Binding of uranyl ion by 2,2′-dihydroxyazobenzene attached to crosslinked polystyrenes covered with highly populated quaternary ammonium cations

2,2′-Dihydroxyazobenzene (DHAB) derivatives were attached to poly(chloromethylstyrene-co-divinylbenzene) (PCD) because of the high affinity of DHAB for uranyl ion. Chloromethyl groups of PCD were converted to quaternary ammonium ions by treating them with tertiary amines. Two strategies were adopted to improve the uranyl-binding ability of the immobilized DHAB: (1) the creation of a highly cationic microenvironment around the DHAB moieties and (2) the introduction of electron-withdrawing groups to DHAB. Capacity of the resins for uranyl uptake was measured, revealing that about 10 to 46 mg of uranium could be complexed to 1 g of the resins. Formation constants (K_f) for the uranyl complexes of the resins were determined. In the presence of ≥0.02 M bicarbonate ion at pH 8.02, log K_f values of 14.3 to 15.8 were obtained. Uranium extraction from seawater with two kinds of resins prepared in this study was carried out on the east coast of the Korean peninsula. The amount of uranium extracted from seawater was up to 150 μg/g resin. Thus, the uranium-extracting capability of the DHAB-containing polystyrene resins was improved significantly by the structural modifications. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4117–4125, 1999     

Equilibrium constant for coordinative polymerization of an o,o′-dihydroxyazobenzene derivative with Ni(II) ion in water

Equilibrium constant (K_CP) for coordinative polymerization is measured for the first time. Constant K_CP is defined as [L]_cp/[M][L], where [L]_cp represents the concentration of the ligand present in the coordination polymer. Plot of absorbance changes measured for 3, a water-soluble derivative of o,o′-dihydroxyazobenzene, against the concentration of Ni(II) ion indicates formation of a 1 : 1-type complex in water at pH 7.74 and 25°C when Ni (II) is added in excess of 3. The 1 : 1-type complex can be either Ni 3, the monomeric complex, or (Ni 3 )_n, the coordination polymer. The equilibrium constant for formation of the 1 : 1-type complex is estimated as 10^13.10 by using UO₂²⁺ ion as the competing metal ion. For the Ni(II) complex of an o,o′-dihydroxyazobenzene derivative attached to poly(ethylenimine), the formation constant is estimated as 10^5.36. Due to the structure of the polymer, possibility of coordinative polymerization is excluded for the polymer-based ligand. The much greater equilibrium constant for formation of the Ni(II) complex of 3, therefore, indicates formation of (Ni 3 )_n instead of Ni 3. The value of K_CP for (Ni 3 )_n shows that only 10⁻⁷% of the initially added 3 is left unpolymerized when Ni(II) is added in excess of 3 by 10⁻⁴ M. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1825–1830, 1997     

Uranyl ion complexation of 2,2′-dihydroxyazobenzene enhanced on a backbone of poly(ethylenimine)

The formation constant (K_f) for the uranyl complex of 2,2′-dihydroxyazobenzene (DHAB) was measured with DHAB attached to poly(ethylenimine) (DHAB-PEI) at pH 7.7 to 9.4. The value of K_f was estimated from the equilibrium constant for extraction of uranyl ion from the uranyl complex of DHAB-PEI (UO₂DHAB-PEI) with carbonate ion, which in turn was measured from the absorbance change observed on addition of bicarbonate ion to the solution of UO₂DHAB-PEI. At pH 8.0, the uranyl-binding ability of DHAB was enhanced by about 10⁴ times on attachment of DHAB to PEI. The major origin of the increased ability of uranyl ion complexation is the basic local microenvironment of PEI, which encourages ionization of the phenol groups of DHAB. Various other possible origins are discussed also. The log K_f for DHAB-PEI at pH 8.0 indicates that DHAB moieties of DHAB-PEI are mostly occupied, whereas DHAB unattached to PEI is mostly unoccupied by uranyl ion under conditions of seawater when only the pH and concentrations of bicarbonate and uranyl ions of seawater are considered. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3936–3942, 1999     

Binding of uranyl ion by 2,2′-dihydroxyazobenzene attached to a partially chloromethylated polystyrene

A 2,2′-dihydroxyazobenzene (DHAB) derivative was attached to a chloromethylated cross-linked polystyrene derivative in view of high affinity of DHAB for uranyl ion. Chloromethyl groups of the resin were converted to quaternary ammonium ions by treating with tertiary amines. Capacity of the resins for uranyl-uptake was measured, revealing that about 20 mg of uranium can be complexed to 1 g of the resins. Formation constants (K_f) for uranyl complexes of the resins were determined. In the presence of >0.1 M bicarbonate ion at pH 8.10, log K_f of about 15 was obtained. As bicarbonate concentration was lowered, K_f decreased considerably. Degrees of uranyl-uptake from rapidly flowing uranyl solutions were measured, and the results suggested that rate of uranyl-uptake may not impose a major barrier to application of the resins in uranium extraction from seawater. Uranium extraction from seawater with the resins was carried out on the east coast of Korean peninsula. The amount of uranium extracted from seawater was about 10 µg/g resin. This is not satisfactory for economical processes of uranium recovery from seawater. Results of the present study, however, suggested that modification of the DHAB-containing resins can improve uranyl-binding ability, probably leading to economical recovery of uranium from seawater. In addition, simulation of uranyl-binding processes in seawater with the laboratory procedures developed in this study was satisfactory. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3169–3177, 1999