Observation of nitrate ions at the air/water interface by UV-second harmonic generation (original) (raw)
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Polarizability of the nitrate anion and its solvation at the air/water interface
Physical Chemistry Chemical Physics, 2003
The anisotropic molecular polarizability of the nitrate anion and its decomposition into atomic contributions is studied using ab initio quantum chemistry and the Atoms in Molecules theory. Aqueous solvation of NO 3 À in interfacial environments is investigated by a Car-Parrinello molecular dynamics simulation of a cluster, and classical molecular dynamics of an extended slab system with bulk interfaces using a polarizable force field based on the Atoms in Molecules analysis. Both in aqueous clusters and in systems with extended interfaces the nitrate anion clearly prefers interfacial over bulk solvation. This is primarily due to its large value of molecular polarizability, the gas phase value of which is reduced by only 5-10% in the aqueous environment. For polarizable force field simulations of ionic solvation, we recommend to cast the NO 3 À polarizability into three equal contributions of roughly 1.3 Å 3 placed on the oxygen atoms of the anion.
The Journal of Chemical Physics, 2009
Here we report the polarization dependent non-resonant second harmonic generation (SHG) measurement of the interfacial water molecules at the aqueous solution of the following salts: NaF, NaCl, NaBr, KF, KCl, and KBr. Through quantitative polarization analysis of the SHG data, the orientational parameter D,(D= cosθ / cos 3 θ) value and the relative surface density of the interfacial water molecules at these aqueous solution surfaces were determined. From these results we found that addition of each of the six salts caused increase of the thickness of the interfacial water layer at the surfaces to a certain extent. Noticeably, both the cations and the anions contributed to the changes, and the abilities to increase the thickness of the interfacial water layer were in the following order: KBr > NaBr > KCl > NaCl ∼ NaF > KF. Since these changes can not be factorized into individual anion and cation contributions, there are possible ion pairing or association effects, especially for the NaF case. We also found that the orientational parameter D values of the interfacial water molecules changed to opposite directions for the aqueous solutions of the three sodium salts versus the aqueous solutions of the three potassium salts. These findings clearly indicated unexpected specific Na + and K + cation effects at the aqueous solution surface. These effects were not anticipated from the recent molecular dynamics (MD) simulation results, which concluded that the Na + and K + cations can be treated as small non-polarizable hard ions and they are repelled from the aqueous interfaces. These results suggest that the electrolyte aqueous solution surfaces are more complex than the currently prevalent theoretical and experimental understandings.
The Journal of Physical Chemistry C, 2010
Recent experimental and theoretical work has demonstrated that certain anions can exhibit enhanced concentrations at aqueous interfaces and that the adsorption of bromide is particularly important for chemical reactions on atmospheric aerosols, including the depletion of ozone. UV second harmonic generation resonant with the bromide charge-transfer-to-solvent band and a Langmuir adsorption model are used to determine the affinity of bromide for both the air/water and dodecanol/water interfaces. The Gibbs free energy of adsorption for the former is determined to be-1.4 kJ/mol with a lower 90% confidence limit of-4.1 kJ/mol. For the dodecanol/water interface the data are best fit with a Gibbs free energy of +8 kJ/mol with an estimated lower limit of-4 kJ/mol.
Advances in Sciences and Engineering, 2019
The redox processes, organic substances accumulation, chemical equilibria and adsorption of organic substances on the substrate surface function of natural water compositions and substrate granule sizes have been investigated. Laboratory simulations have been carried out for the Nistru and Isnovat river waters. The natural water models containing laurylsulphate (LS) as anionic surfactant (SAS An) and cetyltrimethylammonium (CTMA) as cationic surfactant (SAS Ct), separately and in a body, as well as the substrates Al(OH)3, Al2O3, CaCO3, H2SiO3, light fraction (clayey) of diatomite and expanded clay powder have been studied. The timely distribution of the soluble nitrogen species containing NH4+, NO2- and NO3- in the samples of natural waters has been analyzed. It has been found that LS diminishes the redox processes braking due to the partial fixation of toxic organic matter. Similar, but more pronounced enhancement impact on oxidation of nitrite ions as a result of fixation and sedi...
