The presence of natural organic matter (NOM) exerts adverse effects on adsorptive removal of various pollutants including fluoride from water. Herein, we designed a novel nanocomposite adsorbent for preferable and sustainable defluoridation from NOM-rich water. The nanocomposite (HZO@HCA) is obtained by encapsulating hydrous zirconium oxide nanoparticles (HZO NPs) inside hyper-cross-linked polystyrene anion exchanger (HCA) binding tertiary amine groups. Another commercially available nanocomposite HZO@D201, with the host of a cross-linked polystyrene anion exchanger (D201) binding ammonium groups, was involved for comparison. HZO@HCA features with abundant micropores instead of meso-/macropores of HZO@D201, resulting in the inaccessible sites for NOM due to the size exclusion. Also, the tertiary amine groups of HCA favor an efficient desorption of the slightly loaded NOM from HZO@HCA. As expected, Sigma-Aldrich humic acid even at 20 mg of DOC/L did not exert any observable effect on fluoride sequestration by HZO@HCA, whereas a significant inhibition was observed for HZO@D201. Cyclic adsorption runs further verified the superior reusability of HZO@HCA for defluoridation from NOM-rich water. In addition, the HZO@HCA column could generate ∼80 bed volume (BV) effluent from a synthetic fluoride-containing groundwater to meet the drinking water standard (<1.5 mg F/L), whereas HCA and HZO@D201 columns could only generate <5 and ∼40 BV effluents, respectively. This study is believed to shed new light on how to rationally design antifouling nanocomposites for water remediation.

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 regeneration, nZVI@D201 could be sustainably utilized for Se(VI) removal. In addition, column experiments showed that nZVI@D201 exhibited great potential for practical trace Se(VI) removal in fixed-bed systems.

Millimeter-sized polymer-based FeOOH nanoparticles (NPs) provide a promising option to overcome the bottlenecks of direct use of NPs in scaled-up water purification, and decreasing the NP size below 10 nm is expected to improve the decontamination efficiency of the polymeric nanocomposites due to the size and surface effect. However, it is still challenging to control the dwelled FeOOH NP sizes to sub-10 nm, mainly due to the wide pore size distribution of the currently available polymeric hosts. Herein, we synthesized mesoporous polystyrene beads (MesoPS) via flash freezing to assemble FeOOH NPs. The embedded NPs feature with α-crystal form, tunable size ranging from 7.3 to 2.0 nm and narrow size distribution. Adsorption of As(III/V) by the resultant nanocomposites was greatly enhanced over the α-FeOOH NPs of 18 × 60 nm, with the iron mass normalized capacity of As(V) increasing to 10.3 to 14.8 fold over the bulky NPs. Higher density of the surface hydroxyl groups of the embedded NPs as well as their stronger affinity toward As(V) was proved to contribute to such favorable effect. Additionally, the as-obtained nanocomposites could be efficiently regenerated for cyclic runs. We believe this study will shed new light on how to fabricate highly efficient nanocomposites for water decontamination.

•A heterogeneous oxidant DOX was synthesized for As(III) pre-oxidation.•As(III) oxidation was independent of pH and ionic strength.•DOX oxidation generated much less DBPs than chlorine in the presence of NOMs.•The exhausted DOX could be fully refreshed with NaClO for cyclic runs.•Column operation demonstrated the great potential of DOX in real application.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.Download high-res image (318KB)Download full-size image

•Decomplexation of Cu-EDTA by UV/PS was investigated for the first time.•UV/PS is more efficient than UV/H2O2 in decomplexation of Cu-complexes.•Self-catalysis of the formed intermediates was observed.•Degradation mechanism was proposed for both oxidation processes.•UV/PS-precipitation process is very effective in treatment of electroplating effluent.Heavy metal-organic complexes are widely present in natural water and industrial effluents. Currently, the widely employed strategy for removal of metal-organic complexes is to combine oxidative decomplexation with further precipitation or adsorption of the released metals. OH and SO4− based advanced oxidation processes (AOPs) are very promising in water purification. However, to the best of our knowledge, there is no open literature concerning the decomplexation efficiency of metal-organic complexes based on SO4− as yet. In this study, a typical SO4− based technology, i.e., UV/PS (persulfate) process, was applied to investigate its decomplexation of Cu(II)-EDTA in water, and the final Cu(II) removal during the subsequent alkaline precipitation was used as a reference of the decomplexation efficiency. UV/H2O2 was employed for comparison throughout the study. Effect of the oxidant dosage, pH, and coexisting substances on the decomplexation was evaluated, and the degradation mechanism was particularly concerned. The results show that degradation of Cu(II)-EDTA by SO4− and OH follows a similar pathway, i.e., successive decarboxylation, while the decomplexation efficiency of UV/PS is much higher than UV/H2O2 under similar conditions. Meanwhile, the coexisting substances (Cl−, NO3−, and NOM) exerted less inhibition on the decomplexation of UV/PS than UV/H2O2. The above advantages of UV/PS are mainly attributed to the better selectivity of SO4− as well as its higher yield of active species. Similarly, satisfactory performance was observed for Cu-citrate and Cu-nitrilotriacetate removal from aqueous solution and for Cu(II) removal from a real electroplating effluent as well, further demonstrating the promising applicability of the UV/PS based combined process in water decontamination from Cu-organic complexes.Download high-res image (111KB)Download full-size image

