Are Keggin’s POMs Charged Nanocolloids or Multicharged Anions?

Autor: Alla Malinenko, Olivier Diat, Sandra Parrès-Maynadié, Alban Jonchère, Luc Girard, Pierre Bauduin
Přispěvatelé: Ions aux Interfaces Actives (L2IA), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Etude de la Matière en Mode Environnemental (L2ME)
Rok vydání: 2018
Předmět:
Zdroj: Langmuir
Langmuir, American Chemical Society, 2018, 34 (5), pp.2026-2038. ⟨10.1021/acs.langmuir.7b03640⟩
ISSN: 1520-5827
0743-7463
DOI: 10.1021/acs.langmuir.7b03640
Popis: International audience; Owing to their multiple charges and their nanometric size polyoxometalates (POMs) are at the frontier between ions and charged colloids. We investigated here the effect of POM-POM electrostatics repulsions on their self-diffusion in water by varying POM and supporting salt concentrations. The self-diffusion coefficients of two Keggin’s POMs: silicotungstate (SiW12O404-) and phosphotungstate (PW12O403-) were determined by dynamic light scattering (DLS) and DOSY 1H/31P NMR whereas POM-POM electrostatic repulsions were investigated by the determination of the static structure factors using small angle X-ray scattering (SAXS). The self-diffusion coefficients for the two POMs and for different POM/background salt concentrations were collected in a master curve by comparing the averaged POM-POM distance in solution to the Debye length. As for “classical” charged colloids, we show that the POM’s counterions should not be considered in the calculation of the ionic strength that governs POM-POM electrostatic repulsions. This result was confirmed by fitting the POM-POM structure factor by considering a pair potential of spherical charged particles using the well-known Hayter mean spherical approximation (MSA). These Keggin’s POMs also behave as (super-)chaotropic anions, i.e. they have a strong propensity to adsorb on (neutral polar) surfaces, was also investigated, here on the surface of octyl-beta-glucoside (C8G1) micelles. The variations of (i) the chemical shift of 1H/31P NMR signals and of (ii) the self-diffusion coefficients obtained by DOSY 1H/31P NMR of PW3- and of C8G1 were in good agreement, confirming the strong adsorption of POMs on the micelle polar surface on a static and a dynamic point of view. We concluded that Keggin’s POMs behave (i) as anions, because they adsorb on surfaces as chaotropic anions do, as well (ii) as colloids because they can be described by a classical colloidal approach by dynamic and static scattering techniques, i.e. by the investigation of their inter-particle electrostatic structure factor and self-diffusion without considering the POM’s counterions in the ionic strength calculation.This work highlights the dynamic properties of POMs at soft interfaces, compared to bulk aqueous solution, which is essential in the understanding of functional properties of POMs, such as (photo)-catalysis or in the rational design of POM-based hybrid nano-materials from soft templating routes i.e. in aqueous solutions at room temperature.
Databáze: OpenAIRE
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