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This report introduces a multi-part study on determining the fundamental mechanisms by which a range of phosphorus-based ligands bind metal ions. FTIR spectroscopy is utilized to propose the mechan...

Water is essential to human health and economic development due to its utilization in sanitation, agriculture, and energy. Supplying water to an expanding world population requires simultaneous consideration of multiple societal sectors competing for limited resources. Water conservation, supply augmentation, distribution, and treatment of contaminants must work in concert to ensure water sustainability. Water is linked to other sectors, and the quantity and quality of water resources are changing. The efficient use of water in agriculture, the largest user of water worldwide, via drip irrigation is described as is the use of energy-intensive reverse osmosis to supplement freshwater supplies. Efforts to manage watersheds and model their responses to severe weather events are discussed along with efforts to improve the predictability of their function. The regional competition for water resources impacts both energy and water supply reliability, which requires that nations balance both for sustainable econ...

ATR-FTIR spectroscopy is shown to be useful in probing metal ion binding to ligands immobilized on polymer beads. Lu(III) is the metal ion, phosphinic and sulfonic acids are the immobilized ligands, and polystyrene beads crosslinked at low and high levels are the support. Analysis is based on ligand band positions and intensities before and after complexation as a function of time. ATR spectra of the phosphinic acid show two types of binding sites with different accessibilities: surface ligands that bind Lu(III) from solution and interior ligands that gain ions by diffusion from the surface. Initially bound Lu(III) ions are mobile within the solid phase and their movement is accompanied by the breaking of hydrogen bonds among the phosphinic acid ligands to form Lu(III) phosphinate complexes. Competition between hydrogen bonding and bond-making with Lu(III) contributes to slow sorption rates compared to results from the sulfonic acid ligand whose strong acidity and ionizability allows rapid Lu(III) sorption. Comparing ATR spectra of the phosphinic acid bound to lightly- and highly-crosslinked polystyrene shows how the extent of crosslinking affects the transport mechanism.

The binding of trivalent metal ions to immobilized ligands is analyzed to determine the principal type of interaction, the extent of ion exchange, and changes due to through-bond communication. FTIR spectroscopy is found to be a readily accessible means of determining through-bond communication and spectra provide support for a molecular level interpretation of the interaction. The affinity of the phosphinic acid ligand for Al(III), La(III), Lu(III), Fe(III), and In(III) is quantified with distribution coefficients from 0.01–6 M nitric acid solutions. High affinities are evident with In(III) > Fe(III) > Lu(III) > La(III) > Al(III). The affinities correlate with the softness parameter and thus the polarizability of the metal ion. The FTIR spectrum of the phosphinic acid has two incompletely separated bands at 1168/1126 cm−1 associated with the P O bond and two similar bands at 967/951 cm−1 due to the P O(H) bond. The bands at 1168/951 and 1126/967 cm−1 are assigned to different hydrogen bonded conformers within the metal-free polymer. Through-bond communication is evident as the extent of metal ion binding increases: the P O and P O bands at 1168 and 951 cm−1, respectively, collapse into a single band between 1040 and 1080 cm−1 representative of PO2(M) while hydrogen bonding among unexchanged P(O)OH ligands gives the bands at 1133 and 981 cm−1.

Ion exchange is an elegant concept whose simplicity has allowed a wide range of applications in separations (e.g., water treatment, chromatography, radiochemistry, food processing), catalysis and synthesis. The objective of this Perspective is to map its origin and present status, then propose a trajectory into the future. This is addressed with data mined from the open literature as reported in the Web of Science Core Collection (Clarivate Analytics) via a search of the keyword “ion exchange” for the period 1900–1960, then narrowed to 1941–1960, followed by subsequent 20-year periods to the present day. Data are sorted into the top ten WoS Categories, Research Areas, Publication Titles and Countries, then further defined with additional keywords. Interest in ion exchange was found to be constant across the vicennial periods as the number of references kept pace with growth in the chemical (open) literature. The period to 1960 had 1213 references with chemistry the dominant area (60.9%) and engineering at only 4.5% of the papers; resins were the dominant material with membranes a distant second. The period 1961–1980 had 5175 references with chemistry retaining its top ranking but engineering significantly increasing; resins and membranes were the primary materials while separations dominated and catalysis barely registered. There were 21,901 references in 1981–2000 with environmental science appearing as a research area for the first time; resins ended the century as they began – the primary material – but by a small margin over membranes. The 21st century (2001−2020) began with 52,187 references, chemistry held steady compared to the preceding period while engineering and materials science increased significantly and environmental science doubled its percentage, joined by water resources; membranes continued their upward trend, surpassing resins. Output from China increased to outperform the USA. In the last three years of that period, environmental science made a stronger showing and energy fuels replaced biotechnology. In comparing the vicennial periods, the rise of engineering, materials science and ecology combined with water was impressive. In comparing Research Areas in the initial period with those from the latest, it is seen that chemistry fell from 61% to 41% while engineering increased from 4% to 25%. Applications were more likely to involve membranes. Separations remained steady from the initial to the current period while catalysis moved equal to them, Examining the most cited papers in the latest period shows an emphasis on metal-organic frameworks, tailored materials, membranes for energy and environmental applications, and to an array of applications in environmental remediation. Ion exchange is applied as a preparative technique in, for example, batteries, photocatalysts, electrocatalysts, supercapacitors, and perovskite nanocrystals. Ion exchange is thus poised to continue well into the 21st century. It has flourished by its ability to adapt. As the analysis of the literature shows, it will continue to flourish.