Iron oxide nanoparticles (NPs) exhibit great potential in water decontamination from arsenic. Embedding NPs inside porous hosts is a very promising approach to inhibit their undesirable but inherent aggregation as well as the subsequent capacity drop during application. In this study, we confined iron oxide NPs inside inert silicates (MPS) of varying pore sizes (3.0, 5.7 and 15.7 nm) and obtained three nanocomposite adsorbents. The effect of MPS pore size on As(V) adsorption by the resultant nanocomposite adsorbents was particularly focused. The maximum As(V) adsorption capacity of the nanocomposites was negatively correlated with their host pore size. Based on the in situ Gran plots of the nanocomposites, the narrower pore size of the host resulted in a higher surface hydroxyl density of the confined iron oxide NPs. More interestingly, the reactivity of the hydroxyl groups binding smaller NPs was significantly enhanced compared to the larger one, as indicated by the higher molar ratio of the adsorbed As to the hydroxyl groups. The effect of pH and competitive anions on As(V) adsorption was also studied to further examine the role of the host pore in tuning the properties of the resultant composites.

Various engineering nanoparticles (NPs) exhibit high reactivity and great potential for water decontamination. Encapsulation of NPs into millimeter-sized polymer hosts is a very promising strategy to address their inherent bottlenecks for scale-up water treatment such as aggregation, difficult operation and potential risks when released into water. However, the inevitable host pore blockage accompanying NP loadings significantly compromise their decontamination reactivity. Herein, a newly developed flash freezing method was utilized to embed α-Fe2O3 NPs (3 nm, 7 nm and 18 × 90 nm) inside millimetric polystyrene to prepare mesoporous nanocomposites Fe2O3@PS. All the as-obtained Fe2O3@PS nanocomposites feature high mesoporosity, well-dispersed NPs and highly accessible sites. The amount of Fe–OH species, i.e., the active sites for As(V) sequestration, of the embedded 3 nm-Fe2O3 is dramatically increased 3.6 times over the bare NPs, resulting in higher adsorption capacity and affinity. The 3 nm-Fe2O3@PS is capable of producing clean water 2000-fold greater in mass successively in column adsorption, with As(V) reducing from 176 μg L−1 initially to <1 μg L−1. Also, Fe2O3@PS can be readily regenerated for cyclic use with negligible NPs leaking into water. This study provides an elaborate strategy to address the trade-off between easy operation and decontamination reactivity of NPs for water treatment.

•Efficient removal of citrate complexed Cr(III) was achieved by UV/Fe(III)+OH.•Negligible Cr(VI) accumulation occurred during the combined process.•Cr(III) oxidation by ·OH and photolysis of Fe(III)-citrate are involved.•The combined process is viable in treatment of real tanning effluent.Most available processes are incapable of removing Cr(III)-organic complexes from water due to their high solubility, extremely slow decomplexation rate, and possible formation of more toxic Cr(VI) during oxidation. Herein, we proposed a new combined process, i.e., UV/Fe(III) followed by alkaline precipitation (namely UV/Fe(III)+OH), to achieve highly efficient and environmentally benign removal of Cr(III)-organic complexes from water. The combined process could remove Cr(III)-citrate from 10.4 mg Cr/L to 0.36 mg Cr/L and ∼60% total organic carbon as well. More attractively, negligible Cr(VI) (<0.06 mg/L) was formed during the process. In the viewpoint of mechanism, the added Fe(III) generates ·OH radicals to transform Cr(III) into Cr(VI) and simultaneously released the citrate ligand to form Fe(III)-citrate simultaneously. Then, the photolysis of Fe(III)-citrate under UV irradiation involved the citrate degradation and the production of massive Fe(II) species, which in turn transformed the formed Cr(VI) back to Cr(III). The free metal ions, including Cr(III), Fe(II) and Fe(III) were removed by the subsequent alkaline precipitation. Also, the combined process is applicable to other Cr(III) complexes with EDTA, tartrate, oxalate, acetate. The applicability of the combined process was further demonstrated by treating two real tanning effluents, resulting in the residual Cr(III) below 1.5 mg/L (the discharge standard of China) and negligible formation of Cr(VI) (<0.004 mg/L) as well. In general, the combined process has a great potential for efficient removal of Cr(III) complexes from contaminated waters.Download high-res image (241KB)Download full-size image

•All the tested salt solutions except Na2SiO3 enhanced ZVI corrosion to different extents.•Dominant corrosion products derived from ZVI varied with the type of brine solution.•Degrees of both H2 evolution and O2 adsorption corrosions were quantified.•Removal of As/Se was positively correlated with the degree of ZVI corrosion.•As/Se removal by pcZVI involved both the adsorption and reduction processes.Zero-valent iron (ZVI) has been extensively applied in water remediation, and most of the ZVI materials employed in practical applications are iron scraps, which have usually been corroded to certain extent under different conditions. In this study, the effects of brining with six solutions (NaCl, Na2SO4, NaHCO3, Na2SiO3, NH4Cl, and NaH2PO4) on the corrosion of ZVI and its performance in the removal of As(III/V)/Se(IV/VI) were systematically investigated. All the studied solutions enhanced the corrosion of ZVI except for Na2SiO3, and the degrees of corrosion followed the order of NH4Cl > NaH2PO4 > Na2SO4 > NaCl > NaHCO3 > H2O > Na2SiO3. The corrosion products derived from ZVI were identified by SEM and XRD, and the dominant corrosion products varied with the type of brine solution. The positive correlation between the degree of ZVI corrosion and As(III/V)/Se(IV/VI) removal by the pre-corroded ZVI (pcZVI) was verified. In addition, As and Se removal by pcZVI was realized via a comprehensive process including adsorption and reduction, as further supported by the XPS analysis. We believe this study will shed new light upon the selection of iron materials pre-corroded under different saline conditions for practical water remediation.Download high-res image (211KB)Download full-size image

