Interaction of NaOH solutions with silica surfaces.
J Colloid Interface Sci
; 516: 128-137, 2018 Apr 15.
Article
em En
| MEDLINE
| ID: mdl-29367063
ABSTRACT
HYPOTHESIS:
Sodium adsorption on silica surfaces depends on the solution counter-ion. Here, we use NaOH solutions to investigate basic environments. SIMULATIONS Sodium adsorption on hydroxylated silica surfaces from NaOH solutions were investigated through molecular dynamics with a dissociative force field, allowing for the development of secondary molecular species.FINDINGS:
Across the NaOH concentrations (0.01â¯Mâ¯-â¯1.0â¯M), â¼50% of the Na+ ions were concentrated in the surface region, developing silica surface charges betweenâ¯-â¯0.01â¯C/m2 (0.01â¯M NaOH) andâ¯-â¯0.76â¯C/m2 (1.0â¯M NaOH) due to surface site deprotonation. Five inner-sphere adsorption complexes were identified, including monodentate, bidentate, and tridentate configurations and two additional structures, with Na+ ions coordinated by bridging oxygen and hydroxyl groups or water molecules. Coordination of Na+ ions by bridging oxygen atoms indicates partial or complete incorporation of Na+ ions into the silica surface. Residence time analysis identified that Na+ ions coordinated by bridging oxygen atoms stayed adsorbed onto the surface four times longer than the mono/bi/tridentate species, indicating formation of relatively stable and persistent Na+ ion adsorption structures. Such inner-sphere complexes form only at NaOH concentrations ofâ¯>â¯0.5â¯M. Na+ adsorption and lifetimes have implications for the stability of silica surfaces.
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Base de dados:
MEDLINE
Idioma:
En
Ano de publicação:
2018
Tipo de documento:
Article