Aminomethylphosphinic acid (AMPA) is immobilized onto cross-linked polystyrene beads and found to have a high affinity for the uranyl ion, especially from solutions as acidic as 6 M H3PO4. The trend in uranyl affinity by different ligands is AMPA > phosphinic > phosphonic > sulfonic. For example, the percent sorbed from 6 M H3PO4 is 89.5% (AMPA), 44.8% (phosphinic), 5.38% (phosphonic), and 2.60% (sulfonic). The high affinity shown by AMPA is due to the decreased hydrogen bonding in the phosphinic acid ligand as well as synergistic coordination of the uranyl ion by a proximate P=O of a second phosphinate ligand. AMPA contacted with synthetic wet process phosphoric acid solution sorbed 72.2% uranium compared to 0.14% for a commercially available sulfonic acid.

Bifunctional amidoxime fibers are synthesized from commercially available polyacrylonitrile as sorbents for the recovery of U(VI) from seawater. The purpose of introducing a second ligand is to enhance the affinity of the amidoxime (AO) ligand via two possible mechanisms: by acting directly upon the AO to increase its ability to ion exchange or providing additional coordination sites to the uranyl ion. Amines are chosen as the second ligand since they have a high affinity for U(VI) at ppm levels from synthetic seawater. Diethylenetriamine (DETA) is utilized as the amine because it is sufficiently flexible to interact with AO and able to bind metal ions. Along with AO and AO-DETA fibers, the primary NH2 moieties were modified with phosphonic acid ligands (AO-phon-DETA). All fibers have high affinities (>99% sorption) for the uranyl ion when initially present at 0.90 ppm in synthetic seawater. When contacted with actual seawater at the Pacific Northwest National Laboratory for 20.8 days, the loadings for th...

A polymer-bound monoprotic phosphoric acid ligand was developed for the sorption of U(VI) from 0.10 to 6.0 M phosphoric acid solutions. The ligands reported are new phosphorylated mono- and triethylene glycol ethyl esters (pEG1M and pEG3M) prepared by combining diethylchlorophosphate and 4-dimethylaminopyridine; they ion exchange through the acid site and coordinate through the phosphoryl oxygen. The binding mechanism is probed by comparing their results to coordinating phosphorylated mono- and triethylene glycol diethyl esters (pEG1 and pEG3) and the diprotic phosphonic acid (DPA) that operates by ion exchange. The affinities for Lu(III), La(III), Fe(III) and Al(III) were also determined. All metal ions were sorbed much more efficiently by the monoprotic ligand relative to the diprotic and coordinating ligands. It is proposed that a decrease in inter-ligand hydrogen bonding within the monoprotic ligand is responsible for the increased metal ion affinities. This is consistent with the FTIR spectra wherein the P=O band appears at 1262 cm−1 for pEG1 and this shifts down to 1229 cm−1 in pEG1M and 1180 cm−1 for DPA. Incorporating ether oxygen into the ligand further enhances metal affinities: pEG3M with three oxygen donors adjacent to the monoprotic site shows the highest affinity for metal ions. The increased affinities compared to pEG1M are due to complexation by the weakly binding ether oxygen donors. High metal ion affinities thus require both ion exchange with acidic protons and coordination with neutral donors. More rapid kinetics evident with pEG3M relative to DPA is further evidence for decreased hydrogen bonding which permits more rapid sorption. The affinity orders of the three acidic polymers are similar: U(VI), Lu(III)>Fe(III) >La(III)>Al(III). Ligand strength is pEG3M>pEG1M>DPA>pEG3>pEG1.

