Characterization of extracellular polymeric substances in the biofilms of typical bacteria by the sulfur K-edge XANES spectroscopy.

A combined approach of physicochemical extraction and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy was applied to characterize the extracellular polymeric substances (EPS) of typical bacterial biofilms in this study. Physicochemical analysis showed variation of the contents of DNA, polysaccharide and protein in different fractions of EPS in different mediums. The sulfur K-edge XANES analysis yielded a variety of spectra. Spectral fitting of the XANES spectra utilizing a large set of model compounds showed that there was more reduced sulfur in both LB-EPS (loosely bound EPS) and TB-EPS (tightly bound EPS) of all the biofilms in LB medium than in R2A medium. More oxidized sulfur was identified in LB-EPS than that in TB-EPS, suggesting different niches and physiological heterogeneity in the biofilms. Our results suggested that the sulfur K-edge XANES can be a useful tool to analyze the sulfur speciation in EPS of biofilms.

Occurrence and variations of five classes of antibiotic resistance genes along the Jiulong River in southeast China.

Antibiotic resistance genes (ARGs) are emerging microbial hazards threatening human health. Many factors, including urban and agricultural activities and water environment changes, can significantly impact the variations of ARGs. An investigation on the occurrence and variations of ARGs in the Jiulong River was done in this study. The water samples were collected from 16 sites ranging from the upper branch to the river mouth of the Jiulong River, in both low- and high-flow periods. Eleven ARG families were tested and quantified by real-time PCR (SYBR Green) methods, and detection assays were conducted for tetA, tetG, aacC1, strA, ermB, cmlA5, vanA, dfrA1, sulll, blaTEM-1 and blaoxa-1 genes. Results showed that nine ARG families were found, then the swine industry and urban activities, including sewage discharge, might be responsible for the high levels of concentrations and relative abundances of ARGs, and the increase of salinity might decrease the relative abundances of ARGs. In addition, some ARG abundances were significantly correlated to the concentrations of NH4+ and PO4(3-), particularly in the high-flow period. The human activities were important sources for ARGs in the Jiulong River, which have already become a threat to the safety of drinking water for the nearby cities.

A preparation method for mRNA-LNPs with improved properties.

The properties of mRNA lipid nanoparticles (mRNA-LNPs), including size, empty particles, morphology, storage stability, and transfection potency, are critically dependent on the preparation methods. Here, a Two-step tangential-flow filtration (TFF) method was successfully employed to improve the properties of mRNA-LNPs during the preparation process. This method involves an additional ethanol removal step prior to the particle fusion process. Notably, this innovative approach has yielded mRNA-LNPs with larger particles, a reduced proportion of empty LNPs, optimized storage stability (at least 6 months at 2-8 °C), improved in vitro transfection efficiency, and minimized distribution in the heart and blood in vivo. In summary, this study represents the implementation of the innovative Two-step TFF method in the preparation of mRNA-LNPs. Our findings indicate substantial enhancements in the properties of our mRNA-LNPs, specifically with regard to the percentage of empty LNPs, stability, transfection efficiency, and in vivo distribution. These improvements have the potential to optimize their industrial applicability and expand their clinical use.

Characterization of G-Quadruplexes in Enterovirus A71 Genome and Their Interaction with G-Quadruplex Ligands.

Human enteroviruses cause many diseases; however, there is no specific therapeutic drug. G-quadruplex is an atypical secondary structure formed in the guanine rich region of DNA or RNA, which can exist in the viral genome. The different positions of G-quadruplex play an important role in the regulation of virus replication and infection. Whether G-quadruplexes are present in human enteroviruses is unknown. In current study, we analyzed the potential quadruplex forming sequences of human enteroviruses, especially EV-A71 virus, which causes hand, foot, and mouth disease. The results showed that there were a certain number of potential quadruplex-forming sequences in human enteroviruses. Through a variety of experimental methods, we evaluated the formation potential of EV-A71 encoded G-quadruplex and analyzed the binding ability of G-quadruplex ligands, including BRACO-19, pyridostatin and TMPyP4 to virus encoded G-quadruplexes. G-quadruplex ligands BRACO-19, PDS and TMPyP4 could inhibit the transcription of constructs containing EV-A71 G-quadruplex sequences. Moreover, we found that BRACO-19 was able to inhibit the replication of EV-A71, suggesting that targeting G-quadruplexes in EV-A71 genome by G-quadruplex ligands could be a novel antiviral way against EV-A71. Our finding not only uncovered the G-quadruplexes in human enteroviruses, but also would provide a new strategy for human enteroviruses therapy. IMPORTANCE G-quadruplex is a stable nucleic acid secondary structure formed by the folding of guanine rich nucleic acid. The important regulatory function of G-quadruplex makes it an attractive target of antiviral effect. Human enteroviruses cause a variety of human diseases, including common cold, nervous system diseases, cardiovascular damage, and diabetes. Enterovirus A71 (EV-A71) is one of pathogens causing hand, foot, and mouth disease; however, whether G-quadruplexes are present in the genomes of human enteroviruses is unknown. The function of G-quadruplexes in the EV-A71 genomes is not clear. We predicted and characterized G-quadruplex sequences in EV-A71. G-quadruplex ligands were identified to stabilize EV-A71 G-quadruplexes with high affinities. We also demonstrated G-quadruplex ligand BRACO-19 inhibited EV-A71 replication. Our studies provide a framework for targeting G-quadruplexes in the enteroviruses genome, which will be a new way to develop antiviral agents against human enteroviruses.

