used to study the adsorption process of
n-heptane molecules in silicalite-1 at 300
K. MD simulated results were compared to experimental neutron ...diffraction (ND) and experimental self-diffusion coefficients. The analysis of MD data indicated a packing of the adsorbed molecules around 4
mol./u.c., which is not the consequence of an enthalpic effect but of an entropic effect. The role of the
n-heptane chain flexibility (
cis–
trans conformation) in relation with the silicalite-1 channel type (straight versus sinusoidal) was outlined and enabled to understand the mobility change arising at 4
mol./u.c., according to previous experimental results. The MD simulation also allowed to identify adsorption sites, three in the straight channels and three in the sinusoidal channels and to characterize their position, energy and occupation. Site position but only relative occupation data were in good agreement with neutron diffraction data. The assumption of a “commensurate freezing” to explain the step isotherm is discussed in the light of the MD simulation and ND refinement results.
PDF