The rational design of sensors, solid phase extractants, and cross-linked polymers for environmental remediation requires a pairing of the electronic properties of a targeted metal ion with a given ligand. Polarizability is a key property and values for metal ions have been tabulated. It is now proposed to evaluate ligand polarizabilities by their affinities for Au(III) and Eu(III) as representative soft and hard metal ions. This report centers on: phosphonate diethyl ester (PDE); pentaerythritol diethyl phosphate (pPenta); diprotic phosphonic acid (DPA); phosphinic acid (PA); pentaerythritol monoethyl phosphate (pPentaM); glycerol monoethyl phosphate (pGlyM); and ethylene glycol monoethyl phosphate (pEG1M). Results show that hydrogen bonding is an additional variable that is superimposed on the affinities observed when ion exchange sites are introduced into ligands. PDE and pPenta are classified as soft ligands since they have a high affinity for Au(III) and a low affinity for Eu(III). DPA has a significant affinity for Au(III) and Eu(III) from less acidic solutions which indicates that the phosphoryl oxygen remains soft but intra- and inter-ligand hydrogen bonding cause a loss in both coordinating and ion exchange strength. Changing from a diprotic to a monoprotic acid decreases hydrogen bonding and increases metal ion affinities as indicated by results with PA, which has a high affinity for Au(III) via coordination to the PO and Eu(III) via ion exchange at the P–OH. FTIR spectra support the change in hydrogen bonding. Monoprotic pPentaM is an alternative with decreased hydrogen bonding and it has high affinities for both Au(III) and Eu(III). The FTIR spectrum for pPentaM exchanged with Eu(III) confirms ion exchange by an hypsochromic shift of 25 cm−1 for the P–O band. The ability to tune metal ion affinities with hydrogen bonding is promising for the design of new ligands.

This is the first of a series of reports that probes the polarizabilities of different immobilized ligands in order to build toward a rational design of ion-selective polymer-supported reagents. In this report, the polarizabilities of four ligands on a polystyrene backbone (phosphorylated ethylene glycol (pEG1), ethylene glycol (EG1), sulfonic acid, and dimethylamine (DMA)) are evaluated with Au(III) and Eu(III) as representative of soft and hard ions, respectively. Interactions are followed by the extent of sorption, the effect of acid concentration, band shifts in FTIR spectra, and Langmuir plots. The phosphoryl oxygen, hydroxyl OH, and amine show an affinity of Au(III) > Eu(III) while Eu(III) > Au(III) is evident with the sulfonic acid. The P O stretching frequency shifts from 1263 to 1249 cm−1 upon Au(III) binding. The affinities indicate that oxygen can be considered soft and hard, depending on its microenvironment: neutral oxygen is soft while anionic oxygen may be classified as hard. Though Eu(III) prefers ionic binding with a strong acid ligand, it is also capable of weak binding with a neutral oxygen donor at pH 3 and 4. Sorption is affected by solution acidity despite the absence of ion exchange. Three routes to enhancing ion–interactions thus emerge: preparing single-site ligands whose polarizability matches the targeted metal ion, preparing ligands with multiple binding sites each of which bind weakly on their own, and preparing single-site ligands with dual ion exchange/coordination character.

A tetramethylmalonamide-functionalized resin (TMMA resin) has been developed and investigated for its ability to separate trivalent, tetravalent, and hexavalent actinide elements. As a fundamental study of the extraction mechanism and to design a chromatographic separation scheme, distribution coefficients (K d) for partitioning of Eu(III), Th(IV), U(VI), and Am(III) onto the resin from HNO3, NaNO3, HCl, and NaCl solutions have been determined. The partitioning of HNO3 onto the resin was also evaluated. The order of the K d values was Th(IV) > U(VI) > Am(III) = Eu(III) in all tested solutions. The competition between metal extraction and HNO3 extraction was confirmed by the extraction data and FT-IR spectra. The loading capacities of Eu(NO3)3 and UO2(NO3)2 at 3 M HNO3, determined by a dynamic method with TMMA resin (TMMA in the resin was 2.05 mmol/g), were 0.83 mmol/g and 1.6 mmol/g, respectively, implying that M:TMMA stoichiometry was 1:2 for Eu(III) and 1:1 for U. Because the K d values for Th(IV) and U...

The primary amine −CH2NH2 ligand bound to cross-linked polystyrene has a high affinity for the uranyl ion from a matrix of artificial seawater. The uranyl capacity is 14.8 mg U/gpolymer, compared to 2.34 mg U/gpolymer for a diamidoxime ligand on a polystyrene support. Secondary and tertiary amines have much lower affinities, indicating that steric effects are important to the complexation. The results with polystyrene-bound −CH2NH2 thus suggest at least a 3-fold increase in uranyl capacity (calculated on a per mole ligand basis (not per gram of polymer, in order to make the results independent of the weight of the polymer support)) and a 4-fold increase when ligands with two primary amines per ligand are utilized. An additional advantage of the primary amine over amidoxime is that it is a simpler ligand to prepare.

The synthesis and arsenic-removal properties of nanocomposite ion-exchange resins based on N -methyl- d -glucamine groups are presented. First, the N -methyl- d -glucamine-based monomer was synthesised by reaction of 4-vinyl benzyl chloride and N -methyl- d -glucamine and was subsequently polymerised by in situ radical polymerisation in the presence of organic modified montmorillonite (as filler) and N , N -methylene- bis -acrylamide as crosslinker reagent. The nano-composite presented an intercalated morphology, and montmorillonite was dispersed at the nano-level, confirmed by X-ray diffraction and transmission electron microscopy. Arsenate sorption properties were evaluated as a function of pH, initial arsenic concentration, maximum retention capacity, and in the presence of interfering anions, such as phosphate and sulphate. The nano-composite presented high arsenic sorption efficiency, reaching final concentrations below the recommendation of the World Health Organization, even in the presence of interfering anions. Equilibrium sorption results are well described by Langmuir isotherms, and the sorption capacities were approximately 55 mg As/g resin. Finally, retention experiments were carried out using a real sample taken from the Camarones River in northern Chile.

