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Changes in the structure and porosity of hollow spherical allophane under alkaline conditions
- Source :
- Applied Clay Science. 166:242-249
- Publication Year :
- 2018
- Publisher :
- Elsevier BV, 2018.
-
Abstract
- This work investigated changes in the chemical composition, structure and porosity of hollow spherical allophane under alkaline conditions, which are significant not only for understanding its fate in natural environment but also for its functional applications. Hollow spherical allophane with a silicon/aluminium (Si/Al) molar ratio of 0.77 was hydrothermally synthesised followed by treatment with dilute sodium hydroxide (NaOH) solutions with different concentrations (indicated by pH values). The allophane and its alkali-treated products were then characterized using a combination of techniques, such as Fourier-transform infrared spectroscopy, nuclear magnetic resonance and nitrogen physisorption analysis. Allophane showed a weak structural stability in alkaline conditions. At pH ≤ 11.0, the framework of allophane particles was almost intact; its polymerised silicates showed only slight dissolution. At a higher pH (> 11.0), desilication and dealumination enhanced, resulting in the destruction of the imogolite local structure (ImoLS) along the edges of defect pores and the formation of amorphous materials. Most of the defect pores increased in size, becoming accessible to nitrogen and the textural parameters of the micropores reached their maximum values at a pH of 12.5. However, the damage to some secondary pores and the collapse of some hollow spherules reduced total pore volume (Vtotal). At a pH of 13.0, most of the hollow spherules were observed to have collapsed, resulting in remarkable decrease in the textural parameters. However, some unbroken and/or mildly broken allophane particles might remain, deduced from the relatively high BET specific surface area (SSA) and Vtotal and the considerable proportion of micropores for Allo13.0. These results reveal the dissolution behaviour of allophane in alkaline conditions and the mechanism underlying this behaviour, providing essential insights into the mineral's potential applications.
- Subjects :
- 020101 civil engineering
Geology
Imogolite
02 engineering and technology
010402 general chemistry
01 natural sciences
0201 civil engineering
0104 chemical sciences
chemistry.chemical_compound
Physisorption
chemistry
Chemical engineering
Geochemistry and Petrology
Sodium hydroxide
Specific surface area
Allophane
Porosity
Chemical composition
Dissolution
Subjects
Details
- ISSN :
- 01691317
- Volume :
- 166
- Database :
- OpenAIRE
- Journal :
- Applied Clay Science
- Accession number :
- edsair.doi...........740a04029757787ca75a4381507c57e6