Premium
Confocal Raman imaging and atomic force microscopy of the surface reaction of NO 2 and NaCl(100) under humidity
Author(s) -
Scolaro S.,
Sobanska S.,
Barbillat J.,
Laureyns J.,
Louis F.,
Petitprez D.,
Brémard C.
Publication year - 2009
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2098
Subject(s) - chemistry , relative humidity , raman spectroscopy , monolayer , analytical chemistry (journal) , crystallization , nano , atomic force microscopy , chemical engineering , nanotechnology , materials science , chromatography , organic chemistry , biochemistry , physics , optics , thermodynamics , engineering
Polarized confocal Raman imaging combined with non‐contact atomic force microscopy (AFM) was used to study the three‐dimensional evolution of the NaCl(100) surface during its reaction with NO 2 at low pressure as a function of relative humidity (RH) from 0% to nearly 80%. Sea salt particles containing NaCl as the main constituent are believed to be the major source of reactive tropospheric chlorine and nitrate fallouts. At an RH of 0%, the reaction of dry NO 2 generates surface conversion to NaNO 3 monolayer capping the NaCl(100) surface and releases NOCl. The subsequent exposure of this NaNO 3 layer to RH below ∼45% induces the formation of rare NaNO 3 tetrahedral crystals less than 0.5 µm in size. The crystallization occurs through two‐dimensional NO 3 − migration under the H 2 O monolayer regime. After another subsequent exposure to RH above 45% and below 75%, supermicrometric NaNO 3 rhombohedral plates were obtained under the H 2 O multilayer regime. On the other hand, the simultaneous exposure of NaCl(100) to NO 2 and H 2 O below ∼45% RH rapidly generates numerous submicrometric NaNO 3 tetrahedra on the NaCl(100) surface. The dramatic increase of NaNO 3 production in the presence of water vapour is explained by the formation of HNO 3 and its easy reaction with the NaCl(100) surface. For RH above 45% and below 75%, the tetrahedra evolve to rhombohedral plates of supermicrometric size. The exposure of NaCl(100) to NO 2 /H 2 O mixtures under RH above 75% induces the coexistence of both solid‐state NaNO 3 and dissolved NO 3 − in droplets. Copyright © 2008 John Wiley & Sons, Ltd.