Donnan Membrane Effect Research Articles

Polymer-microsphere coated with MoS2 nanoflowers for the removal of Pb(II) from water: Polydopamine-mediated MoS2 assembly and efficient Pb(II) adsorption

The engineering of macroscopic architectures by loading MoS2 nanosheets onto larger framework materials is an efficient strategy to overcome the limitations preventing the application of nanosized MoS2-based adsorbents for Pb(II) removal. However, the large-scale utilization of these nanocomposites still faces several challenges as a result of their poor stability, slow adsorption kinetics, and low MoS2 utilization. Herein, a practical and efficient nanocomposite (MoS2/PDA/MPS) was prepared by coating MoS2 nanoflowers onto micron-sized polystyrene beads (MPS) via the construction of a strong adhesive polydopamine (PDA) interlayer. The PDA interface can adhere to the MPS surface and immobilize the MoS2 nanopartices, thus facilitating the application of MoS2/PDA/MPS in flow-through systems. Further, the flower-like structure of the MoS2 on the outer surface of the host exposes active sites and facilitates mass transfer compared to those of traditional nanocomposites. Meanwhile, the R-SO3- groups of MPS can enhance permeation and preconcentrate the Pb(II) ions via the Donnan membrane effect, resulting in improved adsorption kinetics and capacity. Batch adsorption experiments revealed that MoS2/PDA/MPS shows fast adsorption kinetics (<45 min), exceptional adsorption capacity (371.7 mg/g, calculated from the Langmuir model at 298 K), and high adsorption selectivity for Pb(II) uptake. The excellent stabilities and reusability of the nanocomposite were tested over 10 adsorption–desorption cycles. In addition, a considerable working capacity (approximately 2000 BV) in synthetic wastewater was observed in fixed-bed column tests, and the used adsorbent could be readily regenerated with a binary NaCl–EDTANa2 solution for reuse without significant capacity loss. Thus, MoS2/PDA/MPS has great applications for the remediation of lead-containing wastewater, and our findings provide new insights into the preparation of efficient MoS2-based adsorbents having practical applications.

Surfactant-modified adsorptive electrospun nanofiber membrane impregnated with akageneite for phosphorus recovery from wastewater

Phosphorus (P) recovery from wastewater is essential for eutrophication control, water reuse initiatives, and recovery of this depleting non-renewable resource. Herein, a polyacrylonitrile (PAN) electrospun nanofiber membrane (ENM) was fabricated with akageneite (Ak), and modified with benzyldimethyldodecylammonium chloride (BDDA), a cationic surfactant, for phosphorus recovery from wastewater. We examined the influence of BDDA concentration on membrane properties, including fiber diameter, surface area, surface charge, and contact angle. Membrane performance was then evaluated using adsorption isotherms and kinetics, in the presence of competing ions such as Cl-, SO42- and CO32-, using synthetic wastewater and through a total of 7 adsorption-desorption cycles. Akageneite was found to be the only active ingredient responsible for P removal by the membrane. We observed that the increase in BDDA concentration from 0 % to 3 % resulted in a linear increase in P adsorption capacity from 0.30 to 0.61 mmol P/g Ak. No increase in adsorption was observed at concentrations beyond 3 % BDDA. Membranes made of PAN and BDDA alone exhibited a negligible uptake of P at any concentration of BDDA. Since P uptake happened only in the presence of Ak, the improved performance with the addition of BDDA was attributed to increased hydrophilicity and influence of the Donnan membrane effect. The membranes had the highest affinity towards CO32- followed by P. The P adsorption capacity of PAN-Ak membrane was not affected by the presence of other competing ions (Cl-, SO42-). The results also confirmed the reusability of PAN-Ak without loss of adsorption capacity, even after seven cycles. This work demonstrated the potential of surface modification of adsorptive membranes for improved phosphorus recovery.