Halogenated aromatic compounds have attracted increasing concerns due to their toxicity and persistency in the environment, and dehalogenation is one of the promising treatment and detoxification methods. Herein, we systematically studied the debromination efficiency and mechanism of para-bromophenol (4-BP) by a recently developed UV/sulfite process. 4-BP underwent rapid degradation with the kinetics accelerated with the increasing sulfite concentration, pH (6.1–10) and temperature, whereas inhibited by dissolved oxygen and organic solvents. The apparent activation energy was estimated to be 27.8 kJ/mol. The degradation mechanism and pathways of 4-BP were explored by employing N2O and nitrate as the electron scavengers and liquid chromatography/mass spectrometry to identify the intermediates. 4-BP degradation proceeded via at least two pathways including direct photolysis and hydrated electron-induced debromination. The contributions of both pathways were distinguished by quantifying the quantum yields of 4-BP via direct photolysis and hydrated electron production in the system. 4-BP could be readily completely debrominated with all the substituted Br released as Br−, and the degradation pathways were also proposed. This study would shed new light on the efficient dehalogenation of brominated aromatics by using the UV/sulfite process.Download high-res image (75KB)Download full-size image

•Cr(VI) was efficiently reduced to Cr(III) at alkaline pHs by UV/sulfite process.•Common ions and organic matters interfered with Cr(VI) reduction slightly.•Spontaneous precipitation of Cr(III) occurred in the presence of Ca2+ (>2 ppm).•eaq− was identified as the dominant reactive species in UV/sulfite process.Chemical reduction of Cr(VI) to Cr(III) followed by Cr(III) precipitation is a widely employed strategy to mitigate Cr(VI) pollution from industrial effluents. Nevertheless, most of the available reduction processes are feasible at acidic pHs only, and very few technologies are capable of reducing Cr(VI) at alkaline pHs. Herein, we demonstrated that the UV/sulfite process is very promising for alkaline Cr(VI) remediation, including the Cr(VI) reduction to Cr(III) and simultaneous Cr(III) precipitation. In this process Cr(VI) reduction followed near zero-order kinetics, declining with an increase of pH (5–10) but boosting with increasing sulfite concentration. The co-existing Cl− and SO42− in water exerted negligible effect on Cr(VI) reduction, whereas the reduction kinetics was improved in the presence of citrate, EDTA or humic acid possibly due to their complexation with Cr(III). Similarly, the presence of borate buffer would significantly inhibit Cr(VI) reduction to Cr(III) as well as the final Cr(III) removal during precipitation. Fortunately, the presence of calcium ions even at trace level would favor Cr(III) precipitation and result in one-step removal of the total Cr at alkaline pH. The mechanism of Cr(VI) reduction was probed through irradiation manipulation and N2O addition, and the results suggested that excitation of sulfite is essential for alkaline Cr(VI) reduction, and eaq− is the dominant reactive species in the UV/sulfite process.Download high-res image (261KB)Download full-size image

Three composite adsorbents were fabricated via confined growth of hydrous ferric oxide (HFO) nanoparticles within cross-linked anion exchangers (NS) of different pore size distributions to investigate the effect of host pore structure on the adsorption of As(V). With the decrease in the average pore size of the NS hosts from 38.7 to 9.2 nm, the mean diameter of the confined HFO nanoparticles was lessened from 31.4 to 11.6 nm as observed by transmission electron microscopy (TEM), while the density of active surface sites was increased due to size-dependent effect proved by potentiometric titration. The adsorption capacity of As(V) yielded by Sips model was elevated from 24.2 to 31.6 mg/g via tailoring the pore size of the NS hosts, and the adsorption kinetics was slightly accelerated with the decrease of pore size in background solution containing 500 mg/L of Cl–. Furthermore, the enhanced adsorption of As(V) was achieved over a wide pH range from 3 to 10, as well as in the presence of competing anions including Cl–, SO42–, HCO3–, NO3– (up to 800 mg/L), and PO43– (up to 10 mg P/L). In addition, the fixed-bed working capacity increased from 2200 to 2950 bed volumes (BV) owing to the size confinement effect, which did not have adverse effect on the desorption of As(V) as the cumulative desorption efficiency reached 94% with 10 BV of binary solution (5% NaOH + 5% NaCl) for all the three adsorbents. Therefore, this study provided a promising strategy to regulate the reactivity of the nanoparticles via the size confinement effect of the host pore structure.Keywords: composite; ion exchanger; nanoparticle; pore structure; size confinement effect; sorption

Efficient and powerful water purifiers are in increasing need because we are facing a more and more serious problem of water pollution. Here, we demonstrate the design of versatile magnetic nanoadsorbents (M-QAC) that exhibit excellent disinfection and adsorption performances at the same time. The M-QAC is constructed by a Fe3O4 core surrounded by a polyethylenimine-derived corona. When dispersed in water, the M-QAC particles are able to interact simultaneously with multiple contaminants, including pathogens and heavy metallic cations and anions, in minutes. Subsequently, the M-QACs along with those contaminants can be easily removed and recollected by using a magnet. Meanwhile, the mechanisms of disinfection are investigated by using TEM and SEM, and the adsorption mechanisms are analyzed by XPS. In a practical application, M-QACs are applied to polluted river water 8000-fold greater in mass, producing clean water with the concentrations of all major pollutants below the drinking water standard of China. The adsorption ability of M-QAC could be regenerated for continuous use in a facile manner. With more virtues, such as low-cost fabrication and easy scaling up, the M-QAC have been shown to be a very promising multifunctional water purifier with rational design and to have great potential for real water purification applications.