Hydrogen bonding has been proposed as the triggering mechanism for the sorption of lanthanide ions by polymer-supported tetramethylmalonamide (TMMA) and diethylenetriamine (DETA) – substituted malonate ester. In the current study, DETA was immobilized onto cross-linked poly(vinylbenzyl chloride), converted to the urea, and its affinity determined for lanthanide ions from solutions of 2–8 M HCl. Lanthanide affinities significantly increase when the acid concentration exceeds 4 M. The site at which sorption occurs forms after protonation of the carbonyl, stabilization by hydrogen bonding to the interior nitrogen and resultant formation of an iminium ion. This is consistent with the mechanism proposed for the amide polymers. TMMA has the weakest affinities for Ln(III) ions yet is most selective due to attenuation of the (+) charge at the iminium site by two electron-donating methyl groups (=NR 2 (+)); DETA-malonamide (MAm) has higher Ln(III) affinities than TMMA but is less selective because the iminium has only one –CH 2 - moiety attenuating the (+) charge (=NHR(+)); the urea also forms a secondary iminium but its higher basicity makes its iminium more positively charged than that in DETA–MAm and therefore a stronger ligand. The urea has the highest affinities and is unique in having the lanthanide distribution coefficients correlate with the sum of the first, second and third ionization energies. The implication of this for the sorption mechanism is discussed.

Pentaerythritol bonded to cross-linked poly(vinylbenzyl chloride) beads (PE) provides a scaffold onto which ligands can be attached by reaction with reactive compounds such as phosphoryl halides. To broaden the applicability of PE for the preparation of ion-selective polymers, conditions are reported for the conversion of the hydroxyl group to the bromide, which acts as a better leaving group. The CH2Br moiety thus provides a handle on which an array of ligands can be bound through nucleophilic substitution. In this first in a series of reports, immobilization of diethylamine onto the PE and the ion-binding affinities of the resulting polymer are described. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

In a series of phosphorylated polyols bound to a polystyrene support, the position of the FTIR band assigned to hydrogen bonding between the —OH and phosphoryl oxygen correlates with the affinity of that phosphoryl oxygen for metal ions. Polymer with phosphorylated β-cyclodextrin (pCD) ligands is now reported as a further test of this correlation. The metal ion affinity is probed with the uranyl ion. pCD is the most red-shifted of a series of five phosphorylated polyols: the strongest polyol had been phosphorylated pentaerythritol (pPE) with a band at 873 cm ―1 ; pCD has a band at 868 cm . Consistent with the FTIR bands, pCD has a significantly higher affinity for the uranyl ion than pPE: the percents complexed from a 10 ―4 M uranyl solution in a background of 1.0N HNO 3 , HCl, and H 2 SO 4 are 94.7%, 90.5%, and 93.6%, respectively, for pCD and 68.6%, 52.1%, and 40.1%, respectively, for pPE. This further supports the hypothesis that the strong complexing ability of phosphorylated polyols is due to activation of the phosphoryl oxygen through hydrogen bonding between the P=O and the —OH groups within the polyol.

Polymer-bound malonate ligands modified with diethylenetriamine (DETA-MAm) are prepared and the lanthanide ion affinities from solutions of 0.001–8 M HCl are quantified. A mechanism is proposed. The affinities are not due to the triamine ligand alone or the adjacent carbonyl sites alone: protonation of the carbonyl oxygen triggers formation of an iminium ion and it acts as an ion-exchange site. Two competing reactions occur during binding: electrostatic attraction of [Ln(H 2 O) x Cl 4 ] − by the protonated ligand and (partial) loss of the waters of hydration. The affinity and selectivity are affected by substituents on the iminium (C NRR′(+)) ion. Research with tetramethylmalonamide showed that its two methyl groups at the iminium site weaken the positive charge and decrease its affinity for the chlorocomplexes of the later lanthanides; DETA-MAm has at its amide nitrogen only one −CH 2 − (and one H) moiety and therefore is a stronger but less selective ligand since electrostatic attraction is more dominant in the overall mechanism. The higher affinities of malonate monoamidated with ethylenediamine (EDA-MAm) and decreased affinities for those amidated with ethanolamine (EA-MAm) suggest that the protonated –NH– stabilizes the lanthanide chlorocomplex.

Polymer-supported reagents are widely employed in the complexation of metal ions for applications in separations science, organic reactions (as catalysts) and in analytical chemistry (for processes requiring metal ion enrichment, detection and quantification). Various strategies for the continued development and optimization of polymer-supported reagents have evolved. This review cites ways in which polymer-supported reagents can be designed to achieve improved metal ion selectivities from the viewpoint of the mechanisms involved in the complexation of transition metal ions from aqueous solutions.