Designing a 3D-MoS2 nanocomposite based on the Donnan membrane effect for superselective Pb(II) removal from water

Developing more practical and efficient adsorbents is highly desirable for lead purification. Although MoS2 nanosheets have an excellent affinity for lead ions, their narrow layer spacing and ultrafine size hinder their scaled-up application. Herein, a novel type of 3D nanocomposite, W-MoS2@SCA, was synthesized by confining MoS2 nanoparticles with widened interlayer spacing (W-MoS2) in the networking pores of sulfonated cellulose aerogel (SCA). The excellent hydraulic property provided by the porous host overcomes the shortcomings of MoS2 nanomaterials and makes the composite have a satisfactory treatment effect in the flow-through system. Combined with the Donnan membrane effect produced by the positively charged sulfonic group of the host and the excellent affinity of MoS2 for lead ions, W-MoS2@SCA exhibits rapid adsorption kinetics (75 min to reach adsorption equilibrium) and superselectivity for Pb2+ removal. The distribution coefficient for Pb2+ is up to 1.01 × 105 mL/g even in complex wastewater mixed with multiple metal ions. Fixed-bed column tests indicate that an efficient application is achieved with a treatment capacity of 9000 kg wastewater/kg sorbent based on the wastewater discharges of China. Specifically, residual Pb2+ in the first 7000 kg effluent was virtually undetectable. In addition, the exhausted sorbent could be easily regenerated by the NaCl-Na2EDTA binary solution and maintained good reusability without significant capacity loss after 10 adsorption–desorption cycles. The results demonstrate that W-MoS2@SCA has great potential for use in deep purification for lead sequestration in advanced wastewater treatment.

Removal of iodide anions in water by silver nanoparticles supported on polystyrene anion exchanger

The removal of iodide (I−) from source waters is an effective strategy to minimize the formation of iodinated disinfection by-products (DBPs), which are more toxic than their brominated and chlorinated analogues. In this work, a nanocomposite Ag-D201 was synthesized by multiple in situ reduction of Ag-complex in D201 polymer matrix, to achieve highly efficient removal of iodide from water. Scanning electron microscope /energy dispersive spectrometer characterization showed that uniform cubic silver nanoparticles (AgNPs) evenly dispersed in the D201 pores. The equilibrium isotherms data for iodide adsorption onto Ag-D201 was well fitted with Langmuir isotherm with the adsorption capacity of 533 mg/g at neutral pH. The adsorption capacity of Ag-D201 increased with the decrease of pH in acidic aqueous solution, and reached the maximum value of 802 mg/g at pH 2. This was attributed to the oxidization of I−, by dissolved oxygen under the catalysis of AgNPs, to I2 which was finally adsorbed as AgI3. However, the aqueous solutions at pH 7 – 11 could hardly affect the iodide adsorption. The adsorption of I− was barely affected by real water matrixes such as competitive anions (SO42−, NO3−, HCO3−, Cl−) and natural organic matter, of which interference of NOM was offset by the presence of Ca2+. The proposed synergistic mechanism for the excellent performance of iodide adsorption by the absorbent was ascribed to the Donnan membrane effect caused by the D201 resin, the chemisorption of I− by AgNPs, and the catalytic effect of AgNPs.

Phosphate removal by a La(OH)3 loaded magnetic MAPTAC-based cationic hydrogel: Enhanced surface charge density and Donnan membrane effect

Cationic hydrogels have received great attention to control eutrophication and recycle phosphate. In this study, a type of La(OH)3 loaded magnetic MAPTAC-based cationic hydrogel (La(OH)3@MMCH) was developed as a potential adsorbent for enhanced phosphate removal from aqueous environment. La(OH)3@MMCH exhibited high adsorption capacity of 105.72±5.99 mg P/g, and reached equilibrium within 2 hr. La(OH)3@MMCH could perform effectively in a wide pH range from 3.0 to 9.0 and in the presence of coexisting ions (including SO42−, Cl−, NO3−, HCO3−, SiO44− and HA). The adsorption-desorption experiment indicated that La(OH)3@MMCH could be easily regenerated by using NaOH-NaCl as the desorption agent, and 73.3% adsorption capacity remained after five cycles. Moreover, La(OH)3@MMCH was employed to treat surface water with phosphate concentration of 1.90 mg/L and showed great removal efficiency of 95.21%. Actually, MMCH showed high surface charge density of 34.38-59.38 meq/kg in the pH range from 3.0 to 11.0 and great swelling ratio of 3014.57% within 24 h, indicating that MMCH could produce the enhanced Donnan membrane effect to pre-permeate phosphate. Furthermore, the bifunctional structure of La(OH)3@MMCH enabled it to capture phosphate through electrostatic attraction and ligand exchange. All the results prove that La(OH)3@MMCH is a promising adsorbent for eutrophication control and phosphate recovery.