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.

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).Keywords: Cu(II); fast removal; Fe3O4; magnetic chitosan beads;

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[PO43–]/L to 0.5 mg P[PO43–]/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.

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.

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.Keywords: acidic mining effluent; enhanced removal; heavy metals; hydrated zirconium oxide; polymeric nanocomposite; XPS study;

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.

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.

Elucidating the effect of porous host on the intrinsic physicochemical properties and reactivity of the encapsulated nanosized hydrous ferric oxides (HFOs) is believed important to better understand how HFOs interact with ionic pollutants inside the pore region. Here we prepared a hybrid adsorbent (HFO–CMPS) by dispersing nanosized HFOs onto an inactive porous polymeric support (i.e., chloromethylated polystyrene, CMPS). A surface complexation model (SCM) was employed to quantitatively evaluate the acid–base reactions and adsorption behaviors of HFO–CMPS as compared to the bare HFOs. Results demonstrated that the intrinsic equilibrium constants for acid–base reactions of surface sites of HFOs distinctly changed upon loading, that is, the log K(+) values decreased, while its log K(−) values increased, resulting in its pHpzc value shifting from ∼8.2 to ∼6.3. Meanwhile, the titration curves of HFO–CMPS showed a markedly weaker dependence upon ionic strength. The results of model fittings of Cu(II) and As(V) adsorption indicate that the change of Coulombic terms, reflecting the effect of the electrical potential on the adsorption activities, played an important role in the difference in pH-dependent adsorption of Cu(II) and As(V) between HFO–CMPS and bare HFOs. Additionally, the greater tendency of the encapsulated HFOs to dissolve in acidic solution was observed and may be due to its weaker pH buffering capacity, which possibly results from size-dependency of surface charges. All the results indicated that porous hosts play a significant role in the properties of the attached metal oxides for their application in water treatment.

Adsorption is one of the widely used processes in the chemical industry environmental application. As compared to mathematical models proposed to describe batch adsorption in terms of isotherm and kinetic behavior, insufficient models are available to describe and predict fixed-bed or column adsorption, though the latter one is the main option in practical application. The present review first provides a brief summary on basic concepts and mathematic models to describe the mass transfer and isotherm behavior of batch adsorption, which dominate the column adsorption behavior in nature. Afterwards, the widely used models developed to predict the breakthrough curve, i.e., the general rate models, linear driving force (LDF) model, wave propagation theory model, constant pattern model, Clark model, Thomas model, Bohart-Adams model, Yoon-Nelson model, Wang model, Wolborska model, and modified dose-response model, are briefly introduced from the mechanism and mathematical viewpoint. Their basic characteristics, including the advantages and inherit shortcomings, are also discussed. This review could help those interested in column adsorption to reasonably choose or develop an accurate and convenient model for their study and practical application.

The efficient removal of phosphorous from water is an important but challenging task. In this study, we validated the applicability of a new commercially available nanocomposite adsorbent, i.e., a polymer-based hydrated ferric oxide nanocomposite (HFO-201), for the further removal of phosphorous from the bioeffluent discharged from a municipal wastewater treatment plant, and the operating parameters such as the flow rate, temperature and composition of the regenerants were optimized. Laboratory-scale results indicate that phosphorous in real bioeffluent can be effectively removed from 0.92 mg·L−1 to <0.5 mg·L−1 (or even<0.1 mg·L−1 as desired) by the new adsorbent at a flow rate of 50 bed volume (BV) per hour and treatable volume of 3500–4000 BV per run. Phosphorous removal is independent of the ambient temperature in the range of 15°C–40°C. Moreover, the exhausted HFO-201 can be regenerated by a 2% NaOH + 5% NaCl binary solution for repeated use without significant capacity loss. A scaled-up study further indicated that even though the initial total phosphorus (TP) was as high as 2 mg·L−1, it could be reduced to <0.5 mg·L−1, with a working capacity of 4.4–4.8 g·L−1 HFO-201. In general, HFO-201 adsorption is a choice method for the efficient removal of phosphate from biotreated waste effluent.

Surface groups of the host polystyrene beads play an important role in the properties of the polymer-based nano-CdS composites in terms of the distribution, dispersion, crystal structure, pH-dependent stability of nano-CdS, and thereafter affect their photocatalytic activity. Surface modification of the host materials can be taken as an effective and general approach to mediate the structure and properties of the nanocomposite materials.Keywords: functional groups; nano-CdS; nanocomposite; photocatalytic activity; polystyrene;

A new polymeric nanocomposite photocatalyst A15-CdS with large spherical beads (0.70–0.80 mm in diameter) was fabricated for efficient Rhodamine B (RhB) photodegradation with facile separation during cyclic runs, and photocorrosion, a congenital drawback of CdS, was successfully inhibited for A15-CdS. The nanocomposite catalyst was obtained by impregnating CdS nanoparticles within porous polymeric cation exchanger A15 through a facile inner-surface deposition. CdS nanoparticles (<20 nm) immobilized in A15 were deliberately distributed within an outside ring-like region of 40–50 μm in depth, which is dominant for photoreaction because visible light is not expected to permeate through the inner region of nontransparent A15. As expected, efficient RhB photodegradation by A15-CdS was achieved under visible light irradiation, and large-size A15-CdS beads are expected to result in their facile separation from solution for repeated use. More significantly, negligible photocorrosion for the hybrid catalyst A15-CdS was demonstrated by the constant photodegradation efficiency and negligible CdS loss during five-cycle runs. The results indicated that nano-CdS immobilization within A15 would greatly improve the applicability of CdS nanoparticles in practical environmental remediation.

