Polystyrene Anion Exchange Research Articles

Enhanced selective adsorption of benzotriazole onto nanosized zeolitic imidazolate frameworks confined in polystyrene anion exchanger

A new nanocomposite adsorbent ZIF-67/D201, in which nanocrystalline ZIF-67 were immobilized inside the networking pores of a commercial polystyrene anion exchanger D201 by an alternate deposition method, with high capacity and enhanced selective affinity toward benzotriazole (BTA) was fabricated and characterized. ZIF-67/D201 demonstrated precise selective adsorption of BTA when benzimidazole (BMA), with very similar chemical structure to BTA, coexisted. After the uptake of BTA, ZIF-67/D201 could be regenerated for repeated use with slight capacity loss. According to kinetics data, two diffusion steps driven by electrostatic attraction were found prior to adsorption equilibrium: a fast diffusion of the contaminant into mesopores of D201 and then a relatively slow diffusion into micropores of ZIF-67. The underlying mechanism for the enhanced selective adsorption was revealed by spectral analysis and density functional theory (DFT) calculations. Three sorts of interactions (coordination, electrostatic attraction and π-π interaction) contributed to the fixing of contaminants. Among them, coordination was the predominant effect. For each sort of interaction, the binding energy of adsorbent-BTA was always larger than that of adsorbent-BMA, which was the intrinsic reason of the high selectivity in molecular level. The above results provided a strategy for precise separation of components with similar structures in water.

Self-crosslinking of comb-shaped polystyrene anion exchange membranes for alkaline fuel cell application

A series of crosslinked, comb-shaped polystyrene (PS) anion exchange membranes (AEMs) having C-16 alkyl side chain were synthesized by a Cu(I)-catalyzed “click chemistry” reaction, and subsequently azide-assisted self-crosslinking for alkaline fuel cell application. The as-obtained crosslinked AEMs showed lower water uptake, and thus good dimensional stability as a result of crosslinking. The chemical stabilities of the AEMs were evaluated under severe conditions, and minor degradation was observed by measuring IEC and ion conductivity changes after stability testing. The crosslinked membranes retained their high ion conductivity even in 10M NaOH at 80°C for 400h. Moreover, the PS-based AEMs shown higher hydroxide conductivity than that of the AEMs based on poly(2,6-dimethyl-phenylene oxide) (PPO) with similar architecture under the same testing condition probably due to the excellent compatibility between polystyrene backbone and alkyl side chain which may have helped to build a more efficient morphology for water uptake and thus the ion transport. These crosslinked cationic polymers were employed as membranes for alkaline fuel cells. The results indicated that the AEMs based on PPO having C-16 alkyl side chain had not initial performance, e.g. no open circuit voltage (OCV). In contrast, the initial fuel cell performance with the peak power density of 88mW/cm2 was observed for the alkaline fuel cell with xPS-65 membrane. It is assumed that the polystyrene polymer backbone may have helped to build a more efficient phase boundary between the catalyst layer and membrane probably resulted from the high water uptake though a more complete study would be needed to explain this phenomenon.

UV-crosslinking of polystyrene anion exchange membranes by azidated macromolecular crosslinker for alkaline fuel cells

Poly(2,6-dimethyl-phenyleneoxide)s (PPO)s with photo-crosslinkable azide groups were employed as macromolecular crosslinker for poly(vinylbenzyl chloride) (PVBC)-based anion exchange membranes (AEMs). The crosslinked AEMs were achieved by solution casting and UV- irradiation, subsequently quaternization with trimethylamine. Although the presence of azide groups in IR spectra in crosslinked AEMs suggested the incomplete reaction of azide groups using UV-irradiation, the gel fractions were more than 85% indicating the successful crosslinking between PVBC and PPO macromolecular crosslinker. The key properties of the crosslinked AEMs, such as mechanical property, ion exchange capacity, thermal stability, water uptake, ion conductivity, alkaline stability and initial H2/O2 fuel cell performance were investigated. Excellent mechanical properties were observed for all of the crosslinked AEMs. The as-obtained AEMs showed comparable λ-normalized hydroxide conductivity with previous reported crosslinked AEMs. The highest hydroxide conductivity of 14.8mS/cm at 20°C was achieved for the crosslinked AEMs with IEC value of 1.95meq./g in spite of its low water uptake (19.8wt%). Moreover, excellent alkaline stability was observed for crosslinked AEMs, 15% decrease in hydroxide conductivity after alkaline stability testing 1M NaOH at 80°C for 500h, while the conductivity of uncrosslinked membrane with similar IEC value decreased sharply with 58% of conductivity loss after only 120h. The improved alkaline stability of the crosslinked AEMs may be derived from its compact crosslinked architecture, protecting the cations from severe degradation. A peak power density of 11mW/cm2 was obtained at 16mA/cm2 when the crosslinked AEM was used as polymer electrolyte membrane in H2/O2 alkaline fuel cell at 60°C.