Development of an acidized biochar-supported hydrated Fe(III) oxides for highly efficient cadmium and copper sequestration from water

Biochar-supported metallic oxides are attractive adsorbents for heavy metal cleanup, but the adsorption performance is still unsatisfactory as a result of the self-aggregation of the incorporated metallic oxides. A new hybrid nano-material was prepared through impregnating hydrated ferric oxide (HFO) nanoparticles within biochar bearing high-density charged oxygen-containing groups (e.g., carboxyl and hydroxyl groups) (ABC) derived from HNO3 treatment. The as-made adsorbent, denoted as HFO-ABC, possesses highly dispersed HFO nanoparticles with typical size lower than 20 nm, and exhibits greater sorption capacity for Cd(II) and Cu(II) than the pristine biochar-supported HFO. It also shows great sorption preference toward Cd(II) and Cu(II) in co-presence of high levels of Ca2+, Mg2+ and humic acid (HA). Such prominent performance is put down to the high-density charged functional groups on the host ABC, which not only promote the dispersion of the immobilized HFO nanoparticles but also generate the potential Donnan membrane effect, i.e., the pre-concentration and permeation of target metals prior to their preferable adsorption by nano-HFO. The predicted effective coefficients of intra-particle diffusion for Cu(II) and Cd(II) are 3.83 × 10−9 and 4.33 × 10−9 cm2/s, respectively. HFO-ABC exhibits excellent performance for fixed-bed column application, and yields 513 and 990 BV effluents for Cd(II) and Cu(II) to achieve their discharge standards, respectively. The spent HFO-ABC could be in situ regenerated using binary HCl-CaCl2 solution with desorption efficiency higher than 95%. All results manifest that increasing charged functional groups via HNO3 treatment is an effective measure for boosting sorption performance of biochar-based nanocomposites.

The impact of background wastewater constituents on the selectivity and capacity of a hybrid ion exchange resin for phosphorus removal from wastewater

Conventional sorption media are inefficient for phosphorus removal from wastewater due to preference for competing species such as sulphate, nitrate and organics. This work investigates whether the use of hybrid ion exchange resins effectively negates such concerns. Trials were conducted with a hybrid anion exchange (HAIX) media which was preloaded with different background constituents and operated over multiple regeneration cycles to ascertain the likely impacts. The work revealed that whilst the impact of the other constituents was seen in regards to direct competition, the major impact was on reduction of the rate of intraparticle mass transfer through sorption of the constituents onto the base resin thereby reducing the Donnan membrane effect. Comparison of the impact of the background water constituents on the individual components (hybrid resin, base resin, nanoparticles) revealed the importance of the nanoparticle whereby they effectively transform the ion exchange media into a mono component absorber for phosphorus that enables sustained removal even in complex wastewaters.

