Conformation and protonation of 2,2'-bipyridine and 4,4'-bipyridine in acidic aqueous media and acidic ZSM-5 zeolites: A Raman scattering study

In situ FT-Raman scattering spectroscopy was used to monitor the sorption kinetics of 2,2'- and 4,4'-bipyridine in acidic ZSM-5 zeolites. The data processing of all the Raman spectra was applied to extract the characteristic Raman spectra of occluded species and respective Raman contribution generated from many spectral data which resolves spectrum of mixture into pure component spectra without any prior information. The assignment of the extracted spectra was performed according to careful comparison with corresponding spectra extracted from a set of Raman spectra recorded during the protonation of 2,2'- or 4,4'-bipyridine (bpy) in hydrochloric acid aqueous solutions. The data processing of the Raman spectra recorded during the slow sorption of 4,4'-bpy in acidic HnZSM-5 (n = 3, 6) zeolites provides specific Raman spectrum of N,N'-diprotonated dication 4,4'-bpyH22+ as unique species generated in the void space of acidic ZSM-5 zeolites. No evidence of Lewis acid sites was found during the sorption of 4,4'-bpy by Raman scattering spectroscopy. The data processing of the Raman spectra recorded during the slow sorption of 2,2'-bpy in acidic HnZSM-5 (n = 3, 6) zeolites provides specific Raman spectrum of trans-N-monoprotonated cation 2,2'-bpyH+ as major species generated in the void space of acidic ZSM-5 zeolites at loading corresponding to 1 mol per unit cell. The trans/cis interconversion occurs at higher loading even after the complete uptake of the sorbate and indicates some rearrangement in the void space over a long time. The cations were found to be located in straight channels in the vicinity of the intersection with the zigzag channel of the porous materials with the expected conformations deduced from ab initio calculations. However, the motions of occluded species within the channel of ZSM-5 are hindered but remain in the range of the isotropic limit of a liquid at room temperature

Raman diagnostic of the reactivity between ZnSO₄ and CaCO₃ particles in humid air relevant to heterogeneous zinc chemistry in atmosphere

Laboratory experiments using Raman imaging demonstrated the behaviour of ZnSO4⋅7H2O (goslarite) microparticles in contact with a 1014 CaCO3 (calcite) surface under three different experimental conditions representative of remote atmosphere. Contact between the ZnSO4⋅7H2O particles and the CaCO3 surface in humid air (RH ~40-80%) did not induce any deliquescence and chemical phenomena. In contrast, condensation of a water drop at the ZnSO4⋅7H2O-CaCO3 interface caused free dissolution of the ZnSO4⋅7H2O particle and rapid precipitation of Zn4SO4(OH)6 onto the CaCO3 surface. This coating inhibited the surface reaction and subsequent drying resulted in the deposition of residual ZnSO4⋅7H2O, then ZnSO4⋅H2O (gunningite) and CaSO4⋅2H2O (gypsum) superimposed onto the Zn4SO4(OH)6 layer. The deposition of ZnSO4⋅7H2O particles in a water drop, previously in contact with a CaCO3 particle for a long time, resulted in the coprecipitation of Zn4SO4(OH)6 and Zn5(CO3)2(OH)6 (hydrozincite). Subsequent drying caused the deposition of residual ZnSO4⋅7H2O, ZnSO4⋅H2O and CaSO4⋅2H2O as small particles. These results indicated the possible fates of ZnSO4 particles in a humid atmosphere, when externally mixed with CaCO3 mineral dust after atmospheric events such as aggregation, water condensation and evaporation. This study indicated the fundamental role of water that typically existed on the surface of aerosol particles in the troposphere. These heterogeneous chemical processes have substantial consequences on particle size and solubility, and thus on bioavailability and toxicity of metal-rich particles

Spontaneous Ionization and Electron Transfer of Polyaromatics by Sorption in ZSM-5 Zeolites