Effective removal of glyphosate from water by resin-supported double valent nano-sized hydroxyl iron oxide

The double valent composite resin (DR) was prepared within nano-sized Fe(ii) and Fe(iii) hydroxyl oxide crosslinking polystyrene anion exchanger resin for efficient glyphosate removal from water.

Efficient defluoridation of water using reusable nanocrystalline layered double hydroxides impregnated polystyrene anion exchanger

Water decontamination from fluoride is still a challenging task of global concern. Recently, Al-based layered double hydroxides (LDHs) have been extensively studied for specific fluoride adsorption from water. Unfortunately, they cannot be readily applied in scaled-up application due to their ultrafine particles as well as the regeneration issues caused by their poor stability at alkaline pHs. Here, we developed a novel (LDH)-based hybrid adsorbent, i.e., LALDH-201, by impregnating nanocrystalline Li/Al LDHs (LADLH) inside a commercial polystyrene anion exchanger D201. TEM image and XRD spectra of the resultant nanocomposite confirmed that the LDHs particles were nanosized inside the pores of D201 of highly crystalline nature and well-ordered layer structure. After impregnation, the chemical and mechanical stability of LALDH were significantly improved against pH variation, facilitating its application at a wide pH range (3.5–12). Fluoride adsorption onto LALDH-201 was compared to D201 and activated alumina, evidencing the preferable removal fluoride of LALDH-201. Fluoride adsorption onto LALDH-201 followed pseudo-second-order model, with the maximum capacity (62.5 mg/g from the Sips model) much higher than the other two adsorbents. Fixed-bed adsorption run indicated the qualified treatable volume of the fluoride contaminated groundwater (4.1 mg/L initially) with LALDH-201 was about 11 times as much as with the anion exchanger D201 when the breakthrough point was set as 1.5 mg/L. The capacity of LALDH-201 could be effectively refreshed for continuous column operation without observable loss by using the mixed solution of 0.01 M NaOH + 1 M NaCl. The above results suggested that the hybrid adsorbent LALDH-201 is very promising for water defluoridation in scaled-up application.

Hydroxide ion transfer in anion exchange membrane: A density functional theory study

A theoretical investigation of hydroxide ion transport mechanism in quaternary ammonium functionalized polystyrene (QAPS) anion exchange membrane (AEM) was studied by density functional theory (DFT). The results showed that there were two steps for OH− transferring through QAPS-AEM. The first step was the movement of OH− in water channel, which was induced by frequently forming and breaking of hydrogen bonds (H-bonds) between H2O and OH−. The second step was that OH− transferred across the quaternary ammonium (QA) groups by following the rotation about CC single bond, which was the rate-determining step for OH− transferring in QAPS-AEM. We presented that the ionic groups on the side chain of polymer with smaller space steric should provide higher ion conductivity due to their lower rotation energy barriers.

Enhanced Phosphate Removal by Nanosized Hydrated La(III) Oxide Confined in Cross-linked Polystyrene Networks.