Manganese oxide nanoparticles impregnated graphene oxide aggregates for cadmium and copper remediation

Loading metal oxide nanoparticles (NPs) into porous granular materials with excellent hydraulic characteristics offers a promising option to break the technical barriers of direct application of NPs in scaled-up water decontamination. By taking advantage of graphene oxide (GO) mediating the formation of manganese oxide (MO) nanoparticles at the same time aggregating to form macroporous structure under highly alkaline conditions, we fabricated a novel GO-MO composite (D = ∼160 μm). The intraparticle diffusivity of Cd(II) and Cu(II) onto GO-MO was determined to be 3.17 × 10−9 and 4.67 × 10−9 cm2 s−1, respectively, similar to macroporous resin. The GO-MO showed synergistic sorption capacity for Cd(II) and Cu(II) compared to bulky MO and GO due to the high dispersion of MO NPs (<10 nm) in the aggregated GO matrix and Donnan membrane effect. The GO-MO also had strong sorption selectivity in the presence of Ca(II) and humic acid. HADDF-EDS characterization visually showed that Cu(II) and Cd(II) was selectively adsorbed to MO even in the presence of 50 times higher competing Ca(II) ions, which was quantified as ∼93% of the total adsorbed metal for both Cu(II) and Cd(II) by XPS analysis. Moreover, GO-MO was successfully employed in the column operation with effective treatment volume of ∼1650 and ∼1995 BV for simulated Cd(II)- and Cu(II)-contaminated wastewater, respectively. The exhausted GO-MO can be effectively regenerated using acid-salt binary solution with desorption rate >97%. The results from this study may offer insights to rationally design highly efficient engineered nanocomposites for water purification.

Size-selective adsorption of methyl orange using a novel nano-composite by encapsulating HKUST-1 in hyper-crosslinked polystyrene networks

A novel nano-composite adsorbent, NDA88-Cu, was successfully prepared by immobilization of HKUST-1 (a typical MOF) into hyper-crosslinked polystyrene networks NDA88 (loading ratio: 350 mg of MOFs with particle size in the range of 10–100 nm per gram of polystyrene networks). The adsorbent demonstrated advantages of improved stability without leakage of metal ions during the adsorption assays compared to HKUST-1 itself, and faster solid-liquid separability than NDA88 or HKUST-1, which could effectively avoid the shortcomings of MOFs like potential secondary pollution and poor performance in separation. When applied for the adsorption of five typical dyes with various charges and molecular sizes (cationic: methylene blue (MB) and rhodamine-B (RhB); anionic: methyl orange (MO), methyl red (MR) and acid green (AG25)), NDA88-Cu worked for the removal of anionic ones but showed almost no adsorption capacity towards cationic ones because of Donnan membrane effect exerted by the host NDA88. For the three anionic dyes, NDA88-Cu displayed not only heightened adsorption capacity towards MO (398.8 mg/g), but also size-selective uptake of MO from solution with mixed dyes. The adsorption capacity remained high levels after ten adsorption-desorption cycles. Mechanism investigations, including macroscopic physico-chemical analyses, instrumental investigation and density functional theoretical calculations, gave direct evidences of the size selectivity of NDA88-Cu with hierarchical pore structure. Coordination effect of Cu-MO predominated, while π-π interactions and electrostatic attraction also took place, in the fixing of MO onto the adsorbent. The current work provides a useful idea for the separation of contaminants with similar structure from water, and acts as a good case for the application of nanotechnology in wastewater treatment and resource recovery.

Enhanced lead and cadmium removal using biochar-supported hydrated manganese oxide (HMO) nanoparticles: Behavior and mechanism

Hydrated manganese oxide (HMO) nanoparticles were impregnated into a peanut shell-derived biochar (BC) to obtain a remarkable nanocomposite adsorbent, HMO-BC, which overcomes the technical barriers of singly applying either HMO or BC in practical heavy metal-containing wastewater treatment. HMO-BC can effectively sequestrate Pb(II) and Cd(II) in a wide pH range of 3–7 and exhibited more preferable sorption than bare BC in the presence of high-level competing cations. BC also significantly lowered the Mn leaching at acidic pH. Fixed-bed column adsorption tests showed that the effective treatment volume of HMO-BC for a simulated Pb(II)- or Cd(II)-laden wastewater is about 4–6 times higher than that of the BC host. In addition, HMO-BC was effective in removing Pb(II) from a real Pb-containing electroplating wastewater to discharge limit (0.2mgL−1) with treatable volume of 525BV, much higher than that of the bare BC (60BV). More importantly, the saturated HMO-BC can be thoroughly regenerated for repeated uses without any observable capacity loss. Such attractive results of HMO-BC were attributed to the complementary effect of its two components. The embedded HMO nanoparticles provide preferable capture of target cations through specific inner-sphere complexation, as illustrated by XPS spectra of Pb 4f7/2 and O1s, while the non-diffusive negatively charged oxygen-containing groups bound to BC facilitate the pre-enrichment and permeation of Pb(II) and Cd(II) cations into the pore channels prior to their preferable sorption through the Donnan membrane effect.

