Dear Anish,

There is a carboxylic acid functional group in halloysites which can be exploited in a variety of uses. For details please see the following:

Aggregation and Stabilization of Carboxylic Acid Functionalized Halloysite Nanotubes (HNT-COOH)

Yongho Joo†, Yangjun Jeon†, Sang Uck Lee‡, Jae Hyun Sim¶, Jungju Ryu†, Sungyoung Lee†, Hoik Lee†, and Daewon Sohn*†

† Department of Chemistry, Hanyang University, Seoul 133-791, Korea

‡ Department of Chemistry, University of Ulsan, Ulsan 680-749, Korea

¶ Department of Chemistry, Virginia Tech., Blacksburg, Virginia 24061, United States

J. Phys. Chem. C, 2012, 116 (34), pp 18230–18235

DOI: 10.1021/jp3038945

Publication Date (Web): July 16, 2012

Copyright © 2012 American Chemical Society

*E-mail: [email protected].

http://pubs.acs.org/doi/abs/10.1021/jp3038945?journalCode=jpccck

We modified the functional groups of holloysite nanotubes (HNT) from hydroxyl groups (HNT-OH) to carboxylic acids (HNT-COOH). Aggregation and dispersion properties of HNT-COOH under dry conditions were probed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the degree of aggregation and dispersion of HNT-COOH in acidic, basic, and neutral solutions were measured by multiple angle polarized dynamic light scattering (MA-DLS). HNT-COOH formed aggregates in neutral solution; however, the material was dispersed in basic and acidic solutions. This occurrence is due to hydrogen bonds (HB) between the carboxyl groups of HNT-COOH in neutral solution, which decrease in acidic and basic solution due to charge dispersion.

Hoping this will be helpful,

Rafik

Dear Anish,

There is a carboxylic acid functional group in halloysites which can be exploited in a variety of uses. For details please see the following:

Aggregation and Stabilization of Carboxylic Acid Functionalized Halloysite Nanotubes (HNT-COOH)

Yongho Joo†, Yangjun Jeon†, Sang Uck Lee‡, Jae Hyun Sim¶, Jungju Ryu†, Sungyoung Lee†, Hoik Lee†, and Daewon Sohn*†

† Department of Chemistry, Hanyang University, Seoul 133-791, Korea

‡ Department of Chemistry, University of Ulsan, Ulsan 680-749, Korea

¶ Department of Chemistry, Virginia Tech., Blacksburg, Virginia 24061, United States

J. Phys. Chem. C, 2012, 116 (34), pp 18230–18235

DOI: 10.1021/jp3038945

Publication Date (Web): July 16, 2012

Copyright © 2012 American Chemical Society

*E-mail: [email protected].

http://pubs.acs.org/doi/abs/10.1021/jp3038945?journalCode=jpccck

We modified the functional groups of holloysite nanotubes (HNT) from hydroxyl groups (HNT-OH) to carboxylic acids (HNT-COOH). Aggregation and dispersion properties of HNT-COOH under dry conditions were probed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the degree of aggregation and dispersion of HNT-COOH in acidic, basic, and neutral solutions were measured by multiple angle polarized dynamic light scattering (MA-DLS). HNT-COOH formed aggregates in neutral solution; however, the material was dispersed in basic and acidic solutions. This occurrence is due to hydrogen bonds (HB) between the carboxyl groups of HNT-COOH in neutral solution, which decrease in acidic and basic solution due to charge dispersion.

Hoping this will be helpful,

Rafik

 Dear Rafik Karaman,

Thanks for your answer and the link. I read the article but still my question hasn't answered. I am unclear about the fact whether siloxane groups on the outer surface of halloysites can make it acidic or not? 

Dear Anish

if the siloxane group has a pka of 5.3-6.3, slightly acidic. For more details see the following link:

https://books.google.ps/books?id=Wn_dpL5OcKwC&pg=PA677&lpg=PA677&dq=siloxane+groups+pka&source=bl&ots=k_CdW3zyNi&sig=QlVIKMRYkWmH7RyvA3smw0oDbbc&hl=en&sa=X&ved=0ahUKEwjvqpeW2oDKAhULvnIKHekcA_sQ6AEILzAD#v=onepage&q=siloxane%20groups%20pka&f=false

Rafik