Impact of Electrostatics on the Chemodynamics of Highly Charged Metal–Polymer Nanoparticle Complexes

• Published in: Langmuir Vol. 29; no. 45; pp. 13821 - 13835
• Main Authors: Duval, Jérôme F. L, Farinha, José Paulo S, Pinheiro, José P
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 12.11.2013
• Subjects: Cadmium - chemistry; Chemistry; Colloidal state and disperse state; Environmental Sciences; Exact sciences and technology; General and physical chemistry; Hydrogen-Ion Concentration; Latex - chemistry; Lead - chemistry; Nanoparticles - chemistry; Organometallic Compounds - chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Sciences of the Universe; Static Electricity; Surface Properties; Temperature; Metal complex; Polymer; Nanoparticle; Electrostatics; STRIPPING CHRONOPOTENTIOMETRY; ELECTROKINETIC PROPERTIES; DEPOSITION POTENTIAL SSCP; SUSPENSIONS; COLLOIDAL LIGAND DISPERSIONS; ELECTROPHORETIC MOBILITY; NETWORK METHOD; SOFT PARTICLES; SPECIATION DYNAMICS; BIOAVAILABILITY
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la403106m

In this work, the impact of electrostatics on the stability constant, the rate of association/dissociation, and the lability of complexes formed between Cd(II), Pb(II), and carboxyl-modified polymer nanoparticles (also known as latex particles) of radius ∼ 50 nm is systematically investigated via electroanalytical measurements over a wide range of pHs and NaNO3 electrolyte concentrations. The corresponding interfacial structure and key electrostatic properties of the particles are independently derived from their electrokinetic response, successfully interpreted using soft particle electrohydrodynamic formalism, and complemented by Förster resonance energy transfer (FRET) analysis. The results underpin the presence of an ∼0.7–1 nm thick permeable and highly charged shell layer at the surface of the polymer nanoparticles. Their electrophoretic mobility further exhibits a minimum versus NaNO3 concentration due to strong polarization of the electric double layer. Integrating these structural and electrostatic particle features with recent theory on chemodynamics of particulate metal complexes yields a remarkable recovery of the measured increase in complex stability with increasing pH and/or decreasing solution salinity. In the case of the strongly binding Pb(II), the discrepancy at pH > 5.5 is unambiguously assigned to the formation of multidendate complexes with carboxylate groups located in the particle shell. With increasing pH and/or decreasing electrolyte concentration, the theory further predicts a kinetically controlled formation of metal complexes and a dramatic loss of their lability (especially for lead) on the time-scale of diffusion toward a macroscopic reactive electrode surface. These theoretical findings are again shown to be in agreement with experimental evidence.