Issue 1, 2017

Effect of surfactants, pH and water hardness on the surface properties and agglomeration behavior of engineered TiO2 nanoparticles

Abstract

The influence of sodium dodecyl sulfate (SDS) on the stability of TiO2 engineered nanoparticle (ENP) dispersions is investigated under various pH conditions, SDS and divalent cation concentrations. Based on different scenarios and systematic measurements of surface charges and z-average sizes, a detailed mechanistic approach is proposed assuming surfactant adsorption/desorption, charge inversion, cation bridging, specific adsorption, hydrophobic effects, agglomeration and disagglomeration. Adsorption of SDS on oppositely charged TiO2 nanoparticles is found to strongly modify their stability. Formation of large agglomerates can be achieved via several routes: i) in the absence of SDS and by adjusting the pH close to the TiO2 point of zero charge, and ii) in the presence of SDS at a concentration where the positive surface charges of the TiO2 nanoparticles are counterbalanced by the SDS negative charges (charge neutralization). It is also found that hydrophobic interaction mechanisms between the SDS molecules can also promote the formation of large structures. The influence of pH variations on TiO2–SDS electrostatic complexes, formed at low pH, indicates that an excess of SDS is required to prevent the formation of large agglomerates upon pH changes. At low or intermediate SDS concentrations, TiO2 stability is governed by the subtle interplay of SDS adsorption and TiO2 surface charge acid–base properties. The presence of divalent electrolytes (water hardness) is found to reduce the SDS amount adsorbed on TiO2 ENPs and to promote the formation of large micron-sized agglomerates by cation bridging. Our results also indicate that the dispersion preparation protocol is an important issue to consider when ENPs and SDS mixtures have to be prepared and that for the formation of “individually” coated and stable nanoparticles, punctual addition of SDS is required at concentrations higher than the isoelectric point.

Graphical abstract: Effect of surfactants, pH and water hardness on the surface properties and agglomeration behavior of engineered TiO2 nanoparticles

Article information

Article type
Paper
Submitted
16 Aug 2016
Accepted
03 Nov 2016
First published
07 Nov 2016
This article is Open Access
Creative Commons BY-NC license

Environ. Sci.: Nano, 2017,4, 203-211

Effect of surfactants, pH and water hardness on the surface properties and agglomeration behavior of engineered TiO2 nanoparticles

F. Loosli and S. Stoll, Environ. Sci.: Nano, 2017, 4, 203 DOI: 10.1039/C6EN00339G

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements