Bingcai Pan

Development of polymer-based nanosized hydrated ferric oxides (HFOs) for enhanced phosphate removal from waste effluents

Phosphate originated from industrial effluents is one of the key factors responsible for eutrophication of the receiving waterways especially in the developing countries such as China. In the current study we proposed a novel process to immobilize nanoparticulate hydrated ferric oxide (HFO) within a macroporous anion exchange resin D-201, and obtained a hybrid adsorbent (HFO-201) for enhanced phosphate removal from aqueous system. The resulting HFO-201 possesses two types of adsorption sites for phosphate removal, the ammonium groups bound to the D-201 matrix and the loaded HFO nanoparticles. The coexisting sulfate anion strongly competes for ammonium groups, which bind phosphate through electrostatic interaction. However, it does not pose any noticeable effect on phosphate adsorption by the loaded HFO nanoparticles, which is driven by the formation of the inner-sphere complexes. Batch adsorption experiments also indicated that HFO-201 exhibits a little higher capacity for phosphate than the commercially available phosphate-specific adsorbent ArsenX(np), which possesses similar structure of HFO-201 and is produced by another patented technique. Fixed-bed column tests indicate that phosphate retention by HFO-201 from the synthetic waters results in the significant decrease of P from 2mg/L to less than 0.01 mg/L, with the treatment capacity of approximately 700 bed volume (BV) per run, while that for D-201 was less than 200 BV under otherwise identical conditions. Such satisfactory performance of the hybrid adsorbent is mainly attributed to the specific affinity of HFO toward phosphate as well as the Donnan membrane effect exerted by the anion exchanger support D-201. Moreover, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH-NaCl solution for repeated use without any significant capacity loss. Similar satisfactory results were also observed by using a phosphate-containing industrial effluent as the feeding solution.

Highly efficient removal of heavy metals by polymer-supported nanosized hydrated Fe(III) oxides: Behavior and XPS study

The present study developed a polymer-based hybrid sorbent (HFO-001) for highly efficient removal of heavy metals [e.g., Pb(II), Cd(II), and Cu(II)] by irreversibly impregnating hydrated Fe(III) oxide (HFO) nanoparticles within a cation-exchange resin D-001 (R-SO(3)Na), and revealed the underlying mechanism based on X-ray photoelectron spectroscopy (XPS) study. HFO-001 combines the excellent handling, flow characteristics, and attrition resistance of conventional cation-exchange resins with the specific affinity of HFOs toward heavy metal cations. As compared to D-001, sorption selectivity of HFO-001 toward Pb(II), Cu(II), and Cd(II) was greatly improved from the Ca(II) competition at greater concentration. Column sorption results indicated that the working capacity of HFO-001 was about 4-6 times more than D-001 with respect to removal of three heavy metals from simulated electroplating water (pH approximately 4.0). Also, HFO-001 is particularly effective in removing trace Pb(II) and Cd(II) from simulated natural waters to meet the drinking water standard, with treatment volume orders of magnitude higher than D-001. The superior performance of HFO-001 was attributed to the Donnan membrane effect exerted by the host D-001 as well as to the impregnated HFO nanoparticles of specific interaction toward heavy metal cations, as further confirmed by XPS study on lead sorption. More attractively, the exhausted HFO-001 beads can be effectively regenerated by HCl-NaCl solution (pH 3) for repeated use without any significant capacity loss.

Selective removal of Cu(II) ions by using cation-exchange resin-supported polyethyleneimine (PEI) nanoclusters.

A novel hybrid adsorbent D001-PEI was fabricated for selective Cu(II) removal by immobilizing soluble polyethyleneimine (PEI) nanoclusters within a macroporous cation exchange resin D001. Negligible release of PEI nanoclusters unexpectedly observed during operation may result from the porous cross-linking nature of D-001 as well as the electrostatic attraction between PEI and D001. Increasing solution pH from 1 to 6 results in more favorable Cu(II) retention by D001-PEI, and Cu(II) adsorption onto D001-PEI follows the Langmuir model and the pseudosecond-order kinetic model well. Compared to the host cation exchanger D001, D001-PEI displays more preferable adsorption toward Cu(II) in the presence of competing Mg(2+), Ca(2+), Sr(2+) at greater levels in solution. Fixed-bed adsorption runs showed that Cu(II) sequestration on D001-PEI could result in its conspicuous decrease from 5 mg/L to below 0.01 mg/L. Also, the spent hybrid adsorbent can be readily regenerated by 6-8 BV HCl (0.2 mol/L)-NaCl (0.5 mol/L) binary solution for repeated use with negligible capacity loss. The results reported herein validate that D001-PEI is a promising adsorbent for enhanced removal of Cu(II) and other heavy metals from waste effluents.

Application potential of carbon nanotubes in water treatment: A review.

Water treatment is the key to coping with the conflict between peoples increasing demand for water and the world-wide water shortage. Owing to their unique and tunable structural, physical, and chemical properties, carbon nanotubes (CNTs) have exhibited great potentials in water treatment. This review makes an attempt to provide an overview of potential solutions to various environmental challenges by using CNTs as adsorbents, catalysts or catalyst support, membranes, and electrodes. The merits of incorporating CNT to conventional water-treatment material are emphasized, and the remaining challenges are discussed.

Nitrate reduction using nanosized zero-valent iron supported by polystyrene resins: role of surface functional groups.

To probe the role of host chemistry in formation and properties of the inside nano-zero valent iron (nZVI), we encapsulated nZVI within porous polystyrene resins functionalized with -CH(2)Cl and -CH(2)N(+)(CH(3))(3) respectively and obtained two hybrid nZVIs denoted Cl-S-ZVI and N-S-ZVI. 14.5% (in Fe mass) of nZVI particles were distributed in N-S within a ring-like region (about 0.10 mm in thickness) of size around ∼ 5 nm, whereas only 4.0% of nZVI particles were entrapped near the outer surface of Cl-S of size > 20 nm. -CH(2)N(+)(CH(3))(3) is more favorable than -CH(2)Cl to inhibit nZVI dissolution into Fe(2+) ions under acidic pH (3.0-5.5). 97.2% of nitrate was converted into ammonium when introducing 0.12 g N-S-ZVI into 50 mL 50 mg N/L nitrate solution, while that for Cl-S-ZVI was 79.8% under identical Fe/N molar ratio. Under pH = 2 of the effectiveness of nZVI was 88.8% for nitrate reduction, whereas that for Cl-S-ZVI was only 14.6% under similar conditions. Nitrate reduction by N-S-ZVI exhibits relatively slower kinetics than Cl-S-ZVI, which may be related to different nZVI distribution of both composites. The coexisting chloride and sulfate co-ions are favorable for the reactivity enhancement of N-S-ZVI whereas slightly unfavorable for Cl-S-ZVI. The results demonstrated that support chemistry plays a significant role in formation and reactivity of the encapsulated nZVI, and may shed new light on design and fabrication of hybrid nZVIs for environmental remediation.

Sorption enhancement of lead ions from water by surface charged polystyrene-supported nano-zirconium oxide composites.

A novel hybrid nanomaterial was fabricated by encapsulating ZrO2 nanoparticles into spherical polystyrene beads (MPS) covalently bound with charged sulfonate groups (-SO3(-)). The resultant adsorbent, Zr-MPS, exhibited more preferential sorption toward Pb(II) than the simple equivalent mixture of MPS and ZrO2. Such observation might be ascribed to the presence of sulfonate groups of the polymeric host, which could enhance nano-ZrO2 dispersion and Pb(II) diffusion kinetics. To further elucidate the role of surface functional groups, we encapsulated nano-ZrO2 onto another two macroporous polystyrene with different surface groups (i.e., -N(CH3)3(+)/-CH2Cl, respectively) and a conventional activated carbon. The three obtained nanocomposites were denoted as Zr-MPN, Zr-MPC, and Zr-GAC. The presence of -SO3(-) and -N(CH3)3(+) was more favorable for nano-ZrO2 dispersion than the neutral -CH2Cl, resulting in the sequence of sorption capacities as Zr-MPS > Zr-MPN > Zr-GAC > Zr-MPC. Column Pb(II) sorption by the four nanocomposites further demonstrated the excellent Pb(II) retention by Zr-MPS. Comparatively, Zr-MPN of well-dispersed nano-ZrO2 and high sorption capacities showed much faster breakthrough for Pb(II) sequestration than Zr-MPS, because the electrostatic repulsion of surface quaternary ammonium group of MPN and Pb(II) ion would result in a poor sorption kinetics. This study suggests that charged groups in the host resins improve the dispersion of embedded nanoparticles and enhance the reactivity and capacity for sorption of metal ions. Suitably charged functional groups in the hosts are crucial in the fabrication of efficient nanocomposites for the decontamination of water from toxic metals and other charged pollutants.

Adsorption of aromatic acids on an aminated hypercrosslinked macroporous polymer

Abstract In the present study a hypercrosslinked macroporous polymer CHA-111 was chemically modified by amination with dimethylamine. Adsorption of five aromatic acids on the modified polymer MCH-111 was investigated and adsorption capacities of aromatic acids from aqueous solution increased significantly after amination. The Freundlich and Langmuir isotherm equations were employed to fit the adsorption processes to describe adsorption mechanism. Hydrogen-bonding interaction should be regarded as a fundamental contributor to increasing adsorption capacities of aromatic acids on MCH-111. Surface structure of MCH-111 caused by postcrosslinking reaction will enhance the NPM–matrix interaction and then lead to higher activity of amino group on MCH-111 than a macroporous weakly anion exchanger D301. The negative isosteric enthalpy changes for adsorption of benzenesulfonic acid and naphthalenesulfonic acid indicate an exothermic process on the aminated polymer.

Use of hydrous manganese dioxide as a potential sorbent for selective removal of lead, cadmium, and zinc ions from water

Selective removal of three toxic metal ions, Pb(II), Cd(II), and Zn(II), from aqueous solution by amorphous hydrous manganese dioxide (HMO) was evaluated. Two polymeric exchangers, a polystyrene-sulfonic cation exchanger, D-001, and an iminodiacetic acid chelating exchanger, Amberlite IRC 748, were involved for comparison. Hydrogen ion release is accompanied by metal uptake onto HMO, implying that metal sorption could be generally represented by an ion-exchange process. As compared to both exchangers, HMO exhibits preferable sorption toward the toxic metals in the presence of Ca(II) ions at greater levels. FT-IR of the HMO samples laden with different metals indicate that Ca(II) uptake onto HMO is mainly driven by outer-sphere complexation, while that of three toxic metals might be related to inner-sphere complex formation. In addition, uptake of heavy metals onto HMO approaches equilibrium quickly and the exhausted HMO particles can be regenerated readily for repeated use by HCl solution. The results reported strongly display the potential of HMO as an economic and selective sorbent for removal of toxic metals from contaminated waters.

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.

Facile Fabrication of Magnetic Chitosan Beads of Fast Kinetics and High Capacity for Copper Removal

In this study, magnetic chitosan (CS) beads of ∼200 nm in diameter were successfully prepared by a facile one-step method. The resultant composite Fe3O4-CS was characterized using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Its adsorption toward Cu(II) ions was investigated as a function of solution pH, CS dosage, Cu(II) concentration, and contact time. The maximum capacity of Fe3O4-CS was 129.6 mg of Cu(II)/g of beads (617.1 mg/g of CS). More attractively, the adsorption equilibrium could be achieved within 10 min, which showed superior properties among the available CS-based adsorbents. Continuous adsorption-desorption cyclic results demonstrated that Cu(II)-loaded Fe3O4-CS can be effectively regenerated by ethylenediaminetetraacetic acid (EDTA) solution, and the regenerated composite beads could be employed for repeated use without significant capacity loss. Additionally, Fe3O4-CS beads can be readily separated from water within 30 s under a low magnetic field (<0.035 T).