Croatica Chemica Acta, 2009
Ca(NO) , 3 2 Sr(NO) , 3 2 Ba(NO) , 3 2 Mn(NO) , 3 2 Co(NO) , 3 2 Ni(NO) , 3 2 Cu(NO) , 3 2 Zn(NO) , and 3 2 Cd(NO) was studied by means of UV spectrometry. In all cases, except for 3 2 Zn(NO) (aq), the principalcomponents (PCA) and evolving-factor (EFA) analyses of the spectra indicated formation of associated ion pairs-1 3 [MNO ] z (M z denotes the cation) at higher salt concentrations. The (dis)similarities of the-1 3 [MNO ] z spectral profiles (computed by EFA) were examined by means of cluster analysis. The influence of transition-metal ions on the nitrate UV spectrum was found to be remarkably different compared to that of non-transition cations. That could be a consequence of different types of cation-anion interactions. The ion pairs containing non-transition metal ions could be regarded as classical electrostatic ones, whereas a weak coordination interaction was presumably present in the ion pairs formed by the nitrate and the cations of transition metals.
Journal of Physical Chemistry C, 2018
Molecular adsorption and orientation of an organic anion, p-nitrophenolate (p-NP −), at the air−aqueous interface have been studied using second harmonic generation techniques and surface tensiometry. It is shown that p-NP − not only adsorbs to the neat air−aqueous interface but also exhibits an orientational rearrangement at the surface. The average p-NP − orientation with respect to the surface normal is found to increase from ∼36 to ∼52°with increasing p-NP − surface coverage. Dipole−dipole and electrostatic interactions between p-NP − adsorbates are not the source of this orientation change. Exploration of this intriguing behavior in the presence of electrolytes revealed that interaction between inorganic ions and p-NP − augments its binding affinity and the observed orientation fluctuation. This study provides a critical understanding of the role halide, and plausibly hydroxide ions, play in influencing adsorbate orientation at an interface and thus paves the way to better elucidate chemical reactivity in sea salt aerosols and related environmental surfaces.
Enhanced surface photochemistry in chloride–nitrate ion mixtures
Physical Chemistry Chemical Physics, 2008
Heterogeneous reactions of sea salt aerosol with various oxides of nitrogen lead to replacement of chloride ion by nitrate ion. Studies of the photochemistry of a model system were carried out using deliquesced mixtures of NaCl and NaNO 3 on a Teflon s substrate. Varying molar ratios of NaCl to NaNO 3 (1 : 9 Cl À : NO 3 À , 1 : 1 Cl À : NO 3 À , 3 : 1 Cl À : NO 3 À , 9 : 1 Cl À : NO 3 À) and NaNO 3 at the same total concentration were irradiated in air at 299 AE 3 K and at a relative humidity of 75 AE 8% using broadband UVB light (270-380 nm). Gaseous NO 2 production was measured as a function of time using a chemiluminescence NO y detector. Surprisingly, an enhanced yield of NO 2 was observed as the chloride to nitrate ratio increased. Molecular dynamics (MD) simulations show that as the Cl À : NO 3 À ratio increases, the nitrate ions are drawn closer to the interface due to the existence of a double layer of interfacial Cl À and subsurface Na +. This leads to a decreased solvent cage effect when the nitrate ion photodissociates to NO 2 +O À , increasing the effective quantum yield and hence the production of gaseous NO 2. The implications of enhanced NO 2 and likely OH production as sea salt aerosols become processed in the atmosphere are discussed.
Journal of the American Chemical Society, 2007
Photolysis of aqueous NO3with λ g 195 nm is known to induce the formation of NO2and O2 as the only stable products. The mechanism of NO3photolysis, however, is complex, and there is still uncertainty about the primary photoprocesses and subsequent reactions. This is, in part, due to photoisomerization of NO 3to ONOOat λ < 280 nm, followed by the formation of • OH and • NO2 through the decomposition of ONOOH (pKa) 6.5-6.8). Because of incomplete information concerning the mechanism of peroxynitrite (ONOOH/ONOO-) decomposition, previous studies were unable to account for all observations. In the present study aqueous nitrate solutions were photolyzed by monochromatic light in the range of 205-300 nm. It is shown that the main primary processes at this wavelength range are NO 3-98 hν • NO2 + O •-(reaction 1) and NO3-98 hν ONOO-(reaction 2). Based on recent knowledge on the mechanisms of peroxynitrite decomposition and its reactions with reactive nitrogen and oxygen species, we determined Φ(1) and Φ(2) using different experimental approaches. Both quantum yields increase with decreasing the excitation wavelength, approaching Φ(1)) 0.13 and Φ(2)) 0.28 at 205 nm. It is also shown that the yield of nitrite increases with decreasing the excitation wavelength. The implications of these results on UV disinfection of drinking water are discussed.