Effect of Ionic Compounds of Different Valences on the Stability of Titanium Oxide Colloids

Abstract

Titanium oxide particles of various morphologies have been prepared for applications of scientific or industrial interest in recent decades. Besides development of novel synthetic routes and solid-state characterization of the obtained particles, colloidal stability of titanium oxide dispersions was the focus of numerous research groups due to the high importance of this topic in applications in heterogeneous systems. The influence of dissolved ionic compounds, including monovalent salts, multivalent ions and polyelectrolytes, on the charging and aggregation behaviour of titanium oxide materials of spherical and elongated structures will be discussed in the present review.

Effect of Polyelectrolyte Mono- and Bilayer Formation on the Colloidal Stability of Layered Double Hydroxide Nanoparticles

“…The critical salt level, which separates the stable and unstable regimes, is the so-called critical coagulation concentration (CCC). Polyelectrolyte functionalization has proved to be powerful tool to improve the stability of LDH or other colloidal particles [13,14,35,57,58]. In other words, particles coated with a saturated polyelectrolyte layer possessed higher CCC values than the bare ones.…”

“…Different substrates were applied as base for the multilayer formation including both planar surfaces [10] and colloidal particles [11]. In the latter case, once polyelectrolytes are applied as building blocks, the choice of the appropriate dose is critical, since polyelectrolyte adsorption on oppositely charged particles may lead to charge neutralization and unstable particle dispersions containing large aggregates, which are insufficient for further applications [12,13,14]. At higher polyelectrolyte loadings, however, stable dispersions of primary polyelectrolyte coated particles are formed and these samples can be processed well.…”

Contaminant removal by efficient separation of in situ formed layered double hydroxide compounds from mine wastewaters

“…37 Adsorption of PSS and DXS caused higher magnitude of charge reversal at high flocculant concentration than phosphate owing to their excess of unbound negative charge centres following surface adsorption. Previous studies 33,35,37,41,48 indicate that stable dispersions can also form at high flocculant doses, while destabilization of the dispersions are expected at the isoelectric points. In the four separate samples investigated here spanning model systems (samples 1 and 4) and realworld systems derived from acid mine waters (samples 2 and 3), effective destabilisation could not be achieved despite the use of two separate polyelectrolytes or phosphate.…”

“…† Similar charge neutralization processes often give rise to rapid particles aggregation and to destabilization of colloidal samples. 35,37,[41][42][43][44] With increasing flocculant dose, particle surface charge became negative due to the progressive adsorption of negatively charged species onto the LDH/hydrotalcite surface. Similar charge reversal effects have been reported previously in systems containing colloidal particles and multivalent ions or polyelectrolytes [45][46][47] and also for LDH.…”

“…As discussed above, neutralizing the charge of colloidal particles often leads to rapid aggregation and to unstable dispersions, from which the solids may settle. 35,37,41 This phenomenon may be particularly advantageous in environmental applications, where contaminant-laden LDH/ hydrotalcite needs to be removed prior to wastewater reuse or environmental discharge. 13 With the development of a neutral charge, it is expected that repulsive interparticle interaction will be eliminated, thus leading to the destabilization of the particle aggregates.…”