Surface Charge Measurements with Scanning Ion Conductance Microscopy Provide Insights into Nitrous Acid Speciation at the Kaolin Mineral–Air Interface

Unique surface properties of aluminosilicate clay minerals arise from anisotropic distribution of surface charge across their layered structures. Yet, a molecular-level understanding of clay mineral surfaces has been hampered by the lack of analytical techniques capable of measuring surface charges...

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Bibliographic Details
Published in:Environmental science & technology 2021-09, Vol.55 (18), p.12233-12242
Main Authors: Zhu, Cheng, Jagdale, Gargi, Gandolfo, Adrien, Alanis, Kristen, Abney, Rebecca, Zhou, Lushan, Bish, David, Raff, Jonathan D, Baker, Lane A
Format: Article
Language:English
Subjects:
Aluminosilicates
Aluminum silicates
Anthropogenic Impacts on the Atmosphere
Chemical precipitation
Clay
Clay minerals
Conductance
Engineering
Environmental Sciences & Ecology
Ion exchange
Kaolin
Microscopy
Minerals
Nitrous acid
pH effects
Protonation
Scanning
Speciation
Subgroups
Surface charge
Surface properties
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Summary:Unique surface properties of aluminosilicate clay minerals arise from anisotropic distribution of surface charge across their layered structures. Yet, a molecular-level understanding of clay mineral surfaces has been hampered by the lack of analytical techniques capable of measuring surface charges at the nanoscale. This is important for understanding the reactivity, colloidal stability, and ion-exchange capacity properties of clay minerals, which constitute a major fraction of global soils. In this work, scanning ion conductance microscopy (SICM) is used for the first time to visualize the surface charge and topography of dickite, a well-ordered member of the kaolin subgroup of clay minerals. Dickite displayed a pH-independent negative charge on basal surfaces whereas the positive charge on edges increased from pH 6 to 3. Surface charges responded to malonate addition, which promoted dissolution/precipitation reactions. Results from SICM were used to interpret heterogeneous reactivity studies showing that gas-phase nitrous acid (HONO) is released from the protonation of nitrite at Al–OH2 + groups on dickite edges at pH well above the aqueous pK a of HONO. This study provides nanoscale insights into mineral surface processes that affect environmental processes on the local and global scale.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.1c03455