Effect of surfactants, pH and water hardness on the surface properties and agglomeration behavior of engineered TiO2 nanoparticles
| Autor: | Serge Stoll, Frédéric Loosli |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Materials Science (miscellaneous)
Analytical chemistry 02 engineering and technology 010501 environmental sciences 01 natural sciences Hydrophobic effect chemistry.chemical_compound Surfactant-nanoparticle complexes Adsorption Pulmonary surfactant Desorption ddc:550 Point of zero charge Surface charge Sodium dodecyl sulfate 0105 earth and related environmental sciences General Environmental Science ddc:333.7-333.9 Agglomeration 021001 nanoscience & nanotechnology Disagglomeration Isoelectric point chemistry Chemical engineering 0210 nano-technology TiO2 nanoparticles |
| Zdroj: | Environmental Science: Nano, Vol. 4, No 1 (2017) pp. 203-211 |
| ISSN: | 2051-8161 2051-8153 |
| DOI: | 10.1039/c6en00339g |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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