Gel-type Anion Exchange Resin Research Articles

Effective oxidation and adsorption of As(III) in water by nanoconfined Ce-Mn binary oxides with excellent reusability

Herein, a highly efficient As(III) purifier Ce-Mn@N201 with excellent reusability was developed by stepwise precipitating hydrated cerium(IV) oxides (HCO) and hydrated manganese(IV) oxides (HMO) inside N201, a widely-used gel-type anion exchange resin. Owing to confinement of unique nanopores in N201, the in-situ generated nanoparticles (NPs) inside Ce-Mn@N201 were highly dispersed with ultra-small sizes of around 2.6 nm. Results demonstrated that HMO NPs effectively oxidized As(III) to As(V) with the conversion of Mn(IV) to Mn(II), while the generated Mn2+ was mostly re-adsorbed onto the negatively-charged surface of HMO NPs. During the regeneration process by simple alkaline treatment, the re-adsorbed Mn2+ was firstly precipitated as (hydr)oxides of Mn(II) and then oxidized to HMO NPs by dissolved oxygen to fully refresh its oxidation capacity. Though HCO NPs mainly served as adsorbent for arsenic, they could partially oxidize As(III) to As(V) at the beginning, while the oxidation capacities continuously diminished with the irreversible conversion of Ce(IV) to Ce(III). In 10 consecutive adsorption-regeneration cycle, Ce-Mn@N201 efficiently decontaminated As(III) from 500 μg/L to below 5 μg/L with Mn2+ leaching less than 0.3% per batch. During 3 cyclic fixed-bed adsorptions, Ce-Mn@N201 steadily produced 8500–9150 bed volume (BV) and 3150–3350 BV drinkable water from the synthesized and real groundwater, respectively, with Mn leaching in effluent constantly < 100 μg/L.

Commercial Gel-Type Ion Exchange Resin Enables Large-Scale Production of Ultrasmall Nanoparticles for Highly Efficient Water Decontamination

• Gel-type anion exchange resin enables large-scale production of sub-5 nm particles. • The nanocomposites are millimetric beads applicable in flow-through systems. • Sub-5 nm HFO exhibit >3 times As(III/V) adsorption capacities than 17 nm HFO. • Adsorption capability is fully refreshed for cyclic use by using NaOH-NaCl solution. • The nanocomposite column produces 4800 BV clean water from simulated groundwater. Nanotechnology presents innovative solutions in advanced water treatment; however, its application is limited by the challenging large-scale production of ultrasmall (< 5 nm) nanoparticles (NPs) with extraordinary decontamination reactivity and the difficulty of handling such tiny NPs in engineering. To address these challenges, we propose a straightforward route for synthesizing ultrasmall NPs using the commercial gel-type anion exchange resin N201 as the host. N201 is a millimeter-scale poly(styrene- co -divinylbenzene) bead modified with quaternary ammonium groups. Nanoparticles of hydrated ferric oxide (HFO), hydrated manganese oxide (HMO), cadmium sulfide (CdS), and zero-valent iron (ZVI) were obtained through simple impregnation-precipitation in N201, and all of the NPs possessed an ultrasmall size of sub-5 nm. A pilot-scale production assay indicated that the synthetic system could be enlarged proportionally to prepare massive sub-5 nm HFO. Regarding the underlying mechanism, each N201 bead contained a continuous water phase, allowing the rapid diffusion of the reactants (7 s for diffusion from the bead surface to the center), resulting in burst nucleation to produce ultrasmall NPs with a narrow size distribution. Moreover, the crosslinked polymer chains provided a confined space (< 5 nm diameter) to prevent the excessive growth of the formed NPs. Owing to the millimetric N201 host, the resultant nanocomposite can be applied in flow-through systems. The batch and column adsorption assays demonstrate the dramatically enhanced adsorption performance of the ultrasmall HFO toward As(III/V) than the ∼17 nm analogs. This study can advance the widespread use of nanotechnology in practical water treatment.

Utilization of gel-type polystyrene host for immobilization of nano-sized hydrated zirconium oxides: A new strategy for enhanced phosphate removal

The urgent need for eutrophication control motivated the development of many novel adsorbents for enhanced phosphate polishing removal. Among these, zirconium-based nanomaterial was regarded as an effective kind because of its ability to bind phosphate specifically via inner-sphere complexation. In this study, we proposed a new strategy to improve the efficiency of zirconium oxides (HZO) nanoparticles by immobilizing them onto a gel-type anion exchange resin covalently attached with ammonium groups, denoted as HZO@N201. A previously developed macro-porous polymeric nanocomposite HZO@D201 was used for comparison. The immobilized nanoparticles in HZO@N201 were well dispersed in the gel matrix, manifesting smaller particle size and richer surface hydroxyl groups in comparison to HZO@D201. As a result of the structural merits in collective, HZO@N201 not only exhibited superior phosphate adsorptive capacity and affinity towards phosphate to HZO@D201, but also facilitate phosphate diffusion, based on isotherm, pH and kinetic tests. Mechanistic study by XPS and 31P SS-NMR substantiated the selective phosphate adsorption pathway as the formation of inner-sphere complexes by HZO@N201, which exhibited enhanced reactivity than HZO@D201. Lastly, fixed-bed runs of HZO@N201 was conducted, achieving an effective treatable volume of 2000 BV, which was 600 BV more than HZO@D201. Additional adsorption-regeneration cycle confirmed its reusability and potential for practical application. We believe the gel-type polymeric host could facilitate the formation and dispersion of smaller sized nanoparticles, exposing more surface hydroxyl groups highly accessible to phosphate. The results of this paper offer insights to a new strategy for immobilization of functional nanoparticles aiming at enhanced adsorptive removal of phosphate.

Ion Exchange Equilibrium between DOWEX 1X8 Resin Modified by Polyethyleneimine and Electrolyte Solutions

In order to improve the selectivity of anion exchange resin, the surface of gel type anion exchange resin was modified with polyethyleneimine (PEI). In the proposed work an attempt to the utilization of commercial anion exchange resin modified by adsorption of polyethyleneimine was investigated. Many conditions of modification of anion exchange resin surface were studied. The influent parameters on the DOWEX 1X8 resin modification were determined using a factorial experimental design. The ion exchange reactions were studied for modified and unmodified resin and electrolyte solutions containing Cl-，NO3-，SO42-. All experiments were performed at constant ionic strength I = 0.3 mol·L-1 and constant temperature T = 298 K. Ionic exchange isotherms were established for the binary systems:Cl-/NO3-，Cl-/SO42- and NO3-/SO42-. The obtained results show that nitrate ion was more sorbed than chloride and sulfate. The order of preference for the anions studied in this investigation is:NO3->Cl->SO42-. All the results given by this resin were compared with those obtained with the AMX anion exchange membrane. Selectivity coefficients and thermodynamic constants for the three binary systems and for the two resins were determined. The modified resin became more selective towards monovalent anions.

Adsorption Thermodynamics and Kinetics of Uridine 5′-Monophosphate on a Gel-Type Anion Exchange Resin

The adsorption behavior of uridine 5′-monophosphate (UMP) on a gel-type anion-exchange resin SD3 at different temperatures was investigated by the batch method. The dissociation equilibrium of UMP in aqueous solution has been studied. Effects of solution pH, contact time, and initial concentrations of UMP on the adsorption have been discussed. Adsorption equilibrium data had been fitted to three different isotherms including Langmuir, Freundlich, and Sips isotherms, which have been widely used in biosorption processes, and the accuracy for all models has been evaluated by the residual-root-mean-square error. For adsorption kinetics, the adsorption rate of UMP on the resin was interpreted by the Fick model, first- and second-order kinetic models, and the adsorption process was found to be well represented by the Fick model. The solution diffusivities of UMP at different temperatures were estimated by the Wilke-Chang equation. The sorption process was found to be controlled by the intraparticle diffusion. The Fick model and Sips isotherm were chosen to simulate the concentration diffusion of UMP on SD3 resin during the adsorption process. An intraparticle two-dimensional profile of SD3 resin at 0, 1, 4, 15, and 25 min for 293.15, 303.15, and 313.15 K was shown with a satisfactory description of the adsorption process. The thermodynamic parameters such as Gibbs free energy and enthalpy and entropy changes were calculated, and the values indicated that the adsorption process of UMP on SD3 resin was spontaneous and endothermic.

Investigation of Factors Affecting the Bioregeneration Process for Perchlorate-Laden Gel-Type Anion-Exchange Resin

ABSTRACT Ion exchange is the most common process for perchlorate removal from waters. Selective ion-exchange resins are widely used for perchlorate removal from waters, but are incinerated after one-time use, making the ion-exchange process incomplete for perchlorate removal. As perchlorate ions are readily biodegradable, direct contact of spent ion-exchange resins with perchlorate-reducing bacteria for its regeneration has been studied recently. In this research, some factors affecting the bioregeneration of perchlorate-laden gel-type anion-exchange resin were investigated. Bioregeneration is a sustainable process when compared to one-time use of resin and disposal by incineration. Batch bioregeneration experiments were performed to determine (a) the effect of initial perchlorate load in the resin, (b) the effect of microbial concentration, and (c) the effect of nitrate load on the degradation of perchlorate in the resin bead. The results of the bioregeneration tests suggested that the bioregeneration process may be controlled by both kinetics and diffusion. Higher perchlorate load in the resin had a positive effect on perchlorate degradation rates, whereas varying microbial concentration did not have a significant effect on perchlorate degradation in gel-type resin. The presence of nitrate suppressed perchlorate degradation initially, but once all nitrate was utilized, perchlorate degradation took place.

Alcohol splitting for the production of methyl methoxyacetate: Integration of ion-exchange with bipolar membrane electrodialysis

As a green technology for organic synthesis, alcohol splitting by using bipolar membrane electrodialysis (BMED) is restricted from industrial practice due to the unacceptable electrical resistance of the organic medium. This research proposes an integration strategy to reduce the electrical resistance, i.e., filling ion-exchange resins in a BMED stack. This strategy is adopted for the production of methyl methoxyacetate in methanol, and the performance of 4 kinds of ion-exchange resins are assessed in terms of the voltage drop, product yield, and current efficiency. Under the experimental conditions, the lowest voltage drop was achieved by using D201 macroreticular anion-exchange resin, and the voltage drop decreased by 44.3–61.4%. However, there was a slight decrease in the product yield and current efficiency due to the adsorption of methyl methoxyacetate onto the resins. As a compromise, 201*7 gel-type anion-exchange resin is the best choice.

Bioregeneration of perchlorate-laden gel-type anion-exchange resin in a fluidized bed reactor

Selective ion-exchange resins are very effective to remove perchlorate from contaminated waters. However, these resins are currently incinerated after one time use, making the ion-exchange process incomplete and unsustainable for perchlorate removal. Resin bioregeneration is a new concept that combines ion-exchange with biological reduction by directly contacting perchlorate-laden resins with a perchlorate-reducing bacterial culture. In this research, feasibility of the bioregeneration of perchlorate-laden gel-type anion-exchange resin was investigated. Bench-scale bioregeneration experiments, using a fluidized bed reactor and a bioreactor, were performed to evaluate the feasibility of the process and to gain insight into potential mechanisms that control the process. The results of the bioregeneration tests suggested that the initial phase of the bioregeneration process might be controlled by kinetics, while the later phase seems to be controlled by diffusion. Feasibility study showed that direct bioregeneration of gel-type resin was effective in a fluidized-bed reactor, and that the resin could be defouled, reused, and repeatedly regenerated using the method applied in this research.

Ion-exchange selectivity of anion exchange resin modified with polystyrenesulfonic acid.

In order to change the ion-exchange selectivity of anion-exchange resin, the surface of a gel-type anion exchange resin was modified with anionic polyelectrolyte, polystyrenesulfonic acid. Using this modified resin, the ion-exchange rate of nitrate was little decreased, but that of sulfate was evidently decreased. It is considered that the ion-exchange reaction of the multivalent anion is suppressed by the greater electrostatic repulsive force against the modification layer than that against the monovalent anion. Thus, this modified resin may be suitable for the selective separation of monovalent anions. The influence of the modified condition on the ion-exchange rate was examined. Furthermore, this modified resin was used to separate nitrate ions from sulfate ions in the aqueous solution.

Selectivity of Anion Exchange Resin Modified with Anionic Polyelectrolyte

In order to change the ion-exchange selectivity of anion exchange resin, especially to make the ion-exchange of divalent anions more difficult, the surface of gel-type anion exchange resin was modified by the adsorption of an anionic polyelectrolyte: polycondensation product of sodium naphthalene sulfonate and formaldehyde. After the adsorption of the polymer, ion exchange capacity decreased and the rate of ion exchange reaction became slow, though ion exchange equilibrium constants between two anions did not change. Especially, the ion exchange rate of divalent anions was slower than that of the monovalent anions. Because an anionic polyelectrolyte layer was formed on the resin particle, the ion exchange of anions with anion exchange site was retarded by a sieving effect due to the layer. The divalent anions became difficult to ion exchange compared with the monovalent anions due to the existence of the layer which was charged opposite to the charge of the ion exchange groups. Using the modified anion exchange resin, separation of nitrate ions from sulfate ions was attempted.

Separation of Anions by Use of the Surface Modified Anion Exchange Resin.

The surface of gel-type anion exchange resin was modified by the adsorption of an anionic polyelectrorite: polycondensation product of sodium naphthalene sulfonate and formaldehyde (trade name, Demol N). After the adsorption of the polymer, ion exchange capacity decreased and the rate of ion exchange reaction became slow though ion exchange equilibrium constants between two anions did not changed. Especially, the ion exchange rate of divalent anions was slower than that of the monovalent anions. Because an anionic polyelectrorite layer was formed on the resin particle, the ion exchange of anions with anion exchange site was retarded by sieving effect with the layer and the divalent anions were difficult to ion exchange compared with the monovalent anion due to existence of the opposite charged layer to ion exchange groups. Using the modified anion exchange resin in the hydroxide ion form, separation of nitrate ion from sulfate ion was attempted. The modified resin was immersed in the mixture solution of nitrate and sulfate ions, and the solution was shaken for definite time. The nitrate ion was preferentially adsorbed on the resin. The resin was separated and introduced in the potassium perchlorate solution. After shaking for 90 minutes, the nitrate ion in the solution was determined by use of ion-chromatography. The separation and enrichment of nitrate ion from 50-fold amount of sulfate ions was accomplished.