This article reviews the recent works of the authors about the spontaneous ionization and subsequent electron transfer of polyaromatic molecules upon sorption into ZSM-5 zeolites. The results demonstrate once again that the tight fit between the size of rod shape polyaromatic molecules and the diameter of the straight channel can stabilize radical cation-electron pairs or electron–hole pairs over long periods. Applying diffuse reflectance UV–visible absorption (DRUVv) spectrometry, Raman scattering spectrometry and continuous wave electron paramagnetic resonance (CW-EPR) we were able to monitor with in situ conditions the sorption and ionization of biphenyl (BP), naphthalene (NPH) and anthracene (ANTH) in ZSM-5 zeolite samples with Mn(AlO2)n(SiO2)96–n composition per unit cell (UC) (n = 0–6.6; M = H+, Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+). Particular emphasis was placed on pulsed electron paramagnetic resonance (EPR) spectrometry, which has shown to be a powerful technique for a new insight of the ejected electron. The spontaneous ionization is an intrinsic property of the inner surface of the porous materials, which depends both on the ionization potential of sorbate and the polarization energy of the host at the sorption site. For molecules with relatively low ionization potential such as ANTH (IP 7.44 eV) the ionization can occur in both dehydrated acidic and non acidic MnZSM-5 (n > 2; M = H+, Li+, Na+, Mg2+, Ca2+) zeolites. However, the ionization yield was found to highly depend on the nature of the extraframework cation and was found to decrease from H+ (100%) > Li+ (30%) ~ Mg2+ ~ Ca2+ >> Na+ >> K+, Rb+, Cs+ (0%). It was established that the ejected electron is trapped as isolated electron in the oxygen framework in close proximity of Al atoms and extraframework cations with some pairing electronic effect with the ANTH•+ radical cation. Calcination of acidic HnZSM-5 under molecular oxygen is a prerequisite for the spontaneous ionization of BP (IP 8.16 eV) and NPH (IP 8.14 eV) with higher ionization potential. The spontaneous ionization of molecules with relatively high ionization potential such as NPH and BP was effective upon sorption after generation of electron acceptor Lewis acid sites. The oxidizing power of radical cations BP•+ and NPH•+ initiates at room temperature subsequent electron abstraction from the framework and generates unusual long-lived electron–hole pairs. The oxidizing power of ANTH•+ is inefficient at room temperature but is effective at 450 K. The electron and positive hole are trapped in the oxygen framework in close proximity of Al and proton with electronic interactions with the occluded sorbate before the final charge recombination. To cite this article: S. Marquis et al., C. R. Chimie 8 (2005)

PM₁₀ air quality variations in an urbanized and industrialized harbor

In this paper we investigate the PM10 pollution episodes associated with meteorological situations in an urban and industrialized coastal site of the southern part of the North Sea, representative of a typical harbor for trade. In a first part, the spatio-temporal variability of PM10, SO2, NOx and O3 concentrations at the urban scale suggests that both regional air masses and local emissions affect harbor's pollution. In a second part, hierarchical clustering analysis (HCA) performed on meteorological data and PM10 concentrations reveals two main air quality (AQ) regimes. The first one is related to low PM10 levels, which occur under low-pressure conditions due to meteorological conditions favoring a good dispersion of pollutants. The second one is characterized by higher PM10 concentrations appearing under high-pressure conditions. The highest polluted days are characterized by the highest temperatures and hardly any rain. These pollution episodes predominantly occur during sea breeze days, but also as the result of occasional industrial releases. The HCA proved to be an appropriate method to define AQ regimes and to identify meteorological conditions favoring or not PM pollution episodes in Dunkerque conurbatio

Long-lived spin-correlated pairs generated by photolysis of naphthalene occluded in non-Brønsted acidic ZSM-5 zeolites

Long-lived spin-correlated pairs were generated by laser irradiation of naphthalene (NAP) occluded as intact molecule within non-Brønsted acidic MnZSM-5 zeolites with MnSiO2)96-n(AlO2)n formula per unit cell. The laser UV photoionization generates primary NAP+-electron pair as a fast phenomenon. These charge carriers exhibit lifetimes that extend over less than 1 h at room temperature and disappear according to two parallel competitive ways: direct charge recombination and electron transfer. This subsequent electron transfer takes place between the electron-deficient radical cation (NAP+) and the electron-donor oxygen atom of zeolite framework. The aluminum rich MnZSM-5 zeolites (n = 3.4, 6.6) hinder efficiently the charge recombination and promote the electron transfer to generate a very long electron-hole pair which exceeds several weeks at room temperature in [email protected]. The electron-hole pair exhibits broad visible absorption bands at 482 and 525 nm. The electron-hole distance, 1.3 nm, was deduced from the dipolar interaction term (D) value. The spin density of trapped electron appears spread over 27Al, 29Si, 7Li, and 1H nuclei as deduced by two-dimensional approach of hyperfine sublevel correlation (HYSCORE). The very low recombination rate by tunneling effect was found to be in agreement with the very low value (J 0) of the magnetic exchange. The combined effects of tight fit between NAP size and straight-channel dimension, the high aluminum content of the framework, and the highly polarizing cation Li+ trapped efficiently the ejected electron in the conduction band and the hole in the valence band of the porous materials