In this paper, new information on physical and chemical properties of the widely used nanostructured Halloysite mineral are reported. Given that the Halloysite has a tubular structure formed by a variable number of wrapped layers containing Si-OH and Al-OH groups, their proton binding affinity was measured at different ionic strengths and ionic media by means of potentiometric measurements in heterogeneous phase. One protonation constant for the Si-OH groups and two for the Al-OH groups were determined. The protonation constant values increase with increasing of the ionic strength in all the ionic media. This suggests that the presence of a background electrolyte stabilizes the protonated species through the formation of weak complexes between ions of the supporting electrolytes and the protonated species. Ten weak species were determined with different stoichiometry. It was shown that the interactions do not depend on the nature of the supporting electrolytes but on the charge. The surface charge of Halloysite was estimated by (potential measurements as a function of pH, and the values obtained are consistent with the nanotubes ionization predicted by using the protonation constants for the Si-OH and Al-OH groups. The total solubility of the Halloysite nanotubes, was also determined in NaCl aqueous solution. These measurements showed that the solubility slightly increases with increasing ionic strength and contact time between Halloysite and NaCl solution. Goodness-of-fit (GOF) criteria were used to test the application of these models with good results. The obtained results confirm that the behavior of Halloysite in water is strictly correlated to the experimental conditions of the aqueous suspension (e.g., pH, ionic strength, and ionic media). The thermodynamic data here reported are of main importance in the several applications where is exploited the charge separation between the inner and outer surfaces of this nanotubular material.

Thermodynamics of Proton Binding of Halloysite Nanotubes

BRETTI, CLEMENTE
Primo
;
LANDO, GABRIELE;SAMMARTANO, Silvio
Ultimo
2016-01-01

Abstract

In this paper, new information on physical and chemical properties of the widely used nanostructured Halloysite mineral are reported. Given that the Halloysite has a tubular structure formed by a variable number of wrapped layers containing Si-OH and Al-OH groups, their proton binding affinity was measured at different ionic strengths and ionic media by means of potentiometric measurements in heterogeneous phase. One protonation constant for the Si-OH groups and two for the Al-OH groups were determined. The protonation constant values increase with increasing of the ionic strength in all the ionic media. This suggests that the presence of a background electrolyte stabilizes the protonated species through the formation of weak complexes between ions of the supporting electrolytes and the protonated species. Ten weak species were determined with different stoichiometry. It was shown that the interactions do not depend on the nature of the supporting electrolytes but on the charge. The surface charge of Halloysite was estimated by (potential measurements as a function of pH, and the values obtained are consistent with the nanotubes ionization predicted by using the protonation constants for the Si-OH and Al-OH groups. The total solubility of the Halloysite nanotubes, was also determined in NaCl aqueous solution. These measurements showed that the solubility slightly increases with increasing ionic strength and contact time between Halloysite and NaCl solution. Goodness-of-fit (GOF) criteria were used to test the application of these models with good results. The obtained results confirm that the behavior of Halloysite in water is strictly correlated to the experimental conditions of the aqueous suspension (e.g., pH, ionic strength, and ionic media). The thermodynamic data here reported are of main importance in the several applications where is exploited the charge separation between the inner and outer surfaces of this nanotubular material.
2016
File in questo prodotto:
File Dimensione Formato  
Allosite.pdf

solo utenti autorizzati

Tipologia: Altro materiale allegato (es. Copertina, Indice, Materiale supplementare, Brevetti, Spin off, Start up, etc.)
Licenza: Tutti i diritti riservati (All rights reserved)
Dimensione 2.82 MB
Formato Adobe PDF
2.82 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/3096070
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 50
  • ???jsp.display-item.citation.isi??? 48
social impact