A new nanocomposite adsorbent La-201 of extremely high capacity and specific affinity toward phosphate was fabricated and well characterized, where hydrated La(III) oxide (HLO) nanoclusters were immobilized inside the networking pores of the polystyrene anion exchanger D-201. La-201 exhibited enhanced phosphate adsorption in the presence of competing anions (chloride, sulfate, nitrate, bicarbonate, and silicate) at greater levels (up to molar ratio of 20), with working capacity 2-4 times higher than a commercial Fe(III) oxide-based nanocomposite HFO-201 in batch runs. Column adsorption runs by using La-201 could effectively treat ∼6500 bed volumes (BV) of a synthetic feeding solution before breakthrough occurred (from 2.5 mg P/L in influent to <0.5 mg P/L in effluent), approximately 11 times higher magnitude than that of HFO-201. The exhausted La-201 could be regenerated with NaOH-NaCl binary solution at 60 °C for repeated use without any significant capacity loss. The underlying mechanism for the specific sorption of phosphate by La-201 was revealed with the aid of STEM-EDS, XPS, XRD, and SSNMR analysis, and the formation of LaPO4·xH2O is verified to be the dominant pathway for selective phosphate adsorption by the immobilized nano-HLO. The results indicated that La-201 was very promising in highly efficient removal of phosphate from contaminated waters.

Photocatalysis of chloroform decomposition by tetrachlorocuprate (II) on Dowex 2-X8.

Heterogenized on a polystyrene anion exchange resin and in the presence of oxygen, CuCl4(2-) catalyzes the photodecomposition of chloroform at wavelengths above 345 nm with greater efficiency than an equivalent amount in homogeneous solution. The reaction is proposed to proceed in two stages, the first stage yielding CCl4 and HO2(-) as products, the second consisting of a chain reaction resulting from the CuCl4(2-)-catalyzed photodissociation of CCl4, yielding phosgene with CCl3 radicals as chain carriers. Photodecomposition is retarded by added Cl(-), CH3CN, C6H12 or C2H5OH, which is ascribed to the displacement of CHCl3 molecules from the vicinity of the copper by attraction to the polystyrene matrix or to the alkylammonium cation sites.

A new polymer-based laccase for decolorization of AO7: Long-term storage and mediator reuse

To address the bottlenecks of laccase-based catalysis, i.e., poor long-term stability and potential secondary pollution caused by synthetic mediator, we fabricated a new biocatalyst (N-PS-Lac) through adsorption of laccase onto polystyrene anion exchangers (N-PS) binding quaternary ammonium groups. After 2-year storage, the residual activity of N-PS-Lac remained as high as 101.7%, while that for native laccase was only 14.6%. Also, N-PS-Lac exhibited improved durability against pH variation and thermal treatment at 60°C. Gaussian curve fitting of FT-IR spectra indicated that laccase conformation of N-PS-Lac was rigidified, possibly because of the host geometric restriction and the host-laccase electrostatic attraction. A two-step method, i.e., adsorption of an azo dye AO7 by N-PS and then ectopic degradation by the immobilized laccase, was proposed to reuse the mediator HOBT for seven cyclic runs, where N-PS-Lac kept the constant decolorization efficiency. AO7 solution was detoxified completely after decolorization by the two-step method.

New strategy to enhance phosphate removal from water by hydrous manganese oxide.

Hydrous manganese oxide (HMO) is generally negatively charged at circumneutral pH and cannot effectively remove anionic pollutants such as phosphate. Here we proposed a new strategy to enhance HMO-mediated phosphate removal by immobilizing nano-HMO within a polystyrene anion exchanger (NS). The resultant nanocomposite HMO@NS exhibited substantially enhanced phosphate removal in the presence of sulfate, chloride, and nitrate at greater levels. This is mainly attributed to the pHpzc shift from 6.2 for the bulky HMO to 10.5 for the capsulated HMO nanoparticles, where HMO nanoparticles are positively charged at neutral pH. The ammonium groups of NS also favor phosphate adsorption through the Donnan effect. Cyclic column adsorption experiment indicated that the fresh HMO@NS could treat 460 bed volumes (BV) of a synthetic influent (from the initial concentration of 2 mg P[PO4(3-)]/L to 0.5 mg P[PO4(3-)]/L), while only 80 BV for NS. After the first time of regeneration by NaOH-NaCl solution, the capacity of HMO@NS was lowered to ∼ 300 BV and then kept constant for the subsequent 5 runs, implying the presence of both the reversible and irreversible adsorption sites of nano-HMO. Additional column adsorption feeding with a real bioeffluent further validated great potential of HMO@NS in advanced wastewater treatment. This study may provide an alternative approach to expand the usability of other metal oxides in water treatment.