In the present study, a novel approach was developed to remove dimethyl phthalate (DMP), a representative phthalic acid ester (PAE) pollutant, from an aqueous solution using a macroporous OH-type strong base anion exchange resin D201-OH. As compared to the traditional catalyst aqueous NaOH, D201-OH displayed much higher catalytic efficiency for DMP hydrolytic degradation. Almost 100% of DMP was hydrolyzed to far less toxic phthalic acid (PA) in the presence of D201-OH, while only about 29% of DMP was converted to PA in the presence of NaOH under the identical amount of hydroxyl anions in the reaction system. More attractively, the hydrolysis product PA also can be simultaneously removed by the solid basic polymer D201-OH through a preferable anion exchange process, while NaOH induced hydrolysis products were still left in solution. The underlying mechanism for the hydrolytic degradation and simultaneous ion exchange removal process was proposed. Fixed-bed column hydrolytic degradation and ion exchange removal tests indicate that DMP can be completely converted to PA and subsequently removed from water without any further process, with pH values of the effluent being around 6 constantly. The exhausted D201-OH was amenable to an efficient regeneration by 3 bed volumes (BV) of NaOH solution (2 mol/L) for repeated use without any efficiency loss. The results reported herein indicated that D201-OH-induced catalytic degradation and removal is a promising approach for PAEs treatment in waters.

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 Mg2+, Ca2+, Sr2+ 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.

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.Selective removal of Pb(II), Cd(II), and Zn(II) ions by hydrous manganese oxide was compared to the performance of a macroporous cation exchanger, D-001 and an iminodiacetic acid chelating exchanger, Amberlite IRC 748.

A novel hybrid adsorbent HMO-001 was fabricated by impregnating nanosized hydrous manganese dioxide (HMO) onto a porous polystyrene cation exchanger resin (D-001) for enhanced removal of Cd(II) and Zn(II) ions from waters. The immobilized sulfonate anions covalently bound to the D-001 polymeric matrix are supposed to result in preconcentration and enhanced permeation of both target metal ions for favorable adsorption by HMO. Batch and column adsorption runs demonstrated that HMO-001 exhibited highly preferable Cd(II) and Zn(II) retention from waters in the presence of competing Ca(II) ions at much greater levels. The exhausted adsorbent particles are amenable to efficient regeneration by 2% HCl solution without any HMO loss during operation.

Titanium phosphate (TiP) exhibits preferable sorption toward lead ion in the presence of competing calcium ions at high levels, however, it is present as fine or ultrafine particles and cannot be directly employed in fixed-bed or any flow-through systems due to the excessive pressure drop and poor mechanical strength. In the present study a new hybrid sorbent TiP-001 was fabricated by impregnating titanium phosphate (TiP) nanoparticles onto a strongly acidic cation exchanger D-001 for enhanced lead removal from waters. D-001 was selected as a host material mainly because of the Donnan membrane effect resulting from the immobilized sulfonic acid groups bound on the exchanger matrix, which would enhance permeation of the target metal cation prior to effective sequestration. TiP-001 was characterized by transmission electron micrograph (TEM), X-ray diffraction (XRD), and pH-titration. Batch and column sorption onto TiP-001 was assayed to evaluate its performance as compared to the host exchanger D-001. Lead sorption onto TiP-001 is a pH-dependent process due to the ion-exchange nature, and its sorption kinetics follows the pseudo-second-order model well. Compared to D-001, TiP-001 displays highly selective lead sorption in the presence of competing calcium cations at concentration of several orders higher than the target metal. Fixed-bed sorption of a synthetic feeding solution indicates that lead retention by TiP-001 results in a conspicuous decrease of this toxic metal from 0.50 to below 0.010 mg/L (drinking water standard recommended by WHO). Moreover, its feasible regeneration by dilute HCl solution also favors TiP-001 to be a feasible sorbent for enhanced lead removal from water.A new hybrid sorbent TiP-001 was fabricated by impregnating titanium phosphate (TiP) nanoparticles onto a porous cation exchanger D-001 for enhanced lead removal from waters.

The subject study revealed several unique properties of polymer-based zirconium phosphate (ZrP) for lead removal from waters. ZrP particles were impregnated within two porous polymers, namely, a chloromethylated polystyrene (CP) and a polystyrene cation exchange resin (D-001). Both as-prepared hybrid sorbents (designated ZrP−CP and ZrP−001, respectively) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and a N2 adsorption−desorption test at 77 K. As compared to the fresh particles, ZrP impregnated onto CP exhibits a slight increase in sorption capacity, which may result from their nanosized particles after impregnation. More attractively, ZrP−001 displays much higher sorption preference toward lead ions over calcium ions than ZrP, D-001, and ZrP−CP. Such significant phenomena is mainly attributed to the Donnan membrane effect exerted by the immobilized sulfonate groups on D-001 and further validates its potential application for enhanced removal of the toxic metal from contaminated waters.

Adsorption is one of the most widely applied techniques for environmental remediation. Its kinetics are of great significance to evaluate the performance of a given adsorbent and gain insight into the underlying mechanisms. There are lots of references available concerning adsorption kinetics, and several mathematic models have been developed to describe adsorption reaction and diffusion processes. However, these models were frequently employed to fit the kinetic data in an unsuitable or improper manner. This is mainly because the boundary conditions of the associated models were, to a considerable extent, ignored for data modeling. Here we reviewed several widely-used adsorption kinetic models and paid more attention to their boundary conditions. We believe that the review is of certain significance and improvement for adsorption kinetic modeling.

