•The HFO-201 is obtained by impregnating HFO into the pores of anion exchanger D201.•HFO-201 could simultaneously adsorb As(V) and Cr(VI) in aquatic solution.•Cr(VI) was adsorbed by quaternary ammonium groups, As(V) was captured by HFO.•When competing anions coexisted, HFO-201 revealed superior adsorption than D201.•The saturated HFO-201 could be regenerated by NaOH-NaCl binary solution.As(V) and Cr(VI) are both highly toxic anionic pollutants and commonly co-exist in some industrial effluents and contaminated waters. In this study, simultaneous removal of them was efficiently achieved by employing a composite adsorbent (HFO-201) fabricated by immobilizing nanoscale hydrous ferric oxide (HFO) within a macroporous anion exchanger D201. The HFO-201 composite possesses two types of adsorption sites, i.e. the quaternary ammonium groups fixed on the D201 matrix and the embedded HFO nanoparticles. In the binary solution, the adsorption kinetic processes of both As(V) and Cr(VI) by HFO-201 were well fitted with the pseudo-first order kinetic model. Furthermore, HFO-201 exhibited a significantly higher adsorption capacity toward As(V) than D201 and an identical adsorption capacity toward Cr(VI) to D201. During the removal process, As(V) was captured by both the electrostatic attraction from the fixed quaternary ammonium groups and the formation of inner-sphere complex with the embedded HFO nanoparticles. Whereas, Cr(VI) was primarily adsorbed by the fixed ammonium groups. Fixed-bed treatment of As(V)/Cr(VI) binary synthetic water by HFO-201 resulted in elimination of As (from 1.0 to below 0.01 mg/L) and Cr (from 5.0 to below 0.05 mg/L), with the treatment capacity of 1700 bed volume (BV). Moreover, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH-NaCl solution for repeated use without any significant capacity loss.In As-Cr binary solution, Cr(VI) was primarily adsorbed by quaternary ammonium groups fixed on the matrix of HFO-201, while As(V) was preferentially captured by the embedded HFO nanoparticles.Download high-res image (195KB)Download full-size image

•Both dispersed and resin-supported ZVIs can oxidize As(III) in O2 and H2O2 systems.•As(III) oxidation by dispersed ZVI was mainly through the Fenton-like reactions.•The function of the supported ZVI differs from that of the dispersed ZVI.•The difference suggests that the support matrix interfered in As(III) removal.The goal of this study is to assess the differences in As(III) removal kinetics and mechanisms between dispersed zero-valent iron (d-ZVI) and resin-supported zero-valent iron (D201-ZVI) in the presence of dissolved oxygen and hydrogen peroxide. Experimental results show that As(III) could be removed by all the studied systems (d-ZVI/O2, d-ZVI/H2O2, D201-ZVI/O2, D201-ZVI/H2O2). The d-ZVI/H2O2 system was more efficient than D201-ZVI/H2O2 for the oxidation of As(III). Similar trends were observed in O2 system for both solids. The kinetic behaviors as well as the influence of a hydroxyl radical scavenger (2-propanol) on the oxidation of As(III) at different pH suggest that the oxidation of As(III) in the d-ZVI/O2 and d-ZVI/H2O2 systems occurred mainly through Fenton-like reactions. The oxidation of As(III) in the D201-ZVI/O2 and D201-ZVI/H2O2 systems might be expected as follows: As(III) was firstly adsorbed onto the surface of the D201-ZVI, and then oxidation may proceed mainly through a non-Fenton mechanism that directly converts H2O2 into O2 and H2O. In addition, certain iron oxides in the D201-ZVI could also serve as oxidants for As(III) oxidation. The significant differences between the dispersed and supported ZVIs suggest that the supporting matrix interfered in the removal process, which deserves a further investigation.Graphical abstract

A polystyrene-based ion-exchange resin was employed as the precursor for preparation of resin-derived carbon spheres (RCSs) through KOH activation with various impregnation ratios. Pore structure, yield and hardness, surface functional groups of the samples and their adsorption performance towards dibenzothiophene (DBT) were investigated. The RCSs with large surface areas (up to 2696 m2/g) and total pore volumes (up to 1.46 cm3/g) exhibited larger adsorption capacities than a commercial activated carbon, F400. Polanyi-Dubinin-Mane (PDM) model was applied to fit the adsorption data, which proved that micropore filling was involved during the adsorption process. Moreover, a good linear relationship was observed between the extra-micropore volume and adsorption capacity. Intra-particle diffusion (IPD) model was used to describe the kinetic data of DBT onto the adsorbents. The adsorption processes were divided into three stages according to the different diffusion parameter. The selective adsorption towards DBT in the presence of competing compounds was also investigated and the high selectivity of the RSCs towards DBT may be attributed to the large quantity of acidic oxygen-containing groups.