Treatment of aqueous diethyl phthalate by adsorption using a functional polymer resin.

To study the adsorptive separation efficiency, adsorption and desorption performances of diethyl phthalate (DEP) were investigated with a functional polymer resin (NDA-702). A macroporous polymer resin (XAD-4) and a coal-based granular activated carbon (AC-750) were chosen for comparison. The kinetic adsorption data obeyed the pseudo-second-order rate model, and the adsorption processes were limited by both film and intraparticle diffusions. Adsorption equilibrium data were well fitted by the Freundlich equation, and the larger uptake and higher selection of NDA-702 than AC-750 and XAD-4 was probably due to the microporous structure, phenyl rings and polar groups on NDA-702. Thermodynamic adsorption studies indicated that the test adsorbents spontaneously adsorbed DEP, driven mainly by enthalpy change. Continuous fixed-bed runs demonstrated that there no significant loss of the resin's adsorption capacity and there was complete regeneration of NDA-702. The results suggest that NDA-702 has excellent potential as an adsorption material for water treatment.

Adsorptive selenite removal from water using a nano-hydrated ferric oxides (HFOs)/polymer hybrid adsorbent.

Selenite (SeO(3)(2-)) is an oxyanion of environmental significance due to its toxicity when taken in excess. In the present study, a hybrid adsorbent (HFO-201) was prepared by irreversibly impregnating hydrated ferric oxide (HFO) nanoparticles within a commercial available anion-exchange resin (D-201), and its adsorption towards selenite from water was investigated in batch and column tests. HFO-201 exhibited improved sorption selectivity toward selenite as compared to the polymeric anion exchanger D-201. Two possible adsorption interactions were responsible for selenite removal by HFO-201, the electrostatic interaction from the ammonium groups bound to the D-201 matrix, and the formation of inner-sphere complexes between the loaded HFO nanoparticles and selenite. In a wide pH range (i.e., 3-8), increasing solution pH was found to result in a decrease of selenite removal on HFO-201. Adsorption isotherms fit the Freundlich model well, and selenite adsorption increased with increasing ambient temperature, indicating its endothermic nature. Column adsorption tests suggested that satisfactory removal of selenite from 2 mg/L to less than 0.01 mg/L could be achieved by HFO-201 even in the presence of the commonly encountered anionic competition at greater concentration, with the treatment capacity of approximately 1200 bed volume (BV) per run, while that for D-201 was only less than 30 BV under otherwise identical conditions. Furthermore, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH-NaCl solution.

A novel water-stable two-dimensional zeolitic imidazolate frameworks thin-film composite membrane for enhancements in water permeability and nanofiltration performance.

Polymer membranes for water treatment are constrained by the permeability-separation trade-off. Herein, two-dimensional (2D) zeolitic imidazolate frameworks (ZIFs) made of benzimidazole interconnected with Zn ions are used to create 2D Zn2(Bim)4 molecular sieve nanosheets, which is explored as an asymmetric, thin-film composite (TFC) nanofiltration (NF) membrane for removing organic dyes and salts from water with a high water permeability under a low operating pressure (1 bar). The 2D Zn2(Bim)4 TFC NF membrane is synthesized via ionic bonds between polycations and the peripheral hydroxy groups of 2D Zn2(Bim)4 nanosheets, regulating the assembly of 2D Zn2(Bim)4 to create a novel crack-free functional layer on top of a polyvinylidene fluoride (PVDF) ultrafiltration membrane. FESEM and XPS confirmed the presence of a polycations-regulated ultrathin functional layer with a thickness of ∼37 nm on the PVDF support. Benefiting from its structural feature, our 2D Zn2(Bim)4 TFC NF membrane could achieve an ultra-high flux of ∼290 L/(m2·h·bar) (5-10-fold higher than that of graphene-based membranes), good anti-fouling properties and high rejection rates (above 98%) for organic dyes. Moreover, the desalinization rate is 50-75%. That is, our membrane is endowed with NF capability, and its intrinsic ultrafiltration features (high water permeance, ultrafast, and energy-saving) are also well maintained.