A novel polymeric hybrid sorbent, namely ZrPS-001, was fabricated for enhanced sorption of heavy metal ions by impregnating Zr(HPO3S)2 (i.e., ZrPS) nanoparticles within a porous polymeric cation exchanger D-001. The immobilized negatively charged groups bound to the polymeric matrix D-001 would result in preconcentration and permeation enhancement of target metal ions prior to sequestration, and ZrPS nanoparticles are expected to sequester heavy metals selectively through an ion-exchange process. Highly effective sequestration of lead, cadmium, and zinc ions from aqueous solution can be achieved by ZrPS-001 even in the presence of competing calcium ion at concentration several orders of magnitude greater than the target species. The exhausted ZrPS-001 beads are amenable to regeneration with 6 M HCl solution for repeated use without any significant capacity loss. Fixed-bed column treatment of simulated waters containing heavy metals at high or trace levels was also performed. The content of heavy metals in treated effluent approached or met the WHO drinking water standard.

As a family of hydrophobic ionizable organic compounds, aromatic sulfonates can be present at high levels in industrial wastewaters. They tend to exist as anions over a wide range of pH and cannot be effectively trapped by conventional adsorbents. In the current study, a recyclable acrylic ester polymer (NDA-801) was synthesized for effective removal of aromatic sulfonates from wastewater of high acidity (e.g., pH < 1) and inorganic salts (e.g., ∼5−10% Na2SO4 in mass), for which sodium 2-naphthalene sulfonate (2-NS) was chosen as a representative target contaminant. 2-NS uptake onto NDA-801 increased with the increasing acidity of the solution. The ζ potential of NDA-801 measured at different pH levels as well as batch 2-NS adsorption from methanol/water binary systems demonstrated the favorable roles of electrostatic and hydrophobic interaction in 2-NS adsorption. As compared to a granular activated carbon GAC-1, NDA-801 exhibited much higher removal efficiency and capacity of 2-NS in fixed-bed adsorption. Moreover, the exhausted NDA-801 beads by 2-NS can be completely regenerated by water wash for repeated use, which is more economically desirable than by other regenerants, such as NaOH solution. Continuous column adsorption−regeneration cycles indicated negligible capacity loss of NDA-801 during operation and further validated its feasibility for potential application in associated wastewater treatment.

Sorption of aromatic sulfonates onto two aminated polystyrene sorbents with different pore structures (M-101 and D-301) was investigated for optimization of their potential application in chemical wastewater treatment. Sodium benzenesulfonate (BS), sodium 2-naphthalene sulfonate (2-NS) and disodium 2,6-naphthalene disulfonate (2,6-NDS) were selected as reference solutes and sodium sulfate was as a competitive inorganic salt. Sorption selectivity of both sorbents is dependent upon the concentration levels of aromatic sulfonates in solution coexisting with sodium sulfate at a high level. However, both sorbents exhibit different characters. D-301 presents more favorable sorption for the solutes at relatively high levels (e.g., higher than 5 mM for BS, 0.7 mM for 2-NS and 0.05 mM for 2,6-NS), while M-101 removes aromatic sulfonates more completely when the solute concentration kept at relatively low levels. Based on the experimental results, we proposed an integral process of sorption onto D-301 followed by secondary-sorption onto M-101 to remove aromatic sulfonates from industrial wastewater completely and economically. Furthermore, the satisfactory performance revealed from large-scale application further demonstrated the feasibility of extending this process to dispose of other associated chemical wastewaters.

Hydrated ferric oxide-loaded hybrid sorbents are of considerable concern for arsenic removal from waters. In the current study, several nanosized hydrated ferric oxide (HFO)-loaded polymer sorbents were prepared and assayed to examine the effect of HFO loadings on arsenate sorption from aqueous solution. Batch and column sorption studies showed that the sorption capacity of arsenate increased with the increase of HFO loadings from 3 to 15% (in Fe mass); however, a further increase in the HFO loadings resulted in a dramatic decrease of the sorption capacity. At relatively low arsenate levels (e.g., <1 mg/L), sorbents with lower HFO loadings exhibited higher distribution coefficients (Kd) than others, implying that HFO loaded at a relatively lower level exhibits stronger sorption affinity toward arsenate than the larger one. However, at relatively high arsenate levels, the sorbent with HFO loading of 15% displayed the highest sorption capacity. Additionally, all the exhausted sorbents are amenable to an efficient regeneration by a mixed NaOH−NaCl solution irrespective of their HFO loadings. The results obtained in the current study may serve as a reference for preparation of other hybrid sorbents with similar structures, i.e., composites of nanosized metal (hydro)oxide particles and porous substrates.

In the present study a novel technique was proposed to prepare a polymer-supported hydrated ferric oxide (D201-HFO) based on Donnan membrane effect by using a strongly basic anion exchanger D201 as the host material and FeCl3-HCl-NaCl solution as the reaction environment. D201-HFO was found to exhibit higher capacity for arsenic removal than a commercial sorbent Purolite ArsenX. Furthermore, it presents favorable adsorption selectivity for arsenic removal from aqueous solution, as well as satisfactory kinetics. Fixed-bed column experiments showed that arsenic sorption on D201-HFO could result in concentration of this toxic metalloid element below 10 μg/L, which was the new maximum concentration limit set recently by the European Commission and imposed by the US EPA and China. Also, the spent D201-HFO is amenable to efficient regeneration by NaOH-NaCl solution.