Composites of hydroxyapatite (HAP) and organic compounds have been prepared for biomedical applications. These same composites may be applicable to environmental remediation. The organic compounds used for modification include organic acids, calcium chelating agents, proteins, compounds capable of ring-opening polymerization, and hydrophobic silicon-containing molecules. The methods for modification that have been studied are co-precipitation and post-HAP particle formation. It is proposed that modified-HAP (mHAP) could have enhanced metal ion selectivities. The techniques used to synthesize mHAP are reviewed.

A silicate-selective polymer-supported reagent has been developed that utilizes the reactivity of silicate to generate polyanionic Keggin structures. Heptamolybdate and heptatungstate anions are immobilized onto trimethylammonium ligands bound to microporous poly(vinylbenzyl chloride) beads. The heptamolybdate complexes >90% of the silicate from a 20 ppm solution at pH 7; the heptatungstate has a lower affinity, complexing 40% of the silicate. Complexation by the heptamolybdate remains high throughout the pH range 3.8–10.7. Sorption is unaffected by the presence of chloride, sulfate, and nitrate ions. The apparent rate of reaction is maximized by immobilizing the ligand on an expanded gel support: whereas the microporous polymer requires 24 h to complex all of the silicate from a 100 ppm solution, the expanded gel attains that level in 4 h. The rate-limiting step is thus identified as accessibility of the silicate to the heptamolybdate rather than the rate of reaction to form the silicomolybdate. FTIR spectra confirm silicomolybdate formation: The heptamolybdate polymer has four characteristic bands at 715, 845, 912 and 945 cm −1 and these bands get weaker as silicate reacts with the heptamolybdate; at complete reaction, the band at 845 cm −1 disappears. The spectrum of the silica-saturated polymer has strong bands at 900–904 cm −1 and 790–800 cm −1 , consistent with the spectrum of tert-butylammonium silicododecamolybdate.

Ion-exchange resins comprise one of the most important scientific developments of the 20th century. Their applicability to water softening, environmental remediation, wastewater treatment, hydrometallurgy, chromatography, biomolecular separations, and catalysis was recognized in numerous publications. The principle of covalently bonding ligands to cross-linked polymer networks became the basis for the area of polymer-supported reagents. The journal Industrial & Engineering Chemistry Research and its predecessors have published some of the most important papers in this field. In celebration of its 100th anniversary, this review provides a retrospective of ion-exchange resins through publications appearing in this journal.

In developing ion-selective polymer-supported reagents, the inherent affinity of a given ligand for a targeted metal ion is found to be affected by auxiliary groups on a scaffold. A series of polyols (ethylene glycol, glycerol, tris(hydroxymethyl)ethane, pentaerythritol, and pentaerythritol triethoxylate) are immobilized onto cross-linked poly(vinylbenzyl chloride), then monophosphorylated. The pentaerythritol, glycerol, and pentaerythritol triethoxylate polymers have the highest affinities for both trivalent and divalent ions. The distribution coefficients of divalent ions (Pb(II), Cd(II), Cu(II), Ni(II), and Zn(II)) correlate with the Misono softness parameter, reflecting a single-site interaction between the metal ion and the phosphoryl oxygen. The distribution coefficients for trivalent ions are in the order Fe(III)Al(III)Y(III) less, approximatelyLa(III) approximately Eu(III) approximately Lu(III). For example, the phosphorylated pentaerythritol polymer has distribution coefficients (also reported as percent complexed) for Fe of 68.4 (75.3%); for Al of 182 (88.5%); and for the rare earth ions Y, Lu, Eu, and La of 374 (94.4%), 1390 (98.4%), 1690 (98.4%), and 708 (96.9%), respectively, from solutions at pH 2.0. The opposite trend (i.e., Fe(III)Al(III)(rare earths)) correlates with their hardness, acidity, electron affinity, electronegativity, and formation constants with soluble complexants, including tributyl phosphate. A binding mechanism is proposed wherein the polymer initially has the auxiliary -OH groups hydrogen-bonded to the phosphate ligand; then, binding to the polarizable phosphoryl oxygen with the divalent ions dominates, while the trivalent ions are drawn closer to the phosphoryl oxygen because of their greater charge and, once closer, bind in a multisite interaction with both the phosphate and -OH groups.

The measurement of mercury in aqueous solutions by ICP-AES is adversely affected by the memory effect wherein mercury accumulates within the sample introduction system and is slowly released over time to give increasing response signals at the same initial mercury concentration. The memory effect is obviated by the addition of Hg(II) complexants: thiourea and gold(III) chloride are both effective in preventing mercury sorption and vapor buildup with the latter being preferred because the memory effect vanishes more rapidly. Conditions are described wherein it is possible to quantify low levels of mercury(II) in aqueous solutions by ICP-AES under routine operating conditions that can be applied to other metal ions by adding 1 mg of gold(III) chloride per 3 mg of mercury(II) to those solutions.

