The Effect of Hydrogen Bonding in Enhancing the Ionic Affinities of Immobilized Monoprotic Phosphate Ligands

Abstract

Environmental remediation requires ion-selective polymers that operate under a wide range of solution conditions. In one example, removal of trivalent and divalent metal ions from waste streams resulting from mining operations before they enter the environment requires treatment at acidic pH. The monoethyl ester phosphate ligands developed in this report operate from acidic solutions. They have been prepared on polystyrene-bound ethylene glycol, glycerol, and pentaerythritol, and it is found that intra-ligand hydrogen bonding affects their metal ion affinities. The affinity for a set of trivalent (Fe(III), Al(III), La(III), and Lu(III)) and divalent (Pb(II), Cd(II), Cu(II), and Zn(II)) ions is greater than that of corresponding neutral diethyl esters and phosphonic acid. In an earlier study, hydrogen bonding was found important in determining the metal ion affinities of immobilized phosphorylated polyol diethyl ester coordinating ligands; their Fourier transform infrared (FTIR) band shifts indicated that the basicity of the phosphoryl oxygen increased by hydrogen bonding to auxiliary –OH groups on the neighboring polyol. The same mechanism is operative with the monoprotic resins along with hydrogen bonding to the P–OH acid site. This is reflected in the FTIR spectra: the neutral phosphate diethyl ester resins have the P=O band at 1265 cm−1 while the monoethyl ester resins have the band shifted to 1230 cm−1; hydrogen bonding is further indicated by the broadness of this region down to 900 cm−1. The monoprotic pentaerythritol has the highest metal ion affinities of the polymers studied.

Synthesis of Eco-Friendly Biopolymer, Alginate-Chitosan Composite to Adsorb the Heavy Metals, Cd(II) and Pb(II) from Contaminated Effluents

“…The difference in the sorption of the two elements may regard the radius of hydrated species for each metal ion or softness. The ionic radius (Å) of hydrated species for Cd (II) and Pb(II) is around 0.95–0.96 Å [ 72 ] and 1.20 Å [ 73 ] respectively, while the softness of both metals ranged about +0.58 and +0.41 respectively. Other details about the diffusivity in water were shown in Table S7 [ 74 ].…”

Synthesis and adsorption characteristics of grafted hydrazinyl amine magnetite-chitosan for Ni(II) and Pb(II) recovery

“…The deprotonation of some reactive changing the preference of the sorbent for target metals through the effect of changes in the apparent softness of these reactive groups. Alexandratos and Zhu [73] reported the impact of acid base properties of a family of phosphate-based ligands on the affinity of sorbents for metal binding: this effect is modulated by the type(base metal vs. rare earth element) and charge of metal ions (divalent vs. trivalent).…”

Functionalized biobased composite for metal decontamination – Insight on uranium and application to water samples collected from wells in mining areas (Sinai, Egypt)

“…In addition to the specific ion-exchange properties of sulfonic groups (strong cationic exchanger), their presence increases the hydrophilic behavior of the sorbent [42]. Alexandratos and co-workers reported the criteria that can control the reactivity of sorbents [43][44][45]. More specifically, they pointed out the importance of the multifunctionality, the inter-and intra-ligand interactions, and the hydrophilic behavior for the design of efficient and selective sorbent.…”