Zirconium phosphate (ZrP) has recently been demonstrated as an excellent sorbent for heavy metals due to its high selectivity, high thermal stability, and absolute insolubility in water. However, it cannot be readily adopted in fixed beds or any other flowthrough system due to the excessive pressure drop and poor mechanical strength resulting from its fine submicrometer particle sizes. In the present study a hybrid sorbent, i.e., polymer-supported ZrP, was prepared by dispersing ZrP within a strongly acidic cation exchanger D-001 and used for enhanced lead removal from contaminated waters. D-001 was selected as a host material for sorbent preparation mainly because of the Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid group on the exchanger surface, which would enhance permeation of the targeted metal ions. The hybrid sorbent (hereafter denoted ZrP-001) was characterized using a nitrogen adsorption technique, scanning electron microscope (SEM), and X-ray diffraction (XRD). Lead sorption onto ZrP-001 was found to be pH dependent due to the ion-exchange mechanism, and its sorption kinetics onto ZrP-001 followed the pseudo-first-order model. Compared to D-001, ZrP-001 exhibited more favorable lead sorption particularly in terms of high selectivity, as indicated by its substantially larger distribution coefficients when other competing cations Na+, Ca2+, and Mg2+ coexisted at a high level in solution. Fixed-bed column runs showed that lead sorption on ZrP-001 resulted in a conspicuous decrease of this toxic metal from 40 mg/L to below 0.05 mg/L. By comparison with D-001 and ZrP-CP (ZrP dispersion within a neutrally charged polymer CP), enhanced removal efficiency of ZrP-001 resulted from the Donnan membrane effect of the host material D-001. Moreover, its feasible regeneration by diluted acid solution and negligible ZrP loss during operation also helps ZrP-001 to be a potential candidate for lead removal from water. Thus, all the results suggested that ZrP-001 offers excellent potential for lead removal from contaminated water.A new hybrid sorbent ZrP-D001 based on the Donnan membrane effect was prepared for enhanced lead removal from contaminated water.

The adsorption equilibria of phenol and aniline on nonpolar polymer adsorbents (NDA-100, XAD-4, NDA-16 and NDA-1800) were investigated in single- and binary-solute adsorption systems at 313 K. The results showed that all the adsorption isotherms of phenol and aniline on these adsorbents can be well fitted by Freundlich and Langmuir equations, and the experimental uptake of phenol and aniline in all binary-component systems is obviously higher than predicted by the extended Langmuir model, arising presumably from the synergistic effect caused by the laterally acid–base interaction between the adsorbed phenol and aniline molecules. A new model (MELM) was developed to quantitatively describe the synergistic adsorption behavior of phenol/aniline equimolar mixtures in the binary-solute systems and showed a marked improvement in correlating the binary-solute adsorption of phenol and aniline by comparison with the widely used extended Langmuir model. The newly developed model confirms that the synergistic coefficient of one adsorbate is linearly correlated with the adsorbed amount of the other, and the larger average pore size of adsorbent results in the greater synergistic effect of phenol/aniline equimolar mixtures adsorption.A new model (MELM) was developed to quantitatively describe the synergistic adsorption property of phenol/aniline equimolar mixtures in the binary-solute solution on porous polymer adsorbent surfaces.MELM equation:Qeacal=KlaQmaCea1+KlaCea+KlbCeb(1+aa(C0b−Ceb)V1/W+ba),Qebcal=KlbQmbCeb1+KlaCea+KlbCeb(1+ab(C0a−Cea)V1/W+bb).

A hydrophilic hyper-cross-linked polymer resin (NDA-702) was synthesized, and the adsorption performance of dimethyl phthalate (DMP) on NDA-702 was compared with that on the commercial hydrophobic macroporous resin (Amberlite XAD-4) and granular activated carbon (AC-750). The kinetic adsorption of DMP onto NDA-702 and AC-750 is limited mainly by intraparticle diffusion and obeys the pseudo-second-order rate model, while the uptake on XAD-4 is limited mainly by film diffusion and follows the pseudo-first-order rate model. All the associated adsorption isotherms are well described by the Freundlich equation, and the larger uptake and stronger affinity of NDA-702 than AC-750 and XAD-4 probably result from the microporous structure, phenyl rings, and polar groups on NDA-702 polymer matrix. An interesting observation is that in the aqueous phase all the adsorbents spontaneously adsorb DMP driven mainly by enthalpy change, but the hydrophilic nature of NDA-702 and AC-750 surfaces results in less entropy change compared to hydrophobic XAD-4. Dynamic adsorption studies show that the high breakthrough and the total adsorption capacities of NDA-702 are 388 and 559 mg per gram dry resin at 313 K. Nearly 100% regeneration efficiency for the resin was achieved by methanol at 313 K.

In the present study a carboxylated polymeric adsorbent ZK-1 was synthesized for enhanced removal of p-nitroaniline (PNA) from aqueous solution. A commercial polymeric adsorbent XAD-4 was selected for comparison purpose. Characterization of ZK-1 was characterized by infrared spectroscopy and pore size distribution analysis. Experimental results showed that PNA adsorption onto ZK-1 was greatly enhanced due to its micropore structure and the carboxylic group introduced onto polymeric matrix. Different pH-dependent adsorption tendency of PNA onto XAD-4 and ZK-1 was observed mainly due to the role of carboxyl group on the ZK-1 surface. Isotherms of PNA adsorption onto ZK-1 and XAD-4 could be represented by Langmuir model reasonably. More favorable PNA adsorption onto ZK-1 than XAD-4 was further demonstrated by thermodynamic ananlysis. Kinetic studies demonstrated that PNA uptake onto ZK-1 followed the pseudo-second order model, while that onto XAD-4 would be more suitably represented by the pseudo-first order model. Column adsorption runs indicated that PNA could be completely removed from aqueous system by ZK-1. Moreover, efficient regeneration of the spent adsorbent ZK-1 was readily achieved by ethanol and water for its repeated use.