Application of the Polanyi potential theory to phthalates adsorption from aqueous solution with hyper-cross-linked polymer resins.

The adsorption equilibria of dimethyl phthalate (DMP) and diethyl phthalate (DEP) on two hyper-cross-linked polymer resins (NDA-99 and NDA-150) in aqueous solution were investigated at 298 K. And a coal-based granular activated carbon (AC-750) was chosen for comparison. All the adsorption equilibrium data of DMP were well fitted by the Polanyi-based isotherm modeling (Polanyi-Manes (PM) equation), and the characteristic curves of the three adsorbents were obtained. It is noteworthy that a reasonably good agreement was obtained between the combined micropore and mesopore volume of adsorbents and the corresponding adsorption volume capacity for phthalates. Compared to the granular activated carbon (AC-750), the greater adsorption performances of the two resins (NDA-99 and NDA-150) were assumed to result from their more abundant micro- and mesopore structure, where phthalates can be intensively adsorbed by pore-filling mechanism. According to the exponent b value of the PM equation, NDA-99 and NDA-150 show the more micro- and mesopore heterogeneity than AC-750. On the other hand, the functional groups on the adsorbent surfaces did not take a notable effect on the adsorption equilibria of phthalates. The theory equilibrium adsorption amounts of DEP, predicted by the specific characteristic curve of each adsorbent, agree well with the experimental ones, respectively. The characteristic curve of hyper-cross-linked polymer resins and its prediction of phthalates adsorption calculated by Polanyi-based isotherm modeling have a potential applicability for field applications.

Nanotechnology-enabled materials for hemostatic and anti-infection treatments in orthopedic surgery.

The hemostatic and anti-infection treatments in the field of orthopedics are always the pivotal yet challenging topics. In the first part of this review, synthesized or naturally derived nanoscale agents and materials for hemostatic treatment in orthopedic surgery are introduced. The hemostatic mechanisms and the safety concerns of these nanotechnology-enabled materials are discussed. Beside the materials to meet hemostatic needs in orthopedic surgery, the need for antimicrobial or anti-infection strategy in orthopedic surgery also becomes urgent. Nanosilver and its derivatives have the most consistent anti-infective effect and thus high translational potential for clinical applications. In the second part, the factors affecting the antimicrobial effect of nanosilver and its application status are summarized. Finally, the status and translational potential of various nanotechnology-enabled materials and agents for hemostatic and anti-infective treatments in orthopedic surgery are discussed.

Efficient removal of nickel(II) from high salinity wastewater by a novel PAA/ZIF-8/PVDF hybrid ultrafiltration membrane.

Enhanced removal of trace toxic metals (ppm level) from high-salinity wastewater is crucial to ensure water safety but still a challenging task. In this study, we fabricated a new hybrid ultrafiltration membrane (PAA/ZIF-8/PVDF) by immobilizing zeolitic imidazolate framework-8 (ZIF-8) particles onto the surface of trimesoyl chloride (TMC)-modified polyvinylidene fluoride (PVDF) membrane under protection of polyacrylic acid (PAA) layer. The resultant PAA/ZIF-8/PVDF membrane exhibited relatively high water flux of 460 L·m-2 h-1 and outstanding nickel ion (Ni(II)) capacity (219.09 mg/g) from a synthetic high-salinity ([Na+] = 15000 mg/L) wastewater. X-ray photoelectron spectroscopic studies revealed that preferable Ni(II) uptake was mainly attributed to the specific interaction between Ni(II) and hydroxyl groups on ZIF-8 frameworks and carboxyl groups in PAA layer as well. Compared to PAA, ZIF-8 could selectively bind Ni(II) with negligible effect exerted by concentrated sodium ion. The filtration study showed that the 12.56-cm2 membrane could effectively treat 5.76 L high-salinity wastewater ([Ni(II)0 = 2 mg/L, [Na+]0 = 15000 mg/L) to conspicuously reduce Ni(II) below the maximum contaminant level of China, 0.1 mg/L. Moreover, the hybrid membrane could be regenerated by HCl-NaCl solution (pH = 5.5) for repeated use under direct current electric field. Generally speaking, the newly developed ZIF-8 hybrid ultrafiltration membrane showed a very promising potential in enhanced removal of toxic metals from high-salinity wastewater treatment.