The complexation of uranium(VI) by polymer-supported phosphonate and phosphate diester ligands has been studied in acid solutions up to 4 N. Hydroxy groups proximate to the phosphoryl oxygen increase its basicity which enhances uranium(VI) sorption, particularly in low acid solutions. The mechanism of complexation entails coordination of UO 2 2 + in low acid solutions and anion exchange of UO 2 X n − in high acid solutions. Counterions affect the complexation, especially as solution acidity increases, with uranium distribution being preferred in the order HNO 3 > HCl > H 2 SO 4 . The different behavior of the counterions is due to their free energies of hydration.

Amine ligands (-CH2NR2, where R = H, CH3, or CH2CH2OH) immobilized on cross-linked polystyrene beads have a high affinity and selectivity for Hg(II) from aqueous solutions. The high affinity is dependent on solution pH and the background acid (HNO3 or HCl). There is no affinity for Pb(II), Cu(II), Cd(II), Zn(II), and Ca(II) cations from solutions up to pH 3.5; high background levels of NO3-, Cl-, and SO42- anions do not affect complexation of Hg(II) by the resins. Key results include the following: (1) simple monoamines have a high affinity for Hg(II); (2) tertiary amines have a higher affinity than the primary amine resin; (3) electron donors on the nitrogen allow for high levels of Hg(II) complexation but the trend is affected by the counterion in solution; and (4) linear correlations in the log−log plot of the distribution coefficient and solution acidity with a slope of 0.6−0.8 from HNO3 and 1.3−1.5 from HCl suggest that Hg(II) uptake occurs through ion exchange and coordination with Hg(II) speciatio...

N-Methyl-d-glucamine (NMDG) immobilized onto cross-linked poly(vinylbenzyl chloride) beads is found to have a high affinity and selectivity for Hg(II) from nitric and hydrochloric acid solutions. In HNO3, complexation is >98% from a solution at pH 3, which decreases to 11.2% from 1 M HNO3. Hg(II) is complexed to a greater extent from HCl: 95.4% is complexed from 1 M HCl and >99.5% from solutions at pH 1.0 and greater. Control studies with immobilized sorbitol show that coordination of Hg(II) by the -OH groups is an important component of the mechanism. Complexation by sorbitol is dependent on the pH. Log−log plots of the distribution coefficients versus the hydrogen ion concentration at equilibrium show the importance of the changing nature of the solution species: since ion exchange is not mechanistically possible with sorbitol, the pH dependency reflects the effect of pH on shifting the species in solution from noncoordinating Hg(NO3)42- and HgCl42- to coordinating Hg(NO3)+ and HgCl2. Comparison to re...

The immobilization of octamethyl-14-crown-4 onto crosslinked polymer supports is reported and the selectivity for Li(I) from aqueous solutions quantified. The amount of Li(I) complexed by the crown ether is affected by the polarity of the polymer matrix: Complexation increases with increasing matrix hydrophilicity. Poly(glycidyl methacrylate) is the preferred support matrix for the crown ether.

A series of coordinating polymers are synthesized by immobilizing polyols (ethylene glycol, glycerol, 1,1,1-tris(hydroxymethyl)ethane, pentaerythritol, and pentaerythritol triethoxylate) onto cross...

Solvent impregnated resin (SIR) beads with bis(2‐ethylhexyl)hydrogen phosphate (DEHPA) as the complexant have been coated with a semi‐permeable membrane consisting of poly(glycidyl methacrylate‐co‐N,N′‐methylene‐bis(acrylamide)). The coated SIR beads have been studied through six contact/regeneration cycles with no loss of complexing ability, in contrast to the behavior of uncoated SIR beads. The semi‐permeable membrane does not hinder the complexation of Cu(II) ions: results with the coated SIR beads are identical at 15 min and 24 hr contact times.

Crown ethers are a unique category of ionic complexants whose recognition properties derive from both the atoms within the molecule and the overall structure. Immobilization of the crown ethers onto polymers allows for ease of handling, recyclability and adaption to continuous processes for this important set of complexants. The purpose of this review is to examine the different immobilization schemes for crown ethers having varying sets of donor atoms on organic polymers and the resulting metal ion affinities in order to provide an understanding of the strategies which are available to the synthesis chemist. The syntheses may be divided into three categories: (1) step-growth polymerization, (2) chain-growth polymerization, and (3) post-functionalization of pre-formed polymers. It is found that apparent metal ion affinities may be influenced by accessibility of the ions into the matrix. Use of hydrophilic polymers can be important for a high degree of ionic complexation.