•Nanotechnology exhibits great potential to improve current water and wastewater treatment process.•Applications of free nanomaterial in water and wastewater treatment and their mechanism are reviewed.•Applications and advantages of various nanocomposites are discussed.•Nanoimpact is a major issue facing the application of nanotechnology in water treatment.With the fast development of nanomaterials and nanotechnology, environmental nanotechnology has attracted increasing concerns in the past decades. In the field of water treatment, nanotechnology exhibited great potential in improving the performance and efficiency of water decontamination as well as providing a sustainable approach to secure water supply. In this review, the current applications of nanomaterials in water and wastewater treatment were briefly discussed. The synthesis and physiochemical properties of diverse free nanomaterials, including carbon based nanomaterial, metal and metal oxides nanoparticles as well as noble metal nanoparticles, were focused on, and their performance and mechanisms towards removal of various contaminants were discussed. When concerning the large-scale application in water treatment, nanoparticles have to face some inherent technical bottlenecks such as aggregation, difficult separation, leakage into the contact water, as well as potential adverse effect imposed on ecosystem and human health. The emerging nanocomposite materials integrate the merits of functional nanoparticles and varying solid hosts of large size, and exhibit great advantages in scaled-up application. This review particularly covered the topic of environmental nanocomposites, such as those of organic and inorganic supports, nanocomposite membranes and magnetic nanocomposites. The advantages and perspectives of various nanocomposites are briefly discussed.Download high-res image (249KB)Download full-size image

•ZVI immobilization in anionic exchanger D201 enhancedEDTA-complexed Cu(II) removal.•D201 favored the permeation of the complexed Cu(II) for its removal by ZVI.•D201-ZVI promoted Fe(III) replacement and Cu(II) reduction during Cu(II) removal.•Satisfactory results were observed for fixed-bed operation for Cu(II) removal.In this study, a polymeric anion exchanger (D201) was utilized as the support for nanoscale zero-valent iron (NZVI), and the resultant nanocomposite (D201-ZVI) was employed to remove EDTA-chelated Cu(II) from water. The removal of EDTA-chelated Cu(II) was significantly enhanced by D201-ZVI in comparison with NZVI over a wide pH range from 5 to 9. Most of the removed Cu (97.2%) was immobilized inside the D201-ZVI beads, implying the enhanced permeation of CuEDTA2− by the fixated quaternary ammonium groups of the host D201. HPLC analysis revealed that the EDTA-chelated Cu(II) was gradually replaced by Fe(III) originated from Fe0 oxidation. Then, the released Cu(II) was in situ removed via adsorption/precipitation, or further reduced into Cu0, as quantified by XPS spectra. The higher removal of EDTA-chelated Cu(II) by D201-ZVI than NZVI was mainly ascribed to the enhanced permeation of the host D201 as well as to the better dispersion and higher reactivity of the confined ZVI nanoparticles. Through the combination of periodic regeneration and complete regeneration, D201-ZVI could be sustainably employed for EDTA-chelated Cu(II) removal. Also, D201-ZVI exhibited great potential for practical application in the fixed-bed column operation. Therefore, the D201-ZVI nanocomposite was promising in highly efficient removal of EDTA-chelated Cu(II) from water.Download high-res image (92KB)Download full-size image

•The nanocomposite HZO-201 was stable under varying solution chemistry.•HZO-201 exhibited preferable phosphate removal over other ubiquitous anions.•Selective sorption mechanism was probed and discussed.•HZO-201 could be regenerated for cyclic use with constant efficiency.In this study, we employed a new nanocomposite adsorbent HZO-201, which featured high stability under varying solution chemistry, for preferable removal of phosphate from synthetic solution and a real effluent. An anion exchange resin (D-201) was employed as the host of HZO-201, where nano-hydrous zirconium oxide (HZO) was encapsulated as the active species. D-201 binds phosphate through nonspecific electrostatic affinity, whereas the loaded HZO nanoparticles capture phosphate through formation of the inner-sphere complexes. Quantitative contribution of both species to phosphate adsorption was predicted based on the double-Langmuir model. Preferable removal of phosphate by HZO-201 was observed in the presence of the competing anions at higher levels (Cl−, NO3−, SO42−, HCO3−). Fixed-bed adsorption indicated that the effective volume capacity of a synthetic water (2.0 mg P-PO43−/L) by using HZO-201 was ∼1600 BV in the first run (<0.5 mg P-PO43−/L), comparable to Fe(III)-based nanocomposite HFO-201 (∼1500 BV) and much larger than D-201 (<250 BV). The exhausted HZO-201 can be in situ regenerated by using a binary NaOH–NaCl solution for cyclic runs, whether fed with the synthetic solution or real effluent. In general, HZO-201 is a promising alternative to Fe(III)-based adsorbents for trace phosphate removal from effluent particularly at acidic pH.Download full-size image

In the past decades polymeric adsorbents have been emerging as highly effective alternatives to activated carbons for pollutants removal and subsequent recovery from industrial effluents. More recently, the development of polymer-based hybrid adsorbents has opened up the new opportunities of their application in deep removal of inorganic pollutants like heavy metals from waters. The present review focuses on preparation of these polymeric-based adsorbents, their physicochemical properties, adsorption characteristics and mechanism, as well as their application in water purification.