Magnetic vs. non-magnetic colloids – A comparative adsorption study to quantify the effect of dye-induced aggregation on the binding affinity of an organic dye

• Published in: Journal of colloid and interface science Vol. 481; pp. 20 - 27
• Main Authors: Williams, Tyler A., Lee, Jenny, Diemler, Cory A., Subir, Mahamud
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-11-2016
• Subjects: Adsorption isotherm; Aggregation detection; Magnetic nanoparticle; Nanotechnology; Pollution remediation; SHG spectroscopy; Magnetic nanoparticle; Pollution remediation; PSC; MP; SHG; m-PSC; Adsorption isotherm; Aggregation detection; MG; SHG spectroscopy; Nanotechnology
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2016.07.038

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Due to attractive magnetic forces, magnetic particles (MPs) can exhibit colloidal instability upon molecular adsorption. Thus, by comparing the dye adsorption isotherms of MPs and non-magnetic particles of the same size, shape and functional group it should be possible to characterize the influence of magnetic attraction on MP aggregation.
For a range of particle densities, a comparative adsorption study of malachite green (MG+) onto magnetic and non-magnetic colloids was carried out using a combination of a separation technique coupled with UV–vis spectroscopy, optical microscopy, and polarization dependent second harmonic generation (SHG) spectroscopy.
Significant MP aggregation occurs in aqueous solution due to MG+ adsorption. This alters the adsorption isotherm and challenges the determination of the adsorption equilibrium constant, Kads. The dye-induced aggregation is directly related to the MG+ concentration, [MG+]. A modified Langmuir equation, which incorporates loss of surface sites due to this aggregation, accurately describes the resulting adsorption isotherms. The Kads of 1.1 (±0.3)×107 and a loss of maximum MP surface capacity of 2.8 (±0.7)×103M−1 per [MG+] has been obtained. Additionally, SHG has been established as an effective tool to detect aggregation in nanoparticles.