Adsorption of Organic Dyes on Magnetic Iron Oxide Nanoparticles. Part I: Mechanisms and Adsorption-Induced Nanoparticle Agglomeration

Abstract

This series of two papers is devoted to the effect of organic dye (methylene blue, MB; or methyl orange, MO) adsorption on the surface of either bare or citrate-coated magnetic iron oxide nanoparticles (IONPs) on their primary agglomeration (in the absence of an applied magnetic field) and secondary field-induced agglomeration. The present paper (Part I) is focused on physicochemical mechanisms of dye adsorption and adsorption-induced primary agglomeration of IONPs. Dye adsorption to oppositely charged IONPs is found to be mostly promoted by electrostatic interactions and is very sensitive to pH and ionic strength variations. The shape of adsorption isotherms is correctly reproduced by the Langmuir law. For the particular MB/citrated IONP pair, the maximum surface density of adsorbed MB seems to correspond to the packing density of an adsorbed monolayer rather than to the surface density of the available adsorption sites. MB is shown to form H-aggregates on the surface of citrate-coated IONPs. The effective electric charge on the IONP surface remains nearly constant in a broad range of surface coverages by MB due to the combined action of counterion exchange and counterion condensation. Primary agglomeration of IONPs (revealed by an exponential increase of hydrodynamic size with surface coverage by MB) probably comes from correlation attractions or π-stacking aromatic interactions between adsorbed MB molecules or H-aggregates. From the application perspective, the maximum adsorption capacity is 139 ± 4 mg/g for the MB/citrated IONP pair (pH = 4–11) and 257 ± 16 mg/g for the MO/bare IONP pair (pH ∼ 4). Citrated IONPs have shown a good potential for their reusability in water treatment, with the adsorption efficiency remaining about 99% after nine adsorption/desorption cycles.

From Adsorbent to Photocatalyst: The Sensitization Effect of SnO2 Surface towards Dye Photodecomposition

“…This parameter allows characterizing the agglomeration tendency of nanopowders in aqueous solutions [ 21 ]. Moreover, the analysis of d h values makes it possible to indirectly evaluate the adsorption behavior of powders towards various molecules, such as organic dyes [ 22 ]. Therefore, we conducted d h measurements in deionized water (DIW) and aqueous solutions containing dyes with a net positive/negative charge.…”

“…On the one hand, this may indicate the strong affinity of these samples for cationic dyes and therefore confirm the assumption based on zeta potential measurements. On the other hand, these higher values may be related to the agglomeration of nanoparticles induced by the adsorption of RhB [ 22 ]. According to Talbot et al [ 22 ], such agglomeration can affect the spatial distribution of dye molecules and, consequently, have an impact on adsorption equilibrium.…”

“…On the other hand, these higher values may be related to the agglomeration of nanoparticles induced by the adsorption of RhB [ 22 ]. According to Talbot et al [ 22 ], such agglomeration can affect the spatial distribution of dye molecules and, consequently, have an impact on adsorption equilibrium. This effect was also observed during our experiment.…”

Ferrofluids and bio-ferrofluids: looking back and stepping forward

“…However, their high sensitivity against changes of the pH-value of the carrier medium can easily lead to a complete destabilization of electrostatically stabilized ferrofluids, which could be a drawback both for engineering 39 and biomedical applications. 122 However, chemically induced destabilization of citric acid stabilized ferrofluids, followed by magnetic manipulation of clustered MNPs, 123 is possible to be the key for successful biotechnology applications, such as immunoassays, protein purification and, especially, water remediation. 124 Cationic methylene blue (MB) organic dyes as model pollutants added to citrate stabilized ferrofluids are adsorbed onto the IONP surface and reduce the repulsive interactions between them.…”

“…[742][743][744][745][746][747][748] Ferrofluids are used, by exploiting highly sensitive detection and imaging techniques based on nonlinear properties of nanomagnets or various liquid-phase adsorption/magnetic separation processes, to extract toxic and harmful analytes from different matrices. 123,124,[749][750][751][752][753] A ferrofluid-based biosensor for histamine detection in red wines is a combination of magnetic competitive lateral flow immunoassay strips and an inductive sensor using recombinant protein functionalized 10 nm mean size superparamagnetic iron-oxide NPs for the magnetic quantification of the toxic component. 754 The ferrofluid aided inductive biosensor was validated against ultrahigh-performance liquid chromatography analyses and proved to be successful as a histamine point-of-use analytical technique.…”