Dispersion and stability of bare hematite nanoparticles: Effect of dispersion tools, nanoparticle concentration, humic acid and ionic strength

Abstract

The aggregation and sedimentation of iron oxide nanoparticles (IONPs) can significantly affect the mobility and reactivity of IONPs and subsequently influence the interaction between IONPs and environmental contaminants. Dispersing bare IONPs into a stable suspension within nanoscale range is an important step for studying the interaction of IONPs with contaminants (e.g., toxic metals). In this study, different techniques to disperse bare IONPs (vortex, bath sonication and probe ultrasonication) and the effects of important environmental factors such as dissolved organic matter and ionic strength on the stability of IONPs dispersions were investigated. Vortex minimally dispersed IONPs with hydrodynamic diameter outside the “nanosize range” (698–2400nm). Similar to vortex, bath sonication could not disperse IONPs efficiently. Probe ultrasonication was more effective at dispersing IONPs (50% or more) with hydrodynamic diameters ranging from 120–140 nm with minimal changes in size and sedimentation of IONPs for a prolonged period of time. Over the course of 168 hours, considerable amounts of IONPs remained dispersed in the presence and absence of low ionic strength (0.1 mM of NaCl) and 100 mg/L of humic acid (HA). These results indicate that IONPs can be broken down efficiently into “nanosize range” by probe ultrasonication and a degree of stability can be achieved without the use of synthetic modifiers to enhance colloidal stability. This dispersion tool could be used to develop a laboratory method to study the adsorption mechanism between dispersed bare IONPs and toxic contaminants.

A predictive model of iron oxide nanoparticles flocculation tuning Z-potential in aqueous environment for biological application

“…This is presumably due to the fact that the Fe 3 O 4 NPs immediately after the synthesis suffered from the magnet used for the sample collection. MNPs suspension exhibited a slow precipitation and an evident agglomeration because of the increasing attractive interactions; it is known that superparamagnetic NPs can be magnetised with an external magnetic field and immediately re-dispersed once the magnet is removed as indicated by the reduction of agglomerates size after 6 h. The NPs suspension is diluted 50-fold and this concentration is maintained for all DLS measurements because previous works have demonstrated a particle size dependence at NPs concentration (Baalousha 2009;Dickson et al 2012). The Z-potential measures give information on colloidal suspension stability as explained by DLVO theory.…”

Impact of environmental conditions on aggregation kinetics of hematite and goethite nanoparticles

“…The effects of organic matter or indifferent ions on colloid stability are largely documented (Amal et al 1992;Mylon et al 2004;Dickson et al 2012). However, nanoparticles, such as iron (hydr)oxides, have high activity with different ions (Antelo et al 2005).…”

“…Hematite aggregation behaviors have been investigated extensively (Liang and Morgan 1990;Amal et al 1992;Mylon et al 2004;He et al 2008;Dickson et al 2012), while few studies are involved in goethite aggregation. The lack of enough information about goethite aggregation might be a result of the special geometry of goethite particles.…”

Influence of hydrothermal synthesis conditions on size, morphology and colloidal properties of Hematite nanoparticles

“…For example, we seek the experimental conditions whereby crystallites of suitable size could trigger multi-particle aggregation phenomena, which may be relevant at a circumneutral pH occurring in natural environment. This is an important issue since it has been well documented that interparticle aggregation and dispersion can significantly alter the mobility of the hemNP in aquatic environment and reduce the efficacy of using these nanoparticles for remediation purpose [45][46][47][48].…”