Highly efficient and environmentally benign As(III) pre-oxidation in water by using a solid redox polymer.

As(III) preoxidation to As(V) is usually a requisite step for its efficient removal from water. Traditional oxidants reacting with As(III) homogenously in water suffer from the excessive dosage as well as the possible formation of disinfection byproducts. Herein, we developed a heterogeneous oxidant, i.e., a solid redox polymer (DOX), by covalently binding chlorine to a commercially available cation-exchange resin, D001. As(III) pre-oxidation by DOX is independent upon the solution pH (6-8) and ionic strength (0-0.1 M NaNO3). The presence of natural organic matters (NOMs) exhibits slightly adverse effect on the As(III) oxidation. More attractively, much less disinfection byproducts (DBPs, CHCl3 in this study) is formed during oxidation by DOX than by chlorine, possibly ascribed to the electrostatic repulsion between NOMs and DOX as well as the steric effect of the solid matrix. The exhausted DOX could be fully refreshed by the NaClO solution for cyclic use. The column oxidation experiment were performed by feeding the synthetic groundwater containing As(III), various minerals, and NOMs. It could result in As(III) decline from 200 × 10-3 mg/L initially to <1 × 10-3 mg/L with the working capacity of >33,200 bed volume (BV) even at the volumetric flow rate of 50 BV/h (i.e., EBCT = 1.2 min, equivalent to the linear velocity of 2.2 m/h). In summary, DOX is a highly efficient and environmental friendly oxidant for As(III) pre-oxidation in water treatment.

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.

Ionic polymer-coated laccase with high activity and enhanced stability: application in the decolourisation of water containing AO7.

Eliminating dyes in environmental water purification remains a formidable challenge. Laccase is a unique, environmentally friendly and efficient biocatalyst that can degrade pollutants. However, the use of laccase for the degradation of pollutants is considerably limited by its susceptibility to environmental changes and its poor reusability. We fabricated a novel biocatalyst (LacPG) by coating polyethylenimine onto the native laccase (Lac) followed by crosslinking with glutaraldehyde. The stability of the resulting LacPG was highly enhanced against pH variations, thermal treatments and provided better long-term storage with a negligible loss in enzymatic activity. Compared to Lac, LacPG exhibited significantly higher decolourisation efficiency in the degradation of a representative azo dye, acid orange 7 (AO7), which resulted from the electrostatic attraction between the coating and AO7. LacPG was separated from the AO7 solution using an ultrafiltration unit. The increased size and modified surface chemistry of LacPG facilitated ultrafiltration and reduced membrane fouling. LacPG exhibited enhanced stability, high catalytic activity and favourable properties for membrane separation; therefore, LacPG could be continuously reused in an enzymatic membrane reactor with a high efficiency for decolourising water containing AO7. The developed strategy appears to be promising for enhancing the applicability of laccase in practical water treatment.

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.

Effective removal of effluent organic matter (EfOM) from bio-treated coking wastewater by a recyclable aminated hyper-cross-linked polymer.

Effluent organic matter (EfOM) is a complex matrix of organic substance mainly from bio-treated sewage effluent and is considered as the main constraint to further advanced treatment. Here a recyclable aminated hyper-cross-linked polymeric adsorbent (NDA-802) featured with aminated functional groups, large specific surface area, and sufficient micropore region was synthesized for effective removal of EfOM from the bio-treated coking wastewater (BTCW), and its removal characteristics was investigated. It was found that hydrophobic fraction was the main constituent (64.8% of DOC) in EfOM of BTCW, and the hydrophobic-neutral fraction had the highest SUVA level (7.06 L mg(-1) m(-1)), which were significantly different from that in the domestic wastewater. Column adsorption experiments showed that NDA-802 exhibited much higher removal efficiency of EfOM than other polymeric adsorbents D-301, XAD-4, and XAD-7, and the efficiency could be readily sustained according to continuous 28-cycle batch adsorption-regeneration experiments. Moreover, dissolved organic matter (DOM) fractionation and excitation-emission matrix (EEM) fluorescence spectroscopy study indicated that NDA-802 showed attractive adsorption preference as well as high removal efficiency of hydrophobic and aromatic compounds. Possibly ascribed to the presence of functional aminated groups, relatively large specific surface area and micropore region of the unique polymer, NDA-802 possesses high and sustained efficiency for the removal of EfOM, and provides a potential alternative for the advanced treatment.