Acid and organic resistant nano-hydrated zirconium oxide (HZO)/polystyrene hybrid adsorbent for arsenic removal from water

Abstract Hydrous zirconium oxide (HZO)-originated nanocomposite adsorbent of excellent stability against pH variation and organic ligands was fabricated for efficient arsenic removal from water. The nanocomposite adsorbent HZO-201 was obtained by encapsulating nanosized HZO particles inside a polystyrene anion exchanger D201. Negligible metal dissolution was observed from HZO-201 in solution of acidic pHs (to ∼1) and oxalate at high levels, while significant metal leaching occurred from a similar hydrated ferric oxide-based nanocomposite HFO-201of the same host. Arsenate adsorption by HZO-201 is a pH-dependent process with maximum capacity of 88.74 mg/g at pH 7.0 ± 0.1, comparable to HFO-201 under similar conditions. As compared to sulfate, chloride, and bicarbonate, silicate and phosphate could inhibit arsenic uptake more strongly by HZO-201. Fixed-bed adsorption indicated that arsenate in simulated groundwater could be effectively captured from 100 μg/L to

Diclofenac removal in urine using strong-base anion exchange polymer resins

One of the major sources of pharmaceuticals in the environment is wastewater effluent of which human urine contributes the majority of pharmaceuticals. Urine source separation has the potential to isolate pharmaceuticals at a higher concentration for efficient removal as well as produce a nutrient byproduct. This research investigated the efficacy of using strong-base anion exchange polymer resins to remove the widely detected and abundant pharmaceutical, diclofenac, from synthetic human urine under fresh and ureolyzed conditions. The majority of experiments were conducted using a strong-base, macroporous, polystyrene resin (Purolite A520E). Ion-exchange followed a two-step removal rate with rapid removal in 1 h and equilibrium removal in 24 h. Diclofenac removal was >90% at a resin dose of 8 mL/L in both fresh and ureolyzed urine. Sorption of diclofenac onto A520E resin was concurrent with desorption of an equivalent amount of chloride, which indicates the ion-exchange mechanism is occurring. The presence of competing ions such as phosphate and citrate did not significantly impact diclofenac removal. Comparisons of three polystyrene resins (A520E, Dowex 22, Dowex Marathon 11) as well as one polyacrylic resin (IRA958) were conducted to determine the major interactions between anion exchange resin and diclofenac. The results showed that polystyrene resins provide the highest level of diclofenac removal due to electrostatic interactions between quaternary ammonium functional groups of resin and carboxylic acid of diclofenac and non-electrostatic interactions between resin matrix and benzene rings of diclofenac. Diclofenac was effectively desorbed from A520E resin using a regeneration solution that contained 4.5% (m/m) NaCl in an equal-volume mixture of methanol and water. The greater regeneration efficiency of the NaCl/methanol–water mixture over the aqueous NaCl solution supports the importance of non-electrostatic interactions between resin matrix and benzene rings of diclofenac. Experiments with ketoprofen, in addition to diclofenac, suggest that polystyrene anion exchange resins can be used to selectively remove other acidic pharmaceuticals from urine.

Enhanced Removal of Fluoride by Polystyrene Anion Exchanger Supported Hydrous Zirconium Oxide Nanoparticles