Intraligand cooperation between carbonyl and phosphoryl moieties in ion bonding was studied by the synthesis of β-ketophosphonic acid (βkPh), phosphonoacetic acid (PhAc), and phosphonic acid (Ph) resins. A subsequent reaction gave bifunctional analogues with sulfonic acid as an additional ligand (βkPhs, PhAcs, and Phs resins). Ionic affinities were quantified with dilute solutions of Cu(II), Cd(II), and Pb(II) in 0.10M HNO3. The effect of an increased solution ionic strength was studied with a second set of 0.10M HNO3/0.04M NaNO3 solutions. The results from the monofunctional resins and nitric acid alone showed that βkPh had the highest metal-ion affinities, whereas PhAc had affinities similar to those of Ph. Comparing βkPh to Ph led to the conclusion that the carbonyl group was a strong contributor to binding through intraligand cooperation with the phosphoryl group, whereas comparing PhAc to Ph led to the conclusion that the carbonyl group played no role in the ion binding. These opposing conclusions were reconciled as follows: (1) the extent of complexation from the 0.10M HNO3 solutions increased significantly when the monofunctional resins were sulfonated and (2) a comparison of the results for the monofunctional resins when contacting Cu(II), Cd(II), and Pb(II) in the absence of NaNO3 with those for the bifunctional resins when contacting those ions in the presence of NaNO3 showed that the ionic affinities were comparable for Ph and Phs, greater for PhAcs than for PhAc, and comparable for βkPhs and βkPh. The resins PhAcs and βkPh displayed comparable ionic affinities that were higher than that of Ph. The results were consistent with the conclusion that, in the monofunctional resin, the affinity of the phosphonoacetate ligand for the metal ions was reduced because of intraligand hydrogen bonding. Intraligand cooperation was, therefore, an important variable in enhancing the metal-ion affinities, but its effect could be attenuated by intraligand hydrogen bonding. This attenuation could be eliminated by the introduction of a highly hydrophilic group into the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 463–468, 2004

The Mannich reaction is applied to the phosphorylation of amine resins with monoamine, ethylenediamine, diethylenetriamine, and tetraethylenepentamine ligands to give a series of bifunctional aminomethylphosphonic acid resins. The microenvironment around each ligand was varied by preparing fully functionalized resins, a second set of resins with 82 mol% phenyl groups in the polymer, and a third set with 82 mol% carbomethoxy groups. The affinity of the resins for Cu(II), Cd(II), Pb(II), and Eu(III) was evaluated from solutions buffered at pH 5. Synergism is observed under certain conditions where both groups operating together complex more metal ions than either one alone. Ion exchange by the phosphonate portion of the ligand and coordination by the amine portion cooperate as a dual mechanism for metal ion complexation. Synergistic complexation of Cd(II) by all bifunctional aminomethylphosphonate resins (regardless of microenvironment) and of all metal ions by all bifunctional resins within the carbomethox...

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.

Calix[4]arene and its diphosphorylated derivative have been immobilized onto cross-linked polystyrene beads through an etherification reaction. The supported calixarene complexes 96.7% Cs(I) from a 10-4 N solution in 1 M NaOH. Poly(hydroxystyrene) complexes 35.6% Cs(I) from the same solution. Immobilization of the calixarene onto a polymer support thus does not affect its inherently high affinity for cesium ions. Substituting two of the three remaining hydroxyl groups on the calixarene with diethoxyphosphoryl moieties allows for quantitative complexation of Fe(III) and Pb(II) from 0.01 M nitric acid solutions. The unsubstituted calixarene complexes 6.00% Fe(III) and 7.36% Pb(II) while diethoxyphosphoryl-substituted poly(hydroxystyrene) complexes 10.0% Fe(III) and 3.76% Pb(II). The calixarene therefore acts as a platform on which ligands can be immobilized in close enough proximity to permit cooperative binding of metal ions.

A novel class of strong-base anion-exchange resins, bearing two different types of exchange sites, is described. These bifunctional resins have anion-exchange sites composed of two separate and differently sized trialkylammonium groups. In pertechnetate (TcO4-) uptake experiments from a solution matrix containing anions commonly encountered in groundwater, bifunctional resins containing exchange sites derived from tri-n-hexylamine in combination with either triethylamine, tri-n-propylamine, or tri-n-butylamine were shown to possess superior 24-h distribution ratios (Kd) for pertechnetate over all monofunctional anion-exchange resins (derived from a single trialkylamine) examined. For example, although monofunctional resins containing a tri-n-hexylammonium exchange site possessed excellent selectivity for pertechnetate over other anions, the exchange kinetics were poor. The superior performance of these resins can be attributed to the combination of a large trialkylammonium site for enhanced selectivity fo...

The design and synthesis of polymer-supported reagents that can selectively complex targeted metal ions from multi-component solutions will continue to be an important area of research into the 21st century. Environmental remediation and sensor technology are only two of a number of areas in which such polymers can be applied. This paper reviews the recent literature with an emphasis on the key ligands that have been immobilized in order to better understand where this research is heading in the near future.