Effect of sulfate on Cu(II) sorption to polymer-supported nano-iron oxides: behavior and XPS study.

Iron oxides tend to be immobilized within nanoporous supports to improve their feasibility for practical environmental remediation including arsenic and heavy metal removal. Contrary to the co-ions, little is known concerning the effect of counter ions on the performance of the resultant composites. In this study, two hybrid sorbents (denoted as HFO-PS(-) and HFO-PS(0), respectively) were prepared by loading hydrous ferric oxide (HFO) nanoparticles onto two polystyrene beads: PS(-), negatively charged with sulfonic acid groups, and PS(0), covalently bonded with neutral chloromethyl groups. Effects of sulfate on their sorption toward Cu ions were investigated. Consistent with the case in bulky HFO particles, the amount of Cu adsorbed on HFO-PS(0) was markedly promoted by introducing sulfate. As for HFO-PS(-), with monovalent cation as background (Na(+)), it exhibited an apparent decrease in Cu sorption as a result of the competing effect of Na ions and the Cu-SO(4) complexation in solution. Contrarily, the adsorbed Cu was increased by introducing sulfate in the divalent cation background (Ca), because sulfate ions were allowed to access to the loaded HFO nanoparticles due to the screening of the sulfonic acid groups caused by Ca ions. XPS spectroscopy further demonstrated that besides the electrostatic effects, the formation of Cu-SO(4) ternary complexes also accounted for the enhanced Cu sorption on both bulky HFO and hybrid HFO sorbents in the presence of sulfate. These results indicated that the effect of counter-ion ligands on metal adsorption to hybrid iron oxides was largely dependent on the surface properties of the host materials.

A fabrication strategy for nanosized zero valent iron (nZVI)-polymeric anion exchanger composites with tunable structure for nitrate reduction.

To reveal how the distribution of nanoscale zero-valent iron (nZVI) affect their reduction efficiency of its polymer-based composites and to further develop a simple strategy to tune the structure of the composites, we prepared four nZVI-polymerstyrene anion exchanger composites with similar nZVI loadings (13.5-14.4 Fe % in mass) but different distributions just through varying the concentration of NaBH(4) (0.9, 1.8, 3.6, and 7.2% in mass) solution during reduction of nZVI precursor (FeCl(4)(-) anions). As observed by SEM-EDX images, increasing the NaBH(4) concentration resulted in a more uniform nZVI distribution within the polymer, and thereto higher NH(4)(+)N production, faster reaction rate and more gaseous products during its reduction of nitrate and nitrite. nZVI distribution of the composites was suggested to greatly depend upon two processes, the hydrolyzation of anionic FeCl(4)(-) into cationic Fe(3+) and the reduction of both Fe(III) species by NaBH(4). Higher NaBH(4) concentration favored its faster diffusion into the inside polymer and in situ reduction of Fe(III) species into nZVI, causing a more uniform nZVI distribution. The results reported herein suggest that adjusting the NaBH(4) concentration was a simple and effective method to control the nZVI distribution in the supporting polymers, and indirectly tune the reactivity of the resultant nZVI hybrids.

Immobilization of polyethylenimine nanoclusters onto a cation exchange resin through self-crosslinking for selective Cu(II) removal.

Donnan membrane principle provides great opportunities for development of highly efficient adsorbents for toxic metals abatement. Based on the principle we prepared a new composite adsorbent by immobilizing polyethylenimine (PEI) nanoclusters within a macroporous cation exchanger D001 through self-crosslinking by glutaraldehyde upon Cu(II)-template process. Negligible PEI loss was observed from the resultant composite adsorbent D001-PEI-GA to solution of pHs 1-12. Increasing solution pH from 1 to 6 results in more favorable Cu(II) retention by D001-PEI-GA, and Cu(II) adsorption onto D001-PEI-GA follows the pseudo-second-order kinetic model well. Compared to D001, D001-PEI-GA displays more preferable Cu(II) sequestration in the presence of co-ions Mg(2+), Ca(2+), Sr(2+) at higher levels. Fixed-bed adsorption of a synthetic solution containing Cu(II) and other co-ions showed that Cu(II) sequestration on D001-PEI-GA could result in its conspicuous decrease from 5mg/L to below 0.01 mg/L with the treatment volume as high as 630 BV per run, while that for D001 was only ∼ 85 BV. Also, the spent composite adsorbent can be readily regenerated by HCl (0.3M)-NaCl (0.5M) binary solution for repeated use with negligible capacity loss.

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.

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.