Figure 3.

(Left) Schematic representations of TiO₂ and SDS interactions and agglomerate formation. (a): TiO₂–SDS agglomerates at pH 3.1. Hydrophobic interactions promote the formation of large agglomerates. (b): TiO₂ agglomerate formation at pH 8.2 in the presence of divalent cations (⊕). Cation bridging between TiO₂ promotes agglomeration. (c): TiO₂–SDS agglomeration in the presence of divalent cations at pH 8.2. Cation bridging between SDS tails destabilizes the complexes. (Right) Z-average diameters and ζ-potential as a function of pH for (a): [SDS] = 40 mg L⁻¹: charge neutralization and inversion is observed. SDS–TiO₂ complex properties are mainly controlled by the TiO₂ surface properties. (b): [SDS] = 200 mg L⁻¹: the impact of SDS properties on the behavior of the TiO₂–SDS complexes is more pronounced. Charge neutralization occurs and the isoelectric point is obtained at pH 5.2; by further increasing the pH, negative values are obtained, due to surface deprotonation. (c): [SDS] = 1442 mg L⁻¹: the SDS–TiO₂ complexes exhibit stable Z-average diameter and ζ-potential in the full pH range. [TiO₂] = 50 mg L⁻¹ (Reprinted from ref. [52]. Copyright 2017 The Royal Society of Chemistry).