Acid−Base Properties of Synthetic and Natural Polyelectrolytes: Experimental Results and Models for the Dependence on Different Aqueous Media

Abstract

Protonation constants of several natural and synthetic humates and fulvates were determined by ISE-H+ potentiometry in different ionic media (alkali metal halides and tetraethylammonium iodide) at different ionic strengths and T = 298.15 K. Experimental data obtained in previous studies of different synthetic (polyacrylates, polymethacrylates, polyacrylate-co-maleate) and naturally occurring (alginate, humic substances) polycarboxylates were also taken into account in the general analysis of acid−base properties of polyelectrolytes. Protonation constants were expressed as a function of the dissociation degree (α) using three models, namely, a simple linear model, the Högfeldt three-parameter equation, and the modified Henderson−Hasselbalch equation. Moreover, a model, independent of α, according to which acid−base properties of polyelectrolytes in the whole acidic pH range can be described by two protonation constants (Diprotic-like model), was also tested. This model allows us to analyze protonation and complex formation data as for simple low molecular weight ligands. In general, all the models taken into consideration give satisfactory results with fitting errors in the order Högfeldt three-parameter equation < Diprotic-like model < modified Henderson−Hasselbalch equation < simple linear model. For each type of polyelectrolyte investigated, a detailed discussion is reported. The parameters involved in the different models are strictly correlated, and canonical correlation analysis is reported. A statistical analysis on the protonation constants of all the polyelectrolytes investigated was made confirming that very similar results can be obtained using any considered model and, as a consequence, that the Diprotic-like model is a valid alternative simple approach to study acid−base properties of polyelectrolytes.

Interaction of Natural Organic Matter with Layered Minerals: Recent Developments in Computational Methods at the Nanoscale

“…This is an important finding in the development of specific organic-mineral FF parameters, and it is consistent with experimental results showing that metal complexation behavior in NOM is similar to well-characterized polymers with similar functionalization [109][110][111][112][113]. The fact that different organic FF parameters yield similar structural and energetic properties for surface complexes indicates a very broad energy minimum for such complexes.…”

Stability of core/shell quantum dots—role of pH and small organic ligands

“…2). The different binding capacity at both pH values is explained by the dissociation constants of the PAA reported in the literature; pK a,1 =4.8-5.4, and pK a,2 =6.5-7.5 extrapolated to I=0 M at 25°C for PAA with molecular weights from 2 to 750 kDa (Katchalsky 1954;Hogfeldt et al 1989;de Stefano et al 2000de Stefano et al , 2003David et al 2008;Crea et al 2009;de Stefano et al 2010). Accordingly with these values the largest dissociation degree of the PAA, and, therefore, the largest binding capacity for Cd would be expected at pH 8.5.…”

Enhancement of adsorption ability of calcium alginate gel beads towards Pd(II) ion. A kinetic and equilibrium study on hybrid Laponite and Montmorillonite–alginate gel beads

“…In particular, calcium alginate (CA) gel beads have been recently used to remove Pd(II) ion from NaCl aqueous solutions in the pH range of 2-5 and in the ionic strength range of 0-0.01 mol L −1 (Cataldo et al, in press). The choice of these restricted experimental conditions was done on the basis of some considerations: (i) a sufficient part of carboxylate groups of alginate must be deprotonated and available to bind positively charged species of palladium(II) (Crea et al, 2009), (ii) palladium(II) undergoes hydrolysis at very low pH and the formation of sparingly soluble hydrolytic species at higher pH than 2 can be avoided and translated up to pH = 5 in presence of chloride ions, which form with Pd (II) quite stable and soluble species (Gianguzza et al, 2010), (iii) the chosen pH range and chloride medium are typical of many industrial wastewaters and electronic scrap leachates, as well as the leaching solution obtained in one of the classical procedures used to selectively dissolve PGE from waste materials like, e.g. spent automotive catalysts (Nikoloski et al, 2015).…”