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.

Aminated polystyrene resins (NDA-101 and NDA-103) were synthesized, and their adsorption performances for phenol in aqueous solution were investigated and compared with the commercial polystyrene resin (Amberlite XAD-4) and weakly basic polystyrene resin (Amberlite IRA-96). All the associated adsorption isotherms are well described by Freundlich and Langmuir equations. The results indicated that all the four resins spontaneously adsorb phenol driven mainly by enthalpy change, and their adsorption capacities, free energy changes, enthalpy changes, and entropy changes for phenol followed the same order as: NDA-101 > NDA-103 > XAD-4 > IRA-96. Surface energy heterogeneity analysis by Do's model also suggested that the surfaces of XAD-4 and IRA-96 were more homogeneous, and the better adsorption capacity and affinity of the aminated resins (NDA-101 and NDA-103) are probably due to their multiple hydrogen bonding and π–π stacking interactions with phenol molecule.

Removal of phthalate esters from water has been of considerable concern recently. In the present study, the adsorptive removal performance of diethyl phthalate (DEP) from water was investigated with the aminated polystyrene resin (NDA-101) and oxidized polystyrene resin (NDA-702). In addition, the commercial homogeneous polystyrene resin (XAD-4) and acrylic ester resin (Amberlite XAD-7) as well as coal-based granular activated carbon (AC-750) were chosen for comparison. The corresponding equilibrium isotherms are well described by the Freundlich equation and the adsorption capacities for DEP followed the order NDA-702 > NDA-101 > AC-750 > XAD-4 > XAD-7. Analysis of adsorption mechanisms suggested that these adsorbents spontaneously adsorb DEP molecules driven mainly by enthalpy change, and the adsorption process was derived by multiple adsorbent–adsorbate interactions such as hydrogen bonding, π–π stacking, and micropore filling. The information related to the adsorbent surface heterogeneity and the adsorbate–adsorbate interaction was obtained by Do's model. All the results indicate that heterogeneous resins NDA-702 and NDA-101 have excellent potential as an adsorption material for the removal of DEP from the contaminated water.The five resins exhibit different surface energy heterogeneities for the adsorption of DEP in aqueous solution and can be quantitatively described by Do's model.

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.The theory DEP adsorption capacities (Figure A), predicted by the characteristic curves obtained from DMP experimental adsorption data (Figure B), agrees well with the experimentally determined values for all the test adsorbents.

A hydrophilic polymer resin (NDA-150) was synthesized, and the adsorption performance of 1-naphthylamine on NDA-150 was compared with that on the commercial hydrophobic resin (XAD-4). The kinetic adsorption of 1-naphthylamine onto the two resins is limited by the successive steps of film diffusion and intraparticle diffusion, and obeys the pseudo-second-order rate model. But the adsorption rate on XAD-4 is greater than NDA-150. All the associated adsorption isotherms can be well represented by Langmuir equation, and the larger uptake and stronger affinity of NDA-150 than XAD-4 probably results from the abundant microporous structure and polar groups of NDA-150. It is obviously observed that hydrophobic XAD-4 spontaneously adsorbs 1-naphthylamine driven mainly by enthalpy change, while hydrophilic NDA-150 does driven mainly by both entropy change and enthalpy change. Dynamic breakthrough and the total adsorption capacity of NDA-150 at 293 K are 1.49 and 1.82 mmol mL−1 resin, respectively. More than 99.5% regeneration efficiency for the resin was achieved by ethanol at 313 K.

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.

Adsorption equilibria of 1-naphthol and 1-naphthylamine were investigated in single-solute and binary-solute (primary-co-solute and equimolar solute experiments) adsorption systems at 293 K. Two commercial nonpolar polystyrene adsorbents (NDA-16 and NDA-1800) were employed here for their frequent use in organic pollutants removal from contaminated waters. All the adsorption isotherms of 1-naphthol and 1-naphthylamine in single-solute and equimolar binary-solute adsorption systems were found to be well fitted by Langmuir equation. Adsorption uptake of the primary solute was enhanced in the presence of the co-solute, arising presumably from the cooperative effect caused by the laterally attractive acid–base interaction between the adsorbed 1-naphthol and 1-naphthylamine molecules. Due to the stronger adsorption affinity of 1-naphthylamine to nonpolar adsorbents, adsorption enhancement of 1-naphthylamine in the presence of 1-naphthol is greater than that of 1-naphthol in the presence of 1-naphthylamine. A model (modified extended Langmuir model, MLM) is proved to well describe the cooperative adsorption of 1-naphthol and 1-naphthylamine in the equimolar binary-solute system. The cooperative coefficient of one adsorbate is linearly correlated with the amount of the other adsorbed on the adsorbent.