The microenvironmental effect on catalysis is quantified by the neighboring group content. Opposing variables in the reaction mechanism are then identified by the critical neighboring group content. The Prins reaction between formaldehyde and styrene is probed in the present study with immobilized sulfonic acid ligands as the catalyst. Cross-linked polystyrene beads were sulfonated to varying degrees of substitution. Styrene was also copolymerized with butyl methacrylate and methyl methacrylate followed by complete sulfonation of the phenyl rings. The reaction kinetics were correlated with the neighboring group content, defined as the mole percent of neighboring groups (i.e., phenyl, carbobutoxy, or carbomethoxy) relative to the total sites (neighboring and sulfonic acid) in the polymer. Increasing the phenyl group content from 0 to 25% (i.e., decreasing the degree of substitution from 100 to 75%) increases the rate constant from 23.1 to 56.2 M-1 s-1 while a further increase lowers the rate constant. The ...

The present study evaluated a new class of bifunctional anion-exchange resins with improved selectivity and sorption kinetics for removing pertechnetate (TcO4-) from contaminated groundwater. Both ...

Phosphonic acid ion exchange resins have been synthesized from polystyrene beads and sorption studies with Eu(III) and Fe(III) from acid solutions are reported. The effect of increasing matrix rigidity by crosslinking with 5, 12, and 20% divinylbenzene (DVB) on the extent of complexation is quantified. In a representative example, complexation decreases from 97.7% to 3.60% Eu(III) at a 0.5 h contact time from 10−4 N Eu(NO3)3/0.10 N HNO3 solution as the crosslink level in microporous (i.e., gel) resins changes from 5 to 20% DVB. Complexation at the two crosslink levels decreases to 31.7% and 0.61%, respectively, from 1.00 N HNO3 solution. Macroporosity can increase the level of complexation, but the effect under the present conditions is minimal for 5 and 20% DVB macroporous resins (98.3% and 31.2% Eu(III) from 0.10 N HNO3; 28.8% and 1.26% Eu(III) from 1.00 N HNO3). It is now reported that immobilizing sulfonic acid ligands on to the aromatic rings bearing the phosphonic groups allows the latter to rapidly complex metal ions to levels exceeding 90% from highly acidic solutions. Under the conditions noted above, bifunctional 5 and 20% DVB gel resins complex >99% Eu(III) from 0.10 N HNO3 and 94% Eu(III) from 1.00 N HNO3 solutions. The principle of bifunctionality is thus proposed as an alternative to macroporosity: polymer-supported reagents with enhanced metal ion complexation kinetics require the presence of an access ligand along with a recognition ligand for the targeted selectivity.

A copolymer comprised of glycidyl methacrylate and N,N-methylenebis(acrylamide) has been defined that can be used to coat solvent-impregnated resins (SIRs). Vinyl groups on the surface of a cross-linked macroporous support were used to anchor the polar copolymer to the surface of the bead. The coated SIR containing di(2-ethylhexyl)phosphoric acid maintained a high level of metal ion complexation (96% Cu(II)) over five cycles while the uncoated SIR dropped from 93% to 11% Cu(II) complexed in three cycles.

A bifunctional monophosphonic/sulfonic acid ion exchange resin with high capacity has been synthesized. Metal ion studies have been carried out with europium, americium, and ferric nitrate in solutions of varying acidity, with and without sodium nitrate added. The bifunctional resin complexes far higher levels of Eu(III) from 0.5 and 1 N nitric acid than the monofunctional phosphonic acid resin. It is postulated that the sulfonic acid ligand provides an access mechanism for the metal ions into the polymer matrix by hydrating the matrix and preventing its collapse in high ionic strength solutions thus allowing for rapid ionic complexation by the selective phosphonic acid ligands. The bifunctional monophosphonic/sulfonic acid resin has both ligands bound to a polystyrene support. It complexes higher levels of metal ions than a comparable resin differing only by having the monophosphonic acid ligand directly bound to the C-C backbone. Results are compared to a diphosphonic / sulfonic acid resin.

Foams prepared from vinylbenzyl chloride and crosslinked with divinylbenzene were functionalized with trialkylphosphite and tetralkylvinylidene diphosphonate. It was determined that the foams could be uniformly functionalized. Batch studies with the functionalized foams show that high levels of metal ion complexation can be achieved. Foams may therefore offer an important alternative to beads for rapid complexation reactions due to their highly porous structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1911–1916, 1998

The recently developed Diphonix® resin contains the geminally substituted diphosphonic acid ligand chemically bonded to a styrene-divinylbenzene copolymer. The resin exhibits an extraordinarily strong affinity for actinides, especially in the terra- and hexavalent oxidation states. Therefore the resin has potential for application in TRU removal from nuclear wastes. The Diphonix-CS resin is a Diphonix-type resin that contains also phenolic groups chemically attached to the polymeric matrix. The phenolic groups exhibit high affinity for Cs+ ions from highly alkaline media. Thanks to the combined action of the diphosphonic acid and the phenolic groups, the Diphonix-CS resin can simultaneously remove actinide species, Cs and Sr from alkaline media. In this paper the results obtained in the characterization of the new resin are reported, with regard to the uptake equilibrium and kinetics of Cs+ and Sr+2 removal from NaOH solutions and from synthetic alkaline wastes. The chemical and radiolytic stabil...