Efficient Removal of Trace Se(VI) by Millimeter-Sized Nanocomposite of Zerovalent Iron Confined in Polymeric Anion Exchanger

The removal of trace Se(VI) from water is a great challenge because its adsorption or ion-exchange is significantly inhibited by other coexisting anions at much greater levels. To address this problem, the millimeter-sized nanocomposite nZVI@D201 was fabricated by in situ preparation of nanoscale zerovalent iron (nZVI) confined in the pore channels of a polymeric anion exchanger (D201). Preferable removal of trace Se(VI) in the presence of sulfate by nZVI@D201 over D201, nZVI, and their mixture was attributed to the significant roles of pore confinement effect and the Donnan membrane effect from the polymeric host. Moreover, the removal of trace Se(VI) by nZVI@D201 was insignificantly affected by pH (3–10), dissolved oxygen, coexisting anions, and humic acid at their environmental levels. The XPS spectrum revealed that the Se immobilized in nZVI@D201 was mainly Se(IV) (84.9%), indicating the synergistic removal mechanism involving ion-exchange, adsorption, and reduction. Through the periodic/complete rege...

Synthesis, Characterization and Performance Validation of Hybrid Cation Exchanger Containing Hydrated Ferric Oxide Nanoparticles (HCIX-Fe) for Lead Removal from Battery Manufacturing Wastewater

This study is aimed to synthesize, characterize and validate the performance of a novel hybrid nanoadsorbent for selective removal of lead from a battery manufacturing wastewater. The hybrid nanosorbent, named as HCIX-Fe, was prepared by impregnating hydrated Fe (III) oxide (HFO) nanoparticles inside polymeric cation exchange resin containing negatively charged sulfonic acid (-SO3-) fixed functional groups. HCIX-Fe was characterized by SEM-EDX and XRD to confirm the distribution and determination of phase of HFO dispersed inside the hybrid nanosorbent. Fixed-bed column runs with HCIX-Fe beads were carried out using wastewater from a battery manufacturing plant. The wastewater had a pH of 1.8 and contained of 3.5 mg/L of Pb2+ coexisted with 250 mg/L Ca2+ ions. The results have shown that HCIX-Fe column could treat lead-contaminated water up to 6,500 bed volumes (BVs) before the occurrence of breakthrough concentration of 0.2 mg/L Pb2+ resulting in a removal capacity of 6.85 mg Pb2+/ml of the HCIX-Fe bed. Under similar condition, adsorbent columns with cation exchange resin (C100), granulated activated carbon (GAC) and granulated activated carbon impregnated with HFO (GAC-Fe), could treat the same wastewater only until 400, 900 and 1,500 BVs, respectively. When compared with the parent adsorbents, impregnation by HFO greatly enhanced the Pb2+ removal capacity of C100 and GAC by 1,625% and 167%, respectively. Both HFO and high density of sulfonic acid (-SO3-) in the host cation exchanger are individually capable of selective removal of Pb2+ ions; however the hybrid material demonstrated a synergistic effect for Pb2+ removal through the Donnan Membrane effect. Due to amphoteric behavior of HFO, the HCIX-Fe could be regenerated and reused with 10 BVs of 2% HNO3 and 1% FeCl3·6H2O solution.