Here we fabricated a novel nanocomposite HZO-201, an encapsulated nanosized hydrous zirconium oxide (HZO) within a commercial porous polystyrene anion exchanger D201, for highly efficient defluoridation of water. HZO-201 exhibited much higher preference than activated alumina and D201 toward fluoride removal when competing anions (chloride, sulfate, nitrate, and bicarbonate) coexisted at relatively high levels. Fixed column adsorption indicated that the effective treatable volume of water with HZO-201 was about 7-14 times as much as with D201 irrespective of whether synthetic solution or groundwater was the feeding solution. In addition, HZO-201 could treat >3000 BV of the acidic effluent (around 3.5 mg F(-)/L) per run at pH 3.5, compared to only ∼4 BV with D201. The exhausted HZO-201 could be regenerated by NaOH solution for repeated use without any significant capacity loss. Such attractive performance of HZO-201 resulted from its specific hybrid structure, that is, the host anion exchanger D201 favors the preconcentration of fluoride ions inside the polymer based on the Donnan principle, and the encapsulated nanosized HZO exhibits preferable sequestration of fluoride through specific interaction, as further demonstrated by XPS spectra. The influence of solution pH, competitive anions, and contact time was also examined. The results suggested that HZO-201 has a great potential in efficient defluoridation of groundwater and acidic mine drainage.

Removal of Cr(VI) and As(V) ions from aqueous solutions by polyacrylate and polystyrene anion exchange resins

The sorption of Cr(VI) and As(V) from the aqueous solutions with the polyacrylate anion exchangers of the strong base functional groups Amberlite IRA 458 and Amberlite IRA 958 was studied. The studies were carried out by the static-batch method. The concentration of Cr(VI) and As(V) ions in the aqueous solution was determined by the UV–VIS spectrophotometer. The influence of several parameters was studied with respect to sorption equilibrium. The phase contact time and the concentration affect the sorption process. The equilibrium state was established already after 15 min of phase contact time. Maximum uptake of Cr(VI) and As(V) occurred at pH 5 and 10, respectively. The determined kinetic parameters imply that the sorption process proceeds according to the equation type of pseudo second-order. Sorption equilibrium data were correlated with the Langmuir and Freundlich isotherms. Removal of As(V) ions on macroporous Amberlite IRA 900 decreased about 12 % in presence of other anions (Cl−, NO3−, SO42−) in the solution. The sorption was temperature dependent.

Catalysis of the Photodecomposition of Chloroform by a Polystyrene Anion Exchange Resin

Irradiation at wavelengths above 360 nm of a suspension of Dowex 2-X8 anion exchange resin (Cl¯ form) in chloroform causes the decomposition of chloroform with formation of COCl2 and HCl. The presence of CCl4 as the most important secondary product, along with the lack of any photodecomposition in CDCl3, the absence of photodecomposition when O2 is excluded, and the lack of any secondary products related to CHCl2 radicals rule out a mechanism based on sensitized C–Cl dissociation, as occurs in the direct UV photolysis of chloroform. A mechanism is proposed in which an initial photoreaction produces COCl2 and HCl at a slow rate, along with CCl4. A second photoreaction causes Cl dissociation from CCl4, greatly increasing the net rate of COCl2 and HCl formation after a sufficient concentration of CCl4 is attained.

Dependence of Photocatalytic Reaction Yields on Catalyst Mass in Solid-Liquid Suspensions

When the yield of a heterogeneously photocatalyzed reaction is seen to pass through maximum as the mass of catalyst is increased in a suspension, this behavior may be attributable to a regime in which back-reflection most often occurs after a single photon-particle encounter, while absorption requires multiple internal reflections. This was modeled with a double exponential equation, which predicts that the yield will pass through a maximum with increasing catalyst mass when the catalyst has low absorptivity, but approach an asymptotic limit when the absorptivity is high. The rate of photodecomposition of chloroform, catalyzed by the chloride form of a polystyrene anion exchange resin (low absorptivity), was found to pass through a maximum as the amount of resin was increased, while catalysis by the CuCl4 2- form of the resin (higher absorptivity) caused an increase in the rate of decomposition with catalyst mass to an asymptotic value. Keywords: Heterogeneous photocatalysis, suspensions, chloroform photodegradation, reflectance, catalyst mass

Evaluation of polystyrene anion exchange resin for removal of reactive dyes from aqueous solutions

The Amberlite IRA-900 resin was tested to remove C.I. Reactive Black 5, C.I. Reactive Red 2 and C.I. Reactive Red 120 dyes from solutions. Batch adsorption studies concerning effects of the phase contact time, pH, temperature, the presence of salts and surfactants were run. A pseudo second-order kinetic model was used to evaluate the rate constants. The Langmuir equation provided good fit for the experimental data of the equilibrium adsorption. The studies of dyes uptake using the dynamic method were run. The treatment efficiency of Amberlite IRA-900 to model wastewaters was tested. Desorption experiments by the batch method were performed.

Modified polystyrene anion exchange resins with long chain alkyl groups to enhance the aldolization reaction selectivity

The aldolization of formaldehyde and acetone to form 4-hydroxy-2-butanone over anion exchange resins with and without modifications is investigated in this work. Attempts such as surfactants addition and Soxhlet extraction are taken aiming to improve the aldolization selectivity thus the product yield. Subsequently, resins grafted long alkyl chains intrigue us for its steric hindrance effect and the synergic effect of weak and strong basic sites. Two types of modifications are carried out (1) one long alkyl chain on the copolymer tertiary amine via Menshutkin N-alkylation reaction; (2) two long alkyl chains: one on polystyrene aromatic ring through Friedel–Crafts alkylation under the circumstances of tertiary amine and the other on the copolymer tertiary amine using the Menshutkin N-alkylation reaction. The reaction results indicate that the yield for 4-hydroxy-2-butanone can be increased from 44.3% to around 50% for the resin with one long alkyl chain (the first case), while this can achieve up to 71.3% for the resin with two long alkyl chains.

Degradation and Removal of Sulfadiazine from Waters by a Novel Polymer-supported Hydrous Manganese Dioxide(HMO)

A new polymer-supported hydrous manganese dioxide(HMO-201) was prepared by impregnating HMO onto a porous polystyrene anion exchange resin(D201) through ion exchange,oxidation and reduction.The removal of sulfadiazine(SD) by HMO-201 was evaluated as a function of solution pH,background electrolyte NaCl and dissolved organic matter(DOM).HPLC-MS results showed that the removal of SD by HMO-201 was due to degradation rather than adsorption.The results indicated that the removal of 0.01 mmol/L SD reached 99.9% at pH=1.0 within 120 min.The SD degradation followed the pseudo-first-order kinetics.SD removal efficiency was little affected by ionic strength and DOM.With simulated SD wastewater containing NaCl and DOM,SD removal efficiency remained above 99% within 240 min for up to ten batches of continuous operation.Fixed-bed column experiment results of HMO-201 showed that SD remained undetected after 2000 bed volume simulated SD wastewater was passed through the column.HMO-201 was effective for the removal of sulfonamide antibiotics commonly found in the environment.It could be reused without a significant loss of capacity and thus has a great potential of real-world applications.

Efficient As(III) removal by macroporous anion exchanger-supported Fe–Mn binary oxide: Behavior and mechanism

Fe–Mn binary oxide is a promising material for As(III) removal through a combined oxidation and adsorption process. To improve its applicability in column or other flow-through systems, we developed a new nanocomposite motivated by the Donnan membrane principle, i.e., Fe–Mn binary oxide encapsulated within a polystyrene anion exchanger D201 (designated D201-Fe/Mn), for efficient As(III) removal from water. As compared to single Fe(III) oxide-loaded D201, the resultant D201-Fe/Mn was less sensitive to pH variation in the range of 4–10 and exhibited higher As(III) capacity. X-ray photoelectron spectroscopy (XPS) analysis confirmed that As(III) was oxidized to As(V) by Mn(IV) oxide during its sequestration by D201-Fe/Mn, whereas Mn(IV) was reduced to MnOOH* and consequently to Mn(II) simultaneously. The exhausted D201-Fe/Mn could be regenerated by NaOH–NaCl–NaClO solution for repeated use without any significant capacity loss, where the adsorbed As species was effectively desorbed to solution and the Mn(II) species was oxidized back to Mn(IV). High-level phosphate and silicate would pose strong competition for As(III) adsorption by D201-Fe/Mn, while sulfate and chloride did not show significant competition under similar conditions. Fixed-bed adsorption further validated that D201-Fe/Mn would be of considerable potential in As(III) removal from contaminated waters.