Segregation of NaBr in NaBr/NaCl crystals grown from aqueous solutions: Implications for sea salt surface chemistry

Surface segregation of NaBr in mised NaBr/NaCl crystals precipitated from a queous solutions containing Br is investigated. Crystals were grown from so lutions of a nide range of Br:Cl values and studied using a-ray photoelectr on spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersiv e x-ray fluorescence (EDX), and atomic force microscopy (AFM). Results indi cate that NaBr surface-segregates to cover 4-5% of the surface at the Br:Cl value found in sea water (1:660). The surface NaBr:NaCl values are -35 tom es higher those of bulk crystals. The surface NaBr forms domains of average size 635 nm x 635 nm x 53 nm. Large areas of the surface contain NaClwith no detectable NaBr. Complete surface segregation of all Br found in sea sal t particles is likely to occur, therby making a greater amount of Br availa ble for surface reactions with gas-phase constituents than would be predict ed based on bulk consumption.