Rapid and highly selective removal of lead from water using graphene oxide-hydrated manganese oxide nanocomposites

To overcome the limits of graphene oxide (GO) as a novel sorbent for heavy metal removal (e.g., low sorption selectivity and difficulty in solid-liquid separation), a nanocomposite (HMO@GO) with excellent settling ability (<2min) was fabricated through in situ growing nanosized hydrated manganese oxide (HMO) (10.8±4.1nm) on GO. As a graphene-based adsorbent, HMO@GO exhibited fast sorption kinetics (<20min). Meanwhile, the introduced HMO endowed HMO@GO with outstanding sorption selectivity and capacity toward Pb(II) (>500mgg−1) in the presence of high-level competing Ca(II). Cyclic sorption batches showed that 1kg HMO@GO can treat at least 22m3 Pb(II)-laden synthetic industrial drainage (5mgL−1 Pb(II)) and 40m3 drinking water (0.5mgL−1 Pb(II)) to their corresponding limits (0.1mgL−1 for wastewater and 10μgL−1 for drinking water) enforced in China. Additionally, the exhausted HMO@GO can be effectively regenerated using 0.3 M HCl for repeated uses. The eminent performance of HMO@GO was attributed to its specific structure, that is, the abundant oxygen-containing groups on GO mediated the growth of highly dispersed HMO that preferably sequestrated Pb(II) through specific interaction, and the host GO offered the preconcentration of Pb(II) for enhanced sequestration through the Donnan membrane effect.

Removal of Arsenic (III) Present in Ground Water of Bangladesh with Polymer Supported Hydrated Fe(III) Oxides

In the present study, a technique to remove arsenic has been developed with a polymer-supported hydrated Fe(III) oxide (HFO) by using a strongly basic anionic exchanger IRA-420 as the host material and FeCl3-HCl-NaCl solution as the reaction environment. The optimized conditions were applied to a sample collected from Sonargaon, Dhaka. The removal efficiency of this method was more than 80%, which indicates that this method can be used as an efficient method for arsenic removal in Bangladesh. IRA-420-HFO exhibits more preferential adsorption of arsenic ions which is attributed to the Donnan membrane effect exerted by the host resin (IRA-420) as well as to the loaded HFO particles for specific interaction toward arsenic (III) ions. All the results indicated that HFO polymer derivative is an attractive adsorbent for efficient arsenic (III) removal from contaminated groundwater of Bangladesh.Dhaka Univ. J. Sci. 63(2):85-89, 2015 (July)

Nexus between polymer support and metal oxide nanoparticles in hybrid nanosorbent materials (HNMs) for sorption/desorption of target ligands

Metal oxide nanoparticles like hydrated ferric oxide (HFO) or hydrated zirconium oxide (HZrO) are excellent sorbents for environmentally significant ligands like phosphate, arsenic, or fluoride, present at trace concentrations. Since the sorption capacity is surface dependent for HFO and HZrO, nanoscale sizes offer significant enhancement in performance. However, due to their miniscule sizes, low attrition resistance, and poor durability they are unable to be used in typical plug-flow column setups. Meanwhile ion exchange resins, which have no specific affinity toward anionic ligands, are durable and chemically stable. By impregnating metal oxide nanoparticles inside a polymer support, with or without functional groups, a hybrid nanosorbent material (HNM) can be prepared. A HNM is durable, mechanically strong, and chemically stable. The functional groups of the polymeric support will affect the overall removal efficiency of the ligands exerted by the Donnan Membrane Effect. For example, the removal of arsenic by HFO or the removal of fluoride by HZrO is enhanced by using anion exchange resins. The HNM can be precisely tuned to remove one type of contaminant over another type. Also, the physical morphology of the support material, spherical bead versus ion exchange fiber, has a significant effect on kinetics of sorption and desorption. HNMs also possess dual sorption sites and are capable of removing multiple contaminants, namely, arsenate and perchlorate, concurrently.

