Surface Charge Density of Maghemite Nanoparticles:  Role of Electrostatics in the Proton Exchange

Abstract

In the present work, we focus on the surface charge properties of well-defined maghemite (γ-Fe 2 O 3 ) nanoparticles dispersed in water. Because of the acidic properties of surface groups, the nanoparticles' surface can be positively or negatively charged depending on the pH. Consequently, there are electrostatic repulsion forces between particles that allow stabilizing the suspensions in water. Acid-base titrations of the surface groups starting from acidic, alkaline, and neutral pH are performed to access the dependence of the surface charge density with the pH. Titrations are followed by potentiometric and conductometric measurements. Simultaneous zetametry measurements by acoustophoresis are implemented. The experimental curves are analyzed using several hypotheses; in particular, we assume that the sites on the surface of the particles behave as weak diacids. The interpretation of the experimental determinations of the charge implies taking into account an electrostatic term due to the potential developed at the surface of the particles. Thanks to the complementarity of the potentio-conductometric titrations and of the zetametry measurements, it is possible to better understand the phenomena of protonation and deprotonation of the colloidal particles as a function of the medium of dispersion (acidic, alkaline, neutral pH, and nature of the counterions) and of the nature of the reagent.

Surface Charge Density Determination in Water Based Magnetic Colloids: a Comparative Study

“…In this method, in agreement with the literature. In this way, according to table 1, the saturation value of the surface charge density determined with the two methods show excellent agreement with each other and they are consistent with previous determinations in similar magnetic colloids 10,14,15,24 proving that both are effective. Nevertheless, the methods exhibit a significant different profile of the pH dependence of the surface charge density as shown in figure 4.…”

“…In the SPM 14,15 the pH of the magnetic colloid sample is adjusted to the PZC inducing rapid coagulation. Then, the coagulated nanoparticles are washed thoroughly with distilled water to ensure the particles are uncharged and the solvent is free of ions.…”

Polyelectrolyte assisted charge titration spectrometry: Applications to latex and oxide nanoparticles

“…However the technique requires large sample quantity, which depending on the particle synthesis is not always possible. To determine the charge density of iron oxide particles for instance, Lucas et al used potentio--conductometric titration with dispersions containing 5--10 g of iron oxide dry matter [18]. Colloid titration is another method that was introduced by Terayama some 50 years ago [22].…”

Nanocomposite Materials with Oriented Functionalized Structure

“…The elimination of surface impurities is indicated in the case of oxidic nanomaterials and amorphous material structures, whose surface is likely to be impurified with traces of water, hydroxyl groups, metals, ions, etc. The most efficient method to eliminate these impurities from the surface of oxidic structures or of amorphous material structures consists of treating the interest surfaces with acid mixtures (HNO 3 , H 2 SO 4 , H 3 PO 4 ) (Lucas et al, 2007). As a result of the acid treatments, part of the treated support structure is partially degraded, and the metals and metal ions are removed.…”