Nanoscale iron oxides loaded granular activated carbon (GAC-NSIO) for cadmium removal

A new hybrid material was prepared by loading the nanoscale iron oxide particles within the pores of granular activated carbon (GAC-NSIO) and used as adsorbent to remove Cd(II) in aqueous phase. The new material is characterized by the pHpzc, TEM, XRD, BET, and XPS analytical techniques to deduce the potential adsorptive mechanism, and further it along with GAC were assessed in the removal of Cd(II) from aqueous solution for various physico-chemical factors iron-loaded content, pH, humic acid, isotherm, kinetics, and thermodynamics, under the batch reactor studies and rapid small-scale column tests also appended dealing with the breakthrough volume. Characterization of adsorbent indicated that the amorphous nanoscale iron oxides were successfully immobilized on GAC. Adsorption mechanism mainly included surface complexation, Donnan membrane effect, and electrostatic attraction. The optimum iron-loaded content of GAC-NSIO was 17%. The adsorption process was more favorable at high pH, and iron oxide was almost no leaching (<0.25%) in the pH range of 3–6. Adsorption isotherm fitted well with Langmuir and Freundlich models. And adsorption kinetics fitted well with pseudo-second-order and intraparticle diffusion models. Results indicated that loaded nanoscale iron oxides significantly increased adsorption capacity of Cd(II) though the adsorption rate declined slightly and the adsorption process was endothermic. The maximum adsorptive capacity of GAC-NSIO (7.84 mg/g) increased by 700%, compared to that of GAC (0.98 mg/g). The presence of humic acid could greatly impact Cd(II) adsorption which promoted adsorption at low concentrations (1–10 mg/L) and inhibited adsorption at high concentrations (10–300 mg/L). Rapid small-scale column tests were conducted to obtain Cd(II) breakthrough profile. The results corresponded well with those from batch tests. Results demonstrate that the GAC-NSIO is a promising adsorbent for the removal of Cd(II) in contaminated water environment.

Hybrid Anion Exchanger with Dispersed Zirconium Oxide Nanoparticles: A Durable and Reusable Fluoride-Selective Sorbent

More than 300 million people across the world are currently at risk for skeletal and dental fluorosis due to drinking fluoride-contaminated groundwater. Current treatment solutions are not adequate in a number of manners: short adsorbent lifespan, high waste generation, poor treated water aesthetics, continuous dependence on electricity, poor recovery of extracted groundwater, and economic unsustainability. Hybrid anion exchange resin, referred to as HAIX-Zr, was synthesized in this investigation by impregnating strong base anion exchange resins with nanoscale zirconium oxide (ZrO2) particles at a loading rate of >10% zirconium content (w/w). Nanoparticles of ZrO2 were <50 nm and had a mean diameter of 15 nm. Polymeric anion exchange resins are durable hosts with an environment of fixed positive charges (e.g., quaternary ammonium functional groups, R4N+) that create enhanced local anion concentrations via the Donnan membrane effect. Synergy of the robust polymer phase and high surface area of dispersed zirconium oxide nanoparticles resulted in high fluoride sorption capacity even in the presence of high concentrations of other competing anions. Most notably, high concentrations of sulfate (500 mg/L) showed practically no noticeable competing effect and demonstrated the high fluoride selectivity of HAIX-Zr. No physical fragmentation or loss in capacity occurred during cycles of exhaustion-regeneration; ZrO2 is chemically stable from pH 3 to 12. Kinetics of the sorption process during a fixed-bed column run was controlled by intraparticle diffusion, and intraparticle fluoride diffusivity for HAIX-Zr was found comparable to other selective processes. HAIX-Zr was regenerated efficiently (>90%) over two cycles of exhaustion-regeneration with alkali (3% NaOH/3% NaCl) and acid (CO2 sparged water) without any noticeable loss in capacity. HAIX-Zr is ready for field applications under representative conditions.

Fabrication of a New Hydrous Zr(IV) Oxide-Based Nanocomposite for Enhanced Pb(II) and Cd(II) Removal from Waters

To overcome the technical bottleneck of fine hydrated Zr(IV) oxide particles in environmental remediation, we irreversibly impregnated nanosized hydrated Zr(IV) oxide inside a commercial cation exchange resin D-001 and obtained a new nanocomposite NZP. NZP exhibited efficient removal of lead and cadmium ions in a pH range of 2-6, where no Zr(IV) leaching was detected from NZP. As compared to D-001, NZP showed more preferable adsorption toward both toxic metals from the background Ca(II) solution at greater levels. The synthetic Pb(II) or Cd(II) solution containing other ubiquitous metal ions was employed as the feeding influent for column adsorption, and the results indicated that the treatable volume of NZP is around 3-4 times that of D-001 before reaching the breakthrough point set according to the effluent discharge standard of China. With respect to Pb(II) removal from an acidic mining effluent, the treatable volume of NZP was 13 times higher than that of D-001. The exhausted NZP could be effectively regenerated by HNO3-Ca(NO3)2 binary solution for repeated use without any significant capacity loss. The superior performance of NZP was attributed to the Donnan membrane effect exerted by the host D-001 as well as the impregnated HZO nanoparticles of specific interaction toward toxic metals, as confirmed by the comparative isothermal adsorption and X-ray photoelectron spectroscopic study.

Recyclable polymer-based nano-hydrous manganese dioxide for highly efficient Tl(I) removal from water

Tl(I) in water even at a trace level is fatal to human beings and the ecosystem. Here we fabricated a new polymer-supported nanocomposite (HMO-001) for efficient Tl(I) removal by encapsulating nanosized hydrous manganese dioxide (HMO) within a polystyrene cation exchanger (D-001). The resultant HMO-001 exhibited more preferable removal of Tl(I) than D-001 and IRC-748, an iminodiacetic chelating polymer, particularly in the presence of competing Ca(II) ions at greater levels in solution. Such preference was ascribed to the Donnan membrane effect caused by D-001 as well as the specific interaction between Tl(I) and HMO. The adsorbed Tl(I) was partially oxidized into insoluble Tl(III) by HMO at acidic pH, while negligible oxidation was observed at circumneutral pH. The exhausted HMO-001 was amenable to efficient regeneration by binary NaOH-NaClO solution for at least 10-cycle batch runs without any significant capacity loss. Fixed-bed column test of Tl(I)-contained industrial effluent and natural water further validated that Tl(I) retention on HMO-001 resulted in a conspicuous concentration drop from 1.3 mg/L to a value lower than 0.14 mg/L (maximum concentration level for industrial effluent regulated by US EPA) and from 1–4 μg/L to a value lower than 0.1 μg/L (drinking water standard regulated by China Health Ministry), respectively.

Polymer-supported metals and metal oxide nanoparticles: synthesis, characterization, and applications

Metal and metal oxide nanoparticles exhibit unique properties in regard to sorption behaviors, magnetic activity, chemical reduction, ligand sequestration among others. To this end, attempts are being continuously made to take advantage of them in multitude of applications including separation, catalysis, environmental remediation, sensing, biomedical applications and others. However, metal and metal oxide nanoparticles lack chemical stability and mechanical strength. They exhibit extremely high pressure drop or head loss in fixed-bed column operation and are not suitable for any flow-through systems. Also, nanoparticles tend to aggregate; this phenomenon reduces their high surface area to volume ratio and subsequently reduces effectiveness. By appropriately dispersing metal and metal oxide nanoparticles into synthetic and naturally occurring polymers, many of the shortcomings can be overcome without compromising the parent properties of the nanoparticles. Furthermore, the appropriate choice of the polymer host with specific functional groups may even lead to the enhancement of the properties of nanoparticles. The synthesis of hybrid materials involves two broad pathways: dispersing the nanoparticles (i) within pre-formed or commercially available polymers; and (ii) during the polymerization process. This review presents a broad coverage of nanoparticles and polymeric/biopolymeric host materials and the resulting properties of the hybrid composites. In addition, the review discusses the role of the Donnan membrane effect exerted by the host functionalized polymer in harnessing the desirable properties of metal and metal oxide nanoparticles for intended applications.